Experiments and observations bearing on the origin of highly- fractionated granites and their critical metal endowment

An important paradigm guiding the exploration of granite-hosted critical metal deposits is the association between highly evolved rock compositions (i.e., aplites and pegmatites) and critical metal enrichment. To better understand this association, we have conducted melt extraction experiments at 400 and 1000 MPa and 750-900oC to assess models of critical metal enrichment by extreme crystal fractionation.  Two-stage experiments involved first melting a natural granodiorite starting material, then extracting the melt in the second stage using porous vitreous carbon.  Results demonstrate crystal-melt separation, and therefore the feasibility of the method. Experiment glass compositions show significant chemical fractionation, and reveal insights into the origin of the compositional variation in natural granites.