<p> The May Lake interpluton screen is a 4 km long, &sim;0.5 km wide swath of metamorphic rock cropping out between plutons of the &sim;103 Ma Yosemite Valley Intrusive Suite and the &sim;93-85 Ma Tuolumne Intrusive Suite in Yosemite National Park, California. Metasomatic alteration and recrystallization due to contact metamorphism and fluid infiltration resulted from the emplacement of the Cretaceous plutons. Mineral assemblages are consistent with metamorphism to hornblende-hornfels and amphibolite facies. The presence of sillimanite-bearing metapelite and more Mg-rich clinopyroxene in calc-silicate assemblages of the northeast section of the screen than the southwest suggest higher grade metamorphism was experienced to the northeast. Pseudosection diagrams created from whole rock chemical analyses of three metapelite rocks also indicate higher temperatures in the northeastern section of the screen with minimum temperatures estimated from &sim;540-617&deg;C. Based on petrographic analysis of andalusite- and sillimanite-bearing metapelite, it is likely that the screen experienced two stages of contact metamorphism: relatively lower temperature metamorphism during intrusion of the Yosemite Valley Intrusive Suite followed by relatively higher temperature contact metamorphism during intrusion of the more mafic Tuolumne Intrusive Suite. Stable isotope data suggest that rock permeability and preexisting structures were the strongest factors controlling fluid infiltration through the contact aureole.</p><p>

Rich gold-telluride lodes (steeply dipping and flatly dipping) and minor gold-quartz stockwork mineralization characterize the Kalgoorlie gold-field. The origin of these gold deposits, the relationship between deposits and then nature of the host rocks are the major problems considered in this thesis. Extensive diamond drilling at the essentially unmineralized southern end of the field provided excellent material for stratigraphic studies and for country rock analysis whilst ore samples were obtained from both mines and drill core.

Rich gold-telluride lodes (steeply dipping and flatly dipping) and minor gold-quartz stockwork mineralization characterize the Kalgoorlie gold-field. The origin of these gold deposits, the relationship between deposits and then nature of the host rocks are the major problems considered in this thesis. Extensive diamond drilling at the essentially unmineralized southern end of the field provided excellent material for stratigraphic studies and for country rock analysis whilst ore samples were obtained from both mines and drill core.

The manganese mineralization near Kato Nevrokopi, Drama, in the Falakron mountains, is hosted by the Precambrian to Early Paleozoic Upper Marble. The marble and the underlying Lower Schist unit were metamorphosed between the Late Cambrian and the Carboniferous and were extensively deformed during the Alpine orogeny. The Alpine deformation is considered to have occurred between the Early Cretaceous and the Oligocene. Granodiorites and rhyodacites of Oligocene age outcrop also in the area. The mineralization near Kato Nevrokopi is confined to intersecting Alpine fault zones of northeast and northwest trends. Negligible mineralization occurs into the schist, the richest orebodies being present as lateral extensions in the marble. Mineralization diminishes with increasing distance from the fault zones. The shape of the orebodies is irregular with individual offshoots being lenticular, pod-like or tabular. Sizes can be up to 50m in length, 20m in width and 5-10m in thickness. The boundaries between the orebodies and the marble are sharp and replacement and alteration phenomena around the orebodies include: dolomitization of the marble and clay mineral alteration. Two distinctly different mineralizing processes took place at Kato Nevrokopi: a) A hydrothermal process, characterized by mineral zoning in time and space, present as abundant rhodochrosite, ankerite, sphalerite, pyrite, pyrrhotine, chalcopyrite and marcasite in the stratigraphically deeper veins and "black calcite" (mixture of calcite and todorokite) and galena in the upper veins. b) A supergene process, in which the hydrothermal minerals in the veins were weathered. During this process, rhodochrosite in the veins was oxidized to MnO-gel and todorokite and in low altitude karstic cavities the mineral assemblage is: MnO-gel-nsutitechalcophanite. In high altitude karsts the mineral assemblage is: MnO-gel-nsutite-birnessite-cryptomelane-pyrolusite. During weathering Zn derived by dissolution of sphalerite was also mobile, being transported together with Mn to karstic cavities where it substituted for Mn in the Mn-oxides. The minerals pyrrhotine, marcasite, ankerite and birnessite are for first time recorded at Kato Nevrokopi. The lack of useable fluid inclusions severely limited the information on the composition of the hydrothermal fluids. From the mineral pair kaolinite-sericite, the pH of the hydrothermal fluids was estimated to have been between 3-4. Hydrothermal mineral precipitation took place mainly by reaction of the fluids with the marble and pH increase (cf., rhodochrosite) or by mixing of the hydrothermal fluids with near surface aquifers (black calcite). Thermodynamic data for the overall transformation of rhodochrosite to pyrolusite and the contemporaneous decomposition of chalcopyrite to azurite and malachite were used and the oxygen fugacity of the meteoric fluids was calculated to have ranged between 10-22 and 10-17. Mn-oxide precipitation during weathering took place either by oxidation of the primary veins (cf., MnO-gel, todorokite) or by reaction of the groundwaters with the marble in karstic cavities and precipitation of Mn-oxides as layers and encrustations above the local ground water table. Evidence from the whole rock geochemistry of the mineralized samples emphasizes the role of the thrust and fault zones as solution passageways and stresses their importance for the development of hydrothermal and supergene mineralization at Kato Nevrokopi. During weathering, downward percolation of C02-rich oxygenated meteoric waters within the veins, caused the breakdown and dissolution of sulphides and oxidation of rhodochrosite to Mn-oxides. The pH of these meteoric fluids was buffered by the dissolution of sulphides and the formation of karstic cavities was favoured by the high permeability induced by the occurrence of the thrust zone and the percolation of acidic meteoric waters through the marble. Chemical transport of MnZ+ to karstic cavities was possible in reduced meteoric waters at the beginning of weathering (pH"4-5), and as Mn(HCO3)2 in slightly alkaline groundwaters during advanced weathering (pH"6-8). Alkalies (K, Na) and alkaline earths (Ca, Mg, Ba, Sr) where leached away from the ore and the country rocks during weathering and the order of element mobility in the karstic cavities was: Na>K>MgaSr>Mn>As>Ca>Zn>Ba>Al>Fe>Cu>Cd>Pb. The Mn-oxide orebodies near Kato Nevrokopi are located in a northeast trending line parallel to the axes of major Alpine folds and significantly the rhyodacite volcanics outcrop also in a parallel fashion to this line providing evidence of an underlying pluton. This northeast trending line may therefore represent a zone of crustal weakness that was exploited by andesitic magma and subsequently by hydrothermal fluids. An average age of 33 Ma for the Kato Nevrokopi mineralization is provided. This age is similar to that of magmatism in and around the Drama area. It is therefore reasonable to conclude that the hydrothermal activity near Kato Nevrokopi and generally of the northeast Drama area was related to the Oligocene magmatism. On the basis of its age, style, morphology and genesis, the mineralization near Kato Nevrokopi is placed in the metallogenic province of N. Greece/S. Bulgaria which also includes the Madan hydrothermal Pb-Zn-Mn vein deposits and the Chalkidiki Pb-Zn deposits which have Mn-oxides in their upper parts.

