Gold-bearing quartz vein mineralization at the Big Hurrah Mine, Seward Peninsula, Alaska

摘要: The Big Hurrah mine, located near Nome, Alaska, is an example of gold-bearing quartz vein mineralization in uplifted metamorphic terrain. host rocks are sheared carbonaceous metasedimentary and metavolcanic that underwent Jurassic regional blueschist metamorphism. Penetrative deformation the includes shearing later faulting.Five types veins can be distinguished at mine based upon structural style, mineralogy, fluid inclusion populations. From oldest to youngest they are: type I, early lenses; II, tabular veins; III, ribbon IV, quartz-albite + or - arsenopyrite V, late carbonate-quartz veins. Type I II strongly premineralization. Gold occurs predominantly in.the III veins, which discontinuous lodes occupying northwest-striking fissures. These fissures thought conjugate faults developed stages shearing. Wall-rock alteration limited minor silicification, carbonatization, stockwork V postdate not sheared. Mineralization consists coarsegrained native gold associated with scheelite. Much ribbons A geochemical arsenic anomaly extends beyond mineralized used as a guide for exploration.Fluid studies indicate presence multiple generations fluids have evolved from CO 2 -CH 4 -bearing aqueous salinities 2.1 6.6 equiv wt percent NaCl. Fluid homogenization temperatures range 390 degrees 90 C, decrease time single type. Pressure temperature estimates secondary inclusions -H O immiscibility may occurred 250 C 0.8 kb. precipitation been triggered by change pH immiscibility, drop temperature, reduction ore wall-rock carbon. deposit broadly similar other deposits occur deformed generally considered formed result