DESCRIPTIVE MODEL OF Zn-Pb SKARN DEPOSITS
By Dennis P. Cox
DESCRIPTION Sphalerite and galena in calc-silicate rocks.
GENERAL REFERENCES Einaudi and Burt (1982); Einaudi and others (1981).
Rock Types Granodiorite to granite, diorite to syenite. Carbonate rocks, calcareous clastic rocks.
Textures Granitic to porphyritic; granoblastic to hornfelsic.
Age Range Mainly Mesozoic, but may be any age.
Depositional Environment Miogeoclinal sequences intruded by generally small bodies of igneous rock.
Tectonic Setting(s) Continental margin, late-orogenic magmatism.
Associated Deposit Types Copper skarn.
Mineralogy Sphalerite + galena ± pyrrhotite ± pyrite ± magnetite ± chalcopyrite ± bornite ± arsenopyrite ± scheelite ± bismuthinite ± stannite ± fluorite. Gold and silver do not form minerals.
Texture/Structure Granoblastic, sulfides massive to interstitial.
Alteration Mn-hedenbergite ± andradite ± grossular ± spessartine ± bustamite ± rhodonite. Late stage Mn-actinolite ± ilvaite ± chlorite ± dannemorite ± rhodochrosite.
Ore Controls Carbonate rocks especially at shale-limestone contacts. Deposit may be hundreds of meters from intrusive.
Weathering Gossan with strong Mn oxide stains.
Geochemical Signature Zn, Pb, Mn, Cu, Co, Au, Ag, As, W, Sn, F, possibly Be.
Ban Ban, AUQU (Ashley, 1980_)
Hanover-Fierro district, USNM (Hernon and Jones, 1968)