Hydrothermal sulfur geochemistry on molybdenite deposition of the Questa Mo-deposit, New Mexico, USA

Abstract

We conducted combined microthermometry and LA-ICP-MS microanalysis in the several brine inclusion assemblages of the Questa porphyry Mo deposits, USA and the nearby cogenetic Rito del Medio granitoid to study the hydrothermal geochemistry responsible for a molybdenite deposition in the Climax-type Mo deposit. We analyzed S concentrations in the fluid inclusions by using a recent technique on S quantification in the singly-targeted fluid inclusions. We found plenty of S in the fluid inclusions adequate to precipitate molybdenite, and the molybdenite might be precipitated in the tight temperature range of 350-450 A degrees C in the Questa. A fractional crystallization in the causative magma would enrich Mo in the evolving magmatic-hydrothermal fluids from the early-stage hydrothermal breccias (MHBX) to the postdating stockwork veinlets (STW), while maintaining S to precipitate molybdenite in the Questa.