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In order to improve our understanding of poorly studied Mexican Porphyry Copper Deposits in the SW regional metallogenetic province, a detailed study of the hydrothermal fluid evolution of La Caridad porphyry copper-molybdenum deposit, and its connection to a high sulfidation epithermal deposit, was performed using oxygen, hydrogen and sulfur stable isotopes combined with fluid inclusion studies. In addition, UPb and Re-Os geochronology from La Caridad, Milpillas and El Arco porphyry deposit were performed to constrain the timing of mineralization and magmatism in northwest Mexico. Uranium-lead zircon ages from La Caridad suggest a short period of magmatism, between 55.5 and 53.0 Ma. Re-Os molybdenite ages from potassic and phyllic hydrothermal veins yielded identical ages within error, 53.6 ± 0.3 Ma and 53.8 ± 0.3 Ma, respectively. Four stages of hypogene alteration and mineralization are recognized at La Caridad porphyry copper deposit. The isotopic composition of the water in equilibrium with hydrothermal alteration minerals is consistent with highly evaporated lacustrine waters mixed with magmatic waters or vapor separated from magmatic fluids, however, sulfur isotopes and fluid inclusions data support the lacustrine-magmatic water hypothesis. Milpillas porphyry copper deposit in the Cananea Mining District, yielded a crystallization age of 63.9 ± 1.3 Ma. Two Re-Os molybdenite ages yielded an identical age of 63.1 ± 0.4 Ma, Suggesting a restricted period of mineralization. Re-Os data indicate that mineralization in Cananea District, spanned ~4 m.y. in three discrete pulses at ~59 Ma, ~61 Ma and ~63Ma. El Arco porphyry copper deposit, Baja California, Mexico, yielded a Middle Jurassic crystallization age (U-Pb) of 164.7 ± 6.7 Ma and a Re-Os mineralization age of 164.1 ± 0.4 Ma and not ~100 Ma as previously determinated. Porphyry copper deposits in Mexico range in age from 164 Ma to 54 Ma and the mineralization in Sonora state occurred in two different periods, but magmatism overlaps in space and time.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Four folded plates in pocket. Includes bibliographical references (leaves 285-303). Available also in a digital version from Dissertation Abstracts.

xviii, 177 p. : ill., maps. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This dissertation explores several important consequences of H 2 O-rich fluids in magmatic and ore-forming systems within continental arc crust. North Sister, a stratovolcano in the Oregon High Cascades, provides a window into magma generation processes in the deep crust. Eruption of a remarkably limited basaltic andesite composition over the lifespan of this volcano may reflect last equilibration of mantle derived magma within a deep crustal hot zone. High pressure, water-undersaturated phase equilibrium experiments show that an anhydrous, augite-rich gabbro at ∼12 kbar (40 km depth) and ∼ 1175°C is the most probable lithology with which North Sister basaltic andesite with ∼3.5 wt% H 2 O last equilibrated within the deep crust before erupting. While magma often erupts at the planets surface as at North Sister, a greater volume never reaches the surface and solidifies within the upper crust. Exsolution of magmatic fluids is an inevitable consequence of crystallization of hydrous crustal magmas. The fate of these fluids is the focus of the remainder of this dissertation. Modeling of CO 2 and H 2 O variations during crystallization of granitic magma reveals that exsolution of a large mass of fluid occurs only after CO 2 is largely degassed, creating ideal conditions for hydrofracturing and formation of porphyry copper deposits. CO 2 and H 2 O solubility relations suggest that H 2 O-rich magma was required to produce the porphyry-Cu-Mo deposit at Butte, Montana, which may explain its distinctively deep generation. Electron microprobe analyses of Ti in quartz and Zr in rutile in samples from Butte yield porphyry magma temperatures (630-770°C) that overlap substantially with hydrothermal vein temperatures (<430-750°C). Veins display large temperature ranges (50-250°C) that signify variable degrees of cooling of hot magmatic fluids upon contact with cooler wall rock during vein growth. Modeling of Ti diffusion in quartz suggests that individual dikes and veins likely cooled over short timescales (10s-1000s years), indicating that porphyry systems may evolve by episodic magmatic fluid injections with discrete thermal spikes. Modeling of Ti diffusion in quartz combined with electron backscatter diffraction maps show that small hydrothermal quartz veins likely formed by epitaxial growth. This dissertation includes co-authored material both previously published and in preparation for submission. / Committee in charge: A. Dana Johnston, Chairperson, Geological Sciences; Mark Reed, Member, Geological Sciences; Paul Wallace, Member, Geological Sciences; Richard P. Taylor, Outside Member, Physics

