Proterozoic mineral deposits near plate margins of the archean wyoming province, USA

Abstract

Abstract Proterozoic mineral deposits located near the margin of the Archean Wyoming Province can be interpreted in a plate tectonic context. The southern margin of the Archean Wyoming Province is exposed in southeastern Wyoming where Early Proterozoic island areas have been sutured to an Early Proterozoic passive margin developed during rifting of the Archean Wyoming craton. Mineral deposits include uranium-thorium-gold bearing quartz pebble conglomerate deposited during rifting, stratiform sulphide in black shale of the foredeep basin, anomalous platinum group element values in layered complexes of the island arcs, and a variety of mineral deposits that formed during closure of the arcs and passive margin. The eastern margin of the Wyoming Province is probably located under Phanerozoic cover just east of the Black Hills of South Dakota. The Black Hills is a segment of the Early Proterozoic Trans-Hudson Orogen which is interpreted here as an area exhibiting evidence of opening and closing of an intracratonic basin. In the Black Hills, domes underlain by Archean rocks are overlain by an Early Proterozoic clastic successions that preserves evidence of rifting. These clastic successions are succeeded by marine quartzite which is, in turn, overlain by a eugeosynclinal succession containing iron formation, graywacke, and a variety of volcanic units. The basal Early Proterozoic clastic succession contains uranium and gold-bearing quartz pebble conglomerate formed during rifting. The eugeosynclinal succession contains the Homestake iron formation which is host to the Early Proterozoic Homestake type gold deposits. Geologic and geochemical evidence can be marshalled to support either an epigenetic or syngenetic origin for the Homestake-type gold deposits. If the gold deposits are syngenetic they may have formed in a foredeep basin developed during closure of the intracratonic basin.