The Jackson Mountains (JM) are part of the early Mesozoic continental arc in northwest Nevada, which was constructed upon previously accreted Paleozoic basement. The stratigraphy of the Paleozoic basement exposed in the JM has been revised and correlations with nearby age-equivalent rocks in the Pine Forest Range and Bilk Creek Mountains are now more clearly recognized. Upper Triassic strata in the JM (the Carnian-Norian Boulder Creek Beds) herald the onset of Mesozoic arc activity in the region. The Boulder Creek Beds are both overlain and intruded by rocks of the Happy Creek Igneous Complex (HCC). Contact relations and internal features of the HCC indicate that mostly hypabyssal intrusive rocks are now exposed and that the bulk of the supracrustal volcanic succession was eroded prior to deposition of the King Lear Formation (KLF), which unconformably overlies the HCC. The HCC intrudes Norian strata and is cut by plutons that have yielded U-Pb zircon dates of 196-190 Ma and is probably entirely of Early Jurassic age. Igneous rocks associated with the KLF have yielded U-Pb zircon dates that indicate KLF deposition took place in the Early Cretaceous ($\sim$125 Ma). Two phases of Mesozoic deformation are recognized in the JM. The D$\sb1$ phase produced NW trending folds, an axial planar cleavage, and was associated with subgreenschist to amphibolite grade metamorphism. D$\sb1$ structures are found only in rocks older than the HCC and are truncated along intrusive contacts of the HCC. D$\sb2$ deformation produced NE trending folds, an axial planar cleavage, and was associated with very low grade metamorphism. D$\sb2$ affected the HCC and older rocks, but is absent in the KLF. Thus, D$\sb2$ shortening is constrained between late Early Jurassic to Early Cretaceous. D$\sb1$ correlates in style, orientation, and age with deformation in the adjacent Pine Forest Range, but the later D$\sb2$ event is apparently localized in the JM. In the JM, D$\sb2$ fabrics are better developed to the east, towards the back-arc region and may, therefore, have formed during juxtaposition of the arc terrane with the back-arc.

Two mud volcanoes in the Gulf of Mexico were examined to understand barium cycling in shallow seafloor sediment at regions of intense methane expulsion. Due to anaerobic oxidation of methane and sulfate reduction, barium interacts with methane and sulfate, producing barite fronts at the sulfate-methane transition and barium-rich pore fluids underneath. Formation waters likely feed volcanoes and deliver large amounts of Ba2+ to the system from below. Locally elevated Ba2+ concentrations amplified cycling, producing sigmodial pore water profiles in the shallowest sediment. The expulsion of Ba-rich fluids directly to the water column concentrates barite in surficial sediments, which can also enhance cycling. Further, two types of barium-rich, carbonate nodules were recovered. Rocky nodules resemble buried carbonate crusts, diagenetically altered by pore fluids. Smooth nodules are likely preserved barite fronts marking past sulfate-methane transitions. Both types of nodules can serve as a modern analogue for barite deposits in the geologic record.

Analyses of Oregon Cascades basalts reveal two groups of High Cascades (9-0 Ma) lavas: (1) "enriched" basalts with high Ba, Sr, Ba/Nb, and Ba/La, and (2) "depleted" basalts with flat rare earth element patterns and relatively low Sr and Ba. Fluid mobile elements, such as B, are depleted in High Cascades basalts. The decoupling of B and Ba presents an interesting problem for volcanic arc magma generation, since both elements are believed to be controlled through fluid input from the subducting slab. Petrogenetic modeling reveals that most Cascade magmas can be derived by uniform. partial melting of variably metasomatized primitive or NMORB-source mantle or by varying degrees of melting of a mineralogically inhomogeneous metasomatized mantle. The decoupling of B and Ba may result from shallow dehydration reactions in the slab which release B into the overlying mantle, while Ba is retained in the slab and released during subsequent dehydration reactions.

