The Three Rivers stock, a molybdenum-related alkalic hypabyssal complex in south-central New Mexico, consists of three major intrusive phases: (1) an early and passively emplaced thick shell of coarse syenite porphyry, (2) nordmarkite intruded along the northeastern margin of the stock, and (3) late equigranular quartz syenite to alkali granite forcibly injected along a northeasterly trending arch in the syenite porphyry shell. These comagmatic phases developed as the result of extended fractional crystallization of hypersolvus alkalic (high albite) melts, in which disequilibrium precipitation of alkali feldspar played a key role. Rock and mineral textures and compositions vary markedly but systematically within and between phases, and record petrochemical trends culminating with emplacement of the residual alkali granite. Significant molybdenum, with related mineralization and hydrothermal alteration, occurs in a narrow belt along the northeastern margin of the stock. Several lines of field and laboratory evidence indicate that the spatially contiguous metal deposition and hydrothermal activity were generated by and occurred within the framework of Three Rivers magmatic activity and cooling. The hydrothermal mineral assemblage is interpreted as a relatively unfractionated and rapidly quenched derivation of the hydrous phase released by the equigranular quartz syenite, the last major intrusive.

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