Re-evaluating genetic models for porphyry Mo mineralization at Questa, New Mexico: Implications for ore deposition following silicic ignimbrite eruption

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Rosera, Joshua M.
- Affiliation: College of Arts and Sciences, Department of Geological Sciences

Abstract

The Questa Mo deposit in New Mexico provides an opportunity to study the relationship between pluton assembly and mineralization. Magmatism along the Questa caldera margin initiated at 25.20 Ma and continued for ~ 770 ka. Emplacement of mineralizing intrusions progressed westward and culminated in the assembly of the Questa Mo deposit between 24.76 and 24.50 Ma. Molybdenite Re-Os ages are integrated with zircon U-Pb and biotite Ar-Ar ages to evaluate the cooling histories within the deposit. These data show that the mineralizing intrusions were generated via rapid melting, separation, and intrusion into the shallow crust without involvement in a long-lived magma chamber. It is proposed that the anomalously high magma flux associated with ignimbrite eruption introduces materials necessary for mineralization. Partial melting and scavenging within a deep-crustal hybridized zone generated Mo-rich magma that formed the Questa deposit. This hypothesis predicts an important connection between caldera-forming systems and porphyry-style mineralization.

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