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Ministry of Energy Mines and Responsible for Core Review

E - Sediment-Hosted

(Example Deposits)

BC Profile # Deposit Type Approximate Synonyms USGS Model #
E01* Almaden Hg Carbonate-hosted Au-Ag 27b
E02 Carbonate-hosted Cu-Pb-Zn Kipushi Cu-Pb-Zn 32c
E03 Carbonate-hosted disseminated Au-Ag Carlin-type Au, Sediment-hosted micron Au 26a,19c
E04 Sediment-hosted Cu Sediment-hosted stratiform Cu 30b
E05 Sandstone Pb - - 30a
E06 Bentonite Volcanic clay, Soap clay 28e?*
E07 Sedimentary kaolin Secondary kaolin 31k*
E08 Carbonate-hosted talc Dolomite-hosted talc 18?i*
E09 Sparry magnesite Veitsch-type, carbonate-hosted magnesite 18i*
E10 Carbonate-hosted barite Mississippi Valley-type barite - -
E11 Carbonate-hosted fluorspar Mississippi Valley-type fluorite 32d*
E12 Mississippi Valley-type Pb-Zn Carbonate-hosted Pb-Zn, Appalachian Zn 32a/32b
E13 Irish-type carbonate-hosted Zn-Pb Kootenay Arc-type Zn-Pb, Remac-type - -
E14 Sedimentary exhalative Zn-Pb-Ag Sedex, Sediment-hosted massive sulphide 31a
E15 Blackbird sediment-hosted Cu-Co Sediment-hosted Cu-Co massive sulphide 24d
E16 Shale-hosted Ni-Zn-Mo-PGE Sediment-hosted Ni - -
E17 Sediment-hosted barite Bedded barite 31b
E18 Carbonate-hosted, Nonsulphide Zn Hypogene - -

 

CARBONATE HOSTED Cu±Pb±Zn


E02
by E.A.G. (Ted) Trueman
Trueman Consulting Ltd.

 

Trueman, E.A.G. (1998): Carbonate Hosted Cu±Pb±Zn, in Geological Fieldwork 1997, British Columbia Ministry of Employment and Investment, Paper 1998-1, pages 24B-1 to 24B-4.

 

IDENTIFICATION

 

SYNONYMS: Tsumeb or Kipushi type.

 

COMMODITIES (BYPRODUCTS): Cu, Pb, Zn, Ge (Ag, Ga, As, Cd).

 

EXAMPLES (British Columbia - Canada/International): Blue (MINFILE 094F 005); Grinnell and Kanuyak Island (Northwest Territories, Canada), Kennecott, Ruby Creek and Omar (Alaska, USA), Apex (Utah, USA), Gortdrum (Ireland), Tsumeb and Kombat (Namibia), Kipushi (Zaire), M'Passa (Congo), Timna (Israel), Nifty (Australia), and portions of Dongchuan deposits (China).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Irregular, discordant bodies of Cu sulphides (bornite, chalcopyrite, chalcocite, tennantite), sometimes with significant galena and sphalerite, form massive pods, breccia/fracture fillings and stockworks in carbonate or calcareous sediments. Igneous rocks are absent or unrelated to the deposition of metals.

 

TECTONIC SETTING: Intracratonic platform and rifted continental margin sedimentary sequences; typically gently folded and locally faulted.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Host carbonate sediments were deposited in shallow marine, inter-tidal, sabkha, lagoonal or lacustrine environments and are often overlain disconformably by oxidized sandstone-siltstone-shale units. Largest deposits are within thick sedimentary sequences.

 

AGE OF MINERALIZATION: Hosts rocks are Middle Proterozoic to Triassic; the largest deposits are in Upper Proterozoic rocks. Mineralization is at least slightly younger than host lithologies and may have spanned a large time interval.

 

HOST / ASSOCIATED ROCK TYPES: Dolomite or limestone, often stromatolitic or arenaceous, hosts the mineralization within a sequence which typically includes fine to coarse grained clastic sediments and evaporite. Occasionally basalt flows are nearby or part of sequence. Intrusive rocks are absent or different age than mineralization.

 

DEPOSIT FORM: The pipe-like to tabular deposits are irregular, discordant and often elongated in one direction up to 2 000 m or more. In cross section, deposits can be up to 100 by 200 m or 60 by 500 m in size. Sometimes Zn-Pb rich mantos project from the main zone of mineralization as replacement bodies parallel to bedding.

 

TEXTURE / STRUCTURE: Massive, stringer/stockwork and disseminated mineralization styles occur and grade into one another; clots of sulphides are common. Features characteristic of a karst environment, including collapse breccias, are typical. Two or more breccia types may be present as a result of karst dissolution and hydrothermal fracturing. Open spaces within deposits are common. Narrow bodies or irregular masses of arenaceous sediment may occur within deposit. These clastics may have developed as a result of dissolution of an arenaceous carbonate host, with accumulation of clastic lag sediments, or by clastic sedimentation into karst openings as a result of submergence.

 

ORE MINERALOGY (Principal and subordinate): Chalcopyrite, bornite, chalcocite, tennantite (tetrahedrite), galena, sphalerite, pyrite, enargite, renierite, germanite, arsenopyrite, marcasite, magnetite, gallite, Co-Ni arsenides, carrollite, molybdenite and others. Deposits contain low to moderate Fe; pyrite may be common or virtually absent. Cu is sometimes crudely zoned vertically in deposits relative to Fe with the Cu-rich phases closer to surface. Cu may also be spatially partitioned with respect to Pb-Zn.

 

GANGUE MINERALOGY (Principal and subordinate): Dolomite, quartz, calcite, barite, fluorite, clay minerals, sericite, hematite, siderite and minor pyrobitumen.

 

ALTERATION MINERALOGY: Dolomite, silica, calcite and argillic alteration. Deposits are usually coincident with a zone of dolomitization. Dolomitization may be pre-, syn- and/or post-mineralization, and may extend 100's of metres beyond mineralization. Vuggy openings are often lined with calcite or baroque dolomite.

 

WEATHERING: Wide variety of secondary products form especially limonite, goethite, Cu minerals (malachite, azurite, dioptase), cerussite and smithsonite. Some deposits are deeply oxidized (Kennecott, Tsumeb, Apex) as a result of fluid circulation through/along solution cavities, faults/fractures and bedding planes. Oxidation is typically developed at surface but there may also be an oxidized profile at considerable depth (>1,000m) as a result of continuation/reactivation of fluid flow along bedding planes aquifers.

 

ORE CONTROLS: The openings in carbonate rocks are created by brecciation, karsting, faulting, and/or alteration. Deposits form in proximity to a redox boundary between reduced carbonates and oxidized clastic sediments or ocassionally oxidized basalt. Evaporites in the sedimentary sequences may have enhanced brine salinity and contributed sulphur.

 

GENETIC MODEL: Pre-mineralization plumbing systems were created by karsting, collapse zones, faulting/fracturing, collapse related to evaporite removal, and/or bedding plane aquifers and were enhanced by volume reduction during dolomitization, ongoing carbonate dissolution and hydrothermal alteration. Oxidized, diagenetic fluids scavenged metals from clastic sediments and their source area, with deposition in open spaces in reduced carbonates, often immediately below an unconformity. In a few examples, nearby basalts could have provided Cu. Fluid inclusion data indicate mineralizing solutions were saline and generally low temperature, in the 100-240oC range. Mineralization may have

 
been initiated soon after host sediments became indurated and was likely a prolonged event, possibly continuing intermittently over 100's of millions of years in larger deposits. Deposits are basically formed through diagenetic processes and are an integral part of basin evolution. In some deposits, different fluids could have prevailed within oxidized and reduced strata leading to different metal sources - this could explain why only some deposits have a significant Zn-Pb-Ge component.

 

ASSOCIATED DEPOSIT TYPES: Genetic processes which form carbonate-hosted CuPbZn may be analogous to stratiform Cu (E04), carbonate hosted Zn-Pb (E12), unconformity U (I16) and sandstone U (D05) deposit types. Carbonate hosted CuPbZn deposits have many similarities with carbonate hosted Zn-Pb deposits (E12), and are possibly a link between these deposits and stratiform Cu (E04).

 

COMMENTS: Deposits often occur in the same basin as stratiform Cu or carbonate-hosted Zn-Pb deposits. Other possible candidates for this type include: Mount Isa Cu, Kilgour, Yah Yah and Cooley (Australia), Nite and Ellesmere (Northwest Territories, Canada), Lord Aylmer and Acton Vale (Quebec, Canada).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Dominantly elevated Cu but Zn, Pb, As, Ag and Ge are key indicators in rock samples; subtle Cu-stream silt geochemical anomalies occur in proximity to some deposits. Other elements which may be useful pathfinders are Co, Ga, Bi, Cd, V, Mo and Ba.

 

GEOPHYSICAL SIGNATURE: Resistivity, IP and gravity could be useful but there are no definitive tools.

 

OTHER EXPLORATION GUIDES: Tectonically disturbed zones and karsted areas within carbonate/oxidized clastic couplets of major basins are regional targets. Dolomitized zones should be carefully examined. Deposits often occur in clusters and/or in proximity to associated deposit types. Deposits oxidize readily forming gossans with secondary Cu and Fe minerals; many other secondary products and malachite-coated nuggets of copper sulphides may be present. Thermal maturation anomalies and clay mineral zoning, as applied to carbonate hosted Zn-Pb and unconformity uranium deposits, may be useful tools.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Tsumeb produced ~30 million tonnes at 4.0% Cu, 9.0% Pb and 3.2% Zn. Production plus reserves at Kipushi are believed to be about 70 million tonnes at 4.8% Cu, 8.8% Zn and 0.5% Pb. Kennecott production was 4.4 million tonnes at 12.4% Cu and 95 g/t Ag. These three deposits are the most significant producers and also reflect the highest average grades for Cu (Kennecott), Pb (Tsumeb) and Zn (Kipushi). The Ruby Creek resource is 90 million tonnes grading 1.2% Cu. Ge and Ga were produced at Tsumeb, Kipushi(?) and Apex; Apex grades were in the order of 0.06% Ge and 0.03% Ga.

 

ECONOMIC LIMITATIONS: Although several deposits have been partially mined by open pit methods, the elongate morphology usually requires underground mining. The complex suite of metallic minerals in some deposits could complicate metallurgy.

 

IMPORTANCE: Gross and unit metal values can be very high. Few significant deposits are recognized; however, the type is poorly understood and exploration efforts have been minimal.

 

SELECTED BIBLIOGRAPHY

 

ACKNOWLEDGEMENTS: Work leading to this summary was supported by BHP Minerals Canada Ltd. and their Canadian Exploration Manager, Neil le Nobel. Numerous other geologists have enhanced my understanding of this deposit type, including Tom Pollock, Murray Hitzman, Rod Kirkham, Hans Trettin and Arno Günzel. Dave Lefebure and Trygve Höy reviewed drafts and significantly improved this profile.

 

Bateman, A.M. and McLaughlin, D.H. (1920): Geology of the Ore Deposits of Kennecott, Alaska; Economic Geology, Volume 15, pages 1-80.

Bernstein, L.R. (1986): Geology and Mineralogy of the Apex Germanium-Gallium Mine, Washington County, Utah; U.S. Geological Survey, Bulletin 1577, 9 pages.

Bernstein, L.R. and Cox, D.P. (1986): Geology and Sulfide Mineralogy of the Number One Orebody, Ruby Creek Copper Deposit, Alaska; Economic Geology, Volume 81, pages 1675-1689.

Blockley, J.G. and Myers, J.S. (1990): Proterozoic Rocks of the Western Australian Shield - Geology and Mineralisation; in Geology of the Mineral Deposits of Australia and Papua New Guinea, F.E. Hughes, Editor, Australian Institute of Mining and Metallurgy, Monograph 14, pages 607-615.

British Columbia Department of Mines and Petroleum Resources (1971): Blue; in Geology, Exploration and Mining in B.C., pages 72-75.

Buffet, G., Amosse, J., Mouzita, D. and Giraud, P. (1997): Geochemistry of the M'Passa Pb-Zn Deposit, Niari syncline, People's Republic of the Congo - Arguments in Favor of a Hydrothermal Origin; Mineralium Deposita, Volume 22, pages 64-77.

Chabu, M. (1990): Metamorphism of the Kipushi Carbonate Hosted Zn-Pb-Cu deposit, Shaba, Zaire; in Regional Metamorphism of Ore Deposits, P.G. Spry and L.T. Bryndzia, Editors, Proceedings of 28th International Geological Conference, VSP, pages 27-47.

Cox, D.P. and Bernstein, L.R. (1986): Descriptive Model of Kipushi Cu-Pb-Zn; in Mineral Deposit Models, D.P. Cox and D.A. Singer, Editors, U.S. Geological Survey, Bulletin 1693, 227 pages.

Deane, J.G. (1995): The Structural Evolution of the Kombat Deposits, Otavi Mountainland, Namibia; Communications, Geological Survey of Namibia, Volume 10, pages 99-107.

De Magnee, I. and Francois, A. (1988): The Origin of the Kipushi (Cu, Zn, Pb) Deposit in Direct Relation with a Proterozoic Salt Diapir, Copperbelt of Central Africa, Shaba, Republic of Zaire; in Base Metal Sulphide Deposits, G.H. Friedrich and P.M. Herzig, Editors, Springer-Verlag, pages 74-93.

Folger, P.F. and Schmidt, J.M. (1986): Geology of the Carbonate-hosted Omar Copper Prospect, Baird Mountains, Alaska; Economic Geology, Volume 81, pages 1690-1695.

Hitzman, M.W. (1986): Geology of the Ruby Creek Copper Deposit, Southwestern Brooks Range, Alaska; Economic Geology, Volume 81, pages 1644-1674.

Hoeve, J. and Quirt, D. (1989): A Common Diagenetic-hydrothermal Origin for Unconformity-type Uranium and Stratiform Copper Deposits?; in Sediment-hosted Stratiform Copper Deposits, R.W. Boyle et al., Editors, Geological Association of Canada, Special Paper 36, pages 151-172.

Innes, J. and Chaplin, R.C. (1986): Ore Bodies of the Kombat Mine, South West Africa/Namibia; in Mineral Deposits of Southern Africa, C.R. Anhaeusser and S. Maske, Editors, Geological Society of South Africa, pages 1789-1805.

Lhoest, J.J. (1995): The Kipushi Mine, Zaire; Mineralogical Record, Volume 26, Number 3, pages 163-192.

Lombaard, A.F., Günzel, A., Innes, J. and Kruger, T.L. (1986): The Tsumeb Lead-copper-zinc-silver Deposit, South West Africa/Namibia; in Mineral Deposits of Southern Africa, C.R. Anhaeusser and S. Maske, Editors, Geological Society of South Africa, pages 1761-1787.

Ran, C. (1989): Dongchuan-type Stratabound Copper Deposits, China - a Genetic Model; in Sediment-hosted Stratiform Copper Deposits, R.W. Boyle et al., Editors, Geological Association of Canada, Special Paper 36, pages 667-677.

Ruan, H., Hua, R. and Cox, D.P. (1991): Copper Deposition by Fluid Mixing in Deformed Strata Adjacent to a Salt Diapir, Dongchuan Area, Yunnan Province, China; Economic Geology, Volume 86, pages 1539-1545.

Sagev, A. (1992): Remobilization of Uranium and Associated Metals through Karstification Processes - a Case Study from the Timna Formation (Cambrian), Southern Israel; Ore Geology Reviews, Volume 7, pages 135-148.

Steed, G.M. (1986): The Geology and Genesis of the Gortdrum Cu-Ag-Hg Orebody; in Geology and Genesis of Mineral Deposits in Ireland, C.J. Andrew, et al., Editors, Irish Association, Economic Geology, pages 481-499.

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CARBONATE-HOSTED DISSEMINATED Au-Ag

E03
by Tom Schroeter and Howard Poulsen
British Columbia Geological Survey

 

Schroeter, Tom and Poulsen, Howard (1996): Carbonate-hosted Disseminated Au-Ag, in Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, Lefebure, D.V. and Hõy, T., Editors, British Columbia Ministry of Employment and Investment, Open File 1996-13, pages 9-12.

 

IDENTIFICATION

 

SYNONYMS: Carlin-type gold, sediment-hosted micron gold, siliceous limestone replacement gold, invisible ("no-seeum") gold.

 

COMMODITIES (BYPRODUCTS): Au (Ag). In rare cases Ag dominates over Au.

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Golden Bear (104K 079); parts of Brewery Creek (Yukon, Canada), Carlin, Getchell, Cortez, Gold Acres, Jerrett Canyon, Post and Gold Quarry (Nevada, USA), Mercur (Utah, USA), Mesel? (Indonesia),Guizhou (China).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Very fine grained, micron-sized gold and sulphides disseminated in zones of decarbonated calcareous rocks and associated jasperoids. Gold occurs evenly distributed throughout hostrocks in stratabound concordant zones and in discordant breccias.

 

TECTONIC SETTINGS: Passive continental margins with subsequent deformation and intrusive activity, and possibly island arc terranes.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Host rocks to the Nevadan deposits were deposited in shelf-basin transitional (somewhat anoxic) environments, formed mainly as carbonate turbidites (up to 150 m thick), characterized by slow sedimentation. These rocks are presently allochthonous in thrust fault slices and have been overprinted by Miocene basin and range extension. There are Mesozic to Tertiary felsic plutons near many deposits.

 

AGE OF MINERALIZATION: Mainly Tertiary, but can be any age.

 

HOST/ASSOCIATED ROCK TYPES: Hostrocks are most commonly thin-bedded silty or argillaceous carbonaceous limestone or dolomite, commonly with carbonaceous shale. Although less productive, non-carbonate siliciclastic and rare metavolcanic rocks are local hosts. Felsic plutons and dikes are also mineralized at some deposits.

 

DEPOSIT FORM: Generally tabular, stratabound bodies localized at contacts between contrasting lithologies. Bodies are irregular in shape, but commonly straddle lithological contacts which, in some cases, are thrust faults. Some ore zones (often higher grade) are discordant and consist of breccias developed in steep fault zones. Sulphides (mainly pyrite) and gold are disseminated in both cases.

 

TEXTURE/STRUCTURE: Silica replacement of carbonate is accompanied by volume loss so that brecciation of hostrocks is common. Tectonic brecciation adjacent to steep normal faults is also common. Generally less than 1% fine-grained sulphides are disseminated throughout the hostrock.

 

ORE MINERALOGY (Principal and subordinate): Native gold (micron-sized), pyrite with arsenian rims, arsenopyrite, stibnite, realgar, orpiment, cinnabar, fluorite, barite, rare thallium minerals.

 

GANGUE MINERALOGY (Principal and subordinate): Fine-grained quartz, barite, clay minerals, carbonaceous matter (late-stage calcite veins).

 

ALTERATION MINERALOGY: Strongly controlled by local stratigraphic and structural features. Central core of strong silicification close to mineralization with silica veins and jasperoid; peripheral argillic alteration and decarbonation (“sanding”) of carbonate rocks common in ore. Carbonaceous material is present in some deposits.

