Effects of Mother Lode-Type Gold Mineralization on 187Os/188Os and Platinum Group Element Concentrations in Peridotite: Alleghany District, California

Abstract

The major Au-quartz veins of the western Sierra Nevada foothills occur within pervasively metamorphosed, sheared, folded, and faulted rocks of widely varying rock types and ages. In the Alleghany district, diverse host-rock types of mineralized veins range from serpentinized peridotite to granite, with metamorphic grades ranging from blueschist to amphibolite (Figs. 1, 2). Geochronologic and geologic constraints indicate that the Sierran Au-bearing veins most likely formed after the peak of the regional pervasive deformation of the Nevadan (ca. 155 Ma) compressional event (Böhlke and Kistler, 1986). Dating of minerals associated with the ores by the Rb-Sr and K-Ar methods indicate that Au-bearing veins formed in the Sierra Nevada foothills during the interval of 108 to 144 Ma (Evans and Bowen, 1977; Kistler et al., 1983; Böhlke and Kistler, 1986). The mineralization evidently occurred during a period of active faulting, associated in part with major structural features such as the Melones fault zone (MFZ; Fig. 2). The veins formed from CO 2-bearing fluids

Geochronology and characteristics of Ni-Cu-(PGE) mineralization at Rožany, Lusatian Granitoid Complex, Czech Republic

“…If barren dolerite and surrounding Lusatian granitoids are considered to be representative of a parental melt and assimilant, respectively, their interaction should lead to development of a well-defined mixing trend in Os-γOs space as continental crust has typically very low Os content paralleled by very high γOs (e.g., Esser and Turekian 1993; Peucker-Ehrenbrink and Jahn 2001). In contrary, an opposite, rather scattered trend can be rec- (Walker et al 1994(Walker et al , 2007 or dehydration (Becker 2000). Taking into account several observations described above giving the clear evidence for late-stage hydrothermal alteration, variable Re loss is the most viable explanation for the observed Re-Os compositions of the Rožany ores.…”