نوع مقاله : علمی -پژوهشی
نویسندگان
گروه زمینشناسی، دانشکده علوم، دانشگاه سیستان و بلوچستان، زاهدان، ایران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
IntroductionThe Taktalar is located 140 km northwest of Zahedan in Sistan suture zone (SSZ). The SSZ is divided into ophiolitic complexes of Ratuk and Neh which are separated by Sefidabeh basin in the central parts (Tirrul et al., 1983). The Neh and Ratuk complex consists of Cretaceous ophiolites, Cretaceous to Eocene phyllite and Paleogene deep sedimentary and continental clastic rocks. The Sefidabeh basin mainly consists of flysch-like rocks. Various basic to acidic extrusive and intrusive rocks occur in these subzones. The hydrothermal alteration and mineralization types are associated with the igneous rocks. There are also intensive and extensive alterations and weak Au, Cu, Pb and Zn mineralization evidences in the Taktalar. The aim of this paper is to examine petrology, alteration and mineralization of the study area.Method and materialSixty-three thin sections and 22 polish and thin-polish sections were examined by polarizing microscope under transmission and reflected light. Eight samples from the igneous rocks were analyzed by XRF and ICP-MS for major and trace and rare earth elements, respectively. 400 rock samples and cores were analyzed by ICP-OES to interpret grade and variation of Cu, Au, Mo, Ag, Pb and Zn.Result and discussionThe phyllite, sandstone and siltstone were intruded by intermediate stocks in the study area. These unites were also intruded by E-W intermediate dikes. Mineralized and non-mineralized silicic and carbonate veins were formed in E-W and NE faults. The stocks are diorite porphyry and granodiorite porphyry. They occur as a large ellipsoid with a fine-sized groundmass similar to completely altered dacite and andesite and contain plagioclase, amphibole, biotite and quartz. The intermediate dikes are also diorite porphyry and contain plagioclase, quartz, hornblende and biotite. The host rocks including sedimentary and igneous rocks in the study area are extensively and intensively altered. The alteration types are potassic, phyllic, silicic-argillic, propylitic and show the zoning. The potassic alterations are centered on a diorite porphyry stock and are characterized by biotite, orthoclase and mineralized quartz veins. The most extensive and intensive alteration is phyllic alteration which is centered on more than 80 % of outcrops of igneous and sedimentary rocks. This alteration is characterized by quartz, sericite, pyrite and tourmaline. The silicic-argillic alteration extensively occurs near silicic veins. The propylitic alteration occurs in marginal parts, associated with intermediate dikes, diorite porphyry and the flysch-like rocks. In Taktalar, pyrite is the most abundant sulfide which is sometimes associated with little amounts of chalcopyrite, bornite and covellite. The Cu mineralization is mainly characterized with Cu carbonates such as malachite and azurite and iron oxide veins. The maximum contents of Cu, Au, and Mo in the porphyry stock are 33000, 0.75 and 210 ppm, respectively. The vein mineralization occurs in marginal parts of the area and are associated with silicic and argillic alteration in oxidized parts. The veins are three types: gold-bearing silicic-iron oxide, Cu-bearing silicic-sulfide and poly-metal. The maximum contents of Au, Cu, Ag, Pb and Zn are 48 ppm, 10 %, 70 ppm, 27 % and 0.11 %, respectively.The igneous rocks are calc-alkaline and shoshonitic. SiO2 contents in them range from 57.51 to 69.33 wt. %. The minor and rare earth elements which are normalized to the MORB and the primitive mantle, respectively, show that LREE and LILE are enriched more than LREE and HESE, respectively. The enrichment of LREE and LILE, negative anomalies of Ba Ti, Nb and Zr and positive anomalies of Rb, Th, Ce, Sm suggest that the igneous rocks were emplaced in a volcanic arc related environment.ConclusionThe mineralization in Taktalar occurs as stock works and is disseminated in central parts and as vein in marginal parts. In the disseminated type, Cu and Mo are anomalous but of low grade. In vein type, there are high grades of Au. The mineralization is a low-grade porphyry system in terms of its alteration, mineralization style and sub-volcanic igneous rocks. The epithermal vein mineralization occurs mainly as lead and gold veins in the marginal parts of the area and telescoped onto a porphyry system.
کلیدواژهها [English]
)