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Ministry of Energy Mines and Responsible for Core Review

L - Porphyry

BC Profile # Deposit Type Approximate Synonyms USGS Model #
L01 Subvolcanic Cu-Ag-Au (As-Sb) Enargite Au, Transitional Au-Ag 22a/25e
L02 Plutonic-Related Au Quartz Veins Intrusion-related gold systems

- -

L03 Alkalic porphyry Cu-Au Diorite porphyry copper - -
L04 Porphyry Cu ± Mo ± Au Calcalkaline porphyry 17,20,21a1
L05 Porphyry Mo (Low F- type) Calcalkaline Mo stockwork 21b
L06 Porphyry Sn Subvolcanic tin 20a
L07 Porphyry W Stockwork W-Mo 21c*
L08 Porphyry Mo (Climax-type) Granite molybdenite 16
 L09* Porphyry-related Au Granitoid Au, Porphyry Au 20d
 

SUBVOLCANIC Cu-Au-Ag (As-Sb)


L01
by Andre Panteleyev
British Columbia Geological Survey
 

Panteleyev, A. (1995): Subvolcanic Cu-Au-Ag (As-Sb), in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 79-82.

 

IDENTIFICATION

 

SYNONYMS: Transitional, intrusion-related (polymetallic) stockwork and vein.

 

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

 

EXAMPLES (British Columbia - Canada/International): Equity Silver (093L 001); Thorn prospect (104K031, 116); Rochester District (Nevada, USA), Kori Kollo (Bolivia), the 'epithermal gold' zones at Lepanto (Philippines), parts of Recsk (Hungary) and Bor (Serbia).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Pyritic veins, stockworks and breccias in subvolcanic intrusive bodies with stratabound to discordant massive pyritic replacements, veins, stockworks, disseminations and related hydrothermal breccias in country rocks. These deposits are located near or above porphyry Cu hydrothermal systems and commonly contain pyritic auriferous polymetallic mineralization with Ag sulphosalt and other As and Sb-bearing minerals.

 

TECTONIC SETTINGS: Volcano-plutonic belts in island arcs and continental margins; continental volcanic arcs. Subvolcanic intrusions are abundant. Extensional tectonic regimes allow high-level emplacement of the intrusions, but compressive regimes are also permissive.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: Uppermost levels of intrusive systems and their adjoining fractured and permeable country rocks, commonly in volcanic terrains with eroded stratovolcanoes. Subvolcanic domes and flow-dome complexes can also be mineralized; their uppermost parts are exposed without much erosion.

 

AGE OF MINERALIZATION: Mainly Tertiary, a number of older deposits have been identified.

 

HOST/ASSOCIATED ROCK TYPES: Subvolcanic (hypabyssal) stocks, rhyodacite and dacite flow-dome complexes with fine to coarse-grained quartz-phyric intrusions are common. Dike swarms and other small subvolcanic intrusions are likely to be present. Country rocks range widely in character and age. Where coeval volcanic rocks are present, they range from andesite to rhyolite in composition and occur as flows, breccias and pyroclastic rocks with related erosion products (epiclastic rocks).

 

DEPOSIT FORM: Stockworks and closely-spaced to sheeted sets of sulphide-bearing veins in zones within intrusions and as structurally controlled and stratabound or bedding plane replacements along permeable units and horizons in hostrocks. Veins and stockworks form in transgressive hydrothermal fluid conduits that can pass into pipe-like and planar breccias. Breccia bodies are commonly tens of metres and, rarely, a few hundred metres in size. Massive sulphide zones can pass outward into auriferous pyrite-quartz-sericite veins and replacements.

 

TEXTURE/STRUCTURE: Sulphide and sulphide-quartz veins and stockworks. Open space filling and replacement of matrix in breccia units. Bedding and lithic clast replacements by massive sulphide, disseminations and veins. Multiple generations of veins and hydrothermal breccias are common. Pyrite is dominant and quartz is minor to absent in veins.

 

ORE MINERALOGY (Principal and subordinate): Pyrite, commonly as auriferous pyrite, chalcopyrite, terahedrite/tennantite; enargite/luzonite, covellite, chalcocite, bornite, sphalerite, galena, arsenopyrite, argentite, sulphosalts, gold, stibnite, molybdenite, wolframite or scheelite, pyrrhotite, marcasite, realgar,hematite, tin and bismuth minerals. Depth zoning is commonly evident with pyrite-rich deposits containing enargite near surface, passing downwards into tetrahedrite/tennantite + chalcopyrite and then chalcopyrite in porphyry intrusions at depth.

 

GANGUE MINERALOGY (Principal and subordinate): Pyrite, sericite, quartz; kaolinite, alunite, jarosite (mainly in supergene zone).

 

ALTERATION MINERALOGY (Principal and subordinate): Pyrite, sericite, quartz; kaolinite, dickite, pyrophyllite, andalusite, diaspore, corundum, tourmaline, alunite, anhydrite, barite, chalcedony, dumortierite, lazulite (variety scorzalite), rutile and chlorite. Tourmaline as schorlite (a black Fe-rich variety) can be present locally; it is commonly present in breccias with quartz and variable amounts of clay minerals. Late quartz-alunite veins may occur.

 

WEATHERING: Weathering of pyritic zones can produce limonitic blankets containing abundant jarosite, goethite and, locally, alunite.

 

GENETIC MODEL: These deposits represent a transition from porphyry copper to epithermal conditions with a blending and blurring of porphyry and epithermal characteristics. Mineralization is related to robust, evolving hydrothermal systems derived from porphyritic, subvolcanic intrusions. Vertical zoning and superimposition of different types of ores is typical due, in large part, to overlapping stages of mineralizations. Ore fluids with varying amounts of magmatic-source fluids have temperatures generally greater than those of epithermal systems, commonly in the order of 300* C and higher. Fluid salinities are also relatively high, commonly more than 10 weight per cent NaCl-equivalent and rarely in the order of 50 %, and greater.

 

ORE CONTROLS: Strongly fractured to crackled zones in cupolas and internal parts of intrusions and flow-dome complexes; along faulted margins of high-level intrusive bodies. Permeable lithologies, both primary and secondary in origin, in the country rocks. Primary controls are structural features such as faults, shearz, fractured and crackled zones and breccias. Secondary controls are porous volcanic units, bedding plane contacts and unconformities. Breccia pipes provide channelways for hydrothermal fluids originating from porphyry Cu systems and commonly carry elevated values of Au and Ag. The vein and replacement style deposits can be separated from the deeper porphyry Cu mineralization by 200 to 700 m.

 

ASSOCIATED DEPOSIT TYPES: Porphyry Cu-Au±Mo (L04); epithermal Au-Ag commonly both high-sulphidation (H04) and low-sulphidation (H05) pyrite-sericite-bearing types; auriferous quartz-pyrite veins, enargite massive sulphide also known as enargite gold.

 

COMMENTS: This deposit type is poorly defined and overall, uncommon. It is in large part stockworks and a closely spaced to sheeted sulphide vein system with local massive to disseminated replacement sulphide zones. It forms as a high- temperature, pyrite-rich, commonly tetrahderite, and rarely enargite-bearing, polymetallic affiliate of epithermal Au-Ag mineralization. Both low and high- sulphidation epithermal styles of mineralization can be present. As and Sb enrichments in ores are characteristic. If abundant gas and gas condensates evolve from the hydrothermal fluids there can be extensive acid leaching and widespread, high-level advanced argillic alteration. This type of alteration is rarely mineralized.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Elevated values of Au, Cu, Ag, As, Sb, Zn, Cd, Pb, Fe and F; at deeper levels Mo, Bi, W and locally Sn. In some deposits there is local strong enrichment in B, Co, Ba, K and depletion of Na. Both depth zoning and lateral zoning are evident.

 

GEOPHYSICAL SIGNATURE: Induced polarization to delineate pyrite zones. Magnetic surveys are useful in some cases to outline lithologic units and delineate contacts. Electromagnetic surveys can be used effectively where massive sulphide bodies are present.

 

OTHER EXPLORATION GUIDES: Association with widespread sericite-pyrite and quartz-sericite-pyrite that might be high-level leakage from buried porphyry Cu ± Au ± Mo deposits. Extensive overprinting of sericite/illite by kaolinite; rare alunite. In some deposits, high-temperature aluminous alteration minerals pyrophyllite and andalusite are present but are generally overprinted by abundant sericite and lesser kaolinite. Tourmaline and phosphate minerals can occur. There is commonly marked vertical mineralogical and geochemical depth-zoning.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: The deposits have pyritic orebodies of various types; vertical stacking and pronounced metal zoning are prevalent. Small, high-grade replacement orebodies containing tetrahedrite/tennantite, and rarely enargite, can form within larger zones of pyritization. The massive sulphide replacement ores have associated smaller peripheral, structurally controlled zones of sericitic alteration that constitute pyritic orebodies grading ~ 4 g/t gold. Similar tetrahedrite-bearing ores with bulk mineable reserves at Equity Silver were in the order of 30 Mt with 0.25% Cu and ~86 g/t Ag and 1 g/t Au. At the Recsk deposit, Hungary, shallow breccia-hosted Cu-Au ores overlie a porphyry deposit containing ~1000 Mt with 0.8 % Cu. The closely spaced pyritic fracture and vein systems at Kori Kollo, La Joya district, Bolivia contained 10 Mt oxide ore with 1.62 g/t Au and 23.6 g/t Ag and had sulphide ore reserves of 64 Mt at 2.26 g/t Au and 13.8 g/t Ag.

