Classification and genesis of stockwork molybdenum deposits; discussion

Abstract

DISCUSSIONScipitating it by the Boudouard reaction. The isotope ratios of epigenetic graphite are affected by the isotope ratios of the source material, reaction or nonreaction with carbonate minerals, and probably to a lesser extent upon the PT (pressure-temperature) con- ditions."The graphite in epigenetic veins in high grade schists and gneisses would thus have variable carbon isotope ratios depending on whether it was derived from organic material in carbonate or noncarbonate metasediments.

Arc-related porphyry molybdenum deposit model

“…Westra and Keith (1981) attribute this basic difference in geochemistry to be a result of the location within the subduction zone and depth of the subducted slab. However, Christiansen and Wilson (1982) question the validity of this model and instead suggest that differences in geochemistry result from deep crustal melting for alkali-feldspar rhyolite-granite porphyry molybdenum deposits. Differences in fluorine, niobium, rubidium, and strontium concentrations within these two different deposit types also is stressed as being important by Westra and Keith (1981).…”

The Geology and Geochemistry of Cenozoic Topaz Rhyolites from the Western United States

“…The intervening lowlands were covered by widespread dacitic to rhyolitic ash flows erupted from collapse calderas. The older F-rich rhyolite domes (20 to 18 Ma) are nearly contemporaneous with the latter portion of this episode but were accompanied by the eruption of trachyandesite (62 to 54% SiOz) lavas in the Wah Wah Mountains, forming a bimodal suite there (Fig-ure 42;Keith 1980;Best et al 1985;Christiansen and Wilson 1982). High-K andesites erupted along the belt from 25 to 21 Ma (Best et al 1980(Best et al , 1985.…”