The magmatic-hydrothermal transition in pegmatites and its effects on rare metal mineralization: insights from melt-crystal-fluid interactions in phosphate minerals from the Buranga dike (Rwanda)

This PhD project aims to understand the magmatic-hydrothermal differentiation process recorded at the Buranga pegmatite system (Gatumba District, Western Province, Rwanda). The Buranga dike is a type-example of a phosphorus- and boron-rich lithium-cesium-tantalum (LCT) pegmatite and well-known for its Ta-Sn-Nb mineralisation and its rich variety of primary and secondary phosphate minerals. The phosphate mineralogy records the magmatic, magmatic-hydrothermal and weathering-leaching evolutionary stages of the pegmatitic system. The project will focus on the role of fluids in the magma and its influence on melt differentiation and rare-metal (Nb-Ta-Li-Sn-W) metallogenesis. This research will be based on the mineralogical study of the Buranga pegmatite for 1) paragenetic sequencing of phosphate minerals and accessory phases, 2) the analyses of fluid and melt inclusions through microthermometry and micro-analytical techniques to characterize the chemical evolution of the magmatic fluid, and 3) applying new techniques of Raman spectroscopy, such as Raman mapping to recognize the accessory phases which occur at Buranga and also to quantify the chemical composition of minerals, fluids and melt inclusions. The ultimate goal of this PhD will be the establishment of a generic petro- and metallogenic model for the evolution of phosphorus-rich, lithium-caesium-tantalum pegmatites.