Dixie Valley Exploration Project
The six Dixie Valley claim blocks cover the majority of the Humboldt Salt Marsh playa located in Dixie Valley, Churchill County, Nevada. There are 910 placer claims in total, covering about 7,363 hectares (28.4 square miles) of playa and alluvial fan. Hot Springs and other active geothermal features are found along a 30 km long fault system on the west side of Dixie Valley. Numerous geologic studies have been conducted on the geothermal system during production drilling and as a test case for geothermal exploration methods. Of seven characteristics of Lithium Brine deposits outlined in the USGS deposit model, all seven are found in Dixie Valley; however very little exploration work has been directed at lithium in this area. The lithium target model for Dixie Valley is a Clayton Valley style playa brine type deposit.
On July 15, 2016 Nevada Energy Metals has agreed to an Option Agreement where Wildcat Exploration Ltd. can acquire a 100% interest, subject to a 3% Net Smelter Royalty, in 348 of 911 mineral claims located in Dixie Valley, Churchill County, Nevada. The Option Agreement is “non-arms’ length” and so constitutes a related party transaction, as the Company’s President and CEO, Rick Wilson, is also a director of Wildcat Exploration Ltd
Dixie Valley is located in west central Nevada, about 160 km east northeast of Reno. The entire basin is about 98 km long and up to 16 km wide. Humboldt Salt Marsh, the central playa is about 10 km northeast – southwest and 6 km east – west. The basin is bounded on the west by Stillwater range on the east by the Clan Alpine Range.
The Stillwater and Clan Alpine Ranges are composed of thrust sheets of Triassic and Jurassic age marine sedimentary rocks and Jurassic intrusive complexes that were accreted to the North American continent during the Cretaceous. These rocks have in turn been intruded by Cretaceous and Tertiary stocks and dikes and covered by their volcanic equivalents. In the southern Stillwater Range, an entire Tertiary caldera complex, including the sub-volcanic intrusive body is exposed. At the end of the last ice age, water filled the central part of Dixie Valley to a depth of about 70 meters. Radiocarbon dating of tufa in Dixie Valley and adjacent valleys indicate high water stands at about 12,000 to 14,000 and 45,000 to 50,000 years ago. Hydrogen and oxygen isotope data indicates the vast majority of the water in Dixie Valley is ice age in origin indicating very little modern input into the basin.
These ranges are fault bounded, with the most movement along Stillwater Range (west) side of the valley. Vertical displacement along this fault complex is at least 3,000 meters as evidenced by volcanic rocks exposed near the top of range also being found under 1,500 to 2,000 meters of post-volcanic valley fill. These fault are still very active with earthquakes greater than magnitude 6 occurring in 1915 and 1954.
In the area of the Humboldt Salt Marsh Playa, the valley appears to be about 2,000 meters deep, primarily filled with poorly sorted coarse conglomerate, gravel, sand and silt with volcanic rocks, and tuff beds, and finer sediments in the lower third of the section (Blackwell et al, 2014). Multiple governmental, academic and industrial geophysical studies have been conducted in the valley to help guide geothermal exploration in other basins. However, many of the conclusions of these studies were shown to be incorrect by production drilling so studies continue to find surface exploration methods that hold up better to drill testing.
Dixie Valley is home to a large and long-lived geothermal system that is still active. The Caithness Dixie Valley geothermal plant, about 18 km northeast of the center of the playa, is currently producing about 66 megawatts of power. The active geothermal system extends about 30 km roughly north – south along the range front fault. The heat source appears to be simple very deep circulation into the crust; it is not related to igneous activity.
Geothermal production wells and re-injection wells provide some subsurface data but the majority of these have targeted the range bounding structures on the western side of the valley that host the hottest water; not the more static and cooler central valley which hosts the lithium target. At this point the lithium target in this basin is highly conceptual. Although several workers have studied the geology of Dixie Valley in some detail, the lithium potential has not been specifically addressed.
The target model is a lithium brine model based on Clayton Valley, Nevada and several basins in South America. US Geological Survey Open File Report 2013-1006 lays out seven characteristics of Lithium Brine deposits (Bradley et al 2013). The characteristics are:
- Arid Climate
- Closed Basin containing a playa or salar
- Tectonically driven subsidence
- Associated igneous or geothermal activity
- Suitable lithium source rocks
- One or more adequate aquifers
- Sufficient time to concentrate brine
The Dixie Valley Project is known to have all seven of these characteristics. How closely this project fits the model for a lithium brine deposit is not necessarily a warranty that an economic deposit will be found here but it is useful as a screening tool to guide exploration efforts.