 

WEATHERING: Nevada deposits have undergone deep supergene alteration due to Miocene weathering. Supergene alunite and kaolinite are widely developed and sulphides converted to hematite. Such weathering has made many deposits amenable to heap- leach processing.

 

GENETIC MODELS:

a) Epithermal model: Once widely accepted but now discounted for most deposits. Mineralization was thought to result from shallow Miocene magmatism related to basin and range extension. New discoveries of deep orebodies, overprinting basin and range deformation, and recognition of a supergene origin of alunite have cast doubt on this model.
b) Distal skarn model: Currently very popular because many deposits occur near intrusions, skarns and calcsilicate rocks. Carbonate-hosted disseminated gold is thought to be related to collapse of intrusion-centred porphyry-type hydrothermal systems. Although compelling for many deposits, this model fails to explain several districts (e.g., Jerritt Canyon; Guizhou, China) where no related magmatism has been observed.
c) Deep crustal fluid model: Recently proposed to account for inferred deep mixing of different fluids from different reservoirs as demanded by light stable isotopic and fluid inclusion data. Variants of this model imply only indirect links to magmatism, suggest a single Paleogene age for the Nevadan deposits and relate them to a unique period of pre-basin and range crustal extension and associated faults that are controlled by pre-existing Paleozoic and Mesozoic structures.

ORE CONTROLS:

1. Selective replacement of carbonaceous carbonate rocks adjacent to and along high-angle faults, regional thrust faults or bedding.
2. Presence of small felsic plutons (dikes) that may have caused geothermal activity and intruded a shallow hydrocarbon reservoir or area of hydrocarbon-enriched rocks, imposing a convecting geothermal system on the local groundwater.
3. Deep structural controls are believed responsible for regional trends and may be related to Precambrian crystalline basement structures and/or accreted terrane boundaries.

ASSOCIATED DEPOSIT TYPES: Porphyry (L04, L05), Au, W or Mo skarns (K04, K05, K07), polymetallic manto (J01).

 

COMMENTS: B.C.: 1. Limestone fault slices (part of accreted Stikine terrane) which have been intruded by felsic plutons, especially near high-angle fault zones, may host deposits (e.g., Golden Bear mine area). 2. Interior Plateau region - if carbonate units present - potential basin and range setting.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Two geochemical asemblages - Au+As+Hg+W or ? Mo and As+Hg+ Sb+Tl or Fe. NH3 important in some deposits. Au:Ag 10:1 or greater. Anomalous values in rock: As (100-1000 ppm); Sb (10-50 ppm); Hg (1-30 ppm).

 

GEOPHYSICAL SIGNATURE: Resistivity lows for some deposits. Aeromagnetic surveys may highlight spatially associated intrusions, skarns if present and possibly regional trends.

 

OTHER EXPLORATION GUIDES: In Nevada the deposits exhibit regional alignments or trends. Satellite imagery is useful to identify regional structures.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Grades range from 1 to 35 g/t Au and deposit sizes from 1 to 150 Mt of ore. For 43 significant deposits the median tonnages and grades for low-grade oxide and higher grade hypogene deposits are 20 Mt grading 1.2 g/t Au and 6 Mt containing 4.5 g/t Au, respectively. Supergene deposits amenable to heap leaching typically grade 1-2 g/t Au; whereas, production grades for deposits with hypogene ore typically grade 5 to 10 g/t or greater.

 

ECONOMIC LIMITATIONS: Parts of deposits are amenable to open-pit mining and heap leaching (especially oxidized zones), but roasting and autoclave extraction is required for more refractory ores. New discoveries of high-grade hypogene ore have resulted in increased underground mining.

 

IMPORTANCE: Between 1965 and 1995, deposits along the Carlin Trend (70 x 10 km), have yielded approximately 750 t of Au. Deposits that are unquestionably of this type are not presently known in Canada but may be present.

 

REFERENCES

 

Bagby, W.C. and Berger, B.R. (1985): Geologic Characteristics of Sediment-hosted, Disseminated Precious-metal Deposits in the Western United States; in Geology and Geochemistry of Epithermal Systems, Berger, B.R. and Bethke, P.M., Editors, Reviews in Economic Geology, Volume 2, Society of Economic Geologists, pages 169-202.

Bakken, B.M. and Einaudi, M.T. (1986): Spatial and Temporal Relations Between Wallrock Alteration and Gold Mineralization, Main Pit, Carlin Gold Mine, Nevada; in Proceedings of Gold '86 Symposium, Macdonald, A.J. , Editor, Geological Association of Canada, pages 388-403.

Berger, B.R. and Bagby, W.C. (1991): The Geology and Origin of Carlin-type Gold Deposits; in Gold Metallogeny and Exploration, Foster, R.P., Editor, Blackie, Glasgow and London, pages 210-248.

Christensen, O.D., Editor (1993): Gold Deposits of the Carlin Trend, Nevada; Society of Economic Geologists, Guidebook Series, Volume 18, 95 pages.

Cunningham, C.G., Ashley, R.P., I.-Ming, C., Huang, Z., Wan, C. and Li, W. (1988): Newly Discovered Sedimentary Rock-hosted Disseminated Gold Deposits in the People’s Republic of China; Economic Geology, Volume 83, pages 1462-1467.

Kuehn, C.A. and Rose, A.W. (1992): Geology and Geochemistry of Wall-rock Alteration at the Carlin Gold Deposit, Nevada; Economic Geology, Volume 87, pages 1697-1721.

Radtke, A.S., Rye, R.O. and Dickson, F.W. (1980): Geology and Stable Isotope Studies of the Carlin Gold Deposit, Nevada; Economic Geology, Volume 75, pages 641-672.

Romberger, S.B. (1988): Disseminated Gold Deposits, in Ore Deposit Models, Roberts, R.G. and Sheahan, P.A., Editors, Geoscience Canada, Ore Deposits #9, Volume 13, No. 1, pages 23-31.

Sawkins, F.J. (1990): Sediment-hosted Gold Deposits of the Great Basin; in Metal Deposits in Relation to Plate Tectonics, Springer-Verlag, pages 159-162.

Schroeter, T.G. (1986): Muddy Lake Project; in Geological Fieldwork, 1985, B. C. Ministry of Energy, Mines and Petroleum Resources, Paper 1986-1, pages 175-183.

Sillitoe, R.H. and Bonham, H.F. Jr. (1990): Sediment-hosted Gold Deposits: Distal Products of Magmatic-Hydrothermal Systems; Geology, Volume 18, pages 157-161.

 

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SEDIMENT-HOSTED Cu+/-Ag+/-Co


E04

by David V. Lefebure and Dani J. Alldrick
British Columbia Geological Survey

 

Lefebure, D.V. and Alldrick, D.J. (1996): Sediment-hosted Cu+/-Ag+/-Co, in Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, Lefebure, D.V. and Hõy, T., Editors, British Columbia Ministry of Employment and Investment, Open File 1996-13, pages 13-16.

 

IDENTIFICATION

 

SYNONYMS: Sediment-hosted stratiform copper, shale-hosted copper, Kupferschiefer-type, redbed Cu, Cu-shale, sandstone Cu.

 

COMMODITIES (BYPRODUCTS): Cu, Ag (Co, Pb, Zn, rarely PGE, Au, U, Va).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Roo (082GSW020), Commerce (082GSE065, Chal 4 (092K 068); Redstone (Northwest Territories, Canada), Kennicott (Alaska, USA), Spar Lake (Troy), Rock Creek and Montanore (Montana, USA), White Pine (Michigan, USA), Creta (Oklahoma, USA), Corocoro (Bolivia), Mansfield-Sangerhausen and Spremberg, Kupferschiefer district (Germany), Konrad and Lubin (Poland), Dzherkazgan (Kazakhstan), Copper Claim (Australia), Kamoto and Shaba, Zambia-Zaire copperbelt (Zaire).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Stratabound disseminations of native copper, chalcocite, bornite and chalcopyrite in a variety of continental sedimentary rocks including black shale, sandstone and limestone. These sequences are typically underlain by, or interbedded with, redbed sandstones with evaporite sequences. Sulphides are typically hosted by grey, green or white strata.

 

TECTONIC SETTINGS: Predominantly rift environments located in both intracontinental and continental-margin settings; they can also occur in continental-arc and back- arc settings.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: The characteristic presence of redbed and evaporite sequences points to deposition of sediments in a hot, arid to semi-arid paleoclimate near the paleoequator. The host rocks are produced in a variety of local anoxic depositional environments, including deltaic sediments, Sabkha-type lagoonal carbonate basins or high intertidal mudflats, and shallow “coal basins”.

 

AGE OF MINERALIZATION: Proterozoic or younger; Middle Proterozoic, Permian and early Mesozoic most favourable ages.

 

HOST/ASSOCIATED ROCK TYPES: Most deposits are hosted by pale gray to black shale, but some are found in sandstone, siltstone, limestone, silty dolomite, laminated carbonate units (sabkha origin) and quartzites. Favourable horizons contain reactive organic matter or sulphur. Algal mats, mudcracks and scour-and-fill structures indicative of shallow-water deposition are common. Local channel- conglomerate beds sometimes contain wood fragments. The associated sequence includes redbed sediments, evaporites and sometimes volcanics. In many cases the rift-related layered rocks rest unconformably on older basement rocks.

 

DEPOSIT FORM: Orebodies are generally conformable with the bedding, although in detail ore may transgress bedding at low angles and is typically more transgressive near the margins of the deposit. Mineralized horizons are from tens of centimetres to several metres thick (rarely more than 5 m); they are often contained within broader zones of anomalous copper values. Tabular ore zones extend laterally for kilometres to tens of kilometres. Less commonly the deposits are elongate lobes. Some deposits have a C-shaped, “roll front” configuration in cross-section. Common lateral and/or vertical zoning is from hematite (barren) > chalcocite > bornite > chalcopyrite > pyrite, or from a chalcociteñbornite core grading to chalcopyrite with peripheral galena and sphalerite.

 

TEXTURE/STRUCTURE: Sulphides are fine grained and occur as disseminations, concentrated along bedding, particularly the coarser grained fractions, or as intergranular cement. Sharp-walled cracks or veinlets (< 1 cm thick, < than a metre in length) of chalcopyrite, bornite, chalcocite, galena, sphalerite or barite with calcite occur in some deposits, but are not an important component of the ore. Pyrite can be framboidal or colloform. Cu minerals often replace pyrite grains, framboids and nodules; less commonly they form pseudomorphs of sulphate nodules or blade-shaped gypsum/anhydrite grains. They also cluster around carbonaceous clots or fragments.

 

ORE MINERALOGY (Principal and subordinate): Chalcocite, bornite and chalcopyrite; native copper in some deposits. Pyrite is abundant in rocks outside the ore zones. Enargite, digenite, djurleite, sphalerite, galena, tennantite, native silver with minor Co-pyrite and Ge minerals. In many deposits carrollite (CuCo2S4) is a rare mineral, however, it is common in the Central African Copperbelt.

 

GANGUE MINERALOGY (Principal and subordinate): Not well documented; in several deposits carbonate, quartz and feldspar formed synchronously with the ore minerals and exhibit zonal patterns that are sympathetic with the ore minerals. They infill, replace or overgrow detrital or earlier authigenic phases.

 

ALTERATION MINERALOGY: Lateral or underlying reduced zones of green, white or grey colour in redbed successions. In the Montana deposits these zones contain chlorite, magnetite and/or pyrite. Barren, hematite-rich, red zones grade into ore in the Kupferschiefer. Kupferschiefer ore hosts also show elevated vitrinite reflectances compared to equivalent stratigraphic units.

 

WEATHERING: Surface exposures may be totally leached or have malachite and azurite staining. Near surface secondary chalcocite enrichment is common.

 

ORE CONTROLS: Most sediment-hosted Cu deposits are associated with the sag phase of continental rifts characterized by deposition of shallow-water sediments represented by redbed sequences and evaporites. These formed in hot, arid to semi-arid paleoclimates which normally occur within 20-30øof the paleoequator. Hostrocks are typically black, grey or green reduced sediments with disseminated pyrite or organics. The main control on fluid flow from the source to redoxcline is primary permeability within specific rock units, commonly coarse-grained sandstones. In some districts deposits are located within coarser grained sediments on the flanks of basement highs. Growth faults provide local controls in some deposits (e.g. Spar Lake).

 

ASSOCIATED DEPOSIT TYPES: Sandstone U (D05), volcanic redbed Cu (D03), Kipushi Cu-Pb-Zn (E02), evaporite halite, sylvite, gypsum and anhydrite (F02); natural gas (mainly CH4) in Poland.

 

GENETIC MODELS: Traditionally these deposits have been regarded as syngenetic, analogous to sedex deposits or late hydrothermal epigenetic deposits. Currently most researchers emphasize a two-stage diagenetic model. Carbonaceous shales, sandstones and limestones deposited in reducing, shallow subaqeuous environments undergo diagenesis which converts the sulphur in these sediments to pyrite. At a later stage during diagenesis, saline low-temperature brines carrying copper from a distant source follow permeable units, such as oxidized redbed sandstones, until they encounter a reducing unit. At this point a redoxcline is established with a cuperiferous zone extending “downstream” until it gradually fades into the unmineralized, often pyritic, reducing unit. The source of the metals is unresolved, with possible choices including underlying volcanic rocks, labile sediments, basement rocks or intrusions.

 

COMMENTS: Sediment-hosted Cu includes Sabkha Cu deposits which are hosted by thin- bedded carbonate-evaporite-redbed ‘sabkha’ sequences.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Elevated values of Cu, Ag, Pb, Zn and Cd are found in hostrocks, sometimes with weaker Hg, Mo, V, U, Co and Ge anomalies. Dark streaks and specks in suitable rocks should be analysed as they may be sulphides, such as chalcocite.

 

GEOPHYSICAL SIGNATURE: Weak radioactivity in some deposits.

 

OTHER EXPLORATION GUIDES: Deposits often occur near the transition from redbeds to other units which is marked by the distinctive change in colour from red or purple to grey, green or black. The basal reduced unit within the stratigraphy overlying the redbeds will most often carry the highest grade mineralization.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Average deposit contains 22 Mt grading 2.1 % Cu and 23 g/t Ag (Mosier et al., 1986). Approximately 20% of these deposits average 0.24 % Co. The Lubin deposit contains 2600 Mt of >2.0% Cu and ~ 30-80 g/t Ag. Spar Lake pre-production reserves were 58 Mt grading 0.76% Cu and 54 g/t Ag. Montanore contains 134.5 Mt grading 0.74% Cu and 60 g/t Ag, while Rock Creek has reserves of 143.7 Mt containing 0.68 % Cu and 51 g/t Ag.

 

ECONOMIC LIMITATIONS: These relatively thin horizons require higher grades because they are typically mined by underground methods. The polymetallic nature and broad lateral extent of sediment-hosted Cu deposits make them attractive.

 

IMPORTANCE: These deposits are the second most important source of copper world wide after porphyry Cu deposits. They are an interesting potential exploration target in British Columbia, although there has been no production from sediment-hosted Cu deposits in the province. The stratigraphy that hosts the Spar Lake, Montanore and Rock Creek deposits in Montana extends into British Columbia where it contains numerous small sediment-hosted Cu-Ag deposits.

 

REFERENCES

 

ACKNOWLEDGEMENTS: Nick Massey contributed to the original draft of the profile.

 

Bartholom, P., Evrard, P., Katekesha, P., Lopez-Ruiz, J. and Ngongo, M. (1972): Diagenetic Ore-forming Processes at Kamoto, Katanga, Republic of the Congo; in Ores in Sediments, Amstutz, G.C. and Bernard, A.J., Editors, Springer Verlag, Berlin, pages 21-41.

Bateman, A.M. and McLaughlin, D.H. (1920): Geology of the Ore Deposits of Kennecott, Alaska; Economic Geology, Volume 15, pages 1-80.

Boyle, R.W., Brown, A.C., Jefferson, C.W., Jowett, E.C. and Kirkham, R.V., Editors, (1989): Sediment-hosted Stratiform Copper Deposits; Geological Association of Canada, Special Paper 36, 710 pages.

Brown, A.C. (1992): Sediment-hosted Stratiform Copper Deposits; Geoscience Canada, Volume 19, pages 125-141.

Ensign, C.O., White, W.S., Wright, J.C., Patrick, J.L., Leone, R.J., Hathaway, D.J., Tramell, J.W., Fritts, J.J. and Wright, T.L. (1968): Copper Deposits of the Nonesuch Shale, White Pine, Michigan; in Ore Deposits of the United States, 1933- 1967; The Graton-Sales Volume, Ridge, J.D., Editor, American Institute of Mining, Metallurgy and Petroleum Engineers, Inc., New York, pages 460-488.

Fleischer, V.D., Garlick, W.G. and Haldane, R. (1976): Geology of the Zambian Copperbelt; in Handbook of Strata-bound and Stratiform Ore Deposits, Wolf, K.H., Editor, Elsevier, Amsterdam, Volume 8, pages 223-352.

Gustafson, L.B. and Williams, N. (1981): Sediment-hosted Stratiform Deposits of Copper, Lead and Zinc; in Economic Geology Seventy-Fifth Anniversary Volume, Skinner, B.J., Editor, Economic Geology Publishing Company, pages 139-178.

Hayes, T.S. and Einaudi, M.T. (1986): Genesis of the Spar Lake Strata-bound Copper- Silver Deposit, Montana: Part I. Controls Inherited from Sedimentation and Preore Diagenesis; Economic Geology, Volume 81, pages 1899-1931.

Kirkham, R.V. (1989): Distribution, Settings, and Genesis of Sediment-hosted Stratiform Copper Deposits, in Sediment-hosted Stratiform Copper Deposits, Boyle, R.W., Brown, A.C., Jefferson, C.W., Jowett, E.C. and Kirkham, R.V., Editors, Geological Association of Canada, Special Paper 36, pages 3-38.

Kirkham, R.V., Carriere, J.J., Laramie, R.M. and Garson, D.F. (1994): Global Distribution of Sediment-hosted Stratiform Copper Deposits; Geological Survey of Canada, Open File Map 2915, 1: 35 000 000.

Mosier, D.L., Singer, D.A. and Cox, D.P. (1986): Grade and Tonnage Model of Sediment- hosted Cu; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, pages 206-8.

Renfro, A.R. (1974): Genesis of Evaporite-associated Stratiform Metalliferous Deposits - a Sabkha Process; Economic Geology, Volume 69, pages 33-45.

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SANDSTONE-Pb


E05
by D.F. Sangster
Geological Survey of Canda, Ottawa

 

Sangster, D.F. (1996): Sandstone-Pb, in Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, Lefebure, D.V. and Hõy, T, Editors, British Columbia Ministry of Employment and Investment, Open File 1996-13, pages 17-19.

 

IDENTIFICATION

 

COMMODITIES (BYPRODUCTS): Pb (Zn, Ag).

 

EXAMPLES (British Columbia - Canada/International): None in British Columbia; only two are known in Canada; Yava (Nova Scotia) and George Lake (Saskatchewan), Laisvall (Sweden), Largentière (France), Zeida (Morocco), Maubach and Mechernich (Germany).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Disseminated galena with minor sphalerite, in transgressive basal quartzite or quartzofeldspathic sandstones resting on sialic basement.

