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The alteration at the low-sulphidation epithermal Banderas Au-Ag prospect, Guatemala, was characterized using a portable infrared mineral analyzer (PIMA) spectrometer and shown to comprise illite, buddingtonite and, on surface, kaolinite associated with gold mineralization. The Spextract python program, developed by the author, was used to measure variations in the short-wave infrared spectra (SWIR) which were then mapped as equal-area-of-influence or voronoi diagrams. Voronoi maps of the 2200 and 2350 nm absorption features, position and depth, respectively, for illite and 1560 and 2120 nm feature depths for buddingtonite indicate that illite crystallinity and ammonium alteration intensity increase towards gold mineralization. The latter observation suggests that gold transport and deposition may have been controlled by ammonia complexation. At conditions likely to have prevailed during mineralization, i.e., temperatures between 150° and 250°C, a pH between 5 and 8.5, an oxygen fugacity ( fO2 ) near the hematite-magnetite buffer, a chlorinity of 0.5 m, a total sulfur activity of 0.001 m, and a total nitrogen activity of 0.004 m, AuNH3 +2 is the dominant ammonia complex and gold solubility at optimal pH- fO2 conditions reaches ∼65 ppm at 250°C. In contrast, the maximum solubility of gold as AuHS -2 , the species normally assumed to control gold transport in epithermal systems, is approximately four orders lower at 250°C; at 150°C the solubility of AuNH3 +2 and AuHS -2 are essentially the same, i.e., ∼9 ppb. A model for Au-Ag mineralization is proposed in which hydrothermal fluids were focused along NW-SE extensional faults and at the contacts of rhyolite domes and tuffs, and gold transport and deposition were controlled mainly by ammonia-dominated complexation and boiling-induced temperature decrease, respectively.

Thesis (Ph. D.)--University of Nevada, Reno, 2006. / "December, 2006." Includes bibliographical references (leaves 152-157). Online version available on the World Wide Web.

Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics 1999. / Bibliography: leaves 233-260.

Thesis (Ph.D.)--University of Western Australia, 2003.

Thesis (Ph.D.)--University of Western Australia, 2005.

Thesis (Ph.D.) -- James Cook University, 2006. / CD-ROM contains appendices 5-9, 12. Typescript (photocopy) Includes bibliography.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1905. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed November 12, 2008)

Thesis--University of Missouri, School of Mines and Metallurgy, 1900. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed February 3, 2009)

M.Sc. / A prominent zone of deformation, identified as a possible hydrothermal fluid pathway, has recently been discovered by the author in the 64 SW4 21Line workings at Kopanang Gold Mine. The zone is between 3m and 16m wide, has a NE SW trend and dips steeply (65°-70۫°) towards the SE. Very little to no displacement seems to occur along this zone of alteration that is marked by intensive albite veining; the surrounding host rocks are also intensively altered (albitized). Albitization resulted from sodium metasomatism, during which Na was exchanged for K, and was accompanied by quartz dissolution which resulted in vug formation. This alteration event is also characterized by REE enrichment, which was found to be most intense in carbonate (ankerite) rich albitized vein fill material. A study of fluid inclusions indicates that the main hydrothermal fluid was of relatively low salinity (14.46 to 19.84 wt% NaCl ), having homogenization temperatures between 59.6 and 117°C. From these measurements it was concluded that a likely emplacement temperature for the studied feature would be in the order of 200°C-300°C at a pressure of roughly 0.5 to 1Kbar. A marked increase of Au grades is observed where the Vaal Reef, the most important economical reef horizon exploited at the mine, is affected by deformation, veining, and associated alteration. In light of the above observations it appears only reasonable to expect that this zone of deformation and hydrothermal alteration could either be the direct cause of, or at least have a prominent influence on the high gold values occurring in the area. A causal link between high Au grades, deformation and hydrothermal fluid flow would have obvious economic implications. The study therefore strives to characterise the extent and style of deformation, constrain the effects of hydrothermal alteration and nature of hydrothermal fluids associated with the structure, and assess its importance for Au mineralization