Water-Rock reactions in a deep barite-fluorite underground mine, Black Forest, Germany

摘要

Mineralization in the more than 700 m deep underground barite and fluorite mine Clara (Black Forest, Germany) occurs in 3 major vein systems within the gneisses. They are associated with quartz, carbonate, various sulfides, natural alloys and about 250 species of secondary minerals. Water transport is strongly focused within the mineral veins owing to their high fracture and cavity related permeability. Water from 25 different sampling points in and around the mine were collected and analyzed monthly during one year in order to elucidate the interaction of surface water with the various rock types. On the basis of the relative proportions of the major ions 3 types of water could be distinguished: Ca-HCO_3-, Ca-SO_4-HCO_3- and Ca-SO_4-Cl-water. The source of the solutes is related to fluid-rock reaction, especially feldspar weathering. All waters within the mine are very close to quartz saturation. They are saturated or a bit undersaturated with respect to calcite after relatively short flow distances through the fracture pore space. All waters are undersaturated regarding dolomite or gypsum. All waters fall in the stability field of kaolinite which is an observed major alteration product in veins and rocks.