O sistema pórfiro Yarumalito, caracterizado por concentrar minério em veios controlados por estruturas e stockworks encontra-se localizado no distrito mineiro de Marmato, que é considerado um dos mais antigos distritos de ouro da Colômbia, com atividades de extração que remontam da época dos Incas. O sistema ígneo da região é relacionado ao magmatismo Miocênico da Formação Combia. Neste trabalho foram descritas as rochas subvulcânicas diretamente relacionadas às zonas mineralizadas do sistema pórfiro Yarumalito com o objetivo de, após caracterizar as intrusões, realizar datação através do método U-Pb em zircão. Amostras selecionadas de duas intrusões férteis, uma andesítica mais abundante na área e outra diorítica com características intrusivas na primeira e de ocorrência mais restrita, foram criteriosamente descritas e tiveram zircões separados e posteriormente analisados por SHRIMP na Universidade de São Paulo. Os resultados apontaram para um intervalo bastante restrito para as idades, com médias ponderadas das idades 206Pb/238U variando de 7 ± 0.15 Ma para o andesito pórfiro a 6.95 ± 0.16 Ma para o diorito pórfiro. Estes resultados sugerem um período restrito no tempo para a cristalização das intrusivas portadoras de mineralizações na área do projeto e posicionam o sistema Yarumalito para o final do magmatismo Combia. / The Yarumalito porphyry system, characterized to concentrate ore in structure related veins and stockworks is located in the mining district of Marmato, that is considered one of the oldest gold mining districts of Colombia, with exploration activities since the Inca Empire. The igneous system of the region is related to the miocenic magmatism of the Combia formation. In this paper, the subvolcanic rocks directly related with the mineralized zones of the Yarumalito porphyry were described in order to, after characterization, obtain UPb ages in zircon to the intrusions. Selected samples of the two fertile intrusions, one andesitic more abundant in the area and one dioritic more restricted, were carefully described and had their zircon grains separated and analyzed by SHRIMP in the University of São Paulo. The results points to a very restricted interval for the ages, with weighted average 206Pb/238U varying from 7 ± 0.15 Ma for the andesitic porphyry and 6.95 ± 0.16 Ma for the dioritic porphyry. These results suggest a brief period for the crystallization of the mineralized subvolcanic rocks in the area and constrain the Yarumalito system to the final stages of the Combia magmatism.

O sistema pórfiro Yarumalito, caracterizado por concentrar minério em veios controlados por estruturas e stockworks encontra-se localizado no distrito mineiro de Marmato, que é considerado um dos mais antigos distritos de ouro da Colômbia, com atividades de extração que remontam da época dos Incas. O sistema ígneo da região é relacionado ao magmatismo Miocênico da Formação Combia. Neste trabalho foram descritas as rochas subvulcânicas diretamente relacionadas às zonas mineralizadas do sistema pórfiro Yarumalito com o objetivo de, após caracterizar as intrusões, realizar datação através do método U-Pb em zircão. Amostras selecionadas de duas intrusões férteis, uma andesítica mais abundante na área e outra diorítica com características intrusivas na primeira e de ocorrência mais restrita, foram criteriosamente descritas e tiveram zircões separados e posteriormente analisados por SHRIMP na Universidade de São Paulo. Os resultados apontaram para um intervalo bastante restrito para as idades, com médias ponderadas das idades 206Pb/238U variando de 7 ± 0.15 Ma para o andesito pórfiro a 6.95 ± 0.16 Ma para o diorito pórfiro. Estes resultados sugerem um período restrito no tempo para a cristalização das intrusivas portadoras de mineralizações na área do projeto e posicionam o sistema Yarumalito para o final do magmatismo Combia. / The Yarumalito porphyry system, characterized to concentrate ore in structure related veins and stockworks is located in the mining district of Marmato, that is considered one of the oldest gold mining districts of Colombia, with exploration activities since the Inca Empire. The igneous system of the region is related to the miocenic magmatism of the Combia formation. In this paper, the subvolcanic rocks directly related with the mineralized zones of the Yarumalito porphyry were described in order to, after characterization, obtain UPb ages in zircon to the intrusions. Selected samples of the two fertile intrusions, one andesitic more abundant in the area and one dioritic more restricted, were carefully described and had their zircon grains separated and analyzed by SHRIMP in the University of São Paulo. The results points to a very restricted interval for the ages, with weighted average 206Pb/238U varying from 7 ± 0.15 Ma for the andesitic porphyry and 6.95 ± 0.16 Ma for the dioritic porphyry. These results suggest a brief period for the crystallization of the mineralized subvolcanic rocks in the area and constrain the Yarumalito system to the final stages of the Combia magmatism.

