In December of 2018, the U.S. Geological Survey (USGS) signed a Technical Assistance Agreement with a third party to reanalyze 2,324 archived sample splits collected as part of the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) project from selected areas in Idaho and Montana. A small amount (approximately 0.25 grams [g]) of sieved <75-micron sample material was retrieved from the USGS National Geochemical Sample Archive for geochemical analysis. These samples were analyzed for 48 elements by ALS Global laboratories using their ultra-trace four-acid-digestion dual-mode inductively coupled plasma mass spectrometry (ICPMS) (ALS ME-MS61L) method (Ag, Al, As, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Fe, Ga, Ge, Hf, In, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Rb, Re, S, Sb, Sc, Se, Sn, Sr, Ta, Te, Th, Ti, Tl, U, V, W, Y, Zn, Zr). These data are comparable to those reported by Smith and others (2018, 2019). A subset of these samples, as identified by the collaborating party, was additionally analyzed by ALS Global laboratories for stable lead isotopes (204Pb, 206Pb, 207Pb, and 208Pb, using the MS61L-PbIS method).
Blind standard reference materials (SRM) and sample duplicates were inserted by the USGS into every job of 36 samples to ensure the quality of the data. The results from these quality control (QC) samples, along with QC samples inserted by the laboratory, were evaluated for every job by a QC Manager. Only data that passed these checks were approved for release. Samples with analytical results that failed to pass the QC checks were reanalyzed and re-evaluated before the data were approved for release.
The archived sample splits came from the NURE program, which began in 1973 with a primary goal of identifying uranium resources in the U.S. As one of nine components of the NURE program, the HSSR project systematically sampled the U.S. between 1976 and 1980 under the direction of four U.S. Department of Energy (DOE) national laboratories. Although there was some collaboration, each DOE laboratory developed its own sample collection, analytical, and data management methodologies, and hired contractors to do much of the actual work.
Initially, Lawrence Livermore Laboratory (LLL) was responsible for the western states of Arizona, California, Idaho, Nevada, Oregon, Utah, and Washington; Los Alamos Scientific Laboratory (LASL) was responsible for the Rocky Mountain States (Colorado, Montana, New Mexico, and Wyoming) as well as Alaska; the Oak Ridge Gaseous Diffusion Plant (ORGDP) was responsible for 12 central Plains and upper Great Lakes States; and Savannah River Laboratory (SRL) was responsible for the remaining 23 states along the Eastern Seaboard, lower Great Lakes, Appalachians, and Gulf Coast. However, by 1979 the areas of responsibility had changed from state lines to 2-degree quadrangle boundaries and SRL had taken over the responsibility for completing the seven western states formerly assigned to LLL. Thus, quadrangles in the western third of the U.S. were variously sampled and analyzed by LLL, LASL, and SRL. Due to the enormous number of samples collected by these laboratories, some were sent to ORGDP for additional chemical analyses (Information Systems Programs, 1985; Smith, 1997).
Geochemical samples were collected from multiple sources (78 percent stream-, 8 percent lake-, and 2 percent spring-sediments, and 12 percent soils). Analytical methods differed between laboratories and evolved over time so that 29 single- and multi-element analytical procedures, or variations thereof, were used during the project. The NURE-HSSR sediment and soil database compiled by Smith (1997) provides analytical results for 54 different elements (Ag, Al, As, Au, B, Ba, Be, Bi, Br, Ca, Cd, Ce, Cl, Co, Cr, Cs, Cu, Dy, Eu, F, Fe, Hf, Hg, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Pt, Rb, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Th, Ti, U, V, W, Y, Yb, Zn, and Zr). However, no sample was analyzed for more than 46 elements, some were analyzed for uranium only, and a few samples were never analyzed at all.
Funding cuts after 1980 curtailed the NURE-HSSR sampling efforts and left the project incomplete with only 65% coverage of the U.S. The NURE program effectively ended about 1983-84. Out of a total of 625 quadrangles that cover the entire lower 48 States and Alaska, only 307 quadrangles were completely sampled, and another 86 quadrangles were partially sampled. In 1984, all of the NURE-HSSR data, maps, field notes, and archived samples splits were transferred to the USGS (Grimes, 1984).
Despite inconsistencies in sample media, elements analyzed, and analytical methods used, the original data, and particularly data from reanalysis of archived NURE-HSSR samples, have been very useful for a variety of USGS studies ranging from regional-scale mineral resource assessments to environmental investigations (Smith and others, 2013). Due to the number of different DOE laboratories, analytical methods, and sample media used, the NURE-HSSR data from the western third of the United States have the largest number of inconsistencies and are the most difficult to use on a regional basis. This area contains several large mining districts and continues to be an area of exploration interest for undiscovered mineral resources.