Tracing fluid evolution during batholith and deposit formation: In-situ and bulk rock Mo isotopes from the Questa porphyry Mo deposit, New Mexico, USA
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Abstract
The Oligocene Questa porphyry Mo deposit, located in New Mexico, USA, is a well-characterized system that formed over 400 kyr, punctuating the 8 Myr formation of the Questa-Latir batholith. Detailed sampling of the intrusions and minerals associated with magmatichydrothermal mineralization, as well as bookending barren intrusions, allows for examination of the Mo isotope record of the deposit and its host batholith. Through this established chronologic framework, such data can yield insights into the metallogenesis of deposit formation and long-term magma genesis evolution for upper crustal magmatism. The Mo isotopic compositions of barren intrusions yield a younging trend towards lighter δ98Mo. However, intrusions associated with Mo deposit formation yield heavier δ98Mo relative to barren magmatism, by up to 2.0‰. This indicates that they were affected by an isotopically heavy and Mo-rich fluid. The in-situ data from molybdenite covers the range observed in mineralized bulk rocks. However, individual samples consistently yield Mo isotopic variations of 0.4‰ to 0.5‰. The consistency of the δ98Mo variation in in-situ analyses of molybdenite within hand samples and individual mineral grains is likely the result of MoS2 crystallization in a closed system and reflects an almost complete precipitation of Mo.
Study Area
| Publication type | Conference Paper |
|---|---|
| Publication Subtype | Conference Paper |
| Title | Tracing fluid evolution during batholith and deposit formation: In-situ and bulk rock Mo isotopes from the Questa porphyry Mo deposit, New Mexico, USA |
| Volume | 2 |
| Year Published | 2025 |
| Language | English |
| Publisher | Society for Geology Applied to Mineral Deposits |
| Contributing office(s) | Geology, Geophysics, and Geochemistry Science Center |
| Description | 4 p. |
| First page | 447 |
| Last page | 450 |
| Conference Title | 18th SGA Biennial Meeting |
| Conference Location | Golden, CO |
| Conference Date | August 3-7, 2025 |
| Country | United States |
| State | New Mexico |
| Other Geospatial | Questa porphyry Mo deposit |