XRF ANALYSIS OF METALS IN PONDEROSA PINE CORES FROM THE SILVER VALLEY, IDAHO

We present results from a study analyzing metal concentrations in Ponderosa Pine tree cores from the Silver Valley, Idaho using x-ray fluorescence spectrometry (XRF) and flame atomic absorption spectrometry (FAAS). Geochemical and dendrochronological analyses allow us to determine the spatial and temporal spread of metals in the forests surrounding concentrated mining activities within the Silver Valley. Mining in Idaho's Silver Valley began with the discovery of gold in the North Fork of the Coeur d'Alene River in 1883. Large-scale mining began with the later discovery of silver, lead, and zinc-bearing ore; this second phase made the Silver Valley one of the richest mining regions in the country. Mines and mills dumped waste rock and tailings directly into the river or on steep hillsides. By the early 1900's, contaminated water was poisoning plants and animals. The Bunker Hill Mine's smelter, constructed in 1917, added airborne pollutants to an already toxic environment. Metal production in the Silver Valley peaked in the 1960's, but increased concern for public health and the environment led to more costly pollution controls and the eventual declaration of the Bunker Hill Complex as a Superfund Site in 1983. Contaminants remain in sediment in the Silver Valley; lead, for example, is found in concentrations of several tens of thousands of parts per million in the most polluted sediment. Previous studies in areas impacted by mine waste have demonstrated that trees take up and sequester metals. A USGS study using laser ablation inductively-coupled plasma mass spectrometry (LA-ICPMS) demonstrated that pine trees in California recorded a history of mine-related metal pollution in the environment. Analysis via LA-ICPMS is an expensive and time-consuming process, whereas XRF analysis is quick, cheap, and nondestructive. We test the validity of XRF results of metals in tree cores by comparison with FAAS analysis.