عنوان مقاله [English]
The Senj Cu-Mo deposit is located in the central part of the Alborz Magmatic Arc (AMA), northern Alborz province (Karaj). Geology of the Senj area composed of mafic to intermediate Tertiary intrusive rocks and various types of volcaniclastic rocks. The early stage volcaniclastic rocks of Karaj Formation were intruded by the Oligocene Karaj Dam basement sill (composed of monzogabbro, monzodiorite and diorite) and Cu-Mo (±Ag and Au) mineralization occurred in contact of this rocks. Ore minerals such as sulfides (chalcopyrite, bornite, molybdenite, and pyrite), oxides (magnetite and hematite), and carbonates (malachite and azurite) are the main mineralogical paragenesis in the area. Stockwork quartz-sulfide mineralization as the richest part of ore body have average grade of 3.0 wt% Cu and 0.2 wt% Mo occur in porphyritic tuff host rock with potassic-phyllic alteration. The disseminated mineralization consist of chalcopyrite and molybdenite disseminated minerals with average grade of 1.8 wt% Cu and 0.1 wt% Mo occur in the porphyritic andesite tuff and intermediate argillic alteration. The supergene enrichment zone with limited exposure is composed of oxide-hydroxide upper ore with low grade Cu mineralization and sulfidation replacement lower ore zone with highest grade of 2.8 wt% Cu. The magnetite-biotite (K-silicate), potassic-phyllic (K-feldsapr-biotite-sericite-quartz±pyrite), intermediate argillic (kaolinite-illite±quartz±calcite) and propylitic (epidote-chlorite-laumontite-calcite±pyrite) are the main alteration assemblages related to mineral deposit. Based on geochemistry of alteration assemblages, the highest concentration of Cu and Mo mineralized elements occurred in the potassic-phyllic alteration and the intermediate argillic alteration and propylitic alteration have lower ore grade.