Geochemistry of Mine Effluents in the Front Range Mineral Belt of Colorado.

摘要

Results of the chemical analyses of water draining from 7mine adits within five mining districts were compared to the ore petrology,ore mineralogy,and type of ore deposit. The water samples were collected in the Front Range Mineral Belt of Colorado in which most of the metal deposits are predominantly a complex mixture of copper,lead,zinc,and silver sulfides,gold tellurides and arsenides. The oxidation of pyrite which is associated with these complex ores yields acid water containing high concentrations of iron,sulfate and other trace metals contained in its structure. This acidity promotes the dissolution and oxidation of the other sulfides which release high concentrations of base metals to the water,but no additional acidity. The position and movement of the water table related to the ore veins and the type of ore play an important role in determining changes in the water quality from metal mine drainages. From these results,it was found that all the mine effluents fit the diffuse aquifer system. The Emmett and Clyde Mines are a good example of the type of ore vs. the water quality. In the Emmett Mine the acidity generated from the oxidation of pyrite promotes the solubility of fluorite which releases hydrofluoric acid which attacks the silicate rocks. All these reactions are responsible for the chemistry of the water found in this adit. The Clyde Mine,which shows almost complete absence of sulfide minerals,has the best water quality of all the mine effluents studied. Calculated values for redox potentials using the ferric/ferrous couple and taking into account the ionic strength activity coefficients and ferric sulfate and fluoride complexes agree very well with the measured Eh values. Conductivity was also found to correlate really well with the total dissolved solids. These results demonstrate the utility of Eh and conductance measurements in acid mine drainages.