MINERALIZED KARST SPRINGS OF CENTRAL TEXAS: LAMPASAS AND SAN SABA COUNTIES

Mineralized springs occur within the northern Llano Uplift of Central Texas where extensive karst development occurs in Paleozoic strata, including dense concentrations of hypogene features in Ordovician carbonates. Sulphur Spring occurs as an isolated mineral spring adjacent to the Colorado River; Gooch, Cooper, Hannah and Hancock springs occur as a cluster of mineral springs within the Lampasas city limits. These and other documented mineralized springs in the region were utilized as medicinal waters by pre-historic native inhabitants and in recent times by European settlers that migrated into the region. Today, they remain as significant cultural sites for local residents; however, little attention has focused on the origin and source of mineralization.

While most springs in the region have typical physicochemical properties of karst terrains, mineralized springs are associated with mildly elevated temperatures, high total dissolved solids and hydrogen sulfide degassing. Mineralized springs exhibit elevated sulfate concentrations as well as elevated metals, including copper, iron and zinc. These springs occur in regions of more intense fracturing as indicated by lineament analyses, which combined with geochemical characteristics suggests deep circulation flow paths where lateral migration and ascending fluids interact with mineralized zones proximal to basement rocks and overlying Cambrian strata within the region. Near vertical fractures provide fast flow routes for cross-formational fluid migration, enabling mineralized water to be delivered from depths of more than 700 meters and discharge as mineralized, artesian springs with limited connectivity to the local surficial hydrogeologic system. Extensive hypogene karst development in the region further supports a speleogenetic model of semi-confined karst processes dominating the region.