A note on the occurrence and formation of magnetite in the carbonatites of Sevvattur, North Arcot district, Tamil Nadu, Southern India
TL;DR: In this paper, the detailed ore petrographic features of magnetite occurring within carbonatites of the Sevvattur complex are presented, and it is suggested that fine dust-like inclusions in the carbonate minerals may have formed at a late stage through dissociation of ankerite to calcite and magnetite.
Abstract: The important accessory mineral magnetite is ubiquitously present within all constituent members of the Proterozoic zoned carbonatite body of the Sevvattur complex, North Arcot District, Tamil Nadu in southern India. The carbonatite appears to have been mainly emplaced as an arcuate or crescent-shaped, zoned intrusion. The carbonatite contain two generations of magnetite that occur as (1) opaque dust-like inclusions in the carbonate minerals, and (2) large euhedral phenocrysts. The latter measures up to 10 cm in length, are primary in nature and found mainly associated with essential minerals within the ferro-carbonatites (para-ankeritic carbonatites). In this paper, we present the detailed ore petrographic features of magnetite occurring within carbonatites of the Sevvattur complex. It is suggested that fine dust-like inclusions in the carbonate minerals may have formed at a late stage through dissociation of ankerite to calcite and magnetite. This occurred during upward migration of melts from a deep magma chamber that subsequently suffered secondary oxidation. The phenocryst variety, however, crystallized directly as primary minerals in the magma.
Cites background from "A note on the occurrence and format..."
...Occurrence of large, euhedral magnetite in association with iron carbonates is also reported from the Sevvattur carbonatites in Southern India (Ramasamy et al., 2001), where magnetite occurrence has been related to pressure drops in an ascending magma under low f O2 conditions....
Cites background or methods from "A note on the occurrence and format..."
...Generally, the bulk of early formed magnetite from carbonatitic rocks is variably enriched in Mg and Ti (cf. Ramasamy et al. 2001; Reguir et al. 2008 and references therein)....
...The Paleo- and Neoproterozoic carbonatites in south India were emplaced along a NE-SW trending fault system into the Precambrian terrain (Viladkar and Subramanian 1995; Ramasamy et al. 2001)....
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