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New analytical techniques have been developed for the determination of selenium concentrations in sulphide minerals to assess the utility of the Se/S concentration ratios in tracing fluids associated with ore deposit formation. This has been accomplished via a new hydride generation (HG) sample introduction method for the determination of selenium contents in sulphide minerals, development of solid calibration standards by a sol-gel process, and the establishment of protocols for the measurement of selenium/sulphur ratios in sulphides using laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The low concentrations of selenium in sulphides require the use of hydride generation, which also requires the removal of metals to be effective. A process for the determination of selenium in sulphide minerals (~ 50 mg sample weight) wherein metals are removed by precipitation under alkaline conditions, followed by further removal by chelating resin, was developed. Determinations by HG-ICPMS on reference materials showed quantitative recoveries (100±5 %). Precision is 10 % relative standard deviation and the detection limit is 4 µg g-1 in a sulphide mineral. A sol-gel method for the fabrication of multi-element calibration standards, suitable for laser ablation, was developed. The addition of selenium and sulphur to a normal sol-gel method does not introduce detectable heterogeneity. Xerogel heterogeneity is less than that of the NIST glass standards. Calculated sulphur contents in the NIST glass SRMs are comparable to published data. Xerogels are potentially useful as standards in studies of glasses, minerals, and other materials. The development of a laser ablation technique allowed measurement of Se/S ratios in sulphide minerals. Sulphide minerals were sampled from volcanic hosted massive sulphide (VHMS) (Flin Flon area, Canada), high-sulphidation epithermal (Pierina, Peru), and iron oxide copper gold (IOCG) (Mantoverde, Chile) deposits. Thermodynamic data, mineral assemblages, and isotopic compositions are used to define depositional conditions and Se/S ratios of ore generating fluids. Although the elements can fractionate from each other, high Se/S ratios and low δ34S values generally reflect magmatic fluids, typical of VHMS and epithermal deposits, whereas the opposite is true for basinal or evaporitic sources, such as recorded by sulphides at the Mantoverde deposits. The Se/S ratios aid in the identification of ore generating fluid sources and can indicate mixing of fluids. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2008-02-19 18:51:32.656

The Karku unconformity-type uranium deposit is located in the Proterozoic Pasha-Ladoga Basin in western Russia. The deposit is located in basinal sandstones near a reverse fault that offsets the unconformable contact with underlying graphite-bearing biotite schist basement rocks. Meteoric water-sourced diagenetic fluids altered sandstones outside mineralized zones, producing clay assemblages of interstratified illite-smectite with minor dickite and Fe-rich chlorite, and fluid isotopic compositions of d18O = 3.3‰ to 6.0‰ and dD = -55‰ to -44‰ at 130°C. Altered sandstones within zones of mineralization include a clay mineral assemblage of Fe-rich chlorite with minor illite, and fluid isotopic compositions of d18O = 6.0‰ to 12.7‰ and dD = -8‰ to -4‰ at 210°C, caused by seawater-derived fluids related to ore formation. In addition, a Mg-chlorite occurring with uraninite in the mineralized lenses was identified. Dating of Karku uraninite using U/Pb isotope systematics from LA-MC-ICP-MS, LA-HR-ICP-MS, and SIMS gave upper-intercept ages of 1467 ± 39 Ma, 1459 ± 74 Ma, and 1302 ± 150 Ma respectively. The lower-intercept age of all methods was around 300 Ma. A formation model for the Karku uranium deposit is proposed based on the results of this study and incorporating previously published. Early, low-temperature diagenesis resulted in cementation of distal, basin-marginal sandstones by mixed-layer illite-smectite clays, preventing later, higher-temperature diagenetic alteration in this unit. Sandstones towards the centre of the basin allowed the circulation of higher-temperature basinal fluids that later flowed along the unconformity to the graphitic schist unit. A fault intersecting this unit facilitated the mixing of basement and basinal fluids, causing uraninite to precipitate at the unconformity. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-09-12 17:10:28.124

