The western portion of the project area is dominated by the uplifted basement rocks of Angel Island which consist of metavolcanic and clastic rocks, and colluvium. The southern and eastern portions are dominated by uplifted, lacustrine sedimentary units of the Esmeralda Formation. Locally the Esmeralda Formation is comprised of fine grained sedimentary and tuffaceous units, with some occasionally pronounced local undulation and minor faulting. The resulting topography consists of elongate, rounded ridges of exposed Esmeralda Formation separated by washes and gullies filled with alluvial cobble, gravel and fine sediment. The ridge tops are commonly mantled weathered fragments of rock (desert pavement) sourced from the surrounding highlands. Cypress provides the following description of the stratigraphic units of the Esmeralda Formation in the project area, which form a laterally and vertically continuous stratigraphic section which underlies the south and eastern portions of the project area.

Elevated lithium concentrations, generally > 600 ppm, are encountered in the local sedimentary units of the Esmeralda Formation from surface to at least 142 meters below surface grade (bsg). The lithium-bearing sediments primarily occur as silica-rich, moderately calcareous, interbedded tuffaceous mudstone, claystone and siltstone. The overall mineralized sedimentary suite is a laterally and vertically extensive, roughly tabular zone with at least two prominent oxidation horizons. The primary area of mineralization is in a claystone unit consisting of three zones: oxidized claystone, unaltered claystone and an oxidized claystone. The claystone unit is overlain by tuffaceous mudstone in the eastern portion of the project and underlain by a siltstone. Elevated lithium concentrations occur in all the uplifted lacustrine strata encountered; however, lithium concentrations are notably higher and more consistent in the claystone unit.

The deposit type is represented by the USGS deposit model. The model consists of light-colored, ash-rich, lacustrine rocks that contain swelling clays and occur within hydrologically closed basins proximal to silicic volcanic rocks. The geometry of the deposit at the project is roughly tabular, with the lithium concentrated in gently dipping, locally undulating, sedimentary strata of the Esmeralda Formation. The sedimentary units are interbedded silica-rich, ash-rich mudstone and claystone, with interbeds of sandy and tuffaceous mudstone/siltstone and occasional poorly cemented silt and sandstone. The lithium concentrations are highest within the mudstone and claystone, but lithium is still present in a siltstone unit underlying the claystone.

The deposition of the lithium-rich sediments likely occurred late in the history of the associated paleo brine lake, based largely on the stratigraphic position of the mudstone and claystone above the thick overall sandstone- and siltstone-dominated basin fill events. Such a setting would be ideal for concentration of lithium from ash and groundwater inputs over an extensive period.

All materials within the project’s resource area are relatively flat lying soft sediments. The deposit is covered by a thin veneer of alluvial gravels and extends to a depth of 100 to 140 meters.

Mining will be carried out using conventional surface methods. Excavation will use a single Caterpillar 6020B or equivalent shovel (hydraulic excavator configuration) with a 12 m³ bucket capacity. The material is very soft, so drilling and blasting will not be required.

Truck haulage was studied as an alternative. Conveyor transport to the mill is preferred due to reduced traffic and water for dust control. Conveyors should also result in lower operating cost due to the consumption of electric power instead of diesel.

Material at the mining face will be fed directly to a mobile feeder-breaker and then moved out of the pit using a series of jump conveyors. The material will then be transferred to over-land conveyors and transported to a radial stacker and run-of-mine (ROM) stockpile located at the processing plant.

An ultimate pit shell was used to limit the mine plan and was generated using the variable pit slope.

The bench height and width were set at 7.5 meters and 6 meters, respectively, based on operating equipment reach and minimum road width.


Within the ultimate pit shell, 16 pit phases were generated. The first eight of these were used to design a production schedule with uniform mill feed and minimal waste. At the design nominal production rate of 15,000 tpd, the mine life represented by these eight phases is about 40 years.

The eight phases used the variable slope angles by material type and were designed with maximum road grades in pit of 8%.

Within each verburden and waste material will be removed using CAT 657G or equivalent scrapers with a waste removal rate of 166 tonnes/hour. Ore mining will be done with a hydraulic shovel with a bucket capacity of 12 cubic meters and a production rate of 1,265 tonnes/hour. The shovel will dig and fphase, oeed material to a mobile feeder breaker. Material from the feeder breaker will be transferred to a series of portable jump conveyors, to move the material out of the pit. Finally, the material will be transferred to over-land conveyors and directed to the processing plant or a stockpile as appropriate.

Each pit phase bench will be subdivided into 10-meter wide sections longitudinally. The feederbreaker will initially be set up at one end of the first 10-meter-wide section on the side of the pit phase closest to the plant. Portable jump conveyors, each approximately 30.5 meters long, will be positioned from each end of the pit phase along the outside edge of the 10-meter wide section, converging at the mid-line of the pit phase to transport excavated ore from the working area to the mid-line of the pit phase.

Additional jump conveyors will be positioned transverse to the longitudinal conveyors along the mid-line of the pit phase to transport excavated ore out of the pit. Excavation will proceed from the distant end of the pit phase bench toward the pit phase mid-line. To achieve the production, 153 linear meters of 10-meter wide 7.5-meter-deep section will be excavated daily.

As the excavation proceeds, in-pit longitudinal conveyors along the previous days’ excavation will be moved to the next 10-meter wide section.

This mining method has a low operating cost and requires the least amount of support equipment. There is very little traffic on the haul roads, which reduces road maintenance requirements, water usage, and related costs.

Feed Preparation
Material in the ROM stockpile will be fed to the plant via a linear reclaimer discharging into a two-way splitter and pair of roll crushers with 125-mm openings and discharging into two 350-tonne fine ore bins. Material from the bins will be fed onto variable speed drive feed conveyors and into a set of four stainless steel rotary attritors which will disaggregate the clay by rotary action and reclaim water. Each attritor will operate at 175 tph and feed slurry into slurry feed tanks where additional water will be added to adjust the slurry to 20-25% solids.

Mine to ROM Stockpile
Mine production will use a backhoe type excavator to dig below grade and dump material into a mobile feeder/breaker. The mobile feeder/breaker will break large lumps of material and effectively lower the run of mine (ROM) material to a nominal 125 mm to allow for conveying. The feeder breaker will feed the claystone onto a belt conveyor extending from the mine pit face to a ROM stockpile at the processing plant via a series of jump- and mainline-mobile conveyors. Conveyor haulage from the mine was selected to eliminate truck haulage and allow better efficiency in mine production and is also intended to conserve water by minimizing heavy equipment and dust control for haul road maintenance. Mine feed will be conveyed to a ROM stockpile and will be stored in a 30,000-tonne stockpile by a linear stacker.

Leaching & Filtration
Non-acidified slurry discharging from the attritor will pass through a scalping screen and into a pump box. The scalping s ........