Summary:
The Bonnie Claire lithium deposit appears to be a lacustrine salt deposit hosted in sediments. The Project area as a sedimentary basin, from an environment and geology point of view, is reasonably well represented by the USGS preliminary deposit model, which describes the most readily ascertainable attributes of such deposits as light-colored, ash-rich, lacustrine rocks containing swelling clays, occurring within hydrologically closed basins with some abundance of proximal silicic volcanic rocks. The geometry of the Bonnie Claire Deposit is roughly tabular, with the lithium concentrated in gently dipping, locally undulating Quaternary sedimentary strata. The sedimentary units consist of interbedded calcareous, ashrich mudstones and claystones, and tuffaceous mudstone/siltstone and occasional poorly cemented sandstone and siltstone.
From a lithium deposit point of view, Bonnie Claire is interpreted to be a new type of sediment- hosted lithium deposit whereby lithium compounds such as lithium carbonate and lithium salts have been deposited within the fine grain clay, silt, and sand pore space. Although most of the sediment-hosted lithium in the literature occurs in clays, it does not at Bonnie Claire.
Bonnie Claire is the lowest in elevation of a series of intermediate-size playa-covered floodplains, with an area of about 85 km2 that receives surface drainage from an area of more than 1,200 km2. The plain and alluvial fans around it are fault-bounded on all sides, delineated by the Coba Mountain and Obsidian Butte to the east, Stonewall Mountain to the north, the Bullfrog Mountains and Sawtooth Mountains to the south, Grapevine to the southwest, and Mount Dunfee to the northwest.
The area surrounding the Project area is dominated by uplifted basement rocks that were mostly built from silicic ash-flow tuff. The four reverse circulation (RC) borings drilled on the Project, with a maximum depth of 603.5 meters (1,980 feet) (BC-1602), did not encounter the bottom of the sediments.
Lithium mineralization comes from the evaporation of surface and groundwater. As a highly-soluble salt, lithium mobility and deposition are driven by the movement of surface and groundwater rich in lithium into a closed basin and by the concentration of salts resulting from evaporation.
Significant lithium concentrations were encountered in the alluvial fans and playa within the Project area. Elevated lithium was encountered at ground surface and to depths of up to 603.5 meters (the deepest depth of RC-drilling so far). The lithium in the sediments at the Project occurs as lithium carbonate or lithium salts deposited in the fine grain clay, silt, and sand pore space. The lithium is not found within the clay crystal lattices as is common with most sediment hosted deposits. The overall mineralized sedimentary package is laterally and vertically extensive, containing roughly tabular zones of fine-grained sediments grading down to claystone.
The average grade of lithium appears to depend on the sedimentary layers:
• Sand or sandstone appears to have the lowest grade, averaging about 30 ppm Li near the surface to 570 ppm Li at depth;
• Silt or siltstone appears to have approximately 135 ppm Li near to the surface to 1,270 ppm Li at depth;
• Clay, claystone, and mudstone appear to have 300 ppm Li near the surface to 2,550 ppm Li at depth.
It also appears that fine-grained materials trap and contain lithium and therefore form the highest-grade portions of the deposit.
The Quaternary sedimentary deposits are of primary interest to this study. They consist of clastic materials ranging in size from large boulders on the alluvial fans to fine-grained clay in the playa. The deposits are fluvial, lacustrine, or aeolian, depending on the location and the energy of the deposition environment. The fluvial deposits were deposited in alluvial fans, along stream channels, and in flood plains. Finegrained lacustrine deposits were deposited in the bottom of ephemeral lakes. Aeolian deposits exist throughout the Project area.
The fluvial quaternary sedimentary deposits have been subdivided into Older Alluvium and Younger Alluvium. Older Alluvium has been deformed and dissected in places, and parts of it are cemented into a firm fanglomerate. Younger Alluvium consists mostly of unconsolidated gravel, sand, silt, and clay which form recent fluvial and lacustrine deposits.
The quaternary sediments have created a flat landscape over most of the Project area. The alluvial fans located in the eastern portions of the Project area are commonly mantled with weathered remnants of rock washed down from the surrounding highlands. Alluvial fans are also covered with sporadic shrubs, which are the only vegetation in the region. The playas are completely covered by mud and salt and are commonly referred to as mud flats in this report.
Drilling logs show that within the Project area, the extensional sedimentary basin has been filled by sand, silt, and clay. From the available drilling, it appears the material grades from clay to sand in particle size and minor amounts of cementation. However, all sediments appear to contain between 5% and 10% clay.