PORPHYRY Mo (LOW-F-TYPE) / L05

Cortesia del Gobierno de BRITISH COLUMBIA. Ministerio de Enegia y Minas

Metallics And Coal

GEOLOGICAL CHARACTERISTICS	ECONOMIC FACTORS
EXPLORATION GUIDES	REFERENCES

IDENTIFICATION

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

Mo (Cu, W)

(British Columbia - Canada/International): Endako (093K006), Boss Mountain (093A001), Kitsault (103P120), Adanac (104N052), Carmi (082ESW029), Bell Moly (103P234), Red Bird (093E026), Storie Moly (104P069), 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

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.

Subduction zones related to arc-continent or continent- continent collision.

High-level to subvolcanic felsic intrusive centres; multiple stages of intrusion are common.

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

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.

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.

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

Molybdenite is the principal ore mineral; chalcopyrite, scheelite, and galena are generally subordinate.

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

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.

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

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

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.

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

EXPLORATION GUIDES

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.

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.

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

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.

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.

Mineral Deposit

Cortesia del Gobierno de BRITISH COLUMBIA. Ministerio de Enegia y Minas