Structural setting,style and timing of vein-hosted gold mineralization at the Pogo deposit,east central Alaska |
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| Authors: | Email author" target="_blank">David?RhysEmail author Jack?DiMarchi Moira?Smith Robert?Friesen Cameron?Rombach |
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| Institution: | (1) Panterra Geoservices Inc., 14180 Greencrest Drive, Surrey, BC, V4P 1L9, Canada;(2) Teck Resources Inc. , 3520 International Way, Fairbanks, AK 99701, USA;(3) TeckCominco Ltd., 200 Burrard St., Vancouver, BC, V6C 3L9, Canada;(4) Department of Geology and Geophysics, University of Alaska Fairbanks, P.O. Box 755780, Fairbanks, AK 99775-5780, USA |
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| Abstract: | Gold-bearing veins within the Liese zone of the Pogo deposit display a two-stage evolutionary history that records temporal variation in kinematics, fluid chemistry and temperature. Several stacked shallow northwest-dipping shear veins are developed at Pogo, and collectively comprise the Liese Zone. Veins consist of: (1) early, narrow biotite-bearing shear veins; (2) white quartz veins with pyrite-arsenopyrite bands, referred to as main stage quartz veins, that have sericite-Fe-Mg carbonate alteration envelopes and which exploit the early shear veins; and (3) extension veins that form as steeper offshoots from the main stage veins. The presence and orientation of oblique fabrics developed in the older biotite-bearing shear veins are indicative of top-to-the-south displacement under ductile to semi-brittle conditions at higher temperatures. In contrast, the orientation of the extension veins and local sigmoidal shapes indicate a component of top-to-the-northwest normal displacement on the main stage veins in their present orientation, and brittle to semi-brittle conditions of formation. Dolomite-sericite alteration surrounding main stage veins may represent late to post-mineral hydrothermal fluid exploitation of vein margins during ongoing normal displacement along vein systems. All types of veining overprint 107–106 Ma, post-metamorphic granitic dykes. Molybdenite in main stage quartz assemblages has returned Re-Os ages of 104.2±1.1 Ma, significantly older than 96 to 91 Ma 40Ar/39Ar ages obtained from vein alteration assemblages that may reflect thermal resetting during post-mineral fault related hydrothermal activity, magmatism and/or retrograde cooling of the lithologic sequence. Unlike typical mesothermal shear vein hosted gold systems, Pogo is temporally and tectonically separated from metamorphic deformation events, and has a comparable kinematic and geometric architecture to Cretaceous plutonic gold deposits in the region. We interpret the deposit to have formed during a regional Cretaceous extensional event during multi-stage exploitation of extensional fault surfaces by hydrothermal fluid from a cooling magmatic source.Editorial handling: S.G. Hagemann |
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