A funnel-shaped alteration pipe in Archean tholeiitic to transitional rhyolite and andesite underlying massive Zn-Cu sulphide ore at the Norbec mine in northwestern Quebec was outlined from drill core samples. Geochemical parameters, including mass changes and mobile element ratios were used with normative alteration mineralogy and thin section petrography to determine the extent of the alteration. The alteration was initially characterised by a peripheral zone of sericite-chlorite-quartz and a central chlorite-quartz zone. Isochemical metamorphism of the alteration pipe within the contact aureole of the Lac Dufault stock has converted these assemblages to cordierite-anthophyllite-biotite bearing rocks. / Bulk oxygen isotope data for the altered rhyolite suggest that the Norbec deposit formed at temperatures between 200$ sp circ$C and 300$ sp circ$C, with highest temperatures in the central chloritic zone of the alteration pipe. Calculations using SiO$ sb2$, K and Fe solubilities in typical sea-floor hydrothermal fluids suggest that water/rock ratios of 250 to 900 were necessary to introduce the added mobile elements to the alteration pipe.

The Amba Dongar carbonatite complex, India is host to a large fluorite deposit. The complex consists of a small ring structure comprised of early carbonatite breccia, a large, outer lining of calcitite and a number of small ankeritic carbonatite plugs. Surrounding the carbonatite ring are numerous plugs of nephelinitic and phonolitic syenites. The complex was intruded into Late Cretaceous Bagh Sandstones and Late to Early Paleocene Deccan Volcanics. / The hydrothermal history of the complex is extensive, consisting of two main systems, the first resulted in large amounts of fenitization, causing extensive K and Na metasomatism of the surrounding sandstones and the second, dealt with here, was responsible for the silicification of large amounts of the calcitite and the deposition of economic quantities of fluorite. / The deposit consists of veins and vug fillings of blue, purple, white, yellow and colorless fluorite. The main ore zone, which is currently under production, and most other showings, are found near the carbonatite-sandstone contact. / Chemical analyses and mass balance calculations show that the fluids responsible for silicification removed significant quantities of Ca from the rock while adding large amounts of Si, Al and F. Alteration associated with fluorite deposition involved the removal of Al from the rock and the addition of large quantities of F and Si. / Fluid inclusions in fluorite point to a low temperature-low salinity ore fluid, which decreased in temperature and salinity with evolution. Crushing experiments performed on fluid inclusions in both fluorite and quartz reveal the presence of ${ approx0.08}$ m of dissolved CO$ sb2$ in solution while analyses of leachates and decrepitate residues from fluid inclusions show significant concentrations of Ca, Al, Na, Cl and S in their fluids. (Abstract shortened by UMI.)

Large caldera-forming eruptions are among the greatest hazards faced by mankind. Eruptive sequences from caldera-forming eruptions at Ossipee ring complex, New Hampshire, and Lake City caldera, Colorado, reveal that magmas underwent crystal fractionation to produce a zoned silicic magma chamber in each case before caldera formation. At Ossipee, magmatic inclusions with resorbed phenocrysts and positive Eu anomalies demonstrate that magma replenishment caused chamber rejuvenation and the initiation of caldera collapse. At Lake City, two ignimbrite units associated with episodes of caldera collapse have mafic-rich bases; this indicates that these collapse events were initiated by mafic magma replenishment. A numerical model is developed that describes how magma chamber rejuvenation causes a reduction in crystal content, a decrease in gas pressure, and hence caldera collapse. During caldera formation at Ossipee and Lake City, magmas from progressively deeper levels in the chambers were erupted and intruded to shallower levels. Periods of reverse compositional zonation and lateral compositional variation at the top of ignimbrite units and in post-collapse intrusions indicate that a period of accelerated magma interaction occurred in the chambers towards the end of subsidence. Scaled analogue experiments of caldera collapse into density-stratified magma chambers reveal a similar period of reverse zonation and dynamic fluid interaction as the subsiding block approaches the chamber base. Additionally, the experiments indicate that piecemeal or asymmetric collapse cause vortices to develop in the chamber which efficiently disrupt stratification. After caldera collapse at Ossipee and Lake City, replenishing magma caused mixed residual magma to intrude along caldera faults to shallow levels and drive resurgence. The work illustrates how particular magmatic processes influence caldera collapse, and in turn, how caldera collapse affects particular magmatic processes.