Natural Resource Partners L.P. own a 49% non-controlling equity interest in Sisecam Wyoming. Prior to 2023, Sisecam Resources LP owned 51% interest in Sisecam Wyoming. Sisecam Resources LP was a publicly traded master limited partnership that depended on distributions from Sisecam Wyoming in order to make distributions to its public unitholders. In 2023, Sisecam Resources LP was dissolved and Sisecam Chemicals Wyoming LLC ("SCW LLC") became the direct owner of 51% of Sisecam Wyoming. SCW LLC is an operating partner, and controls and operates Sisecam Wyoming. SCW LLC is 100% owned by Sisecam Chemicals Resources LLC ("Sisecam Chemicals,") which is 60% owned by Sisecam USA Inc. ("Sisecam USA") and 40% owned by Ciner Enterprises Inc. ("Ciner Enterprises"). Sisecam USA is a direct wholly-owned subsidiary of Türkiye Sise ve Cam Fabrikalari A.S, a Turkish Corporation, which is an approximately 51%-owned subsidiary of Turkiye Is Bankasi Turkiye Is Bankasi.
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Summary:
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 of the Green River Formation.
Within the hydrogeographic basin of approximately 77,300 km (48,500 square miles), the greatest expanses of Lake Gosiute and surrounding mudflats occurred during the Tipton and Laney stages. Bradley (1964) estimated the lake expanded to over 24,000 km (15,000 square miles). Total evaporation of Lake Gosiute during the restrictive phases of the Wilkins Peak stage is indicated by the presence of sedimentary structures in the deposit.
TRONA BEDS OF THE GREEN RIVER BASIN
The US Geological Survey recognizes 25 trona beds of economic importance (at least 1 meter in thickness and 300 km in areal extent) within the Green River Basin. Identified in ascending order, the trona beds are numbered 1 through 25 from the oldest (stratigraphically lowest) to the youngest (stratigraphically highest). Sisecam Wyoming has mineable reserves in the shallowest mechanically minable Trona Beds 24 and 25 (800 to 1,100-feet deep). Currently Genesis.
Alkali, Solvay, and Tata are mining Bed 17 occurring at greater depth. Pacific Soda is focused on the lower trona beds, Bed 1 through Bed 4, utilizing solution mining due to the trona depth.
Trona Bed 1 through 18 of the Lower Wilkins Peak are relatively tabular with a fine grain sugary appearance. Various amounts of halite are present and can become more salt, halite, than trona towards the southwestern portion of the depositional basin. Halite is a significant contaminate in the refining process and reduces recovery and increases production cost. A stable depositional environment is implied by uniformity and minimal variation of the depocenters of Beds 1 through 18.
Trona Beds 19 through 25 are relatively halite free and consist of amber translucent coarse-crystalline blades to coarse granular “sugary” textured masses. Trona Beds 19through 22 are located in the northwestern corner of the Green River Basin saline depositional basin. Trona Beds 24 and 25, mined by Sisecam Wyoming, are located in the northeastern corner of the Green River Basin.
Local Geology
Mineral reserves within the Sisecam Wyoming lease area are confined to Trona Beds 24 and 25. Isotope analysis of a volcanic layer, known as the Big Island Tuff, located between these beds, has dated deposition at approximately 49 million years. Local structural gradient is oriented west/southwest at a grade of approximately 50-feet per mile and was influenced by the structural high of the Rock Springs Uplift to the east. Overburden depths of Beds 24 and 25 increases along the strike of the dip from typically 800-feet to 1,100-feet with increasing surface topography.
Depositional and post-depositional sedimentary structures have been observed in the Sisecam Wyoming Mine and have had some impact on production grades and/or mining. These structures include:
Polygonal, vertically oriented, clay filled features are common, suggesting intense evaporation and desiccation, resulting in the formation of large “mud-cracks” within the deposit. Sisecam Wyoming Bed 25 exhibits these features in greater detail than Bed 24.
“Blow-outs” occurring in both beds, represent a massive dewatering event from vertical brine movement eroding the trona bed. Results of this movement have been observed to completely obliterate the beds from a 12-foot seam thickness to zero within a 50-foot distance span.
Geological faulting, movement, and fracturing have been observed in Bed 25. The occurrence of locally identified “root-beer” seams is associated with this type of disturbance.
Post-depositional dissolution from moisture/groundwater has been observed in the Lower Bed 24. Relatively isolated, the trona bed appears to be dissolved from the top after deposition, resulting in thinning of the bed and an increase in insoluble content in the upper portion of the seam.