WHITE SODIUM MICAS OF GAISKOYE MASSIVE SULPHIDE ORE DEPOSIT (THE SOUTHERN URALS)

摘要

Sodium-bearing anchimicaceous schists from the local bodies in stress zones, usually at contacts of massive sulphide ores. They ought to have been developed at the final stage of forming of the background chlorite-sericite-quartz metasomatites. White micas are represent by the fine-flaky aggregate of paragonite (Pa_(95)Mu_5), a K-Na mica and muscovite (Mu_(87)Pa_(13)). The existance of K-Na mica was proved by the high-voltage electronography and X-ray powder diffraction. According to microprobe and chemical analyses data, micas have the clear K+Na+Ca+Ba (0.75-0.85 f.u.) deficit, minor quatity of Fe+Mg (0.02-0.05 f.u.), but the higher content of Si (3.14-3.20 f.u.), i.e. they relate to illite group. They are characterized also by the higher quantity of unbound interlayer water. Taking into consideration that K-bearing micas belong to the 2M_1 modification, it could be supposed that the primary micas had been the hydromicas of 1M modification conversed afterward into illite-like micas under the low-temperature (up to 300-350 deg C) metamorphism. Later, in separate zones, these micas were effected by an imposed hydration, but they retained the 2M_1 modification. The mere forming of this three micas association was caused by the high Na/K ratio in a primary fluid connecting with essentially sodium composition of parent migmatites and frame rocks.