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Yucca Mountain was designated as the proposed high-level radioactive waste repository by the U.S. Government in 1987. The proposed repository design requires high safety for a long maintenance period of 10,000 years. To satisfy this requirement, evaluation of the influence of earthquakes on the repository is necessary. Prediction of earthquake-induced ground motions around the repository requires knowledge of the dynamic properties of the geologic materials around the repository. The main geologic materials in the vicinity of Yucca Mountain are tuffs (ignimbrites) which are formed by the deposition of volcanic ash mixed with erupted volcanic gas, water vapor and pyroclastic material. Two types of dynamic tests, (1) the free-free, unconfined, resonant column and direct arrival test (freefree URC test) and (2) the fixed-free resonant column and torsional shear test (fixed-free RCTS test), were used to measure the dynamic properties of tuffs. The emphasis in this dynamic testing was evaluation of shear modulus (G) and material damping ratio (D) of the tuffs in the small-strain (linear) and mildly nonlinear (to strains of about 0.02 %) ranges. To evaluate the influence of various parameters on G and D of tuffs, correlations with other features such as total unit weight, porosity and stratigraphic unit were performed and general relationships between them are proposed. In addition, an unconfined, slow-cyclic torsional shear (CTS) device was developed and used to measure the cyclic shear properties of the tuffs from Yucca Mountain at larger strain amplitudes than possible in the fixed-free RCTS tests. Additionally, the CTS device was also used to determine the shear failure strength of the tuffs. By combining the cyclic shear properties of the tuffs from the CTS tests and the dynamic properties of the tuffs from the fixed-free RCTS tests, complete dynamic property curves from small-strain to failure strain were evaluated.

Oxidized hydrous intermediate composition magmas are responsible for porphyry copper (Cu ±Mo ±Au) deposits and epithermal Au ore deposits formed globally in the shallow crust (Sillitoe, 2010; Seedorff et al., 2005). Recently, zircon geochemistry has been used to characterize both productive and barren intrusions associated with porphyry Cu-Au ore deposits. Zircon composition differs slightly between the two intrusive groups, and researchers have proposed that zircon in productive intrusions has crystallized from a relatively more oxidized melt compared to barren intrusions (Ballard et al., 2002; Muñoz et al., 2012). Zircon rare earth elements record anomalies in Ce and Eu contents that allow estimation of the ratio of oxidized versus reduced species, i.e. Ce⁴⁺/Ce³⁺ (Ce[superscript IV]/Ce[superscript III]) and Eu³⁺/Eu²⁺ (Eu/Eu*)[subscript CN]. This study focuses on understanding the compositions of Eocene magmas associated with sediment hosted Carlin gold deposits and the gold-copper ores of the Battle Mountain porphyry Cu-Au-skarn district in northern Nevada. Zircon trace element composition was analyzed using LA-ICP-MS and SHRIMP-RG to determine differences between mineralizing and non-mineralizing intrusions in northern Nevada and to compare these compositions with known porphyry Cu-Au type magmas. These zircon and rock compositional data was then used to test the hypothesis of a magmatic origin of the Carlin type gold deposits (Muntean et al., 2011). Zircon U-Pb ages were calculated using multiple SHRIMP-RG spot analyses of each sample for two Carlin biotite porphyry dikes, two Battle Mountain porphyry dikes and the granodiorite of the Copper Canyon stock. The new U-Pb age dates for Carlin porphyry dikes are 38.7 ± 0.5 Ma and 38.8 ± 0.4 Ma. The age of the Copper Canyon stock is 38.0 ± 0.7 Ma, and the age of the Battle Mountain porphyry dikes are 40.2 ± 0.4 Ma and 41.3 ± 0.4 Ma. The Carlin dike ages are the same age, within uncertainty, with previous studies conducted (Mortensesn et al., 2000). The productive porphyry dikes from the Battle Mountain district have Ce(IV)/Ce(III) ratios of 500 to 10000 and a wide range of (Eu/Eu*)[subscript CN] values between 0.3 and 0.7 respectively. Carlin porphyry dikes have Ce(IV)/Ce(III) values between 100 and 1000, and a more limited (Eu/Eu*)[subscript CN] range of 0.5 to 0.7. Barren Eocene intrusions at Harrison Pass and Caetano have much lower Ce(IV)/Ce(III) ratios that range from 20 to 500, and have a very large span of (Eu/Eu*)[subscript CN] from 0.03 to 0.6. Calculated Ce(IV)/Ce(III) and (Eu/Eu*)[subscript CN] of zircon of this study illustrate a distinction between productive and barren intrusions in northern Nevada, and demonstrate a geochemical link between porphyry type magmas and dikes associated with Carlin type gold deposits. These ratios may provide a useful means of evaluating potentially economic geologic terranes and serving as a method to infer relative oxidation state of zircon bearing intrusive rocks. / Graduation date: 2013

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