New Mexico Geological Society Annual Spring Meeting — Abstracts

The geochemistry of the Red River stream system of northern New Mexico is affected by natural exposures of sulfide-enriched rocks (alteration scars) and extensive waste-rock dumps associated with mining activities. Both environments generate acidic, metal-laden water that infiltrates the groundwater system discharging into the Red River, significantly affecting the geochemistry of the stream system. Geochemical analysis of aquifer sediments is an important component to environmental assessments of hydrologic systems like Red River. This investigation explores the spatial and vertical variability of the metal precipitates in the shallow alluvial aquifer with respect to the (a) source of acid rock drainage (ARD), (b) associated groundwater chemistry, and (c) site-specific hydrology and aquifer characteristics.

The Hansen Creek locality is located along an inferred groundwater flow path below an extensive alteration scar, a natural source of ARD. The Capulin Canyon locality is located along an inferred groundwater flow path below a mining-related waste-rock dump. Environmentally available metals were extracted from aquifer sediment by a strong acid technique and the relative concentrations of AI, Cu, Fe, Mn, Mo, and Zn were determined. Particle size analysis and limited SEM examination were conducted on selected samples. Metal extraction analysis of the < 2mm size fraction reveals a strong difference between the Capulin and Hansen secondary precipitates and metal concentrations. For example, iron concentrations at the shallow Capulin location ranges up to 27 wt %, compared to 2-7 wt % at the Hansen location. Copper values range from 60-680 ppm in the sediment at Capulin and 20-50 ppm in the sediment at Hansen.

Combined with results of previous studies, examination of metals precipitated in aquifer sediments supports differential metal mobility between the two sites. This analysis of the behavior of metals combined with the existing hydrochemical data adds to our understanding of surface water contamination within the Red River Valley.