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

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 t he traps or peridotite-pyroxenite-norite intrusions hosting copper-nickel s ulfide deposits. A novel method of analyzing trapped gases, involving the g rinding of samples under high vacuum at room temperature, was employed. A m odified gas-chromatography and mass-spectrometry approach was used to analy ze the composition of the extracted gases. The concentrations of reduced ga ses (CH4 and H-2) are higher in inclusions trapped by silicate minerals, wh ereas oxidized,oases (H2O, CO2) are less common. The content of reduced gas es (H-2, CH4, CO), N-2, He, radiogenic Ar, and C2H6 increases upward throug h the layered series of the massif. The distribution of all gases, especial ly methane and hydrogen, show peak concentrations coincident with the PGE a nd gold reef type horizons. A correlation of the gas peaks and noble metal contents appears to be related to their geochemical affinities. This conclu sion is supported by the experimental modeling.