Geological and eochemical survey at northwest of Karaj was conducted in an area of 300 Km2 by stream-sediment and heavy mineral sampling, based on the contract between Industries and Mines Organization of Tehran and Tehran Padir Consulting Engineers. Field works for geological studies started after geochemical survey to conduct the study toward proper trends of mineralization.
Generally, the lithology of the area consists of Precambrian – Paleozoic carbonate and siliciclastic rocks. Precambrian Kahar formation is the oldest exposed rock with a basal fault contact. Limestone and dolomite of Soltanieh overlies the Kahar. Cambrian Zagun and Lalun formations show extensive fracturing. These units are cut by younger small dykes that not mapped due to their size. Some fault zones in the area show evidences of mineralization where the sedimentary rocks adjacent to the intrusive rocks are lowly metamorphosed. Dominant rocks in the area are volcano-sedimentary rocks of Karaj formation that include shaly tuff, sandy tuff, limy tuff and conglomerate with andesitic lavas.
A monzonitic intrusion in the Eocene rocks that has sill geometry exist at south of the Senj village. This intrusion shows Cu-Mo mineralization, when the Cu is concentrated in the body itself and Mo in the outer shell. However Cu enrichment is lower than economic value. Andesite and basalt of southeastern region exhibit low porphyry copper mineralization. Fault zones in the Eocene rocks also show Cu, Pb and Ag mineralization. Baritic veins in the Karaj formation are between 1 cm and 1 m thick and sometimes contain Pb-Zn and Cu mineralization.