MINERALOGY OF PYROMETAMORPHIC ROCKS ASSOCIATED WITH NATURALLY BURNED COAL-BEARING SPOIL-HEAPS OF THE CHELYABINSK COAL BASIN, RUSSIA

Abstract

Pyrometamorphic rocks generated during spontaneous burning of spoil-heaps in the Chelyabinsk coal basin, South Urals, contain a variety of high-temperature minerals, some with diverse and unusual compositons. Optical microscopy, X-ray diffraction, X-ray fluorescence, and microprobe analyses were performed to study the mineralogy of annealed and fused waste rocks. A wide spectrum of rare minerals was found, including tridymite, crystobalite, mullite, K-bearing cordierite, K-Mg-osumilite, and Fe3+,Al-rich Ca-clinopyroxene, as well as hexagonal and orthorhombic analogues of anorthite. It is suggested that the mineralogy of pyrometamorphic rocks is mainly governed by bulk chemical composition, annealing temperature, and oxygen fugacity; moreover, varying degrees of disequilibrium melting, mixing, crystallization, volatilization and a variety of reaction mechanisms influence the formation, structure and chemistry of the constituent minerals.