 

REFERENCES

 

Baksa, C., Cseh-Nemeth, J., Csillag, J., Foldessy, J. and Zelenka, T. (1980): The Recsk Porphyry and Skarn Deposit, Hungary; in European Copper Deposits, Jankovic, S. and Sillitoe, R.H., Editors, Society for Geology Applied to Mineral Deposits (SGA), Special Publication No. 1, pages 73-76.

Columba, M. and Cunningham, C.G. (1993): Geologic Model for the Mineral Deposits of the La Joya District, Oruro, Bolivia; Economic Geology, Volume 88, pages 701-708.

Cyr, J.B., Pease, R.B. and Schroeter, T.G. (1984): Geology and Mineralization at Equity Silver Mine; Economic Geology, Volume 79, pages 947-968.

Jankovic, S., Terzic. M., Aleksic, D., Karamata, S., Spasov, T., Jovanovic, M., Milicic, M., Grubiv, A. and Antonijevic, I. (1980): Metallogenic Features of Copper Deposits in the Volcano-Intrusive Complexes of the Bor District, Yugoslavia; in European Copper Deposits, Jankovic, S. and Sillitoe, R.H., Editors, Society for Geology Applied to Mineral Deposits (SGA), Special Publication No. 1, pages 42-49.

Learned, R., Allen, M.S., Andre*-Ramos, O. and Enriquez, R. (1992): A Geochemical Study of the La Joya District; U. S. Geological Survey, Bulletin 1975, pages 25-46.

Long, K., Ludington, S., du Bray, E., Andre*-Ramos, O. and McKee, E.H. (1992): Geology and Mineral Deposits of the La Joya District, Bolivia, SEG Newsletter, Society of Economic Geologists, Volume 10, Number 1, pages 13-16.

Sillitoe, R.H. (1983): Enargite-bearing Massive Sulfide Deposits High in Porphyry Copper Systems; Economic Geology, Volume 78, pages 348-352.

Sillitoe, R.H. (1992): The Porphyry-epithermal Transition; in Magmatic Contributions To Hydrothermal Systems, Geological Survey of Japan, Report No. 279, pages 156-160.

Sillitoe, R.H. (1994): Erosion and Collapse of Volcanoes; Cuases of Telescoping in Intrusion-centered Ore Deposits, Geology, Volume 22, pages 945-948.

Vikre, P.G. (1981): Silver Mineralization in the Rochester District, Pershing County, Nevada; Economic Geology, Volume 76, pages 580-609.

 
 

PLUTONIC-RELATED AU QUARTZ VEINS

L02
by David V. Lefebure and Craig HartBritish Columbia Geological Survey

 

http://www.geology.gov.yk.ca/pdf/l02_plutonic_related_au_quartz_veins_and_veinlets.pdf

 

PORPHYRY Cu-Au: ALKALIC

L03
by Andre Panteleyev
British Columbia Geological Survey
 

Panteleyev, A. (1995): Porphyry Cu-Au: Alkalic, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 83-86.

 

IDENTIFICATION

 

SYNONYMS: Porphyry copper, porphyry Cu-Au, diorite porphyry copper.

 

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

 

EXAMPLES (British Columbian - Canada/International): Iron Mask batholith deposits - Afton (092INE023), Ajax (092INE012, 013), Mt. Polley (Cariboo Bell, 093A008), Mt. Milligan (093N196, 194), Copper Mt./Ingerbelle (092HSE001, 004), Galore Creek (104G 090), Lorraine (093N 002); Ok Tedi (Papua New Guinea); Tai Parit and Marian? (Philippines).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Stockworks, veinlets and disseminations of pyrite, chalcopyrite, bornite and magnetite occur in large zones of economically bulk-mineable mineralization in or adjoining porphyritic intrusions of diorite to syenite composition. The mineralization is spatially, temporally and genetically associated with hydrothermal alteration of the intrusive bodies and hostrocks.

 

TECTONIC SETTING(S): In orogenic belts at convergent plate boundaries, commonly oceanic volcanic island arcs overlying oceanic crust. Chemically distinct magmatism with alkalic intrusions varying in composition from gabbro, diorite and monzonite to nepheline syenite intrusions and coeval shoshonitic volcanic rocks, takes place at certain times in segments of some island arcs. The magmas are introduced along the axis of the arc or in cross-arc structures that coincide with deep-seated faults. The alkalic magmas appear to form where there is slow subduction in steeply dipping, tectonically thickened lithospheric slabs, possibly when polarity reversals (or `flips') take place in the subduction zones. In British Columbia all known deposits are found in Quesnellia and Stikinia terranes.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: High level (epizonal) stock emplacement levels in magmatic arcs, commonly oceanic volcanic island arcs with alkalic (shoshonitic) basic flows to intermediate and felsic pyroclastic rocks. Commonly the high-level stocks and related dikes intrude their coeval and cogenetic volcanic piles.

 

AGE OF MINERALIZATION: Deposits in the Canadian Cordillera are restricted to the Late Triassic/Early Jurassic (215-180 Ma) with seemingly two clusters around 205-200 and ~ 185 Ma. In southwest Pacific island arcs, deposits are Tertiary to Quaternary in age.

 

HOST/ASSOCIATED ROCK TYPES: Intrusions range from fine through coarse-grained, equigranular to coarsely porphyritic and, locally, pegmatitic high-level stocks and dike complexes. Commonly there is multiple emplacement of successive intrusive phases and a wide variety of breccias. Compositions range from (alkalic) gabbro to syenite. The syenitic rocks vary from silica- undersaturated to saturated compositions. The most undersaturated nepheline normative rocks contain modal nepheline and, more commonly, pseudoleucite. The silica-undersaturated suites are referred to as nepheline alkalic whereas rocks with silica near-saturation, or slight silica over saturation, are termed quartz alkalic (Lang et al., 1993). Coeval volcanic rocks are basic to intermediate alkalic varieties of the high-K basalt and shoshonite series and rarely phonolites.

 

DEPOSIT FORM: Stockworks and veinlets, minor disseminations and replacements throughout large areas of hydrothermally altered rock, commonly coincident wholly or in part with hydrothermal or intrusion breccias. Deposit boundaries are determined by economic factors that outline ore zones within larger areas of low-grade, laterally zoned mineralization.

 

TEXTURE/STRUCTURE: Veinlets and stockworks; breccia, sulphide and magnetite grains in fractures and along fracture selvages; disseminated sulphides as interstitial or grain and lithic clast replacements. Hydrothermally altered rocks can contain coarse-grained assemblages including feldspathic and calcsilicate replacements ('porphyroid' textures) and open space filling with fine to coarse, granular and rarely pegmatitic textures.

 

ORE MINERALOGY [Principal and subordinate]: Chalcopyrite, pyrite and magnetite; bornite, chalcocite and rare galena, sphalerite, tellurides, tetrahderite, gold and silver. Pyrite is less abundant than chalcopyrite in ore zones.

 

GANGUE MINERALOGY: Biotite, K-feldspar and sericite; garnet, clinopyroxene (diopsidic) and anhydrite. Quartz veins are absent but hydrothermal magnetite veinlets are abundant.

 

ALTERATION MINERALOGY: Biotite, K-feldspar, sericite, anhydrite/gypsum, magnetite, hematite, actinolite, chlorite, epidote and carbonate. Some alkalic systems contain abundant garnet including the Ti-rich andradite variety - melanite, diopside, plagioclase, scapolite, prehnite, pseudoleucite and apatite; rare barite, fluorite, sodalite, rutile and late-stage quartz. Central and early formed potassic zones, with K-feldspar and generally abundant secondary biotite and anhydrite, commonly coincide with ore. These rocks can contain zones with relatively high-temperature calcsilicate minerals diopside and garnet. Outward there can be flanking zones in basic volcanic rocks with abundant biotite that grades into extensive, marginal propylitic zones. The older alteration assemblages can be overprinted by phyllic sericite-pyrite and, less commonly, sericite-clay-carbonate-pyrite alteration. In some deposits, generally at depth in silica-saturated types, there can be either extensive or local central zones of sodic alteration containing characteristic albite with epidote, pyrite, diopside, actinolite and rarer scapolite and prehnite.

 

ORE CONTROLS: Igneous contacts, both internal between intrusive phases and external with wallrocks; cupolas and the uppermost, bifurcating parts of stocks, dike swarms and volcanic vents. Breccias, mainly early formed intrusive and hydrothermal types. Zones of most intensely developed fracturing give rise to ore-grade vein stockworks.

 

ASSOCIATED DEPOSIT TYPES: Skarn copper (K01); Au-Ag and base metal bearing mantos (M01, M04), replacements and breccias in carbonate and non-carbonate rocks; magnetite-apatite breccias (D07); epithermal Au-Ag : both high and low sulphidation types (H04, H05) and alkalic, Te and F-rich epithermal deposits (H08); auriferous and polymetallic base metal quartz and quartz-carbonate veins (I01, I05); placer Au (C01, C02).

 

COMMENTS: Subdivision of porphyry deposits is made on the basis of metal content, mainly ratios between Cu, Au and Mo. This is a purely arbitrary, economically based criterion; there are few differences in the style of mineralization between the deposits. Differences in composition between the hostrock alkalic and calcalkalic intrusions and subtle, but significant, differences in alteration mineralogy and zoning patterns provide fundamental geologically based contrasts between deposit model types. Porphyry copper deposits associated with calcalkaline hostrocks are described in mineral deposit profile L04.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Alkalic cupriferous systems do not contain economically recoverable Mo (< 100 ppm) but do contain elevated Au (> 0.3 g/t) and Ag (>2 g/t). Cu grades vary widely but commonly exceed 0.5 % and rarely 1 %. Many contain elevated Ti, V, P, F, Ba, Sr, Rb, Nb, Te, Pb, Zn, PGE and have high CO2 content. Leaching and supergene enrichment effects are generally slight and surface outcroppings normally have little of the copper remobilized. Where present, secondary minerals are malachite, azurite, lesser copper oxide and rare sulphate minerals; in some deposits native copper is economically significant (e.g. Afton, Kemess).

