Howald, William C., and Conelea, Radu R., Rye Patch Gold US, Inc., 220 S. Rock Blvd., Suite 9, Reno, NV 89502
The Wilco project area is located in the Willard Mining District, approximately 100 miles northeast of Reno, Nevada, and contains the Willard and Colado gold and silver resources representing epithermal, low-sulfidation-type (quartz ± calcite ± adularia) deposits. Mineralization is controlled by favorable lithology and structure.
The Wilco property area has a long history of exploration, development and production dating back to the early 1900’s. The Willard mines produced free-milling gold from surface exposures, and in the 1990’s, Western States recovered gold and silver from heap-leach operations. Rye Patch Gold optioned the Wilco Project from Newmont Mining Company in 2006 and based on recent exploration drilling completed a new resource estimate for the Wilco project containing 788,000 ounces of gold and gold equivalent in the measured and indicated category and 1,980,000 ounces of gold and gold equivalent in the inferred category.
The Willard gold and silver mineralization is hosted by Late Triassic to Early Jurassic shallow marine and deltaic sediments of the Auld Lang Syne Group. The lithologies are represented by reactive calcareous siltstones and limestone overlain by fissile non-calcareous siltstone. The underlying claystone and siltstone are only locally mineralized along fault zones. The most important structural features controlling the gold mineralization are the siltstone–claystone contact which is gently folded into an easterly-trending, gently westward-plunging antiform, and high-angle faults trending E-W, N-S and NE. This contact was structurally activated, forming a highly fractured and brecciated zone, used by the gold- and silver-bearing hydrothermal solutions. Alteration is dominated by decarbonatization, silicification and quartz ± calcite ± adularia veining. Radiometric data from adularia rendered an age of 6.1 ± 0.3 m.y. for the mineralizing event at Willard; however, altered siltstone fragments have been found in the overlying rhyolitic volcanics suggesting multiple precious metal bearing events.
The Colado gold and silver resource is centered at the intersection of several high-angle faults trending NS, NW and E-W. From this center of hydrothermal activity, the mineralizing solutions spread laterally into a lithologic package consisting of Late Triassic to Early Jurassic siltstones and Tertiary andesite and rhyolitic rocks. The alteration follows bedding planes and internal layering within the volcanics, forming a westward-skewed, mushroom-shaped silica zone that approximates the mineralized envelope. High-level alteration of the low-sulfidation, epithermal type is present at Colado and is represented by a combination of very fine grained silica replacement, quartz-chalcedony-opal veining, hydrothermal breccias, argillization, propylitization, pyritization and oxidation. There is a rough correlation between the overall dimension of the strongly silica-altered zone and gold mineralization. Gold is probably controlled by fine, randomly oriented silica stockworks and veinlets. Higher grade zones occur along favorable bedding horizons, in close proximity to the intersecting feeder structures. The Colado project area lies within a weak geothermal system with hot water approaching 180˚F encountered in most drill holes.