Reed S. Lewis, David E. Stewart, Vincent H. Isakson, Niki E. Wintzer, Eric D. Stewart, Jeffrey D. Vervoort
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引用次数: 0
Abstract
Abstract Geologic mapping and associated U-Pb geochronologic work in the Stibnite-Edwardsburg area of central Idaho have provided regional geologic context for the gold-antimony-tungsten-mercury mineralization in this area. Roughly 6,000 m of strata that postdate the Mesoproterozoic Belt-Purcell Supergroup are preserved; overall, the strata young to the southwest and are found as roof pendants or septa within the Idaho batholith. Rocks suspected to be lower Paleozoic in age by early workers in the area contain detrital zircons as young as 500 Ma, confirming that age assignment. We recognized four mappable phases of Cretaceous intrusive rocks, ranging in age from about 95 to 85 Ma, but suspect additional dating and detailed mapping would better show the complexity of the intrusive history. Regional metamorphism ranges from greenschist to amphibolite facies and contact metamorphism is conspicuous near Cretaceous plutonic rocks. Lu-Hf garnet geochronology shows that regional metamorphism of the strata northwest of Stibnite occurred at about 113 Ma and thus prior to batholith intrusion. Contact metamorphism likely occurred some 15 to 30 m.y. later, depending on the specific pluton age. Four large-volume Eocene ash-flow deposits (and their hypothesized eruptive centers) were recognized. Important structures in the Stibnite area include a SW-directed thrust fault, now overturned, that repeats part of the section, and N- to NE-striking faults that have localized mineralization.
期刊介绍:
The journal, now published semi-quarterly, was first published in 1905 by the Economic Geology Publishing Company (PUBCO), a not-for-profit company established for the purpose of publishing a periodical devoted to economic geology. On the founding of SEG in 1920, a cooperative arrangement between PUBCO and SEG made the journal the official organ of the Society, and PUBCO agreed to carry the Society''s name on the front cover under the heading "Bulletin of the Society of Economic Geologists". PUBCO and SEG continued to operate as cooperating but separate entities until 2001, when the Board of Directors of PUBCO and the Council of SEG, by unanimous consent, approved a formal agreement of merger. The former activities of the PUBCO Board of Directors are now carried out by a Publications Board, a new self-governing unit within SEG.