MOLYBDENITE SPHERULES IN NA-AL-F-RICH MELT, CAVE PEAK PORPHYRY MO DEPOSIT, TRANS-PECOS TEXAS: EVIDENCE FOR GROWTH AND PHYSICAL TRANSPORT OF METAL SULFIDES IN MAGMATIC SYSTEMS

The Paleogene Cave Peak deposit is diatreme-hosted, fluorine-rich molybdenum porphyry system enriched in Nb, REE, and other critical minerals. The Cave Peak intrusive system was emplaced into Paleozoic strata near the western boundary of the north-trending Salt Basin graben during incipient regional extension that culminated in the Rio Grande Rift in central New Mexico. Cave Peak is genetically related to the nearby but unmineralized Marble Canyon Stock and is a highly evolved endmember of this alkalic magmatic system. The Cave Peak intrusive system consists of an outer rhyolite breccia mass with a complex intrusive core, which has been overprinted by multiple hydrothermal events that formed the molybdenum and associated mineralization. Molybdenite is the primary Mo-bearing mineral and typically occurs in stockwork veinlets, commonly with quartz, biotite, and fluorite. Anomalous Cu, Pb, Zn, Sn and W mineralization is also present. Unique molybdenite occurrences are locally present within the Cave Peak deposit, where disseminated molybdenite spherules occur within a matrix of cryolite, ralstonite, elpasolite, pachnolite, chiolite, biotite, and amphibole. High resolution x-ray computed tomography studies of these aluminofluoride veins confirm the molybdenite spherules range from resolution-limited 23-µm to a maximum observed 554-µm diameter. Textural features and buoyancy considerations indicate that these spherules were formed at depth and were transported by an immiscible alkali fluoride melt. We suggest that these previously unrecognized spherules provide evidence for physical transport of mineral grains as a mechanism to enrich the metal content of F-rich magmas emplaced into shallow crustal rift environments.