The Keweenaw Peninsula native copper district of Michigan, USA is the largest concentration of native copper in the world. The copper isotopic composition of native copper was measured from stratabound and vein deposits, hosted by multiple rift-filling basalt-dominated stratigraphic horizons over 110 km of strike length. The δ65Cu of the native copper has an overall mean of +0.28‰ and a range o...

Scientists participating in the USGS Abandoned Minelands Initiative have quantified metal concentrations and loadings from mining-related and natural background sources in the upper Animas River of southwestern Colorado, with the goal of guiding remediation decisions by federal landmanagement agencies. We have compared site-specific toxicity thresholds with frequencies of dissolved metal concen...