New Data on Granitoids of the Kara Gold Ore Cluster (Eastern Transbaikalia): Age, Genesis, and Sources of Material

Abstract

Abstract —Study of granitoids spatially and genetically associated with gold mineralization within the Kara gold ore cluster has provided a new insight into their genesis, association with ore mineralization, and the sources of their ore material. The regional granitoids associated with gold mineralization are part of two individual complexes. One of them, earlier assigned to the Amanan complex, has an isotopic age of 182.9 ± 2.6 Ma and must be related to the subduction zone that existed on the southern margin of the Siberian continent in that period. Its granitoids differ in age and composition from the granitoids of the Amanan complex and must be separated as an independent taxonomic unit after an additional geological study. The second, Amudzhikan–Sretensk, complex has an isotopic age of 151.7 ± 1.9 Ma and might be related to the collision of the Siberian and Mongol–Chinese continents after the closure of the Mongol–Okhotsk ocean. In geochemistry the granitoids of the Amanan(?) complex correspond to adakites and must be considered melting products of the basaltic layer of the oceanic lithosphere. The granitoids of the Amudzhikan-Sretensk complex are similar in geochemistry to sanukitoids, melting products of subcontinental sources contaminated with continental-crust material. The granitoids of both complexes have high contents of gold and must be considered gold-bearing. In the Amanan(?) complex, adakites are the gold-richest rocks (as estimated from the slab melt composition), which indicates the primary nature of this gold. In the Amudzhikan–Sretensk complex, the highest contents of gold are specific to primitive sanukitoids, melting products of a mantle source with gold signatures. This suggests the primary nature of gold, whose content is determined by the portion of slab melt in the source of the rock material. The presence of adakites and primitive sanukitoids in the regional granitoid complexes indicates the existence of a subcontinental mantle source with gold signatures during the magma generation. The source formed in the subduction zone that existed on the southern margin of the Siberian continent in the Early Jurassic and was remobilized under collision of the Siberian and Mongol–Chinese continents in the Late Jurassic. This source might have controlled both granitoid magmatism and ore mineralization.