EXPERIMENTAL STUDY ON THE METAMORPHIC CONDITIONS OF METAMORPHOSED MANGANIFEROUS IRON ORE DEPOSIT

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This project was planned to investigate (1) the stability relations between piemontite, pumpellyite-(Mn^<2+>) and okhotskite in the experimental system and natural system, and (2) crystal chemistry on the piemontite, pumpellyite-(Mn^<2+>) and okhotskite. At first, as a check as to whether equilibrium fO_2 condition were attained, a series of runs was made in which various transition metals or their oxides (e.g., Cu, Cu_2O, CuO, Fe_2O_3) were sealed with H_2O in an Ag_<90>Pd_<10> capsule, then enclosed within Ag cupsules with the various buffer mixtures and water and held at 450ﾟC and 2-4 kbar for 3 weeks. Based on these experiments, it was concluded that the runs above 450ﾟC need 3-4 weeks and those below 450ﾟC need 6-10 weeks to attain equilibrium. Three kinds of oxide mixtures were used as starting materials, which correspond to the compositions of following piemontites ; Ca_2Al_2MnSi_3O_<12>(OH), (Ca_<0.8>Sr_<0.2>)_2Al_2MnSi_3O_<12>(OH) and (Ca_<0.6>Sr_<0.4>)_2Al_2MnSi_3O_<12>(OH). Runs at 2 kbar and 500, 550 and 600ﾟC, with Cu_2O-CuO buffer, revealed that piemontite is stable. At 4 kbar and same temperatures as above, piemontite also stable with the Cu_2O-CuO buffer. Runs products at the same pressures and temperatures with the hematite-magnetite buffer are garnets. At 4 kb and 250ﾟC with hematite-magnetite buffer, X-ray powder diffraction peaks of pumpellyite and chlorite were observed. These results suggest that the stability fields of pumpellyite, piemontite and garnet range in this order from lower temperature to high temperature.