Metalliferous Carbonaceous Metasomatites as a New Type of Rhenium Accumulation (Evidence from the Russian Far East)

摘要

Carbonaceous metasomatites were first found in ore districts of the Russian Far East and almost simultaneously in Central Asia and Siberia. To date, they have been discovered in many regions of Russia. Carbonaceous metasomatites are universally controlled by folding, schistosity, and boudinage zones, and, in some regions, form cement of explosive breccia. When these dark to black fine-grained rocks are strongly schistosed, they are often mistaken for carbonaceous schists. Carbonaceous metasomatites contain graphite, shungite, anthraxolite, and other carbon forms. In most cases, graphite predominates and associates with ilmenite, rutile, and magmatic sulfides. Carbonaceous metasomatites contain nanoinclusions of native metals, carbides, and intermetallic compounds. Native metals (Fe, Zn, Pb, Sn, Cu, and Al) occur both as nanoinclusions and as larger (globular and platy) aggregates of tenths of millimeters in size. Intermetallic compounds are mainly represented by CuZn, ZnAl and SnPb mixtures. Native forms of accessory minerals indicate the reducing conditions of their formation and are a deep-seated source of hydrocarbon fluids. The metasomatites formed at a maximal temperature of 800-850℃. Gases in closed pores are compositionally similar to those in deep-seated rocks of the Yakutian diamondifer-ous pipes. They include helium, hydrogen, oxygen, nitrogen, methane, ethane, propane, butane, carbon oxide, and dioxide.