Genetical Significance of Saline Relics in Carbonate Host Rocks of Alpine Pb-Zn Deposits
Geochemical research on saline relics in Alpine Pb-Zn deposits established important indications as to the composition and concentration of ore-bearing solutions. The investigations proceed from the principle that saline solutions are commonly responsible for the formation of ore deposits. Therefore the mere existence of saline relics in Alpine Pb-Zn deposits had to be proved initially. For this purpose a leaching method was developed and applied to barren and mineralized rocks of the Bleiberg-Kreuth (Austria) and Raibl (Italy) Pb-Zn deposits. Predominantly Ca2+, Mg2+, SO 4 2- , accompanied by generally minor amounts of Na+, K+, and Cl- were found in the leachates. Only Na+, Cl-, and Mg2+ (Ca2+) can be assigned to fluid inclusions and salt crystals, here referred to as ”saline relics”.
The concentration of the entrapped solutions was estimated by the Na/Cl ratio of the leachates. For barren rocks, these ratios frequently indicate solutions saturated with respect to NaCl (halite). In strongly mineralized domains the salinity is significantly increased. Here the existence of MgSO4 saturated brines seems to be probable.
Additionally Na/Cl ratios of fluid inclusions and oil field brines from Mississippi Valley type deposits are very much in line with our results and emphasize the reliability of our method of investigation. The high salinity of entrapped solutions (saline relics) indicates that formation water itself might be of major importance for transport, precipitation, and mobilization of ore matter.
KeywordsFluid Inclusion Host Rock Salt Crystal Econ Geol Mississippi Valley Type
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