RI 4513 Investigation Of Henderson Gulch Tungsten Deposit, Granite County, Mont.

This report describes Bureau of Mines investigations of a low-grade scheelite-bearing granodiorite intrusive situated on Henderson Creek, Granite County, Mont. The intrusive is in a narrow, V-shaped valley at the head of extensive placer workings. Since May 1943 the H. & R. Mines Co. of Portland, Oreg., has recovered scheelite sand and gold from the placer workings. A modified Yuba, 4?cubic foot bucket dredge was used in the operation. By February 1947 this operation had recovered and marketed over 215,000 pounds of scheelite concentrates containing 63 percent WO3. The scheelite in the placer was found to be derived principally from erosion of the granodiorite intrusive. The intrusive is one of a series of four similar, dikelike masses of granodiorite whose outcrops are aligned along a 10-mile zone of weakness trending N. 60° E. The intrusive has a triangular outcrop exposed over an area of 57 acres. Trenching and sampling by the Bureau of Mines demonstrated that scheelite is sparsely distributed throughout the granodiorite. This work delimited the outcrop of the intrusive and indicated a large submarginal reserve of low-grade tungsten mineralization. The deposit is ideally suited for exploitation by large-scale, open-pit mining operations; it would be easily available in a national emergency. Additional exploration would be necessary, however, before large-scale production plans could be made efficiently or accurately.