Geology and ore deposits of the Dillon nickel prospect, southwestern Montana

Abstract

The Dillon Nickel Prospect is 23 miles southeast of Dillon, Montana, where a pre-Cambrian ultramafic complex about four and one-half miles long and one mile wide has intruded pre-Cambrian gneiss and schist of the Cherry Creek series. The complex is composed of saxonite, peridotite, nickeliferous serpentine, and related rocks. The chief nickel-bearing mineral is annabergite, found only as incrustations restricted to one intermediate phase of the saxonite. No sulphides were found other than a small amount of pyrrhotite and pentlandite, in a small body of gabbro on one claim. The gabbro assays 0.003 to 0.09 per cent nickel and the ultramafic complex proper 0.15 to 1.25 per cent.There is large amount of low-grade nickel silicate ore, but the economic possibilities of the annabergite outcrops can only be determined by further prospecting. The area is within easy access to the railroad at Dillon and from the writer's study merits further prospecting.