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Digital Data from Mineral Investigation of Sangre de Cristo Wilderness Study Area, Alamosa, Custer, Fremont, Huerfano, and Saguache Counties, Colorado, USA

April 21, 2021

This Data Release provides tabular and geospatial data digitized by the U.S. Geological Survey (USGS) from a U.S. Bureau of Mines (USBoM) report titled Mineral Investigation of Sangre de Cristo Wilderness Study Area, Alamosa, Custer, Fremont, Huerfano, and Saguache Counties, Colorado. The original preliminary paper report, numbered Mineral Land Assessment 65-83 (MLA 65-83; Ellis and others, 1983), presented the results of a mineral resource potential survey of areas in and around the Sangre de Cristo Range flanking the northeastern extent of San Luis Valley in south-central Colorado. Included in this Data Release are georeferenced scans of the regional plate maps, digitized sample site locations, analytical chemistry, and structural geologic data from MLA 65-83 in a modern and searchable geospatial database. In addition to the maps and associated point locations, the dataset contains 1,262 rows and 58 columns of contextual and numeric information in the main data table, as well as a table describing 97 samples excluded from the MLA report, a table of summary deposit information, a table of USBoM inventory data for the prepared and stored rock samples, and geospatial boundary data of the Sangre de Cristo Wilderness, Wilderness Study Area (WSA), and mineralized sampling areas. Prospecting, claiming, and some mining of largely polymetallic precious- and base-metal veins occurred in the Sangre de Cristo Range from the late 1800s through the early 1930s, with sporadic prospecting and some mining through the late 1980s (Ellis and others, 1983). Many of the vein networks are found along the western side of the mountains that are bounded by the Sangre de Cristo normal fault, a principal structure delineating a major segment of the Rio Grande rift. There also are mines along the crest and the northeast side of the range such as the Rita Alta copper mine. However, the locations of many claims, prospects, and mines were hand located on topographic and mine maps without modern spatial coordinate data and there were few analytical chemistry data available with properly associated geologic context. As a mandated component of the 1964 Wilderness Act, the USGS and USBoM were charged with identifying and assessing mineral resources in Federal lands known as Wilderness Study Areas (WSA; for example, Johnson and others, 1984). The Sangre de Cristo WSA included the mountainous areas from Poncha Pass in the north to the Blanca Peak area in the south. Approximately 75 to 85 percent of the study area was covered by aerial photographic inspection and sites were visited by Ellis and others (1983) as access allowed. One thousand three hundred and ten samples were fire assayed for gold and silver and spectrographically analyzed for 40 other elements including copper, lead, molybdenum, tungsten, and uranium. Select samples were also analyzed for specific elements by various other state-of-the-art analytic methods of the time: copper, lead, and molybdenum by atomic absorption, tungsten by colorimetry, and uranium by fluorimetry. Integration of mapping, field characterization, mineralogical, and chemical data resulted in the identification of 18 more or less distinct mineralized areas. Sample locations and a variety of site and mine maps were compiled and integrated into the MLA 65-83 report along with extensive tabulation on paper with all data organized by mineralized area. Most of the study area was ultimately designated as Wilderness in 1980 and the unique sand dunes and associated watersheds on the western side of the central portion of the range, originally designated Great Sand Dunes National Monument in 1932, were redesignated as a National Park and Preserve in 2004. During the late 1990's and 2000's the USGS completed extensive research in the Rio Grande Rift (for example, Hudson and Grauch, 2013) including the Sangre de Cristo Mountains and adjacent San Luis Valley. Much of the work focused on interpretation of new geophysical data and new geologic mapping as well as new analyses of mineralized areas and associated geologic structures. Overall, the absolute age, petrogenetic, and metallogenic affinities of the mineralized areas are poorly understood. However, some combination of magmatic, hydrothermal, structural, chemical, and fluid-related processes all contributed to the formation of the Sangre de Cristo mineral system. The digital data and information provided in this Data Release allows for public access to the information contained in the archived paper data record, report, and plates. This publication is useful in developing a better understanding of the geologic and tectonic framework, occurrences and controls on mineralization, and other Earth resources such as groundwater. References Cited Above Ellis, C.E., Hannigan, B.J., and Thomson, J.R., 1983, Mineral Investigation of Sangre de Cristo Wilderness Study Area, Alamosa, Custer, Fremont, Huerfano, and Saguache Counties, Colorado: U.S. Bureau of Mines Mineral Land Assessment preliminary report MLA 65-83, 190 p., 2 plates. Hudson, M.R., and Grauch, V.J.S., 2013, Introduction, in Hudson, M.R., and Grauch, V.J.S., eds., New Perspectives on Rio Grande Rift Basins: From Tectonics to Groundwater: Geological Society of America Special Paper, v. 494, p. v-xii, https://doi.org/10.1130/SPE494. Johnson, B.R., Lindsey, D.A., Ellis, C.E., Hannigan, B.J., and Thompson, J.R., 1984, Mineral Resource Potential of the Sangre de Cristo Wilderness Study Area, South-central Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-1635-A and Pamphlet, 13 p., https://doi.org/10.3133/mf1635A.