New Mexico Geological Society Annual Spring Meeting — Abstracts

The metal mercury has been known since prehistoric times. The Romans discovered the amalgamation properties of mercury around 100 A.D. and used it to extract gold from ore. This process has been used up to the present.

The Cuba Smelter is in southeast Socorro between Interstate Highway 25 and Cuba Road. The smelter was first opened in 1881, and was operated intermittently, under several names, until about World War 1. It was primarily a facility to process lead, silver, and gold. The Torrance Stamp Mill is 230 feet south of the smelter. It operated briefly from 1882 to 1884, but any periods of operation after that are questionable. While in operation, mercury was used to extract gold and silver from ore. During operation or at the time of closing, the mercury was either dumped or leaked around and below the stamp mill which is at the top of a steep slope. In the past, liquid mercury was collected by local residents from two pits which are about 15 feet from the foot of the slope.

The mercury contamination was brought to the attention of the New Mexico Environmental Improvement Division (EID) by local residents during their preliminary assessment of lead contamination at the site. EID found elevated mercury levels throughout most of the Cuba Smelter site as compared to background levels. Mercury levels were especially high at the base of the stamp mill.

My data show several trends as to the extent and movement of the contamination. Mercury concentrations range from 1 ppm on the slope of the hill below the stamp mill, to 2515 ppm in a collector's pit. The concentration below the base level of the collector's pits roughly doubles with every six inches downward to 18 inches. My research indicates 1) the high levels of contamination drop off quickly with distance from the collector's pits; 2) at lower levels of contamination, no consistent pattern is obvious with changes in depth; and 3) the mercury at highest levels of contamination increases in concentration with depth.