Showing papers by "Richard J. Goldfarb published in 1993"

Orogenesis, high-T thermal events, and gold vein formation within metamorphic rocks of the Alaskan Cordillera

Abstract: Mesothermal, gold-bearing quartz veins are widespread within allochthonous terranes of Alaska that are composed dominantly of greenschist-facies metasedimentary rocks. The most productive lode deposits are concentrated in south-central and southeastern Alaska; small and generally nonproductive gold-bearing veins occur upstream from major placer deposits in interior and northern Alaska. Oreforming fluids in all areas are consistent with derivation from metamorphic devolatilisation reactions, and a close temporal relationship exists between high-T tectonic deformation, igneous activity, and gold mineralization. Ore fluids were of consistently low salinity, CO2-rich, and had 6~SO values of 7%o12%o and 6D values between -15%o and -35%o. Upper-crustal temperatures within the metamorphosed terranes reached at least 450-500 ~ before onset of significant gold-forming hydrothermal activity. Within interior and northern Alaska, latest Paleozoic through Early Cretaceous contractional deformation was characterised by obduction of oceanic crust, low-T/high-P metamorphism, and a lack of gold vein formation. Mid-Cretaceous veining occurred some 50-100 m.y. later, during a subsequent high-T metamorphic/magmatic event, possibly related to extension and uplift. In southern Alaska, gold deposits formed during latter stages of Tertiary, subduction-related, collisional orogenesis and were often temporally coeval with calc-alkaline magmatism. KEYWO~DS: mesothermal gold, Alaska, fluid inclusion~ stable isotope, geochronology, orogensis.