 

GEOPHYSICAL SIGNATURE: Ore zones, particularly those with high Au content, are frequently found in association with magnetite-rich rocks and can be located by magnetic surveys. Pyritic haloes surrounding cupriferous rocks respond well to induced polarization surveys. The more intensely hydrothermally altered rocks produce resistivity lows.

 

OTHER EXPLORATION GUIDES: Porphyry deposits are marked by large-scale, markedly zoned metal and alteration assemblages. Central parts of mineralized zones appear to haver higher Au/Cu ratios than the margins. The alkalic porphyry Cu deposits are found exclusively in Later Triassic and Early Jurassic volcanic arc terranes in which emergent subaerial rocks are present. The presence of hydrothermally altered clasts in coarse pyroclastic deposits can be used to locate mineralized intrusive centres.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE:

* Worldwide according to Cox and Singer (U.S. Geological Survey Open File Report 88-46, 1988) 20 typical porphyry Cu-Au deposits, including both calcalkaline and some alkalic types, contain on average:
160 Mt with 0.55 % Cu, 0.003 % Mo, 0.38 g/t Au and 1.7 g/t Ag.

* British Columbia alkalic porphyry deposits range from <10 to >300 Mt and contain from 0.2 to 1.5 % Cu, 0.2 to 0.6 g/t Au and >2 g/t Ag; Mo contents are negligible. Median values for 22 British Columbia deposits with reported reserves (with a heavy weighting from a number of small deposits in the Iron Mask batholith) are: 15.5 Mt with 0.58 % Cu, 0.3 g/t Au and >2 g/t Ag.

 

 

 

 

 

 

 

 

 

 

END USES: Production of chalcopyrite or chalcopyrite-bornite concentrates with significant Au credits.

 

IMPORTANCE: Porphyry deposits contain the largest reserves of Cu and close to 50 % of Au reserves in British Columbia; alkalic porphyry systems contain elevated Au values.

 

REFERENCES

 

Barr, D.A., Fox, P.E., Northcote, K.E. and Preto, V.A. (1976): The Alkaline Suite Porphyry Deposits - A Summary; in Porphyry Deposits of the Canadian Cordillera, Sutherland Brown, A. Editor, Canadian Institute of Mining and Metallurgy, Special Volume 15, pages 359-367.

Lang, J.R., Stanley, C.R. and Thompson, H.F.H. (1993): A Subdivision of Alkalic Porphyry Cu-Au Deposits into Silica-saturated and Silica-undersaturated Subtypes; in Porphyry Copper-Gold Systems of British Columbia, Mineral Deposit Research Unit, University of British Columbia, Annual Technical Report - Year 2, pages 3.2-3.14.

McMillan, W.J. (1991): Porphyry Deposits in the Canadian Cordillera; in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, B. C. Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, pages 253-276.

McMillan, W.J. and Panteleyev, A. (1988): Porphyry Copper Deposits; in Ore Deposit Models, Roberts, R.G. and Sheahan, P.A, Editors, Geoscience Canada, Reprint Series 3, pages 45-58.

Mutschler, F.E. and Mooney, T.C. (1993): Precious Metal Deposits Related to Alkaline Igneous Rocks - Provisional Classification, Grade-Tonnage Data, and Exploration Frontiers; IUGS/UNESCO Conference on Deposit Modeling, Ottawa, 1990, Proceedings Volume, Geological Association of Canada, Special Paper 40, pages 479-520.

Sutherland Brown, A., Editor, (1976): Porphyry Deposits of the Canadian Cordillera; Canadian Institute of Mining and Metallurgy, Special Volume 15, 510 pages.

 
 

PORPHYRY Cu+/-Mo+/-Au


L04
by Andre Panteleyev
British Columbia Geological Survey
 

Panteleyev, A. (1995): Porphyry Cu+/-Mo+/-Au, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 87-92.

 

IDENTIFICATION

 

SYNONYM: Calcalkaline porphyry Cu, Cu-Mo, Cu-Au.

 

COMMODITIES (BYPRODUCTS): Cu, Mo and Au are generally present but quantities range from insufficient for economic recovery to major ore constituents. Minor Ag in most deposits; rare recovery of Re from Island Copper mine.

 

EXAMPLES (British Columbia - Canada/International):

Volcanic type deposits (Cu + Au * Mo) - Fish Lake (092O 041), Kemess (094E 021,094), Hushamu (EXPO, 092L 240), Red Dog (092L 200), Poison Mountain (092O 046), Bell (093M 001), Morrison (093M 007), Island Copper (092L 158); Dos Pobres (USA); Far Southeast (Lepanto/Mankayan), Dizon, Guianaong, Taysan and Santo Thomas II (Philippines), Frieda River and Panguna (Papua New Guinea).
Classic deposits (Cu + Mo * Au) - Brenda (092HNE047), Berg (093E 046), Huckleberrry (093E 037), Schaft Creek (104G 015); Casino (Yukon, Canada), Inspiration, Morenci, Ray, Sierrita-Experanza, Twin Buttes, Kalamazoo and Santa Rita (Arizona, USA), Bingham (Utah, USA),El Salvador, (Chile), Bajo de la Alumbrera (Argentina).
Plutonic deposits (Cu * Mo) - Highland Valley Copper (092ISE001,011,012,045), Gibraltar (093B 012,007), Catface (092F 120); Chuquicamata, La Escondida and Quebrada Blanca (Chile).

 

 

 

 

 

 

 

 

 

 

 

 

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Stockworks of quartz veinlets, quartz veins, closely spaced fractures and breccias containing pyrite and chalcopyrite with lesser molybdenite, bornite and magnetite occur in large zones of economically bulk-mineable mineralization in or adjoining porphyritic intrusions and related breccia bodies. Disseminated sulphide minerals are present, generally in subordinate amounts. The mineralization is spatially, temporally and genetically associated with hydrothermal alteration of the hostrock intrusions and wallrocks.

 

TECTONIC SETTINGS: In orogenic belts at convergent plate boundaries, commonly linked to subduction-related magmatism. Also in association with emplacement of high-level stocks during extensional tectonism related to strike-slip faulting and back-arc spreading following continent margin accretion.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: High-level (epizonal) stock emplacement levels in volcano-plutonic arcs, commonly oceanic volcanic island and continent-margin arcs. Virtually any type of country rock can be mineralized, but commonly the high-level stocks and related dikes intrude their coeval and cogenetic volcanic piles.

 

AGE OF MINERALIZATION: Two main periods in the Canadian Cordillera: the Triassic/Jurassic (210-180 Ma) and Cretaceous/Tertiary (85-45 Ma). Elsewhere deposits are mainly Tertiary, but range from Archean to Quaternary.

 

HOST/ASSOCIATED ROCK TYPES: Intrusions range from coarse-grained phaneritic to porphyritic stocks, batholiths and dike swarms; rarely pegmatitic. Compositions range from calcalkaline quartz diorite to granodiorite and quartz monzonite. Commonly there is multiple emplacement of successive intrusive phases and a wide variety of breccias. Alkalic porphyry Cu-Au deposits are associated with syenitic and other alkalic rocks and are considered to be a a distinct deposit type (see model L03).

 

DEPOSIT FORM: Large zones of hydrothermally altered rock contain quartz veins and stockworks, sulphide-bearing veinlets; fractures and lesser disseminations in areas up to 10 km2 in size, commonly coincident wholly or in part with hydrothermal or intrusion breccias and dike swarms. Deposit boundaries are determined by economic factors that outline ore zones within larger areas of low-grade, concentrically zoned mineralization. Cordilleran deposits are commonly subdivided according to their morphology into three classes - classic, volcanic and plutonic (see Sutherland Brown, 1976; McMillan and Panteleyev, 1988):

* Volcanic type deposits (e.g. Island Copper) are associated with multiple intrusions in subvolcanic settings of small stocks, sills, dikes and diverse types of intrusive breccias. Reconstruction of volcanic landforms, structures, vent-proximal extrusive deposits and subvolcanic intrusive centres is possible in many cases, or can be inferred. Mineralization at depths of 1 km, or less, is mainly associated with breccia development or as lithologically controlled preferential replacement in hostrocks with high primary permeability. Propylitic alteration is widespread and generally flanks early, centrally located potassic alteration; the latter is commonly well mineralized. Younger mineralized phyllic alteration commonly overprints the early mineralization. Barren advanced argillic alteration is rarely present as a late, high-level hydrothermal carapace.
* Classic deposits (e.g., Berg) are stock related with multiple emplacements at shallow depth (1 to 2 km) of generally equant, cylindrical porphyritic intrusions. Numerous dikes and breccias of pre, intra, and post-mineralization age modify the stock geometry. Orebodies occur along margins and adjacent to intrusions as annular ore shells. Lateral outward zoning of alteration and sulphide minerals from a weakly mineralized potassic/propylitic core is usual. Surrounding ore zones with potassic (commonly biotite-rich) or phyllic alteration contain molybdenite * chalcopyrite, then chalcopyrite and a generally widespread propylitic, barren pyritic aureole or 'halo'.
* Plutonic deposits (e.g., the Highland Valley deposits) are found in large plutonic to batholithic intrusions immobilized at relatively deep levels, say 2 to 4 km. Related dikes and intrusive breccia bodies can be emplaced at shallower levels. Hostrocks are phaneritic coarse grained to porphyritic. The intrusions can display internal compositional differences as a result of differentiation with gradational to sharp boundaries between the different phases of magma emplacement. Local swarms of dikes, many with associated breccias, and fault zones are sites of mineralization. Orebodies around silicified alteration zones tend to occur as diffuse vein stockworks carrying chalcopyrite, bornite and minor pyrite in intensely fractured rocks but, overall, sulphide minerals are sparse. Much of the early potassic and phyllic alteration in central parts of orebodies is restricted to the margins of mineralized fractures as selvages. Later phyllic-argillic alteration forms envelopes on the veins and fractures and is more pervasive and widespread. Propylitic alteration is widespread but unobtrusive and is indicated by the presence of rare pyrite with chloritized mafic minerals, saussuritized plagioclase and small amounts of epidote.

