Mineral resource potential of the Stillwater Complex and adjacent rocks in the northern part of the Mount Wood and Mount Douglas quadrangles, southwestern Montana

Abstract

The Stillwater Complex contains the largest potential chromite and platinum metal resources and second largest nickel resources in the United States. The Ultramafic zone has produced about 900,000 long tons of chromite concentrate and contains unmined reserves equivalent to 2,520,000 long tons of Cr2O3. Nickel and copper sulfide minerals that occur in the Basal zone and adjacent hornfelsed metasedimentary rocks represent one of the largest nickel potentials in the United States---a known reserve of 150 million tons of 0.25 percent nickel and 0.25 percent copper. The complex has been estimated to contain the largest potential source of platinum metals in the United States---possibly over 150 million troy ounces in the lower chromite zones and the Basal zone. In addition, the anorthosites in the Banded and Upper zones are reported to represent a potential alumina resource of almost 2 billion tons. An iron-formation also is present in the adjacent Precambrian metasedimentary rocks, and a coal bed is present in the Upper Cretaceous Eagle Sandstone nearby. The eventual utilization of these resources depends on the availability of large quantities of energy, and thus they may not be recovered unless new sources of energy or new recovery techniques are developed.