Origin of tourmaline and oxide minerals from the metamorphosed Rampura Agucha Zn-Pb-(Ag) deposit, Rajasthan, India

The sediment-hosted exhalative Rampura Agucha Zn-Pb-(Ag) deposit in Rajasthan, India, contains a number of oxide minerals which have been formed as a result of high-grade metamorphism. Gahnite (Zn0.66-0.75Fe0.13-0.24Mg0.06-0.13Al1.98-2.01O4) is a common minor phase in the ores and formed from breakdown of sphalerite and Al-rich silicates. Pyrophanite-ilmenite solid solution (Fe0.42-0.68Mn0.32-0.58Ti0.99-1.01O3) is very rare and occurs, intergrown with rutile, as a result of unmixing of a Ti-Fe-Mn bearing precursor mineral. Dravite-rich tourmaline with Fe/(Fe+Mg) ratios around 0.02 occurs at the hanging wall contact of the orebody with the paragneisses and is intergrown with the ore minerals. Tourmaline from the stratabound ores is distinguished from schorl-rich tourmaline of two pegmatite samples which show Fe/(Fe+Mg) ratios of 0.43 and 0.62, respectively. It is argued that dravite-rich tourmaline (or another B-rich precursor mineral) is of premetamorphic origin. This dravite-rich tourmaline recrystallized during high-grade metamorphism when the metamorphic fluid, represented by H2O-CO2+CH4-N-2 inclusions, was trapped. Amphiboles, muscovites and biotites from metamorphic rocks of the deposit display radiometric Ar-39/Ar-40 cooling ages between 788 and 909 Ma.