 

TEXTURE/STRUCTURE: Quartz, quartz-sulphide and sulphide veinlets and stockworks; sulphide grains in fractures and fracture selvages. Minor disseminated sulphides commonly replacing primary mafic minerals. Quartz phenocrysts can be partially resorbed and overgrown by silica.

 

ORE MINERALOGY (Principal and subordinate): Pyrite is the predominant sulphide mineral; in some deposits the Fe oxide minerals magnetite, and rarely hematite, are abundant. Ore minerals are chalcopyrite; molybdenite, lesser bornite and rare (primary) chalcocite. Subordinate minerals are tetrahedrite/tennantite, enargite and minor gold , electrum and arsenopyrite. In many deposits late veins commonly contain galena and sphalerite in a gangue of quartz, calcite and barite.

 

GANGUE MINERALOGY (Principal and subordinate): Gangue minerals in mineralized veins are mainly quartz with lesser biotite, sericite, K-feldspar, magnetite, chlorite, calcite, epidote, anhydrite and tourmaline. Many of these minerals are also pervasive alteration products of primary igneous mineral grains.

 

ALTERATION MINERALOGY: Quartz, sericite, biotite, K-feldspar, albite, anhydrite/gypsum, magnetite, actinolite, chlorite, epidote, calcite, clay minerals, tourmaline. Early formed alteration can be overprinted by younger assemblages. Central and early formed potassic zones (K-feldspar and biotite) commonly coincide with ore. This alteration can be flanked in volcanic hostrocks by biotite-rich rocks that grade outward into propylitic rocks. The biotite is a fine-grained, 'shreddy' looking secondary mineral that is commonly referred to as an early developed biotite (EDB) or a 'biotite hornfels'. These older alteration assemblages in cupriferous zones can be partially to completely overprinted by later biotite and K-feldspar and then phyllic (quartz-sericite-pyrite) alteration, less commonly argillic, and rarely, in the uppermost parts of some ore deposits, advanced argillic alteration (kaolinite-pyrophyllite).

 

WEATHERING: Secondary (supergene) zones carry chalcocite, covellite and other Cu*2S minerals (digenite, djurleite, etc.), chrysocolla, native copper and copper oxide, carbonate and sulphate minerals. Oxidized and leached zones at surface are marked by ferruginous 'cappings' with supergene clay minerals, limonite (goethite, hematite and jarosite) and residual quartz.

 

ORE CONTROLS: Igneous contacts, both internal between intrusive phases and external with wallrocks; cupolas and the uppermost, bifurcating parts of stocks, dike swarms. Breccias, mainly early formed intrusive and hydrothermal types. Zones of most intensely developed fracturing give rise to ore-grade vein stockworks, notably where there are coincident or intersecting multiple mineralized fracture sets.

 

ASSOCIATED DEPOSIT TYPES: Skarn Cu (K01), porphyry Au (K02), epithermal Au-Ag in low sulphidation type (H05) or epithermal Cu-Au-Ag as high-sulphidation type enargite-bearing veins (L01), replacements and stockworks; auriferous and polymetallic base metal quartz and quartz-carbonate veins (I01, I05), Au-Ag and base metal sulphide mantos and replacements in carbonate and non- carbonate rocks (M01, M04), placer Au (C01, C02).

 

COMMENTS: Subdivision of porphyry copper deposits can be made on the basis of metal content, mainly ratios between Cu, Mo and Au. This is a purely arbitrary, economically based criterion, an artifact of mainly metal prices and metallurgy. There are few differences in the style of mineralization between deposits although the morphology of calcalkaline deposits does provide a basis for subdivision into three distinct subtypes - the 'volcanic, classic, and plutonic' types. A fundamental contrast can be made on the compositional differences between calcalkaline quartz-bearing porphyry copper deposits and the alkalic (silica undersaturated) class. The alkalic porphyry copper deposits are described in a separate model - L03.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Calcalkalic systems can be zoned with a cupriferous (* Mo) ore zone having a ‘barren’, low-grade pyritic core and surrounded by a pyritic halo with peripheral base and precious metal-bearing veins. Central zones with Cu commonly have coincident Mo, Au and Ag with possibly Bi, W, B and Sr. Peripheral enrichment in Pb, Zn, Mn, V, Sb, As, Se, Te, Co, Ba, Rb and possibly Hg is documented. Overall the deposits are large-scale repositories of sulphur, mainly in the form of metal sulphides, chiefly pyrite.

 

GEOPHYSICAL SIGNATURE: Ore zones, particularly those with higher Au content, can be associated with magnetite-rich rocks and are indicated by magnetic surveys. Alternatively the more intensely hydrothermally altered rocks, particularly those with quartz-pyrite-sericite (phyllic) alteration produce magnetic and resistivity lows. Pyritic haloes surrounding cupriferous rocks respond well to induced polarization (I.P.) surveys but in sulphide-poor systems the ore itself provides the only significant IP response.

 

OTHER EXPLORATION GUIDES: Porphyry deposits are marked by large-scale, zoned metal and alteration assemblages. Ore zones can form within certain intrusive phases and breccias or are present as vertical 'shells' or mineralized cupolas around particular intrusive bodies. Weathering can produce a pronounced vertical zonation with an oxidized, limonitic leached zone at surface (leached capping), an underlying zone with copper enrichment (supergene zone with secondary copper minerals) and at depth a zone of primary mineralization (the hypogene zone).

 

ECONOMIC FACTORS

 

TYPICAL GRADE AND TONNAGE:

Worldwide according Cox and Singer (1988) based on their subdivision of 55 deposits into subtypes according to metal ratios, typical porphyry Cu deposits contain (median values): Porphyry Cu-Au: 160 Mt with 0.55 % Cu, 0.003 % Mo, 0.38 g/t Au and 1.7 g/t Ag. Porphyry Cu-Au-Mo: 390 Mt with 0.48 % Cu, 0.015 % Mo, 0.15 g/t Au and 1.6 g/t Ag. Porphyry Cu-Mo: 500 Mt with 0.41 % Cu, 0.016 % Mo, 0.012 g/t Au and 1.22 g/t Ag.
A similar subdivision by Cox (1986) using a larger data base results in: Porphyry Cu: 140 Mt with 0.54 %Cu, <0.002 % Mo, <0.02g/t Au and <1 g/t Ag. Porphyry Cu-Au: 100 Mt with 0.5 %Cu, <0.002 % Mo, 0.38g/t Au and 1g/t Ag. (This includes deposits from the British Columbia alkalic porphyry class, B.C. model L03.) Porphyry Cu-Mo: 500 Mt with 0.42 % Cu, 0.016 % Mo, 0.012 g/t Au and 1.2 g/t Ag.
British Columbia porphyry Cu * Mo ± Au deposits range from <50 to >900 Mt with commonly 0.2 to 0.5 % Cu, <0.1 to 0.6 g/t Au, and 1 to 3 g/t Ag. Mo contents are variable from negligible to 0.04 % Mo. Median values for 40 B.C. deposits with reported reserves are: 115 Mt with 0.37 % Cu, *0.01 % Mo, 0.3g /t Au and 1.3 g/t Ag.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ECONOMIC LIMITATIONS: Mine production in British Columbia is from primary (hypogene) ores. Rare exceptions are Afton mine where native copper was recovered from an oxide zone, and Gibraltar and Bell mines where incipient supergene enrichment has provided some economic benefits.

 

END USES: Porphyry copper deposits produce Cu and Mo concentrates, mainly for international export.

 

IMPORTANCE: Porphyry deposits contain the largest reserves of Cu, significant Mo resources and close to 50 % of Au reserves in British Columbia.

 

REFERENCES

 

Beane, R.E. and Titley, S.R. (1981): Porphyry Copper Deposits Part II. Hydrothermal Alteration and Mineralization; in 75th Anniversary Volume, Economic Geology, pages 235-269.

Cox, D.P. (1986): Descriptive Model of Porphyry Cu, also Porphyry Cu-Au and Porphyry Cu-Mo; in Mineral Deposit Models; United States Geological Survey, Bulletin 1693, pages 76-81, also pages 110-114 and 115-119.

Cox, D.P. and Singer, D.A. (1988): Distribution of Gold in Porphyry Copper Deposits; U.S. Geological Survey, Open File Report 88-46, 23 pages.

Gustafson, L.B. and Hunt, J.P. (1975 ): The Porphyry Copper Deposit at El Salvador, Chile; Economic Geology, Volume 70, pages 857-912.

Lowell, J.D. and Guilbert, J.M. (1970): Lateral and Vertical Alteration- Mineralization Zoning in Porphyry Ore Deposits; Economic Geology, Volume 65, pages 373-408.

McMillan, W.J. (1991): Porphyry Deposits in the Canadian Cordillera; in Ore Deposits, Tectonics and Metallogeny in the Canadian Cordillera, B. C. Ministry of Energy, Mines and Petroleum Resources, Paper 1991-4, pages 253-276.

