Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Jyotiranjan S. Ray ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Ahmedabad 380 009, IN

Abstract

A fluid-rock interaction model for treating the stable carbon and oxygen isotopic variations in altered carbonatites is presented and illustrated with an example using data from the ferrocarbonatites of Amba Dongar, Gujarat. The Amba Dongar ferrocarbonatites appear to have been altered by a fluid of magmatic origin at 100 to 200°C contrary to an earlier suggestion of meteoric groundwater alteration at ∼50°C.

Keywords

Isotope Geology, Ferrocarbonatite, Fluorite, Fluid-Rock Interaction Model, Carbon and Oxygen Isotopes, Amba Dongar, Gujarat.

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Jyotiranjan S. Ray ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad 380009, IN

Abstract

Accurate analysis of coexisting calcite and dolomite for δ¹³C and δ¹⁸O is generally hindered by the difficulty in the physical separation of these minerals. The difference in the reaction rates of calcite and dolomite with phosphoric acid, has been used to chemically separate these carbonates. Previously established procedures are only suitable for samples containing 1:1 calcite-dolomite pairs. However, these are sometimes tedious and time-consuming. Using mixtures of calcite and dolomite, two different selective acid extraction procedures (for reactions at 25°C), one for calcite-rich and the other for dolomite-rich carbonates, have been developed. Reduction of grain size (to 37μm - 45μm) increased the reaction rate and hence decreased the total reaction time to a reasonable interval (≤72 hours for dolomite). Applying these procedures, δ¹³C and δ¹⁸O of calcite and dolomite/ankerite of carbonatites from Amba Dongar and Sung Valley carbonatite complexes of India were measured and their temperatures of crystallization determined. Accurate isotopic compositions of individual carbonates of calcite-dolomite mixtures can be determined for geological interpretations by these procedures.

Keywords

Stable Isotopes, Carbonate Mixtures, CO₂ Extraction Technique, Calcite, Dolomite, Ankerite, Carbonatite, Amba Dongar, Sung Valley.

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