A preliminary summary of multidisciplinary studies in the upper Pecos River area, Santa Fe and San Miguel Counties, New Mexico
Virginia T. McLemore, Lynn A. Brandvold, Donald K. Brandvold, Kevin Kirk, Carl Popp, Steve Hansen, R. Radkte, Philip P. Kyle, and Anwar M. Hossain

Abstract:

The Pecos mine and Alamitos Canyon mill in the upper Pecos River area have been identified by state and federal agencies as point sources of contamination for Pb, Zn, Cu, Se, Cd and Cr. Atmospheric Hg is suspected as a possible non-point source contaminant. The U.S. Bureau of Reclamation, in cooperation with the NMIMT and NMBMMR, initiated a multidisciplinary study of the headwaters of the Pecos River in 1992 in order to identify and prioritize point and non-point sources of contamination so that measures can be taken to protect water supplies for municipal, irrigation, and recreational use and to protect wildlife habitat. The largest mine in the area is the Pecos mine, a massive-sulfide deposit containing Pb, Zn, Cu, Ag and Au. Waste rock generated during mining activities (1902-1904, 1927-1939, 1943-1944) was piled at the Pecos mine site and is now a source of acidic drainage that carries elevated concentrations of metals and other elements. The crushed ore from the mine was transported by aerial tramway to the Alamitos Canyon mill (El Molino site) 18 km south of the mine. This mill site is also a source of acidic drainage that carries elevated concentrations of metals. FAAS, XRF and INAA analyses confirm that elevated concentrations of Cu, Pb, Zn and Cd occur in stream sediments below both the Pecos mine and Alamitos Canyon mill sites. In addition, Zn is elevated in sediments collected at a dam above the fish hatchery. Elevated concentrations of Cs, As, Ag, Au, W, Br, Se, Sb and Fe are also found in stream sediments collected near the Pecos mine. Chemical analyses of six sediment size fractions from six sites suggests that the metals are predominantly traveling both as larger mineral or other grains and as suspended material weathered from the mine waste pile and the tailings pile. Partial dissolution techniques designed to estimate exchangeable, organic and oxide-bound forms indicate that the largest amount of Cu and Pb were in forms solubilized by aqua regia but not by the three extraction techniques. The largest amount of Zn was associated with Fe and Mn oxides. Water quality is a major concern in the upper Pecos River and many agencies collect water samples from the river, monitoring wells, and the seeps. These data indicate that drainage from the Pecos mine is not significantly affecting the composition of the surface and groundwater in the area, except in the immediate vicinity of the Pecos mine and the mill site. Collectively, these studies suggest that Cu, Pb, Zn and other metals are eroded and leached from the Pecos mine dump and the tailings piles in Alamitos Canyon. However, the total metal addition from these sources is insignificant compared to sediment input from drainages south of Pecos village. Atmospheric deposition and weathering in the upper Pecos River basin, not the Pecos mine or mill tailings, appears to account for most of the Hg found in the waters.


Citation:

  1. McLemore, Virginia T.; Brandvold, Lynn A.; Brandvold, Donald K.; Kirk, Kevin; Popp, Carl; Hansen, Steve; Radkte, R.; Kyle, Philip P.; Hossain, Anwar M., 1995, A preliminary summary of multidisciplinary studies in the upper Pecos River area, Santa Fe and San Miguel Counties, New Mexico, in: Geology of the Santa Fe Region, Bauer, Paul W.; Kues, Barry S.; Dunbar, Nelia W.; Karlstrom, K. E.; Harrison, Bruce, New Mexico Geological Society, Guidebook, 46th Field Conference, pp. 331-338.

More information...