Fluid regime of platinum group elements (PGE) and gold-bearing reef formation in the Dovyren mafic-ultramafic layered complex, eastern Siberia, Russia

Abstract

The Dovyren layered dunite–troctolite–gabbro massif (northern Transbaikalia region, Russia) contains precious metal mineralization related to sparsely disseminated sulfides (Stillwater type). The distribution of gases trapped in micro-inclusions and intergranular pores of the Dovyren massif has been investigated. This type of study had previously only been undertaken on the traps or peridotite–pyroxenite–norite intrusions hosting copper–nickel sulfide deposits. A novel method of analyzing trapped gases, involving the grinding of samples under high vacuum at room temperature, was employed. A modified gas-chromatography and mass-spectrometry approach was used to analyze the composition of the extracted gases. The concentrations of reduced gases (CH4 and H2) are higher in inclusions trapped by silicate minerals, whereas oxidized gases (H2O, CO2) are less common. The content of reduced gases (H2, CH4, CO), N2, He, radiogenic Ar, and C2H6 increases upward through the layered series of the massif. The distribution of all gases, especially methane and hydrogen, show peak concentrations coincident with the PGE and gold reef type horizons. A correlation of the gas peaks and noble metal contents appears to be related to their geochemical affinities. This conclusion is supported by the experimental modeling.