In a project, the bedrock foundation for the ECRD dam is gneiss (quartz feldspathic/muscovitic/
micaceous quartz). Also, the rockfill was made up of the same gneiss. Some leakage captured downstream shows contents of sulfate. What is occurring in the leakage and why is the sulfate appearing? It’s worth to note gneiss has the following minerals: biotite, sphene, epidote, granite, and zoisite, among others. The reservoir water is Calcium-Bicarbonate type (according to Piper Diagram). The main recharge for the leakages mentioned before is the reservoir, according to hydrogeochemical studies, isotopic studies, and geoelectrical tests.
How big are the concentrations of sulfates in water from leaks? Certain, not very high concentrations of sulfates, in the tens of mg/l, are quite common in waters. Almost every rock environment can contain an accessory admixture of sulphides, mainly pyrite. Sulfates (gypsum) are sometimes added to cement clinker.
Most gneisses contain small pyrite grains that can be oxidized to sulfate under the influence of hydrologic weathering.
Dalibor Matýsek@, Noah Lewark@
Long ago we described a range of sulfate and associated minerals (gypsum, natroalunite, huntite, haloysite, pickeringite, K-alum, hydrated Fe-sulfate, epsomite, lecontite), grown along cracks in graphite schist in the huge Tarbela Dam on the Indus River. We figured, like Noah Lewark that they resulted from weathering of pyrite. The paper (Jan et al., 1985. Low-temperature secondary minerals from Tarbela. Geological Bulletin, University of Peshawar (current name-J of Himalayan Earth Sciences) 18, 189-197) should be on the Research Gate, but if not and you are interested in having it, please let me now at
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