Mo SKARNS / K07

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

Metallics And Coal

GEOLOGICAL CHARACTERISTICS	ECONOMIC FACTORS
EXPLORATION GUIDES	REFERENCES

IDENTIFICATION

Pyrometasomatic or contact metasomatic Mo deposits.

Mo (W, Cu, Pb, Zn, Sn, Bi, U, Au).

((British Columbia - Canada/International): Coxey (082FSW110), Novelty (082FSW107); Mount Tennyson (New South Wales, Australia), Little Boulder Creek (Idaho, USA), Cannivan Gulch (Montana, USA), Azegour (Morocco), Yangchiachangtze (China).

GEOLOGICAL CHARACTERISTICS

Molybdenite-dominant mineralization genetically associated with a skarn gangue (includes calcic and magnesian Mo skarns). Mo skarns are broadly separable into polymetallic and "molybdenite-only" types (see comments below).

Late orogenic plutonism (derived from transitional crust) intruding continental margin carbonate sequences. Also, some are associated with Mo- bearing porphyry systems developed within intra-oceanic island arcs.

Mainly Mesozoic and Paleozoic, but may be any age. In British Columbia, they are mainly of Early to mid-Jurassic in age.

Stocks and dikes of evolved, commonly leucocratic quartz monzonite to granite (some containing primary biotite and muscovite) intruding calcareous clastic rocks. Deposits tend to develop close to intrusive contacts. Some of the Mo skarns in British Columbia are associated with high- level intrusions that have explosive breccia textures.

Irregular orebodies along, and controlled by, the intrusive contacts.

Igneous textures in endoskarn; local explosive breccia textures. Coarse to fine-grained, massive granoblastic to mineralogically layered textures in exoskarn. Some hornfelsic textures.

Molybdenite ± scheelite ± pyrrhotite ± powellite ± chalcopyrite ± arsenopyrite ± pyrite ± pyrrhotite ± bismuthinite ± sphalerite ± fluorite. In rare instances also galena ± magnetite ± uraninite ± pitchblende ± cassiterite ± cobalite ± stannite ± gold.

Calcic Mo skarns: Hedenbergite pyroxene (Hd50-80, Jo1-3) ± low Mn grossular-andradite garnet (Ad40-95) ± wollastonite ± biotite ± vesuvianite. Magnesian Mo skarns: olivine (Fo96). Retrograde minerals: Calcic skarns: amphibole ± epidote ± chlorite and muscovite. Magnesian skarns: serpentine ± tremolite ± chlorite.

Clinopyroxene, K-feldspar, hornblende, epidote, quartz veining, sericite, molybdenite.

Carbonate or calcareous rocks in thermal aureoles adjacent to intrusive margins.

Mo porphyries of quartz monzonite type (L05), Mo-sulphide veins, and Zn-sulphide veins (I05). Some Mo skarns in China are associated with distal, sphalerite-rich mineralization.

Mo skarns are broadly separable into two types: polymetallic (containing molybdenite with other W, Zn, Pb, Bi, Sn, Co or U-rich minerals), and "molybedenite-only" (containing mainly molybdenite with no or few other sulphides). Over 85% of the 21 Mo skarns recorded in British Columbia occur in the Omineca Belt. More than 60% are hosted in cratonic, pericratonic and displaced continental margin rocks of the Kootenay, Cassiar and Ancestral North America terranes, and a further 19% are found in the Quesnellia Terrane

EXPLORATION GUIDES

Enriched in Mo, Zn, Cu, Sn, Bi, As, F, Pb, U, Sb, Co (Au).

: Positive magnetic and induced polarization anomalies.

ECONOMIC FACTORS

Worldwide, grades range from 0.1 to 2 % MoS2, and tonnages between 0.1 and 2 Mt. In British Columbia, the Coxey deposit produced 1 Mt of ore grading approximately 0.17 % MoS2. The Novelty and Giant are polymetallic Mo skarns near Rossland, British Columbia with unusually high grades of up to 47 g/t Au, 1.4 % Ni, 30.5 % As and 4.84 % Co.

: Mo skarns tend to be smaller tonnage and less economically important than porphyry Mo deposits.

REFERENCES

• Einaudi, M.T., Meinert, L.D. and Newberry, R.J. (1981): Skarn Deposits; in Seventy-fifth Anniversary Volume, 1906-1980, Economic Geology, Skinner, B.J., Editor, Economic Geology Publishing Co., pages 317-391.

• Theodore, T.G. and Menzie, W.D. (1984): Fluorine-deficient Porphyry Molybdenum Deposits in the Western North American Cordillera; Proceedings of the 6th Quadrennial IAGOD Symposium, Stuttgart, Germany, pages 463-470.

Mineral Deposit

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