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

Pyrometamorphic rocks generated during spontaneous burning of spoil-he aps in the Chelyabinsk coal basin, South Urals, contain a variety of h igh-temperature minerals, some with diverse and unusual compositons. O ptical microscopy, X-ray diffraction, X-ray fluorescence, and micropro be analyses were performed to study the mineralogy of annealed and fus ed 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 orthorho mbic analogues of anorthite. It is suggested that the mineralogy of py rometamorphic rocks is mainly governed by bulk chemical composition, a nnealing temperature, and oxygen fugacity; moreover, varying degrees o f disequilibrium melting, mixing, crystallization, volatilization and a variety of reaction mechanisms influence the formation, structure an d chemistry of the constituent minerals.