PRELIMINARY MAPPING AND CRITICAL MINERAL ASSESSMENT OF THE QUARTZBURG MINING DISTRICT, BLUE MOUNTAINS, NE OREGON

Economic mineral extraction in NE Oregon has been dominated by gold, silver, and copper, with associated critical minerals and other metals often discarded in favor of maximizing gold extraction. Available geologic maps in the region generally are too small-scale to adequately address critical mineral resource potential. Here we present new airborne magnetic and radiometric datasets, and preliminary 1:24,000-scale geologic mapping of the Quartzburg mining district (“Quartzburg”) in Grant County, NE Oregon. Quartzburg lies within two overlapping USGS critical minerals focus areas: (1) the NE-Oregon-Idaho massive sulfides, and (2) NW polymetallic gold-silver vein system. Previous geologic mapping coupled with mineral inventory from historic mining records, indicate the presence of several critical minerals, including multiple occurrences of cobalt, zinc, and nickel. High-resolution magnetic data highlights NE-SW to ENE-WSW lineaments, that are sub-parallel to the trend of basement terranes in NE Oregon, and an additional prominent set of WNW-ESE-trending lineaments, that likely represent Eocene or later fault sets observed elsewhere in the region. Field-based mapping identifies critical minerals as part of the polymetallic vein systems, including N-S- to NE-SW-striking gold-quartz veins, and ENE-WSW-striking copper-cobalt veins. Further detailed geologic mapping using bare-earth lidar topography and supported by high-resolution geophysical data, new geochemical data, and new high-precision geochronology, will provide opportunities to better define mapped geologic relations, understand the timing and character of mineralization events, and evaluate critical mineral resource potential in Quartzburg. Specifically, this study seeks to establish whether mineralization is related to a Jurassic volcanogenic island arc system, or to younger (early Oligocene) porphyry systems in the region, and address the timing of mineralization relative to newly recognized cobalt resources elsewhere in NE Oregon.