Geology
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Item Hydrothermally Altered Basalt as a Source for Indium in Ore Deposits(2018) Hollingsworth, John Walter; Piccoli, Philip M; Candela, Philip A; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Indium is an element integral to various emerging technologies. Despite the demand for indium, little is known about its geochemical behavior in hydrothermal systems that generate economic deposits. The aim of this study is to estimate the efficiency with which indium can be removed from basalt during hydrothermal alteration in order to develop better exploration vectors. This can be accomplished by studying how indium partitions between an aqueous solution and the products of hydrothermal alteration. To evaluate the magnitude of this efficiency, two sets of experiments were performed. The first set used a low initial pH, indium+HCl-bearing aqueous solution, whereas the second used a higher initial pH, indium+sulfur-bearing seawater solution. The water/rock mass ratio ranged from 1-10. Experiments were performed at 500°C and 50 MPa for 2-8 weeks. Water/rock was found to have the greatest affect on the partition coefficient of indium between the altered basalt and the aqueous solution.Item Quantitative modeling of mantle heterogeneity and structure(2010) Arevalo, Jr., Ricardo David; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mantle-derived rocks, particularly mid-ocean ridge basalts (MORB) and intraplate ocean island basalts (OIB), provide insights into the compositional heterogeneity and first-order structural make-up of the modern mantle; laser ablation (LA-) ICP-MS analysis provides the ideal analytical tool for the in situ chemical characterization of these materials. The silicate Earth, as defined by the MORB and OIB source regions plus the continental crust, is determined to have a representative W/U and K/U ratio of 0.65 ± 0.45 (2σ) and 13,800 ± 2600 (2σ), respectively, equating to 13 ± 10 ng/g W and 280 ± 120 μg/g K in the silicate Earth. Although both the isotopic composition of W and the constancy of the terrestrial W/U ratio may serve as tracers of putative core-mantle interactions, both of these proxies are sensitive to the chemical composition of the mantle source and have yet to resolve a core signal in Hawaiian picrites. The abundance of K in the silicate Earth indicates a current convective Urey ratio of ~0.34 and mantle cooling rate of 70-130 K*Gyr−1, after taking into account potential heat flux across the core-mantle boundary. The Earth's balance of radiogenic heat and budget of 40Ar necessitate a lower mantle reservoir enriched in radioactive elements. The bulk Earth Pb/U ratio, determined here to be ~85, suggests ~1200 ng/g Pb in the bulk Earth and ≥3300 ng/g Pb in the core. A compositional model of MORB, which is derived from a suite of sample measurements augmented by a critically compiled data set, shows that Atlantic, Pacific and Indian MORB can be distinguished based on both trace element abundances and ratios. The geochemical signatures associated with global MORB are not entirely complementary to the continental crust, and require an under-sampled reservoir enriched in Ti, Nb and Ta. A compositional model of OIB, which is based on the inferred chemical composition of OIB parental melts from Hawaiian shield volcanoes as well as the Austral-Cook islands, indicates that the OIB source region may only be ≥1.0x as enriched in incompatible elements as the unfractionated silicate Earth, and constitute up to ≤50% of the modern mantle mass.