New Mexico Geological Society Annual Spring Meeting — Abstracts

For accurate interpretations of geochemical data in environmental and exploration studies it is crucial that the natural concentrations of elements in a study area are known. A regional geochemical atlas for part of Socorro County, New Mexico was begun in 1996. Stream sediment samples were used because they represent a composite of the lithological variations within a drainage basin. Sampling began with the construction of a grid with 9 km² grid cells. To date, sampling has been completed for approximately 205 cells. Criteria for sample site selection included an absence of obvious contamination, accessibility, and representation of the cell. Samples consisted of a composite of the <150 µm sediment fraction taken over 50 m of the stream bed. The monitoring ofanalytical reproducibility as well as within stream variation involved the use of triplicate samples in an unbalanced two level design. Samples were analyzed by wavelength dispersive x-ray fluorescence for Fe₂O₃, MnO, TiO₂, As, Ba, Cr, Cu, Ga, Mp, Nb, Ni, Pb, Rb, Sr, Th, U, V, Y, Zn, and Zr. Analysis of international standard reference materials ensured detection of instrumental variations as well as the precision of the data. Preliminary results show that nearly all elements have trends that are correlative with the varying geology of the region (e.g., Paleozoic sediments, Tertiary andesitic and rhyolitic volcanics). Anomalous elemental concentrations occur near Magdalena as well as to the southeast in the Water Canyon region.