Copper-silver mineralization at Sam Goosly occurs as a conformable lens within pyroclastic dacites of probable late early Cretaceous age. Most mineralization is contemporaneous with development of aluminous alteration minerals. Distribution zones of scorzalite, andalusite, and an innermost corundum zone, are concentric and broadly outline the mineralized zone. Southwards, along strike, the andalusite zone becomes an andalusite-pyrophyllite zone in which mineralization post-dates aluminous alteration. Regional metamorphlsm has overprinted a propylitic, or greenschist, assemblage on aluminous alteration. Country rocks and mineralization are intruded by two stocks: a 59 ± 3 m.y. quartz monzonite to the west of the ore zone, and a 51 ± 3 m.y. gabbro-monzonite stock to the east. Contact metamorphlsm associated with the gabbro-monzonite has produced a narrow, discontinuous zone of biotite hornfels and recrystallized metallic minerals in the ore zone. Alteration mineral assemblages and sulphide exsolution textures imply temperatures between 350°C and 625°C in the main ore zone. The assemblage andalusite-pyrophyllite-quartz indicates alteration temperatures of about 350°C in the andalusite-pyrophyllite zone. Chemical analysis of the altered volcanic host rocks suggests significant loss of soda and lime, and residual concentration of silica and alumina. These chemical changes probably result from exchange of Na⁺ and Ca⁺⁺ for H⁺ from a hydrothermal fluid, resulting in formation of aluminous minerals and quartz. The value of log mK+/mH+ of the fluid phase is deduced to be between 1 and 2. By analogy with other occurrences, this process probably takes place in a high-temperature solfataric, or geothermal environment. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

A thesis submitted to the Faculty of Science (Geology), for the Degree of Doctor of Philosophy,University of the Witwatersrand, Johannesburg,1979 / This study is concerned with the geological history and porphyry- type copper molybdenum of the southeastern Richtersveld Province, in southern South West Africa. An area of approximately 300 km2 centred on the Haib copper prospect, was mapped at a scale of 1:10 000 and subsequently reduced. Observations of facies changes, textural changes, structural and other geological features were recorded and processed. Field work was followed by petrological and geochemical investigations. [Abbreviated Abstract. Open document to view full version] / WS2017

Potassium metasomatism is a widespread alteration type in porphyry copper deposits and is often spatially associated with hypogene sulfide ore formation. At Ajo, potassic alteration composes the dominant alteration type and is spatially, and to some extent, temporally, associated with chalcopyrite and bornite mineralization. Physiochemical conditions prevailing during potassic alteration thus describe a significant portion of the hydrothermal ore-forming process. Studies of fractures, fluid inclusions in quartz, and structural and compositional characteristics of K-feldspar, all in the potassic alteration zone at Ajo, indicate that: fracturing was strongest during potassic alteration and sulfide deposition, pressure were at approximately 650 bars, temperatures started a a minimum of 580°C, continued through 470°C, log aK+/aH+ changed from 2.6 at 580°C to 3.2 at 470°C, log aNa/aH+ changed from 2.7 at 580°C to 3.8 at 470°C, and the ratio aK+/aNa+ radically decreased from 0.8 to 0.3 in this temperature range.

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The Mineral Park mine is a porphyry copper-molybdenum deposit developed within and adjacent to a Laramide quartz monzonite porphyry stock which intrudes Precambrian rocks in northwestern Arizona. The Precambrain sequence consists of older, broadly folded metasedimentary and metavolcanic rocks which were intruded by a 1700-1800 m.y. old granite gneiss batholith. The contact between the two Precambrian terranes is a major structural element in the district and appears to have been important in localizing the Laramide intrusions and mineralization. Alteration is defined by early pervasive biotitization of hornblende in the Precambrain rocks and by recrystallization of rock biotite in the quartz monzonite porphyry. Pervasively biotitized rocks are crosscut first by biotite and then by K-feldspar veinlets. Fracture-controlled, economic sulfide mineralization then began with quartz-molybdenite-K-feldspar-anhydrite and was followed by quartz-chalcopyrite-K-feldspar-anhydrite. This potassic alteration and accompanying mineralization occur throughout the deposit and are crosscut by later quartz-pyrite-sericite veinlets. Orientations of mineralized fractures evolved through time from EW during molybdenum mineralization to NW during quartz-pyrite-sericite mineralization. Fracture densities during molybdenum mineralization averaged 0.05 cm⁻¹ and increased to 0.14 cm⁻¹ during quartz-pyrite-sericite mineralization. Sulfides were deposited from low salinity fluids (0.5 - 2.0 molal) in the temperature range 330°-360°C. High salinity fluids occurred only with quartz that was earlier than sulfide deposition. No homogenization temperatures greater than 440°C were observed. Molybdenum mineralization cuts all rock types and defines a vertical cylinder with a distinct low-grade core. Ore grade molybdenum mineralization is equally distributed between Laramide and Precambrian rocks, and overall grade decreases with depth. Hypogene copper mineralization has a greater lateral distribution than molybdenum mineralization, and surrounds a low grade core coincident with the low grade molybdenum core. The distribution of alteration and mineralization assemblages and the fact that both of these features crosscut all exposed rock types suggest that copper-molybdenum mineralization was not temporally related to the quartz monzonite porphyry exposed in the mine area. The narrow range of homogenization temperatures observed and the lack of high homogenization temperatures compared with the results of computer modelled systems indicate formation of mineralization 2 to 3 km above a source intrusion. Because no evidence for boiling was observed, only minimum pressures of formation can be determined. Minimum pressures during sulfide deposition varied from 180 to 80 bars. These pressures correspond to minimum depths of formation of 2 to 3 km which is in good agreement with an inferred depth of burial of approximately 3 km based on stratigraphy restored from the adjacent Colorado Plateau.

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Mémoire (M.Sc.T.)--Université du Québec à Chicoutimi, 1990. / Document électronique également accessible en format PDF. CaQCU