Petrology of Mn carbonate–silicate rocks from the Gangpur Group, India

Mohapatra, B K and Nayak, B (2005) Petrology of Mn carbonate–silicate rocks from the Gangpur Group, India. Journal of Asian Earth Sciences, 25 (5). pp. 773-780.



Metamorphosed Mn carbonate–silicate rocks with or without oxides (assemblage I) and Mn silicate–oxide rocks with minor Mn carbonate (assemblage II) occur as conformable lenses within metapelites and metacherts of the Precambrian Gangpur Group, India. The petrology of the carbonate minerals: rhodochrosite, kutnahorite, and calcite that occur in these two assemblages is reported. Early stabilisation of spessartine, aegirine, quartz, and carbonates (in a wide solid solution range) was followed by pyroxmangite, tephroite, rhodonite through decarbonation reactions. Subsequently, jacobsite, hematite, braunite, hollandite and hausmannite have formed by decarbonation–oxidation processes during prograde metamorphism. Textural characteristics and chemical composition of constituent phases suggest that the mineral assemblages reflect a complex relationship between protolithic composition, variation of XCO2 (<0.2 to 0.3) and oxygen fugacity. A variation of XCO2 and fO2 would imply internal buffering of pore fluids through mineral reactions that produced diverse assemblages in the carbonate bearing manganiferous rocks. A minor change in temperature (from around 400 to 450 °C) does not appear to have had any major influence on the formation of different mineral associations.

Item Type:Article
Official URL/DOI:
Uncontrolled Keywords:Mn carbonates; Mn carbonate–silicate rocks; Gondites; Gangpur Group; India
Divisions:Mineral Processing
ID Code:578
Deposited By:Sahu A K
Deposited On:01 Jun 2010 14:52
Last Modified:25 Jan 2012 11:00
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