Present-day precipitation of lead and zinc from groundwaters

Small quantities of galena and sphalerite are currently precipitating 26m below the surface, at the Vinemount quarry, Ontario, Canada from sulfurous spring waters, issuing from carbonates of the Lockport Formation. At the spring orifices, these sulfides are present in both fracture coatings and an associated black sludge. These precipitates are overlain by a crust rich in native sulfur. The mineralogy of the precipitates, and the chemistry of waters taken from three consistent spring horizons, indicates that downward-moving meteoric groundwaters leach metals from the host rocks and precipitate galena and sphalerite on encountering H₂S-rich waters at the water table. While our observation of the transport and deposition of lead and zinc by shallow groundwaters lends support to intra-karstic models for the direct precipitation of galena and sphalerite, it also enables us to propose that many carbonate-hosted Pb-Zn deposits, of differing theories of origin, may have been enriched during periods of uplift.