Taknar Polymetal (Cu-Zn-Au-Ag-Pb) Deposit: A New Type Magnetite-Rich VMS Deposit, Northeast of Iran

The massive sulfide of Taknar deposits are part of meta volcanic-sedimentary complex (Taknar Formation, Ordovician) and consist of clastic sediments, carbonate, felsic and mafic volcanic and sub-volcanic rocks. The Taknar polymetal deposit shows good layering; therefore it is syngenetic in origin. Taknar zone was affected by low grade metamorphism (Green Schist facies) in the late Paleozoic. As a result, pelitic and subarkosic rocks were changed to sericite or sericite-chlorite schist. Taknar deposit is situated within Taknar zone which is an allochthonous block. This block is situated between two major faults, Drouneh Fault to the south and Rivash (Taknar) Fault to the north. These deposits which are called Tak-I, II, III, and IV, originally were part of one big deposit but due to faulting they are being truncated and moved at least 1 km from each other. Three types of mineralization such as layered, massive and stockwork are present. The layered section is composed of alternating layers of pyrite, chalcopyrite, magnetite, sphalerite, galena and chlorite. The Individual sulphide layers range in thickness from millimeters to 2 cm. Chlorite is the dominate silicate mineral within the layered ore. Massive ore horizons, having >50% magnetite, occur at the stratigraphic top of the mineralized zone. Major minerals are: magnetite + pyrite + chalcopyrite + sphalerite ± galena + chlorite ± quartz ± sericite ± calcite. Pyrite and chalcopyrite content are higher in the lower layers and magnetite, sphalerite and galena are higher within the upper layers. In stockwork mineralization, major minerals are: pyrite + chalcopyrite ± magnetite + quartz + chlorite + sericite ± calcite. Chemical variations of some elements in different deposit are: Tak-I: Cu=0.01-5.86%, Zn=269-15600 (ppm), Pb=27-4400 (ppm), Au=0.86-7 (ppm), Ag=2-95 (ppm), Bi=34-2200 (ppm), and Mo=85-1300 (ppm). Tak-II: Cu=0.33-2.56%, Zn=0.3-7.7%, Pb=93-5000 (ppm), Au=0.33-11 (ppm), Ag=19-105 (ppm), Bi=79-214 (ppm), and Mo=54-116 (ppm). Tak-III: Cu=0.05-5.54%, Zn=62-179 (ppm), Pb=17-47 (ppm), Au=0.06-0.33 (ppm), Ag=2-40 (ppm), and Bi=11-250 (ppm). Based on paragenesis, alteration, style of mineralization, petrography, geochemistry, and structure, Taknar is a new type of magnetite rich polymetal volcanic massive sulfide deposit. Lack of pyrrhotite and high magnetite associated with sulfide minerals make this deposit very different from other VMS deposit. Based on the mineral paragenesis the estimated physiochemical conditions of formation are: Tak-I: T °C ≥ 250, Log f O2=(-29) to (-30), pH=5-7. Tak-II: T °C ≤ 250, Log f S2=(-11) to (-12), Log f O2=(-36) to (-39), 59. Tak-III: T °C ≥ 270, Log f O2=(-28) to (-29), pH>5.