Day Three
North American Perspectives
Description
The Keno Hill Ag-Pb-Zn vein-type (Yukon) and Fort Knox intrusion related gold system (IRGS; Alaska) deposits are world-class deposits. The Keno Hill district produced 214 million ounces of silver between 1913 and 1990, and the Fort Knox deposit produced 7.5 million ounces of gold up to 2019. The deposits are spatially separated by approximately 600 km, and differ in their in their styles and ages of mineralisation. Gold mineralisation at Fort Knox occurred between 94.5 and 91.2 Ma (Re-Os, molybdenite and U-Pb, zircon; Hart, 2004) and silver mineralisation at Keno Hill occurred between 81 and 78 Ma (40Ar/39Ar, sericite). Palinspastic restoration of 430 km of dextral displacement along the Eocene Tintina Fault reveals a potential structural link between the two deposits. Interpretation of palinspastically restored airborne magnetic data and comparison of detailed structural mapping in the Keno Hill district with historic mapping in Alaska show the presence of a major, ENE-trending structural zone that accommodates both the Keno Hill and Fort Knox deposits and numerous other past-producing, or advanced exploration projects. It is proposed that formation of the Keno Hill and Fort Knox deposits was related to a long-lived, reactivated Precambrian basement structure that is present beneath the North American margin platformal and basinal rocks during the middle and Late Cretaceous.
Authors
- Simon Craggs | University of New Brunswick | SRK Canada
- David Lentz | UNB Research Chair in Economic Geology at University of New Brunswick
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