 

TECTONIC SETTING: Platformal deposits commonly found in sandstones resting directly on basement (usually cratonic) of sialic composition.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Hostrocks were deposited in environments ranging from continental fluvial to shallow marine or tidal beach. The most common environment is one of mixed continental and marine character (i.e., paralic). Host rocks in most districts are succeeded by marine sediments, suggestive of marine transgression onto the craton. Terrestrial organic debris, ranging from trace to abundant, is present in most of the post- Devonian deposits. Paleomagnetic data available in several districts indicate a low paleolatitude position (0-30 ) for all deposits. Paleoclimatic conditions ranged from warm arid to cool humid but in a majority of cases, were semiarid and warm.

 

AGE OF MINERALIZATION: Mineralization age has not been established with certainty; however, deposits are found in rocks ranging from Middle Proterozoic to Cretaceous age. Rocks of Late Proterozoic - Early Cambrian and Triassic ages contain a majority of deposits of this type.

 

HOST/ASSOCIATED ROCK TYPES: Hostrocks are grey or white (never red) quartzitic or quartzo-feldspathic sandstones and conglomerates; they are rarely siltstone or finer grained clastics. Sialic basement rocks, typically granites or granitic gneisses, underly sandstone lead deposits. Shales and associated evaporites as beds, nodules or disseminations are intercalated with the host sandstones.

 

DEPOSIT FORM: Orebodies are commonly conformable with bedding in the sandstone, especially on a mine scale. In detail, however, the ore zones may actually transgress bedding at a low angle. Sedimentary channels in the sandstone are preferentially mineralized; consequently, most deposits have a generally lensoid form. In plan, ore zones tend to be sinuous and laterally discontinous. Ore zones tend to be delimited by assay, rather than geological, boundaries. Characteristically, a higher grade core is surrounded by material that progressively decreases in grade outward. Rarely, higher grade zones occur in, and adjacent to, steep faults; consequently, in these deposits, many ore zones are narrow, lenticular bodies oriented at high angles to bedding.

 

TEXTURE/STRUCTURE: The preferred site of ore minerals is as cement between sand grains resulting in disseminated sulphide blebs or spots in massive sandstones or concentrations of sulphides along the lower, more porous portions of graded beds. The disseminated sulphides are not normally homogeneously dispersed throughout the sandstone. Two very common textures are:

i) spots, representing local accumulations of galena, as much as 2 cm in diameter. Spots may be randomly distributed in the sandstone or may show a slight preferential alignment parallel to bedding;


ii) discontinous galena-rich streaks distributed parallel to bedding, including crossbedding. Where carbonaceous material is present, sulphides fill wood cells or replace cell walls. Concretionary-like sulphide concentrations are abundant in some deposits. Epitaxial quartz overgrowths on detrital quartz grains are very common and in some deposits more abundant within or near ore zones than regionally. Paragenetic studies indicate the epitaxial quartz predates galena.

ORE MINERALOGY (Principal and subordinate): Galena, sphalerite, and pyrite, chalcopyrite and various Ni-Co-Fe sulphides. Replacement of sulphides by secondary analogues has been reported in one or more deposits.

 

GANGUE MINERALOGY (Principal and subordinate): Silica, usually chalcedonic, and various carbonate minerals constitute the most abundant non-sulphide cement.

 

ALTERATION MINERALOGY: If the hostrocks were originally arkosic, pre-mineralization alteration (sometimes referred to as "chemical erosion") of the host sandstones commonly results in complete, or near-complete, destruction of any feldspars and mafic minerals which may have been present. Otherwise, alteration of quartz sandstone hosts is nil. Neomorphic formation of quartz overgrowths and authigenic clay minerals, however, is a common feature of these deposits; calcite and sulphates are less common cements. Pre-sandstone weathering of granitic basement, as evidenced by the presence of paleoregolith and the destruction of feldspar and mafic minerals, has been observed beneath several deposits.

 

ORE CONTROLS: 1. Sialic basement; those with average lead content greater than ~30 ppm are particularly significant. 2. Basal portion of grey or white (not red) quartzitic sandstone of a transgressive sequence on sialic basement. The "cleaner" portions, with minimum intergranular material, are the preferred host lithologies because they are more porous. 3. Channels in sandstone, especially on the periphery of the sedimentary basin. These channels may also be evident in the basement.

 

GENETIC MODEL: Groundwater transport of metals leached from lead-rich basement, through porosity channels in sandstone; precipitation of metals by biogenically- produced sulphide. A genetic model involving compaction of brine-bearing basins by over-riding nappes has been proposed for deposits in Sweden.

 

ASSOCIATED DEPOSIT TYPES: Sandstone Cu and sandstone U (D05).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Stream sediment and soil geochemical surveys; analyze for Pb and Zn.

 

GEOPHYSICAL SIGNATURE: Induced polarization anomalies (?)

 

OTHER EXPLORATION GUIDES: Epitaxial quartz overgrowths are abundant, especially within and near the ore zones. Host sandstones deposited at low paleolatitudes. Sialic basement with high lead content (>30 ppm). Basal quartz sandstone of a transgressive sequence, overlying basement. Channels in sandstone as evidenced by thickening, lateral conglomerate-to-sandstone facies changes, etc. Permeable zones in sandstone (i.e., “cleanest” sandstone, minimum of intergranular clayey material).

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Deposits range in grade from 2 to 5% Pb, 0.2 to 0.8% Zn, 1 to 20 g/t Ag; most are less than 10 Mt in size. Because of the disseminated nature of the ore, tonnages and grades can be markedly affected by changes in cut-off grades. At Yava, for example, at cut-off grades of 1, 2, and 3%, tonnages and grades are as follows: 71.2 Mt at 2.09% Pb, 30.3 Mt at 3.01%, and 12.6 Mt at 3.95%, respectively.

 

ECONOMIC LIMITATIONS: Because of the typically low Pb grades and the general paucity of byproduct commodities, this deposit type has always been a minor player in the world's base metal markets.

 

IMPORTANCE: In some countries where other sources of Pb are limited, sandstone-Pb deposits have constituted major national resources of this metal (e.g. Sweden).

 

REFERENCES

 

Bjírlykke, A. and Sangster, D.F. (1981): An Overview of Sandstone-Lead Deposits and their Relation to Red-bed Copper and Carbonate-Hosted Lead-Zinc Deposits; in Economic Geology 75th Anniversary Volume, 1905- 1980, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 179-213.

Bjírlykke, A., Sangster, D.F. and Fehn, U. (1991): Relationships Between High Heat-producing (HHP) Granites and Stratabound Lead-Zinc Deposits; in Source, Transport and Deposition of Metals, Proceedings of the 25th Anniversary Meeting, Pagel, M. and Leroy, J.L., Editors, Society of Geology Applied to Mineral Deposits, pages 257-260.

Bjírlykke, A. and Thorpe, R.I. (1983): The Source of Lead in the Olsen Sandstone-Lead Deposit on the Baltic Shield, Norway; Economic Geology, Volume 76, pages 1205-1210.

Rickard, D.T., Wildn, M.Y., Marinder, N.E. and Donnelly, T.H. (1979): Studies on the Genesis of the Laisval Sandstone Lead-Zinc Deposits; Economic Geology, Volume 74, pages 1255-1285.

Sangster, D.F. and Vaillancourt, P.D. (1990): Paleo-geomorphology in the Exploration for Undiscovered Sandstone-lead Deposits, Salmon River Basin, Nova Scotia; Canadian Institute of Mining and Metallurgy, Bulletin, Volume 83, pages 62-68.

Sangster, D.F. and Vaillancourt, P.D. (1990): Geology of the Yava Sandstone- Lead Deposit, Cape Breton Island, Nova Scotia, Canada; in Mineral Deposit Studies in Nova Scotia, Volume 1, Sangster, A.L., Editor, Geological Survey of Canada, Paper 90-8, pages 203-244.

 [Back to top]

BENTONITE


E06
by Z.D. Hora
British Columbia Geological Survey

 

Hora, Z.D. (1999): Bentonite; in Selected British Columbia Mineral Deposit Profiles, Volume 3, Industrial Minerals, G.J. Simandl, Z.D. Hora and D.V. Lefebure, Editors, British Columbia Ministry of Energy and Mines, Open File 1999-10, pages 27-29

 

IDENTIFICATION

 

SYNONYMS: Sodium and calcium montmorillonites, montmorillonite clay, smectite clay, volcanic clay, soap clay, mineral soap. Other terms for sodium montmorillonites are sodium bentonite, swelling bentonite, Wyoming or Western bentonite, while calcium montmorillonites are referred to as calcium bentonites, non-swelling bentonite, Southern bentonite or fuller's earth, sub-bentonite.

 

COMMODITY: Bentonite (many different grades for a variety of applications and end uses).

 

EXAMPLES (British Columbia (MINFILE #)- Canada/International): Hat Creek (092INW084), Princeton (092HSE151), Quilchena (092ISE138), French Bar (092099); Rosalind (Alberta, Canada), Truax (Saskatchewan, Canada) Morden (Manitoba, Canada), Black Hills District, Big Horn Basin (Wyoming, USA), Gonzales and Lafayette Counties (Texas, USA), Itawambaand and Monroe Counties (Mississippi, USA), Milos (Greece), Landshut (Germany), Sardinia (Italy), Annaka (Japan), Campina Grande (Brazil).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Montmorillonite-rich clay beds intercalated with shales, sandstones and marls which are part of shallow marine or lacustrine environment deposits.

 

TECTONIC SETTINGS: Virtually all continental or continental platform settings; also common in island arcs.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Bentonite deposits form when volcanic ash is deposited in a variety of freshwater (sometimes alkaline lakes) and marine basins characterized by low energy depositional environments and temperate climatic conditions.

 

AGE OF MINERALIZATION: Mostly Cretaceous to Miocene age, but are known to be as old as Jurassic and as recent as Pleistocene.

 

HOST/ASSOCIATED ROCK TYPES: Bentonites are hosted by and associated with argillite, mudstone, siltstone, sandstone, tuff, agglomerate, ignimbrites, marl, shale, zeolite beds and coal.

 

DEPOSIT FORM: Beds range in thickness from several centimeters to tens of meters and can extend hundreds of kilometres. In island arc environment, bentonite can also occur as lens-shaped bodies with a limited lateral extent.

 

TEXTURE/STRUCTURE: Bentonite is bedded, with a soapy texture and waxy appearance. It ranges in colour from white to yellow to olive green to brown to blue. In outcrop, bentonite has a distinctive "popcorn" texture.

 

ORE MINERALOGY [Principal and subordinate]: Montmorillonite, beidellite, illite.

 

GANGUE MINERALOGY [Principal and subordinate]: Mica, feldspar, quartz, calcite, zeolites, gypsum, opaline silica, cristobalite, unaltered volcanic glass. These minerals rarely constitute more than 10% of a commercially viable deposit.

 

ALTERATION MINERALOGY: Alteration consists of devitrification of the volcanic ash with hydration and crystallization of the smectite mineral. In some instances there is evidence of a loss of alkalies during the alteration. Also, silicification of beds underlying some bentonites indicates downward migration of silica. There is also sometimes an increase in magnesium content compared to parent material. Besides smectite minerals, other alteration products in the volcanic ash include cristobalite, opaline silica, zeolites, calcite, selenite and various iron sulphate minerals.

 

WEATHERING: Yellow colouration (the result of oxidized iron ions) may improve the colloidal properties of bentonite. Also, weathering may decrease exchangeable calcium and increase exchangeable sodium. Some soluble impurities like calcite, iron sulphates or selenite may be removed by weathering process.

 

ORE CONTROLS: The regional extent of bentonite deposits is controlled by the limit of the regional deposition environment, paleogeography and distribution of the volcanic pyroclastic unit. Porosity of the host rocks may be important for the alteration process. Deposits in the continental and continental platform settings are the largest.

 

GENETIC MODELS: Volcanic pyroclastic material is ejected and deposited in shallow marine or lacustrine setting.

Bentonite is a product of alteration of the glass component of ashes and agglomerates. Alteration of the glassy pyroclastic material possibly starts when the ash contacts the water or may occur soon after the ash reaches the seafloor or lake bottom. Wyoming bentonites, however, were altered after burial by reaction with diagenetic seawater pore fluids.

 

ASSOCIATED DEPOSIT TYPES: Other clays, zeolite (D01, D02), lignite coal (A02), sepiolite, palygorskite (F05).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Nil

 

GEOPHYSICAL SIGNATURE: Apparent resistivity and refraction seismic survey may help to interpret the lithology.

 

OTHER EXPLORATION GUIDES: Sedimentary basins with volcanic ash layers. In some locations bentonite layers can form a plane of weakness that results in landslides. Montmorillonite displays popcorn texture on the dry surface.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Montmorillonite content is usually more than 80%. Other properties depend on specifications for particular applications. Published data on individual deposits are very scarce. Typically, commercial beds in Wyoming are 0.9 to 1.5 metres thick. Individual bentonite beds are continuous for several kilometres. The Wilcox mine in Saskatchewan has three bentonite seams - 61, 46 and 30 centimetres thick within a 6 metre thick sequence of shale. In Manitoba, another mine has 6 beds which have a cumulative thickness of about 76 centimetres within a 1 meter sequence.

 

ECONOMIC LIMITATIONS: Value of the product depends on the type of impurities, colour, size of clay particles, cation exchange capability, rheological properties and structures of the clay. Sodium bentonites are of more interest because of swelling properties and in general higher cation exchange capacity. Calcium bentonites are frequently activated by acids or soda ash to provide better performing product. Economic viability is often determined by the thickness of the overlying strata and overburden. The Wyoming deposits are mined with up to 12 metres of overburden. The 1997 quoted price for Wyoming bentonite is from US$25 to 40 a short ton.

 

END USES: Main uses for bentonite are in foundry sands, drilling muds, iron ore pelletizing and absorbents. Important applications are also in civil engineering for a variety of composite liners and as a food additive for poultry and domestic animals. (Special uses include filtration in food processing, cosmetics and pharmaceuticals.)

 

IMPORTANCE: Bentonite is an important industrial mineral; about 6 million tonnes are produced annually in North America. Declining markets in drilling mud and pelletizing will likely be easily offset by increasing use in environmental applications like liners and sealers.

 

SELECTED BIBLIOGRAPHY

 

Elzea, J. and Murray, H.H. (1994): Bentonite; in Industrial Minerals and Rocks, D.D. Carr, Editor, Society for Mining, Metallurgy, and Exploration, Inc., Littleton, Colorado, pages 233-246.

Grim, R.E. and Güven, N. (1978): Bentonites: Geology, Mineralogy, Properties and Uses; Developments in Sedimentology 24, Elsevier Publishing Company, New York, 256 pages.

Guillet, G.R. and Martin, W. Editors (1984): The Geology of Industrial Minerals in Canada; Special Volume 29, The Canadian Institute of Mining and Metallurgy, 350 pages.

Güven, N. (1989): Smectites; in Hydrous Phyllosilicates, Bailey, S.W., Editor, Reviews in Mineralogy, Volume 19, Mineralogical Society of America, pages 497-560.

Harben, P.W. and Bates, R.L. (1990): Industrial Minerals and World Deposits; Metal Bulletin, London, 312 pages.

Robertson, R.H.S. (1986): Fuller's Earth - a History of Calcium Montmorillonite; Mineralogical Society, Occasional Publication, Volturna Press, 412 pages.

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SEDIMENTARY KAOLIN


E07

by Z.D. Hora
British Columbia Geological Survey

 

Hora, Z.D. (1999): Sedimentary Kaolin; in Selected British Columbia Mineral Deposit Profiles, Volume 3, Industrial Minerals, G.J. Simandl, Z.D. Hora and D.V. Lefebure, Editors, British Columbia Ministry of Energy and Mines, Open File 1999-10, pages 31-33.

 

IDENTIFICATION

 

SYNONYMS: Secondary kaolin deposits, fireclay, underclays, high-alumina clay, china clay.

 

COMMODITIES (BYPRODUCTS): Kaolin (many different grades for specific applications), ceramic clay, ball clay, refractory clay (cement rock, bauxite, silica sand).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Sumas Mountain (092GSE004, 092GSE024), Blue Mountain (092GSE028), Lang Bay (092F 137), Quinsam (092F 319), Giscome Rapids (093J 020); Cypress Hills (Alberta, Canada), Eastend, Wood Mountain, Ravenscrag (Saskatchewan, Canada), Moose River Basin (Ontario, Canada), Shubenacadie Valley (Nova Scotia, Canada), Aiken (South Carolina, USA), Wrens, Sandersville, Macon-Gordon, Andersonville (Georgia, USA), Eufaula (Alabama, USA), Weipa (Queensland, Australia), Jari, Capim (Brazil).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Beds, lenses and saucer-shaped bodies of kaolinitic claystones hosted by clastic sedimentary rocks, with or without coaly layers or coal seams. They usually occur in freshwater basins filled with sediments derived from deeply weathered, crystalline feldspathic rocks.

 

TECTONIC SETTINGS: Low-lying coastal plains at continental edge; extension basins in orogenic belts; stable continental basins; back arc basins.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Clay beds are generally deposited in low energy environments within freshwater basins. Temperate to tropical climatic conditions can produce intensive kaolinitic weathering of feldspathic rocks of granitic composition. The kaolin is then eroded and transported to estuaries, lagoons, oxbow lakes and ponds.

 

AGE OF MINERALIZATION: Most of the world class deposits are Upper Cretaceous to Eocene age. Some "fireclay" and "underclay" deposits are Late Carboniferous.

 

HOST/ASSOCIATED ROCK TYPES: Kaolin beds are associated with variably kaolinitic, micaceous sandstones within mudstone, siltstone, sandstone and conglomerate sequences which often are cross-bedded. Coal (sub-bituminous and liqnite) may be associated with kaolin beds. Diatomite may also be present.

 

DEPOSIT FORM: Beds exhibit variable thickness, usually a few metres; sometimes multiple beds have an aggregate thickness of approximately 20 metres. Deposits commonly extend over areas of at least several square kilometers.

 

TEXTURE/STRUCTURE: Kaolin is soft and exhibits conchoidal or semiconchoidal fracture; it can be bedded or massive. Most kaolins will slake in water, but some "flint" varieties break into smaller angular fragments only. Depending on kaolin particle size and presence of organic matter, some clays may be very plastic when moist and are usually called "ball clays".

 

ORE MINERALOGY [Principal and subordinate]: Kaolinite, halloysite, quartz, dickite, nacrite, diaspor, boehmite, gibbsite.

 

GANGUE MINERALOGY [Principal and subordinate]: Quartz, limonite, goethite, feldspar, mica, siderite, pyrite, illmenite, leucoxene, anatas.

 

WEATHERING: The kaolin forms by weathering which results in decomposition of feldspars and other aluminosilicates and removal of fluxing components like alkalies or iron. Post depositional weathering and leaching can produce gibbsitic bauxite. In some deposits, post depositional weathering may improve crystallinity of kaolin particles and increase the size of crystal aggregates.

 

ORE CONTROLS: The formation and localization of clay is controlled by the location of the sedimentary basin and the presence of weathered, granitic rocks adjacent to the basin, particularly rapidly eroding paleotopographic highs.

