Minor Ultramafic-mafic Intrusions of Devonian Altai-Sayan LIP (South Siberia): Petrogenesis and Ore Potential

English Abstract:

There are several hundred minor ultramafic-mafic and mafic bodies of Early Devonian age in the central part of the Altai-Sayan folded area (part of Central Asia Orogenic Belt). It is assumed that they are derived from one of the earliest and most primitive melts formed during the formation of the Altai-Sayan LIP. Altai-Sayan LIP formed simultaneously with Vilyui LIP (NE Siberia), the bulk of which are intracontinental rift basalts filled large depressions like Minusa and Tuva troughs. We have studied more than 20 minor intrusions of this age in the Tsagaan Shiveet Ridge in NW Mongolia. Rocks composition varies greatly and there are different types of intrusions: minor homogeneous, layered and minor differentiated. However, the geochemical characteristics of these rocks are relatively close to each other, and in this way are significantly different from the bodies of the Cambrian age also situated in the area, suggesting a common mantle source, but different ways of evolution of the initial melts. In one of the intrusions a small occurence of Cu-Ni ores with PGE mineralization was found. The total content of PGE in the samples is about 750 ppb, with 0.35 wt.% Cu and 0.5 wt.% Ni. Thus there is potential to find similar deposits in other intrusions of this age.

This works were funded by Russian Foundation for Basic Research (grants 12-05-00435, 13-05-01132, 13-05-00951 and 13-05-12056).