Thesis (Ph. D.)--University of Alberta, 2009. / Title from PDF file main screen (viewed on Oct. 16, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geology, Department of Earth and Atmospheric Sciences, University of Alberta." Includes bibliographical references.

In the UK, large quantities of intermediate level waste pose complex radiological remediation challenges. Chemical understanding of uranium in these Mg-rich sludges is vital. Previous studies have examined uranium uptake by calcium carbonate minerals (calcite and aragonite) under conditions pertinent to both natural and anthropogenically perturbed systems. However, research on uranyl uptake by magnesium-rich minerals such as magnesite [MgCO3], brucite [Mg(OH)2], nesquehonite [MgCO3·3H2O] and hydromagnesite-[Mg5(CO3)4(OH)2·4H2O] has not, to the best of our knowledge, been previously conducted. Such experiments will improve our understanding of the mobility of uranium and other actinides in natural lithologies such as dolomitic limestones or mafic igneous emplacements, as well as provide key information applicable to nuclear waste repository strategies involving Mg-rich phases. By two EXAFS techniques, we determined: (1) where uranyl (UO22+) is adsorbed, and (2) how uranyl is attached to the mineral surface. Therefore powder experiments of U(VI) were performed with magnesite, brucite, nesquehonite and hydromagnesite. The second experiment (GIXAFS) consisted of single crystals of magnesite (10.4) and brucite (0001). The powders were reacted in solution pH ~8.5 with U(VI)nitrate for 48 hrs. under ambient PCO2 = -3.5. The single crystals were reacted under ambient and reduced PCO2 ~ -4.5 for 48 hrs. with concentrations of U(VI)chlroride above (500; 50 ppm) and below (5 ppm) solubility of schoepite [UO2(OH)2·H2O]. The GIXAFS measurements were made at χ = 0˚ and χ = 90˚ relative to the synchrotron beam polarisation to uequivocally determine the adsorbate structures. Kd values for Mg-carbonate phases were comparable to or exceeded those published for calcium carbonates. GIXAFS results clearly showed polarisation for both ambient and reduced PCO2. XANES results showed uranyl is oriented with the axial oxygens perpendicular to the mineral surface. This implies, using also X-ray reflectivity and diffuse scatter, local hydrated bayleyite [Mg2(UO2)(CO3)3∙18H2O] and possible rutherfordine-like [UO2CO3] regions, which will be useful to predict uranium behaviour in various remediation processes.