Siliceous-rhodochrosite rocks of the Sikhote-Alin

Abstract

The stratified position of siliceous-rhodochrosite rocks of the Sikhote-Alin, replacing manganese-silicate (composed mainly of Mn-silicates) rocks outside the contact large granitoid massifs of Cretaceous-Paleogene age, indicates their primary sedimentary nature. The discovery of siliceous-rhodochrosite rocks – protoliths of manganese-silicate rocks of the Triassic chert formation of the Sikhote-Alin is of crucial importance for understanding the genesis of the latter. The same position of these formations in the section of Triassic deposits of the Taukha and Samarka terranes indicates the synchronous accumulation of enriched with Mn original sediments in a single sedimentary basin. The occurrence in radiolarites, as well as the enrichment of siliceous-rhodochrosite rocks with organic matter, indicates their formation as a result of the reductive diagenesis of siliceous silts enriched with Mn hydroxides, clay and organic matter of biogenic origin.
The presence of organic matter inclusions explains not only the exclusively divalent form of Mn, but also the widespread occurrence in siliceous-rhodochrosite and their contact-metamorphosed (in Cretaceous-Paleogene time) analogues – manganese-silicate rocks of various native elements and intermetallic compounds.