The Painted Hills project is in northwestern Nevada, in Humboldt County, 17 miles southwest of the town of Denio. The project exposes the upper parts of a low-sulfidation epithermal vein system of probable Middle Miocene age and lies along the regional northeast-trending Black Rock Structural Boundary, at its intersection with a northwest-trending fault zone. Host rocks consist of a gently-dipping sequence of basalt flows and successively overlying felsic tuffs and volcaniclastic sandstone. These units underlie the Middle Miocene (~15 Ma) Cañon rhyolite exposed largely west of the mineralized area. A silicified tuff in the southwest part of the project area is interpreted as an exogenous flow dome and has been dated at 14 Ma.
Strongly-argillized (kaolinite) and hematitic felsic tuffs are exposed in lower areas in the central part of the project and contain anomalous As, Hg and Sb. The overlying sandstone is largely unaltered, but locally contains stratiform opal and steeply-dipping opal veins, which in one area form a 100m-wide stockwork zone, and are only weakly anomalous in As, Sb and Hg. A northerly-trending steep silicified fault is exposed about 500m south of and on strike with the opal stockwork zone, contains elevated As, Hg and Sb, and has apparent east-side-down offset. The fault was identified by a geophysical survey completed in 2007. The opal veins, silicified structure and argillic alteration occur along a 1.6km north-northeast trend inboard and broadly parallel to the modern range front, but the trend merges with the range front in the northern portion of the project area. Pyritic chalcedonic silica float from below the opal vein stockwork contains anomalous gold (to 107 ppb) and strongly-anomalous Hg, As, Sb and Mo, indicating that gold is present in the system and that metal contents and paleo-temperatures are increasing at depth.
A drilling program in 2007 was the first to be completed in the project area and was designed to test the deeper levels of the system toward an inferred boiling level, where high-grade gold-bearing veins would be expected. Four core holes totaling 1,852m (6076.5 ft) were completed by International Tower Hill Mines, Ltd., who is earning a majority interest in the project from Redstar under terms announced March 16, 2007 (see news releases). Holes were angled to cross beneath the exposed vein and alteration trend. About 440m of strike was tested. All holes intersected multiple zones of strong pyritic silicification typically 25-40m thick with local stockworks of variably sulfidic, multiple-generation chalcedony veins. The silicified zones, hosted in the tuff sequence, are surrounded by pyritic argillic alteration and are interpreted as steeply dipping. The silicification occurs across a plan width of about 200m. Gold values are anomalous in silicified and veined intervals, reaching 330 ppb, and correlate strongly with Mo. Mercury and Sb tend to be enriched in shallower zones, with Mo-As-Au enriched in deeper zones.
The 2007 drilling program validated the exploration model by demonstrating increasing gold with depth (it is essentially absent at surface) and a change from opal to chalcedony with depth, which is consistent with increasing temperature. However, the presence of vein sediment and absence of bladed calcite/quartz and absence of sugary-type quartz indicate that the potentially gold-silver rich boiling level remains deeper or lateral to the area drilled. The presence of Mo and its correlation with gold is a favorable element, as Mo is enriched in nearby, productive low-sulfidation gold deposits of similar Middle Miocene age, such as Sleeper and Hog Ranch. At Sleeper the strongest correlation to gold in high-grade veins is Mo and Ag.
Additional drilling is recommended to explore other portions of the mineralized trend, the range front and pediment to the east, and follow-up in the area drilled in 2007.
