No description available.

No description available.

No description available.

No description available.

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.

Nickel matte is a nickel &de concentrate produced by smelting. It consists mainly of two components: a nickel-copper alloy and heazlewoodite (Ni3S2); but also contains varying amounts of djurleite,Cu 1.96 S.There are several hydrometallurgical routes for processing nickel matte. The most recent of these involves an oxidative leach in acid chloride or sulfate solution. Nickel is subsequently recovered fiom the leach solution by electrowinning or by hydrogen reduction. In the work described in this thesis, various aspects of the acid leaching of nickel matte are investigated using mostly electrochemical methods. The first section concerns the use of copper(II) as an oxidant for the alloy component of nickel matte. In this cementation reaction, nickel goes into solution while copper is deposited on the dissolving metal swf8ce. The same reaction is important in removing traces of copper present in the nickel solution. Here nickel powder is added to the process liquor. A survey of the literature pertaining to the cementation of copper by nickel shows that there is considerable dispute as to the conditions under which cementation takes place. Evans' diagrams for the cementation reaction were constructed by superimposing the polarisation curves for the oxidation of nickel and the reduction of copper. It was found that cementation occurred provided that the two polarisation curves intersected in the region of active nickel dissolution. Outside this region, a copper deposit could not be seen. The second part of the thesis presents some investigations into the electrochemistry of nickel sulfides and nickel matte, and compares both chloride and sulfate media. Oxidation and dissolution rates of nickel matte powders using copper(I1) as an oxidant were also carried out. Dissolution was chemically controlled and so the rate was very dependent upon temperature and solution potential. Displacement of copper(II) from solution to form copper sulfide was also found to be important. In addition to the above studies, which relate directly to the oxidative leaching ofnickel matte, an investigation of the oxidation of HzS to sulfUr in acidic solution was carried out. S u k deposition was found to be strongly dependent on substrate and pH. Under some conditions, two types of sulfUr were deposited, with the more crystalline s u k being reduced at the more negative potential.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references. Also available via World Wide Web.

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.)--Murdoch University, 1998. / Thesis submitted to the Division of Science. Includes bibliographical references (leaves 234-248).

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