Mineralogical, Textural and Geochemical evidence to identify potassicmetasomatism in Karaj Dam sill and its influence on country rocks

At the NE of Baraghan, gabbroic to monzonitic sill, known as Karaj Dam sill, intruded into the tuffs. Based on field observations and microscopic studies, the sill is differentiated from margin to center. Plagioclase crystals sometimes show zoning, but the zoning is not present in rocks with myrmekite texture from the lower part of the sill. However, twinning is preserved in unzoned crystals. Myrmekite is wart like type. High temperature ferromagnesian minerals are decomposed but plagioclases mostly are remained fresh. Based on whole rock XRF analyses, Rb-SiO2 and K2O-Na2O diagrams show non-linear trends. Based on norm calculations, Na2O values decreased and K2O values increased in samples from the contact with country rocks. It could be due to extraction of Na2O from the rocks by fluids. Such textural, mineralogical and geochemical features are evidences for low pottasic metasomatism in lower part of Karaj Dam sill. Fluid had influenced on tuffs and caused kaolinitization of K -feldspar, sosuritization of plagioclase and chloritization of ferromagnesian minerals. In the other hand, fluids made chemical re-mobilization of ore minerals and accumulation of secondary copper minerals in the tuffs.