Mineral resources of the Roberts Wilderness Study Area, Eureka County, Nevada

Abstract

The Roberts Wilderness Study Area (NV-060-541) encompasses 15,090 acres and includes Roberts Creek Mountain, Cooper Peak, and Western Peak, three of the highest peaks in the Roberts Mountains, Eureka County, Nev. Field work for this report was carried out between May and August 1984 and augmented geologic mapping and other geologic studies that have continued for more than 20 years. Stream-sediment samples from the Kelley Creek drainage contain anomalous amounts of silver, lead, and zinc; the area including this drainage has low mineral resource potential for these metals in hydrothermal veins that follow faults and shear zones in carbonate host rock. The abandoned Kelley mine produced 397 tons of silver, lead, and zinc ore prior to 1940. Some rock samples from outcrops along the east edge of the study area contain anomalous amounts of gold and silver, as well as a suite of volatile elements including arsenic, antimony, and mercury that locally are indicators of precious-metal mineralization. These samples are associated with silicified zones that formed in dolomitic rock beneath the Roberts Mountains thrust fault. These zones have high, moderate, and low resource potential for gold and silver. Two similar areas of silicified and altered dolomite in the southwest part of the study area have moderate-to-low resource potential for gold and silver. An east-west trending zone in the central part of the study area and two areas near its western edge contain anomalous amounts of gold and silver in altered dolomite and limestone associated with major faults and shear zones. These areas have moderate-to-low potential for gold and silver resources. Several mining companies have done extensive exploration for gold and silver and have claim blocks that extend into the study area from the east, west, and south (pi. 1; Benjamin and Johnson, 1986). The areas claimed are included in areas of high and moderate resource potential in this report. Character and Setting The Roberts Wilderness Study Area includes about one-third of the Roberts Mountains in Eureka County, Nevada. The area is about 30 mi northwest of Eureka and 50 mi south of Carlin (fig. 1). The study area is underlain by a folded and faulted sequence of marine sedimentary rocks of Cambrian through Devonian age (about 570 to 360 million years ago) capped in places by Tertiary (about 65 to 2 million years ago) lava and ash flows and intruded by many Tertiary basalt dikes. Most of the Cambrian through Devonian rocks in the study area are limestone and dolomite. The Roberts Mountains thrust, an important regional structural feature, is present in the southeast part of the wilderness study area. The Antelope mining district extends into the wilderness study area and is represented by the Kelley mine, a silver, lead, and zinc mine inactive since 1937. Other mines in this district lie outside the wilderness study area. There are extensive mining claims around the study area, and some extend into it. Identified Resources The Kelley mine produced 397 tons of silver, lead, and zinc ore prior to being abandoned in 1937. No resources were identified, at this mine during this study. Anomalous amounts of gold and silver were detected in some rock samples collected elsewhere in the study area, but no identified resources were found. Mineral Resource Potential There are three areas of high mineral resource potential for gold and silver with gradational areas of