Morenci is located in southeast Arizona. Copper grade hypogene mineralization averages 0.15%; one or more generations of supergene enrichment have increased mineralization to 0.96%. Intense supergene alteration has made it difficult to determine phyllosilicate paragenesis. The purpose of this study is to differentiate hypogene from supergene phyllosilicates. Forty-nine samples from five drill holes were obtained for petrographic, geochemical, mineralogical, and stable isotope data. Petrographic examination, X-ray diffraction and X-ray powder camera techniques established alteration of feldspars to kaolinite, montmorillonite, and sericite. Whole rock analyses using XRF determined cationic gains and losses that correspond with kaolinite and sericite. Stable isotopes of oxygen and hydrogen using kaolinite and sericite from 14 samples were tested to determine provenance of water. Stable isotope data show a trimodal distribution of phyllosilicates consistent with early hypogene alteration of magmatic origin, and two generations of supergene enrichment due to meteoric waters.

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This research has evaluated the engineering behaviour of the tropical clay soils of Dhaka, Bangladesh. Attempts have been made to show the relationship of mineralogy and fabric with engineering properties. The engineering behaviour has been investigated by comparing the soil properties in a natural and destructured state at the same void ratio. Consolidation behaviour of the soils are discussed, based on oedometer and triaxial tests. Undrained and drained mechanical behaviour have been evaluated from triaxial tests in terms of stress-strain curves, stress paths, bonding effects, critical state conditions, stiffness and yielding behaviour. A framework for the tropical clay soils of Dhaka is presented. The tropical clay soils of Dhaka are intermediate to high plasticity inorganic clay. These soils are mainly composed of illite,. kaolinite, chlorite and some non clay minerals mainly quartz and feldspar. It was observed that these sods showed a random open microfabric of silt and clay. There was also some evidence that aluminosilicates, iron compounds and silica formed bonds between and within the grains. An apparent preconsolidation pressure of 170 kPa to 250 kPa was estimated for the natural soils, which is likely to be due to the bonded structure of the soils. The compressibility of the soil is very low to medium. The consolidation results are consistent with the mineralogy of the soils. It is established that the tropical clay soils of Dhaka are bonded. Bonding has an influence on the development of stress-strain and stiffness of these soils. Under undrained shearing, samples initially showed peak positive values of excess pore water pressure followed by negative values at higher strains due to the tendency of the samples to dilate. No negative pore water pressures were observed at high confining pressures. Only a few samples at low confining pressures reach the critical state at very large strains approximately in excess of 20%. High confining pressure samples may not have reached the critical state due to the formation of distinct shear surfaces. A significant difference between the natural and destructured failure surfaces was observed due to the presence of bonds in the natural soils. Differences in failure type were observed between the natural and destructured soils of three boreholes. It was observed that stiffness values gradually decreased with increasing strain. For the natural soils, two yield points could be identified at low confining pressures below the final yield. It was also observed that bond breakdown would occur in isotropic compression for tests at high confining pressures. At the final yield, the soil looses almost all of its stiffness due to bonding. After final yield, a soil’s behaviour is controlled only by friction. It was observed that three zones of behaviour could be identified for these soils in the stress space.

Illustrations in pocket. / Digitized by Kansas State University Libraries

Mineralogical and geochemical effects of alteration were studied in three early Mesozoic diabase/host-rock systems: (1) the Rocky Ridge dike and aureole, Gettysburg basin, Maryland; (2) the West Gainesville and Nokesville diabase sheets and subjacent host rocks, Culpeper basin, Virginia; and (3) the East Gainesville diabase sheet and associated host rocks, Culpeper basin, Virginia. The Rocky Ridge diabase is relatively unaltered and its thermal aureole formed under predominately isochemical conditions. The West Gainesville/Nokesville system exhibits apparent isovolumetric, complementary exchange of volatiles and alkalis(?) from the host rocks with Si, Al, Fe(?), Mn, Mg, Ca, Co and V(?) from the diabase sheet. Mass-balance calculations for this system indicate that, except for loss of Si and gain of volatiles and perhaps alkalis, it behaved isochemically. The East Gainesville diabase sheet is characterized by multiple injection of two magma types from different mantle sources. Alteration in this system is more complex and aureole temperatures were lower than those in the West Gainesville/Nokesville system. / Observed mineral reactions in the diabase are consistent with relative mobilities; the dominant mechanisms for this mass transfer are apparently infiltration metasomatism and intergranular diffusion. Relative mobilities of cations can be correlated with ionic radius. Rare-earth elements and Zr were immobile with respect to the diabase sheets, but Ti, commonly used to distinguish magma types in these and other mafic rocks, was not. In all studies Si, Al, Fe, Ca, and V were lost from the diabase during metasomatism, whereas volatiles, Rb and K were gained. / Source: Dissertation Abstracts International, Volume: 55-04, Section: B, page: 1344. / Director: Paul C. Ragland. / Thesis (Ph.D.)--The Florida State University, 1994.

