ABSTRACT

The Stillwater Complex of Montana is noted for its chromite, platinum and palladium. It also has a potential for gold,—how great or small remains to be seen. Colors can be panned out of the East Boulder River in Placer Basin. On Chrome Mountain, a faulted zone in the peridotite member of the ultramafic zone of the Stillwater Complex contains values in gold of over one ounce per ton. The gold occurs in native form and amalgamated with silver. Evidence indicates that the gold mineralization is associated with a fracturing and hydrothermal alteration event which probably used the fault zone as a conduit for the mineralizing fluids. Secondary contact metamorphic minerals indicate the possible existence of a nearby intrusive body that could have been the gold source. The gold may also have originated within the ultramafic rocks and then remobilized and concentrated in fracture zones. If this latter hypothesis is true, distribution of the gold is related to depth within the Stillwater ultramafic rocks, alteration and local structure.