VIRGINIA T. McLEMORE, NELIA DUNBAR, MATT T. HEIZLER, AND KELLY DONAHUE
ABSTRACT-Three types of mineral deposits (carbonate-hosted Pb-Zn replacement, W-Be-Mo skarn/vein, and porphyry Mo deposits) occur in the Victorio mining district. Some or all of these deposit types may be related to one or more of multiple episodes of igneous activity recognized in the district. Intrusive rocks in the area have been dated using the 40Ar/39Ar technique, suggesting a possible intrusion age of around 35 Ma. However, another interpretation of the age data suggests that the intrusive rocks are older than 35 Ma but underwent a reheating event and partial argon loss at around 30-35 Ma. Adularia present in one sample suggests that high-temperature alteration may have taken place at ca. 35 Ma. Within the Victorio district, the carbonate-hosted replacement deposits are epithermal and occur along faults and fractures. Brecciation and dissolution/recrystallization of dolostones are observed associated with the carbonate-hosted replacement deposits. The W-Be-Mo skarn/vein deposits occur within Paleozoic dolostones, limestones, and sandstones. The skarn/vein and porphyry Mo deposits appear to be related to the Victorio granite based on the spatial association and the presence of fluorine-rich phases and Mn-rich garnets in both skarn and granite. Mineralogic and geochemical analysis of the skarns indicate magnesian, rather than calcic, composition. The range of mineral assemblages observed represent both prograde and retrograde phases of skarn formation. The age, genetic relationships, and paragenesis of the carbonate-hosted replacement deposits to the skarn/vein and porphyry Mo deposits are unknown. It is possible that the three types of deposits may be related genetically or that there may have been more than one mineralizing event forming the deposits at different times. A number of questions remain unanswered and will be addressed in future work.