MAYENITE SUPERGROUP MINERALS IN BURNED ROCKS FROM THE CHELYABINSK COAL BASIN
V.V. Sharygin
Keywords: Mayenite, eltyubyuite, wadalite, mayenite supergroup, Ca-ferrites, CaFe
O
, metacarbonate rocks, combustion metamorphism, burned dumps, Chelyabinsk coal basin
Abstract
Three minerals of the mayenite supergroup have been found in fluorellestadite-bearing metacarbonate rock (former fragment of petrified wood of ankerite composition) from the burned dump of the Baturinskaya-Vostochnaya-1-2 mine. These are eltyubyuite Ca
12Fe
3+
10Si
4O
32Cl
6, its fluorine analog Ca
12Fe
3+
10Si
4O
30F
10, and chlormayenite-wadalite Ca
12(Al,Fe)
14O
32Cl
2-Ca
12(Al,Fe)
10Si
4O
32Cl
6. The first two phases occur in the reaction mantle around hematite, magnesioferrite, and Ca-ferrite aggregates (“calciohexaferrite” CaFe
12O
19, “grandiferrite” CaFe
4O
7, and “dorrite phase” Ca
2(Fe
3+
5Mn
3+
0.5Mg
0.5)(Si
0.5Fe
3+
5.5)O
20) and, rarely, as individuals in the fluorellestadite-cuspidine (± larnite ± rusinovite Ca
10(Si
2O
7)
3Cl
2) granular aggregate. Assemblages of zoned chlormayenite-wadalite crystals are found in the fluorellestadite-cuspidine granular aggregate, which lacks Ca-ferrite aggregates. Also, harmunite CaFe
2O
4, chlorellestadite, fluorapatite, anhydrite, rondorfite Ca
8Mg(SiO
4)
4Cl
2, fluorine analog of rondorfite Ca
8Mg(SiO
4)
4F
2, “Mg-cuspidine” Ca
3.5(Mg,Fe)
0.5(Si
2O
7)F
2, fluorite, barioferrite BaFe
12O
19, zhangpeishanite BaFCl, and other rare phases are identified in this rock. Data on the chemical composition and Raman spectroscopy of the mayenite supergroup minerals are given. The genesis of metacarbonate rock is considered in detail: “oxidizing calcination” of Ca-Fe-carbonates with the formation of hematite and lime; reaction between hematite and lime with the formation of different Ca-ferrites; formation of larnite as a result of reaction between SiO
2 and lime or CaCO
3; and reactionary impact of hot Cl-F-S-bearing gases on early assemblages. Eltyubyuite and its fluorine analog crystallized at the stages of gas impact. It is presumed that the maximum temperature during the formation of rock reached 1200-1230 ºC.
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