GEOCHEMISTRY OF NATURAL ACID ROCK DRAINAGE IN THE JUDITH MOUNTAINS, CENTRAL MONTANA, USA
Although the Judith Mountains contain a number of historic precious metal mines, the watersheds of interest in this study, including Red Mountain itself, have been minimally impacted by mining. A comparison of the trace metal concentration in a longitudinal set of ferricrete samples in one of the watersheds with actively forming FeOx precipitates in the adjacent stream suggests that the acidity and trace metal loads witnessed today are broadly similar to conditions prior to settlement in the late 1800s. Although the ferricrete deposits in the headwaters of each stream have not been dated, their considerable size and the lack of Quaternary glaciation in the Judith Mountains suggest that they could be hundreds of thousands if not millions of years old. The study area is a potential reference site to help constrain pre-mining water quality in nearby mining districts with similar geology but more severe mining disturbance, such as the Kendall and Zortman-Landusky gold-mining districts.