New Mexico Geological Society Annual Spring Meeting — Abstracts

Hanover Mining District has been mined since at least the 1600's. The majority ofmineral extraction was for iron and non-ferrous metals such as Cu, Zn, and Pb. The Hanover and Bullfrog tailings piles are located east of Silver City in southwest New Mexico. Tailings were produced from a Zn-Pb sulfide vein deposits. The main ore mineral at Hanover was sphalerite. Ankerite, specular hematite, pyrite, and pyrrhotite are common gangue minerals. The main ore minerals at Bullfrog were sphalerite and galena. Gangue minerals include quartz, pyrite, manganiferous calcite, chlorite, and rarely barite.

Movement of heavy metals from the tailings piles may occur by wind transport of metal-containing particles, fluvial transport, aqueous transport, and/ or plant uptake. To determine the mobility ofheavy metals present at the sites, surrounding soils, vegetation, and surface water were sampled and analyzed. Soils were sampled at the surface and at depth to determine possible downward movement. Foliar samples were taken to determine metal concentrations in plants on and near the tailings. Surface water samples were taken from Hanover Creek above, adjacent to, and below the Hanover tailings to determine possible contamination from the tailings.

Surface soil samples taken in an area affected by wind-transported tailings material show slightly elevated Pb, Zn, and Cu concentrations. Concentrations of these metals drop to background levels below 2-4 cm in depth. Plant samples show little uptake ofheavy metals even in samples taken on the edge of the tailings piles where wind transported material had engulfed the plant. Water samples taken adjacent to and below the Hanover tailings contain fewer total dissolved solids and lesser concentrations ofthe main ions SO₄ and Ca.

These results, together with the alkaline soils and arid climate of the Southwest, indicate the low probability of dissolved aqueous transport of heavy metals away from the tailings. It is recommended that the tailings be covered with topsoil and revegetated.