This kyanite quartzite deposits at Leigh, Baker and Willis Mountains located in the south central Virginia Piedmont were investigated to determine their genesis, extent, and geologic and petrographic character. Kyanite quartzite in Virginia typically contains 20-40 per cent kyanite, 0-5 per cent pyrite, 0.5-1.5 per cent rutile, a per cent or so of mica or clay with the balance quartz. They occur as single beds within metamorphic rocks ranging from slates and phyllites of the greenschist facies south of Leigh Mountain, to schists and gneisses of the amphibolite facies at Baker and Willis Mountains. Post-kyanite hydrothermal alteration along fractures has altered large segments of the Baker Mountain deposit to clay and topaz. The protolith of kyanite quartzite is believed to have been extraordinarily pure mixture of quartz and kaolinite which was produced by either Iateritic weathering or by circulating meteoric waters. Isochemical regional metamorphism is believed to have occurred in a high pressure, moderate temperature environment in which water was either deficient or able to escape. Fluorine may have had a catalytic effect in promoting kyanite crystallization. No evidence was found of hydrothermal introduction of alumina, or localization of kyanite as a result of differential stress. The rocks enclosing kyanite quartzite in the Leigh Mountain area are believed to be basal members of the lower Paleozoic (?) Volcanic-Slate series. The gneisses surrounding Willis and Baker Mountains may be more highly metamorphosed, infolded remnants of the same series. The kyanite deposits of Virginia are extensive and well situated for mining. Possible reserves of kyanite quartzite containing over 25 per cent kyanite available for open pit mining are measured in tens of millions of tons.

Thesis (M.Sc.) -- Memorial University of Newfoundland. / Typescript. Bibliography : leaves 198-210. Also available online.

abstract: The historic Cacachilas mining district is located in Baja California Sur, approximately 20 kilometers east of La Paz, and has a series of gold- and silver-hosted veins, faults, and shear zones within Cretaceous granodioritic plutons. The remote geographic location and past political events within Mexico left the district essentially unexplored after the late 1800s, when the Mexican Revolution began. More recent discovery of gold deposits along the Baja peninsula instigated a renewed interest in mineralization in the Sierra Cacachilas. The area lacks detailed previous geologic data, so this study focused on characterizing the controls of mineralization and the locations of mineralized trends of deposits within the northeastern Sierra Cacachilas, with a goal toward helping assess economic viability of the deposits. I mapped surficial geologic data, such as outcrop locations, alteration assemblages, limonite intensities, and structural measurements. I then synthesized these into geologic maps and cross sections. I combined field data with geochemical assays and structural plots to better characterize individual historic district trends and newly located trends to understand the distribution of mineralization at surface and at depth. Lastly, I synthesized geology of the Sierra Cacachilas with other gold and silver deposits located in the southern Baja peninsula to better characterize the mineralization and deposit style of the Cacachilas district. Mineralization in the northeastern Sierra Cacachilas is mainly restricted to steeply dipping quartz veins, faults, and brittle-ductile shear zones that trend generally northeast. Some veins are en-echelon within the mineralized zones, implying some lateral movement along the zones. Veins are dominated by milky to clear quartz with trace sulfides, abundant limonite (after sulfides), and local open-space textures. Mineralization is interpreted to be intermediate between classic epithermal and mesothermal veins. Within mineralized trends and commonly associated with mineralization are greisen-like zones that are defined by intense sericitic to muscovitic overprint, trend northeast, and are with or without sulfides. The intensity of sulfide abundance and limonitic alteration after sulfides within and near mineralized zones is overall a good guide to mineralization. Based on past reports and on my recent studies, the Cacachilas district has very promising potential for relatively small, high-grade deposits. / Dissertation/Thesis / Masters Thesis Geological Sciences 2015

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Greenstone belts are dominated by volcanic rocks with lithogeochemical characteristics that reflect a range of possible geodynamic settings. Many analogies with modern tectonic settings have been suggested. Increasing exploration and comprehensive sampling of volcanic rocks in modern oceans provides the unique opportunity to characterize different melt sources from intraoceanic settings. This thesis examines geochemical data from more than 2850 submarine mafic and more than 2200 submarine felsic volcanic rocks, representing a wide range of settings. The results show significant geochemical variability spanning the full range of compositions of volcanic rocks found in ancient greenstone belts. This diversity reflects complex rift and spreading regimes, variations in crustal thickness, dry melting versus wet melting, mantle mixing and crustal contamination. Highly variable melting conditions are thought to be related to mantle heterogeneities, complex mantle flow regimes and short-lived tectonic domains, such as those caused by diffuse spreading, multiple overlapping spreading centers and microplate breakouts. Systematic differences in the volcanic rocks are revealed by a combination of principal components analysis and unsupervised hierarchical clustering. Rocks from most arc-backarc systems have strongly depleted mantle signatures and well-known subduction-related chemistry. This contrasts with rocks in Archean greenstone belts, which show no, or at least weaker, subduction-related chemistry and stronger mantle enrichment resulting from a less-depleted mantle, less wet-melting, and variable crustal contamination. The geochemistry of the modern volcanic rocks reflects lower mantle temperatures, thinner crust and subduction-related processes of present-day settings. However, rocks that are geochemically identical to those in Archean greenstone belts occur in many modern back-arc basins, such as the Lau Basin. Crustal growth and area-age relationships in the Lau Basin are similar to observed ages and compositions of volcanic assemblages in greenstone belts, such as the Blake River Group of the Abitibi Greenstone Belt. Such settings are recognized as favorable locations for volcanogenic massive sulfide (VMS) deposits, and therefore the particular geochemical signatures of the volcanic rocks are important for enhanced area selection in base and precious metal exploration.

