New Mexico Geological Society Annual Spring Meeting — Abstracts

The Red River drainage in Taos County, northern New Mexico, contains a wide range of rock types, from Precambrian schists through Tertiary volcanic rocks that host deposits of volcanic- epithermal Au-Ag-Cu vein and porphyry molybdenum deposits. This geological setting affects the stream water and sediment geochemistry in a number of ways. In this study, water chemistry and trace element data of stream sediments are combined to determine which elements were being carried in solution, and which elements are being transported as components of specific minerals. There is a distinct change in water chemistry at the town of Red River, downstream of the Mallette Creek drainage, notably as increased concentrations of Mg, Si, F, SO₄, and Na. Mg increases from <5 to >7 ppm, Si increases from below detection limits (<10 ppm) to >13 ppm. F increased from below detection limits to >0.22 ppm, SO₄ increases from approximately 15 ppm to 55-90 ppm, and Na increases from 1.5-4.5 ppm to 5.5-9.5 ppm. This same break point marks an increase in non-carbonate hardness, conductivity, and total dissolved solids.

Sediment samples were divided into two fractions, a large fraction (2 mm-63 µ), similar to the probable bed load of the stream, and a fine fraction (>63 µ), approximately equivalent to the suspended load. In general, sediment geochemistry does not show a correspondingly distinct change in composition as the water samples, but S concentrations in the sediment increased downstream of the Bitter Creek drainage. Pearson correlations between As and S (>0.80) seem to indicate that As is present in the large sediment fraction as a sulfide, probably as arsenopyrite. Strong Pearson correlation coefficients exist between Fe, Ti, and V (>0.85) in both the fine fraction and the coarse fraction, while strong Pearson correlation coefficients between Zn, Cu Pb, Rb, Mo, and Ba (>0.75) exist in the large fraction but not in the fine fraction but not in the fine fraction, probably due to variable adsorption onto clays in the fine fraction. Cl concentrations in water samples increased downstream, but remained uniformly low (<500 ppm) in the sediments. A sample of the scoria mixture is used to prevent icing on the roads (primarily NM 38), contained high Cl concentration (7,000 ppm), indication that this treatment was probably adding Cl, and possibly Na and K, to the stream.

The Red River drainage in Taos County, northern New Mexico, contains a wide range of rock types, from Precambrian schists through Tertiary volcanic rocks, hosting deposits of copper, gold, and molybdenum. Due to the presence of these features as its status as one of the most beautiful scenic drives in northern New Mexico, the Red River has been the subject of extensive research in the areas of stream water chemistry, sediment geochemistry, and associated geological studies, but none have addressed the exact forms in which various elements are being transported within the stream environment. In this study, water chemistry data and XRF trace element analyses of stream sediments are combined to gain an idea of which elements were being carried in solution, and which elements are being transported as components of which minerals. The final goal of this study is to characterize element mobility in this geologically complex watershed, providing a more comprehensive model of water and sediment conditions upstream of the town of Red River, and between the town of Red River and the Molycorp Questa molybdenum mine property.