ARSENIC ENRICHMENT ASSOCIATED WITH HISTORIC GOLD MINING IN JULIAN, CA: A CASE STUDY FOR ECOSYSTEM AND PUBLIC HEALTH IMPACTS RELATED TO ARTISANAL MINING

The co-occurrence of arsenic with gold mineralization is well known, given that both elements are soluble and reactive in hot mineralizing fluids. Recent findings of arsenic impacted groundwater (Fairbanks, Alaska), human exposure to arsenic via drinking water (Nova Scotia), and elevated arsenic mobility in ecosystems (Mojave Desert) as a result of historic gold mining operations have prompted further investigation into the occurrence and mobility of arsenic as a result of anthropogenic redistribution. In Julian, CA, small scale artisanal gold mining has left several tens of abandoned tailings piles exposed, providing an excellent opportunity to examine the impact of small-scale gold mining operations on current ecosystem and human health. This study seeks to characterize the distribution and mobility of arsenic in the tailings piles and surrounding country rock (Julian Schist) to better understand the behavior of arsenic in such systems. Analysis of tailings found arsenic to be enriched above average crustal values and as high as 2822 mg kg^-1 in waste rock found in tailings piles. Leaching of such tailings material with locally collected rainwater indicates that this arsenic is mobile (up to 481 μg/L leached over a 24 hour period) at levels well above the EPA guidelines for both ecosystem health (150 ug/L) and drinking water (10μg/L). Therefore, local ecosystems and consumers of potentially arsenic influenced groundwater may be at risk. The degree of impact remains unknown, as tailings piles are currently culturally protected and, thus, may represent an unidentified environmental and/or health risk. Discrete occurrence of arsenic up to 243 mg kg^-1 also remains in-situ in the surrounding Julian Schist. Given that many Julian residents obtain their water from domestic wells installed in bedrock, these findings may indicate a public health threat if groundwater is impacted. In addition to providing an enhanced understanding of the impacts associated with artisanal mining, findings of discrete arsenic enrichment in surrounding metamorphic rocks provide valuable information to those examining the tectonic relationship between arsenic enrichment in rocks and its release into groundwater.