39. Discovery of the Little Boulder Creek Molybdenum Deposit, Custer County, Idaho

The Little Boulder Creek molybdenum deposit is in central Idaho, in the White Cloud Range about 3.2 km (2 miles) northeast of Castle Peak, the highest peak in the range. The elevation of the deposit is about 2591 m (8500 ft). The deposit is accessible only by helicopter or by a 12.9-km (8-mile) trail from the county road along the East Fork of the Salmon River. The nearest towns are Clayton [25.7 km (16 miles) northeast], Stanley [33.8 km (21 miles) northwest], and Ketchum [45 km (28 miles) south-southeast]. The principal known deposit at Little Boulder Creek is called the "North Zone." In this zone, the molybdenite occurs both in stock- work veinlets and disseminated through metamorphosed quartzite of Pennsylvanian age. Pyrite is ubiquitous, averaging perhaps 0.05%. Scheelite and/or powellite are present in trace amounts. An intrusive quartz monzonite stock, probably of Cretaceous age, bounds the deposit on the west. A steep fault which drops Tertiary age Challis volcanics into contact with the mineralization limits the deposit on the east.