The Role of Magmatic Sulfides and Mafic Alkaline Magmas in the Bingham and Tintic Mining Districts, Utah

Abstract

This paper reports the existence of abundant magmatic sulfides in INTRODUCTION latite lava vitrophyres and vent-facies dikes from the Bingham and The eruption of sulfur-rich magmas from El Chichon Tintic districts in central Utah. These dikes and flows appear to (Luhr et al., 1984) and Mt Pinatubo (Westrich & Gerlach, be comagmatic with the ore-related monzonite intrusions. In addition, 1992) in recent years has attracted attention to the limited analytical data suggest that the magmatic sulfides contain most of solubility of sulfur in intermediate magmas and the factors the Cu and Ag present in the latites. Magmatic sulfides are preserved potentially responsible for the formation of magmatic only in the least oxidized and least degassed lavas and vitrophyres. sulfides and anhydrite. However, the occurrence of magPetrography of comagmatic dikes and intrusions suggests that matic sulfides in intermediate magmas is not universal; resorption and oxidation (S-degassing) of the globules may make many volcanic suites appear to be sulfide unsaturated. the metal content available to a magmatic ore-fluid. Minette and Inasmuch as magmatic sulfides may sequester chalcophile shoshonite lavas occur in subordinate amounts in the latitic volcanic metals, what would their presence signify in magmatic fields associated with latite–monzonite intrusions and hydrothermal systems that formed porphyry Cu and mesothermal vein ore deposits of the Tintic (Ag–Pb–Zn–Cu–Au) and Bingham deposits? Do they sequester a significant portion of the (porphyry Cu–Au–Mo) districts, Utah. The ages, chemical and magmatic Cu, Pb, Zn, Ag, and Au, thereby restricting modal compositions, and field relations of the mafic alkaline lavas metal availability of subsequent ore-forming fluids? suggest that such magmas mixed and fractionated at shallow crustal We have examined the volcanic rocks from the Tintic levels to form the ore-related latites and monzonites. The unaltered and Bingham mining districts (Fig. 1), Utah, and found mafic alkaline lavas in these districts are some of the most Cu-rich that almost all of the volcanic units contain magmatic lavas in the Great Basin province. sulfides. Some quenched dikes and intrusion margins also have preserved magmatic sulfides comparable with those in the volcanic rocks. Several lines of evidence indicate that the volcanic and intrusive rocks are comagmatic (Keith et al., 1989, 1991; Waite, 1996). The Tintic district and East Tintic sub-district in Utah have recorded over