Copperstone is a mid-Tertiary "detachment gold" deposit that is herein classified as a new subtype of epithermal deposit. Copperstone is similar to many active geothermal systems in terms of host lithology, temperature, and related siliceous alteration mineralogy, except in the hypogene oxide assemblages, the high salinity, and the lack of sulfides and the pathfinder toxic elements. The host rock is mainly Jurassic quartz latite porphyry and Tertiary sedimentary breccias. Early stages of alteration were K-metasomatic and propylitic, and alteration that accompanied gold mineralization was mainly chloritization and silicification. Mineralization is structurally controlled and is restricted along the Copperstone Listric Fault with minor mineralization along high-angle NE and NW faults, as with many other deposits in west-central Arizona. The gold stage of mineralization was superimposed on previously K-metasomatized rocks. Hypogene mineralization can be divided into 3 paragenetic stages: early amethyst-quartz-Fe-rich-chlorite-specularite-hematite-Au° of stage C; late-stage fine-grained euhedral quartz-adularia-chrysocolla ± malachite ± magnetite ± chalcopyrite-pink fluorite-barite-ankerite-calcite-Au° of stage D; and barren quartz-pale green fluorite-barite-calcite-hematite of stage E. Gold occurs as free particles or is encapsulated in amethyst and late fine-grained euhedral quartz. The time of mineralization is Miocene or younger and the depth of mineralization was 1 Km. Gold mineralization was related to boiling such that a hot spring system did operate at Copperstone. Copperstone is a hydrothermal system created during the last stages of detachment faulting, with mineralization controlled by boiling, and "second boiling" was the principal trigger of Copperstone gold deposition in an environment of falling temperatures and pressures on chloride-rich brine fluids. Variation in δ³⁴S indicates that two different fluids are involved in this system, and that a deeper, "lighter" hydrothermal fluid mixed with a "heavier" basin brine. δ¹⁸O values from carbonates confirm the extent of isotopic exchange with an aqueous reservoir and indicates that oxidation accompanied gold deposition.

Several scenarios set forth to explain the siderophile element abundance patterns in the mantles of the Earth and the Moon involve the segregation of Ni-rich metal to the cores of those bodies under oxidizing conditions. To test these models, the partition coefficients of Ni, Co, Mo, W, P, and Ga between basaltic liquid, Ni-rich metal, and Ni-rich sulfide were experimentally determined under a wide range of oxygen fugacities. The partition coefficients are then used in mass balance calculations to test these scenarios involving oxidizing conditions during the formation of both the Earth's and the Moon's cores. The results show that the siderophile element pattern in the Earth's mantle is consistent with a late stage segregation of a small fraction of metal that consists of approximately 70% Ni at low degrees of partial melding of the silicates. This result is not consistent with the early Earth being substantially molten as the result of a giant impact to form the Moon. The results for the Moon show that the siderophile element pattern in the lunar mantle is consistent with the segregation of a small Ni-rich core at high degrees of melting of the silicates if some elements are initially depleted by some other process--presumably volatility during a giant impact. The high degree of partial melting of silicates is consistent with the postulated magma ocean on the Moon.

The biotite + muscovite ± garnet-bearing Texas Canyon (TC), Presumido Peak (PP), and Gunnery Range (GR) granites are members of an enigmatic suite of Eocene age granites in southern Arizona. The late orogenic granites intrude Precambrian through Jurassic metasediments and metavolcanics. The major and minor element geochemistry of the high silica, weakly peraluminous granites is rather uniform. However, trace element concentrations, REE patterns, and isotopic compositions imply gross similarities between the TC and GR granites when both are compared to the PP granite. The TC and GR granites were derived from a depleted Precambrian lower crustal source area with low Rb/Sr, while the PP granite was the result of anatectic melting of an enriched Precambrian mid-to-upper crustal source. The PP granite is an integral part of a metamorphic core complex, and this tectonic setting accounts for the geochemical differences between it and both the TC and GR granites.

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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