The Lower Triassic Sorkh Shale Formation is a dominantly red colored marginal marine succession deposited in the north-south trending Tabas Basin of east central Iran. It is correlated with the unconformity-bounded lower limestone member of the Elika Formation of the Alborz Mountains of northern Iran. The Sorkh Shale is bounded by the pre-Triassic and post-Lower Triassic interregional unconformities and consists mainly ofcarbonates, sandstones, and evaporites with shale being a minor constituent. Detailed facies analysis of the Sorkh Shale Formation resulted in recognition of several genetically linked peritidal facies that are grouped into restricted subtidal, carbonate tidal flat, siliciclastic tidal flat, coastal plain and continental evaporite facies associations. These were deposited in a low energy, storm-dominated inner-ramp setting with a very gentle slope that fringed the Tabas Block of east central Iran and passed northward (present-day coordinates) into deeper water facies of the Paleotethys passive margin of northern Cimmerian Continent. Numerous carbonate storm beds containing well-rounded intraclasts, ooids and bioclasts of mixed fauna are present in the Sorkh Shale Formation ofthe northern Tabas Basin. The constituents of the storm beds are absent in the fair weather peritidal facies of the Sorkh Shale Formation, but are present throughout the lower limestone member of the Elika Formation.The Tabas Block, a part of the Cimmerian continent in east central Iran, is a rift basin that developed during Early Ordovician-Silurian Paleotethys rifting. Facies and sequence stratigraphic analyses of the Sorkh Shale Formation has revealed additional evidence supporting the Tabas Block as a failed rift basin related to the Paleotethys passive margin. Absence of constituents of the storm beds in the fair weather peritidal facies of the Sorkh Shale Formation, presence of the constituents of the storm beds in the fair weather facies of the Elika Formation (the Sorkh Shale equivalent in the Alborz Paleotethys margin) and southward paleocurrent directions of carbonate storm beds suggest that the low topographic gradient of the ramp in the Tabas failed rift basin was facing the Paleotethys Ocean, where the storms were generated. In addition, northward paleocurrent directions of the fair weather facies and northward increase in carbonate content of the Sorkh Shale sequence further indicate that the Tabas Basin was tectonically a part of the Paleotethys passive margin. It is apparent that relative sea level, basin geometry and tectonic movements along the bounding faults played significant roles during deposition of the Sorkh Shale Formation by controlling accommodation space and facies variations along the Tabas failed rift basin.
Problem statement:The Muteh mining district is located in 70 km northeast of Golpaygan city within the Sanandaj-Sirjan metamorphic belt. There are 2 gold mines, 7 gold occurrences and numerous mineral indices in the Muteh gold district. There are few researches on Muteh gold district, but a detailed model is not clear yet. The aim of this study is to determine mineralogy of gold-bearing rocks and the role of these rocks in concentration of gold and to improve our knowledge about Muteh model. Approach: Detailed fieldwork carried out at different scales at the Muteh district. About 50 outcrops samples examined petrographically. Fifteen samples containing veinlets of sulfides and quartz selected for H, O and S stable isotope analysis. Petrography characterized by optical microscopy, Scanning Electron Microscopy (SEM) and X-Ray powder Diffraction (XRD) analysis. Results: Geological studies indicated that the study area show a major poly-phase metamorphism. Since the latest metamorphism was weaker than the earlier ones, the older rocks were affected by more intense metamorphism. The metamorphic rocks mainly consist of schists, quartzite, marble, amphibolite and gneisses. These rocks show two foliations (S 1 and S 2 ). The S 2 foliation is the major phase in the metamorphic rocks. Pyrite is the most abundant and the important gold-bearing mineral at the study area. Based on evidences of deformation (S 2 ) and crystallization, three main types of pyrites can be distinguished in the Muteh deposit: (1) pre-tectonic or gold bearing pyrite (2) syn-tectonic or disseminated pyrites along the foliation of the host rocks. (3) pyrite aggregates in the host rocks or in the metamorphic segregation quartz veins crosscutting the foliation of the host rocks. The sulfur isotope studies were carried out on pyrites within quartz veinlets, biotite schist and meta-volcanic rocks at the Muteh deposit. Five available data are highly variable even from the same types of hosted rocks and their 34 S are +2.2, 6.6, 9.1, 13.9 and 16.9‰. Conclusion: There are three generations of pyrite in Muteh gold district. According to isotope data, it seems that source of sulfurs were not homogenous. The values showed more than one geological event for generation of pyrites in the study area. Compositions of sulfur isotopes indicated several different sources or processes for the sulfide fluids. The sulfur of these pyrites might have derived either directly from regional metamorphism that produced the metamorphic fluid or through dissolution and leaching of pre-existing sulfide-bearing minerals.
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