23-1 Evaluating the Magmatic Duration of Climax-type Porphyry Deposits and Mineral Systems

Session: Distributed volcanic fields of the southwestern U.S. (Posters)

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Abstract:

Porphyry mineral systems are associated with high-tonnage, low-grade stockwork mineralization and more distal (e.g., high-sulfidation epithermal) magmatic-hydrothermal deposits. A positive correlation has been observed between ore tonnage and the duration of magmatism in porphyry Cu±Au deposits, indicating that the ore endowment of individual deposits is related to the lifespan of the causative magmatic system. Prolonged magmatic histories can allow for stepwise addition of magmas, fluids and metals to the upper crust, creating larger deposits over time, with the largest discovered Cu deposits associated with systems with >1 Myr lifespans. Therefore, evaluating the magmatic-hydrothermal lifespan of porphyry deposits may serve as a tool to evaluate total metal endowment. While the relationship between subduction to post-subduction Cu and Au ore endowment and lifespan of magmatic-hydrothermal systems is well-studied, the endowment-duration hypotheses has not been rigorously evaluated in other porphyry systems that occur in other tectono-magmatic settings.

Climax-type mineral systems form during continental extension and are associated with small volume, episodic, upper crustal intrusive systems. The magmas may be bimodal, where the silicic end-member is enriched in F and associated with Mo, W, Sn, Be, U, F, or alunite mineralization. Compilation and recalculation of geochronology from such systems reveals that much of the available data are highly imprecise and/or inaccurate. Estimating magmatic duration with these data yields timespans with uncertainties significantly greater than 1 Myr. For systems with more modern, high-precision geochronology data, the total durations for Climax-type mineralization and related magmatic systems is consistently on the scale of 100’s of kyr, indicating that the assembly of such systems is distinct from other styles of porphyry systems. For example, the Questa porphyry Mo deposit in New Mexico formed by multiple short-lived pulses over <500 kyr. Mineralization of alunite at the Alunite Ridge and Deer Trail Mountain deposits in Utah was also the result of at least two periods of magmatic degassing from ca. 15.7–15.1 Ma and from ca. 14.7–13.8 Ma, associated with episodic vapor-phase mineralization. More modern, high-precision geochronology data are required to better understand how these systems form, but we suggest that the total duration of episodic porphyry Mo mineralization is unlikely to exceed that of well-characterized porphyry Cu systems.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4, 2026

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