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 latite lava vitrophyres and vent-facies dikes from the Bingham and Tintic districts in central Utah. These dikes and flow appear to be comagmatic with the ore-related monzonite intrusions. In addition, analytical data suggest that the magmatic sulfides contain most of the Cu and Ag present in the latites. Magmatic sulfides are preserved only in the least oxidized and least degassed lavas and vitrophyres. Petrography of comagmatic dikes and intrusions suggests that resorption and oxidation (S-degassing) of the globules may make the metal content available to a magmatic ore-fluid. Minette and shoshonite lavas occur in subordinate amounts in the latitic volcanic fields associated with latite–monzonite intrusions and hydrothermal ore deposits of the Tintic (Ag–Pb–Zn–Cu–Au) and Bingham (porphyry Cu–Au–Mo) districts, Utah. The ages chemical and modal compositions, and field relations of the mafic alkaline lavas suggest that such magmas mixed and fractionated at shallow crustal levels to form the ore-related latites and monzonites. The unaltered mafic alkaline lavas in these districts are some of the most Cu-rich lavas in the Great Basin province.