Soil and stream sediment geochemical dispersion over the Bell Springs deposit, Hog Ranch Mine, Washoe County, Nevada

Natural Background Determination and Impact Quantification in Trace Metal-Contaminated River Sediments

“…Metal-rich sediment is quickly diluted by un-enriched tributary sediments, attenuating the anomaly a short distance downstream. Even the largest ore deposits rarely have dispersion trains detectable more than 10-20 km downstream, a fact well documented in the exploration geochemistry literature ( 25). Exploration geochemists first realized that the downstream dispersion of naturally occurring metal anomalies was primarily governed by dilution mixing with tributary sediments.…”

“…Even the largest ore deposits ra re ly have dispersion tra in s detectable m ore than 10-20 kilom eters downstream , a fa ct w ell docum ented in the e xp lo ra tio n geochem istry h te ra tu re (Bradshaw, 1975;Bogoch and Brenner, 1977;Lovering and McCarthy, 1978;M cLaurin, 1978;Bussey et al, 1993). Exploration geochemists studying dispersion tra in s firs t reaUzed th a t the dow nstream concentrations.…”

“…Figure 7 shows m odel fits to fo u r contam inated rive rs. In each case, an acceptable f it to the sedim ent data was achieved using the measured param eters and a best- P rio r to m in in g , m etal levels greater th a n twice th e regional background ra re ly extend m ore than 20 kilom eters dow nstream , even fo r the largest ore deposits (Bradshaw, 1975;Bogoch and Brenner, 1977;Lovering and M cCarthy, 1978;M cLaurin, 1978;Bussey et al, 1993). By contrast, m etal levels o f twice the regional background were fo u n d to extend 500 km dow nstream in one o f the contam inated riv e r systems exam ined ( Figure 8A).…”

“…The lengths of the calculated dispersion trains are within the range of reported dispersion trains for undisturbed ore deposits. Prior to mining, metal levels greater than twice the regional background rarely extend more than 20 km downstream, even for the largest ore deposits ( − ). By contrast, metal levels of twice the regional background were found to extend 500 km downstream in one of the contaminated river systems examined (Figure a).…”

Metallic mineral resources in the U.S. Bureau of Land Management's Winnemucca District and Surprise Resource Area, northwest Nevada and northeast California

“…Gold-silver ore is present in veins, breccia, banded quartz veins, and pyrite with late opaline quartz. Ores are enriched in arsenic, antimony, mercury, and molybdenum Rytuba, 1989;Peters and others, 1987;Bussey andothers, 1991, 1993).…”