The Weepah project is in the Weepah Hills southwest of Tonopah, NV in the central portion of the Walker Lane. The Walker Lane is a northwest-southeast oriented dextral shear zone situated in between the Sierra Nevada batholith to the west and the Basin and Range to the east. The Walker Lane is a long-lived structural discontinuity, subparallel to the San Andreas fault, and is associated with a series of gold and silver deposits that host over 52.6 M oz Au and 549 M oz Ag. The greatest concentration of mineral deposits are volcanic-hosted precious metal deposits (Roberts, 1966) but also include orogenic shear zone related gold deposits such as Mineral Ridge and Weepah (Claypoole, 2018). Mineral Ridge and Weepah are hosted in metamorphosed sediments and intrusive rocks that have been subjected to extensive folding, thrust faulting, low-angle detachment extensional faulting, and younger high-angle normal faulting.
Gold hosting metasediments at Weepah include Proterozoic rocks of the Wyman Formation, which consists of quartzites, quartz-mica schists, phyllites, calc-silicate rocks with an overlying subunit of deformed dolomite (the Reed Dolomite). The Reed dolomite is itself overlain by Cambrian Campito Formation, consisting of interbedded siliciclastic rocks and quartzites, and the Poleta Formation, consisting of interbedded silty limestones, quartzite, and dolomite, as described by McKee (1968). Metamorphic grade seems to increase down section. This entire metasedimentary sequence is intruded by Mesozoic and Cenozoic rocks (Figure 5), including Cretaceous age quartz monzonites of the 85.3±4.3 Ma Lone Mountain series (John and Robinson, 1989) and plutons, diorite sills, silicic porphyry dikes and mafic dikes of the Weepah Complex (Sonderman, 1971).
The Weepah district is located in a southeastern plunging anticline cored by the granitic Weepah pluton. Structure at Weepah is characterized by broad flexures, minor thrusting and high-angle faults (Sonderman, 1971). Deep drilling of the Weepah shear zone west of the historic mine intersected the mineralized fault zone completely within the Weepah pluton (Price, 2016), indicating that shear zone development and mineralization post-dates magmatism. The brittle and often planar nature of the shear zone indicates that mineralization took place well after the intrusions had cooled. As such, the relative timing of mineralization may be similar to mineralization at Mineral Ridge, which postdates intrusive host rocks by ~15 Ma, occurring at 76.0±1.8 Ma (Claypoole, 2018).
The two known gold deposits at Weepah are; the Weepah West shear zone where the historic pit is located, and the Weepah East zone. The Weepah shear zone is a quartz-iron oxide filled, northeast-trending, dextral oblique slip shear zone dipping ~45° to the west. Gold occurs predominantly as free grains, (or within iron oxides) in a silicified gouge composed of quartz and altered country rock zone (Sonderman, 1971). The quartz is multi-episodic, some crushed by later continued movement on the shear zone, and some uncrushed, presumably post-tectonic.
The Weepah East zone is characterized as a near-surface, shallowly dipping, recrystallized carbonate or carbonate replacement horizon (Price, 2016). Less is known about Weepah East as there is no reliable bedrock and drilling has been limited (only RC/no core) and erratic (fanned holes instead of grid drilling). Mineralization at the Weepah East zone may be structurally controlled by one of two new faults zones identified during the Phase I exploration program. Surface geochemistry reveals these new faults to be associated with signature elements associated with gold and drill holes along the margins of these fault zones contain strong intercepts of gold mineralization. These indicators support the new conceptual model of mineralization along fault zones bounding the pediment.
Geologic mapping, rock chip sampling and soil sampling during the Phase I exploration program has identified two new target fault zones where mineralization is indicated (Figure 2). Pediment soil sampling has proven to be an important tool in this program, delineating surface mineralization through cover that correlates spatially with these newly identified faults.
Pediment soil sampling is designed to detect even the most subtle geochemical signature from bedrock and structures buried beneath the overlying pediment. Arsenic, thallium and gold can all be water soluble. In the proper conditions, such as fault zones that act as fluid conduits, these signature elements can be carried from their source, through pediment cover to the surface (Muntean and Taufen, 2006). These transported metals can be detected at very low concentrations when appropriate methods of collection and lab analyses are applied. The results of such pediment soil sampling have helped in discovery of large, buried, Carlin-type deposits, such as the Pipeline deposit in Nevada (Muntean and Taufen, 2006). Applying this method to the exploration program at Weepah, along with mapping and field observations has led the Company’s technical team to develop the two new fault zone targets shown.
Overall, the Phase I exploration program has been successful in redefining the potential for new deposit discoveries at the Weepah project.