Geology, mineralization, Rb-Sr & Sm-Nd geochemistry, and U- Pb zircon geochronology of Kalateh Ahani Cretaceous intrusive rocks, southeast Gonabad

Kalateh Ahani is located 27 km southeast of Gonabad within the Khorasan Razavi province. The area is part of Lut Block. Sub-volcanic monzonitic rocks intruded regional metamorphosed Shemshak Formation (Jurassic age). Magnetic susceptibility of less altered monzonitic rocks is < 25 ×10-5 SI، therefore they belong to reduced type ilmenite granitoid series. Both intrusive and metamorphic rocks are altered to argillic، propylitic، silicification and some iron oxides. Argillic alteration is dominant within the intrusive rocks. Two major quartz sulfide (sulfides are oxidized) veins trending NW-SE are recognized within the study area. Based on core logging، both disseminated and veinlet mineralization types are recognized within the intrusive and metamorphic rocks. Eight types of veinlet and vein are identified within the intrusive rocks. Maximum density of the veinlets is about 35 per meter within the biotite monzonite porphyry. Hypogene minerals include pyrite، chalcopyrite، sphalerite، galena and quartz. Secondary minerals comprise malachite، hematite، chrysocolla، goethite and gangue minerals are quartz and siderite. Rock geochemistry shows high anomalies of Cu، Pb، Zn، Sn، As، and Au both in the surface and within the mineralized core. Cu > 0. 6%.، As، Pb and Zn > 1%، Au up to 150 ppb and Sn = 133 ppm. The Sn content of vein in the northern part of Kalateh Ahani (Rud Gaz) is > 1%. Based on mineralization، alteration and geochemistry، it seems that Sn mineralization is associated with the Cretaceous monzonitic rocks. Zircon U–Pb dating indicates that the age of the monzonitic rocks associated with mineralization is 109 Ma (Lower Cretaceous). Based on (87Sr/86Sr) i = 0. 71089-0. 710647 and (143Nd/144Nd) i = 0. 512113-0. 51227 of the monzonitic rocks، the magma for these rocks were originated from the continental crust. This research has opened new window with respect to Sn-Cu mineralization and exploration within the Lut Block which is associated with Cretaceous granitoid rocks (reduced type، ilmenite series) originated from the continental crust.