Original paper
Petrology of jacobsite bearing assemblages from Sausar Group, India
Bhattacharya, P. K.; Dasgupta, Somnath; Chattopadhyay, G.; Banerjee, H.; Fukuoka, M.; Roy, Supriya
Neues Jahrbuch für Mineralogie - Abhandlungen Band 159 Heft 1 (1988), p. 101 - 111
23 references
published: May 10, 1988
DOI: 10.1127/njma/159/1988/101
ArtNo. ESP154015901006, Price: 29.00 €
Abstract
Jacobsite-bearing assemblages are often recorded in Mn oxide ores, Mn silicate - oxide rock and Mn silicate - carbonate oxide rocks, metamorphosed to upper amphibolite facies (P ~ 6Kb, T ~ 600 °C - 700 °C), occurring in the Precambrian Sausar Group, India. Hematite, with or without braunite and hausmannite, is associated with jacobsite in oxide ores, silicate - oxide rocks and oxidic interbands in silicate - carbonate -oxide rocks. In the silicate - carbonate-oxide rocks, however, jacobsite coexists with tephroite in the absence of hematite. Chemical composition of jacobsites reveals that the spinel in hematite-free and hematite-bearing assemblages is a solid solution of Fe+2Fe +3 O4-Mn+2Fe2+3O4 and Mn+2Mn2+3O4 - Mn+2Fe2+3O4 respectively. The present study indicates that the variable compositions of jacobsites reflect different progenitors and that the mineral was formed both by prograde reduction and decarbonation -oxidation reactions in carbonate-free and carbonate-bearing rocks respectively. Strong internal buffering of fO2 by mineral reactions during prograde metamorphism produced diverse assemblages in closely spaced units.
Keywords
jacobsite • assemblage • prograde metamorphism • rocks • Precambrian Sausar Group • India