 

GENETIC MODELS: Ideal conditions to produce kaolinitic chemical weathering are high rainfall, warm temperatures, lush vegetation, low relief and high groundwater table. The kaolin is eroded and transported by streams to a quiet, fresh or brackish, water environment. Post-depositional leaching, oxidation, and diagenesis can significantly modify the original clay mineralogy with improvement of kaolin quality.

 

ASSOCIATED DEPOSIT TYPES: Peat (A01), coal seams (A02, A03, A04), paleoplacers (C04), some bentonites (E06), lacustrine diatomite (F06).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: None. Enrichment in Al does not provide sufficient contrast with host sediments.

 

GEOPHYSICAL SIGNATURE: Apparent resistivity and refraction seismic surveys can be used in exploration for fireclay beds.

 

OTHER EXPLORATION GUIDES: Most readily ascertainable regional attribute is sedimentary basins with Upper Cretaceous and Eocene unconformities. Within these basins kaolin occurs with sediments, including coal seams, deposited in low energy environments.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Published data on individual deposits are very scarce. Deposits in Georgia, USA contain 90 to 95% kaolinite. Individual Cretaceous beds are reported to be up to 12 m thick and extend more than 2 km while those in the Tertiary sequence are 10 to 25 m thick and up to 18 km along strike. The Weipa deposit in Australia is 8 to 12 m thick and contains 40 to 70% kaolinite. The Jari deposit in Brazil is reported to contain more than 250 Mt of "good, commercial grade kaolin". Over 200 Mt of reserves "have been proven" at Capim deposit in Brazil. Ball clay deposits in Tennessee and Kentucky consist of kaolin with from 5 to 30% silica; individual deposits may be more than 9 m thick and extend over areas from 100 to 800 m long and up to 300 m wide.

 

ECONOMIC LIMITATIONS: Physical and chemical properties affect end use. Physical properties include brightness, particle size distribution, particle shape and rheology. Limonite staining is a negative feature. The high level of processing required to meet industry specifications and minimize transportation cost to the end user are the main limiting factors for kaolin use. While local sources compete for low value markets, high quality products may be shipped to users several thousand km from the plant. Most production is from open pits; good quality fireclay seams more than 2 meters thick are sometimes mined underground. Typically, paper coating grade sells for up to US$120, filler grade for up to US$92 and sanitary ceramics grade for $US55 to $65 per short ton (Industrial Minerals, 1997). Refractory and ball clay prices are within the same range.

 

END USES: The most important use for kaolin is in the paper industry, both as a filler and coating pigment. A variety of industrial filler applications (rubber, paints, plastics, etc.) are another major end use. Kaolin's traditional use in ceramic products is holding steady, but the refractory use has declined substantially in the last two decades because of replacement by other high performance products.

 

IMPORTANCE: One of the most important industrial minerals in North America. Over 11 Mt is produced annually and production is on a steady increase.

 

SELECTED BIBLIOGRAPHY

 

Bristow, C.M. (1987): World Kaolins - Genesis, Exploitation and Application, Industrial Minerals, No. 238, pages 45-59.

Guillet, G.R. and Martin, W., Editors (1984): The Geology of Industrial Minerals in Canada, Special Volume 29, The Canadian Institute of Mining and Metallurgy, 350 pages.

Harben, P.W. and Bates, R.L. (1990): Industrial Minerals and World Deposits, Metal Bulletin, London, 312 pages.

Malkovsky, M. and Vachtl, J., Editors (1969): Kaolin Deposits of the World, A-Europe, B-Overseas Countries; Proceedings of Symposium 1, 23rd International Geological Congress, Prague, 1968, 460 pages.

Malkovsky, M. and Vachtl, J., Editors (1969): Genesis of the Kaolin Deposits; Proceedings of the Symposium 1, 23rd International Geological Congress, Prague, 1988, 135 pages.

Murray, H.H. (1989): Kaolin Minerals: Their Genesis and Occurrences, Hydrous Phyllosilicates, in Reviews in Mineralogy, Bailey, S.W., Editor, Mineralogical Society of America, Volume 19, pages 67-89.

Murray, H.H., Bundy, W.M. and Harvey, C.C., Editors (1993): Kaolin Genesis and Utilization, The Clay Minerals Society, Boulder, Colorado, 341 pages.

Patterson, S.H. and Murray, H.H. (1984): Kaolin, Refractory Clay, Ball Clay and Halloysite in North America, Hawaii, and the Caribbean Region; U.S. Geological Survey, Professional Paper 1306, 56 pages.

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CARBONATE-HOSTED TALC


E08
by G.J. Simandl1 and S. Paradis2

1 British Columbia Geological Survey, Victoria, B.C., Canada
2Geological Survey of Canada, Pacific Geoscience Centre, Sidney, B.C., Canada

 

Simandl, G.J. and Paradis, S. (1999): Carbonate-hosted talc; in Selected British Columbia Mineral Deposit Profiles, Volume 3, Industrial Minerals, G.J. Simandl, Z.D. Hora and D.V. Lefebure, Editors, British Columbia Ministry of Energy and Mines, Open File 1990-10, pages 35-38.

 

IDENTIFICATION

 

SYNONYMS: "Dolomite-hosted" talc deposits.

 

COMMODITIES: Talc and/or tremolite. Some of the commercial products derived from carbonate-hosted deposits and marketed as talc, contain over 50% tremolite.

 

EXAMPLES (British Columbia - Canada/International): Gold Dollar (082O 001), Red Mountain (082O 002), Saddle Occurrences (082O 003); Henderson Talc Deposit (Ontario, Canada), Treasure mine (Montana, USA), Gouverneur Talc (New York State, USA) and Trimouns deposit (France).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Most of the economic carbonate-hosted deposits are lenticular or sheet-like bodies and are concordant with surrounding dolomitic marbles, siliceous dolomitic marbles, dolomites, schists and phyllites. The massive or schistose ore consists mainly of talc ± dolomite, ± tremolite, ± calcite, ± magnesite, ± chlorite, ± serpentine, ± phlogopite.

 

TECTONIC SETTING: Protolith deposited mainly in pericratonic environments; in most cases the talc formed later within metamorphic, fold or thrust belts.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING:  Dolostones, dolomitic marbles or magnesite beds metamorphosed to greenschist facies or lower amphibolite facies represent a typical host environment. Upper amphibolite-grade marbles, where talc would not normally be stable, may contain retrograde talc zones.

 

AGE OF MINERALIZATION:  Mainly Precambrian to Early Paleozoic but may be younger. In most cases syn- or post-metamorphic.

 

HOST/ASSOCIATED ROCK TYPES: Dolomitic marbles and dolomites are the typical host, however some of the deposits are hosted by magnesite or mica schists. Phyllites, chlorite or mica schists, paragneiss and intrusive and metavolcanic rocks may be present adjacent to, or in the proximity of the talc deposits. Deposits may be crosscut by minor intrusions, such as diabase dikes.

 

DEPOSIT FORM: In most cases, podiform or deformed, sheet-like bodies oriented subparallel to the compositional layering within marbles and to geologic contacts. They commonly pinch and swell. Typical dimensions would be 2 to 20 m thick and tens to hundreds of m along strike and dip. Where fluids were the principal source of heat and/or silica, breccia zones and irregular deposits may occur near fault intersections.

 

TEXTURE/STRUCTURE:  Ore varies from fine-grained, massive or layered talc to coarse talc schists. Pseudomorphs of talc after tremolite are common in deposits that formed after the peak of metamorphism.

 

ORE [Principal and subordinate]:  Talc and tremolite (in some ores and commercial products tremolite is a principal constituent).

 

GANGUE MINERALOGY [Principal and subordinate]:  Dolomite, ± tremolite, ± calcite, ± magnesite, ± chlorite, ± serpentine, and ± phlogopite may be principal gangue minerals. Pyrite, ± graphite, ± mica, ± dravite, and ± anorthite are common accessory impurities.

 

ALTERATION MINERALOGY: In some deposits at least a portion of talc is believed to have formed by retrograde reactions from tremolite. In some cases, there is a replacement of biotite by chlorite and feldspar by sericite or chlorite in the host rock.

 

WEATHERING: Talc-bearing zones may form ridges where chemical processes dominate and topographic lows where physical weathering and/or glaciation are most important.

 

ORE CONTROLS: The main controls are the presence of dolomite or magnesite protolith, availability of silica and favourable metamorphic/metasomatic conditions. Talc deposits hosted by carbonate rocks may be divided into several subtypes according to the source of silica and geological setting:

a) contacts between carbonates, usually dolomitic marbles, and silica-bearing rocks, such as biotite-quartz-feldspar gneisses, schists, cherts and quartzites;
b) horizons or lenses of siliceous dolomite or magnesite protolith;
c) crests of folds, breccia zones, faults, and intersections of fault systems that permit circulation of metasomatic fluids carrying silica within dolomite or magnesite host; and
d) carbonates within the contact metamorphic aureole of intrusions, where silica has been derived from adjacent host rock.

GENETIC MODEL:  Most carbonate-hosted talc deposits are believed to be formed by the reaction:

3 dolomite + 4 SiO2 + H2O = 1 talc + 3 calcite + 3 CO2

 

Silica may be provided either from adjacent quartz-bearing rocks, from silica layers within the carbonates, or by hydrothermal fluids. Absence of calcite in ores from several deposits indicates that talc may have formed in an open system environment and calcium was allowed to escape. The source of heat may be provided by regional metamorphism, contact metamorphism or by heat exchange from hydrothermal fluid. In environments where sedimentary-hosted magnesite deposits are known to occur, talc could have been produced by the reaction:

3 magnesite + 4 SiO2 + H2O = 1 talc + 3 CO2

 

In this second reaction calcite precipitation is not expected. This reaction takes place at lower temperature (given identical pressure and XCO2 conditions) than the dolomite reaction, therefore, magnesite may be almost

completely converted to talc before dolomite starts to react.

 

Pseudomorphs of talc after tremolite and the presence of upper amphibolite grade, metamorphic assemblages in host rocks of some of the deposits indicate that talc post-dates the metamorphic peak and is probably of retrograde origin. Depending on the individual deposits, metamorphic or metasomatic (hydrothermal) characteristics may be predominant.

 

ASSOCIATED DEPOSIT TYPES: Chlorite deposits, marble (R04), high-calcium carbonate (filler-grade) and limestone (R09), dolostone (R10), sedimentary-hosted magnesite deposits (E09) and deposits such as Balmat, which is probably a metamorphosed sedex deposit (E14).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE:  Systematic study of soils to identify anomalous concentrations of talc using the X-ray diffraction method has proven successful.

 

GEOPHYSICAL SIGNATURE:  Electromagnetic methods can be used to identify carbonate contacts with other lithologies or talc-related fault zones impregnated with water.

 

OTHER EXPLORATION GUIDES:  Talc in residual soils. Talc occurs within belts of dolomitic rocks in metamorphosed terranes or adjacent to intrusive rocks. Contacts with silica-bearing metasediments or intrusions are favourable loci for deposits.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE:  Grade is highly variable. For example, New York state talc ores commonly contain over 50% tremolite.

 

ECONOMIC LIMITATIONS:  Major talc producing countries are China, USA, Finland, France, Brazil and Australia. Underground mining is economically feasible in case of high quality ores, but most mining is by open pit. Actinolite, tremolite and anthophyllite impurities are undesirable because of environmental restrictions on these minerals. The most common properties measured to determine possible applications for talc concentrates are: mineral composition, dry brightness (green filter), whiteness, specific gravity, oil absorption, pH, particle size distribution, tapped density, loose density, Hegman fineness and chemical composition including L.O.I.

 

END USES: In 1996, almost 1 million tonnes of talc valued at $US 100 million was sold or used in the USA. Talc is used in ceramics (28%), paint (18%), paper (17%), plastics (6%), roofing (11%) and cosmetics (4%). Insecticides, rubber refractories and other applications account for 16% (in USA). Cut or sawed blocks of fine-grained talc (steatite which is also used for carving) may sell for up to $US 2000.00 tonne. Paint and ceramic-grade talc is sold for $US 110.00 to 200.00/tonne, depending on the degree and method of processing. Some filler grades are sold at $US 600.00/tonne and cosmetic-grade talc and surface treated materials may sell for more than $US 2000.00/tonne.

 

IMPORTANCE:  Talc may be substituted by clay or pyrophyllite in ceramics; by high calcium carbonate and kaolin in some paper applications and by other fillers and reinforcing agents in plastics. Talc from carbonate-hosted deposits also has to compete with products derived from ultramafic-hosted talc deposits (M07) in a number of applications. In North America carbonate-hosted deposits supply mainly the ceramic, paint and, to some extent the plastic markets.

 

REFERENCES

 

Andrews, P.R.A. (1994):  The Beneficiation of Canadian Talc and Pyrophyllite Ores: a Review of Processing Studies at CANMET; Canadian Institute of Mining and Metallurgy Bulletin, Volume 87, No.984, pages 64-68.

Anonymous (1993):  The Economics of Talc and Pyrophyllite; 7th Edition; Roskill Information Services Ltd.,

London, England, 266 pages.

Bates, R.I. (1969):  Geology of Industrial Rocks and Minerals; Dover Publications Inc, New York, 459 pages.

Benvenuto, G. (1993):  Geology of Several Talc Occurrences in Middle Cambrian Dolomites, Southern Rocky Mountains, British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Geological Survey Branch, Geological Fieldwork, Paper 1993-1, pages 361-379.

Berg, R.B. (1991):  Geology of Talc and Chlorite Deposits in Montana. Proceedings of the 27th Forum on Geology

of Industrial Minerals, Banff, Alberta; B.C. Ministry of Energy Mines and Petroleum Resources, Open File 1991-23, pages 81-92.

Blount, A.M. and Vassiliou, A.H. (1980):  The Mineralogy and Origin of the Talc Deposits near Winterboro, Alabama. Economic Geology, Volume 75, pages 107-116.

Brown, C.E. (1982):  New York Talc; in Characteristics of Mineral Deposit Occurrences, R.L. Erickson, Compiler, U.S. Geological Survey, Open File 1982-795,
pages 239-240.

Harris, M. and Ionides, G.N. (1994):  Update of a Market Study for Talc; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1994-24, 44 pages.

MacLean, M. (1988):  Talc and Pyrophyllite in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1988-19, 108 pages.

Piniazkiewicz, J., McCarthy, E.F. and Genco, N.A. (1994): Talc; in Carr, D.D. Editor, Industrial Minerals and Rocks, 6th Edition, Society for Mining, Metallurgy, and Exploration, Inc., Littleton, Colorado, pages 1049-1069.

 

Sims, C. (1997): Talc Markets - A World of Regional Diversity; Industrial Minerals, May 1997, pages 39-51.

Simandl, G.J. (1985): Geology and Geochemistry of Talc Deposits in Madoc Area, Ontario; Carleton University, Ottawa, unpublished M. Sc. Thesis, 154 pages.

Spence, H.S. (1940): Talc, Steatite and Soapstone; Pyrophyllite; Canada Department of Mines and Resources, Number 803, 146 pages.

Virta, R.L., Roberts, L. and Hatch, R. (1997): Talc and Pyrophylite, Annual Review; U.S. Geological Survey, 8 pages.

Wright, L.A. (1968): Talc Deposits of the Southern Death Valley-Kingston Range Region, California; California Division of Mines and Geology; Special Report 38, 79 pages.

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SPARRY MAGNESITE


E09

by G.J. Simandl and K. Hancock
British Columbia Geological Survey

 

Hora, Z.D. (1999): Sparry Magnesite; in Selected British Columbia Mineral Deposit Profiles, Volume 3, Industrial Minerals, G.J. Simandl, Z.D. Hora and D.V. Lefebure, Editors, British Columbia Ministry of Energy and Mines, Open File 1999-10, pages 39-41

 

IDENTIFICATION

 

SYNONYMS: Veitsch-type, carbonate-hosted magnesite, crystalline magnesite.

 

COMMODITY: Magnesite.

 

EXAMPLES (British Columbia (MINFILE) - Canada/International): Mount Brussilof (082JNW001), Marysville (082GNW005), Brisco area and Driftwood Creek (082KNE068); Veitsch, Entachen Alm, Hochfilzen, Radenthein and Breitenau (Austria), Eugui (Navarra Province, Spain), deposits of Ashan area, Liaoning Province (China), Satka deposit (Russia).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Stratabound and typically stratiform, lens-shaped zones of coarse-grained magnesite mainly occurring in carbonates but also observed in sandstones or other clastic sediments. Magnesite exhibits characteristic sparry texture.

 

TECTONIC SETTING: Typically continental margin or marine platform, possibly continental settings, occur in belts.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: The host sediments are deposited in a shallow marine environment adjacent to paleobathymetric highs or a lacustrine evaporitic environment.

 

AGE OF MINERALIZATION: Proterozoic or Paleozoic.

 

HOST/ASSOCIATED ROCK TYPES: Magnesite rock, dolostone, limestones, shales, chert. Associated with sandstone, conglomerate and volcanics and their metamorphic equivalents.

 

DEPOSIT FORM: Commonly strata, lenses or rarely irregular masses, typically few hundred metres to several kilometres in strike length. Shortest dimension of the orebody (metres to tens of metres) is commonly normal to the bedding planes.

 

TEXTURE/STRUCTURE: The magnesite-bearing rocks exhibit sparry, pinolitic, zebra-like, or xenotopic (anhedral) textures on the fresh surface. Magnesite or dolomite pseudomorphs after sulphates. "Box-textures", rosettes, monopolar and antipolar growths are locally present.

 

ORE MINERALOGY: Magnesite.

 

GANGUE MINERALOGY (Principal and subordinate): Dolomite ± quartz ± chert ± talc ± chlorite ± sulphides ± sulphosalts, ± calcite, ± mica, ± palygorskite, ± aragonite, ± clay (as veinlets), organic material. In highly metamorphosed terrains, metamorphic minerals derived from above precursors will be present.

 

ALTERATION MINERALOGY: Talc may form on quartz-magnesite boundaries due to low temperature metamorphism.

 

WEATHERING: Surface exposures are typically beige or pale brown and characterized by "granola-like" appearance. Most sulphides are altered into oxides in near surface environment.

 

ORE CONTROLS: Deposits are stratabound, commonly associated with unconformities. They are typically located in basins characterized by shallow marine depositional environments. Lenses may be located at various stratigraphic levels within magnesite-hosting formation.

 

GENETIC MODELS: There are two preferred theories regarding the origin of sparry magnesite deposits:
1) Replacement of dolomitized, permeable carbonates by magnesite due to interaction with a metasomatic fluid.
2) Diagenetic recrystallization of a magnesia-rich protolith deposited as chemical sediments in marine or lacustrine settings. The sediments would have consisted of fine-grained magnesite, hydromagnesite, huntite or other low temperature magnesia-bearing minerals.


