A mass balance study to determine Copper Creek metals sources

An inactive mining operation in northern California is known to be a source of acid mine drainage and heavy metals which have impacted adjacent creeks. Elevated concentrations of copper and zinc are a concern to aquatic populations, particularly steelhead trout and salmon downstream in the Sacramento River. Previous regional geological surveys of mineralization by the U.S. Geological Survey located and mapped outcrops of massive sulfides and gossan. Recent investigations indicate that a substantial amount of the metals in the local creeks are due to natural causes. The investigations include locating and mapping surface and subsurface minerals, sampling, and chemical analysis. Groundwater, seeps, and surface water were also sampled and analyzed. A water balance is conducted on a sub-basin level following delineation of surface water drainage and groundwater divides. The chemical mass balance incorporates the metal concentrations and water volumes and is then used with other data to determine the contribution of metals from natural versus mining-related causes.