Petrology, Geochemistry and Mineralization potential of igneous rock in North-Northeast Semnan

The studied area is located in the 10-12 Km of the N-NE of Semnan. From point of view structural and geological units, this is belonging to the end of central Alborz zone. Rock units sedimentary, Igneous and metamorphic outcrops. Igneous outcrops include gabbros and granitoids. Nokeh granitoides contain mainly granodiorite and alkali feldspar granite. Igneous plutons of Attari area have gabbroic and monzogabbroic compositions.Quatrz, plagioclase and k-feldspar are essential rock forming minerals of the granites.
Biotites, green hornblende, sphen and opaque minerals are the other rock forming minerals of the gabbros. Granitic rocks show the granular, graphic, myrmekitic and perthite textures. Plagioclase, ougite and olivine are the essention minerals of gabbros. Chlorite, epidote and calcite the secondary minerals of gabbroic rocks. Gabbros show granular, inter granular and ophitic textures. Plotted geochemical diagram on the base of major and trace elements of the studied rocks indicate that there isn’t a magmatic and genetic relation between gabbros and granites and also they aren’t originated from the same magma source regions. With attention to field, petrography and geochemistry investigation, gabbros are originated from melting of an enriched mantel and the other hand granitic rocks are originated from melting of crustal igneous rocks. These rocks have metaluminous to weak peraluminous nature and belong to I-type granitioids of continental volcanic arcs. Metasomatism process along the contact of granitoids rocks and their host rocks is resulted to from iron skarnization, skarnization(ingeneral concept) and producing garnet-megnetite-diposide paragenesis and scapolitizating in the alkali-feldspar granites and their tuffite host rocks. Contact metamorphism upgrade progressed to pyroxene hornfels facies and maximum P-T condition is : 500-600 ° C temperatures and about 2 Kbar.