Mineralogy and petrography of technogenic parabasalts from the Chelyabinskbrown-coal basin

Spontaneous burning in the largest spoil heaps of the Chelyabinsk coal basi n led to high-temperature conditions (1000-1300 degrees C). At these parame ters, Fe-rich basic liquids resulted from the complete melting of a fine-cr ushed mixture of mudstones, calcareous clays, and siderites in zones of hea ps with reduced gas annealing. Crystallization of these melts under dry red uctive conditions (f(O2) = 10(-9) - 10(-12), T = 1200 - 1000 degrees C) at pressure close to 1 atm led to formation of parabasalts. These rocks differ greatly from all natural paralavas and terrestrial basalts in high Al2O3, FeO, CaO, P2O5 and low SiO2, MgO, Fe2O3, and Na2O contents. Plagioclase (An (100-90)), Mg-Fe-clinopyroxene (diopside, low- and high-alumina augite), an d Mg-Fe-olivine (Fo(60-15)) are the main rock-forming minerals in the parab asalts. Fayalite (Fo(10-3)) Ti-magnetite, Al-spinel, leucite, hedenbergite, kirschsteinite, pyrrhotite, K-feldspar, fluorapatite, ilmenite,and glasses of two compositions (K-acid and Fe-basic) are minor phases. Low-Ca pyroxen es (orthopyroxene, pigeonite), tridimite and other SiO2 polymorphs, mullite , nepheline, chalcopyrite, pyrite, native iron, and shungite are found as a ccessories. Some minerals contain uncommon admixtures. Olivines contain up to 15 mole % larnite end-member, some olivines and kirschsteinites have P2O 5 (up to 0.7 wt.%), apatite is rich in SiO2 (up to 6 wt.%), and K-feldspar is rich in BaO (up to 7.5 wt.%). in textural features, modal compositions, mineral ratios, and order of mineral crystallization the technogenic paraba salts correspond to shallow-depth basic rocks.