Porphyry copper deposits represent one of the largest copper reserves on Earth. They typically contain large, low-grade reserves of primary ore and higher-grade, supergene enrichment blankets of sulfide and oxide ores. Understanding the mineralogy of porphyry copper ores and ores related to porphyry copper systems is exceedingly important for several reasons, foremost of which are the information provided by ore mineral parageneses, assemblages, and mineral chemistry on evolution of these magmatic-hydrothermal systems, and information on mineral processing characteristics of the ores. The focus of this work is to better understand the mineralogy of supergene copper sulfides in porphyry copper systems and hypogene base metal lodes related to porphyry copper systems, and use this mineralogical knowledge to improve our understanding of the processes responsible for ore formation. The objectives of this study are accomplished by two means: focusing on the crystallography and crystal chemistry of minerals, and then applying this mineralogical knowledge to a supergene sulfide enrichment blanket and hypogene massive sulfides from base metal lodes in southeastern Arizona. The discovery of a new mineral, natropalermoite, NaSr2Al4(PO4)4(OH)4, provided the opportunity to use single-crystal X-ray diffraction to solve a crystal structure, and electron-probe microanalysis (EPMA) to study the crystal chemistry of natropalermoite and how the accommodation of Na in the structure changes lengthens the unit cell along [010] and shortens it along [100] and [001] compared to its lithium analogue, palermoite. Solution of the crystal structure of the mineral nickelskutterudite, (Ni,Co,Fe)As3, allowed for the investigation of anion deficiency in minerals of the skutterudite group, a problem whose solution has eluded researchers for nearly 100 years. Two skutterudite (CoAs3) and two nickelskutterudite samples were analyzed using single-crystal X-ray diffraction, EPMA, and procrystal electron density. The results showed fully-occupied anion sites and a cation surplus, which was accommodated in the icosahedral site, proving that minerals of the skutterudite group are not anion deficient. This mineralogical knowledge was applied to the supergene enrichment blanket in the Western Copper section of the Morenci mine, Greenlee County, and hypogene massive sulfide deposits associated with a porphyry copper deposit at Bisbee, Cochise County, Arizona. This is one of very few studies of supergene sulfide blankets ever completed. One drill hole through the supergene blanket at Western Copper was examined using ore microscopy and EPMA. Results showed dominant (Cu+Fe):S ratios of 1.80 ± 0.05, 1.92 ± 0.03, and 1.10 ± 0.10, with higher (Cu+Fe):S dominant high in the blanket and low ratios dominant near the base of the blanket. These values were interpreted to be controlled by activity of Cu2+, Fe2+, and Fe3+ in solution. Massive sulfide deposits at Bisbee were investigated using ore microscopy and EPMA in order to correct the previous conflicting reports of the mineralogy and paragenesis of this famous district and interpret constraints on conditions of ore-forming fluids. Results show four types of ore: chalcopyrite-rich with hematite and/or pyrite, bornite-rich, chalcocite-rich, and a Zn-Pb association. Chalcopyrite-rich ores formed first, followed by bornite-rich and chalcocite-rich ores. All ores were formed at relatively shallow depths from oxidized, moderately sulfur-rich fluids; early fluids were higher temperature and later fluids were lower temperature and considerably more sulfidized. Zinc-lead ores formed early and were continuously dissolved and reprecipitated distal to Cu-mineralization. These patterns are similar to many other base-metal lode districts worldwide, however Bisbee contains more Zn-Pb ore than other districts with hematite-containing ores and less than those without hematite.