Dixie Valley is arid; the State of Nevada Division of Water Resources website (www.water.nv.gov/mapping/et/et_general.cfm) shows a 1.3 meter (4.3 ft.) Net Irrigation Water Requirement (NIWR – the net of evapotranspiration minus effective precipitation) for shallow open water and about 1 meter for low managed pasture grass. Isotopic studies (Blackwell et al 2014) indicate the majority of the water in the basin is of ice-age origin that what little modern precipitation that reaches the valley does not contribute significantly to the ground water. Dixie Valley is a closed fault-bounded basin with the lowest elevation point (1031 m, 3383 ft.) in the Northern Great Basin on the Humboldt Salt Marsh Playa. Age dating and other work at the Dixie Comstock Mine indicate gold mineralization occurred about 500, 000 to 350,000 years ago along a range bounding structure that has been offset at least 100 meters since that time (Vikre, 1995). Faulting dated at about 11.1 to 15 million years before present resulted in at least an ancestral Dixie Valley existing from that time until the present. The basin is tectonically active with visible fault scarps formed during earthquakes in 1915 (Mw ~ 7.2) and 1954 (Mw ~ 6.9). With up to 6 meters of dip-slip offset along some of these scarps, it is clear that Dixie Valley is still subsiding. Given the valley has been a closed basin for at least 500,000 years and probably much, much longer, plenty of time has elapsed for evaporative concentration of lithium bearing geothermal and surface water.
Specific lithium-rich source rocks have not been clearly identified in this basin but Miocene age felsic ashflows are found in the ranges on all sides along with shallow intrusive bodies of similar composition. Geothermal water in the basin contains up to 4.89 ppm Li and stream sediment samples from the Stillwater range show values to 80 ppm li. Geologically recent volcanic ash from the Long Valley Caldera (Bishop Tuff) and Mono craters are expected to be found within catchment area of the basin and within the basin fill sediments. One major productive horizon in the Clayton Valley brine field is thought to be Bishop Tuff deposited and preserved in the basin (Zampirro, 2004).
The conceptual model is as the basin went through multiple wet and dry periods; lithium dissolved by deep circulating geothermal fluids or leached from local rock units by surface and near surface water is concentrated by evaporation beneath the playa. Heavier brines sink into the deeper levels of the basin or flow downward along tilted permeable beds, potentially forming subsurface pools of lithium rich fluids. The process can be likened to an inverted oil field, with the target material being descending fluids caught in gravity traps instead of ascending fluids caught in the tops of structures. This model is somewhat akin to placer gold deposits wherein large areas of very low grade sources are concentrated into economic grades.
The Dixie Valley lithium project is a speculative, conceptual exploration play based on solid geologic information and comparison to productive playas in Nevada and South America. Essentially no exploration work for lithium has been done in this valley. A substantial body of geophysical work has been done related to the active geothermal systems that will serve as a base to build more detailed work on. Gravity surveys have proven to be the most useful method in defining subsurface topography and sufficient drilling data exists to calibrate three dimensional modeling of the data. The majority of the drilling has been directed at the basin bounding faults which host the geothermal fluids. The target for lithium exploration will be more towards the center of the basin where evaporative concentration of geothermal and meteoric water into brines and subsequent sinking of the denser brines into gravity traps may produce economic concentrations. Understanding (largely through geo-physical surveys) of the subsurface topography and stratigraphy will be critical to identifying trapping features and drill targets. Initial work will also include auger or push rod type mud sampling to prove lithium has concentrated in evaporite minerals and interstitial fluids within the playa sediments.
Blackwell, David D., Smith, Richard P., and Richards, Maria C., 2007, Exploration and Development at Dixie Valley, Nevada: Summary of DOE studies. Proceedings, Thirty Second Workshop on Geothermal Reservoir Engineering Stanford University, Stanford California, January 22-24, 2007
Blackwell, David D., Smith, Richard P., and Richards, Maria C., 2014 Editors, Description, Synthesis, and Interpretation of the Thermal Regime, Geology, Geochemistry, and Geophysics of the Dixie Valley, Nevada Geothermal System; Southern Methodist University Geothermal Laboratory.
Bradley, Dwight, Munk, LeaAnn, Jochens, Hillary, Hynek, Scott, and LaBay, Keith, 2013, A Preliminary Deposit Model for Lithium Brines, USGS Open File Report 2013-1006.
Vikre, Peter C., 1994, Gold mineralization and fault evolution at the Dixie Comstock Mine, Churchill County, Nevada; Economic Geology, 89, N. 4, 707 – 719.
Zampirro, D., 2004, Hydrology of Clayton Valley brine deposits, Esmeralda County, Nevada in Castor, S.B., Papke, K.G., and Meeuwig, R.O., eds., BETTING ON INDUSTRIAL MINERALS: PROCEEDINGS OF THE 39TH FORUM ON THE GEOLOGY OF INDUSTRIAL MINERALS, RENO-SPARKS, NEVADA, MAY 18-24; Nevada Bureau of Mines and Geology Special Publication 33, p.271 -280.
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