McMillan, W.J. and Panteleyev, A. (1988): Porphyry Copper Deposits; in Ore Deposit Models, Roberts, R.G. and Sheahan, P.A., Editors, Geoscience Canada Reprint Series 3, Geological Association of Canada, pages 45-58; also in Geoscience Canada, Volume 7, Number 2, pages 52-63.

Schroeter, T.G., Editor (1995): Porphyry Copper Deposits of the Northwestern Cordillera of North America; Canadian Institute of Mining, Metallurgy and Petroleum, Special Volume 46, in preparation.

Sutherland Brown, A., Editor, (1976): Porphyry Deposits of the Canadian Cordillera; Canadian Institute of Mining and Metallurgy, Special Volume 15, 510 pages.

Titley, S.R. (1982): Advances in Geology of the Porphyry Copper Deposits, Southwestern North America; The University of Arizona Press, Tucson, 560 pages.

Titley, S.R. and Beane, R.E. (1981): Porphyry Copper Deposits Part I. Geologic Settings, Petrology, and Tectogenesis, in 75th Anniversary Volume, Economic Geology, pages 214-234.

 
 

PORPHYRY Mo (LOW-F-TYPE)


L05
by W. David Sinclair
Geological Survey of Canada, Ottawa
 

Sinclair, W.D. (1995): Porphyry Mo (Low-F-type), in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 93-96.

 

IDENTIFICATION

 

SYNONYMS: Calcalkaline Mo stockwork; Granite-related Mo; Quartz-monzonite Mo.

 

COMMODITIES (BYPRODUCTS): Mo (Cu, W)

 

EXAMPLES (British Columbia - Canada/International): Endako (093K 006), Boss Mountain (093A 001), Kitsault (103P 120), Adanac (104N 052), Carmi (082ESW029), Bell Moly (103P 234), Red Bird (093E 026), Storie Moly (104P 069), Trout Lake (082KNW087); Red Mountain (Yukon, Canada), Quartz Hill (Alaska, USA), Cannivan (Montana, USA), Thompson Creek (Idaho, USA), Compaccha (Peru), East Kounrad (Russia), Jinduicheng (China).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Stockwork of molybdenite-bearing quartz veinlets and fractures in intermediate to felsic intrusive rocks and associated country rocks. Deposits are low grade but large and amenable to bulk mining methods.

 

TECTONIC SETTING(S): Subduction zones related to arc-continent or continent-continent collision.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: High-level to subvolcanic felsic intrusive centres; multiple stages of intrusion are common.

 

AGE OF MINERALIZATION: Archean (e.g. Setting Net Lake, Ontario) to Tertiary; Mesozoic and Tertiary examples are more common.

 

HOST/ASSOCIATED ROCK TYPES: All kinds of rocks may be hostrocks. Tuffs or other extrusive volcanic rocks may be associated with deposits related to subvolcanic intrusive rocks. Genetically related intrusive rocks range from granodiorite to granite and their fine-grained equivalents, with quartz monzonite most common: they are commonly porphyritic. The intrusive rocks are characterized by low F contents (generally <0.1 % F) compared to intrusive rocks associated with Climax-type porphyry Mo deposits.

 

DEPOSIT FORM: Deposits vary in shape from an inverted cup, to roughly cylindrical, to highly irregular. They are typically hundreds of metres across and range from tens to hundreds of metres in vertical extent.

 

TEXTURE/STRUCTURE: Ore is predominantly structurally controlled; mainly stockworks of crosscutting fractures and quartz veinlets, also veins, vein sets and breccias.

 

ORE MINERALOGY (Principal and subordinate): Molybdenite is the principal ore mineral; chalcopyrite, scheelite, and galena are generally subordinate.

 

GANGUE MINERALOGY: Quartz, pyrite, K-feldspar, biotite, sericite, clays, calcite and anhydrite.

 

ALTERATION MINERALOGY: Alteration mineralogy is similar to that of porphyry Cu deposits. A core zone of potassic and silicic alteration is characterized by hydrothermal K-feldspar, biotite, quartz and, in some cases, anhydrite. K-feldspar and biotite commonly occur as alteration selvages on mineralized quartz veinlets and fractures but may be pervasive in areas of intense fracturing and mineralization. Phyllic alteration typically surrounds and may be superimposed to various degrees on the potassic-silicic core; it consists mainly of quartz, sericite and carbonate. Phyllic alteration is commonly pervasive and may be extensive. Propylitic alteration consisting mainly of chlorite and epidote may extend for hundreds of metres beyond the zones of potassic-silicic and phyllic alteration. Zones of argillic alteration, where present, are characterized by clay minerals such as kaolinite and are typically overprinted on the other types of alteration; distribution of argillic alteration is typically irregular.

 

WEATHERING: Oxidation of pyrite produces limonitic gossans; oxidation of molybdenite produces yellow ferrimolybdite.

 

ORE CONTROLS: Quartz veinlet and fracture stockwork zones superimposed on intermediate to felsic intrusive rocks and surrounding country rocks; multiple stages of mineralization commonly present.

 

GENETIC MODEL: Magmatic-hydrothermal. Large volumes of magmatic, highly saline aqueous fluids under pressure strip Mo and other ore metals from temporally and genetically related magma. Multiple stages of brecciation related to explosive fluid pressure release from the upper parts of small intrusions result in deposition of ore and gangue minerals in crosscutting fractures, veinlets and breccias in the outer carapace of the intrusions and in associated country rocks. Incursion of meteoric water during waning stages of the magmatic-hydrothermal system may result in late alteration of the hostrocks, but does not play a significant role in the ore-forming process.

 

ASSOCIATED DEPOSIT TYPES: Ag-Pb-Zn veins (I05), Mo-bearing skarns (K07) may be present.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Mo, Cu, W and F may be anomalously high in hostrocks close to and overlying mineralized zones; anomalously high levels of Pb, Zn and Ag occur in peripheral zones as much as several kilometres distant. Mo, W, F, Cu, Pb, Zn and Ag may be anomalously high in stream sediments. Mo, W and Pb may be present in heavy mineral concentrates.

 

GEOPHYSICAL SIGNATURE: Magnetic anomalies may reflect presence of pyrrhotite or magnetite in hornfels zones. Radiometric surveys may be used to outline anomalous K in altered and mineralized zones. Induced polarization and resistivity surveys may be used to outline high-pyrite alteration zones.

 

OTHER EXPLORATION GUIDES: Limonitic alteration of pyrite can result in widespread gossan zones. Yellow ferrimolybdite may be present in oxidized zones. Ag-Pb-Zn veins may be present in peripheral zones.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Typical size is 100 Mt at 0.1 to 0.2 % Mo. The following figures are for production plus reserves.

Endako (B.C.): 336 Mt at 0.087 % Mo;
Boss Mountain (B.C.): 63 Mt. at 0.074 % Mo;
Kitsault (B.C.): 108 Mt at 0.115 % Mo;
Lucky Ship (B.C.): 14 Mt at 0.090 % Mo;
Adanac (B.C.): 94 Mt at 0.094 % Mo;
Carmi (B.C.): 34 Mt at 0.091 % Mo;
Mount Haskin (B.C.): 12 Mt at 0.090 % Mo;
Bell Moly (B.C.): 32 Mt at 0.066 % Mo;
Red Bird (B.C.): 34 Mt at 0.108 % Mo;
Storie Moly (B.C.): 101 Mt at 0.078 % Mo;
Trout Lake (B.C.): 50 Mt at 0.138 % Mo;
Glacier Gulch (B.C.): 125 Mt at 0.151 % Mo;
Red Mountain (Yukon): 187 Mt at 0.100 % Mo;
Quartz Hill (Alaska): 793 Mt at 0.091 % Mo;
Thompson Creek (Idaho): 181 Mt at 0.110 % Mo;
Compaccha (Peru): 100 Mt at 0.072 % Mo;
East Kounrad (Russia): 30 Mt at 0.150 % Mo.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IMPORTANCE: Porphyry Mo deposits associated with low-F felsic intrusive rocks have been an important source of world molybdenum production. Virtually all of Canada’s Mo production comes from these deposits and from porphyry Cu-Mo deposits.

 

REFERENCES

 

Boyle, H.C. and Leitch, C.H.B., (1983): Geology of the Trout Lake Molybdenum Deposit, B.C.; Canadian Institute of Mining and Metallurgy, Bulletin, Volume 76, No. 849, pages 115-124.

Brown, P. and Kahlert, B. (1986): Geology and Mineralization of the Red Mountain Porphyry Molybdenum Deposit, South-central Yukon; in Mineral Deposits of Northern Cordillera, Morin, J.A., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 37, pages 288-297.

Carten, R.B., White, W.H. and Stein, H.J. (in press): High-grade Granite-related Mo Systems; Classification and Origin; 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 521-554.

Kirkham, R.V. and Sinclair, W.D. (1984): Porphyry Copper, Molybdenum, Tungsten; in Canadian Mineral Deposit Types; A Geological Synopsis; Geological Survey of Canada, Economic Geology Report 36, pages 51-52.

Kirkham, R.V., McCann, C., Prasad, N., Soregaroli, A.E., Vokes, F.M. and Wine, G. (1982): Molybdenum in Canada, Part 2: MOLYFILE -- An index-level computer file of molybdenum deposits and occurrences in Canada; Geological Survey of Canada, Economic Geology Report 33, pages 208.

Mutschler, F.E., Wright, E.G., Ludington, S. and Abbott, J. (1981): Granite Molybdenite Systems; Economic Geology, v. 76, pages 874-897.

