Chapter K GEOENVIROMENTAL MODEL FOR LOW-SULFIDE GOLD-QUARTZ VEIN DEPOSITS

Deposit geology These deposits include quartz and quartz-carbonate veins mined primarily for gold. They are found in accreted terranes dominated by greenstone and slate sequences that have been metamorphosed to greenschist, or less commonly to amphibolite or granulite facies (Berger, 1986a; Goldfarb and others, 1995). These veins generally contain no more than a few percent sulfide minerals. Wall rocks, which in some deposits include disseminated ore bodies, contain abundant carbonate minerals, quartz, sericite, and sulfides. Mineralization is commonly associated with regional shear zones, which may include melange zones with varied lithologies and tectonically-emplaced ultramafic rocks and serpentinite. Deposits spatially associated with plutonic rocks tend to have more varied suites of metals, and are more likely to contain more silver and to yield copper, lead, and zinc as byproducts. Arsenic is the minor element most commonly enriched in alteration haloes. These deposits are also known as mesothermal, Mother Lode-type, orogenic, metamorphic rock-hosted, shear zone-hosted, greenstone-hosted or greenstone gold, turbidite-hosted, and slate-belt gold (Groves and others, 1998). Low-sulfide gold-quartz veins are found in deformed metamorphic rocks of all ages, world-wide; they are the most widespread type of gold-bearing mineral deposit. Since the late 1970’s, accreted terranes of all ages in the United States have been explored for these deposits, resulting in production from the southern Appalachians, the Lake Superior region, the Sierra Nevada region of California, and southeastern and central Alaska. Individual deposits have yielded from a few tonnes to more than 100 tonnes of gold