THE ROLE OF ORGANIC CARBON IN THE FORMATION OF OROGENIC-GOLD DEPOSITS (Bodaibo region, Russia)

The paper summarizes the results of long-term geochemical studies on the regional geology of the Bodaibo synclinorium as a whole and the local (ore) geology of individual orogenic gold deposits located within the world’s largest Lena metallogenic province. The main attention is focused on the role of organic matter in ore genesis. The paper presents results of a study of the transformation of organic matter of carbonaceous shales (soluble (bitumen) and insoluble carbonaceous matter) during catagenetic and metamorphic transformations. The absence of a significant correlation between insoluble carbon and gold has been demonstrated. This is due to the low sorption capacity of graphitized organic matter relative to its primary (precatagenic) counterpart. Carboxylic esters (lipids) have been identified in bitumens of carbonaceous shales, thus confirming the bacterial and planktonogenic origin of the primary organic matter of sediments. The similar gold contents in bitumen from rocks within the studied deposits and in bitumen from remote rocks indicate the presence of gold in the organic fluid. It is concluded that carbon plays one of the leading roles in the gold mobilization and migration at the stage of catagenesis. However, the hypothesis that organic matter can be a barrier to metal-bearing hydrotherms is not confirmed. Based on the model of the catagenetic formation of oil fields, we show the high probability of the formation of gold mineralization at the Dal’naya Taiga–Zhuya stratigraphic level in the Neoproterozoic section of the Baikal–Patom region.