Investigation of metasedimentary and metaigneous units of the northern Alabama Piedmont has revealed the following evidence: (1) stratigraphic continuity exists between previously uncorrelated lithotectonic blocks, (2) petrogenesis of synmetamorphic Rockford-type granite was controlled by the anatectic melting of metasedimentary units of greywacke composition producing S-type geochemical signatures, (3) estimates of pressure and temperature from metamorphic mineral assemblages yield Barrovian-type geothermal gradient terminated by a subsequent near-isothermal decompression event producing a clockwise P-T-time path in P-T space, and (4) estimates of the fluid composition in equilibrium with mineral assemblages of metasedimentary compositions indicate a metamorphic fluid composed of 0.90 H$\sb2$O, and 0.05 CO$\sb2$ and CH$\sb4,$ with the other fluid phases CO, COH, S$\sb2,$ O$\sb2,$ S$\sb8,$ H$\sb2$S being present in trace quantities. Metamorphic total fluid pressure was essentially equivalent to lithostatic pressure during peak metamorphic conditions (P$\sb{\rm T}$ = P$\sb{\rm F}).$ / Analysis of micro-, meso- and megascopic structural relationships has revealed 5 phases of deformation. Previous investigations have established the internal stratigraphy of structural blocks composing the northern Alabama Piedmont. This study identifies the conformable relationships between stratigraphy of the Coosa and Tallapoosa blocks. Because of thermal and structural correlation across the eastern-western Blue Ridge boundary (Hollins Line fault), the Ashland-Wedowee belt may have been proximal to the North American margin prior to the Acadian dynamothermal events. / Source: Dissertation Abstracts International, Volume: 53-09, Section: B, page: 4552. / Major Professor: James F. Tull. / Thesis (Ph.D.)--The Florida State University, 1992.

<p>The Sierra Blanca metamorphic core complex (SBMCC), located 90 miles west of Tucson, is part of the southern belt of metamorphic core complexes that stretches across southern Arizona. The SBMCC exposes Jurassic age sedimentary rocks that have been metamorphosed by intruding Late Cretaceous peraluminous granites and pegmatites. Evidence of this magmatic episode includes polysythetic twinning in plagioclase, albite exsolution of alkali feldspar resulting in myrmekitic texture, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary (Miocene?) tectonic fabric, associated with the exhumation of the Sierra Blanca metamorphic core along a low-angle detachment fault, forming the SBMCC. The NW-SE elongated dome of metamorphic rocks forms the footwall of the detachment shear zone, and is separated from the hanging wall, composed of Paleozoic and Mesozoic metasedimentary rocks, by a low-angle detachment shear zone. Foliation is defined by gneissic layering and aligned muscovite, and is generally sub-horizontal, defining the dome. The NNW-SSE mineral stretching lineation is expressed by plagioclase and K-feldspar porphyroclasts, and various shear sense indicators consistent with a top-to the-NNW shear sense. Lineation trends in a NNW-SSE orientation; however, plunge changes across the domiform shape of the MCC. Much of the deformation is preserved in the blastomylonitic gneiss derived from the peraluminous granite, including epidote porphyroclasts, grain boundary migration in quartz, lozenged amphiboles, mica fish, and retrograde mineral alterations. Detailed petrologic observation and microstructural analysis indicate deformation temperatures of 450-575 ? ?C presented here provide thermomechanical constraints on the evolution of the SBMCC.