Pilcher, S.H. and McDougall, J.J. (1976): Characteristics of some Canadian Cordilleran Porphyry Prospects, in Porphyry Deposits of the Canadian Cordillera, Sutherland Brown, A. , Editor, Canadian Institute of Mining and Metallurgy, Special Volume 15, pages 79-82.

Sutulov, A. (1978): International Molybdenum Encyclopaedia 1778-1978, Volume 1, Intermet Publications, Santiago, Chile, page 402.

Theodore, T.G. (1986): Descriptive Model of Porphyry Mo, Low-F; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, page 120.

Theodore, T.G. and Menzie, W.D. (1984): Fluorine-deficient Porphyry Molybdenum Deposits in the Western North American Cordillera; Proceedings of the Six Quadrennial IAGOD Symposium, E. Schweitzerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Germany, pages 463-470.

Westra, G. and Keith S.B. (1981): Classification and Genesis of Stockwork Molybdenum Deposits; Economic Geology, Volume 76, pages 844-873.

Woodcock, J.R. and Carter, N.C. (1976): Geology and Geochemistry of the Alice Arm Molybdenum Deposits; in Porphyry Deposits of the Canadian Cordillera, Sutherland Brown, A., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 15, pages 462-475.

PORPHYRY Sn


L06
by W. David Sinclair
Geological Survey of Canada, Ottawa

 

Sinclair, W.D. (1995): Porphyry Sn, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 97-100.

 

IDENTIFICATION

 

SYNONYM: Subvolcanic Sn

 

COMMODITIES (BYPRODUCTS): Sn (Ag, W)

 

EXAMPLES (British Columbia - Canada/International): Mount Pleasant (New Brunswick, Canada), East Kemptville (Nova Scotia, Canada), Catavi, Chorolque and Cerro Rico stock (Bolivia), Ardlethan and Taronga (Australia), Kingan (Russia), Yinyan (China), Altenberg (Germany).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Fine-grained cassiterite in veinlet and fracture stockwork zones, breccia zones, and disseminated in porphyritic felsic intrusive rocks and associated country rocks.

 

TECTONIC SETTING: Zones of weak to moderate extension in cratons, particularly post orogenic zones underlain by thick crust, possibly cut by shallow-dipping subduction zones.

 

GEOLOGICAL SETTING: High-level to subvolcanic felsic intrusive centres in cratons; multiple stages of intrusion may be present.

 

AGE OF MINERALIZATION: Paleozoic to Tertiary.

 

HOST/ASSOCIATED ROCK TYPES: Predominantly genetically related intrusive rocks and associated breccias, but may also include related or unrelated sedimentary, volcanic, igneous and metamorphic rocks. Genetically related felsic intrusive rocks are F and/or B enriched and are commonly porphyritic. Tuffs or other extrusive volcanic rocks may be associated with deposits related to subvolcanic intrusions.

 

DEPOSIT FORM: Deposits vary in shape from inverted cone, to roughly cylindrical, to highly irregular. They are typically large, generally hundreds of metres across and ranging from tens to hundreds of metres in vertical extent.

 

TEXTURE/STRUCTURE: Ore is predominantly structurally controlled in stockworks of crosscutting fractures and quartz veinlets, or disseminated in hydrothermal breccia zones. Veins, vein sets, replacement zones may also be present.

 

ORE MINERALOGY (Principal and subordinate): Cassiterite; stannite, chalcopyrite, sphalerite and galena. Complex tin- and silver-bearing sulphosalts occur in late veins and replacement zones.

 

GANGUE MINERALOGY: Pyrite, arsenopyrite, löllingite, topaz, fluorite, tourmaline, muscovite, zinnwaldite and lepidolite.

 

ALTERATION MINERALOGY: In the Bolivian porphyry Sn deposits, sericite + pyrite ± tourmaline alteration is pervasive; in some deposits it surrounds a central zone of quartz + tourmaline. Sericitic alteration is typically bordered by weak propylitic alteration. In other deposits (e.g. , Ardlethan, Yinyan), central zones are characterized by greisen alteration consisting of quartz + topaz + sericite; these zones grade outward to quartz + sericite + chlorite alteration.

 

WEATHERING: Oxidation of pyrite produces limonitic gossans. Deep weathering and erosion can result in residual concentrations of cassiterite in situ or in placer deposits downslope or downstream.

 

ORE CONTROLS: Ore minerals occur in fracture stockworks, hydrothermal breccias and replacement zones centred on 1-2 km2, genetically related felsic intrusions.

 

GENETIC MODEL: Magmatic-hydrothermal. Large volumes of magmatic, highly saline aqueous fluids under pressure strip Sn and other ore metals from temporally and genetically related magma. Multiple stages of brecciation related to explosive fluid pressure release from the upper parts of small intrusions result in deposition of ore and gangue minerals in crosscutting fractures, veinlets and breccias in the outer carapace of the intrusions and associated country rocks. Mixing of magmatic with meteoric water during waning stages of the magmatic- hydrothermal system may result in deposition of some Sn and other metals, particularly in late-stage veins.

 

ASSOCIATED DEPOSIT TYPES: Sn veins (I13), Sn-polymetallic veins (H07).

 

COMMENTS: Some of the deposits listed (e.g. Taronga, East Kemptville) are not "subvolcanic" but they are similar to some porphyry Cu deposits with regard to their large size, low grade, relationship to felsic intrusive rocks and dominant structural control (ie., mineralized veins, fractures and breccias).

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Sn, Ag, W, Cu, Zn, As, Pb, Rb, Li, F, B may be anomalously high in hostrocks close to mineralized zones and in secondary dispersion halos in overburden. Anomalously high contents of Sn, W, F, Cu, Pb and Zn may occur in stream sediments and Sn, W, F (topaz) and B (tourmaline) may be present in heavy mineral concentrates.

 

GEOPHYSICAL SIGNATURE: Genetically related intrusions may be magnetic lows (ilmenite- rather than magnetite-dominant); contact aureole may be magnetic high if pyrrhotite or magnetite are present in associated skarn or hornfels zones. Radiometric surveys may be used to outline anomalous U, Th or K in genetically related intrusive rocks or in associated altered and mineralized zones.

 

OTHER EXPLORATION GUIDES: Sn (-Ag) deposits may be zoned relative to base metals at both regional (district) and local (deposit) scales.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Tens of millions of tonnes at grades of 0.2 to 0.5% Sn. Mount Pleasant (New Brunswick): 5.1 Mt @ 0.79% Sn; East Kemptville (Nova Scotia): 56 Mt @ 0.165% Sn; Catavi (Bolivia): 80 Mt @ 0.3% Sn; Cerro Rico stock, Bolivia: averages 0.3% Sn; Ardlethan (Australia): 9 Mt @ 0.5% Sn; Taronga (Australia): 46.8 Mt @ 0.145% Sn; Altenberg, (Germany): 60 Mt @ 0.3% Sn; Yinyan (China): "large" (50 - 100 Mt?) @ 0.46% Sn

 

ECONOMIC LIMITATIONS: Low grades require high volumes of production which may not be justified by demand.

 

IMPORTANCE: A minor source of tin on a world scale; when it was in production, East Kemptville was the major producer of tin in North America.

 

REFERENCES

 

Grant, J.N., Halls, C., Avila, W. and Avila, G. (1977): Igneous Systems and Evolution of Hydrothermal Systems in some Sub-volcanic Tin Deposits of Bolivia; in Volcanic Process in Orogenesis; Geological Society of London, Special Paper Publication 7, pages 117-126.

Grant, J.N., Halls, C., Sheppard, S.M.F. and Avila, W. (1980): Evolution of the Porphyry Tin Deposits of Bolivia; in Granitic Magmatism and Related Mineralization, Ishihara, S. and Takenouchi, S., Editors; The Society of Mining Geologists of Japan, Mining Geology Special Issue, No. 8, pages 151-173.

Guan, X., Shou, Y., Xiao, J., Liang, S. and Li, J. (1988): A New Type of Tin Deposit - Yinyan Porphyry Tin Deposit; in Geology of Tin Deposits in Asia and the Pacific, Hutchison, C.S., Editor, Springer-Verlag, Berlin, pages 487-494.

Lin, G. (1988): Geological Characteristics of the Ignimbrite-related Xiling Tin Deposit in Guangdong Province; in Geology of Tin Deposits in Asia and the Pacific, Hutchison, C.S., Editor, Springer-Verlag, Berlin, pages 494-506.

Reed, B.L. (1986): Descriptive Model of Porphyry Sn; in Mineral Deposit Models, Cox, D.P. and Singer, D.A. Editors; U.S. Geological Survey, Bulletin 1693, pages 108.

Sillitoe, R.H., Halls, C. and Grant, J.N. (1975): Porphyry Tin Deposits in Bolivia; Economic Geology, Volume 70, pages 913-927.

Taylor, R.G. and Pollard, P.J. (1986): Recent Advances in Exploration Modelling for Tin Deposits and their application to the Southeastern Asian Environment; GEOSEA V Proceedings, Volume 1, Geological Society of Malaysia, Bulletin 19, pages 327-347.

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PORPHYRY W

L07
by W. David Sinclair
Geological Survey of Canada, Ottawa

 

Sinclair, W.D. (1995): Porphyry W, in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 101-104.

 

IDENTIFICATION

 

SYNONYM: Stockwork W-Mo

 

COMMODITIES (BYPRODUCTS): W (Mo, Sn, Ag).

 

EXAMPLES (British Columbia - Canada/International): Boya; Mount Pleasant (New Brunswick, Canada), Logtung (Yukon, Canada), Xingluokeng, Lianhuashan and Yanchuling (China).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Stockwork of W-bearing quartz veinlets and fractures in felsic intrusive rocks and associated country rocks. Deposits are low grade but large and amenable to bulk mining methods.

