Geochemistry of molybdenum in some stream sediments and waters

Elevated concentrations of Mo are present in both the waters and sediments of Tenmile Creek, downstream from the large Mo deposit at Climax. Colorado. Concentrations of Mo reach a maximum of 10mg/1 in the water and 384μ/g in the (?) 80 mesh fraction of the sediment. The Mo anomaly extends for more than 80 km downstream from Climax, and results from the mining and milling at Climax. Background Mo concentrations in the nearby mountainous area are < 10μg/l (water) and < 5μg/g (sediment). Immediately below three small unmined Mo-rich orebodies elsewhere in Colorado < 3μg/l Mo are present in the waters and 20–30μg/g Mo in the fine fraction of the sediments.The Mo in the sediment of Tenmile Creek is chiefly adsorbed on coatings of amorphous Fe oxyhydroxide. and is similar to its form below two small, unmined Mo deposits. Mining has not changed the character of the chemical processes responsible for Mo dispersion from the Climax site.A modified version of the WATEQF computer program (Plummeret al., 1976) predicts that Tenmile Creek is undersaturated with respect to ferrimolybdite. molybdenite, powellite, and ilsemannite. The Mo in the stream water occurs as the molybdate ion which can be adsorbed on amorphous Fe oxyhydroxides. These predictions are supported by the absence of Mo minerals in the sediment of Tenmile Creek.