Fluid-inclusion evidence for the formation conditions of apatite from the Tororo carbonatite complex of eastern Uganda

Abstract

Summary Portions of the carbonatitic fluids responsible for the deposition of apatite from the Tororo car-bonatite complex are trapped and preserved as minute (< 100 µm) inclusions within the apatites. These fluids consist predominantly of alkali-carbonate-bearing brines and demonstrate that water and alkalis played an important role in the formation of the carbonatites from this complex. Furthermore, the opinion that carbonatite ‘magmas’ are richer in alkalis and water than the chemistry of the carbonatites themselves reveal is clearly substantiated. The mean minimum formation temperature of the apatites from five separate carbonatite samples were determined from the homogenization temperatures of 200 primary aqueous inclusions. The results from Limekiln Hill samples (328 °C 321 °C 359 °C) are similar to those from samples of the separate carbonatite mass at Tororo Rock (353 °C, 365 °C).