Robert Mahin Thesis: The Mineralogy and Geochemistry of the Apex Gallium-Germanium Mine, Southwestern Utah. Support: Musto Exploration, Inc., University of Utah Abstract The Apex germanium-gallium mine is located in the Beaver Dam Mountains in southwestern Utah and is hosted by a solution-collapse breccia that is progressively dolomitized and silicified toward the center of the pipe. The ore minerals consist of germanium-bearing goethite and gallium-bearing jarosite family minerals and iron oxides. Primary minerals deposited by hydrothermal fluids include pyrite, marcasite, galena, chalcopyrite, bornite, sphalerite, anhydrite, quartz, and goyazite. Secondary minerals include base metal carbonates, chalcocite, covellite, beudantite, and various oxides. Three types of jarosite occur: fine-grained (Type 1), crystalline (Type 2), and massive (Type 3). The presence of other primary sulfate minerals, the lack of any local source of potassium and the absence of samples clearly indicating a secondary weathering relationship of sulfide to jarosite suggests that some of the jarosite may be hydrothermal in origin. Thermodynamic stability of jarosite permit the formation of hypogene jarosite for the postulated conditions of Apex hydrothermal mineralization. Most sulfides are relatively high in germanium and gallium (0 to 2200 ppm Ge, 0 to 2200 ppm Ge). Exceptions are pyrite, which is low in germanium, and sphalerite, which is low in both elements. Galena showed the highest gallium content averaging 1100 ppm Ga. Type 2 jarosite is low in gallium while Type 1 and Type 3 jarosites are relatively high in gallium. Gallium-beudantite Pb(Fe,Ga)3(AsO4)(SO4)(OH)6 contained up to 18.07 weight percent Ga2O3. Apex goyazite has an average composition of Sr0.93Ca0.17Al3(PO4)1.69(SO4) 0.31(OH)5.31*(H2O)0.69. Coexisting liquid and vapor homogenization fluid inclusions indicate boiling. Microthermometric analyses show that the fluid in inclusions average 0.42 weight percent NaCl equivalent and were trapped at a temperature of 200+/-20°C. Initial ice melt in the range -32 to -30°C indicates the presence of divalent cations. Estimations of other geochemical parameters of the hydrothermal fluid include pH = 4.1-6.2, aCa++ = 10-1.52, aK+ = 10-2.36, log fO2= -39 to -36, log fS2 = -10.9, pCO2 = 4.5 bar, and total sulfur = 10-2.56. Enrichment of gallium in galena and relative depletion of gallium in other sulfides, along with petrographic evidence, suggests that galena may have been deposited in a later stage on primary mineralization. Gallium-beudantite is probably a product of secondary weathering and enrichment of this galena. Mass balance calculations suggest that primary gallium-bearing sulfides observed at the Apex mine could have provided enough gallium but that some primary germanium mineral such as germanite (Cu26Fe4Ge4S32), argutite (GeO2), briartite Cu2(Fe,Zn)GeS4), or renierite ((Cu,Zn)11(Ge,As)2Fe4S16) is probably required to provide enough germanium to match the ore grades at the Apex mine. The probable source rocks for Apex germanium and gallium are the cambrian Bright Angel shale and the precambrian basement metamorphics. The Apex Mine, Utah (circa 1992) Gallium melts at 86°F- "Liquid during the day; solid at night" Mahin, R., 1990, The mineralogy and geochemistry of the Apex gallium-germanium Mine, Southwestern Utah, M.S. Thesis, The University of Utah, 102 p. Mahin, R.A. and Petersen, E.U., 1987, Jarosite-family minerals from the Apex mine: Supergene or hypogene?: Geological Society of America Abstracts, 19, 7, 756. Petersen, E.U., Bowling, D.L. and Mahin, R.A., 1988, Geology, mineralogy and genesis of the Apex Ga-Ge Deposit, Tutsagubet District, Utah: Symposium on Precious and Rare Metals Abstracts, New Mexico Tech. State Mining and Mineral Resource Institute, Albuquerque, New Mexico, April 6-8, 1988. pdf Petersen, E.U., and Mahin, R.A., 1988, Characteristics and timing of rare metal (Ga, Ge) hydrothermal systems: Apex Mine, Tutsagubet District, SW Utah: Geological Society of America Abstracts, 20, 7, A152.