The main difference between these hypotheses is the source of magnesia; external for metasomatic replacement and in situ in the case of diagenetic recrystalization. Temperatures of homogenization of fluid inclusions constrain the temperature of magnesite formation or recrystalization to 110 to 240oC. In British Columbia the diagenetic

 

recrystalization theory may best explain the stratigraphic association with gypsum and halite casts, correlation with paleotopographic highs and unconformities, and shallow marine depositional features of the deposits.
A number of recent cryptocrystalline sedimentary magnesite deposits, such as Salda Lake in Turkey and the Kunwarara deposit in Queensland, Australia, huntite-magnesite-hydromagnesite deposits of Kozani Basin, Northern Greece, and the magnesite- or hydromagnesite- bearing evaporitic occurrences from Sebkha el Melah in Tunesia may be recent analogs to the pre-diagenetic protoliths for British Columbia sparry magnesite deposits.

 

ASSOCIATED DEPOSIT TYPES: Sediment-hosted talc deposits (E08) and Mississippi Valley-type deposits (E12) are geographically, but not genetically, associated with sparry magnesite in British Columbia. The magnesite appears older than cross-cutting sparry dolomite that is commonly associated with MVT deposits.

 

COMMENTS: Magnesite deposits can survive even in high grade metamorphic environments because of their nearly monomineralic nature.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Tracing of magnesite boulders and blocks with pinolitic texture. Magnesite grains in stream sediments.

 

GEOPHYSICAL SIGNATURE: N/A.

 

OTHER EXPLORATION GUIDES: Surface exposures are beige, pale brown or pale gray. White fine-grained marker horizons are useful in southwest British Columbia. "Granola-like" weathering texture is a useful prospecting indicator. Magnesite may be identified in the field using heavy-liquids. In British Columbia the deposits are often associated with unconformities, paleotopographic highs within particular stratigraphic horizons.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Grades range from 90 to 95% MgCO3 with the resources ranging from several

 

to hundreds of million tonnes. British Columbia deposits are characterized by lower iron content than most of the European deposits.

 

ECONOMIC LIMITATIONS: There is large but very competitive market for magnesia-based products. China is the largest exporter of magnesite. Quality of primary raw materials, cost of energy, cost of transportation to markets, availability of existing infrastructure, and the quality of finished product are major factors achieving a successful operation.

 

END USES: Magnesite is used to produce magnesium metal and caustic, dead-burned and fused magnesia. Caustic magnesia, and derived tertiary products are used in chemical and industrial applications, construction, animal foodstuffs and environmental rehabilitation. Fused and dead-burned magnesia are used in high-performance refractories. Magnesium metal has wide range of end uses, mostly in the aerospace and automotive industries. The automotive market for magnesium metal is expected to expand rapidly with current efforts to reduce the weight of vehicles to improve fuel economy and reduce harmful emissions.

 

IMPORTANCE: Sparry magnesite deposits account for 80% of the world production. Significant quantities of magnesite are also produced from ultramafic-hosted deposits and fine grained or nodular deposits.

 

SELECTED BIBLIOGRAPHY

 

ACKNOWLEDGEMENTS: The manuscript benefited from discussion with I. Knuckey and C. Pilarski of Baymag Mines Co. Ltd. Review by D.V. Lefebure is appreciated.

 

Chevalier, P. (1995): Magnesium; in 1994 Canadian Mineral Yearbook, Natural Resources Canada, pages 29.1-29.13.

Grant, B. (1987): Magnesite, Brucite and Hydromagnesite Occurrences in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1987-13, 80 pages.

Hancock, K.D. and Simandl, G.J. (1992): Geology of the Marysville Magnesite Deposit, Southeastern British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Exploration in British Columbia, Part B, pages 71-80.

Harben, P.W. and Bates, R.L. (1990): Industrial Minerals, Geology and World Deposits. Industrial Minerals Division, Metal Bulletin PLC, London, 312 pages.

Kendall, T. (1996): Dead-burned Magnesite, Industrial Minerals, Number 341, pages 25-51.

Möller, P. (1989): Magnesite; Monograph Series on Mineral Deposits, Number 28, Gebrüder Borntraeger, pages 105-113.

Morteani, G. (1989): Mg-metasomatic Type Sparry Magnesites of Entachen Alm, Hochfilzen/Bürglkopf and Spiessnagel (Austria); in Magnesite; Monograph Series on Mineral Deposits, Number 28, Gebrüder Borntraeger, 300 pages.

Niashihara, H. (1956): Origin of bedded Magnesite Deposits of Manchuria; Economic Geology, Volume 51, pages 25-53.

O'Driscoll, M. (1994): Caustic Magnesia Markets; Industrial Minerals, Volume 20, pages 23-45.

O'Driscoll, M. (1996): Fused Magnesia; Industrial Minerals, Number 340, pages 19-27.

Simandl, G.J. and Hancock, K.D. (1996): Magnesite in British Columbia, Canada: A Neglected Resource; Mineral Industry International, Number 1030, pages 33-44.

Simandl, G.J., Simandl, J., Hancock, K.D. and Duncan, L. (1996): Magnesite deposits in B.C. - Economic Potential; Industrial Minerals, Number 343, pages 125-132.

Simandl, G.J., Hancock, K.D., Paradis, S. and Simandl, J. (1993): Field identification of Magnesite-bearing rocks Using Sodium Polytungstate; CIM Bulletin, Volume 966, pages 68-72.

Simandl, G.J. and Hancock, K.D. (1992): Geology of the Dolomite-hosted Magnesite Deposits of Brisco and Driftwood Creek areas, British Columbia; in: Fieldwork 1991, B.C. Ministry of Mines and Petroleum Resources, Paper 1992-1, pages 461-478.

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MISSISSIPPI VALLEY-TYPE Pb-Zn

E12

by Dani Alldrick and Don Sangster

 

http://ygsftp.gov.yk.ca/publications/openfile/2005/of2005_5/e12_mississippi_valley_type_pb_zn.pdf

 

IRISH-TYPE CARBONATE-HOSTED Zn-Pb


E13
by Trygve Hõy
B.C. Geological Survey

 

Hõy, Trygve (1996): Irish-type Carbonate-hosted Zn-Pb, in Selected British Columbia Mineral Deposit Profiles, Volume 2 - Metallic Deposits, Lefebure, D.V. and Hõy, T, Editors, British Columbia Ministry of Employment and Investment, Open File 1996-13, pages 21-24.

 

IDENTIFICATION

 

SYNONYMS: Kootenay Arc Pb-Zn, Remac type.

 

COMMODITIES (BYPRODUCTS): Zn, Pb, Ag; (Cu, barite, Cd).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Reeves MacDonald (082FSW026), HB (082FSW004), Aspen (082FSW001), Jack Pot West (082FSW255), Jersey (082FSW009), Duncan (082KSE020), Wigwam (082KNW068); Navan, Lisheen, Tynagh, Silvermines, Galmoy, Ballinalack, Allenwood West (Ireland); Troya (Spain).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Irish-type carbonate-hosted deposits are stratabound, massive sphalerite, galena, iron sulphide and barite lenses with associated calcite, dolomite and quartz gangue in dolomitized platformal limestones. Deposits are structurally controlled, commonly wedge shaped adjacent to normal faults. Deformed deposits are irregular in outline and commonly elongate parallel to the regional structural grain.

 

TECTONIC SETTING: Platformal sequences on continental margins which commonly overlie deformed and metamorphosed continental crustal rocks.

 

DEPOSITIONAL ENVIRONMENT/GEOLOGICAL SETTING: Adjacent to normal growth faults in transgressive, shallow marine platformal carbonates; also commonly localized near basin margins.

 

AGE OF MINERALIZATION: Known deposits are believed to be Paleozoic in age and younger than their host rocks; Irish deposits are hosted by Lower Carboniferous rocks; Kootenay Arc deposits are in the Lower Cambrian.

 

HOST/ASSOCIATED ROCK TYPES: Hosted by thick, non-argillaceous carbonate rocks; these are commonly the lowest pure carbonates in the stratigraphic succession. They comprise micritic and oolitic beds, and fine-grained calcarenites in a calcareous shale, sandstone, calcarenite succession. Underlying rocks include sandstones or argillaceous calcarenites and shales. Iron formations, comprising interlayered hematite, chert and limestone, may occur as distal facies to some deposits. Deformed Kootenay Arc deposits are enveloped by fine-grained grey, siliceous dolomite that is generally massive or only poorly banded and locally brecciated.

 

DEPOSIT FORM: Deposits are typically wedge shaped, ranging from over 30 m thick adjacent to, or along growth faults, to 1-2 cm bands of massive sulphides at the periphery of lenses. Economic mineralization rarely extends more than 200 m from the faults. Large deposits comprise individual or stacked sulphide lenses that are roughly concordant with bedding. In detail, however, most lenses cut host stratigraphy at low angles. Contacts are sharp to gradational. Deformed deposits are typically elongate within and parallel to the hinges of tight folds. The Reeves MacDonald deposit forms a syncline with a plunge length of approximately 1500 m and widths up to 25 m. Others (HB) are elongate parallel to a strong mineral lineation. Individual sulphide lenses are irregular, but typically parallel to each other and host layering, and may interfinger or merge along plunge.

 

TEXTURE/STRUCTURE: Sulphide lenses are massive to occassionally well layered. Typically massive sulphides adjacent to faults grade outward into veinlet- controlled or disseminated sulphides. Colloform sphalerite and pyrite textures occur locally. Breccias are common with sulphides forming the matrix to carbonate (or as clasts?). Sphalerite-galena veins, locally brecciated, commonly cut massive sulphides. Rarely (Navan), thin laminated, graded and crossbedded sulphides, with framboidal pyrite, occur above more massive sulphide lenses. Strongly deformed sulphide lenses comprise interlaminated sulphides and carbonates which, in some cases (Fyles and Hewlett, 1959), has been termed shear banding.

 

ORE MINERALOGY (Prinicipal and subordinate): Sphalerite, galena; barite, chalcopyrite, pyrrhotite, tennantite, sulfosalts, tetrahedrite, chalcopyrite.

 

GANGUE MINERALOGY (Prinicipal and subordinate): Dolomite, calcite, quartz, pyrite, marcasite; siderite, barite, hematite, magnetite; at higher metamorphic grades, olivine, diopside, tremolite, wollastonite, garnet.

 

ALTERATION MINERALOGY: Extensive early dolomitization forms an envelope around most deposits which extends tens of metres beyond the sulphides. Dolomitization associated with mineralization is generally fine grained, commonly iron-rich, and locally brecciated and less well banded than limestone. Mn halos occur around some deposits; silicification is local and uncommon. Fe in iron formations is distal.

 

WEATHERING: Gossan minerals include limonite, cerussite, anglesite, smithsonite, hemimorphite, pyromorphite.

 

ORE CONTROLS: Deposits are restricted to relatively pure, shallow-marine carbonates. Regional basement structures and, locally, growth faults are important. Orebodies may be more common at fault intersections. Proximity to carbonate bank margins may be a regional control in some districts.

 

GENETIC MODEL: Two models are commonly proposed: (1) syngenetic seafloor deposition: evidence inludes stratiform geometry of some deposits, occurrence together of bedded and clastic sulphides, sedimentary textures in sulphides, and, where determined, similar ages for mineralization and host rocks. (2) diagenetic to epigenetic replacement: replacement and open-space filling textures, lack of laminated sulphides in most deposits, alteration and mineralization above sulphide lenses, and lack of seafloor oxidation.

 

ASSOCIATED DEPOSIT TYPES: Mississippi Valley type Pb-Zn (E12), sediment-hosted barite (E17), sedimentary exhalative Zn-Pb-Ag (E14), possibly carbonate-hosted disseminated Au-Ag (E03).

 

COMMENTS: Although deposits such as Tynagh and Silvermines have structures and textures similar to sedex deposits, and are associated with distal iron formations, they are included in the Irish-type classification as recent work (e.g., Hizman, 1995) concludes they formed by replacement of lithified rocks. Deposits that can be demonstrated to have formed on the seafloor are not included in Irish-type deposits. It is possible that the same continental margin carbonates may host sedex (E14), Irish-type (E13) and Mississippi Valley-type (E12) deposits.

 

EXPLORATION GUIDES GEOCHEMICAL SIGNATURE: Elevated base metal, Ag and Mn values in both silt and soil samples; however, high carbonate content, and hence high Ph may reduce effectiveness of stream silts.

 

GEOPHYSICAL SIGNATURE: Induced polarization surveys are effective and ground electromagnetic methods may work for deposits with iron sulphides. Deposits can show up as resistivity lows and gravity highs.

 

OTHER EXPLORATION GUIDES: The most important control is stratigraphic. All known deposits are in carbonate rocks, commonly the lowest relatively pure carbonate in a succession. Other guides are proximity to growth faults and intersection of faults, regional and local dolomitization and possibly laterally equivalent iron formations.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Irish deposits are typically less than 10 Mt with 5-6% Zn, 1-2% Pb and 30g/t Ag. Individual deposits can contain up to 90 g/t Ag. The largest, Navan, produced 36 Mt and has remaining reserves of 41.8 Mt containing 8% Zn and 2% Pb. Mined deposits in the Kootenay Arc averaged between 6 and 7 Mt and contained 3-4 % Zn, 1-2 % Pb, and 3-4 g/t Ag. Duncan has reserves of 2.76 Mt with 3.3% Pb and 3.1% Zn; Wigwam contains 8.48 Mt with 2.14% Pb and 3.54% Zn.

 

ECONOMIC LIMITATIONS: These deposits are attractive because of their simple mineralogy and polymetallic nature, although significantly smaller than sedex deposits. In British Columbia the Kootenay Arc deposits are generally lower grade with up to only 6 % Pb+Zn. These deposits are also structurally complex making them more complicated to mine. IMPORTANCE: Production from these deposits makes Ireland a major world zinc producer. Recent discovery of concealed deposits (Galmoy in 1986 and Lisheen in 1990) assures continued production. In British Columbia, a number of these deposits were mined intermittently until 1979 when H.B. finally closed. Some still have substantial lead and zinc reserves. However, their current potential for development is based largely on the precious metal content. The high carbonate content of the gangue minimizes acid-rock drainage problems.

 

REFERENCES

 

Addie, G.G. (1970): The Reeves MacDonald Mine, Nelway, British Columbia; in Pb-Zn Deposits in the Kootenay Arc, N.E. Washington and adjacent British Columbia; Department of Natural Resources, State of Washington, Bulletin 61, pages 79-88.

Fyles, J.T. (1970): Geological Setting of Pb-Zn Deposits in the Kootenay Lake and Salmo Areas of B.C.; in Pb-Zn Deposits in the Kootenay Arc, N.E. Washington and Adjacent British Columbia; Department of Natural Resources, State of Washington, Bulletin 61, pages 41-53.

Fyles, J.T. and Hewlett, C.G. (1959): Stratigraphy and Structure of the Salmo Lead-Zinc Area; B. C. Department of Mines, Bulletin 41, 162 pages.

Hitzman, M.W. (1995): Mineralization in the Irish Zn-Pb-(Ba-Ag) Orefield; in Irish Carbonate-hosted Zn-Pb Deposits, Anderson K., Ashton J., Earls G., Hitzman M., and Sears S., Editors, Society of Economic Geologists, Guidebook Series, Volume 21, pages 25-61.

Hitzman, M.W. (1995): Geological Setting of the Irish Zn-Pb-(Ba-Ag) Orefield; in Irish Carbonate-hosted Zn-Pb Deposits, Anderson, K., Ashton, J., Earls, G., Hitzman, M., and Sears, S., Editors, Society of Economic Geologists, Guidebook Series, Volume 21, pages 3-24.

Höy, T. (1982): Stratigraphic and Structural Setting of Stratabound Lead- Zinc Deposits in Southeastern British Columbia; Canadian Institute of Mining and Metallurgy, Bulletin, Volume 75, pages 114-134.

Nelson, J.L. (1991): Carbonate-hosted Lead-Zinc Deposits of British Columbia; in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, pages 71-88.

Sangster, D.F. (1970): Metallogenesis for some Canadian Lead-zinc Deposits in Carbonate Rocks; Geological Association of Canada, Proceedings, Volume 22, pages 27-36.

Sangster, D.F. (1990): Mississippi Valley-type and Sedex Lead-Zinc Deposits: a Comparative Examination; Transactions of the Institution of Mining and Metallurgy, Section B, Volume 99, pages B21-B42. T. Hoy Draft 3: March 27, 1996

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SEDIMENTARY EXHALATIVE Zn-Pb-Ag


E14

by Don MacIntyre
British Columbia Geological Survey

 

MacIntyre, Don (1995): Sedimentary Exhalative Zn-Pb-Ag, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 37-39.

 

IDENTIFICATION

 

SYNONYMS: Shale-hosted Zn-Pb-Ag; sediment-hosted massive sulphide Zn-Pb-Ag; Sedex Zn- Pb.

 

COMMODITIES (BYPRODUCTS): Zn, Pb, Ag, (minor Cu, barite).

 

EXAMPLES (British Columbia - Canada/International): Cirque, Sullivan, Driftpile; Faro, Grum, Dy, Vangorda, Swim, Tom and Jason (Yukon, Canada), Red Dog (Alaska, USA), McArthur River and Mt. Isa (Australia); Megen and Rammelsberg (Germany).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Beds and laminations of sphalerite, galena, pyrite, pyrrhotite and rare chalcopyrite, with or without barite, in euxinic clastic marine sedimentary strata.. Deposits are typically tabular to lensoidal in shape and range from centimetres to tens of metres thick. Multiple horizons may occur over stratigraphic intervals of 1000 m or more.

 

TECTONIC SETTING: Intracratonic or continental margin environments in fault-controlled basins and troughs. Troughs are typically half grabens developed by extension along continental margins or within back-arc basins.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Restricted second and third order basins within linear, fault-controlled marine, epicratonic troughs and basins. There is often evidence of penecontemporaneous movement on faults bounding sites of sulphide deposition. The depositional environment varies from deep, starved marine to ? shallow water restricted shelf.

 

AGE OF MINERALIZATION: The major metallogenic events are Middle Proterozoic, Early Cambrian, Early Silurian and Middle to Late Devonian to Mississippian. The Middle Proterozoic and Devonian-Mississippian events are recognized worldwide. In the Canadian Cordillera, minor metallogenic events occur in the Middle Ordovician and Early Devonian.

 

HOST/ASSOCIATED ROCK TYPES: The most common hostrocks are those found in euxinic, starved basin environments, namely, carbonaceous black shale, siltstone, cherty argillite and chert. Thin interbeds of turbiditic sandstone, granule to pebble conglomerate, pelagic limestone and dolostone, although volumetrically minor, are common. Evaporites, calcareous siltstone and mudstone are common in shelf settings. Small volumes of volcanic rocks, typically tuff and submarine mafic flows, may be present within the host succession. Slump breccia, fan conglomerates and similar deposits occur near synsedimentary growth faults. Rapid facies and thickness changes are found near the margins of second and third order basins. In some basins high-level mafic sills with minor dikes are important.

 

DEPOSIT FORM: These deposits are stratabound, tabular to lens shaped and are typically comprised of many beds of laminae of sulphide and/or barite. Frequently the lenses are stacked and more than one horizon is economic. Ore lenses and mineralized beds often are part of a sedimentary succession up to hundreds of metres thick. Horizontal extent is usually much greater than vertical extent. Individual laminae or beds may persist over tens of kilometres within the depositional basin.