In recent years our understanding of the genesis of porphyry copper systems has advanced to a sufficient level to be able to construct predictive models that enhance exploration for these deposits. Our understanding of primary and secondary geochemical dispersion around these deposits is not so advanced as variables such as climate and topography cause geochemical patterns to be distorted or masked at surface with the result of different deposits having quite different geochemical characteristics. In this study the geology and geochemistry of a porphyry copper-molybdenum from the Canadian Cordillera is examined with the aim of demonstrating how primary geochemical patterns are affected by the development of a supergene enrichment blanket and leached capping. Topographic controls on the extent of leaching and supergene enrichment are also explored. The Berg porphyry copper-molybdenum deposit is in the Tahtsa Mountain Ranges, approximately 84 km southwest of Houston, central British Columbia. Mineralized zones are centered on a circa 50 Ma composite quartz monzonite stock. Hydrothermal alteration zones are similar to those of the classic model by Lowell and Guilbert. Central zones are potassic (orthoclase and biotite) while peripheral zones are propylitic (chlorite, epidote, carbonate). Intense phyllic alteration (quartz, sericite, pyrite) occurs at the north and south margins of the stock. Hypogene mineralization (characterized by pyrite, chalcopyrite and molybdenite) is concentrated in an annular zone straddling the quartz monzonite contact. Best grades are localized in altered quartz diorite and altered and hornfelsed Telkwa Formation (Hazelton Group) volcanic rocks at the east side of the deposit. The nature of these altered hornfelsed rocks has been a subject for much debate in previous studies. One school of thought suggests that they are part of a hornfels aureole associated with the quartz diorite. Others suggest that it is an alteration zone associated with the quartz monzonite stock. Thirteen diamond drill holes on a north south cross section of the deposit were logged (GEOLOG) and sampled. Outcrop samples were collected where possible close to each drill hole. Major elements were determined by XRF, trace metals by flame AAS and fluorine by specific ion electrode. A sequential extraction was used to study the distribution of copper between different host minerals. The origin of the hornfelsed rocks is solved by field mapping and geochemistry. In the field cross cutting relationships show that the quartz diorite predates the stock and that the hornfels zone is spacially related to it. Major element binary and ternary plots demonstrate that significant amounts of potassium have been added to these rocks in the mineralized zone. This implies that biotite alteration was superimposed onto an earlier hornfels. Trace metal data was partitioned into anomalous and background populations with probability graphs. In the hypogene zone Cu, Mo and Ag occur in an annular zone corresponding with the mineralogically defined potential ore zones. Fluorine is anomalous over the area of the potassic alteration zone. Lead and zinc are anomalous in peripheral haloes around the potential orebodies. These zones can be traced to surface through an extensive supergene enrichment blanket and leached capping. Three zones of supergene mineralization are recognized: supergene sulphide (covellite, digenite, chalcocite), supergene oxide (malachite/azurite, cuprite, tenorite, native Cu) and leached capping. Sulphides are the dominant host for Cu throughout most of the deposit but locally on steep slopes where supergene oxide is developed Cu is hosted in carbonate and oxide minerals. Enrichment or depletion of elements in the supergene is demonstrated with interelement ratios. Enrichment factors can be derived in two ways: a) by ratioing supergene values to hypogene values, or, b) by ratioing to a constant (e.g. TiO₂ ) for each zone and then ratioing this value between zones. Enrichment factors of <1 therefore imply depletion and >1, enrichment (1=hypogene grade). Results show that all elements (studied) are enriched in the supergene sulphide and oxide zones. In the leached cap Cu, Mn and Zn are depleted while Mo, Pb and Ag are significantly enriched. These elements are incorporated into immobile limonite mineral's (ferrimolybdite, jarosite, goethite etc.). / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate