Crystallization kinetics and thermodynamics of granitic pegmatite and metallogenic mechanisms of rare metals in pegmatite
The crystallization process of granitic pegmatite involves both nucleation dynamics and growth dynamics.It is characterized by low nucleation rates and high crystal growth rates,influenced by factors such as H2O,volatiles,and undercooling.Furthermore,the phase states(i.e.,the supercritical state)of pegmatite melt may play an important role during the crystallization process and the supernormal enrichment of rare metal elements.The formation of ore-bearing pegmatitic melt,by highly differentiated crystallization of granitic magma or partial melting of metamorphic sedimentary rocks,requires the pre-enrichment of rare metal elements in the source rocks.The low-degree and small-volume pegmatitic melt produced by anatexis has higher concentrations of rare metal elements.During magmatic differentiation,the super-enrichment of rare metal elements is facilitated by factors such as supercritical melts/fluids,magmatic evolution,and undercooling.Magmatic immiscibility leads to preferential partitioning of rare metal elements into the melt rich in volatiles.Additionally,undercooling reduces the saturation concentration of rare metal-bearing minerals and promotes the crystallization of rare metal minerals.The chemical composition of the melt directly influences its physical and chemical properties,wherein volatiles decrease the viscosity of the melt and promote the differential crystallization process of magma.Moreover,the strong affinity of rare metal elements to volatiles significantly enhances the solubility and migration of these elements,thereby promoting their super-enrichment and metallogenesis in pegmatite.
pegmatitecrystallization kineticscrystallization thermodynamicsmetallogenesis of rare metal elements
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