 

TEXTURE/STRUCTURE: Sulphide and barite laminae are usually very finely crystalline where deformation is minor. In intensely folded deposits, coarser grained, recrystallized zones are common. Sulphide laminae are typically monomineralic.

 

ORE MINERALOGY (Principal and subordinate): The principal sulphide minerals are pyrite, pyrrhotite, sphalerite and galena. Some deposits contain significant amounts of chalcopyrite, but most do not. Barite may or may not be a major component of the ore zone. Trace amounts of marcasite, arsenopyrite, bismuthinite, molybdenite, enargite, millerite, freibergite, cobaltite, cassiterite, valleriite and melnikovite have been reported from these deposits. These minerals are usually present in very minor amounts.

 

ALTERATION MINERALOGY: Alteration varies from well developed to nonexistent. In some deposits a stockwork and disseminated feeder zone lies beneath, or adjacent to, the stratiform mineralization. Alteration minerals, if present, include silica, tourmaline, carbonate, albite, chlorite and dolomite. They formed in a relatively low temperature environment. Celsian, Ba-muscovite and ammonium clay minerals have also been reported but are probably not common.

 

ORE CONTROLS: Favourable sedimentary sequences, major structural breaks, basins.

 

GENETIC MODEL: The deposits accumulate in restricted second and third order basins or half grabens bounded by synsedimentary growth faults. Exhalative centres occur along these faults and the exhaled brines accumulate in adjacent seafloor depressions. Biogenic reduction of seawater sulphate within an anoxic brine pool is believed to control sulphide precipitation.

 

ASSOCIATED DEPOSIT TYPES: Associated deposit types include carbonate-hosted sedimentary exhalative, such as the Kootenay Arc and Irish deposits (E13), bedded barite (E17) and iron formation (F10).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: The deposits are typically zoned with Pb found closest to the vent grading outward and upward into more Zn-rich facies. Cu is usually found either within the feeder zone of close to the exhalative vent. Barite, exhalative chert and hematite-chert iron formation, if present, are usually found as a distal facies. Sediments such as pelagic limestone interbedded with the ore zone may be enriched in Mn. NH3 anomalies have been documented at some deposits, as have Zn, Pb and Mn haloes. The host stratigraphic succession may also be enriched in Ba on a basin-wide scale.

 

GEOPHYSICAL SIGNATURE: Airborne and ground geophysical surveys, such as electromagnetics or magnetics should detect deposits that have massive sulphide zones, especially if these are steeply dipping. However, the presence of graphite-rich zones in the host sediments can complicate the interpretation of EM conductors. Also, if the deposits are flat lying and comprised of fine laminae distributed over a significant stratigraphic interval, the geophysical response is usually too weak to be definitive. Induced polarization can detect flat-lying deposits, especially if disseminated feeder zones are present.

 

OTHER EXPLORATION GUIDES: The principal exploration guidelines are appropriate sedimentary environment and stratigraphic age. Restricted marine sedimentary sequences deposited in an epicratonic extensional tectonic setting during the Middle Proterozoic, Early Cambrian, Early Silurian or Devono-Mississippian ages are the most favourable.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: The median tonnage for this type of deposit worldwide is 15 Mt, with 10 % of deposits in excess of 130 Mt (Briskey, 1986). The median grades worldwide are Zn - 5.6%, Pb - 2.8% and Ag - 30 g/t. The Sullivan deposit, one of the largest deposits of this type ever discovered, has a total size of more than 155 Mt grading 5.7% Zn, 6.6% Pb and 7 g/t Ag. Reserves at the Cirque are 32.2 Mt grading 7.9% Zn, 2.1% Pb and 48 g/t Ag.

 

ECONOMIC LIMITATIONS: The large, near-surface deposits are amenable to high volume, open pit mining operations. Underground mining is used for some deposits.

 

IMPORTANCE: Sedimentary exhalative deposits currently produce a significant proportion of the world’s Zn and Pb. Their large tonnage potential and associated Ag values make them an attractive exploration target.

 

REFERENCES

 

Briskey, J.A. (1986): Descriptive Model of Sedimentary Exhalative Zn-Pb; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, 379 pages.

Carne, R.C. and Cathro, R.J. (1982): Sedimentary-exhalative (Sedex) Zn-Pb-Ag Deposits, Northern Canadian Cordillera; Canadian Institute of Mining and Metallurgy, Bulletin, Volume 75, pages 66-78.

Gustafson, L.B. and Williams, N. (1981): Sediment-hosted Stratiform Deposits of Copper, Lead and Zinc; in Economic Geology Seventy-fifth Anniversary Volume, 1905-1980, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 139-178.

Large, D.E. (1981): Sediment-hosted Submarine Exhalative Sulphide Deposits - a Review of their Geological Characteristics and Genesis; in Handbook of Stratabound and Stratiform Ore Deposits, Wolfe, K.E., Editor, Geological Association of Canada, Volume 9, pages 459-507.

Large, D.E. (1983): Sediment-hosted Massive Sulphide Lead-Zinc Deposits; in Short Course in Sedimentary Stratiform Lead-Zinc Deposits, Sangster, D.F., Editor, Mineralogical Association of Canada, pages 1-29.

MacIntyre, D.G. (1991): Sedex - Sedimentary-exhalative Deposits, in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, McMillan, W.J., Coordinator, B. C. Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, pages 25- 69.

Sangster, D.F. (1986): Classifications, Distribution and Grade-Tonnage Summaries of Canadian Lead-Zinc Deposits; Geological Survey of Canada, Economic Geology Report 37, 68 pages.

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BLACKBIRD SEDIMENT-HOSTED Cu-Co


E15
by Trygve Hõy
British Columbia Geological Survey

 

Hõy, Trygve (1995): Blackbird Sediment-hosted Cu-Co, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 41-44.

 

IDENTIFICATION

 

SYNONYM: Sediment-hosted Cu-Co deposit.

 

COMMODITIES (BYPRODUCTS): Cu, Co, (Au, Bi, Ni, Ag; possibly Pb, Zn).

 

EXAMPLES (British Columbia - Canada/International): Canadian examples are not known; Blackbird, Bonanza Copper and Tinker's Pride (Idaho, USA), possibly Sheep Creek deposits (Montana, USA).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Pyrite and minor pyrrhotite, cobaltite, chalcopyrite, arsenopyrite and magnetite occur as disseminations, small veins and tabular to pod-like lenses in sedimentary rocks. Chloritic alteration and tourmaline breccias are locally associated with mineralization.

 

TECTONIC SETTINGS: Near continental margins or in intracratonic basins. Within the Belt-Purcell basin, which may have formed in a large inland sea, extensional tectonics are suggested by possible turbidite deposition, growth faulting, gabbroic sills and (?)tuff deposition. Alternative setting is marine, in an incipient or failed rift along a continental margin.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: These deposits are not well understood. Possible turbidite deposition in marine or inland sea, associated with basaltic pyroclastic volcanics or mafic synsedimentary gabbroic sills; alternatively, tidal flat environment.

 

AGE OF MINERALIZATION: Can be of any age. The Blackbird deposits at the type locality are assumed to be approximately 1460 Ma, the age of the hostrocks.

 

HOST/ASSOCIATED ROCK TYPES: Fine-grained metasedimentary rocks; thin-bedded siltstone, fine-grained quartzite, black argillite and calcareous siltstone; garnet schist, phyllite, quartz-mica schist. In the Blackbird district synaeresis cracks (subaqueous shrinkage cracks) occur within immediate hostrocks, sedimentary structures indicative of shallow water, and locally subaerial exposure in overlying rocks, suggest shallow water environment. Numerous biotite-rich beds within the host succession may be mafic tuff units (or diorite sills ?). Sheep Creek deposits are within correlative Newland Formation dolomitized shales and conglomerates.

 

DEPOSIT FORM: Irregular, tabular to pod-like deposits, from approximately 2 to 10 m thick.

 

TEXTURE/STRUCTURE: Fine to fairly coarse grained, massive to disseminated sulphides; pyrite locally has colloform textures. Locally sheared; vein sulphides in some deposits; quartz-tourmaline breccia pipes (?).

 

ORE MINERALOGY (Principal and subordinate) Cobaltite, chalcopyrite, pyrite, pyrrhotite, gold and silver in breccia pipes; arsenopyrite, magnetite, cobaltian pyrite. Sheep Creek: pyrite, marcasite, chalcopyrite, tennantite plus cobalt minerals; covellite, bornite in barite.

 

GANGUE MINERALOGY: quartz, biotite, barite; tourmaline, hornblende, chlorite, muscovite, ankerite, dolomite, siderite, calcite and apatite.

 

ALTERATION MINERALOGY: Silicification and intense chloritization; locally quartz- tourmaline breccias.

 

WEATHERING: Supergene enrichment with ludlamite and vivianite; erythrite (cobalt bloom); intense gossans at surface.

 

ORE CONTROLS: Regional controls include synsedimentary extensional fault structures, basin margin and growth faults. Local controls include association with mafic tuffs and stacked deposits at several stratigraphic intervals separated by barren rock.

 

GENETIC MODEL: Based on stratabound nature of deposits and similarity with unmetamorphosed Sheep Creek deposits, the Blackbird lenses are interpreted to be either syngenetic or diagenetic.

 

ASSOCIATED DEPOSIT TYPES: Possibly Besshi volcanogenic massive sulphide deposits (G04), Fe formations (F10), base metal veins, tourmaline breccias.

 

COMMENTS: Sheep Creek deposits are a relatively new exploration target in Belt rocks in Montana. They are in equivalent, lower metamorphic grade hostrocks to those of the Blackbird deposits, and have similar mineralogy and trace metal geochemistry. Lower Purcell Supergroup rocks and other structurally controlled sedimentary basins associated with variable mafic magmatism are prospective hosts in Canada.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Enriched in Fe, As, B, Co. Cu, Au, Ag and Mn; may be depleted in Ca and Na. Sheep Creek also contains high Ba.

 

GEOPHYSICAL SIGNATURE: Sulphide lenses usually show either an electromagnetic or induced polarization signature based on the style of mineralization and presence of conductive sulphides.

 

OTHER EXPLORATION GUIDES: Proximity to mafic tuffs or possibly early gabbroic sills, rapid sedimentary facies changes indicative of growth faults; regional pyrite development; may grade laterally to pyritic zones with anomalous Pb-Zn.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: The Blackbird district deposits range from less than 100 000 t to 1.3 Mt containing 0.4 - 0.6 % Co and 1.3% Cu. Two zones of the Sheep Creek deposits contain respectively 4.5 Mt of 2.5% Cu and 0.12% Co, and 1.8 Mt with 6% Cu. Variable gold, up to 20 g/t in Blackbird lenses.

 

ECONOMIC LIMITATIONS: Generally lower copper grades favour open pit mining; Au and Ag are important byproducts.

 

IMPORTANCE: Small past producers of copper, cobalt and gold in Idaho.

 

REFERENCES

 

ACKNOWLEDGMENT: This deposit profile draws heavily from the USGS descriptive deposit model of Blackbird Co-Cu by Robert Earhart.

 

Anderson, A.L. (1947): Cobalt Mineralization in the Blackbird District, Lemhi County, Idaho; Economic Geology, Volume 42, pages 22-46.

Earhart, R.L. (1986): Descriptive Model of Blackbird Co-Cu; in Mineral Deposit Models, Cox, D.P and Singer, D.A., Editors, US Geological Survey, Bulletin 1693, page 142.

Himes, M.D. and Petersen, E.U. (1990): Geological and Mineralogical Characteristics of the Sheep Creek Copper-Cobalt Sediment-hosted Stratabound Sulfide Deposit, Meagher County, Montana; in Gold '90 Symposium, Salt Lake City, Utah, Chapter 52, Society of Economic Geologists, pages 533-546.

Hughes, G.J. (1982): Basinal Setting of the Idaho Cobalt Belt, Blackbird Mining District, Lemhi County, Idaho; in the Genesis of Rocky Mountain Ore Deposits; Changes with Time and Tectonics, Denver Region Geologists Society, pages 21-27.

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SHALE-HOSTED Ni-Zn-Mo-PGE


E16

by David V. Lefebure* and R.M. Coveney Jr.#
* British Columbia Geological Survey
# University of Missouri - Kansas City, Kansas City, Missouri

 

Lefebure, D.V. and Coveney, R.M. Jr.(1995): Shale-hosted Ni-Zn-Mo-PGE, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 45-48.

 

IDENTIFICATION

 

SYNONYMS: Sediment-hosted Ni-Mo-PGE, Stratiform Ni-Zn-PGE.

 

COMMODITIES (BYPRODUCTS): Ni, Mo, ( Zn, Pt, Pd, Au).

 

EXAMPLES (British Columbia - Canada/International): Nick (Yukon, Canada); mining camps of Tianeshan, Xintuguo, Tuansabao and Jinzhuwoin and Zunyi Mo deposits, Dayong-Cili District (China).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Thin layers of pyrite, vaesite (NiS2), jordisite (amorphous MoS2) and sphalerite in black shale sub-basins with associated phosphatic chert and carbonate rocks.

 

TECTONIC SETTING(S): Continental platform sedimentary sequences and possibly successor basins. All known deposits associated with orogenic belts, however, strongly anomalous shales overlying the North American craton may point to as yet undiscovered deposits over the stable craton.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Anoxic basins within clastic sedimentary (flysch) sequences containing black shales.

 

AGE OF MINERALIZATION: Post Archean. Known deposits are Early Cambrian and Devonian, however, there is potential for deposits of other ages.

 

HOST/ASSOCIATED ROCK TYPES: Black shale is the host; associated limestones, dolomitic limestones, calcareous shale, cherts, siliceous shale, siliceous dolomite, muddy siltstone and tuffs. Commonly associated with phosphate horizons. In the Yukon at base of a 10 to 20 m thick phosphatic shale bed and in China the Ni-Mo beds are in black shales associated with phosphorite.

 

DEPOSIT FORM: Thin beds (0 to 15 cm thick, locally up to 30 cm) covering areas up to at least 100 ha and found as clusters and zones extending for tens of kilometres.

 

TEXTURE/STRUCTURE: Semimassive to massive sulphides as nodules, spheroids, framboids and streaks or segregations in a fine-grained matrix of sulphides, organic matter and nodular phosphorite or phosphatic carbonaceous chert. Mineralization can be rhythmically laminated; often has thin discontinuous laminae. Brecciated clasts and spheroids of pyrite, organic matter and phosphorite. In China nodular textures (~ 1 mm diameter) grade to coatings of sulphides on tiny 1-10 mm spherules of organic matter. Fragments and local folding reflect soft sediment deformation. Abundant plant fossils in Nick mineralization and abundant fossils of microorganisms (cyanobacteria) in the Chinese ores.

 

ORE MINERALOGY (Principal and subordinate): Pyrite, vaesite (NiS2), amorphous molybdenum minerals (jordisite, MoS2), bravoite, sphalerite, wurtzite, polydimite, gersdorffite, violarite, millerite, sulvanite, pentlandite, tennanite and as traces native gold, uranitite, tiemannite, arsenopyrite, chalcopyrite and covellite. Discrete platinum group minerals may be unusual. Some ore samples are surprisingly light because of abundant organic matter and large amount of pores.

 

GANGUE MINERALOGY (Principal and subordinate): Chert, amorphous silica, phosphatic sediments and bitumen. Can be interbedded with pellets of solid organic matter (called stone coal in China). Barite laths are reported in two of the China deposits.

 

ALTERATION MINERALOGY: Siliceous stockworks and bitumen veins with silicified wallrock occur in the footwall units. Carbonate concretions up to 1.5 m in diameter occur immediately below the Nick mineralized horizon in the Yukon.

 

WEATHERING: Mineralized horizons readily oxidize to a black colour and are recessive. Phosphatic horizons can be resistant to weathering.

 

ORE CONTROLS: The deposits developed in restricted basins with anoxic conditions. Known deposits are found near the basal contact of major formations. Underlying regional unconformities and major basin faults are possible controls on mineralization. Chinese deposits occur discontinuously in a 1600 km long arcuate belt, possibly controlled by basement fractures.

 

GENETIC MODEL: Several genetic models have been suggested reflecting the limited data available and the unusual presence of PGEs without ultramafic rocks. Syngenetic deposition from seafloor springs with deposition of metals on or just beneath the seafloor is the most favoured model. Siliceous venting tubes and chert beds in the underlying beds in the Yukon suggest a hydrothermal source for metals.

 

ASSOCIATED DEPOSIT TYPES: Phosphorite layers (F07?), stone coal, SEDEX Pb-Zn (E14), Sediment-hosted barite (E17), vanadian shales, sediment-hosted Ag-V, uranium deposits.

 

COMMENTS: Ag-V and V deposits hosted by black shales have been described from the same region in China hosted by underlying late Precambrian rocks.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Elevated values of Ni, Mo, Au, PGE, C, P, Ba, Zn, Re, Se, As, U, V and S in rocks throughout large parts of basin and derived stream sediments. In China average regional values for host shales of 350 g/t Mo, 150 g/t Ni, several wt % P2O5 and 5 to 22% organic matter. Organic content correlates with metal contents for Ni, Mo and Zn.

 

GEOPHYSICAL SIGNATURE: Electromagnetic surveys should detect pyrite horizons.

 

OTHER EXPLORATION GUIDES: Anoxic black shales in sub-basins within marginal basins. Chert or phosphate-rich sediments associated with a pyritiferous horizon. Barren, 5 mm to 1.5 cm thick, pyrite layers (occasionally geochemically anomalous) up to tens of metres above mineralized horizon.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE : The thin sedimentary horizons (not economic) represent hundreds of thousands of tonnes grading in per cent values for at least two of Ni-Mo-Zn with significant PGEs. In China, Zunyi Mo mines yield ~ 1000 t per year averaging ~4 % Mo and containing up to 4 % Ni, 2 % Zn, 0.7 g/t Au, 50 g/t Ag, 0.3 g/t Pt, 0.4 g/t Pd and 30 g/t Ir. The ore is recovered from a number of small adits using labour-intensive mining methods.

 

ECONOMIC LIMITATIONS: In China the Mo-bearing phase is recovered by roasting followed by caustic leaching to produce ammonium molybdate. Molybedenum-bearing phases are fine grained and dispersed, therefore all ore (cutoff grade 4.1% Mo) is direct shipped to the smelter after crushing.

 

IMPORTANCE: Current world production from shale-hosted Ni-Mo-PGE mines is approximately 1000 t of ore with grades of approximately 4 % Mo. Known deposits of this type are too thin to be economic at current metal prices, except in special conditions. However, these deposits contain enormous tonnages of relatively high grade Ni, Mo, Zn and PGE which may be exploited if thicker deposits can be found, or a relevant new technology is developed.

 

REFERENCES

 

ACKNOWLEDGEMENTS: Larry Hulbert of the Geological Survey of Canada introduced the senior author to this deposit type and provided many useful comments. Rob Carne of Archer, Cathro and Associates Limited reviewed a draft manuscript.

 

Coveney, R.M., Jr. and Nansheng, C. (1991): Ni-Mo-PGE-Au-rich Ores in Chinese Black Shales and Speculations on Possible Analogues in the United States; Mineralium Deposita, Volume 26, pages 83-88.

