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Whole rock and microanalytical geochemistry data from rocks collected from the Colorado Mineral Belt, Thirtynine Mile volcanic area, Cripple Creek gold deposit (& environs) and other volcanic and intrusive bodies of the Pikes PEak - Gunnison area of Colorado.
This study explored the links between host rock composition, hydrothermal fluid composition (particularly pH), and the resulting ore minerals and deposits. The progressive water–rock reaction between 1 kg of initially acidic, condensed magmatic vapour and a series of different rock compositions was modelled with CHILLER (Reed, 1982, Reed, 1998), and follows the design of the water-rock reactions of Reed (1997). The thermodynamic data used in the numerical experiments are from the database SOLTHERM.H08 (Reed and Palandri, 2013). Data and calculations within SOLTHERM include: equilibrium constants calculated with SUPCRT92 (Johnson et al., 1992); mineral thermodynamic data for silicates, oxides, hydroxides, carbonates, gases (Holland and Powell, 1998) and sulphides (Shock, 2007). Mineral solid solutions are represented by end-member compositions that are mixed using an ideal multisite mixing scheme. Rock compositions used in the modelling represent a sub-alkaline andesitic control, and a number of alkaline compositions associated with world-class Au deposits. All starting rock compositions are derived from whole rock geochemical data, and have been recalculated to a 100% basis without TiO2 or P2O5 (excluded as minor phases with little to no effect on hydrothermal mineral assemblages). Original total Fe (as Fe2O3) has been recalculated to FeO and Fe2O3 using the method of Müller et al. (2001). The andesite is representative of calc-alkaline, silica saturated compositions, and is derived from and discussed in detail in Reed (1997). The Luise “Phonolite” (a trachyandesite using the Le Maitre et al., 1989 TAS plot; Fig. 1) and Trachyandesite are from the vicinity of the Ladolam epithermal Au deposit, Lihir Island, Papua New Guinea (Müller et al., 2001). The Porgera Mugearite and Feldspar Porphyry represent unaltered host rock compositions (Richards, 1990) from the Porgera Au deposit (Papua New Guinea). The Cripple Creek Phonolite is part of the host suite to the Cripple Creek epithermal Au deposit, Colorado (Kelley et al., 1998). The Savo trachyte (Smith et al., 2009) represents a typical host rock of the active hydrothermal system (Smith et al., 2010), on Savo island, Solomon Islands. With the exception of the Andesite, all compositions are alkaline using the total alkali versus silica definition of Irvine and Baragar (1971). The Savo sample is not associated with known epithermal Au mineralisation; this composition was selected on the grounds that it represents an evolved (SiO2-rich) silica-saturated, alkaline composition. The initial fluid composition is based on a condensate from Augustine volcano (Symonds et al., 1990) mixed 1:10 with pure water (Reed, 1997; Table 2). A single starting fluid for all models was chosen so as to demonstrate the effect of host rock alone.
Whole rock and pyrite geochemistry data from a suite of mineralised and barren rocks from Vatukoula gold mines and the Tavua caldera that hosts the ore body, in the northern part of the island of Viti Levu, Fiji. Vatukoula (also historically known as the Emperor gold mines) is a world class alkaline-associated epithermal gold deposit, noted for the abundance of gold and silver telluride minerals, and the exotic geochemistry of the volcanic host rocks (potassic shoshonites and absarokites). This dataset includes bulk geochemical analysis of whole rocks by X-ray fluorescence, and microanalysis of major and trace element of pyrite in the ore by a combination of electron beam and laser-ablation ICP-MS techniques. Pyrite geochemistry can be a useful tool in the study of epithermal ores, as it can carry evidence of boiling and phase separation, condensation, and fluid mixing. Samples were collected and analysed as part of a larger study looking at the relationship between epithermal gold deposits hosted in alkaline magmatic rocks, and an association with tellurium enrichment and precious metal tellurides. Samples were collected by D J Smith, M Keith, V V Ene, and geologists of Vatukoula Gold Mines. Analysis was carried out by M Keith and F Börner. Collected as part of the Tellurium and Selenium Cycling and Supply (TeaSe) project, part of NERC's Security of Supply of Minerals programme.