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Ministry of Energy Mines and Responsible for Core Review

I - Vein, Breccia, and Stockwork

BC Profile # Deposit Type Approximate Synonyms USGS Model #
I01 Au-quartz veins Mesothermal, Motherlode, saddle reefs 36a
I02 Intrusion-related Au pyrrhotite veins Subvolcanic shear-hosted gold - -
I03 Turbidite-hosted Au veins Meguma type 36a
I04 Iron formation-hosted Au Iron formation-hosted gold 36b
I05 Polymetallic veins Ag-Pb-Zn±Au Felsic intrusionassociated Ag-Pb-Zb veins 22c, 25b
I06 Cu±Ag quartz veins Churchill-type vein Cu ?
 I07* Silica veins - - - -
I08 Silica-Hg carbonate - - 27c
I09 Stibnite veins and disseminations Simple and disseminated Sb deposits 27d,27e
I10 Vein barite - - IM27e
I11 Barite-fluorite veins - - 26c*
 I12* W veins Quartz-wolframite veins 15a
 I13* Sn veins and greisens - - 15b, 15c
I14 Five-element veins Ni-Co-As-Ag±(Bi, U) Ni-Co-native Ag veins, cobalt-type veins - -
I15 Classical U veins Pitchblende veins, vein uranium - -
I16  Unconformity-associated U Unconformity-veins, Unconformity U 37a
I17 Cryptocrystalline magnesite veins Bone magnesite, Kraubath-type magnesite - -

 

Au-QUARTZ VEINS


I01
by Chris Ash and Dani Alldrick
British Columbia Geological Survey

 

Ash, Chris and Alldrick, Dani (1996): Au-quartz Veins, 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 53-56.

 

IDENTIFICATION

 

SYNONYMS: Mother Lode veins, greenstone gold, Archean lode gold, mesothermal gold-quartz veins, shear-hosted lode gold, low-sulphide gold-quartz veins, lode gold.

 

COMMODITIES (BYPRODUCTS): Au (Ag, Cu, Sb).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/ International):

Phanerozoic: Bralorne-Pioneer (092JNE001), Erickson (104P 029), Taurus (104P 012), Polaris-Taku (104K 003), Mosquito Creek (093H 010), Cariboo Gold Quartz (093H 019), Midnight (082FSW119); Carson Hill, Jackson-Plymouth, Mother Lode district; Empire Star and Idaho-Maryland, Grass Valley district (California, USA); Alaska-Juneau, Jualin, Kensington (Alaska, USA), Ural Mountains (Russia).
Archean: Hollinger, Dome, McIntyre and Pamour, Timmins camp; Lake Shore, Kirkland Lake camp; Campbell, Madsen, Red Lake camp; Kerr-Addison, Larder Lake camp (Ontario, Canada), Lamaque and Sigma, Val d’Or camp (Quebec, Canada); Granny Smith, Kalgoorlie and Golden Mile ( Western Australia); Kolar (Karnataka, India), Blanket-Vubachikwe (Zimbabwe, Africa).

 

 

 

 

 

 

 

 

 

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Gold-bearing quartz veins and veinlets with minor sulphides crosscut a wide variety of hostrocks and are localized along major regional faults and related splays. The wallrock is typically altered to silica, pyrite and muscovite within a broader carbonate alteration halo.

 

TECTONIC SETTINGS:

Phanerozoic: Contained in moderate to gently dipping fault/suture zones related to continental margin collisional tectonism. Suture zones are major crustal breaks which are characterized by dismembered ophiolitic remnants between diverse assemblages of island arcs, subduction complexes and continental-margin clastic wedges.
Archean: Major transcrustal structural breaks within stable cratonic terranes. May represent remnant terrane collisional boundaries.

 

 

 

 

 

 

 

 

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Veins form within fault and joint systems produced by regional compression or transpression (terrane collision), including major listric reverse faults, second and third-order splays. Gold is deposited at crustal levels within and near the brittle-ductile transition zone at depths of 6-12 km, pressures between 1 to 3 kilobars and temperatures from 200o to 400 oC. Deposits may have a vertical extent of up to 2 km, and lack pronounced zoning.

 

AGE OF MINERALIZATION: Mineralization is post-peak metamorphism (i.e. late syncollisional) with gold-quartz veins particularly abundant in the Late Archean and Mesozoic.

Phanerozoic: In the North America Cordillera gold veins are post-Middle Jurassic and appear to form immediately after accretion of oceanic terranes to the continental margin. In British Columbia deposits are mainly Middle Jurassic (~ 165-170 Ma) and Late Cretaceous (~ 95 Ma). In the Mother Lode belt they are Middle Jurassic (~ 150 Ma) and those along the Juneau belt in Alaska are of Early Tertiary (~56-55 Ma).
Archean: Ages of mineralization for Archean deposits are well constrained for both the Superior Province, Canadian Shield (~ 2.68 to 2.67 Ga) and the Yilgarn Province, Western Australia (~ 2.64 to 2.63 Ga).

 

 

 

 

 

 

 

 

 

HOST/ASSOCIATED ROCK TYPES: Lithologically highly varied, usually of greenschist metamorphic grade, ranging from virtually undeformed to totally schistose.

Phanerozoic: Mafic volcanics, serpentinite, peridotite, dunite, gabbro, diorite, trondhjemite/plagiogranites, graywacke, argillite, chert, shale, limestone and quartzite, felsic and intermediate intrusions.
Archean: Granite-greenstone belts - mafic, ultramafic (komaitiitic) and felsic volcanics, intermediate and felsic intrusive rocks, graywacke and shale.

 

 

 

 

 

 

 

 

DEPOSIT FORM: Tabular fissure veins in more competent host lithologies, veinlets and stringers forming stockworks in less competent lithologies. Typically occur as a system of en echelon veins on all scales. Lower grade bulk-tonnage styles of mineralization may develop in areas marginal to veins with gold associated with disseminated sulphides. May also be related to broad areas of fracturing with gold and sulphides associated with quartz veinlet networks.

 

TEXTURE/STRUCTURE: Veins usually have sharp contacts with wallrocks and exhibit a variety of textures, including massive, ribboned or banded and stockworks with anastamosing gashes and dilations. Textures may be modified or destroyed by subsequent deformation.

 

ORE MINERALOGY (Principal and subordinate): Native gold, pyrite, arsenopyrite, galena, sphalerite, chalcopyrite, pyrrhotite, tellurides, scheelite, bismuth, cosalite, tetrahedrite, stibnite, molybdenite, gersdorffite (NiAsS), bismuthimite (Bi2S2), tetradymite (Bi2Te2S).

 

GANGUE MINERALOGY (Principal and subordinate): Quartz, carbonates (ferroan-dolomite, ankerite ferroan-magnesite, calcite, siderite), albite, mariposite (fuchsite), sericite, muscovite, chlorite, tourmaline, graphite.

 

ALTERATION MINERALOGY: Silicification, pyritization and potassium metasomatism generally occur adjacent to veins (usually within a metre) within broader zones of carbonate alteration, with or without ferroan dolomite veinlets, extending up to tens of metres from the veins. Type of carbonate alteration reflects the ferromagnesian content of the primary host lithology; ultramafics rocks - talc, Fe-magnesite; mafic volcanic rocks - ankerite, chlorite; sediments - graphite and pyrite; felsic to intermediate intrusions - sericite, albite, calcite, siderite, pyrite. Quartz-carbonate altered rock (listwanite) and pyrite are often the most prominent alteration minerals in the wallrock. Fuchsite, sericite, tourmaline and scheelite are common where veins are associated with felsic to intermediate intrusions.

 

WEATHERING: Distinctive orange-brown limonite due to the oxidation of Fe-Mg carbonates cut by white veins and veinlets of quartz and ferroan dolomite. Distinctive green Cr-mica may also be present. Abundant quartz float in overburden.

 

ORE CONTROLS: Gold-quartz veins are found within zones of intense and pervasive carbonate alteration along second order or later faults marginal to transcrustal breaks. They are commonly closely associated with, late syncollisional, structurally controlled intermediate to felsic magmatism. Gold veins are more commonly economic where hosted by relatively large, competent units, such as intrusions or blocks of obducted oceanic crust. Veins are usually at a high angle to the primary collisional fault zone.

 

Phanerozoic: Secondary structures at a high angle to relatively flat-lying to moderately dipping collisional suture zones.
Archean: Steep, transcrustal breaks; best deposits overall are in areas of greenstone.

 

 

 

 

 

 

 

ASSOCIATED DEPOSIT TYPES: Gold placers (C01, C02), sulphide manto Au (J04), silica veins (I07); iron formation Au (I04) in the Archean.

 

GENETIC MODEL: Gold quartz veins form in lithologically heterogeneous, deep transcrustal fault zones that develop in response to terrane collision. These faults act as conduits for CO2-H2O-rich (5-30 mol% CO2 ), low salinity (<3 wt% NaCl) aqueous fluids, with high Au, Ag, As, (±Sb, Te, W, Mo) and low Cu, Pb, Zn metal contents. These fluids are believed to be tectonically or seismically driven by a cycle of pressure build-up that is released by failure and pressure reduction followed by sealing and repetition of the process ( Sibson et al., 1988). Gold is deposited at crustal levels within and near the brittle- ductile transition zone with deposition caused by sulphidation (the loss of H2S due to pyrite deposition) primarily as a result of fluid-wallrock reactions, other significant factors may involve phase separation and fluid pressure reduction. The origin of the mineralizing fluids remains controversial, with metamorphic, magmatic and mantle sources being suggested as possible candidates. Within an environment of tectonic crustal thickening in response to terrane collision, metamorphic devolitization or partial melting (anatexis) of either the lower crust or subducted slab may generate such fluids.

 

COMMENTS: These deposits may be a difficult deposit to evaluate due to "nugget effect", hence the adage, “Drill for structure, drift for grade”. These veins have also been mined in British Columbia as a source of silica for smelter flux.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Elevated values of Au, Ag, As, Sb, K, Li, Bi, W, Te and B ± (Cd, Cu, Pb, Zn and Hg) in rock and soil, Au in stream sediments.

 

GEOPHYSICAL SIGNATURE: Faults indicated by linear magnetic anomalies. Areas of alteration indicated by negative magnetic anomalies due to destruction of magnetite as a result of carbonate alteration.

 

OTHER EXPLORATION GUIDES: Placer gold or elevated gold in stream sediment samples is an excellent regional and property-scale guide to gold-quartz veins. Investigate broad 'deformation envelopes' adjacent to regional listric faults where associated with carbonate alteration. Alteration and structural analysis can be used to delineate prospective ground. Within carbonate alteration zones, gold is typically only in areas containing quartz, with or without sulphides. Serpentinite bodies, if present, can be used to delineate favourable regional structures. Largest concentrations of free gold are commonly at, or near, the intersection of quartz veins with serpentinized and carbonate-altered ultramafic rocks.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Individual deposits average 30 000 t with grades of 16 g/t Au and 2.5 g/t Ag (Berger, 1986) and may be as large as 40 Mt. Many major producers in the Canadian Shield range from 1 to 6 Mt at grades of 7 g/t Au (Thorpe and Franklin, 1984). The largest gold-quartz vein deposit in British Columbia is the Bralorne-Pioneer which produced in excess of 117 800 kilograms of Au from ore with an average grade of 9.3 g/t.

 

ECONOMIC LIMITATIONS: These veins are usually less than 2m wide and therefore, only amenable to underground mining.

 

IMPORTANCE: These deposits are a major source of the world’s gold production and account for approximately a quarter of Canada’s output. They are the most prolific gold source after the ores of the Witwatersrand basin.

 

REFERENCES

 

Ash, C.H., Macdonald, R.W.J. and Reynolds, P.H. (in preparation): Ophiolite-related Mesothermal Lode Gold in British Columbia: A Deposit Model; B.C. Ministry Energy, Mines and Petroleum Resources, Bulletin.

Berger, B.R. (1986): Descriptive Model of Low-sulphide Au-Quartz Veins; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, pages 239-243.

Bohlke, J.K. and Kistler, R.W. (1986): Rb-Sr, K-Ar and Stable Isotope Evidence for the Ages and Sources of Fluid Components of Gold-bearing Quartz Veins in the Northern Sierra Nevada Foothills Metamorphic Belt; Economic Geology, Volume 81, pages 296- 422.

Gebre-Mariam, M., Hagemann, S.G. and Groves, D.G. (1995): A Classification Scheme for Epigenetic Archean Lode-gold Deposits; Mineralium Deposita, Volume 30, pages 408- 410.

Groves, D.I. (1993): The Crustal Continuum Model for Late Archean Lode-gold Deposits of the Yilgarn Block, Western Australia; Mineralium Deposita, Volume 28, pages 366- 374.

Hodgson, C.J. (1993): Mesothermal Lode-gold Deposits; in Mineral Deposit Modeling, Kirkham, R.V., Sinclair, W.D., Thorpe, R.I. and Duke, J.M., Editors, Geological Association of Canada, Special Paper 40, pages 635-678.

Hodgson, C.J. and Hamilton, J.V. (1989): Gold Mineralization in the Abitibi Greenstone Belt: End Stage of Archean Collisional Tectonics; in The Geology of Gold Deposits: The Perspective in 1988, Economic Geology, Monograph, pages 86-100.

Kerrich, R.W. (1990): Mesothermal Gold Deposits: A Critique of Genetic Hypotheses; in Greenstone Gold and Crustal Evolution, Rober, F., Sheahan, P.A. and Green, S.B., Editors, Geological Association of Canada, NUNA Conference Volume, pages 13-31.

Kerrich, R. and Wyman, D. (1990): Geodynamic Setting of Mesothermal Gold Deposits: An Association with Accretionary Tectonic Regimes; Geology, Volume 18, pages 882-885.

Landefeld, L.A. (1988): The Geology of the Mother Lode Gold Belt, Sierra Nevada Foothills Metamorphic Belt, California; in Proceedings Volume, North American Conference on Tectonic Control of Ore Deposits and the Vertical and Horizontal Extent of Ore Systems, University of Missouri - Rolla, pages 47-56.

Leitch, C.H.B. (1990): Bralorne; a Mesothermal, Shield-type Vein Gold Deposit of Cretaceous Age in Southwestern British Columbia; Canadian Institute of Mining and Metallurgy, Bulletin, Volume 83, Number 941, pages 53-80.

Panteleyev, A. (1991): Gold in the Canadian Cordillera - a Focus on Epithermal and Deeper Environments, in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, B.C. Ministry of Energy, Mines and Petroleum Resources; Paper 1991-4, pages 163-212.

Roberts, R.G. (1987): Ore Deposit Models #11. Archean Lode Gold Deposits; Geoscience Canada, Volume 14, Number 1, pages 37-52.

Schroeter, T.G., Lund, C. and Carter, G. (1989): Gold Production and Reserves in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1989- 22, 86 pages.

Sibson, R.H., Robert, F. and Poulsen, H. (1988): High Angle Faults, Fluid Pressure Cycling and Mesothermal Gold-Quartz Deposits; Geology, Volume 16, pages 551-555.

Thorpe, R.I. and Franklin, J.M. (1984): Volcanic-associated Vein and Shear Zone Gold; in Canadian Mineral Deposit Types, A Geological Synopsis, Eckstrand, O.R., Editor, Geological Survey of Canada, Economic Geology Report 36, page 38.

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INTRUSION-RELATED Au PYRRHOTITE VEINS


I02
by Dani J. Alldrick
British Columbia Geological Survey

 

Alldrick, D.J. (1996): Intrusion-related Au Pyrrhotite Veins, 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 57-58.

 

IDENTIFICATION

 

SYNONYMS: Mesothermal veins, extension veins, transitional veins, contact aureole veins.

 

COMMODITIES (BYPRODUCTS): Au, Ag (Cu).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Scottie Gold (104B 034), Snip (104B 250), Johnny Mountain (104B 107), War Eagle (082FSW097), Le Roi (082FSW093), Centre Star (082FSW094); no international examples known.

