System type: Rochester-type Ag-Au system
Target: Disseminated Ag-Au mineralization
The Root Spring Project is 80 km south of the city of Winnemucca and 26 km east of the world-class open-pit Rochester silver mine operated by Coeur Mining. The project contains an epithermal/mesothermal gold-silver vein stockwork system exposed at the edge of a large alluvial-covered valley. Mineralization is hosted in the Triassic Koipato volcanics, which were not previously identified in the area and consist of interbedded felsic and mafic volcanics. The Koipato hosts the Rochester Ag-Au deposit as well as the Spring Valley gold deposit 27 km northwest of Root Spring.
The project contains gently-dipping quartz veins and quartz-vein stockwork zones exposed for at least 1.2 km along a northwest strike, with individual veins to 5m thick. Extensions of the veins along strike as well as surrounding country rock are concealed by alluvial cover within a northwest-trending alluvial-filled valley corridor along a range front. Like the Rochester deposit to the northwest, the Root Spring Au-Ag system is adjacent to a Triassic granitic pluton. Surface rock-chip gold values in veins reach 9.36 ppm gold (0.273 ounces per ton, opt) accompanied by high silver reaching 1500 ppm (44 opt). The veins are surrounded by widespread, locally mineralized quartz-sericite-pyrite alteration of the host felsic volcanic sequence that is known principally from shallow drilling.
A limited first-phase drilling program in 2012 intersected Ag-Au mineralization down-dip of exposed veins; however, drilling was very shallow (68m average length). Results included 12.1m grading 14.02 g/t Ag and 0.16 g/t Au, 10.7 m grading 17.23 g/t Ag and 0.14 g/t Au and 9.4m grading 16.47 g/t Ag and 0.53 g/t Au. Importantly, the drilling confirmed the Koipato host section containing local disseminated tourmaline and fluorite and also intersected encouraging disseminated gold within felsite far from the exposed veins. Although the first-phase drilling failed to intersect potentially economic grades/widths of Ag-Au mineralization, the similarity of the host Koipato volcanics to nearby Rochester – Spring Valley, the range-front setting, the adjacent Triassic pluton, the extensive alluvial cover, the widespread silicification and sericitic alteration, and both disseminated and vein-style mineralization intersected in the drilling are prospective elements for further exploration.