The Golden Devil Zone, a New Discovery in the Goldbanks District, Nevada

摘要

The Goldbanks low-sulfidation epithermal gold project is located approximately 45 km south of Winnemucca, NV and is 100% controlled by Kinross Gold Corporation. The surrounding district contains numerous gold prospects and past-producing mercury and antimony mines that are temporally and spatially related to mid-Mio-cene Northern Nevada Rift (NNR) bimodal volcanism. The Goldbanks gold deposit was discovered and defined between 1988 and 1998, and includes two resource areas, the Main Zone and the KW zone. Both zones are concealed beneath unmineralized cover, and were discovered as a result of successful application of hot-spring epithermal precious-metal deposit models as well as drilling beneath high-level alteration. An updated, district-scale, geologic and genetic model for mineralization at Gold-banks is presented here. Precious-metal mineralization in the Goldbanks resource areas occurs along a shal-lowly west-dipping unconformity between pre-Cenozoic metasedimentary rocks and an overlying Oligocene-Miocene volcano-sedimentary sequence. The highest gold grades (> 10 g/t Au) usually occur in colloform-crustiform banded quartz veins located at or near the unconformity. Lower-grade stockwork veining and silicification extends above and below the unconformity. A recent ~(40)Ar/~(39)Ar analysis of adularia from a gold-mineralized vein in drill core from the KW zone yielded an age of approximately 12.6 Ma. New geologic interpretations, combined with geophysics, geochronology, and hyperspectral data, have resulted in a revised, predictive geologic model and exploration strategy for high-grade, structurally-hosted, feeder-type veins at Goldbanks. The mineralized unconformity in the resource areas is now recognized as the rotated base of a broad, west-dipping, half-graben basin. A recent gravity survey and new drilling have refined the understanding of stratigraphic architecture and basin geometry (4 km N-S by 2 km E-W, and up to 600 m deep). The basin-fill sequence consists of a basal ca. 32.5 Ma andesitic breccia, ca. 15.3 Ma fanglomerate, ca. 13.6 Ma lacustrine mudstone, and an upper volcanic sequence capped by a < 13.1 Ma basalt. Known precious-metal resources at Goldbanks occur in the relatively shallow, up dip, eastern and northern portions of the half-graben. Historic exploration drilling did not test the western structural basin margin. Three holes drilled in 2013 targeting this zone encountered> 185 m of a mineralized mafic dike complex interpreted to be a syn-mineralization intrusive component of the NNR magmatic suite. All three holes intersected> 10 g/t Au intervals containing visible gold and electrum, with the best interval assaying 192.5 g/t Au and> 1% Ag over a measured length of 1.12 m. This newly discovered mineralization, which is located greater than 1 km from the previously known resource areas, is referred to as the Golden Devil Zone.