Coveney, R.M. Jr., Murowchick, J.B., Grauch, R.I., Nansheng, C. and Glascock, M.D. (1992): Field Relations, Origins and Resource Implications for Platiniferous Molybdenum-Nickel Ores in Black Shales of South China; Canadiun Institute of Mining, Metallurgy and Petroleum, Exploration and Mining Geology, Volume 1, No. 1, pages 21-28.

Coveney, R. M. Jr., Grauch, R. I. and Murowchick, J.B. (1993): Ore Mineralogy of Nickel-Molybdenum Sulfide Beds Hosted by Black Shales of South China; in The Paul E. Queneau International Symposium, Extractive Metallurgy of Copper, Nickel and Cobalt, Volume 1: Fundamental Aspects, Reddy, R.G. and Weizenbach, R.N., Editors, The Minerals, Metals and Materials Society, pages 369-375.

Fan Delian (1983): Poly Elements in the Lower Cambrian Black Shale Series in Southern China; in The Significance of Trace Metals in Solving Petrogenetic Problems and Controversies, Augustithis, S.S., Editor, Theophrastus Publications, Athens, Greece, pages 447-474.

Horan, M.F., Morgan, J.W., Grauch, R.I., Coveney, R.M. Jr, Murowchick, J.B. and Hulbert, L.J. (1994): Rhenium and Osmium Isotopes in Black Shales and Ni-Mo-PGE-rich Sulphide Layers, Yukon Territory, Canada, and Hunan and Guizhou Provinces, China; Geochimica et Cosmochimica Acta, Volume 58, pages 257-265.

Hulbert, L.J., Gregoire, C.D., Paktunc, D. and Carne, R.C. (1992): Sedimentary Nickel, Zinc and Platinum-group-element Mineralization in Devonian Black Shales at the Nick Property, Yukon, Canada: A New Deposit Type; Canadiun Institute of Mining, Metallurgy and Petroleum, Exploration and Mining Geology, Volume 1, No. 1, pages 39 - 62.

Murowchick, J.B., Coveney, R.M. Jr., Grauch, R.I., Eldridge, C.S. and Shelton, K.I. (1994): Cyclic Variations of Sulfur Isotopes in Cambrian Stratabound Ni-Mo-(PGE-Au) Ores of Southern China; Geochimica et Cosmochimica Acta, Volume 58, No. 7, pages 1813-1823.

Nansheng, C. and Coveney, R.M. Jr. (1989): Ores in Metal-rich Shale of Southern China; U.S. Geological Survey, Circular 1037, pages 7-8.

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SEDIMENTARY-HOSTED, STRATIFORM BARITE


E17
by S. Paradis1, G.J. Simandl, D. MacIntyre and G.J. Orris2
1Geological Survey or Canada
2British Columbia Geological Survey

 

Force, E.R., Paradis, S. and Simandl, G.J. (1999): Sedimentary Manganese; in Selected British Columbia Mineral Deposit Profiles, Volume 3, Industrial Minerals, G.J. Simandl, Z.D. Hora and D.V. Lefebure, Editors, British Columbia Ministry of Energy and Mines, Open File 1999-10, pages 47-50.

 

IDENTIFICATION

 

SYNONYM: Bedded barite.

 

COMMODITIES (BYPRODUCTS): Barite (possibly Zn, Pb, Ag).

 

EXAMPLES (British Columbia (MINFILE #)- Canada/International): Kwadacha (094F 020), Gin (094F 017), Gnome (094F 016); Tea, Tyrala, Hess, Walt and Cathy (Yukon, Canada),Walton (Nova Scotia, Canada), Fancy Hill (Arkansas, USA), Mountain Springs, Greystone (Nevada, USA), Jixi and Liulin (China), Fig Tree and Mabiligwe (South Africa).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Sedimentary-hosted, stratiform or lens-shaped barite bodies, that may reach over ten metres in thickness and several kilometres in strike length. Barite-rich rocks (baritites) are commonly lateral distal equivalents of shale-hosted Pb-Zn (SEDEX) deposits. Some barite deposits are not associated with shale-hosted Zn-Pb deposits.

 

TECTONIC SETTINGS: Intracratonic or continental margin-type fault-controlled marine basins or half-grabens of second or third order and peripheral foreland (distal to the continental margin) basins.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Deep, starved marine basins to shallow water shelves. The barite-rich rocks (baritites) were deposited on the seafloor and commonly grade laterally into either shale-hosted Pb-Zn (SEDEX) deposits which formed closer to the submarine hydrothermal vents, or the more distal cherts, hematite-chert iron formations, silica and manganese-enriched sediments.

 

AGE OF MINERALIZATION: Deposits are hosted by rocks of Archean to Mesozoic ages but are most common in rocks of Phanerozoic, especially in the mid to late Paleozoic age.

 

HOST/ASSOCIATED ROCK TYPES: Major rock types hosting barite are carbonaceous and siliceous shales, siltstones, cherts, argillites, turbidites, sandstones, dolomites and limestones.

 

DEPOSIT FORM: Stratiform or lens-shaped deposits are commonly metres thick, but their thickness may exceed 50 metres. Their lateral extent may be over several square kilometres.

 

TEXTURE/STRUCTURE: The barite ore is commonly laminated, layered or massive. Barite may form rosettes, randomly oriented laths or nodules. Some of the barite deposits display breccias and slump structures. In metamorphosed areas, barite may be remobilized (forming veinlets) and/or recrystallized.

 

ORE MINERALOGY[Principal and subordinate]: Barite.

 

GANGUE MINERALOGY [Principal and subordinate]: Quartz, clay, organic material, celsian, hyalophane, cymrite, barytocalcite, calcite, dolomite, pyrite, marcasite, sphalerite, galena, and in some cases witherite.

 

ALTERATION MINERALOGY: None in most cases. Secondary barite veining. Weak to moderate sericitization reported in, or near, some deposits in Nevada.

 

WEATHERING: Barite-rich exposures sometimes create vegetation "kill zones".

 

ORE CONTROLS: Sedimentary depositional environment is mainly half-grabens and basins of second or third order. While Zn-Pb-barite (SEDEX) deposits may require euxinic environment to stabilize sulphides, more oxidized depositional environment may be the key for deposition of high-grade (nearly sulphide-free) barite deposits. Syndepositional faults are extremely important for SEDEX deposits that are commonly proximal to the vents, but may not be essential for all sediment-hosted stratabound barite deposits.

 

GENETIC MODEL: Some stratiform barite deposits form from hydrothermal fluids that exhaled on the seafloor and precipitated barite and other minerals (sulphides, chert, etc.) as chemical sediments. The chemical sediments change composition with distance from the vent reflecting changes in temperature and other parameters of the hydrothermal fluid as it mixed with seawater. Barite-rich sediments can reflect hydrothermal fluids deficient in metals (lack of base metals in the source rock or insufficient temperature or unfavorable physical-chemical fluid conditions to carry base metals) or discharge of hydrothermal fluids in a shallow marine environment that does not favor precipitation of sulphides. Some of the sedimentary-hosted barite deposits are interpreted as chemical sediments related to inversion of stratified basin resulting in oxygenation of reduced waters. Others formed by erosion and reworking of sub-economic chemical sediments (Heinrichs and Reimer, 1977) or of semi-consolidated clays containing barite concretions (Reimer, 1986), resulting in selective concentration of barite.

 

ASSOCIATED DEPOSIT TYPES: Shale-hosted Zn-Pb deposits (E14), Irish-type massive sulphide deposits (E13), sedimentary manganese deposits (F01) and vein barite deposits (I10). In oxygen-starved basins, barite deposits may be stratigraphically associated with black shales enriched in phosphates (F08), vanadium, REE and uranium mineralization and possibly shale-hosted Ni-Mo-PGE (E16) deposits.

 

COMMENTS: There is a complete spectrum from sulphide-rich to barite-rich SEDEX deposits. The Cirque deposit in British Columbia, represents the middle of this spectrum and consists of interlaminated barite, sphalerite, galena and pyrite. Its reserves are in excess of 38.5 million tonnes averaging 8% Zn, 2.2% Pb, 47.2 g/tonne of Ag and 45-50% barite. Witherite, a barium carbonate, occurs as an accessory mineral in some barite deposits and rarely forms a deposit on its own. There has been no commercial witherite production in the western world since the mines in Northumberland, England closed. Recently, the Chengkou and Ziyang witherite deposits have been discovered in China (Wang and Chu, 1994Witherite deposits may form due to severe depletion of seawater in SO-24 and enrichment in Ba (Maynard and Okita, 1991). Alternatively, these deposits could have formed by high temperature replacement of barite by witherite (Turner and Goodfellow,1990).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Barium enrichment on the scale of the basin and other indicators of shale-hosted Zn-Pb deposits, such as high values of Zn, Pb, Mn, Cu and Sr, in rock and stream sediment samples. Strongly anomalous Ba values in stream sediments and heavy sediments are only found in close proximity to barite mineralization because barite abrades rapidly during stream sediment transportation. The difference between 87Sr/86Sr ratios of barite and coeval seawater may be used to distinguish between cratonic rift (potentially SEDEX-related) barite occurrences and those of peripheral foreland basins (Maynard et al.,1995).

 

GEOPHYSICAL SIGNATURE: Deposit may correspond to a gravity-high.

 

OTHER EXPLORATION GUIDES: Appropriate tectonic and depositional setting. Proximity to known occurrences of barite, shale-hosted SEDEX or Irish-type massive sulphide occurrences, exhalative chert, hematite-chert iron formations and regional Mn marker beds. Vegetation "kill zones" coincide with some barite occurrences.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Deposits range from less than 1 to more than 25 million tonnes grading 30% to over 95% barite with a median size of 1.24 million tonnes containing 87.7 % BaSO4 (Orris, 1992). Portions of some

 

deposits may be direct shipping ore. ). The Magcobar mine in the Silvermines district of Ireland produced 4.6 Mt of 85% BaSO4 lump. Barite is produced at some metal mines, including the Ramelsburg and Meggen (8.9 Mt) mines in Germany.

 

ECONOMIC LIMITATIONS: Several modern applications require high brightness and whiteness values and high-purity products. There are different requirements for specific applications. Abrasivity, grade of concentrate, color, whiteness, density and type of impurities, oil index, water index, refractive index and base metal content are commonly reported for commercially available concentrates. Transportation cost, specific gravity and content of water-soluble alkaline earth metals, iron oxides and sulphides are important factors for barite used in drilling applications. Currently sulphide-free barite deposits are preferred by the barite producers. Some of the barite on the market is sold without complex upgrading. Selective mining and/or hand sorting, jigging, flotation and bleaching are commonly required. It is possible that in the future, due to technological progress, a substantial portion of barite on the market will originate as by-product of metal mining.

 

END USES: Barite is used mainly in drill muds, also as heavy aggregate, marine ballast, a source of chemicals, a component in ceramics, steel hardening, glass, fluxes, papers, specialized plastics and radiation shields, in sound proofing and in friction and pharmaceutical applications. Witherite is a desirable source of barium chemicals because it is soluble in acid, but it is not suitable for applications where inertness in acid environments is important.

 

IMPORTANCE: Competes for market with vein-type barite deposits. Celestite, ilmenite, iron oxides can replace barite in specific drilling applications. However the impact of these substitutes is minimized by relatively low barite prices.

 

SELECTED BIBLIOGRAPHY

 

ACKNOWLEDGEMENTS: Reviews of the manuscript by Dr. John Lydon of the Geological Survey of Canada and Dr. D.V. Lefebure of the B.C. Geological Survey are appreciated.

 

Brobst, D.A. (1994): Barium Minerals; in Industrial Minerals and Rocks, 6th edition , D.D. Carr, Senior Editor, Society for Mining, Metallurgy and Exploration, Inc., Littleton, Colorado, pages 125-134.

Clark, S. and Orris, G.J. (1991): Sedimentary Exhalative Barite; in Some Industrial Mineral Deposit Models: Descriptive Deposit Models, Orris, G.J. and Bliss, J.D., Editors, U.S. Geological Survey, Open-File Report 91-11A, pages 21-22.

Heinrichs, T.K. and Reimer, T.O. (1977): A Sedimentary Barite Deposit from the Archean Fig Tree Group of the Barberton Mountain Land (South Africa), Economic Geology, Volume 73, pages 1426-1441.
Large, D.E. (1981)
: Sediment-hosted Submarine Exhalative Sulphide Deposits - a Review of their Geological Characteristics and Genesis; in Handbook of Stratabound and Stratiform Ore Deposits; Wolfe, K.E., Editor, Geological Association of Canada, Volume 9, pages 459-507.

Lydon, J.W. (1995): Sedimentary Exhalative Sulphides (SEDEX); in Geology of Canadian Mineral Deposit Types, Eckstrand, O.R., Sinclair, W.D. and Thorpe, R.I., Editors, Geological Survey of Canada, Geology of Canada, no. 8, pages 130-152.

Lydon, J.W., Lancaster, R.D. and Karkkainen, P. (1979): Genetic Controls of Selwyn Basin Stratiform Barite/Sphalerite/Galena Deposits: An Investigation of the Dominant Barium Mineralogy of the TEA Deposit, Yukon; in Current Research, Part B; Geological Survey of Canada, Paper 79-1B, pages 223-229.

MacIntyre, D.E. (1991): Sedex-Sedimentary-exhalative Deposits; in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, McMillan, W.J., Coordinator; B.C. Ministry of Energy Mines and Petroleum Resources, Paper 1991-4, pages 25-69.

Maynard, J.B. and Okita, P.M. (1991): Bedded Barite Deposits in the United States, Canada, Germany, and China: Two Major Types Based on Tectonic Setting; Economic Geology, volume 86, pages 364-376.

Maynard, J.B. and Okita, P.M. (1992): Bedded Barite Deposits in the United States, Canada, Germany, and China: Two Major Types Based on Tectonic Setting - A Reply; Economic Geology, volume 87, pages 200-201.

Orris, G.J. (1992): Grade and Tonnage Model of Bedded Barite; in Industrial Minerals Deposit Models: Grade and Tonnage Models; Orris, G.J. and Bliss J.D., Editors, U.S. Geological Survey, Open-File Report 92-437, pages 40-42.

Reimer, T.O. (1986): Phanerozoic Barite Deposits of South Africa and Zimbabwe; in Mineral Deposits of South Africa, Volume; Enhauser, C.R. and Maske, S., Editors, The Geological Society of South Africa, pages 2167-2172.

Turner, R.J.W. (1992): Bedded Barite Deposits in the United States, Canada, Germany, and China: Two Major Types Based on Tectonic Setting- A Discussion; Economic Geology, Volume 87, pages 198-199.

Turner, R.J.W. and Goodfellow, W.D. (1990): Barium Carbonate Bodies Associated with the Walt Stratiform Barite Deposit, Selwyn Basin, Yukon: a Possible Vent Complex Associated with a Middle Devonian Sedimentary Exhalative Barite Deposit; in Current Research, Part E, Geological Survey of Canada, Paper 90-1E, pages 309-319.

Wang, Z.-C. and Chu, X.-L. (1994): Strontium Isotopic Composition of the Early Cambrian Barite and Witherite Deposits; Chinese Science Bulletin, Volume 39, pages 52-59.

Wang, Z. and Li, G. (1991): Barite and Witherite in Lower Cambrian Shales of South China: Stratigraphic Distribution and Chemical Characterization; Economic Geology, Volume 86, pages 354-363.

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CARBONATE-HOSTED, NONSULPHIDE ZN (HYPOGENE)

E18
by S. Paradis1 and G.J. Simandl2
1Geological Survey or Canada
2British Columbia Geological Survey

 

Paradis, S. and Simandl, G.J. (2012): Carbonate-hosted, Nonsulphide Zn (hypogene) Mineral Deposit Profile E18; in Geological Fieldwork 2011, BC Ministry of Energy, Mines and Petroleum Resources, Paper 2012-1, pages 211-216.

 

IDENTIFICATION

 

SYNONYMS: Zinc-oxides, willemite-dominant deposits

 

COMMODITIES (BYPRODUCTS): Zn, Pb (Mn, Fe, Cu, V, Cd, Ag)

 

EXAMPLES (British Columbia (MINFILE #)- Canada/International): Structurally-controlled replacement deposits: Abenab West (Namibia), Berg Aukas (Namibia), Kabwe (Zambia), Star Zinc (Zambia), Vazante (Brazil), Ariense (Brazil), Beltana (Australia), Aroona (Australia), Reliance (Australia), Stratiform deposits: Abu Samar (Sudan), Desert View (US), Franklin/Sterling Hill (US).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Zinc oxide minerals, such as willemite, franklinite or zincite, occur as massive to disseminated zones hosted primarily by carbonate rocks.  The two subtypes of hypogene carbonate-hosted nonsulphide Zn-Pb deposits are:

 

1) structurally-controlled replacement deposits in the form of podiform bodies, veins, and irregular pipes consisting mainly of willemite (+/- sphalerite, +/-hematite, +/-franklinite and +/-zincite) and spatially associated with fractures and fault zones; and

2) stratiform deposits forming lenses of franklinite-willemite-zincite (+/-gahnite) located in highly metamorphosed terrains.

 

TECTONIC SETTINGS: The structurally-controlled replacement deposits are located in intracratonic or continental margin environments in fault-controlled sedimentary basins within orogenic belts.

 

The stratiform deposits are located in sedimentary or volcano-sedimentary basins within orogenic belts.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Hostrocks to the structurally-controlled hypogene nonsulphide Zn-Pb deposits are carbonates deposited in platform successions.  Shallowing-upward basins or proximity to major unconformities separating a reduced, carbonate-rich succession (below) from an oxidized sequence of terrestrial sedimentary rocks (above) are frequent settings (e.g., Beltana and Vazante deposits; Groves et al., 2003; Monteiro et al., 2006).

 

AGE OF MINERALIZATION: Ages of hypogene nonsulphide Zn deposits are poorly constrained between the Proterozoic to Paleozoic time.

 

HOST/ASSOCIATED ROCK TYPES: Structurally-controlled deposits are commonly hosted by dolostone, limestone, dolomitized limestone, argillaceous carbonate, marble and slate.

 

Stratiform deposits are typically hosted by metasedimentary rocks, such as calcitic and dolomitic marble, interlayered with metavolcanic and igneous intrusive rocks (Hague et al., 1956; Hitzman et al., 2003).

 

DEPOSIT FORM: Structurally-controlled deposits are highly irregular, consisting of podiform bodies, veins within fault and shear zones, joint and fissure-fills, and open-space fills in breccia pipe-like karst structures.  Individual podiform ore bodies range from a few tens to a few hundreds of metres in the two dimensions parallel with bedding.  Perpendicular to bedding, dimensions are usually a few tens of metres. 

 

Stratiform nonsulphide deposits consist of a series of stratabound discontinuous tabular lenses that considerably vary in thickness and length from few tens of metres to few hundreds of metres.

 

TEXTURE/STRUCTURE: Mineralization in the structurally-controlled deposits is heterogeneous, resulting from various depositional mechanisms such as massive replacement of various hematitic and/or zincian dolomite wallrock facies, dissemination, internal sedimentation, fracture and vein fill, and brecciation.  The massive ore is commonly granular and fine grained, and appears as finely porous to compact cryptocrystalline masses.  The internal sediments consist of fine laminations of zinc oxide minerals in open cavities.  Colloform or crustiform bands, rosettes and spherulites of willemite are deposited as vein and vug fill and in the matrix of breccias.