 

TECTONIC SETTING: Zones of weak to moderate extension in cratons, particularly post- collisional zones in areas of tectonically thickened crust.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: High-level to subvolcanic felsic intrusive centres; multiple stages of intrusion are common.

 

AGE OF MINERALIZATION: Paleozoic to Tertiary, but Mesozoic and Tertiary examples are more common.

 

HOST/ASSOCIATED ROCK TYPES: Highly variable; mineralized rocks may be predominantly genetically related intrusive rocks, but may also be related or unrelated sedimentary, volcanic, igneous and metamorphic rocks. Genetically related felsic intrusive rocks are commonly F-rich (fluorite and/or topaz bearing) and porphyritic; unidirectional solidification features, particularly comb quartz layers, may also be present. Tuffs or other extrusive volcanic rocks may be associated with deposits related to subvolcanic intrusions.

 

DEPOSIT FORM: Deposits vary in shape from inverted cup-shaped, to roughly cylindrical, to highly irregular. They are typically large, generally hundreds of metres across and ranging from tens to hundreds of metres in vertical extent.

 

TEXTURE/STRUCTURE: Ore minerals is structurally controlled; mainly stockworks of crosscutting fractures and quartz veinlets, also veins, vein sets, breccias, disseminations and replacements.

 

ORE MINERALOGY (Principal and subordinate): Main ore mineral is generally either scheelite or wolframite, although in some deposits both are present. Subordinate ore minerals include molybdenite, bismuth, bismuthinite and cassiterite.

 

GANGUE MINERALOGY: Pyrite, pyrrhotite, magnetite, arsenopyrite, löllingite, quartz, K- feldspar, biotite, muscovite, fluorite, topaz.

 

ALTERATION MINERALOGY: Hydrothermal alteration is pervasive to fracture controlled and, at deposit scale, is concentrically zoned. It is commonly characterized by the presence of greisen alteration minerals, including topaz, fluorite and Li- and F-rich micas. At Mount Pleasant, for example, pervasive greisen alteration consisting of quartz + topaz ± sericite ± chlorite associated with high-grade W zones and grades laterally into fracture-controlled quartz- biotite-chlorite-topaz alteration associated with lower grade W zones. Propylitic alteration, mainly chlorite and sericite, extends as far as 1500 m beyond the mineralized zones. Potassic alteration, dominated by K-feldspar, occurs locally within the central areas of pervasive greisen alteration. Other deposits such as Xingluokeng (China) are characterized more by central zones of silicic and potassic alteration (K-feldspar and biotite); zones of weak greisen alteration consisting of muscovite and fluorite may be present. Sericitic alteration forms a broad aureole around the central potassic zone; irregular zones of argillic alteration may be superimposed on both the potassic and sericitic zones. In detail, alteration patterns may be complex; at Logtung, for example, different stages of mineralized veins and fractures are characterized by different assemblages of ore and alteration minerals.

 

WEATHERING: Oxidation of pyrite produces limonitic gossans; oxidation of molybdenite, if present, may produce yellow ferrimolybdenite.

 

ORE CONTROLS: Quartz veinlet and fracture stockwork zones surround or are draped over and are superimposed to varying degrees on small stocks (<1 km2); multiple stages of mineralization commonly present; felsic intrusions associated with the deposits are typically F-rich.

 

GENETIC MODEL: Magmatic-hydrothermal. Large volumes of magmatic, highly saline aqueous fluids under pressure strip W, Mo and other ore metals from temporally and genetically related magma. Multiple stages of brecciation related to explosive fluid pressure release from the upper parts of small intrusions result in deposition of ore and gangue minerals in crosscutting fractures, veinlets and breccias in the outer carapace of the intrusions and associated country rocks. Incursion of meteoric water during waning stages of the magmatic-hydrothermal system may result in late alteration of the hostrocks, but does not play a significant role in the ore forming process.

 

ASSOCIATED DEPOSIT TYPES: Porphyry W deposits may be part of a spectrum of deposits that include Climax-type Mo deposits (L08) as one end-member and porphyry Sn deposits as the other (L06). Vein/replacement W, Sn, Ag deposits may be associated (I05, H07), e.g. Logjam Ag-Pb-Zn veins peripheral to the Logtung W-Mo deposit. Skarn (contact metamorphic) zones associated with genetically related felsic intrusions may be mineralized, but are not typical skarn W (i.e. contact metasomatic) deposits.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: W, Mo and Sn are anomalous in hostrocks close to mineralized zones; anomalously high contents of F, Zn, Pb and Cu occur in wallrocks up to several kilometres from mineralized zones. W, Sn, Mo, F, Cu, Pb and Zn may be anomalously high in stream sediments and W, Sn and F (topaz) may be present in heavy mineral concentrates.

 

GEOPHYSICAL SIGNATURE: Genetically related intrusions may be magnetic lows (ilmenite rather than magnetite dominant); contact aureole may be magnetic high if pyrrhotite or magnetite are present in associated skarn or hornfels zones. Radiometric surveys may be used to outline anomalous U, Th or K in genetically related intrusive rocks or in associated altered and mineralized zones.

 

OTHER EXPLORATION GUIDES: The presence of scheelite can be detected with an ultraviolet lamp.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Tens to more than 100 Mt at grades of 0.2 to 0.3 % W (Lianhushan is exceptional at 0.8 % W). Boya (British Columbia): limited size due to thrust fault truncation, no published resource data. Mount Pleasant (New Brunswick): Fire Tower zone: 22.5 Mt @ 0.21 % W, 0.10 % Mo, 0.08 % Bi, (includes 9.4 Mt @ 0.31 % W, and 0.12 % Mo), North zone: 11 Mt @ 0.2 % W, 0.1 % Mo. Logtung (Yukon): 162 Mt @ 0.10 % W, 0.03 % Mo. Xingluokeng (China): 78 Mt @ 0.18 % W. Lianhuashan (China): ~40 Mt @ 0.8 % W.

 

ECONOMIC LIMITATIONS: Low grades require high production volumes which may not be justified by current demand for tungsten.

 

IMPORTANCE: Not currently an important source of world W production; some W may be recovered from deposits in China (e.g. Lianhuashan), but none is recovered at present (1994) from deposits outside China. Mount Pleasant Tungsten in New Brunswick produced slightly more than 2000 t of concentrate grading 70 % WO3 from 1 Mt of ore mined from 1983 to 1985.

 

REFERENCES

 

Kirkham, R.V. and Sinclair, W.D. (1984): Porphyry Copper, Molybdenum, Tungsten; in Canadian Mineral Deposit Types: A Geological Synopsis; Geological Survey of Canada, Economic Geology Report 36, pages 51-52.

Kirkham, R.V. and Sinclair, W.D. (1988): Comb Quartz Layers in Felsic Intrusions and their Relationship to Porphyry Deposits; in Recent Advances in the Geology of Granite-related Mineral Deposits, Canadian Institute of Mining and Metallurgy, Special Volume 39, pages 50-71.

Kooiman, G.J.A., McLeod, M.J. and Sinclair, W.D. (1986): Porphyry Tungsten-Molybdenum Orebodies, Polymetallic Veins and Replacement Bodies, and Tin-bearing Greisen Zones in the Fire Tower Zone, Mount Pleasent, New Brunswick; Economic Geology, Volume 81, pages 1356-1373.

Liu, W. (1980): Geological Features of Mineralization of the Xingluokeng Tungsten (Molybdenum) Deposit, Fujian Province; in Tungsten Geology, China, Hepworth, J.V. and Lu, H.Z., Editors, ESCAP/RMRDC, Bandung, Indonesia, pages 338-348.

Noble, S.R., Spooner, E.T.C. and Harris, F.R. (1986): Logtung: A Porphyry W-Mo Deposit in the Southern Yukon; in Mineral Deposits of Northern Cordillera, Morin, J.A., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 37, pages 274- 287.

Sinclair, W.D. (1986): Molybdenum, Tungsten and Tin Deposits and associated Granitoid Intrusions in the Northern Canadian Cordillera and adjacent parts of Alaska; in Mineral Deposits of Northern Cordillera, Morin, J.A., Editor, Canadian Institute of Mining and Metallurgy, Special Volume 37, pages 216-233.

Yan, M-Z., Wu, Y-L. and Li, C.-Y. (1980): Metallogenetic Systems of Tungsten in Southeast China and their Mineralization Characteristics; in Granitic Magmatism and Related Mineralization, Ishihara, S. and Takenouchi, S., Editors, The Society of Mining Geologists of Japan, Mining Geology Special Issue, No. 8, pages 215-221.

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PORPHYRY Mo (Climax-type)


L08
by W. David Sinclair
Geological Survey of Canada, Ottawa

 

Sinclair, W.D. (1995): Porphyry Mo (Climax-type), in Selected British Columbia Mineral Deposit Profiles, Volume 1 - Metallics and Coal, Lefebure, D.V. and Ray, G.E., Editors, British Columbia Ministry of Employment and Investment, Open File 1995-20, pages 105-108.

 

IDENTIFICATION

 

SYNONYMS: Granite molybdenite; Climax Mo; granite-related Mo.

 

COMMODITIES (BYPRODUCTS): Mo (W, Sn; pyrite and monazite have also been recovered from the Climax deposit).

 

EXAMPLES (British Columbia - Canada/International): No unequivocal Climax-type porphyry Mo deposits occur in British Columbia or other parts of Canada; Climax, Henderson, Mount Emmons and Silver Creek (Colorado, USA), Pine Grove (Utah, USA), Questa (New Mexico), Malmbjerg (Greenland), Nordli (Norway).

