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The Global ETD Search service is a free service for researchers
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Supergene Mineralogy and Processes in the San Xavier Mine Area-Pima County, ArizonaArnold, L. Clark January 1964 (has links)
This is a study of the supergene mineralogy of the San Xavier West mine located in the Pima mining district, Pima County, Arizona. The number and composition of secondary species collected are found to be closely related to the relative amounts of the various primary minerals and to the manner in which they were emplaced in the host rock. Supergene mineral species were selected that appeared to be in equilibrium with their environment, and certain assumptions are made concerning the stability fields of these minerals. The equilibrium conditions in most cases can be narrowed and often closely defined by combining the stability fields of several secondary minerals. On this basis, two acid environments and one alkaline environment are found to exist and are separable on the basis of mineralogy. The fields of chalcanthite and melanterite define a highly acid environment while those of goslarite and malachite define an environment of lower acidity. The association of calcite, rosasite, hemimorphite, and malachite indicate an alkaline environment. The acidity of the environments is principally determined by the amount of pyrite present, and pH may be lower than 3 if pyrite is abundant and reactive carbonate material lacking. Also, knowledge of stability relations allowed the history of enrichment and subsequent oxidation to be followed in a case where a transitional species had been removed from reaction by inclusion with gypsum.
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The San Alberto Lead-Zinc Ore Body at Cerro de Pasco Mine, Cerro de Pasco, PeruAscencios C., Alejandro January 1966 (has links)
This thesis presents briefly the geology of the Cerro de Pasco district to acquaint the reader with the general geological setting of the district. A study of ore controls for a typical lead-zinc replacement body at the world famous Cerro de Pasco mine in Peru, 102 km northeast of Lima, was undertaken for purposes of better understanding. The particular body selected, the San Alberto Ore Body, occurs as a northeast extension of a main mass of pyrite, known as the "pyrite body", and is enclosed in Triassic- Jurassic limestone. Primary ore controls were determined to be a "Y"-like intersection formed by NS Longitudinal Faulting with a NE striking bedding fault. Resultant brecciation created the necessary permeable conditions whereby ore fluids were channeled away from the pyrite body into the limestone for ore emplacement. Three phases of hydrothermal rock alteration were identified as silicic alteration, chloritic alteration and an outer zone of bleaching and recrystallization. One peculiarity is found in the mineral composition of the silicic alteration, and a hypothesis is presented to explain it. The paragenetic sequence given for hypogene and gangue minerals was determined from the examination of more than 150 thin and polished sections.
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Structural Geologic Controls at the San Luis Mines, Tayoltita, Durango, MexicoBallard, Stanton Neal January 1980 (has links)
In the San Dimas district, on the western flank of the Sierra Madre Occidental, near the small town of Tayoltita, Durango, gold and silver epithermal ore deposits are mined from the complex Arana fault system. The structural relationships of the Tayoltita system are well-mapped, but their kinematic relationship to ore deposition is unclear. In plan view and in cross-section, the Arana system has a horsetail or wedge-shaped geometry. Subsurface mapping of slickenside striae as movement indicators suggest that the N13°W-striking Arana fault, forming the eastern boundary of the system, is a normal slip fault with at least 250 m of throw. Subsidiary system faults display normal separation with varying degrees of dextral horizontal separation (which is a function of fault orientation). Experimental modeling of the Arana system indicated that the system formed under simple shear as the σ₂ and σ₃ stress axes rotated in a subhorizontal plane about σ₁. Rotational strain caused the developing fault strands to rotate and to be captured by the Arana fault, forming the typical wedge-shaped geometry. Later, a more complex rotation of the three major stress axes enabled hydrothermal fluids to progressively mineralize faults, which had more northerly strikes, by a process similar to progressive strain. This is documented by mineral assemblages that record the instants of fault opening and by the lack of mineralization along the high-angle, northwest- striking faults.
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Infra-Red Spectrophotometry and X-Ray Diffractometry as Tools in the Study of Nickel LateritesAzevedo, Luiz Otavio Roffee January 1985 (has links)
Nickel silicate laterite deposits developed on ultra-mafic rocks are similar in many general respects but they vary considerably in detail. The mineralogy of these surficial deposits is very complex and difficult to determine because of the fine grained nature and solid solution characteristics of the hydrous secondary minerals and because many of the phases are actually mineraloids that are poorly ordered or amorphous. To try some new approaches toward clarification of these phases, 24 samples from New Caledonia and Puerto Rico ranging from the ophiolite-ultramafic olivine-pyroxene-chromite-serpentine substrate rocks upward through intermediate phases of weathering to the final oxide -hydroxide iron cap phase were analyzed with the infrared spectrophotometer (IR -10) and with the automated X –ray diffractometer. Four limonite samples were also mineralogically analyzed. Goethite, secondary quartz, cryptomelane, hematite, chromite, talc, thuringite, and garnierite have been identified in various samples as weathering profile products.
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A Re-Os Study of Sulfides from the Bagdad Porphyry Cu-Mo Deposit, Northern Arizona, USABarra-Pantoja, Luis Fernando January 2001 (has links)
Use of Re-Os systematics in sulfides from the Bagdad porphyry Cu-Mo deposit provide information on the timing of mineralization and the source of the ore -forming elements. Analyzed samples of pyrite, chalcopyrite and molybdenite mainly from the quartz monzonite and porphyritic quartz monzonite units are characterized by a moderate to strong potassic alteration (secondary biotite and K- feldspar). Rhenium concentrations in molybdenite are between 330 and 730 ppm. Two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite provide a Re-Os isotope age of 71.7 ± 0.3 Ma. A third sample from a molybdenite vein in Precambrian rocks yields an age of 75.8 ± 0.4 Ma. These molybdenite ages support previous suggestions of two mineralization episodes in the Bagdad deposit. An early event at 76 Ma and a later episode at 72 Ma. Pyrite Os and Re concentrations range between 0.008-0.016 and 3.9-6.8 ppb, respectively. Chalcopyrite contains a wide range of Os (6 to 91 ppt) and Re (1.7 to 69 ppb) concentrations and variable ¹⁸⁷Os/¹⁸⁸Os ratios that range between 0.13 to 22.27. This variability in the chalcopyrite data may be attributed to different copper sources, one of them the Proterozoic volcanic massive sulfides in the district, or to alteration and remobilization of Re and Os. Analyses from two pyrite samples yield an eight point isochron with an age of 77 ± 15 Ma and an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 2.12. This pyrite Re-Os isochron age is in good agreement with the molybdenite ages. We interpret the highly radiogenic initial 1870s/188Os as an indication that the source of Os and, by inference, the ore-forming elements for the Bagdad deposit, was mainly the crust. This conclusion agrees with previous Pb and Nd isotope studies and supports the notion that a significant part of the metals and magmas have a crustal source.
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