Mineral resources of the Pueblo Mountains Wilderness Study Area, Harney County, Oregon, and Humboldt County, Nevada

Abstract

Mineral surveys were conducted on 41,315 acres of the Pueblo Mountains Wilderness Study Area (OR002-08 l/NV-020-642) in southeastern Oregon and northern Nevada, at the request of the U.S. Bureau of Land Management (BLM). The original is larger than the on which mineral surveys were requested. This report discusses the geology, mineralizing processes, and mineral resource potential of an larger than the 41,315-acre on which surveys were requested, in order to more accurately determine the mineral resource potential of the area. Throughout this report wilderness area and study area apply only to the 41,315acre on which surveys were requested. The U.S. Bureau of Mines (USBM) and the U.S. Geological Survey (USGS) conducted geological, geophysical, and geochemical surveys during 1984 and 1985 to assess the mineral resources (known) and mineral resource potential (undiscovered) of the area. No resources were identified in the Pueblo Mountains Wilderness Study Area. However, the indicates high potential for silver and mercury resources in altered rocks located along two northwest-trending fault zones that cross the east boundary of the area; moderate potential for gold, silver, copper, mercury, and molybdenum resources in quartz veins along a fault near the east boundary of the area; low potential for silver, zinc, mercury, and molybdenum resources in intermediate flows located in the central part of the area; and low potential for undiscovered silver and mercury in silicic tuff. The eastern part of the has low potential for copper, lead, and zinc resources in metavolcanic and metasedimentary rocks; and the northeast part of the has low potential for mercury resources in mafic flows. The resource potential for oil, gas, and geothermal energy is considered low in the area. Part of the Pueblo Mountains east of the has four areas of high mineral resource potential and several areas of moderate and low mineral resource potential. All terranes that have high mineral resource potential outside of the are discussed in the text. Metamorphic rocks and Quaternary sedimentary deposits exposed along two segments of the Pueblo Mountains range-front fault, 2 mi east of the area, have high potential for gold and silver resources. Rocks adjacent to the Pueblo caldera ring fault, 1 mi east of the area, have high potential for silver, copper, zinc, mercury, molybdenum, and uranium resources. A metamorphosed quartz diorite intrusion near the southeast boundary of the has high potential for gold, silver, copper, and molybdenum resources. Caldera-fill sedimentary rocks 3 mi east of the have low potential for diatomite and bentonite resources. Character and Setting The Pueblo Mountains Wilderness Study Area (OR-002-81/NV-020-642) is located in southeastern Oregon and northern Nevada about 2 mi northwest of Denio, Nev., and 5 mi south of Fields, Oreg. (fig. 1). The Pueblo Mountains comprise part of a north-