 

GEOLOGICAL CHARACTERISTICS

 

CAPSULE DESCRIPTION: Stockworks of molybdenite-bearing quartz veinlets and fractures in highly evolved felsic intrusive rocks and associated country rocks. Deposits are low grade but large and amenable to bulk mining methods.

 

TECTONIC SETTING: Rift zones in areas of thick cratonic crust.

 

DEPOSITIONAL ENVIRONMENT / GEOLOGICAL SETTING: High-level to subvolcanic felsic intrusive centres; multiple stages of intrusion are common.

 

AGE OF MINERALIZATION: Paleozoic to Tertiary, but mainly Tertiary.

 

HOST/ASSOCIATED ROCK TYPES: Genetically related felsic intrusive rocks are high-silica (>75% SiO2), F-rich (>0.1% F) granite/rhyolite; they are commonly porphyritic and contain unidirectional solidification textures (USTs), particularly comb quartz layers. Contents of Rb, Y and Nb are high; Ba, Sr and Zr are low. Mineralized country rocks may include sedimentary, metamorphic, volcanic, and older intrusive rocks. Tuffs or other extrusive volcanic rocks may be associated with deposits related to subvolcanic intrusions.

 

DEPOSIT FORM: Deposits typically form an inverted cup or hemispherical shell; shapes may be modified by regional or local structures. They are typically large, generally hundreds of metres across and ranging from tens to hundreds of metres in vertical extent.

 

TEXTURE/STRUCTURE: Ore is structurally controlled; mainly stockworks of crosscutting fractures and quartz veinlets, also veins, vein sets and breccias; disseminations and replacements are less common.

 

ORE MINERALOGY (Principal and subordinate): Molybdenite; wolframite, cassiterite, sphalerite, galena, monazite.

 

GANGUE MINERALOGY: Quartz, pyrite, topaz, fluorite and rhodochrosite.

 

ALTERATION MINERALOGY: Potassic alteration (K-feldspar ± biotite) is directly associated with high-grade Mo (>0.2% Mo); pervasive silicic alteration (quartz ± magnetite) may occur locally in the lower parts of high-grade Mo zones. Quartz-sericite-pyrite alteration may extend hundreds of metres vertically above orebodies; argillic alteration may extend hundreds of metres beyond quartz-sericite-pyrite alteration, both vertically and laterally. Spessartine garnet occurs locally within quartz-sericite-pyrite and argillic alteration zones. Greisen alteration consisting of quartz-muscovite-topaz occurs as alteration envelopes around quartz-molybdenite veins below high-grade Mo zones. Propylitic alteration is widespread and may extend for several km.

 

WEATHERING: Oxidation of pyrite produces limonitic gossans; oxidation of molybdenite produces yellow ferrimolybdite.

 

ORE CONTROLS: Quartz veinlet and fracture stockwork zones surround or are draped over, and are superimposed to varying degrees on small, genetically related stocks (area <1 km2); multiple stages of mineralization are commonly present; abundant comb quartz layers and other USTs characterize productive intrusions.

 

GENETIC MODEL: Magmatic-hydrothermal. Large volumes of magmatic, highly saline aqueous fluids under pressure strip Mo and other ore metals from temporally and genetically related magma. Multiple stages of brecciation related to explosive fluid pressure release from the upper parts of small intrusions result in deposition of ore and gangue minerals in crosscutting fractures, veinlets and breccias in the outer carapace of the intrusions and associated country rocks. Incursion of meteoric water during waning stages of the magmatic-hydrothermal system may result in late alteration of the hostrocks, but does not play a significant role in the ore-forming process.

 

ASSOCIATED DEPOSIT TYPES: Ag-base metal veins (I05), fluorspar deposits. Some porphyry W-Mo deposits (e.g. Mount Pleasant) may be W-rich Climax-type deposits. Mo may also be present in adjacent skarn deposits (K07). Climax-type porphyry Mo deposits may be related to rhyolite-hosted Sn deposits (H07, USGS model 25h).

 

COMMENTS: This model is based mainly on descriptions of Climax and Climax-type deposits in Colorado. These deposits tend to have more complex igneous- hydrothermal systems and higher average Mo grades than low-F-type porphyry Mo deposits.

 

EXPLORATION GUIDES

 

GEOCHEMICAL SIGNATURE: Mo, Sn, W, Rb, Mn and F may be anomalously high in hostrocks close to and overlying mineralized zones; Pb, Zn, F and U may be anomalous in wallrocks as much as several kilometres distant. Mo, Sn, W, F, Cu, Pb, Zn may be anomalous in stream sediments and Mo, Sn, W, and F (topaz) may be present in heavy mineral concentrates.

 

GEOPHYSICAL SIGNATURE: Genetically related intrusions may be magnetic lows (ilmenite rather than magnetite dominant). Radiometric surveys may be used to outline anomalous U, Th or K in genetically related intrusive rocks or in associated altered and mineralized zones.

 

OTHER EXPLORATION GUIDES: Deposits occur in extensional tectonic settings in areas of thick continental crust. Genetically related felsic intrusive rocks generally have high contents of Nb (>75 ppm. Ag-Pb-Zn veins, topaz, fluorite and Mn- garnet may be present in peripheral zones. Yellow ferrimolybdite may be present in oxidized zones.

 

ECONOMIC FACTORS

 

GRADE AND TONNAGE: Deposits typically contain hundreds of millions of tonnes at 0.1 to 0.3 % Mo. Following figures are production plus reserves (from Carten et al., 1993): Climax, Colorado: 769 Mt @ 0.216% Mo (mineable), Henderson, Colorado: 727 Mt @ 0.171% Mo (geological), Mount Emmons, Colorado: 141 Mt @ 0.264% Mo (mineable), Silver Creek, Colorado: 40 Mt @ 0.310% Mo (geological), Pine Grove, Utah: 125 Mt @ 0.170% Mo (geological), Questa, New Mexico: 277 Mt @ 0.144% Mo (mineable), Malmbjerg, Greenland: 136 Mt @ 0.138% Mo (geological), Nordli, Norway: 181 Mt @ 0.084% Mo (geological).

 

ECONOMIC LIMITATIONS: Economic viability of these deposits is affected by Mo production from other types of deposits such as porphyry Cu-Mo deposits, which produce Mo as a coproduct or byproduct.

 

IMPORTANCE: Porphyry Mo deposits of the Climax type have been a major source of world Mo production and contain substantial reserves.

 

REFERENCES

 

Carten, R.B., White, W.H. and Stein, H.J. (1993): High-grade Granite-related Mo Systems: Classification and Origin: in Mineral Deposit Modeling, Kirkham, R.V., Sinclair, W.D., Thorpe, R.I. and Dute, J.M. Editors,: Geological Association of Canada, Special Paper 40, pages 521-554.

Kirkham, R.V. and Sinclair, W.D. (1984): Porphyry Copper, Molybdenum, Tungsten; in Canadian Mineral Deposit Types: A Geological Synopsis; Geological Survey of Canada, Economic Geology Report 36, pages 51-52.

Kirkham, R.V. and Sinclair, W.D. (1988): Comb Quartz Layers in Felsic Intrusions and their Relationship to Porphyry Deposits; in Recent Advances in the Geology of Granite-related Mineral Deposits, Canadian Institute of Mining and Metallurgy, Special Volume 39, pages 50-71.

Keith, J.D. and Christiansen, E.H. (1992): The Genesis of Giant Molybdenum Deposits; in Giant Ore Deposits, Whiting, B.H., Masong, R. and Hodgson, C.J., Editors, Proceedings of the Giant Deposits Workshop, Queen’s University, Kingston, 11-13 May, 1992.

Ludington, S.D. (1986): Descriptive Model of Climax Mo Deposits; in Mineral Deposit Models, Cox, D.P. and Singer, D.A., Editors, U.S. Geological Survey, Bulletin 1693, page 73.

Mutschler, F.E., Wright, E.G., Ludington, S. and Abbot, J. (1981): Granite Molybdenite Systems; Geology, Volume 13, pages 469-474.

Wallace, S.R., Muncaster, N.K., Jonson, D.D., MacKenzie, W.B., Bookstrom, A.A. and Surface, V.E. (1968): Multiple Intrusion and Mineralization at Climax, Colorado; in Ore Deposits of the United States, 1933-1967 (The Graton-Sales Volume), Ridge, J.D., Editor, American Institute of Mining, Metallurgy and Petroleum Engineers, New York, pages 605-640.

Westra, G. and Keith, S.B. (1981): Classification and Genesis of Stockwork Molybdenum Deposits; Economic Geology, Volume 76, pages 844-873.

White, W.H., Bookstrom, A.A., Kamilli, R.J., Ganster, M.W., Smith, R.P., Ranta, D.E. and Steininger, R.C. (1981): Character and Origin of Climax-type Molybdenum Deposits; Economic Geology, 75th Anniversary Volume, pages 270-316.

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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 Porphyry Deposits

BC Profile # Global Examples B.C. Examples
L01 Lepanto (Philippines), Resck (Hungary), Kori Kollo (Bolivia) Equity Silver, Thorn
L02 Mokrsko (Czech Republic), Timbarra (New South Wales, Australia)

 - -

L03
Tai Parit (Philippines) 
Afton, Copper Mountain, Galore Creek
L04 Chuquicamata & La Escondida (Chile) Highland Valley, Gibraltar
L05 Quartz Hill (Alaska) Endako, Kitsault, Glacier Gulch
L06 Llallagua (Bolivia), Potato Hills (Yukon) - -
L07 Logtung (Yukon), Xingluokeng (China) Boya
L08 Climax & Henderson (Colorado) - -
 L09* Marte & Lobo (Chile), Lihir (Papua New Guinea)

Snowfields