The trona deposits of SW Wyoming are the world’s largest occurrence of natural soda ash. The deposit was formed from the evaporation of a shallow lake, Lake Gosiute, thatcovered SW Wyoming and NE Utah 50-60 million years ago (wyomingmining.org, 2020). The trona mineral deposits within the Sisecam Wyoming lease area are correlated with the lacustrine sequences of the Eocene Green River Formation. Trona and otherassociated evaporates occur within the Upper Wilkins Peak Member. The lacustrine sequences of the Green River Formation were deposited in a series of lakes. Approximately fifty million years ago, Lake Gosiute, fluctuated in areal extent in response to climatic and tectonic events. At its smallest size, during restrictive phases, the lake was very saline and contained large quantities o fdissolved solids. When evaporation of the water reached critical levels, dissolved solids precipitated to form trona, shortite, halite, and other saline minerals. Trona formed as a chemical precipitate and required a specific range of weight percent of sodium and carbon dioxide in solution, a specific range of temperatures, and a specific range of relative concentrations of other ions (calcium, magnesium, chlorides, sulfates, etc.) within the water column. Sediments eroding from the peripheral mountains created extensive alluvial plains and broad flat pediments. Clastic wedges of the Wasatch and Bridger-Washakie formations intertongue and grade laterally with the lacustrine sequences ........

Mining extraction at the Big Island Mine is designed to avoid any surface subsidence due to its proximity to the Green River and multiple natural gas pipelines.

The underground mining operation uses continuous miners (CM) mining in a modified room and pillar method employing a ‘no surface subsidence’ mine design.

The current CM fleet is made up of seven Joy 12HM26 drum miners with integral roof bolting and ventilation fans. These are highly productive machines due to their ability to mine and roof bolt simultaneously. The height of the roof bolters and fan limit the current minimum mining height to 9-feet. When thinner seam areas are encountered, floor or roof rock must be mined for clearance. This out-of-seam material adversely affects the refining process. To maintain feed grade, the current minimum mining limit is 9-feet.

To date, Sisecam Wyoming has not completed two-seam mining with continuous miner panels below existing historic Upper Bed continuous miner panels. For this reason,two-seam mining using continuous miners and existing geometries is considered unverified. To account for this risk, higher mining costs have been used in the economicanalysis and the affect is discussed in Section 19.0. Given the work completed, the existing test panels, and the cost structure at Sisecam Wyoming, it is reasonable to concludethat these areas can be economically mined and therefore are considered reserves in this study.

Four existing sur ........

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