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Parallel tabular to cymoid veins of massive sulphide and/or bull- quartz-carbonate with native gold, electrum and chalcopyrite are emplaced in a set of en echelon fractures around the periphery of a subvolcanic pluton. Many previous workers have included these veins as mesothermal veins.

 

TECTONIC SETTINGS: Volcanic arcs in oceanic and continental margin settings. Older deposits are preserved in accreted arc terranes.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: The subvolcanic setting for these deposits is transitional between the setting for subvolcanic porphyry copper systems and for subvolcanic epithermal systems.

 

AGE OF MINERALIZATION: Recognized examples of this ’new’ deposit type are all Early Jurassic.

 

HOST/ASSOCIATED ROCK TYPES: Hostrocks are andesitic tuffs, turbidites or early intrusive phases around the periphery of phaneritic, locally porphyritic, granodiorite stocks and batholiths.

 

DEPOSIT FORM: At various deposits the form has been described as: planar, en echelon vein sets, shear veins, cymoid veins, cymoid loops, sigmoidal veins, extension veins, tension gashes, ladder veins, and synthetic Reidel shear veins. Veins vary in width from centimetres to several metres and can be traced up to hundreds of metres.

 

TEXTURE/STRUCTURE: Two vein types may occur independently or together. Veins may be composed of (i) massive fine-grained pyrrhotite and/or pyrite, or (ii) massive bull quartz with minor calcite and minor to accessory disseminations, knots and crystal aggregates of sulphides. These two types of mineralization may grade into each other along a single vein or may occur in adjacent, but separate veins. Some veins have undergone post-ore ductile and brittle shearing that complicates textural and structural interpretations.

 

ORE MINERALOGY (Principal and subordinate): Native gold, electrum, pyrite, pyrrhotite, sphalerite, galena, chalcopyrite, bornite, argentite, arsenopyrite, magnetite, ilmenite, tetrahedrite, tennantite, molybdenite, cosalite, chalcocite, tellurobismuthite, hessite, volynskite, altaite, native bismuth.

 

GANGUE MINERALOGY (Principal and subordinate): Quartz, calcite, ankerite, chlorite, sericite, rhodochrosite, k-feldspar, biotite.

 

ALTERATION MINERALOGY: Chlorite, sericite, pyrite, silica, carbonate, rhodochrosite, biotite, epidote, K-feldspar, ankerite. Alteration occurs as narrow (4 cm) vein selvages and as moderate alteration haloes extending up to several metres into the country rock.

 

ORE CONTROLS: Well defined faults and shears control the mineralization. Veins are peripheral to and spatially associated with porphyritic intrusive rocks which may host porphyry copper mineralization.

 

GENETIC MODEL: Mineralization is syn-intrusive and synvolcanic and formed along the thermally controlled 'brittle-ductile transition envelope' that surrounds subvolcanic intrusions. Late magma movement caused local shear stress, and resultant en echelon vein sets opened and were filled by sulphides and gangue minerals precipitating from circulating hydrothermal fluids. Subsequent shearing may have superimposed foliation or brecciation onto these early-formed veins.

 

ASSOCIATED DEPOSIT TYPES: Typical deposits of a volcanic arc, especially those in the subvolcanic setting: porphyry Cu+/-Mo+/-Au (L04), skarns, epithermal veins and breccias (H04, H05), 'transitional' deposits (volcanogenic Cu-As-Sb-Au-Ag, L01) and surficial fumarolic hotspring (H03) and exhalative deposits.

 

COMMENTS: At least one of these deposits was initially interpreted as a volcanogenic exhalative sulphide lens because a massive sulphide vein was discovered in volcanic rocks with no obvious bedding.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Elevated values of Au, Ag, Cu. (As, Zn).

 

GEOPHYSICAL SIGNATURE: Electromagnetic (ABEM and VLF-EM) and magnetometer (negative anomalies or 'magnetic troughs').

 

OTHER EXPLORATION GUIDES: Intense prospecting swath extending from 100 metres inside the intrusive contact to 1000 metres outside the intrusive contact of a prospective (sub-volcanic; Early Jurassic) pluton. Detailed soil geochemistry and detailed ground geophysics could be designed to investigate this same area. Small, 'hairline' mineralized fractures are good proximal indicators of a nearby major vein. Increased alteration intensity could also be a good proximal indicator, but this is a more subtle feature. Once the vein orientation on an initial discovery is determined, additional parallel veins should be anticipated and investigated with fences of drill holes.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Gold/silver ratios are close to 1:1. Copper may be a recoverable byproduct. Typical grades are 10 to 20 g/t Au.

 

IMPORTANCE: The Snip gold mine is currently British Columbia’s largest gold producer and the Rossland veins are the province’s second largest gold camp.

 

REFERENCES

 

Alldrick, D.J. (1993): Geology and Metallogeny of the Stewart Mining Camp, Northwestern, British Columbia, B. C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 85, 105 pages.

Alldrick, D.J., Drown, T.J., Grove, E.W., Kruchkowski, E.R. and Nichols, R.F. (1989): Iskut-Sulphurets Gold, Northern Miner Magazine, January, 1989, Pages 46-49.

Rhys, D. A. (1993): Geology of the Snip Mine, and its Relationship to the Magmatic and Deformational History of the Johnny Mountain Area, Northwestern British Columbia; unpublished M.Sc. thesis, The University of British Columbia, 278 pages.

Rhys, D. A. (1995): The Red Bluff Gold-copper Porphyry and Associated Precious and Base Metal Veins, Northwestern British Columbia; in Schroeter, T.G., Editor, Porphyry Deposits of the northwestern Cordillera of North America, Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 46, pages 838-850.

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TURBIDITE-HOSTED Au VEINS


I03
by R.H. McMillan
Consulting Geologist, Victoria, British Columbia

 

McMillan, R.H. (1996): Turbidite-hosted Au Veins, 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 59-62.

 

IDENTIFICATION

 

SYNONYMS: Saddle reefs, Bendigo-type.

 

COMMODITIES (BYPRODUCTS): Au (Ag, W, Sb).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Frasergold (093A 150), Valentine Mountain (092B 108), Island Mountain (093H 019), Mosquito Creek (093H 025), Sheep Creek Deposits - Reno (082FSW036), Queen (082FSW048), Kootenay Belle (082FSW044) and Gold Belt (082FSW040); Ptarmigan, Burwash, Thompson-Ludmar and other Yellowknife district deposits (Northwest Territories, Canada), Meguma district (Nova Scotia, Canada), Bendigo and Ballarat (Victoria, Australia).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Gold-quartz veins, segregations, lodes and sheeted zones hosted by fractures, faults, folds and openings in anticlines, synclines and along bedding planes in turbidites and associated poorly sorted clastic sedimentary rocks.

 

TECTONIC SETTING: Hostrocks were deposited in submarine troughs, periarc basins, foreland basins and remnant ocean basins. The sediments were typically formed on continental margins or back-arc basins. Typically these sequences experienced one or two deformational phases with associated metamorphism.

 

DEPOSITIONAL ENVIRONMENT/GEOLOGICAL SETTING: Thick sediment sequences that have been deformed and metamorphosed; relatively few igneous rocks.

 

AGE OF MINERALIZATION: Archean to Tertiary; the Bendigo and Meguma districts are underlain by Early Paleozoic strata. The veins are generally considered to be related to later deformational event.

 

HOST/ ASSOCIATED ROCK TYPES: The predominant rock types are greywackes, siliceous wackes, shales and carbonaceous shales. Bedded cherts, iron formations, fine- grained impure carbonate rocks; minor polymictic conglomerate, tuffaceous members and minor marine volcanic flows may also be part of the stratigraphic sequence. There are younger granitic intrusions in many belts. Metamorphic grade is generally greenschist, but may reach amphibolite rank.

 

DEPOSIT FORM: Typically deposits are composed of multiple quartz veins up to a few metres in width that are commonly stratabound (either concordant or discordant), bedding-parallel, or discordant, and parallel to fold axial planes. Veins are variably deformed and occur as single strands, as sheeted arrays or as stockworks. Bedding-parallel veins within anticlines and synclines in the Bendigo-Ballarat and Meguma districts are commonly called saddle reefs or saddle troughs.

 

TEXTURE/STRUCTURE: Veins are well defined with sharp contacts. Bedding veins can be massive or laminated (ribbon texture) with columnar structures or stylolites, while discordant veins are generally massive. Veins can be associated with a variety of structures. Most common are folded veins and saddle reefs related to anticlinal folds. Sheeted, en echelon sigmoidal veins, ladder veins, tension gashes or stockworks may be related to zones of extension or to Reidel shear structures.

 

ORE MINERALOGY (Principal and subordinate): Native gold, pyrite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite, galena, molybdenite, bismuth, stibnite, bournonite and other sulphosalt minerals. Low sulphide content (<2.5%).

 

GANGUE MINERALOGY (Principal and subordinate): Quartz, carbonates (calcite, dolomite or ankerite), feldspar (albite) and chlorite.

 

ALTERATION: Generally not prominent, however, disseminated arsenopyrite, pyrite and tourmaline, and more pervasive silica, sericite and carbonate, may develop in wallrocks adjacent to veins.

 

WEATHERING: In unglaciated terrains deep weathering and alluvial recycling may produce related rich placer deposits, such as the Bendigo region.

 

ORE CONTROLS: A strong structural control within dilatent areas in fold crests (saddle and trough reefs), discordant veins and tension gashes. This structural control may extend to district scale alignment of deposits. In some districts the veins appear confined to a specific stratigraphic interval, often near a change in lithologies. In the Meguma district, a more subtle stratigraphic control related to the upper (pelitic) portions of individual bouma cycles as well as regionally to the upper portion of the turbidite section. In the Bendigo district there is a relationship between ore and an abundance of graphite in the adjacent wallrocks.

 

GENETIC MODEL: Genetic theories range from veins formed by magmatic hydrothermal fluids or metamorphogenic fluids to deformed syngenetic mineralization. Most current workers prefer the metamorphogenic-deformational or lateral secretion theories and interpret the laminations as “crack-seal” phenomena formed during episodic re-opening of the veins during their formation. Workers favoring a syngenetic origin interpret the laminations as primary layering. Structural relationships in the Meguma and Bendigo districts indicate that the veins formed contemporaneously with, or prior to the major deformational event and were metamorphically overprinted during the intrusion of Devonian batholithic granitic rocks. Late post-deformational tension veinlets are generally non- auriferous.

 

ASSOCIATED DEPOSIT TYPES: Placers (C01), iron formation hosted gold deposits (I04) are also mainly hosted in turbidites - some of the Northwest Territories turbidite- hosted deposits are associated with chemical sediments. In several camps, slate horizons carrying finely disseminated, very low grade gold have been reported.

 

COMMENTS: Although past classification schemes have not recognized this type of deposit in British Columbia, the Valentine Mountain deposit hosted in Leech River schists and Frasergold hosted in Late Triassic clastic Quesnel River Group can be included. Elsewhere, several important vein gold districts in clastic sedimentary (possibly turbiditic) rocks might also be included. For example, the Sheep Creek camp and some of the Barkerville deposits are hosted in siliceous wackes and phyllites.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Si, Fe, S, As, B, Au and Ag generally show strong enrichment in the deposits, while Cu, Mg, Ca, Zn, Cd, Pb, Sb, W and Mn generally show moderate enrichment, and Hg, In, Li, Bi, Se, Te, Mo, F, Co and Ni may show low levels of enrichment.

 

GEOPHYSICAL SIGNATURE: The low sulphide content of the majority of quartz veins renders most geophysical techniques ineffective as direct exploration tools. However, airborne and ground electromagnetic and magnetic surveys and induced polarization surveys can be useful where deposits show an association with iron formation, massive sulphides or graphite.

 

OTHER EXPLORATION GUIDES: Standard prospecting techniques to trace mineralization directly or in float trains in glacial till, talus or other debris derived from the gold mineralization remains the most effective prospecting tool. Areas where there has been past gold production from placers are good candidates for prospecting.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Gold production from the Meguma region has come from 60 deposits at grades ranging from 8 to 50 g/t - a total of 35.13 tonnes has been produced from the district. The Bendigo field is much more significant, having produced a minimum of more than 373.3 t (12 M.oz.) of non-alluvial gold from more than 40 Mt of ore since 1851 - grades ranged from a minimum of approximately 5 g/t to more than 30 g/t. The three Barkerville mines produced an aggregate of 2.75 Mt to yield 38.29 t of gold between 1933 and 1987.

 

ECONOMIC LIMITATIONS: Deposits such as those in the Bendigo and Barkerville districts constitute attractive exploration targets. Although the hand sorting required to recover gold from the Nova Scotia deposits would probably render them uneconomic today, new techniques such as photometric sorting might improve the economics.

 

IMPORTANCE: Some districts/deposits, such as Bendigo, rank as world class and remain attractive exploration targets. The limited information available about the immense Muruntau deposit suggest that it may be similar to this type.

 

REFERENCES

 

ACKNOWLEDGMENTS: Howard Poulsen, Chris Ash, Dani Alldrick and Andre Panteleyev reviewed the profile and provided constructive comments.

 

Boyle, R.W. (1979): The Geochemistry of Gold and its Deposits, Geological Survey of Canada, Bulletin 280, 584 pages.

Boyle, R.W. (1986): Gold Deposits in Turbidite Sequences: Their Geology, Geochemistry and History of the Theories of their Origin, in Keppie, J. Duncan, Boyle, R.W. and Haynes, S.J., Editors, Turbidite-hosted Gold Deposits, Geological Association of Canada, Special Paper 32, pages 1-14.

Graves, M.C. and Zentilli, M. (1982): A Review of the Geology of Gold in Nova Scotia; in Geology of Canadian Gold Deposits, Hodder, R.W. and Petruk W., Editors, Canadian Institute of Mining and Metallurgy, Special Volume 24, pages 233-242.

Haynes, S.J. (1986): Geology and Chemistry of Turbidite-hosted Gold Deposits, Greenschist Facies, Eastern Nova Scotia, in Turbidite-hosted Gold Deposits, Keppie, J. D., Boyle, R.W. and Haynes, S.J., Editors, Geological Association of Canada, Special Paper 32, pages 161-178.

Mathews, W.H. (1953): Geology of the Sheep Creek Camp, B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 31, -- pages.

Padgham, W.A. (1986): Turbidite-hosted Gold-quartz Veins in the Slave Structural Province, N.W.T, in Turbidite-hosted Gold Deposits, Keppie, J. D., Boyle, R.W. and Haynes, S.J., Editors, Geological Association of Canada, Special Paper 32, pages 119-134.

Panteleyev, A.P. (1991): Gold in the Canadian Cordillera - a Focus on Epithermal and Deeper Environments, in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, pages 163-212.

Schroeter, T.G. and Lane, R.A. (1991): A Century of Gold Production and Reserves in British Columbia (1890 to 1990). B.C. Ministry of Energy Mines and Petroleum Resources, Open File 1991-19, 42 pages.

Sharpe, E.N. and MacGeehan, P.J. (1990): Bendigo Goldfield; in Geology of the Mineral Deposits of Australia and Papua New Guinea, Hughes, F.E., Editor, The Australasian Institute of Mining and Metallurgy, Monograph No. 14, Volume 2, pages 1287-1296.

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IRON FORMATION-HOSTED Au


I04
by R.H. McMillan
Consulting Geologist, Victoria, British Columbia

 

McMillan, R.H. (1996): Iron formation-hosted Au, 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 63-66.

 

IDENTIFICATION

 

SYNONYM: Mesothermal veins.

 

COMMODITIES (BYPRODUCTS): Au (Ag, Cu).

 

EXAMPLES (British Columbia - Canada/International): No B.C. examples; Lupin and Cullaton Lake B-Zone (Northwest Territories, Canada), Detour Lake, Madsen Red Lake, Pickle Crow, Musselwhite, Dona Lake, (Ontario, Canada), Homestake (South Dakota, USA), Mt. Morgans (Western Australia); Morro Vehlo and Raposos, Mineas Gerais (Brazil); Vubachikwe and Bar 20 (Zimbabwe); Mallappakoda, Kolar District (India).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Gold in crosscutting quartz veins and veinlets or as fine disseminations associated with pyrite, pyrrhotite and arsenopyrite hosted in iron-formations and adjacent rocks within volcanic or sedimentary sequences. The iron-formations may vary between carbonate-oxide iron-formation and arsenical sulphide-silicate iron-formation.

 

TECTONIC SETTING: In “greenstone belts” believed to be ancient volcanic arcs; and in adjacent submarine troughs.

 

DEPOSITIONAL ENVIRONMENT/GEOLOGICAL SETTING: Sedimentary and submarine volcanic sequences in a range of mutually overlapping settings ranging from turbiditic clastic sedimentary environments to distal mafic (and komatiitic) environments with associated felsic tuffaceous and intrusive porphyries.

 

AGE OF MINERALIZATION: Archean to Proterozoic.

 

HOST/ ASSOCIATED ROCK TYPES: Contained mainly within various facies of Algoma-type iron-formation and cherts, although veins may extend into other units. Associated with variolitic, tholeiitic and komatiitic volcanic and clastic (commonly turbiditic) rocks, rarely felsic volcanic and intrusive rocks. Metamorphic rank ranges from lowest greenschist to upper amphibolite facies. Silicate-facies iron-formations are associated in some cases but are generally not gold-bearing.

 

DEPOSIT FORM: In and near crosscutting structures, such as quartz veins, or stratiform zones within chemical sedimentary rocks. Host strata have generally been folded and deformed to varying degree, consequently the deposits may have developed in axial plane cleavage area or be thickened and remobilized in fold hinges.

 

TEXTURE/STRUCTURE: Highly variable: gold mineralization may be finely disseminated in sulphide minerals in the stratiform examples or occur as the native mineral or in sulphides in crosscutting quartz veins. Sulphidization features such as pyrite overgrowths on magnetite are present in some deposits.

 

ORE MINERALOGY (Principal and subordinate): Native Au, pyrite, arsenopyrite, magnetite, pyrrhotite, chalcopyrite, sphalerite, galena, stibnite, rarely gold tellurides.

 

GANGUE MINERALOGY (Principal and subordinate): Vein quartz, chert, carbonates (calcite, dolomite or ankerite), graphite, grunerite, stilpnomelane, tourmaline, feldspar (albite).

 

ALTERATION: In deposits at low metamorphic rank, carbonatization (generally ankeritic or ferroan dolomite) is generally prominent. Sulphidization (pyritization, arsenopyritization and pyrrhotitization) is common in wallrocks adjacent to crosscutting quartz veins.

 

WEATHERING: Highly variable: sulphide-rich, carbonate-poor deposits will produce significant gossans.

 

ORE CONTROLS: Mineralization is within, or near, favourable iron-formations. Most deposits occur adjacent to prominent regional structural and stratigraphic “breaks” and mineralization is often related to local structures. Contacts between ultramafic (commonly komatiitic) rocks and tholeiitic basalts or sedimentary rocks are important. All known deposits occur in Precambrian sequences, however, there are some potentially favourable chemical sediment horizons in Paleozoic rocks. Pinch outs and facies changes within geologically favourable units are important loci for ore deposition.

 

GENETIC MODELS: One model proposed for iron formation-hosted Au is that the mineralization may form due to deformation focusing metamorphogenic or magmatic hydrothermal fluids, from depth, into a chemically and structurally (brittle- ductile transition zone) favourable depositional environment, late in the orogenic cycle. This theory is consistent with both the crosscutting relationships and radiometric dates for the gold mineralization. Another model emphasizes a syngenetic origin for the widespread anomalous gold values, similarity of the geological environments to currently active submarine exhalative systems, and the association with chemical sedimentary strata. Replacement features could be explained as normal diagenetic features and contact areas between sulphide-rich ore and carbonate wallrock as facies boundaries.

 

ASSOCIATED DEPOSIT TYPES: Au-quartz veins (I01), turbidite-hosted Au-quartz veins (I03), Algoma-type iron-formations (G01).

 

COMMENTS: This type of deposit has not been documented in British Columbia. The closest analogy is the 900 zone on the Debbie property (092F 331) which contains gold in magnetite-jasper-sulphide-bearing bedded chert, in quartz veins and in stockworks cutting ankeritic aphyric pillow basalt. Some workers consider auriferous stratiform pyrite bodies, such as Bousquet, Doyon, and Agnico Eagle in the Canadian Shield, to be closely related to iron formation-hosted Au.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Si, Fe, S, As, B, Mg, Ca, Au and Ag generally show strong enrichment in the deposits, while Cu, Zn, Cd, Pb and Mn generally show moderate enrichment.

 

GEOPHYSICAL SIGNATURE: Airborne and ground electromagnetic and magnetic surveys and induced polarization surveys can be very useful to detect and map the high sulphide and magnetite content of many of the deposits.

 

OTHER EXPLORATION GUIDES: Standard prospecting techniques to trace mineralization directly or in float trains in glacial till, talus or other debris derived from the gold mineralization remains the most effective prospecting tool. Areas with gold placers are potential targets. Exploration programs should focus on the primary depositional environment for stratiform deposits.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: The more significant deposits fall in the ranges from 6 to 17 g/t Au and 1 to 5 Mt (Thorpe and Franklin, 1984). At the adjacent properties of Morro Velho and Raposos in Brazil, approximately 10 million ounces of gold have been produced at a grade of between 15 and 16 g/t since 1834. In Ontario, the Detour Lake mine contains a resource of 48 t Au and the Madsen Red Lake deposit produced 75 t, the Pickle Crow Deposits 45 tonnes and the Central Patricia 19 tonnes. At the Lupin mine 6.66 Mt of ore grading 10.63 g/t Au were produced between 1982 and the end of 1993 with remaining reserves of 5.1 Mt averaging 9.11 g/t.

 

ECONOMIC LIMITATIONS: The narrow veins in some deposits require selective mining techniques which are no longer highly profitable. On the other hand, deposits, such as Lupin, are sufficiently large to be mined very profitably utilizing modern mechanized equipment.

 

IMPORTANCE: Although attention in recent years has been focused on the large epithermal volcanic-hosted gold deposits of the circum-Pacific Belt and on Carlin-type deposits, iron-formation hosted gold deposits, such as Lupin, rank as world class and remain attractive exploration targets. For example, the Homestake mine has produced approximately 300 t of gold since starting production in 1876.

 

REFERENCES

 

ACKNOWLEDGMENTS: Chris Ash, Dani Alldrick, Andre Panteleyev and Howard Poulsen reviewed the profile and provided constructive comments.

 

Berger, B.R. (1986): Descriptive Model of Homestake Au; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors,U.S. Geological Survey, Bulletin 1693, pages 245- 247.

Boyle, R.W. (1979): The Geochemistry of Gold and its Deposits; Geological Survey of Canada, Bulletin 280, 584 pages.

Fyon, J.A., Breaks, F.W., Heather, K.B., Jackson, S.L., Muir, T.L., Stott, G.M. and Thurston, P.C. (1992): Metallogeny of Metallic Mineral Deposits in the Superior Province of Ontario; in Geology of Ontario, Ontario Geological Survey, Special Volume 4, Part 2, pages 1091-1174.

Fripp, R.E.P. (1976): Stratabound Gold Deposits in Archean Banded Iron-Formation, Rhodesia; Economic Geology, Volume 71, pages 58-75.

Kerswill, J.A. (1993): Models for Iron-formation-hosted Gold Deposits; in Mineral Deposit Modeling, Kirkham, R.V., Sinclair, W.D., Thorpe, R.I. and Duke, J.M., Editors, Geological Association of Canada, Special Paper 40, pages 171-200.

Padgham, W.A. and Brophy, J.A. (1986): Gold Deposits of the Northwest Territories; in Gold in the Western Shield, Canadian Institute of Mining and Metallurgy, Special Volume 38, pages 2-25.

Rye, D.M. and Rye, R.O. (1974): Homestake Gold Mine, South Dakota: I. Stable Isotope Studies; Economic Geology, Volume 69, pages 293-317.

Siddaiah, N.S., Hanson, G.N. and Rajamani, V. (1994): Rare Earth Element Evidence for Syngenetic Origin of an Archean Stratiform Gold Sulfide Deposit, Kolar Schist Belt, South India; Economic Geology, Volume 89, pages 1552-1566.

Thorpe, R.I and Franklin, J.M. (1984): Chemical-sediment-hosted Gold; in Canadian Mineral Deposit Types: A Geological Synopsis, Eckstrand, O.R., Editor, Economic Geology Report 36, Geological Survey of Canada, page 29.

Vielreicher, R.M., Groves, D.I., Ridley, J.R. and McNaughton, N.J. (1994): A Replacement Origin for the BIF-hosted Gold Deposit at Mt. Morgans, Yilgarn Block, W.A; Ore Geology Reviews, Volume 9, pages 325-347.

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POLYMETALLIC VEINS Ag-Pb-Zn+/-Au


I05
by David V. Lefebure and B. Neil Church
British Columbia Geological Survey

 

Lefebure, D.V. and Church, B.N. (1996): Polymetallic Veins Ag-Pb-Zn+/-Au, 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 67-70.

 

IDENTIFICATION

 

SYNONYMS: Clastic metasediment-hosted silver-lead-zinc veins, silver/base metal epithermal deposits.

 

COMMODITIES (BYPRODUCTS): Ag, Pb, Zn (Cu, Au, Mn).

 

EXAMPLES (British Columbia (MINFILE # - Canada/International):

 

Metasediment host: Silvana (082FNW050) and Lucky Jim (082KSW023), Slocan-New Denver-Ainsworth district, St. Eugene (082GSW025), Silver Cup (082KNW027), Trout Lake camp; Hector-Calumet and Elsa, Mayo district (Yukon, Canada), Coeur d’Alene district (Idaho, USA), Harz Mountains and Freiberg district (Germany), Pr¡bram district (Czechoslavakia).
Igneous host: Wellington (082ESE072) and Highland Lass - Bell (082ESW030, 133), Beaverdell camp; Silver Queen (093L 002), Duthie (093L 088), Cronin (093L 127), Porter-Idaho (103P 089), Indian (104B 031); Sunnyside and Idorado, Silverton district and Creede (Colorado, USA), Pachuca (Mexico).

 

 

 

 

 

 

 

 

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Sulphide-rich veins containing sphalerite, galena, silver and sulphosalt minerals in a carbonate and quartz gangue. These veins can be subdivided into those hosted by metasediments and another group hosted by volcanic or intrusive rocks. The latter type of mineralization is typically contemporaneous with emplacement of a nearby intrusion.

 

TECTONIC SETTINGS: These veins occur in virtually all tectonic settings except oceanic, including continental margins, island arcs, continental volcanics and cratonic sequences.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING:

Metasediment host: Veins are emplaced along faults and fractures in sedimentary basins dominated by clastic rocks that have been deformed, metamorphosed and intruded by igneous rocks. Veins postdate deformation and metamorphism.
Igneous host: Veins typically occur in country rock marginal to an intrusive stock. Typically veins crosscut volcanic sequences and follow volcano- tectonic structures, such as caldera ring-faults or radial faults. In some cases the veins cut older intrusions.

 

 

 

 

 

 

 

 

AGE OF MINERALIZATION: Proterozic or younger; mainly Cretaceous to Tertiary in British Columbia.

 

HOST/ASSOCIATED ROCK TYPES: These veins can occur in virtually any host. Most commonly the veins are hosted by thick sequences of clastic metasediments or by intermediate to felsic volcanic rocks. In many districts there are felsic to intermediate intrusive bodies and mafic igneous rocks are less common. Many veins are associated with dikes following the same structures.

 

DEPOSIT FORM: Typically steeply dipping, narrow, tabular or splayed veins. Commonly occur as sets of parallel and offset veins. Individual veins vary from centimetres up to more than 3 m wide and can be followed from a few hundred to more than 1000 m in length and depth. Veins may widen to tens of metres in stockwork zones.

 

TEXTURE/STRUCTURE: Compound veins with a complex paragenetic sequence are common. A wide variety of textures, including cockade texture, colloform banding and crustifications and locally druzy. Veins may grade into broad zones of stockwork or breccia. Coarse-grained sulphides as patches and pods, and fine- grained disseminations are confined to veins.

 

ORE MINERALOGY (Principal and subordinate): Galena, sphalerite, tetrahedrite- tennantite, other sulphosalts including pyrargyrite, stephanite, bournonite and acanthite, native silver, chalcopyrite, pyrite, arsenopyrite, stibnite. Silver minerals often occur as inclusions in galena. Native gold and electrum in some deposits. Rhythmic compostional banding sometimes present in sphalerite. Some veins contain more chalcopyrite and gold at depth and Au grades are normally low for the amount of sulphides present.

 

GANGUE MINERALOGY (Principal and subordinate):

Metasediment host: Carbonates (most commonly siderite with minor dolomite, ankerite and calcite), quartz, barite, fluorite, magnetite, bitumen.
Igneous host: Quartz, carbonate (rhodochrosite, siderite, calcite, dolomite), sometimes specular hematite, hematite, barite, fluorite. Carbonate species may correlate with distance from source of hydrothermal fluids with proximal calcium and magnesium-rich carbonates and distal iron and manganese-rich species.

 

 

 

 

 

 

 

 

ALTERATION MINERALOGY: Macroscopic wall rock alteration is typically limited in extent (measured in metres or less). The metasediments typically display sericitization, silicification and pyritization. Thin veining of siderite or ankerite may be locally developed adjacent to veins. In the Coeur d’Alene camp a broader zone of bleached sediments is common. In volcanic and intrusive hostrocks the alteration is argillic, sericitic or chloritic and may be quite extensive.

 

WEATHERING: Black manganese oxide stains, sometimes with whitish melanterite, are common weathering products of some veins. The supergene weathering zone associated with these veins has produced major quantities of manganese. Galena and sphalerite weather to secondary Pb and Zn carbonates and Pb sulphate. In some deposits supergene enrichment has produced native and horn silver.

 

ORE CONTROLS: Regional faults, fault sets and fractures are an important ore control; however, veins are typically associated with second order structures. In igneous rocks the faults may relate to volcanic centers. Significant deposits restricted to competent lithologies. Dikes are often emplaced along the same faults and in some camps are believed to be roughly contemporaneous with mineralization. Some polymetallic veins are found surrounding intrusions with porphyry deposits or prospects.

 

GENETIC MODELS: Historically these veins have been considered to result from differentiation of magma with the development of a volatile fluid phase that escaped along faults to form the veins. More recently researchers have preferred to invoke mixing of cooler, upper crustal hydrothermal or meteoric waters with rising fluids that could be metamorphic, groundwater heated by an intrusion or expelled directly from a differentiating magma. Any development of genetic models is complicated by the presence of other types of veins in many districts. For example, the Freiberg district has veins carrying F-Ba, Ni-As- Co-Bi-Ag and U.

 

COMMENTS: Ag-tetrahedrite veins, such as the Sunshine and Galena mines in Idaho, contain very little sphalerite or galena. These may belong to this class of deposits or possibly the five-element veins. The styles of alteration, mineralogy, grades and different geometries can usually be used to distinguish the polymetallic veins from stringer zones found below syngenetic massive sulphide deposits.

 

ASSOCIATED DEPOSIT TYPES:

Metasediment host: Polymetallic mantos (M01).
Igneous host: May occur peripheral to virtually all types of porphyry mineralization (L01, L03, L04, L05, L06, L07, L08) and some skarns (K02, K03).

 

 

 

 

 

 

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Elevated values of Zn, Pb, Ag, Mn, Cu, Ba and As. Veins may be within arsenic, copper, silver, mercury aureoles caused by the primary dispersion of elements into wallrocks or broader alteration zones associated with porphyry deposit or prospects.

 

GEOPHYSICAL SIGNATURE: May have elongate zones of low magnetic response and/or electromagnetic, self potential or induced polarization anomalies related to ore zones.

 

OTHER EXPLORATION GUIDES: Strong structural control on veins and common occurrence of deposits in clusters can be used to locate new veins.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE : Individual vein systems range from several hundred to several million tonnes grading from 5 to 1500 g/t Ag, 0.5 to 20% Pb and 0.5 to 8% Zn. Average grades are strongly influenced by the minimum size of deposit included in the population. For B.C. deposits larger than 20 000 t the average size is 161 000 t with grades of 304 g/t Ag, 3.47 % Pb and 2.66 % Zn. Copper and gold are reported in less than half the occurrences, with average grades of 0.09 % Cu and 4 g/t Au.

 

ECONOMIC LIMITATIONS: These veins usually support small to medium-size underground mines. The mineralization may contain arsenic which typically reduces smelting credits.

 

IMPORTANCE: The most common deposit type in British Columbia with over 2 000 occurrences; these veins were a significant source of Ag, Pb and Zn until the 1960s. They have declined in importance as industry focused more on syngenetic massive sulphide deposits. Larger polymetallic vein deposits are still attractive because of their high grades and relatively easy benefication. They are potential sources of cadmium and germanium.

 

REFERENCES

 

ACKNOWLEDGEMENTS: Georges Beaudoin and Don Sangster are thanked for their suggestions to improve the profile.

 

Barton, P., Bethke, P., Wetlaufer, P.H., Foley, N., Hayba, D. and Goss, J. (1982): Silver/Base Metal Epithermal Deposits; in Characteristics of Mineral Deposit Occurrences, Erickson, R.L., Compiler, U.S. Geological Survey, pages 127- 130.

Beaudoin, G. and Sangster, D.F. (1992): A Descriptive Model for Silver-Lead-Zinc Veins in Clastic Metasedimentary Terranes; Economic Geology, Volume 87, pages 1005-1021.

Beaudoin, G. and Sangster, D.F. (in press): Clastic Metasediment-hosted Vein Silver- Lead-Zinc; 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 393-398.

Boyle, R.W. (1965): Geology, Geochemistry and Origin of the Lead-Zinc-Silver Deposits of the Keno Hill - Galena Hill Area, Yukon Territory; Geological Survey of Canada, Bulletin 111, 302 pages.

Boyle, R.W. (1968): The Geochemistry of Silver and its Deposits; Geological Survey of Canada, Bulletin 160, 264 pages.

Corbett, G.J. and Leach, T.M. (1995): S.W. Pacific Rim Au/Cu Systems: Structure, Alteration and Mineralization; Mineral Deposit Research Unit, The University of British Columbia, Short Course No. 17 notes, 150 pages.

Cox, D.P. (1986): Descriptive Model of Polymetallic Veins; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors,U.S. Geological Survey, Bulletin 1693, pages 125-129.

Godwin, C.I., Watson, P.H. and Shen, K. (1986): Genesis of the Lass Vein System, Beaverdell Silver Camp, South-central British Columbia; Canadian Journal of Earth Sciences, Volume 23, pages 1615-1626.

Fyles, J.T. (1967): Geology of the Ainsworth-Kaslo Area, British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Bulletin 53, 125 pages.

Little, H.W. (1960): Nelson Map Area, West Half, British Columbia; Geological Survey of Canada, Memoir 308, pages 305.

Steven, T.A. and Eaton, G.P. (1975): Environment of Ore Deposition in the Creede Mining District, San Juan Mountains, Colorado: I. Geologic, Hydrologic, and Geophysical Setting; Economic Geology, Volume 70, pages 1023-1037.

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Cu+/-Ag QUARTZ VEINS


I06
by David V. Lefebure
British Columbia Geological Survey

 

Lefebure, D.V. (1996): Cu+/- Ag Quartz Veins, 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 71-74.

 

IDENTIFICATION

 

SYNONYMS: Churchill-type vein copper, vein copper

 

COMMODITY (BYPRODUCTS): Cu (Ag, rarely Au).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Davis-Keays (094K 012, 050), Churchill Copper (Magnum, 094K 003), Bull River (082GNW002), Copper Road (092K 060), Copper Star (092HNE036), Copper Standard (092HNE079), Rainbow (093L 044); Bruce Mines and Crownbridge (Ontario, Canada), Blue Wing and Seaboard (North Carolina, USA), Matahambre (Cuba), Inyati (Zimbabwe), Copper Hills (Western Australia), Tocopilla area (Chile), Burgas district (Bulgaria), Butte (Montana, USA), Rosario (Chile).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Quartz-carbonate veins containing patches and disseminations of chalcopyrite with bornite, tetrahedrite, covellite and pyrite. These veins typically crosscut clastic sedimentary or volcanic sequences, however, there are also Cu quartz veins related to porphyry Cu systems and associated with felsic to intermediate intrusions.

 

TECTONIC SETTINGS: A diversity of tectonic settings reflecting the wide variety of hostrocks including extensional sedimentary basins (often Proterozoic) and volcanic sequences associated with rifting or subduction-related continental and island arc settings.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Veins emplaced along faults; they commonly postdate major deformation and metamorphism. The veins related to felsic intrusions form adjacent to, and are contemporaneous with, mesozonal stocks.

 

AGE OF MINERALIZATION: Any age; can be much younger than hostrocks.

 

HOST/ASSOCIATED ROCK TYPES: CuñAg quartz veins occur in virtually any rocks although the most common hosts are clastic metasediments and mafic volcanic sequences. Mafic dikes and sills are often spatially associated with metasediment-hosted veins. These veins are also found within and adjacent to felsic to intermediate intrusions.

 

DEPOSIT FORM: The deposits form simple to complicated veins and vein sets which typically follow high-angle faults which may be associated with major fold sets. Single veins vary in thickness from centimetres up to tens of metres. Major vein systems extend hundreds of metres along strike and down dip. In some exceptional cases the veins extend more than a kilometre along the maximum dimension.

 

TEXTURE/STRUCTURE: Sulphides are irregularly distributed as patches and disseminations. Vein breccias and stockworks are associated with some deposits.

 

ORE MINERALOGY (Principal and subordinate):

Metasediment and volcanic-hosted: Chalcopyrite, pyrite, chalcocite; bornite, tetrahedrite, argentite, pyrrhotite, covellite, galena.
Intrusion-related: Chalcopyrite, bornite, chalcocite, pyrite, pyrrhotite; enargite, tetrahedrite-tennantite, bismuthinite, molybdenite, sphalerite, native gold and electrum.

 

 

 

 

 

 

 

GANGUE MINERALOGY (Principal and subordinate): Quartz and carbonate (calcite, dolomite, ankerite or siderite); hematite, specularite, barite.

 

ALTERATION MINERALOGY: Wallrocks are typically altered for distances of centimetres to tens of metres outwards from the veins.

Metasediment and volcanic-hosted: The metasediments display carbonatization and silicification. At the Churchill and Davis-Keays deposits, decalcification of limy rocks and zones of disseminated pyrite in roughly stratabound zones are reported. The volcanic hostrocks exhibit abundant epidote with associated calcite and chlorite.
Intrusion-related: Sericitization, in places with clay alteration and chloritization.

 

 

 

 

 

 

 

 

 

WEATHERING: Malachite or azurite staining; silicified linear “ridges”.

 

ORE CONTROLS: Veins and associated dikes follow faults. Ore shoots commonly localized along dilational bends within veins. Sulphides may occur preferentially in parts of veins which crosscut carbonate or other favourable lithologies. Intersections of veins are an important locus for ore.

 

GENETIC MODEL: The metasediment and volcanic-hosted veins are associated with major faults related to crustal extension which control the ascent of hydrothermal fluids to suitable sites for deposition of metals. The fluids are believed to be derived from mafic intrusions which are also the source for compositionally similar dikes and sills associated with the veins. Intrusion-related veins, like Butte in Montana and Rosario in Chile, are clearly associated with high- level felsic to intermediate intrusions hosting porphyry Cu deposits or prospects.

 

ASSOCIATED DEPOSIT TYPES:

Metasediment and volcanic-hosted: Possibly related to sediment-hosted Cu (E04) and basaltic Cu (D03).
Intrusion-related: High sulphidation (H04), copper skarns (K01), porphyries (L01?, L03, L04) and polymetallic veins (I05).

 

 

 

 

 

 

 

 

COMMENTS: Cu±Ag quartz veins are common in copper metallogenetic provinces; they often are more important as indicators of the presence of other types of copper deposits.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: High Cu and Ag in regional silt samples. The Churchill-type deposits appear to have very limited wallrock dispersion of pathfinder elements; however, alteration halos of silica and carbonate addition or depletion might prove useful. Porpyhyry-related veins exhibit many of the geochemical signatures of porphyry copper systems.

 

GEOPHYSICAL SIGNATURE: Large veins with conductive massive sulphides may show up as electromagnetic conductors, particularly on ground surveys. Associated structures may be defined by ground magnetic, very low frequency or electromagnetic surveys. Airborne surveys may identify prospective major structures.

 

OTHER EXPLORATION GUIDES: Commonly camp-scale or regional structural controls define a dominant orientation for veins.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Typically range from 10 000 to 100 0000 t with grades of 1 to 4% Cu, nil to 300 g/t Ag. The Churchill deposit has reserves of 90 000 t of 3 % Cu and produced 501 019 t grading 3% Cu and the Davis-Keays deposit has reserves of 1 119 089 t grading 3.43 % Cu. The Big Bull deposit has reserves of 732 000 t grading 1.94% Cu. The intrusion-related veins range up to millions of tonnes with grades of up to 6% Cu. The Butte veins in Montana have produced several hundred million tonnes of ore with much of this production from open-pit operations.

 

ECONOMIC LIMITATIONS: Currently only the large and/or high-grade veins (usually associated with porphyry deposits) are economically attractive.

 

IMPORTANCE: From pre-historic times until the early 1900s, high-grade copper veins were an important source of this metal. With hand sorting and labour-intensive mining they represented very attractive deposits.

 

REFERENCES

 

ACKNOWLEDGEMENTS: This deposit profile represents the results of a literature review. It benefited from comments by David Sinclair and Vic Preto.

 

Benes, K. and Hanus, V. (1967): Structural Control and History of Origin of Hydrothermal Metallogeny in Western Cuba; Mineralium Deposita, Volume 2, pages 318-333.

Carr, J.M. (1971): Geology of the Churchill Copper Deposit; The Canadian Institute of Mining and Metallurgy, Bulletin, Volume 64, pages 50-54.

Hammer, D.F. and Peterson, D.W. (1968): Geology of the Magma Mine Arizona; in Ore Deposits of the United States 1933-1967, Ridge, J.D., Editor, American Institute of Mining Engineers, New York, pages 1282-1310.

Kirkham, R.D. (1984): Vein Copper; in Canadian Mineral Deposit Types: A Geological Synopsis, Eckstrand, O.R., Editor, Geological Survey of Canada, Economic Geology Report 36, page 65.

Kirkham, R.D. and Sinclair, W.D. (in press): Vein Copper; 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 383-392.

Kish, S.A. (1989): Post-Acadian Metasomatic Origin for Copper-bearing Vein Deposits of the Virgilina District, North Carolina and Virginia; Economic Geology, Volume 84, pages 1903-1920.

Laznicka, P. (1986): Empirical Metallogeny, Depositional Environments, Lithologic Associations and Metallic Ores, Volume 1, Phanerozoic Environments, Associations and Deposits; Elsevier, New York, 1758 pages.

Nockleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, D., Robinson, M.S., Smith, T.E. and Yeend, W. (1987): Significant Metalliferous Lode Deposits and Placer Districts of Alaska, U.S. Geological Survey, Bulletin 1786, 104 pages.

Pearson, W.N. (1979): Copper Metallogeny, North Shore of Lake Huron, Ontario; in Current Research, Part A, Geological Survey of Canada, Paper 79-1A, pages 289-304.

Pearson, W.N., Bretzlaff, R.E. and Carriere, J.J. (1985): Copper Deposits and Occurrences in the North Shore Region of Lake Huron, Ontario; Geological Survey of Canada, Paper 83-28, 34 pages.

Preto, V.A. (1972): Lode Copper Deposits of the Racing River - Gataga River Area; in Geology, Exploration and Mining in British Columbia 1971, B. C. Ministry of Energy, Mines and Petroleum Resources, pages 75-107.

Roberts, A.E. (1973): The Geological Setting of Copper Orebodies at Inyati Mine, Headlans District, Rhodesia; Geological Society of South Africa, Special Publication 3, , pages 189-196.

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SILICA-CARBONATE Hg

I08
by Chris Ash
British Columbia Geological Survey

 

Ash, Chris (1996): Silica-carbonate Hg, 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 75-76.

 

IDENTIFICATION

 

SYNONYMS: Serpentinite-type, listwanite-type.

 

COMMODITIES (BYPRODUCTS): Hg (Sb, Ag, Au).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Pinchi (093K 049), Bralorne Takla (093N 008), Eagle Mercury (092JNE062), Silverquick (092O 017), Manitou (092O 023); New Almaden, New Idria (California, USA).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Cinnabar occurs associated with quartz and carbonate alteration in zones of intense brittle fracturing at relatively shallow levels along major fault zones. Commonly occur in areas of active geothermal systems.

 

TECTONIC SETTING: Within orogenic belts.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: At shallow levels within high-angle, regional-scale, deep crustal faults marked by the presence of ophiolitic ultramafic rocks. Typically at brittle faulted contacts between competent lithologies, e.g. carbonate-altered ultramafics, limestone, etc. Locally associated with recent volcanism and hotspring activity. Mercury deposits in B.C. are concentrated along several north to northwest-trending, high-angle transcurrent fault zones which border oceanic terranes. These include the Pinchi, Yalakom and Germansen faults.

 

AGE OF MINERALIZATION: Eocene to Recent?

 

HOST/ASSOCIATED ROCK TYPES: Serpentinite, limestone, siltstone, graywacke, conglomerate, mafic volcanic rocks.

 

DEPOSIT FORM: Deposits are typically highly irregular within major fault zones.

 

TEXTURE/STRUCTURE: Thin discontinuous stringers or fracture and cavity coatings in areas of shattering and brecciation along major faults.

 

ORE MINERALOGY (Principal and subordinate): Cinnabar, native mercury (quicksilver), metacinnabar, livingstonite (HgSb4S9).

 

GANGUE MINERALOGY: Pyrite, marcasite, quartz, carbonate, limestone, serpentinite.

 

ALTERATION MINERALOGY: "Silica-carbonate rock" or "listwanite/listvenite", magnesite, ankerite, dolomite, quartz, chalcedony, kaolinite, sericite (fuchsite/mariposite).

 

WEATHERING: Mineralized areas display distinctive limonite stain due to the presence of iron carbonates.

 

ORE CONTROLS: High-angle fault zones marginal to accreted oceanic terranes. In general, grade of ore increases with fracture density in the hostrock.

 

GENETIC MODELS: Deposits form where relatively low temperature (between 100o and 200oC) CO2-H2O aqueous fluids (< 2 wt. % chlorine), charged with Hg migrate upward along permeable fault zones and precipitate cinnabar in fractured hostrocks at shallow levels due to cooling and mixing with meteoric water. At this stage a vapour phase evolves which emanates from hotsprings at surface.

 

ASSOCIATED DEPOSIT TYPES: Sb veins.

 

COMMENTS: Due to the liquid state of this metal, mercury is generally measured in “flasks” and quoted in dollar value per flask. Flasks are standard steel containers that hold 76 lb (about 2.5 L) of the liquid metal.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Hg, Sb (Cu, Zn).

 

GEOPHYSICAL SIGNATURE: Not generally applicable.

 

OTHER EXPLORATION GUIDES: Soil, stream sediment and geobotanical sampling for Hg has proven successful. The spatial association of hotsprings with major fault zones associated with ophiolitic ultramafic rocks.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Deposits of this type are typically less than 1 Mt, but may be up to several million tonnes with mercury grades averaging 0.5% and ranging from 0.2 to 0.8%.

 

ECONOMIC LIMITATIONS: The low grade of these deposits relative to other mercury deposit types, extreme fluctuations in the price of the metal, and inherent pollution problems are all factors in the economics of this deposit type.

 

IMPORTANCE: Although historically significant as a source of mercury, these deposits are not currently mined due to their low grades and small size relative to the much larger and richer Almaden-type mercury deposits. The only significant past-producing mines in B.C. include the Pinchi and Bralorne Takla. Both deposits are along the Pinchi fault.

 

REFERENCES

 

Armstrong, J.E. (1966): Tectonics and Mercury Deposits in British Columbia; in Tectonic History and Mineral Deposits of the Western Cordillera, Canadian Institute of Mining and Metallurgy, Special Volume No. 8, pages 341-348.

Bailey, E.H., Clark, A.L. and Smith, R.M. (1973): Mercury; in United States Mineral Resources, Brobst, D.A. and Pratt, W.P., Editors, U.S. Geological Survey, Professional Paper 820, pages 401-414.

Barnes, I., O’Neill, J.R., Rapp, J.B. and White, D.E. (1973): Silica-Carbonate Alteration of Serpentinite: Wall Rock Alteration in Mercury Deposits of the California Coast Ranges; Economic Geology, Volume 68, pages 388-398.

Henderson, F.B. (1969): Hydrothermal Alteration and Ore Deposition in Serpentinite-type Mercury Deposits; Economic Geology, Volume 64, 489-499.

Rytuba, J.J. (1986): Descriptive Model of Silica-Carbonate Hg; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, page 181.

Rytuba, J.J. and Cargill, S.M. (1986): Grade and Tonnage Model of Silica-Carbonate Hg; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, pages 181-182.

Stevenson, S.J. (1940): Mercury Deposits of British Columbia; B.C. Department of Mines, Bulletin Number 5, 93 pages.

Studemeister P.A. (1984): Mercury Deposits of Western California: An Overview; Mineralium Deposita, Volume 19, pages 202-207.

Varekamp J.C. and Buseck P.R. (1984): The Speciation of Mercury in Hydrothermal Systems, with Applications to Ore Deposition; Geochimica and Cosmochimica Acta, Volume 48, pages 177-185.

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STIBNITE VEINS and DISSEMINATIONS


I09
by Andre Panteleyev
British Columbia Geological Survey

 

Panteleyev, Andre (1996): Stibnite Veins and Disseminations, 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 77-80.

 

IDENTIFICATION

 

SYNONYMS: Quartz-stibnite, simple antimony, syntectonic stibnite, mesothermal Sb-Au.

 

COMMODITIES (BYPRODUCTS): Sb (Au).

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): a) Veins - Minto (092JNE075) and Congress (092JNE029), Bridge River area; Snowbird (093K 036); Becker-Cochran (Yukon, Canada), Lake George (New Brunswick, Canada), Beaver Brook (Newfoundland, Canada), Murchison Range deposits (South Africa), Caracota and numerous other deposits in the Cordillera Occidental (Bolivia). b) Disseminated - Caracota and Espiritu Santo (Bolivia), many deposits (Turkey).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Stibnite veins, pods, disseminations and stibnite-bearing quartz and quartz-carbonate veins occur in, or adjacent to, shears, fault zones and brecciated rocks in sedimentary or metasedimentary sequences.

 

TECTONIC SETTING: Any orogenic area, particularly where large-scale fault structures are present.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Fault and shear zones, notably in fault splays and fault-related breccias in which shallow to intermediate-depth hydrothermal systems have been operative.

AGE OF MINERALIZATION: Deposits range from Paleozoic to Tertiary age.

 

HOST/ASSOCIATED ROCK TYPES: Any faulted lithologies with a wide variety of rock types; sedimentary and metasedimentary rocks are commonly present. British Columbia deposits tend to be near major fault zones with attendant serpentinized mafic and ultramafic rocks.

 

DEPOSIT FORM: Stibnite occurs in veins; also as fine to coarse grains in sheared or brecciated rocks. Some stibnite is disseminated in carbonate-altered wallrocks surrounding structures and may form within pressure shadows at crests of folds. Massive stibnite-pyrite replacements which may form pods or lenses up to tens of metres long, are relatively uncommon, but are sources of rich ore.

 

TEXTURE/STRUCTURE: Veins have fine to coarse-grained, commonly euhedral bladed crystals of stibnite, quartz and carbonate in masses of stibnite. Quartz and quartz-carbonate gangue minerals range from fine to coarse grained, commonly with white ‘bull quartz” present.

 

ORE MINERALOGY (Principal and subordinate): Stibnite, pyrite, arsenopyrite; sphalerite, galena, tetrahedrite, marcasite, chalcopyrite, jamesonite, berthierite, gold, cinnabar, scheelite, argentite and sulphosalt minerals. Other than stibnite, the overall sulphide content of the veins is low.

 

GANGUE MINERALOGY (Principal and subordinate): Quartz, calcite, dolomite; chalcedony, siderite, rare barite and fluorite.

 

ALTERATION MINERALOGY: Quartz-carbonate envelopes on veins; some silicification, sericite, and intermediate argillic alteration. Chlorite, serpentinization and ‘listwanite’ (quartz-carbonate-talc-chromian mica-sulphide minerals) green- coloured alteration may be present when mafic and untramafic rocks are involved.

 

WEATHERING: Stibnite weathers to various oxides of yellowish (kermsite) or whitish (cerrantite or stibiconite) colour.

 

ORE CONTROLS: Fissure, shear zones and breccia associated with faults. Some open-space filling in porous rocks and structurally induced openings (joints, saddle reefs, ladder veins). Minor replacement in limestones.

 

GENETIC MODEL: The origin is not well documented. Deposits are spatially closely associated with, and in many ways resemble, low-sulphide gold-quartz (mesothermal) veins. Their (mutual) origin is thought to be from dilute, CO2 rich fluids generated by metamorphic dehydration. Structural channelways focus the hydrothermal fluids during regional deformation. Some deposits are associated with felsic intrusive bodies, for example a Tertiary rhyolite plug at Becker-Cochran deposit, Yukon, and with porphyry W-Mo mineralization in granitic rocks at the Lake George Sb deposit, New Brunswick.

 

ASSOCIATED DEPOSIT TYPES: Quartz-carbonate gold (low-sulphide gold-quartz vein or I01), polymetallic vein Ag-Pb-Zn (I05), epithermal Au-Ag: low sulphidation (H05), hotspring Au-Ag (H03), Sn-W vein (??), W-Mo porphyry (L07); silica-carbonate Hg (I08), placer gold (C01, C02); possibly Carlin-type sediment-hosted Ag-Ag (E03).

 

COMMENTS: Occurrences of typical stibnite veins in the Bridge River gold camp in British Columbia were thought to be part of a regional deposit zoning pattern. The deposits are now known to be younger than the gold deposits by about 15-20 Ma. Farther north, the Snowbird deposit near Stuart Lake, has been shown to be Middle Jurassic in age by radiometric dating and is interpreted to be related to large-scale crustal structures. This deformation possibly involves the Pinchi fault system in which the largest known mercury deposits in the province are found.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Sb, As, Au, Ag, Pb, Zn; locally W or Hg.

 

GEOPHYSICAL SIGNATURE: VLF surveys may detect faults.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Veins typically have high grade but small ore shoots; the disseminated deposits are also relatively small. Grade-tonnage data from 81 “typical” vein deposits (predominately, hand-sorted ore from USA mines) is 180 t with 35 % Sb; 10 % of the deposits contained > 1 g/t Au and > 16 g/t Ag. The disseminated deposits average 88 000 t with an average grade of 3.6 % Sb.

 

ECONOMIC LIMITATIONS: Antimony is a low-priced metal so only high-grade deposits are mined. Deposits (veins and disseminations) containing gold offer the best potential.

 

IMPORTANCE: Bolivia, Turkey and China dominate the antimony market; Cordilleran production will likely be only as a byproduct from precious metal bearing deposits.

 

REFERENCES

 

Bliss, J.D. and Orris, J. (1986): Descriptive Model of Simple Sb Deposits (and Disseminated Sb Deposits); in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, pages 183-188.

Lehrberger, G. (1988): Gold-Antimonite Deposits in Marine Sediments of the Eastern Cordillera of the Bolivian Andes; in Bicentennial Gold `88, Geological Society of Australia, Extended Abstracts: Poster Session, Volume 23, pages 319-321.

Madu, B.E., Nesbitt, B.E. and Muehlenabachs, K. (1990): A Mesothermal Gold-Stibnite- Quartz Vein Occurrence in the Canadian Cordillera; Economic Geology, Volume 85, pages 1260-1268.

Nesbitt, B.E., Muehlenbachs, K. and Murowchick, J.B. (1989): Genetic Implications of Stable Isotope Characteristics of Mesothermal Au Deposits and Related Sb and Hg Deposits in the Canadian Cordillera; Economic Geology, Volume 84, pages 1489-1506.

Seal, R.R.,II, Clark, A.H., and Morissy, C.J. (1988): Lake George, Southeastern New Brunswick; A Silurian, Multi-stage, Polymetallic (Sb-W-Mo-Au-Base Metal) Hydrothermal Centre; in Recent Advances in the Geology of Granite-Related Mineral Deposits; Taylor, R.P. and Strong, D.F., Editors, Canadian Institute of Mining and Metallurgy, CIM Special Volime 39, pages 252-264.

Wu, J. (1993): Antimony Vein Deposits of China; in Vein-type Ore Deposits, Ore Geology Reviews, Haynes, S.J., Editor, Volume 8, pages 213-232.

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VEIN BARITE


I10
by Z.D. Hora
British Columbia Geological Survey

 

Hora, Z.D. (1996): Vein Barite, 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 81-84.

 

IDENTIFICATION

 

SYNONYM: Epigenetic vein barite.

 

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

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Parson (082N 002), Brisco (082KNE013), Fireside (094M 003); Matchewan (Ontario, Canada), Lake Ainslie (Nova Scotia, Canada), Collier Cove (Newfoundland, Canada), Nevada, Montana, Virginia, Pennsylvania, Georgia in USA; Bonarta, Jbel Ighoud (Morocco); Wolfach, Bad Lauterberg (Germany); Roznava (Slovakia), China.

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Barite in fissure-filling voids resulting from mechanical deformation, including dilatant zones along faults and folds, gash fractures, joints and bedding planes; also in shear and breccia zones along faults.

 

TECTONIC SETTINGS: Highly varied, frequently but not exclusively at or near the margins of basins with sedex or Kuroko type deposits, or abrupt deep basin- platform sedimentation facies change.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Highly varied; almost any type of sedimentary, metamorphic or intrusive rocks. Veins associated with regional faults and lineaments, also the breccia zones along the margins of rift basins. In carbonate rocks, barite may fill karst cavities and collapse structures and forms manto-like replacement orebodies.

 

AGE OF MINERALIZATION: Precambrian to Tertiary.

 

HOST/ASSOCIATED ROCK TYPES: Any sedimentary, metamorphic or even igneous rocks.

 

DEPOSIT FORM: Tabular/lenticular bodies and breccias, collapse breccias and related cavity fills, veins with manto-type orebodies in carbonate hostrocks. The veins are several hundreds up to over 1000 m in length and sometimes up to 20 m thick. Some veins are mined to the depth of 500 m from surface.

 

TEXTURE/STRUCTURE: Massive, banded, brecciated. Texture typical of high-level veins, occasional druzy textures.

 

ORE MINERALOGY (Principal and subordinate): Barite, fluorspar, siderite, Pb-Zn-Cu sulphides.

 

GANGUE MINERALOGY: (Principal and subordinate): Quartz, calcite, siderite, witherite, barytocalcite, cinnabar, pyrite.

 

ALTERATION MINERALOGY: Insignificant.

 

WEATHERING: Barite float and detrital fragments as a result of physical weathering.

 

ORE CONTROLS: Dominant structural control with veins along faults, fractures, and shear zones, sometimes related to dilatant zones in major fault systems.

 

GENETIC MODEL: Epithermal barite veins, with or without sulphides, are common at and near the margins of rift basins, both in continental and continental margin settings. The veins and orebodies occur as open-space fillings in high-angle faults or fractures in sedimentary rocks or adjacent crystalline rocks, sills, and irregular and stratabound collapse structures or mantos. The source fluids are inferred to have been brines of moderate salinity (10 to 16 equivalent weight percent NaCl) and temperatures of 100 degrees to 250 degrees C. Pre-existing fractures and faults are apparently important in localizing the veins and orebodies. Multiple mineralizing episodes and several pulses of fluid migration are evident in many of the vein systems.

 

ASSOCIATED DEPOSIT TYPES: Polymetallic veins (I05) and replacement deposits (J01, E10-E11, E12), sedex (E14) and Kuroko massive sulphide (G06) deposits, carbonatites (N03).

 

COMMENTS: This type of barite vein is distinct from barite associated with fluorspar veins. These (fluorspar-barite) veins may have, at least in part, a different barium source and are closely associated with Mississippi Valley type deposits.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Ba, Sr, sometimes Hg, Ag, Pb, Zn and Cu anomalies in soils and silts.

 

GEOPHYSICAL SIGNATURE: Linear gravity highs over large veins.

 

OTHER EXPLORATION GUIDES: Clastic barite in stream sediments, both in sand and silt fractions.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Most deposits in production are selectively mining high- grade orebodies with over 80% barite. The deposit size varies from a few thousand up to some 3 Mt. Brisco mine produced approximately 250,000 tonnes during its life; Parson is expected to produce close to 1 Mt.

 

ECONOMIC LIMITATIONS: Dependant on the end use. White, high-purity barite is suitable for filler and chemical applications and can be mined from even very small deposits. Drilling mud is a lower priced grade and, if processing is required to reach the required 4.2 specific gravity, only large deposits can be operated successfully. Even a small amount of contamination by siderite or witherite may make the barite unusable in drilling mud applications. Barite which is contaminated with small quantities (ppm) of heavy metals like Pb, Zn, Cu and Hg may result in environmental problems with disposal of spent drilling mud.

 

END USES: Drilling muds, fillers, chemicals, radiation shields, speciality glass and ceramics.

 

IMPORTANCE: Probably the main source of barite worldwide, but in North America very subordinate to bedded barite deposits.

 

REFERENCES

 

Brobst, D.A. (1984): The Geological Framework of Barite Resources; The Institution of Mining and Metallurgy, Transactions Volume 93, pages A123-A130.

Dawson, K.R. (1985): Geology of Barium, Strontium, and Fluorine Deposits in Canada; Economic Geology Report 34, Geological Survey of Canada, 135 pages.

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

Hofmann, R. and Baumann A. (1984): Preliminary Report on the Sr Isotopic Composition of Hydrothermal Vein Barites in the Federal Republic of Germany; Mineral Deposita, Volume 19, pages 166-169.

Kuzvart, M. (1984): Deposits of Industrial Minerals; Academia, Prague, 440 pages. Leach, D.L. (1980): Nature of Mineralizing Fluids in the Barite Deposits of Central and Southeast Missouri; Economic Geology, Volume 75, pages 1168-1180.

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, pp. 364-376.

Morrow, D.W., Krouse, H.R., Ghent, E.D., Taylor, G.C. and Dawson, K.R. (1978): A Hypothesis Concerning the Origin of Barite in Devonian Carbonate Rocks of North- eastern British Columbia; Canadian Journal of Earth Sciences, Volume 15, pages 1391 - 1406.

Papke, K.G. (1984): Barite in Nevada; Nevada Bureau of Mines and Geology, Bulletin 98, 125 pages.

Robinson, G.R. Jr., and Woodruff, L.G. (1988): Characteristics of Base-metal and Barite Vein Deposits associated with Rift Basins, with Examples from some Early Mesozoic Basins of Eastern North America, in Studies of Early Mesozoic Basins of the Eastern US, Frolich, T.J. and Robinson, G.R. Jr., Editors, US Geological Survey, Bulletin 1776, pages 377-390.

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VEIN FLUORITE-BARITE


I11
by Z.D. Hora
British Columbia Geological Survey

 

Hora, Z.D. (1996): Vein Fluorite-barite, 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 85-88.

 

IDENTIFICATION

 

SYNONYM: Epigenetic fluorite/barite vein.

 

COMMODITIES (BYPRODUCTS): Fluorite, sometimes barite (occasionally Pb, Zn, and Cu. Some fluorites contain the recoverable Be minerals bertrandite and phenacite.

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Rock Candy (082ESE070), Eaglet (093A 046), Rexspar (082M 007); Madoc (Ontario, Canada); St. Lawrence (Newfoundland, Canada); Nevada, Utah, New Mexico (USA); Nabburg- Woelsendorf, Ilmenau, Schoenbrunn (Germany); Torgola, Prestavel, Gerrai (Italy); Auvergne, Morvan (France); Mongolia, China.

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Fluorite and barite fill dilatant shear and breccia zones along faults and folds, gash fractures, joints and bedding planes as well as stockworks. In carbonate rocks, the fissure veins are frequently associated with replacement bodies and mantos. Fluorite veins commonly show affinities with barite veins and may grade into polymetallic veins with barite gangue.

 

TECTONIC SETTINGS: Highly varied - but in terrains underlain by sialic crust. In young orogenic belts: postorogenic and lateorogenic granite intrusions or rift-related alkaline rocks (from syenites to nepheline syenites to carbonatites) may be associated with fluorite veins. In old orogenic belts: proximity of major tectonic zones, grabens, tensional rifts and lineaments.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Highly varied, sometimes linked to volatile-rich intrusives of alkaline to granite composition. In the Cordillera, topaz rhyolites, particularly, are associated with many fluorite veins.

 

AGE OF MINERALIZATION: Precambrian to Tertiary; in B.C. Devono-Mississippian (Rexspar), Cretaceous (Eaglet) and Tertiary (Rock Candy).

 

HOST/ASSOCIATED ROCK TYPES: Any sedimentary, metamorphic or igneous rock; in volcanic environment usually associated with topaz rhyolite.

 

DEPOSIT FORM: Tabular or lenticular bodies and breccias or stockworks and breccia pipes. The veins are usually 1-5 m thick and may be over a 1000 m long. Some particularly large veins in Sardinia are 3 km in length; the Torgola vein is reported to be 20 m thick. Some vein deposits were mined up to 500 m below surface, however the usual mining depth is 200 to 300 m down the dip from the outcrop.

 

TEXTURE/STRUCTURE: Massive, banded, brecciated. Drusy textures are common, fluorspar may be coarse grained or fine grained with radiating texture. Banding of different colour varieties of fluorspar is very common (coontail type). Bands of barite in fluorite, or young silica replacement of fluorspar along the cleavage and crystal borders are common features.

 

ORE MINERALOGY (Principal and subordinate): Fluorite, barite, celestite, barytocalcite, galena, sphalerite, chalcopyrite, pyrite, adularia or K-feldspar, red jasper. Dark purple fluorite may contain uraninite. Bertrandite and other Be minerals are sometimes accessory components. Fluorite is often the main or even only vein mineral.

 

GANGUE MINERALOGY: (Principal and subordinate) Gangue may be a variety of minerals such as quartz, chalcedony, jasper, barite and Ca-Fe-Mg carbonates. Barite commonly varies in colour from yellow to pink or red; jasper may have a red colour due to finely dispersed haematite.

 

ALTERATION MINERALOGY: Kaolinization and/or silicification of wallrocks, sometimes pervasive potassic alteration (Eaglet, Rexspar); occasionally montmorillonite in wallrocks.

 

WEATHERING: Physical weathering mostly; in high-sulphide environment fluorspar may be dissolved by sulphuric acid. Floats of vein quartz with voids after weathered out fluorspar crystals are a common feature.

 

ORE CONTROLS: Faults, fractures, shear zones. Vertical zoning of veins is a common feature, but not very well understood.

 

GENETIC MODEL: Fluorite veins are generally found in the proximity of continental rifts and lineaments. In young orogenic belts fluorite can be linked to late or postorogenic granitic intrusions, particularly in areas of sialic crust. Rift- related alkaline intrusions are also linked to some fluorite veins. In old orogenic belts, fluorite veins are also in fracture zones within major faults and graben structures which facilitated circulation of mineralized fluids far from original fluorine source. Fluorite is precipitated from fluids by cooling low-pH solutions or by an increase in the pH of acid ore fluids. The fluids usually have a high Na/K ratio.

 

ASSOCIATED DEPOSIT TYPES: Pb-Zn veins (I05), carbonatite plugs, dikes and sills with Nb-REE (N02); Sn-W greisen (I13), F/Be deposits (Spor Mountain), Pb-Zn mantos (J01) and Mississippi Valley type deposits (E10, E11, E12).

 

COMMENT: End uses of fluorine chemicals in aluminium and chemical industries are very sensitive to P and As contents of only a few ppm.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: F in stream waters.

 

GEOPHYSICAL SIGNATURE: Sometimes gamma radiometric anomalies as an expression of potassic alteration or uranium content in certain types of fluorite.

 

OTHER EXPLORATION GUIDES: Fault control in some districts; regional silicified zones and major quartz veins.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Past producers reported grades in general between 30% and 60% fluorite, with occasional higher grade orebodies. The deposit size varies; up to 6 Mt. In B.C., Eaglet reported 1.8 million tonnes of 15% CaF2, Rexspar 1.4 million tonnes of 23% CaF2.

 

ECONOMIC LIMITATIONS: In recent years, shipments of high quality fluorspar from China, at very low prices, resulted in the collapse of most fluorspar production centres worldwide.

 

END USES: Metallurgy of aluminum and uranium, fluorine chemicals, flux in iron and steel metallurgy, glass and ceramics.

 

IMPORTANCE: Main source of fluorspar worldwide. In B.C., the Rock Candy mine produced 51,495 t of 68% CaF2 between 1918 and 1929.

 

REFERENCES

 

Brecke, E.A. (1979): A Hydrothermal System in the Midcontinent Region; Economic Geology, Volume 74, pages 1327-1335

Burt, D.M., Sheridan, M.F., Bikun, J.V. and Christiansen, E.H. (1982): Topaz Rhyolites Distribution, Origin and Significance for Exploration, Economic Geology, Volume 77, pages 1818-1836

Dawson, K.R. (1985): Geology of Barium Strontium and Fluorine Deposits in Canada; Economic Geology Report 34; Geological Survey of Canada, 135 pages.

Deloule, E. (1982): The Genesis of Fluorspar Hydrothermal Deposits at Montroc and Le Burc, the Tarn, as Deduced from Fluid Inclusion Analysis; Economic Geology, Volume 77, pages 1867-1874.

Harben, P.W. and Bates, R.L. (1990): Industrial Minerals Geology and World Deposits; Metal Bulletin, London, 135 pages.

Kesler, S.E., Gesing, J.A., and Haynes, F.M. (1989): Evolution of Minerallizing Brines in the East Tennessee Mississipi Valley - type Ore Field; Geology, Volume 17, pages 466-469.

Kuzvart, M. (1984): Deposits of Industrial Minerals; Academia, Prague, 440 pages.

McAnulty, W.N. (1978): Fluorspar in New Mexico; New Mexico Bureau of Mines and Mineral Resources, Memoir 34, 64 pages.

Orris, G.J. and Bliss, J.D. (1992): Industrial Minerals Deposit Models: Grades and Tonnage Models; U.S. Geological Survey, Open File Report 92- 431, 84 pages.

Papke, K.G. (1979): Fluorspar in Nevada; Nevada Bureau of Mines and Geology, Bulletin 9377 pages. Pell, J. (1992): Fluorspar and Fluorine in British Columbia, B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1992-16, 82 pages.

VanAlstine, R.E. (1976): Continental Rifts and Lineaments Associated with Major Fluorspar Districts; Economic Geology, Volume 71, pages 977-987.

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FIVE-ELEMENT VEINS


Ag-Ni-Co-As+/-(Bi, U)

I14
by David V. Lefebure
British Columbia Geological Survey

 

Lefebure, D.V. (1996): Five-element Veins Ag-Ni-Co-As+/-(Bi,U), 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 89-92.

 

IDENTIFICATION

 

SYNONYMS: Five-element (Ni-Co-As-Ag-Bi) veins, nickel-cobalt-native silver veins, Cobalt-type silver-sulpharsenide veins, Ni-Co-Bi-Ag-U (As) association, Ag- As (Ni,Co,Bi) veins, Schneeberg-Joachimsthal-type.

 

COMMODITY (BYPRODUCTS): Ag, U, Ni, Co, Bi (barite).

 

EXAMPLES (British Columbia - Canada/International): No B.C. examples; Beaver and Timiskaming, Cobalt camp, Silver Islet, Thunder Bay district (Ontario, Canada), Echo Bay and Eldorado (Port Radium, Northwest Territories, Canada), Black Hawk district (New Mexico, USA), Batopilas district (Mexico), Johanngeogenstadt, Freiberg and Jachymov, Erzgebirge district (Germany), Konsberg-Modum (Norway).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Native silver occurs in carbonate veins associated with a variety of mineral assemblages that are rare in other settings, such as Ni- Co-Fe arsenides, Ni-Co-Fe-Sb sulpharsenides and bismuth minerals. In many cases only some of these minerals are present, although the best examples of this deposit type typically contain significant Ag-Ni-Co. In some deposits uraninite (pitchblende) is an important ore mineral.

 

TECTONIC SETTINGS: Virtually all occur in areas underlain by continental crust and are generally believed to have formed late or post-tectonically. In some cases the veins appear related to basinal subsidence and continental rifting.

 

DEPOSTIONAL ENVIRONMENT/GEOLOGICAL SETTING: Veins are believed to be emplaced at shallow depths in a continental setting along high-angle fault systems.

 

AGE OF MINERALIZATION: Proterozoic or younger, can be much younger than hostrocks.

 

HOST/ASSOCIATED ROCK TYPES: Found in a wide variety of hostrocks, although metasediments, metamorphosed intrusive rocks and granitic sequences are the most common. Diabase sills are an important host in the Cobalt camp and a number of the deposits in the Thunder Bay region are within a gabbro dike.

 

DEPOSIT FORM: Simple veins and vein sets. Veins vary from centimetre to metre thicknesses, typically changing over distances of less than tens of metres. Most vein systems appear to have limited depth extent, although some extend more than 500 m.

 

TEXTURE/STRUCTURE: Commonly open space filling with mineral assemblages and textures commonly due to multiple episodes of deposition. Sulphides are irregularly distributed as massive pods, bands, dendrites, plates and disseminations. The mineralization is more common near the interesections of veins or veins with crosscutting faults. Fragments of wallrock are common in some veins. Faults may be filled with graphite-rich gangue, mylonite or breccia.

 

ORE MINERALOGY (Principal and subordinate): Native silver associated with Ni-Co arsenide minerals (rammelsbergite, safflorite, niccolite, cloanthite, maucherite), sulpharsenides of Co, Ni, Fe and Sb, native bismuth, bismuthinite, argentite, ruby silver, pyrite and uraninite (pitchblende). Chalcopyrite, bornite and chalcocite are common, but minor, constituents of ore. Minor to trace galena, tetrahedrite, jamesonite, cosalite, sphalerite, arsenopyrite and rare pyrrhotite. In many deposits only a partial mineral assemblage occurs containing a subset of the many elements which may occur in these veins. These veins are characterized by the absence of gold.

 

GANGUE MINERALOGY (Principal and subordinate): Calcite and dolomite are usually associated directly with native silver mineralization; quartz, jasper, barite and fluorite are less common. The carbonate minerals are common in the cores of some veins.

 

ALTERATION MINERALOGY: Not conspicuous or well documented. In the Cobalt camp calcite and chlorite alteration extends 2-5 cm from the vein, approximately equivalent in width to the vein.

 

WEATHERING: No obvious gossans because of the low sulphide content; locally “cobalt bloom”.

 

ORE CONTROLS: Veins occupy faults which often trend in only one or two directions in a particular district. Ore shoots may be localized at dilational bends within veins. Intersections of veins are an important locus for ore. Possibly five-element veins are more common in Proterozoic rocks.

 

GENETIC MODEL: In regions of crustal extension, faults controled the ascent of hydrothermal fluids to suitable sites for deposition of metals at depths of approximately 1 to 4 km below surface. The fluids were strongly saline brines at temperatures of 150ø to 250øC, which may have been derived from late-stage differentiation of magmas, convective circulation of water from the country rocks driven by cooling intrusive phases or formation brines migrating upwards or towards the edge of sedimentary basins. Sulphide-rich strata (including Fahlbands) and carbonaceous shales in the stratigraphy are potential sources of the metals. Deposition occurs where the fluid encounters a reductant or structural trap.

 

ASSOCIATED DEPOSIT TYPES: ‘Classical’ U veins (I15), polymetallic veins (I05). In the Great Bear Lake area there are associated “giant” quartz veins with virtually no other minerals.

 

COMMENTS: Several Co-AgñNiñBi veins are found in the Rossland Camp in British Columbia. These may be five-element veins, however, they also contain the atypical elements Au and Mo.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: The rare association of anomalous values of Ag with Ni, Co, Bi, U and As in rock samples is diagnostic.

 

GEOPHYSICAL SIGNATURE: Associated structures may be defined by ground magnetic or VLF-EM surveys. Airborne surveys may identify prospective major structures. Gamma ray scintillometers and spectrometers can be used to detect the uraninite-bearing veins in outcrop or in float trains in glacial till, frost boils, talus or other debris.

 

OTHER EXPLORATION GUIDES: Commonly camp or regional structural controls will define a dominant orientation for veins.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Typically range from tens of thousands of tonnes to a few hundreds of thousands of tonnes with very high grades of silver (more than 1000 g/t Ag for Canadian mines, with grades up to 30 000 g/t Ag).

 

IMPORTANCE: There has been no significant production from a native silver vein in British Columbia, however, these veins have historically been an important Canadian and world source of Ag and U with minor production of Co. More recently the narrow widths and discontinuous nature of these veins has led to the closure of virtually all mines of this type.

 

REFERENCES

 

Andrews, A.J. (1986): Silver Vein Deposits: Summary of Recent Research; Canadian Journal of Earth Sciences, Volume 23, pages 1459-1462.

Andrews, A.J., Owsiacki, L., Kerrich, R. and Strong, D.F. (1986): The Silver Deposits at Cobalt and Gowganda, Ontario. I: Geology, Petrography, and Whole-rock Geochemistry; Canadian Journal of Earth Sciences, Volume 23, pages 1480-1506.

Bastin, E.S. (1939): The Nickel-Cobalt-Native Silver Ore-type; Economic Geology, Volume 34, pages 1-40.

Boyle, R.W. (1968): The Geochemistry of Silver and its Deposits; Geological Survey of Canada, Bulletin 160, 264 pages.

Franklin, J.M., Kissin, S.A., Smyk, M.C. and Scott, S.D. (1986): Silver Deposits Associated with the Proterozoic Rocks of the Thunder Bay District, Ontario; Canadian Journal of Earth Sciences, Volume 23, pages 1576-1591.

Kissan, S.A. (1993): Five-element (Ni-Co-As-Ag-Bi) Veins, in Ore Deposit Models, Sheahan, P.A. and Cherry, M.E., Editors, Geoscience Canada, Reprint Series 6, pages 87-99.

Laznicka, P. (1986): Empirical Metallogeny, Depositional Environments, Lithologic Associations and Metallic Ores, Volume 1: Phanerozoic Environments, Associations and Deposits; Elsevier, New York, pages 1268- 1272.

Rogers, M.C. (1995): Cobalt-type Silver-supharsenide Vein; in Descriptive Mineral Deposit Models of Metallic and Industrial Deposit Types and Related Mineral Potential Assessment Criteria, Ontario Geological Survey, Open File Report 5916, pages 133-136.

Thorpe, R.I. (1984): Arsenide Vein Silver, Uranium; in Canadian Mineral Deposit Types: A Geological Synopsis, Eckstrand, O.R., Editor, Geological Survey of Canada, Economic Geology Report 36, page 63.

Wilkerson, G., Deng, Q., llavon, R. and Goodell, P. (1988): Batopilas Mining District, Chihuahaua, Mexico; Economic Geology, Volume 83, pages 1721- 1736.

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"CLASSICAL" U VEINS


I15
by R.H. McMillan
Consulting Geologist, Victoria, British Columbia

 

McMillian, R.H. (1996): "Classical" U Veins, 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 93-96.

 

IDENTIFICATION

 

SYNONYMS: Pitchblende veins, vein uranium, intragranitic veins, perigranitic veins.

 

COMMODITIES (BYPRODUCTS): U (Bi, Co, Ni, As, Ag, Cu, Mo).

 

EXAMPLES (British Columbia - Canada/International): In the Atlin area structurally controlled scheelite-bearing veins host uranium at the Purple Rose, Fisher, Dixie, Cy 4, Mir 3 and IRA occurrences, Ace Fay-Verna and Gunnar, Beaverlodge area (Saskatchewan, Canada), Christopher Island-Kazan-Angikuni district, Baker Lake area (Northwest Territories, Canada), Millet Brook (Nova Scotia, Canada), Schwartzwalder (Colorado, USA), Xiazhuang district (China), La Crouzille area, Massif Central and Vendee district, Armorican Massif, (France), Jachymov and Pribram districts (Czech Republic), Shinkolobwe (Shaba province, Zaire).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Pitchblende (Th-poor uraninite), coffinite or brannerite with only minor amounts of associated metallic minerals in a carbonate and quartz gangue in veins. These deposits show affinities with, and can grade into, five- element veins which have significant native silver, Co-Ni arsenides, Bi or other metallic minerals.

 

TECTONIC SETTING: Postorogenic continental environments, commonly associated with calcalkaline felsic plutonic and volcanic rocks. “Red beds” and sediments of extensional successor basins are common in the host sequence. The economic deposits appear confined to areas underlain by Proterozoic basement rocks.

 

DEPOSITIONAL ENVIRONMENT: Ore is deposited in open spaces within fracture zones, breccias and stockworks commonly associated with major or subsidiary, steeply dipping fault systems.

 

AGE OF MINERALIZATION: Proterozoic to Tertiary. None are older than approximately 2.2 Ga, the time when the atmosphere evolved to the current oxygen-rich condition.

 

HOST/ ASSOCIATED ROCK TYPES: A wide variety of hostrocks, including granitic rocks, commonly peraluminous two-mica granites and syenites, felsic volcanic rocks, and older sedimentary and metamorphic rocks. The uranium-rich veins tend to have an affinity to felsic igneous rocks. Some veins are closely associated with diabase and lamprophyre dikes and sills.

 

DEPOSIT FORM: Orebodies may be tabular or prismatic in shape generally ranging from centimetres up to a few metres thick and rarely up to about 15 m. Many deposits have a limited depth potential of a few hundred metres, however, some deposits extend from 700 m up to 2 km down dip. Disseminated mineralization is present within the alteration envelopes in some deposits.

 

TEXTURE/STRUCTURE: Features such as drusy textures, crustification banding, colloform, botryoidal and dendritic textures are common in deposits which have not undergone deformation and shearing. The veins typically fill subsidiary dilatant zones associated with major faults and shear zones. Mylonites are closely associated with the St. Louis fault zone at the Ace-Fay-Verna mines.

 

ORE MINERALOGY (Principal and subordinate): Pitchblende (Th-poor uraninite), coffinite, uranophane, thucolite, brannerite, iron sulphides, native silver, Co-Ni arsenides and sulpharsenides, selenides, tellurides, vanadinites, jordesite, chalcopyrite, galena, sphalerite, native gold and platinum group elements. Some deposits have a “simple” mineralogy of with only pitchblende and coffinite. Those veins with the more complex mineralogy are often interpreted to have had the other minerals formed at an earlier or later stage.

 

GANGUE MINERALOGY (Principal and subordinate): Carbonates (calcite and dolomite), quartz (often chalcedonic), hematite, K-feldspar, albite, muscovite, fluorite, barite.

 

ALTERATION: Chloritization, hematization, feldspathization. A few of the intrusive-hosted deposits are surrounded by desilicated, porous feldspar-mica rock called “episyenite” in the La Crouzille area of France and “sponge-rock” at the Gunnar mine in Saskatchewan. In most cases the hematization is due to oxidation of ferrous iron bearing minerals in the wallrocks during mineralization. The intense brick-red hematite adjacent to some high-grade uranium ores is probably due to loss of electrons during radioactive disintegration of uranium and its daughter products.

 

WEATHERING: Uranium is highly soluble in the +6 valence state above the water table. It will re-precipitate as uraninite and coffinite below the water table in the +4 valence state in the presence of reducing agents such as humic material or carbonaceous “trash”. Some uranium phosphates, vanadinites, sulphates, silicates and arsenates are semi-stable under oxidizing conditions, consequently autunite, torbernite, carnotite, zippeite, uranophane, uranospinite and numerous other secondary minerals may be found in the zone of oxidation , particularly in arid environments.

 

ORE CONTROLS: Pronounced structural control related to dilatant zones in major fault systems and shear zones. A redox control related to the loss of electrons associated with hematitic alteration and precipitation of uranium is evident but not completely understood. Many deposits are associated with continental unconformities and have affinities with unconformity-associated U deposits (I16).

 

GENETIC MODEL: Vein U deposits are generally found in areas of high uranium Clarke, and generally there are other types of uranium deposits in the vicinity. The veins might be best considered polygenetic. The U appears to be derived from late magmatic differentiates of granites and alkaline rocks with high K or Na contents. Uranium is then separated from (or enriched within) the parent rocks by aqueous solutions which may originate either as low-temperature hydrothermal, connate or meteoric fluids. Current opinion is divided on the source of the fluids and some authors prefer models that incorporate mixing fluids. Studies of carbon and oxygen isotopes indicate that the mineralizing solutions in many cases are hydrothermal fluids which have mixed with meteoric water. In some cases temperatures exceeding 400 §C were attained during mineralization. The uranium minerals are precipitated within faults at some distance from the source of the fluids. Wallrocks containing carbonaceous material, sulphide and ferromagnesian minerals are favourable loci for precipitation of ore. Radiometric age dating indicates that mineralization is generally significantly younger than the associated felsic igneous rocks, but commonly close to the age of associated diabase or lamprophyre dikes.

 

ASSOCIATED DEPOSIT TYPES: Stratabound, disseminated and pegmatitic occurrences of U are commonly found in older metamorphic rocks. Sandstone-hosted U deposits (D05) are commonly found in associated red-bed supracrustal strata, and surficial deposits (B08) in arid or semi-arid environments.

 

COMMENTS: The Cretaceous to Tertiary Surprise Lake batholith in the Atlin area hosts several fracture-controlled veins with zeunerite, kasolite, autunite and Cu, Ag, W, Pb and Zn minerals. These include the Purple Rose, Fisher, Dixie, Cy 4, Mir 3 and IRA. Southwest of Hazelton, Th-poor uraninite associated with Au, Ag, Co-Ni sulpharsenides, Mo and W is found in high-temperature quartz veins within the Cretaceous Rocher D‚boul‚ granodiorite stock at the Red Rose, Victoria and Rocher Deboule properties. Although the veins are past producers of Au, Ag, Cu and W, no U has been produced.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Uranium and sometimes any, or all, of Ni, Co, Cu, Mo, Bi, As and Ag are good pathfinder elements which can be utilized in standard stream silt, lake bottom sediment and soil surveys. Stream and lake bottom water samples can be analyzed for U and Ra. In addition, the inert gases He and Ra can often be detected above a U-rich source in soil and soil gas surveys, as well as in groundwater and springs.

 

GEOPHYSICAL SIGNATURE: Standard prospecting techniques using sensitive gamma ray scintillometers and spectrometers to detect U mineralization in place or in float trains in glacial till, frost boils, talus or other debris remains the most effective prospecting methods. Because most deposits do not contain more than a few percent metallic minerals, electromagnetic and induced polarization surveys are not likely to provide direct guides to ore. VLF-EM surveys are useful to map the fault zones which are hosts to the veins. Magnetic surveys may be useful to detect areas of magnetite destruction in hematite-altered wallrocks.

 

OTHER EXPLORATION GUIDES: Secondary uranium minerals are typically yellow and are useful surface indicators.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Individual deposits are generally small (< 100 000 t) with grades of 0.15% to 0.25% U, however districts containing several deposits can aggregate considerable tonnages. The large Ace-Fay-Verna system produced 9 Mt of ore at an average grade of 0.21% U from numerous orebodies over a length of 4.5 km. and a depth of 1500 m. Gunnar produced 5 Mt of ore grading 0.15% U from a single orebody. The Schwartzwalder mine in Colorado was the largest “hardrock” uranium mine in the United States, producing approximately 4 300 tonnes U, and contains unmined reserves of approximately the same amount.

 

ECONOMIC LIMITATIONS: The generally narrow mining widths and grades of 0.15% to 0.25% U rendered most vein deposits uneconomic after the late 1960s discovery of the high-grade unconformity-type deposits.

 

IMPORTANCE: This type of deposit was the source of most of the world’s uranium until the 1950s. By 1988, significant production from veins was restricted to France, with production of 3 372 tonnes U or 9.2% of the world production for that year.

 

REFERENCES

 

ACKNOWLEDGMENTS: Sunial Gandhi, Nirankar Prasad, Larry Jones and Neil Church reviewed the profile and provided many constructive comments.

 

Chen, Z. and Fang, X. (1985): Main Characteristics and Genesis of Phanerozoic Vein-type Uranium Deposits; in Uranium Deposits in Volcanic Rocks, International Atomic Energy Agency, IAEA-TC-490/12, pages 69-82.

Evoy, E.F. (1986): The Gunnar Uranium Deposit; in Uranium Deposits of Canada, Evans, E.L., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 33, pages 250-260.

Jones, Larry D. (1990): Uranium and Thorium occurrences in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1990-32, 78 pages.

Lang, A.H., Griffith, J.W. and Steacy, H.R. (1962): Canadian Deposits of Uranium and Thorium; Geological Survey of Canada, Economic Geology Series No. 16, 324 pages.

Leroy, J. (1978): The Magnac and Funay Uranium Deposits of the La Crouzille District (Western Massif Central, France): Geologic and Fluid Inclusion Studies; Economic Geology, volume 73, pages 1611-1634.

Miller, A.R., Stanton, R.A., Cluff, G.R. and Male, M.J. (1986): Uranium Deposits and Prospects of the Baker Lake Basin and Subbasins, Central District of Keewatin, Northwest Territories; in Uranium Deposits of Canada, Evans, E.L., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 33, pages 263-285.

Nash, J.T., Granger, H.C. and Adams, S.S. (1981): Geology and Concepts of Genesis of Important Types of Uranium Deposits; in Economic Geology, 75th Anniversary Volume, pages 63-116.

Ruzicka, V. (1993): Vein Uranium Deposits; Ore Geology Reviews, Volume 8, pages 247-276. Smith, E.E.N (1986): Geology of the Beaverlodge Operation, Eldorado Nuclear Limited. in Uranium Deposits of Canada, Evans, E.L., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 33, pages 95-109.

Stevenson, J.S. (1951): Uranium Mineralization in British Columbia; Economic Geology, Volume 46, pages 353-366.

Tremblay, L.P. (1972): Geology of the Beaverlodge Mining Area, Saskatchewan; Geological Survey of Canada, Memoir 367, 265 pages.

Tremblay, L.P. and Ruzicka, V. (1984): Vein Uranium; in Economic Geology Report 36, Geological Survey of Canada, page 64.

Wallace, A.R. (1986): Geology and Origin of the Schwartzwalder Uranium Deposit, Front Range, Colorado, U.S.A; in Vein Type Uranium Deposits, Fuchs, H., Editor, International Atomic Energy Agency, Vienna, IAEA-TECDOC-361, pages 159 - 168.

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UNCONFORMITY-ASSOCIATED U


I16
by R.H. McMillan
Consulting Geologist

 

McMillan, R.H. (1998): Unconformity-associated U, in Geological Fieldwork 1997, British Columbia Ministry of Employment and Investment, Paper 1998-1, pages 24G-1 to 24G-4.

 

IDENTIFICATION

 

SYNONYMS: Unconformity-veins, unconformity-type uranium, unconformity U.

 

COMMODITIES (BYPRODUCTS): U (Au, Ni).

 

EXAMPLES (British Columbia - Canada/International): None in British Columbia; Rabbit Lake, Key Lake, Cluff Lake, Midwest Lake, McClean Lake, McArthur River, Cigar Lake and Maurice Bay in the Athabasca uranium district (Saskatchewan, Canada), Lone Gull (Kiggavik) and Boomerang Lake, Thelon Basin district (Northwest Territories, Canada), Jabiluka, Ranger, Koongarra and Nabarlek, Alligator River district (Northern Territory, Australia).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Uranium minerals, generally pitchblende and coffinite, occur as fracture and breccia fillings and disseminations in elongate, prismatic-shaped or tabular zones hosted by sedimentary/metasedimentary rocks located below, above or across a major continental unconformity.

 

TECTONIC SETTING: Intracratonic sedimentary basins.

 

GEOLOGICAL SETTING/DEPOSITIONAL ENVIRONMENT: Structurally-prepared and porous zones within chemically favourable reduced or otherwise reactive strata.

 

AGE OF MINERALIZATION: Mid-Proterozoic, however, there is potential for younger deposits.

 

HOST/ ASSOCIATED ROCK TYPES: Shelf facies metasedimentary (amphibolite or granulite facies) rocks of Early Proterozoic age (graphitic or sulphide-rich metapelites, calcsilicate rocks and metapsammites), regolith and overlying continental sandstones of Middle Proterozoic age. The Early Proterozoic hostrocks in many cases are retrograded amphibolite-facies metamorphic rocks on the flanks of Archean gneiss domes. The overlying continental sandstones are well sorted fluviatile quartz-rich psammites; generally with a clay or siliceous matrix and red or pale in colour. Dikes and sills, commonly diabases and lamprophyres, occur in some districts.

 

DEPOSIT FORM: Orebodies may be tabular, pencil shaped or irregular in shape extending up to few kilometres in length. Most deposits have a limited depth potential below the unconformity of less than a 100 m, however, the Jabiluka and Eagle Point deposits are concordant within the Lower Proterozoic host rocks and extend for several hundred metres below the unconformity.

 

TEXTURE/STRUCTURE: Most deposits fill pore space or voids in breccias and vein stockworks. Some Saskatchewan deposits are exceptionally rich with areas of "massive" pitchblende/coffinite. Features such as drusy textures, crustification banding, colloform, botryoidal and dendritic textures are present in some deposits.

 

ORE MINERALOGY (Principal and subordinate): Pitchblende (Th-poor uraninite), coffinite, uranophane, thucolite, brannerite, iron sulphides, native gold, Co-Ni arsenides and sulpharsenides, selenides, tellurides, vanadinites, jordesite (amorphous molybedenite), vanadates, chalcopyrite, galena, sphalerite, native Ag and PGE. Some deposits are "simple" with only pitchblende and coffinite, while others are "complex" and contain Co-Ni arsenides and other metallic minerals.

 

GANGUE MINERALOGY: Carbonates (calcite, dolomite, magnesite and siderite), chalcedonic quartz, sericite (illite) chlorite and dravite (tourmaline).

 

ALTERATION: Chloritization, hematization, kaolinization, illitization and silicification. In most cases hematization is due to oxidation of ferrous iron bearing minerals in the wallrocks caused by oxidizing mineralizing fluids, however, the intense brick-red hematite adjacent to some high grade uranium ores is probably due to loss of electrons during radioactive disintegration of U and its daughter products. An interesting feature of the clay alteration zone is the presence of pseudomorphs of high grade metamorphic minerals, such as cordierite and garnet, in the retrograded basement wallrock.

 

WEATHERING: Uranium is highly soluble in the +6 valence state above the water table. It will re-precipitate as uraninite and coffinite below the water table in the +4 valence state in the presence of a reducing agents such as humic material or carbonaceous "trash". Some U phosphates, vanadates, sulphates, silicates and arsenates are semi-stable under oxidizing conditions, consequently autunite, torbernite, carnotite, zippeite, uranophane, uranospinite and numerous other secondary minerals may be found in the near-surface zone of oxidation, particularly in arid environments.

 

ORE CONTROLS: A pronounced control related to a mid-Proterozoic unconformity and to favourable stratigraphic horizons within Lower Proterozoic hostrocks - these strata are commonly graphitic. Local and regional fault zones that intersect the unconformity may be important features. Generally found close to basement granitic rocks with a high U clarke.

 

GENETIC MODEL: The exceptionally rich ore grades which characterize this type of deposit point to a complex and probably polygenetic origin.

Some form of very early preconcentration of U in the Archean basement rocks seems to have been important.
The hostrocks are commonly Lower Proterozoic in age, and are comprised of metamorphosed rocks derived from marginal marine and near-shore facies sedimentary rocks which may have concentrated U by syngenetic and diagenetic processes.
Although the behaviour of U under metamorphic and ultrametamorphic conditions is poorly known, it is possible that U could have been mobilized in the vicinity of Archean gneiss domes and anatectic granites and precipitated in pegmatites and stratabound deposits as non-refractory, soluable uraninite.
Supergene enrichment in paleo regoliths, that now underlie the unconformity, may have been an important process in the additional concentration of U.
Typically the overlying quartz-rich fluviatile sandstones have undergone little deformation, but are affected by normal and reverse faults that are probably re-activated basement faults. In Saskatchewan, these faults carry ore in several deposits and in others appear to have facilitated the transport of U within the cover sandstones.
Hydrothermal/diagenetic concentration of U through mixing of oxidized basinal and reduced basement fluids appear to have resulted in exceptional concentrations of U and Ni. There is a possibility that radiogenic heat developed in these extremely rich deposits may have been instrumental in heating formational fluids and in remobilizing the metals upwards above the deposit.
Diabase dikes occur in faults near some deposits and some researchers have suggested that the dikes might have provided the thermal energy that remobilized and further upgraded U concentrations. Recent age dates of the Mackenzie dikes in the Athabaska district do not support this interpretation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ASSOCIATED DEPOSIT TYPES: Sandstone-hosted U deposits (D05) are found in associated supracrustal quartz-rich arenites. Stratabound disseminated or skarn deposits, such as the Dudderidge Lake and Burbidge Lake deposits (Saskatchewan) and pegmatitic occurrences are commonly present in the metamorphosed basement rocks. In arid or semi-arid environments surficial deposits may be present in the overburden. The deposits have affinities to "Classical" U veins (I15).

 

COMMENTS: Virtually all the known unconformity-associated uranium deposits are found in the Athabasca Basin, Alligator River district and Thelon Basin. In British Columbia favourable target areas for this style of mineralization might be found within strongly metamorphosed shelf-facies Proterozoic strata near gneiss domes, particularly in plateau areas near the Cretaceous-Tertiary paleosurface. The Midnite mine, located 100 km south of Osoyoos, British Columbia, may be an unconformity-associated U deposit. The ore comprises fracture-controlled and disseminated U and alteration minerals (pitchblende, coffinite as well as autunite and other secondary minerals) within metamorphosed shelf-facies pelitic and calcareous rocks of the Precambrian Togo Formation. Production and reserves prior to closing at the Midnite mine are estimated at approximately 3.9 Mt grading 0.12% U.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: U, Ni, Co, As, Pb and Cu are good pathfinder elements which can be utilized in standard stream silt, lake bottom sediment and soil surveys. Stream and lake bottom water samples can be analyzed for U and Ra. In addition, the inert gases He and Ra can often be detected above a U-rich source in soil and soil gas surveys, as well as in groundwater and springs. In Saskatchewan, lithogeochemical signatures have been documented in Athabasca Group quartz arenites for several hundred metres directly above the deposits and in glacially dispersed boulders located "down ice" - the signature includes boron (dravite) and low, but anomalous U as well as K and/or Mg clay mineral alteration (illite and chlorite).

 

GEOPHYSICAL SIGNATURE: During early phases of exploration of the Athabasca Basin, airborne and ground radiometric surveys detected near surface uranium deposits and their glacial dispersions. Currently, deeply penetrating ground and airborne elecromagnetic surveys are used to map the graphitic argillites associated with most deposits. The complete spectrum of modern techniques (gravity, magnetic, magneto-telluric, electromagnetic, VLF-EM, induced polarization, resistivity) can be utilized to map various aspects of structure as well as hostrock and alteration mineral assemblages in the search for deep targets.

 

OTHER EXPLORATION GUIDES: Standard techniques using sensitive gamma ray scintillometers to detect mineralization directly in bedrock or in float trains in glacial till, frost boils, talus or other debris derived from U mineralization remain the most effective prospecting methods.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: Individual deposits are generally small, but can be exceedingly high-grade, up to several percent U. The median size for 36 Saskatchewan and Australian deposits is 260 000 t grading 0.42% U (Grauch and Mosier, 1986). Some deposits are exceptionally high grade such as the Key Lake Gaertner-Deilmann deposits (2.5 Mt @ 2.3% U), Cigar Lake deposits (900 000 t @ 12.2% U) and McArthur River (1.4 Mt @12.7% U).

 

ECONOMIC LIMITATIONS: Since the early 1980s, average ore grades have generally risen to exceed 0.25% U.

Problems related to the pervasively clay-altered wallrocks and presence of radon gas and other potentially dangerous elements associated with some high-grade uranium deposits in Saskatchewan have resulted in exceptionally high mining costs in some cases.

 

IMPORTANCE: The Rabbit Lake mine, opened in 1975, was the first major producer of unconformity-type ore. Since then the proportion of the world's production to come from unconformity-type deposits has increased to 33% and is expected to rise in the future.

 

SELECTED BIBLIOGRAPHY

 

ACKNOWLEDGMENTS: Nirankar Prasad and Sunil Gandhi of the Geological Survey of Canada, Larry Jones of the British Columbia Geological Survey and Jim Murphy of Uranerz Exploration reviewed the profile and provided many constructive comments.

 

Cady, J.W. and Fox, K.F. Jr. (1984): Geophysical Interpretation of the Gneiss Terrane of Northern Washington and Southern British Columbia, and its Implication for Uranium Exploration; U.S. Geological Survey, Professional Paper 1260, 29 pages.

Farstad, J. and Ayers, D.E. (1986): Midwest Uranium Deposit, Northern Saskatchewan, in Uranium Deposits of Canada, Evans, E.I., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 33, pages 178-183.

Fogwill, W.D. (1985): Canadian and Saskatchewan Uranium Deposits: Compilation, Metallogeny, Models Exploration; in Geology of Uranium Deposits, Sibbald T.I.I. and Petruk W. Editors, Canadian Institute of Mining and Metallurgy, Special Volume 32, pages 3-19.

Jones, L.D. (1990): Uranium and Thorium Occurrences in British Columbia; B.C. Ministry of Energy, Mines and Petroleum Resources, Open File 1990-32, 78 pages.

Grauch, R.I. and Mosier, Dan L. (1986): Descriptive Model of Unconformity U-Au; in Mineral Deposit Models, Cox, D. P. and Singer, D. A., Editors, United States Geological Survey, Bulletin 1693, pages 248-250.

Milne, P.C. (1979): Uranium in Washington State: Proven Deposits and Exploration Targets; The Canadian Institute of Mining and Metallurgy, Bulletin, Volume 72, pages 95-101.

Nash, J.T., Granger, H.C. and Adams, S.S. (1981): Geology and Concepts of Genesis of Important Types of Uranium Deposits; in Economic Geology, 75th Anniversary Volume, pages 63-116.

Ruzicka, Vlad (1986): Uranium deposits of the Rabbit Lake -Collins Bay area, Saskatchewan; in Uranium Deposits of Canada, Evans, E.I., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 33, pages 144-154.

Tremblay, L.P. and Ruzicka, V. (1984): Unconformity-associated Uranium; in Canadian Mineral Deposit Types: A Geological Synopsis, Eckstrand, O.R., Editor, Geological Survey of Canada,Economic Geology Report 36, page 61.

Wallis, R.H., Saracoglu, N., Brummer, J.J., and Golightly, J.P. (1986): The Geology of the McClean Uranium Deposits, Northern Saskatchewan; in Uranium Deposits of Canada, Evans, E.I., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 33, pages 193-217.

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CRYPTOCRYSTALLINE ULTRAMAFIC-HOSTED MAGNESITE VEINS


I17
by S. Paradis and G.J. Simandl
Geological Survey of Canada and British Columbia Geological Survey

 

Paradis, S. and Simandl, G.J. (1996): Cryptocrystalline Ultramafic-hosted Magnesite Veins, 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 97-100.

 

IDENTIFICATION

 

SYNONYMS: Cryptocrystalline or microcrystalline magnesite, "Kraubath-type" magnesite, "Bone magnesite", "amorphous magnesite".

 

COMMODITY: Magnesite.

 

EXAMPLES (British Columbia (MINFILE #) - Canada/International): Sunny (092O 014), Pinchi Lake (093K 065); Chalkidiky area (Greece); Kraubath (Austria); Eskisehir and Kutaya (Turkey).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Cryptocrystalline magnesite deposits are related to faults cutting ultramafic rocks. Individual deposits may consist of two styles of mineralization. Steeply dipping magnesite veins, up to several metres thick, pass gradually upward into magnesite stockworks or breccias cemented by magnesite.

 

TECTONIC SETTINGS: Typically in allochthonous serpentinized ophiolitic sequences or along structural breaks within ultramafic layered complexes; however, other settings containing ultramafic rocks are also favourable.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: The veins are emplaced along steep faults in near surface environments.

 

AGE OF MINERALIZATION: Post-date ultramafic hostrock that is Archean to Paleogene in age.

 

HOST/ASSOCIATED ROCK TYPES: Serpentinite, peridotite; other olivine-rich rocks of the typical ophiolitic sequence and layered ultramafic complexes.

 

DEPOSIT FORM: Stockworks, branching veins, single veins up to several metres in thickness, and less frequently, irregular masses. The maximum reported vertical extent is 200 m. The footwall of the deposits is commonly sharp and slickensided and coincides with a fault zone. The hangingwall of the fault contains magnesite veins and/or magnesite-cemented breccias.

 

TEXTURE/STRUCTURE: Magnesite is commonly cryptocrystalline and massive with microscopic "pinolite" texture; rarely granular, fibrous, or "cauliflower-like".

 

ORE MINERALOGY: Magnesite.

 

GANGUE MINERALOGY (Principal and subordinate): Serpentine, chlorite, talc, iron oxides, dolomite, hydromagnesite, calcite, sepiolite, quartz, opal, chalcedony and quartz in vugs.

 

ALTERATION MINERALOGY: Ultramafic rocks hosting magnesite are typically, but not always, intensely serpentinised. Alteration minerals are dolomite, quartz, montmorillonite, sepiolite, talc, goethite and deweylite.

 

WEATHERING: Varies with climatic environment, gangue mineralogy and iron content in the crystal structure of magnesite.

 

ORE CONTROLS: Tectonic boundaries or major fault breaks, secondary fault zones parallel to major breaks cutting ultramafic rocks. The large magnesite- cemented breccias are commonly located below paleoerosional or erosional surfaces. Most contacts between the magnesite and country rock are sharp and irregular.

 

GENETIC MODEL: Two hypothesis competing to explain the origin of these deposits are:

1) hypogene low-temperature, CO2-metasomatism of ultramafic rocks (Pohl, 1991):
2) low-temperature descending, meteoric waters containing biogenic CO2 and enriched in Mg2+ (Zachmann and Johannes, 1989).

 

 

 

 

 

ASSOCIATED DEPOSIT TYPES: Lateritic deposits, chromite deposits and platinum deposits occur in the same geological environment but are not genetically related. The ultramafic-hosted talc deposits (M07) may be genetically related.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: May contain above average Hg.

 

GEOPHYSICAL SIGNATURE: N/A

 

OTHER EXPLORATION GUIDES: Favourable lithologic and structural setting. Commonly underlying unconformities. Near-surface (or paleosurface) magnesite deposits may be capped by stratiform magnesite, dolomite-quartz (chalcedony) or chert zones. Some of these deposits are overlain by laterites. Boulder tracing in glaciated areas.

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE: For stockwork (upper) portions of the deposits the grades vary from 20 to 40% magnesite and reserves ranging from hundreds of thousands to several millions tonnes are typical. The deeper vein portions of these deposits have higher grades and may be almost monomineralic. A representative specimen of Greek cryptocrystalline magnesite is reported to contain 46.6 % MgO, 49.9 % CO2, 0.70 % SiO2, 1.35 % CaO, 0.85% Fe2O3 and Al2O3 combined (Harben and Bates, 1990).

 

ECONOMIC LIMITATIONS: These deposits compete for markets with sediment-hosted sparry magnesite deposits and seawater or brine-derived magnesia compounds. In the past, European refractory producers preferred cryptocrystalline magnesite over sparry magnesite, because of its higher density and lower iron, manganese and boron content. Recently this advantage was largely lost by availability of excellent quality sparry magnesite exports and by new technical developments in the refractory industry. Natural magnesite-derived compounds in general have to compete with seawater and brine-derived magnesia compounds.

 

END USES: Source of wide variety of magnesia products used mainly in refractories, cements, insulation, chemicals, fertilizers, fluxes and environmental applications.

 

IMPORTANCE: These deposits are substantially smaller and, in the case of stockwork-type portions, lower grade than sparry magnesite deposits.

 

COMMENTS: Stockworks and adjacent ultramafic hostrock are capped in some cases by sediments that may contain nodular magnesite concretions or magnesite/hydromagnesite layers and/or dolomite, quartz or chert. It is not well established if sediments are of sabkha /playa affinity or directly linked to fluids that formed stockworks and veins.

 

REFERENCES

 

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.

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

Pohl, W. (1991): Genesis of Magnesite Deposits - Models and Trends; Geologische Rundschau, Volume 79, pages 291-299.

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*  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 Vein, Breccia, and Stockwork Deposits

BC Profile # Global Examples B.C. Examples
I01 Alaska-Juneau (Alaska), Campbell, Dome(Ontario) Bralorne, Erickson, Polaris-Taku
I02 - - Scottie, Snip, Johnny Mountain, Iron Colt
I03 Ballarat (Australia), Meguma (Nova Scotia) Frasergold, Reno, Queen, Island Mountain
I04 Homestake (South Dakota) - -
I05 Elsa (Yukon), Coeur d'Alene (Idaho), Creede (Colorado) Silver Queen, Beaverdell, Silvana, Lucky Jim
I06 Nikolai (Alaska), Bruce Mines (Ontario), Butte (Montana) Davis-Keays, Churchill Copper, Bull River
 I07*   Granby Point
I08 Red Devil? (Alaska), New Almaden, New Idria (California) Pinchi, Bralorne Takla, Silverquick
I09 Becker-Cochran (Yukon), Lake George (New Brunswick), Bolivia Minto, Congress, Snowbird
I10 Matchewan (Ontario), Jbel Ighoud (Morocco), Wolfach (Germany) Parson. Brisco, Fireside
I11 St. Lawrence (Newfoundland), Mongolian fluorite belt Rock Candy, Eaglet
 I12* Pasto Bueno (Peru), Carrock Fell (England) - -
 I13* Cornwall (England), Lost River (Alaska) Duncan Lake
I14 Cobalt camp (Ontario), Erzgebirge district (Germany) - -
I15 Beaverlodge area (Saskatchewan), Schwartzwalder (Colorado) Purple Rose, Fisher, Dixie
I16 Rabbit lake, Key Lake, Cluff Lake, Midwest Lake, McClean Lake, McArthur River, Cigar Lake and Maurice Bay in the Athabasca uranium district (Saskatchewan, Canada), Lone Gull (Kiggavik) and Boomerang Lake, Thelon Basin district (Northwest Territories, Canada); Jabiluka, Ranger, Koongarra and Nabarlek, Alligator River district (Northern Territory, Australia) - -
I17 Chalkidiky area (Greece), Kraubath (Austria) Sunny, Pinchi Lake