The Owl Head mining District is located in south-central Pinal County, Arizona, within the Basin and Range province. Land forms, particularity pediments, characteristic of this province are abundant in this area. Precambrian rocks of the Owl Head mining district include the Pinal schist; gneiss; intrusions of granite, quartz monzonite and quartz diorite; and small amounts of Dripping Spring quartzite and metamorphosed Mescal limestone. These have been intruded by dikes and plugs of diorite and andesite, and are unconformably overlain by volcanic rocks and continental sedimentary rocks of Tertiary and Quaternary age. No rocks of the Paleozoic and Mesozoic eras have been recognized. The structural trends of the Owl Head mining district probably reflect four major lineament directions. The dominant structural trends found in the area are north and northwest. Subordinate to these directions are northeast and easterly trends. The strike of the northerly trend varies from due north to N30°E and was probably developed during the Mazatzal Revolution. The northwest trend has probably been superposed over the northerly trend at some later date. Copper mineralization is abundant in the area and prospecting by both individuals and mining companies has been extensive. To date no ore body of any magnitude has been found, but evidence suggests that an economic copper deposit may exist within the area. The copper mineralization visible at the surface consists mainly of the secondary copper minerals chrysocolla, malachite, azurite, and chalcocite with chrysocolla being by far the most abundant. Copper minerals are found to occur in all rocks older than middle Tertiary age. Placer magnetite deposits are found in the alluvial material of this area, and one such deposit is now being mined.

Triple junctions form at the intersection of three tectonic plates and are a necessary consequence of new microplate formation. The splitting of a plate into two smaller plates always results in the formation of two triple junctions. As a result, they are fundamental structural elements of ocean floor geodynamics. Their evolution is influenced by the complex interplay of near- and far-field plate dynamics, crustal types, and mantle processes, and they include a wide range of boundary types. The long-term stability and evolution of triple junctions are influenced by continuous plate reorganization, such as in the complex microplate mosaics of the Western Pacific margin. To better understand how triple junctions form and respond to near- and far-field stresses, this study presents a detailed examination of the North Fiji Basin Triple Junction (NFBTJ), which is located within one of the largest and most mature back-arc basins of the Pacific margin. A new geological map of the NFBTJ at a 1:500,000 scale is presented. The mapping provides insight into the factors controlling plate fragmentation and crustal growth during triple junction formation. The map is based on a compilation of more than 50 years of ship-based bathymetry, backscatter data, gravity and magnetics used to reconstruct the spreading history, magmatic productivity, tectonic fabric and origin of geological formations of the basin. These aspects also have important implications for understanding the origins and evolution of large-scale back-arc basin hydrothermal systems. Crustal growth in the NFB is recorded by the area-age relationships of different geological formations identified in the new geological map. The triple junction is the site of volume addition related to enhanced magmatic productivity, with a large Central Volcanic Complex (CVC) (shield volcano and inflated ridge) at its centre and a well-developed spreading ridge along the SW limb. Extensive lava flows emanating from the CVC covers early spreading-related fabric in the NE and NW limbs. The large shield volcano, which is 0.5 km high and occupies an area of at least 62.3 km², has a distinctive 2.5-km diameter summit caldera with extensive hydrothermal activity in the south. The CVC and surrounding lava flows are estimated to have grown in place at a rate of 3,000 m²/yr, thus dominating the recent history of the NFBTJ. By contrast, earlier crustal growth along the SW and NW spreading segments, prior to the emergence of CVC, is estimated to have been ~1,650 m²/yr and 200 m²/yr respectively. The quantitative analysis of rifting and the eruptive history highlight previously unrecognized near and far-field geodynamic influences on the triple junction formation. In particular, the pulse of crustal growth at the NFB beginning at 3 Ma was related to rift propagation from the south in response to rotation of the NFB that produced some of the fastest growing crust in the oceans. Comparisons with a global database of triple junctions show that the evolution of the NFBTJ shares many features with other microplate mosaics and that processes related to triple junction formation is associated with crustal growth wherever triple junctions occur. The high heat flow and voluminous mafic magmatism has been compared to rapid crustal growth in some ancient greenstone belts, such as the Archean Abitibi Greenstone Belt in the Superior Province of Canada. In particular, the NFBTJ is a possible modern analog of large central volcanic complexes that characterize ancient greenstone-belt development.

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.

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.

Mildly metamorphosed Cretaceous siltstones, arkoses and limey shales and a small composite stock of granitic composition are the principal rocks exposed in the Sedimentary Hills area, which lies six miles west of Tucson, Arizona. About 2400 feet of sediments were measured and assigned to the Amole Arkose Formation. The beds dip to the south and strike northwesterly. The stock is composed of two granitic facies. The northern and earlier part of the stock is a quartz monzonite which is mildly altered. The southern part of the intrusive is a granite porphyry which is altered to a greater degree and exhibits significant disseminations of chalcopyrite and pyrite. A quartz-pegmatite plug, probably a late phase of the intrusions, intrudes the quartz monzonite. Structure in the area is dominated by a large thrust zone which strikes generally parallel to the bedding. Within the Sedimentary Hills area, normal faulting and drag folding are tributary to the thrusting. Minor copper oxide minerals are frequent along large and small faults, and in the granite porphyry stock. Wide brick-red and brown gossans occur along the major thrust plane.