 

Mineralization in the stratiform tabular lenses consists of massive to disseminated equigranular, subrounded aggregates of Zn-rich minerals.  The ores may have gneissic or disseminated textures, and minerals are generally coarse grained (>2-3mm) and euhedral to subhedral (Hitzman et al., 2003).

 

ORE MINERALOGY[Principal and subordinate]: Structurally-controlled replacement deposits: Willemite, cerussite, coronadite, covellite, descloizite, franklinite, gahnite, galena, genthelvite, hedyphane, hemimorphite, hetaerolite, hedrozincite, mimetite, native silver, sauconite, scholzite, smithsonite, sphalerite, tarbuttite, vanadinite and zincite. 

 

Stratiform deposits:  Franklinite, willemite, zincite, adamite, anglesite, arsenopyrite, aurichalcite, azurite, chalcophanite, chalcopyrite, cuprite, gahnite, galena, hemimorphite, hetaerolite, hydrozincite, magnetite, malachite, melangerite, sauconite, smithsonite, sphalerite, tephroite and zincian fayalite (roepperite).

 

GANGUE MINERALOGY [Principal and subordinate]: Structurally-controlled replacement deposits:  Calcite, manganoan calcite, dolomite, ferroan dolomite, apatite, barite, hematite, magnetite, quartz, siderite, Zn-rich chlorite.  Stratiform deposits: Calcite, manganoan calcite, dolomite, ferroan dolomite, alleghanyite, apatite, aragonite, barite, fluorite, garnet, goethite, graphite, hematite, leucophoenicite, jacobsite, lôllingite, phlogopite, quartz, siderite, sonolite and rhodonite.

 

ALTERATION MINERALOGY: The structurally-controlled replacement deposits display pre to syn-mineralization alteration of the host carbonate rocks that is largely fracture-controlled and extends for about 50 m to 20 km from the major structures.  Alteration consists of silicification and formation of a broad halo of net-veined breccia filled by dolomite, ankerite, siderite, hematite, jasper, and chlorite.  Post-mineralization alteration locally consists of hematite, Zn-chlorite, and dolomite assemblage, and/or calcite replacing earlier dolomite and zinc minerals.  No alteration mineralogy is reported for stratiform deposits.

 

In the case of stratiform deposits, any original pre-metamorphic alteration mineralogy was probably destroyed by metamorphic overprint.  The exception may be Desert View deposit (United States), which could have a preserved manganese halo (Leavens and Patton, 2008).  Sphalerite present in some structurally-controlled replacement and stratiform deposits is replaced by willemite under hydrothermal conditions (i.e., at temperatures higher than

100°C; Brugger et al., 2003).

 

WEATHERING: Nonsulphides in both deposit types can be altered by supergene processes to minerals observed in supergene nonsulphide zinc deposits.  Supergene mineral assemblages form a near-surface direct-replacement cap above many structurally-controlled replacement deposits.  For example, an assemblage of hemimorphite, hydrozincite, and minrecordite form a cap above the willemite bodies of the Vazante deposit (Brazil).  On the periphery of the Beltana deposit (Australia), hemimorphite and smithsonite formed by weathering of willemite.  An assemblage of hemimorphite, cerussite, smithsonite, quartz, descloizite, phromorphite, goethite, hematite, and iron-aluminum-manganese oxides replaces sulphides and willemite-bearing assemblages within the Kabwe (Zambia) and Berg Aukas (Namibia) deposits (Schneider et al., 2008).

 

In the case of stratiform deposits, at least some goethite and hematite form by surface alteration of franklinite.  Ferric oxide and hydroxide minerals are abundant within the Franklin and Sterlin Hill deposits.  Furthermore, under these conditions, hemimorphite, cerussite and hydrozincite commonly replace zincite.

 

ORE CONTROLS: For structurally-controlled deposits, the main controls are favourable sedimentary successions with proper redox states and potential structural zones for fluid ore mixing, i.e., regional basement structural features, such as growth faults, normal and reverse faults, and shear zones.

 

Favourable sedimentary hosts are important for the localization of stratiform zinc oxide deposits.  Faults may also have played a role in the localization of stratiform deposits but metamorphism and deformation have obliterated all evidences.

 

GENETIC MODEL: Structurally-controlled deposits formed where reduced, moderate to high temperature (100-330°C), Zn-rich, sulphur-poor fluid encountered a cooler, less saline, oxidized, sulphur-poor fluid of seawater, groundwater, or basinal origin (Hitzman et al., 2003).  The fundamental difference between the two deposit subtypes may be the site of fluid mixing (Hitzman et al., 2003).  The structurally-controlled deposits formed where fluids from a reduced sedimentary succession moved upwards along structures and encountered fluids that originated in oxidizing environment.

 

There is no consensus regarding the origin of the stratiform nonsulphide zinc deposits (e.g., Franklin and Sterling Hill metamorphosed orebodies) because the nature of the primary mineralization is difficult to decipher.  The stratiform deposits may have formed where Zn-rich hydrothermal fluids discharged into an oxidized, sulphur-poor body of water (i.e., exhalative Zn carbonate-silicate oxide accumulations).  Such mixing and accumulations of manganiferous sulphides and iron oxides may occur at the sediment/water interface or within sediments immediately beneath such body of water.  There is also a possibility that the current ore assemblages may be the post-metamorphic equivalent of hemimorphite and hydrous Mn and Fe-oxides derived from the oxidation of pre-existing sulphides.  In general high ƒO2/ƒS2, oxidizing and alkaline conditions at neutral to basic pH, and elevated temperatures favour stability of willemite relative to sphalerite (Brugger et al., 2003).

 

 

ASSOCIATED DEPOSIT TYPES: Carbonate-hosted, nonsulphide Zn-Pb (supergene, B09), Mississippi Valley-type (MVT, E12), and Irish-type (E13) are the most commonly associated deposits.  Other potentially associated deposits are stratiform Zn sulphide and Fe (oxide or sulphide), Broken Hill-type (S01), magnetite (i.e., iron oxide deposits), sedimentary manganese (F01), and carbonate-hosted Cu+/-Pb+/-Zn (E02) deposits.

 

 

COMMENTS: These deposits are unusual in that they produce zinc, occasionally lead, and little else.  The chemistry of the fluids responsible for the hypogene structurally-controlled nonsulphide deposits is similar to solutions produced in many continental sedimentary basins.  Therefore these deposits could be found in the same districts as MVT, Irish-type and potentially sedimentary exhalative (SEDEX) deposits.  British Columbia has prospective strata for these deposits in the miogeoclinal carbonate platform rocks of the Ancestral North America continental margin and in the pericratonic rocks of the Kootenay terrane.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Colorimetric field test for secondary zinc minerals ("Zinc Zap) and hand-held x-ray fluorescence spectrometry are useful in exploration for nonsulphide Pb-Zn deposits in general (Paradis and Simandl, 2011; Simandl et al., 2011).  Positive Zn anomalies in residual soils and stream sediments and elevated concentrations of Pb, Mn, Fe, Cu, V, U, La, Cd and As are also expected.  Analysis of heavy mineral concentrates (identification of Zn-Pb nonsulphides) in stream and overburden may be effective in areas lacking deep weathering.  Short wave ultraviolet light may help to detect an increase in the Mn content of calcite in proximity to deposit with these manganoan calcite fluorescing orange-red to red; however, calcite may also appear white, cream, yellow-orange, green or pink.  If fluorescence of calcite is due to divalent Mn the colour of fluorescence will be orange-red to red.  The other colours mentioned are due to different activators (quite diverse in calcite).  Willemite may fluoresce green, yellow-orange or yellow under short wave ultraviolet light.  Under long wave ultraviolet radiation, zincite may fluoresce yellow.  Primary metamorphic zincite at Franklin and Sterling Hill does not fluoresce.  Secondary zincite in veins or disseminated hydrothermal grains fluoresces in some specimens, but such zincite is uncommon and volumetrically insignificant.  Willemite, ferroan dolomite, and supergene minerals such as hydrozincite and smithsonite, give distinct spectral responses in the short-wave near infrared portion of the spectrum (Hitzman et al., 2003; McConachy et al., 2009).  Hyperspectral imaging holds promise as a useful tool for accurate mapping of structures, lithologies, and alteration.

 

GEOPHYSICAL SIGNATURE: Deposits may produce a gravity signature.  Electrical methods will not be successful due to the absence or small amounts of sulphides.  Deposits that contain magnetite and franklinite can produce a magnetic response; a larger response should be observed with stratiform nonsulphide deposits.

 

OTHER EXPLORATION GUIDES: Knowledge of the basin sedimentary succession with proper redox states and identification of potential zones for fluid mixing within major structures permits to focus exploration efforts.  Discovery of outcropping hypogene Zn-Pb nonsulphide deposits depends on recognition and knowledge of the physical properties of common nonsulphide zinc minerals.  The selection of grassroots exploration areas should target sedimentary rock sequences that have known nonsulphide (supergene and hypogene) zinc prospects, stratiform manganese deposits, Mississippi Valley-type deposits or Broken Hill-type deposits.

  

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Most of the known deposits (except Vazante with 28.5 Mt at 18.3%Zn, and Franklin with 21.8 Mt at 19.5% Zn) fall in the range of <1 to 10 Mt and grade 5 to 38% Zn and 0 to 11% Pb.  They may contain low concentrations of Mn, Fe, Cu, V, Cd, Ag and Ba.

 

ECONOMIC LIMITATIONS: Some deposits (e.g., Beltana and Aroona) are amenable to open pit mining operations; however, most hypogene nonsulphide deposits are exploited by underground mining.

 

IMPORTANCE: Non-sulphide deposits were the main source of zinc prior to the 1930s.  Following the development of differential flotation and breakthroughs in smelting technology, the mining industry turned its attention almost entirely to sulphide ores.  Today, most zinc is derived from sulphide ore.  The nonsulphide deposits provided roughly 7% of the world's zinc production in 2009.  Hypogene nonsulphide deposits are relatively rare compared to supergene nonsulphide deposits, and they currently represent less than 2% of the zinc production.

 

SELECTED BIBLIOGRAPHY

 

ACKNOWLEDGEMENTS: This manuscript benefited from reviews by Maria Boni (Università di Napoli, Italy), Donald Sangster (Geological Consultant, Ottawa) and David Lefebure (currently with Lefebure GeoLogic Ltd., Salt Spring Island, B.C. Canada; former chief geologist of the British Columbia Survey, Victoria, Canada).  The project started under the umbrella of the Cordilleran Targeted Geoscience Initiative-3 Program of the Geological Survey of Canada, and was done in collaboration with the British Columbia Geological Survey.

 

Boni, M., Terracciano, R., Blassone, G., Gleeson, S. and Matthews, A. (2011): The carbonate-hosted willemite prospects of the Zambezi metamorphic belt (Zambia); Mineralium Deposita, Volume 46, pages 707-729; http://www.springerlink.com/content/c1817113765j7365/fulltext.pdf.

Brugger, J., McPhail, D.C., Waters, J., Wallace, M. and Lees, T. (2003): Formation of willemite in hydrothermal environments; Economic Geology, Volume 98, pages 819-835.

Groves, I., Carman, C.E. and Dunlap, W.J. (2003): Geology of the Beltana willemite deposit, Flinders Ranges, South Australia; Economic Geology, Volume 98, pages 797-818. 
Hague, J.M., Baum, J.L., Herrmann, L.A. and Pickering, R.J. (1956)
: Geology and structure of the Franklin-Sterling area, New Jersey; Bulletin of the Geological Society of America, Volume 67, pages 436-474.

Heyl, A.V. and Bozion, C.N. (1962): Oxidized zinc deposits of the United States, Part 1, General geology; United States Geological Survey, Bulletin 1135-A, 52 pages.

Hitzman, M.W., Reynolds, N.A., Sangster, D.F., Cameron, R.A. and Carman, C.E. (2003): Classification, genesis, and exploration guides for nonsulphide zinc deposits; Economic Geology, Volume 98, Number 4, pages 685-714.

Johnson, C.A. (2001): Geochemical constraints on the origin of the Sterling Hill and Franklin zinc deposits, and the Furnace magnetite bed, northwestern New Jersey; Society of Economic Geologists Guidebook Series, Volume 35, pages 89-97.

Johnson, C.A. and Skinner, B.J. (2003): Geochemistry of the Furnace magnetite bed, Franklin, New Jersey, and the relationship between stratiform iron oxide ores and stratiform zinc oxide-silicate ores in the New Jersey Highlands; Economic Geology, Volume 98, pages 837-854.

Leavens, P.B. and Patton, J.D. (2008): The Desert View Mine, San Bernardino Mountains, California: a possible intermediate between Långban, Sweden and Franklin, New Jersey; Axis, Volume 4, Number 1, pages 1-13.

McConachy, T.F., Yang, K., Boni, M. and Evans, N.J. (2009): Spectral reflectance: preliminary data on a new technique with potential for non-sulphide base metal exploration; Geochemistry: Exploration, Environment, Analysis, Volume 7, pages 139-151.

Monteiro, L.V.S., Bettencourt, J.S., Spiro, B., Graca, R. and Oliveira, T.F. (1999): The Vazante zinc mine, MG, Brazil: constraints on fluid evolution and willemitic mineralization; Exploration and Mining Geology, Volume 8, pages 21-42.

Monteiro, L.V.S., Bettencourt, J.S., Juliani, C. and Oliveira, T.F. (2006): Geology, petrography, and mineral geochemistry of the Vazante non-sulphide and Ambrosia and Fagundes sulphide-rich carbonate-hosted Zn-(Pb) deposits, Minas Gerais, Brazil; Ore Geology Reviews, Volume 28, pages 201-234.

Paradis, S. and Simandl, G.J. (2011): Carbonate-hosted, Nonsulphide Zn-Pb (supergene) Mineral Deposit Profile B09; in Geological Fieldwork 2010, BC Ministry of Energy, Mines and Petroleum Resources, Paper 2011-1, pages 189-193; http://www.empr.gov.bc.ca/Mining/Geoscience/PublicationsCatalogue/Fieldwork.

Peck., W.H., Volkert, R.A., Mansur, A.T. and Doverspike, B.A. (2009): Stable isotope and petrologic evidence for the origin of regional marble-hosted magnetite deposits and the zinc deposits at Franklin and Sterling Hill, New Jersey Highlands, United States; Economic Geology, Volume 104, pages 1037-1054.

Sangster, D.F. (2003): A special issue devoted to nonsulfide zinc deposits: a new look; Economic Geology, Volume 98, Number 4, pages 683-684.

Schneider, J., Boni, M., Laukamp, C., Bechstädt, T. and Petzel, V. (2008):  Willemite (Zn2SiO4) as a possible Ribs geochronometer for dating nonsulfide Zn-Pb mineralization: Examples from the Otavi Mountainland (Namibia); Ore Geology Reviews, Volume 33, pages 152-167.

Simandl, G.J., Paradis, S., Fajber, R., and Rogers, N. (2011):  Hand-held, portable XRF in exploration for carbonate-hosted sulphide and nonsulphide Pb-Zn deposits; Geofile 2011-6, BC Ministry of Energy, Mines and Petroleum Resources; http://www.empr.gov.bc.ca/Mining/Geoscience/PublicationsCatalogue/GeoFiles.

Paradis, S., and Simandl, G.J. (2012):  Carbonate-hosted, Nonsulphide Zn (hypogene) Mineral Deposit Profile E18; in Geological Fieldwork 2011, BC Ministry of Energy, Mines and Petroleum Resources, Paper 2012-1, pages 211-216. 

 

 

*  Note:  All BC deposit profile #s with an asterisk have no completed deposit profile.  USGS deposit model #s with an asterisk had no published model in the late 1990s.

Examples of Sediment-hosted Deposits

BC Profile # Global Examples B.C. Examples
E01* Almaden (Spain), Santa Barbara (Peru) - -
E02 Grinnell and Kanuyak Island (Northwes Territories, Canada); Kennecott, Ruby Creek and Omar (Alaska, USA), Apex (Utah, USA); Gortdrum (Ireland); Tsumeb and Kombat (Namibia); Kipushi (Zaire); M'Passa (Congo); Timma (Israel); Nifty (Australia); portions of Dongchuan deposits (China)  Blue
E03 Brewery Creek? (Alaska), Carlin, Getchell & Cortez (Nevada) Golden Bear ?
 E04 Kupferschiefer (Germany & Poland), White Pine (Michigan) Roo, Commerce, Chal 4
 E05 Laisvall (Sweden), George Lake (Saskatchewan)  
 E06 Rosalind (Alberta, Canada), Truax (Saskatchewan, Canada), Mordern (Manitoba, Canada); Black Hills District, Big Horn Basin (Wyoming, USA), Gonzales and Lafayette Counties (Texas, USA), Iwambaand and Monroe Counties (Mississippi, USA); Milos (Greece); Landshut (Germany); Sardinia (Italy); Annalka (Japan); Campina Grande (Brazil) Hat Creek , Princeton, Quilchena, French Bar
E07 Cypress Hills (Alberta, Canada), Eastend, Wood Mountain, Ravenscrag (Saskatchewan, Canada), Moose River Basin (Ontario, Canada), Stubenacadie Valley (Nova Scotia, Canada); Aiken (South Carolina, USA), Wrens, Sandersville, Macon-Gordon, Andersonville (Georgia, USA), Eufaula (Alabama, USA); Weipa (Queensland, Australia); Jari Capim (Brazil) Sumas Mountain, Blue Mountain, Lang Bay, Quinsam, Giscome Rapids
 E08 Treasure Mtn (Montana), Trimouns ( France), Henderson (Ontario) Red Mountain, Silver Dollar
 E09 Veitsch, Entachen Alm, Hochfilzen, Radentheim and Breitenau (Austria); Eugui (Navarra Province, Spain); deposits of Ashan area, Liaoning Province (China); Satka deposit (Russia) Mount Brussilof, Marysville, Brisco area and Driftwood Creek
E10 Illinois - Kentucky, Italian Alps Muncho Lake
E11 Illinois - Kentucky, Italian Alps Liard Fluorite
E12 Viburnum Trend (Missouri), Pine Point (Northwest Territories) Robb Lake, Monarch
 E13 Navin, Lisheen & Tynagh (Ireland), Troya (Spain) Reeves MacDonald, HB, Jersey, Duncan
 E14 Mount Isa (Australia), Faro & Grum (Yukon) Sullivan, Cirque, Driftpile
E15 Blackbird & Sheep Creek (Montana), Boleo (Mexico)  - -
 E16 Nick (Yukon), Tianeshan & Zunyi (China) - -
 E17 Tea, Tyrala, Hess, Walt and Cathy (Yukon, Canada), Walton (Nova Scotia, Canada); Fancy Hill (Alaska, USA), Mountain Springs, Greystone (Nevada, USA); Jixi and Liulin (China); Fig Tree and Mabiligwe (South Africa) Kwadacha, Gin, Gnome
E18 Carbonate-hosted, Nonsulphide Zn (hypogene)

- -