JOURNAL OF GEOTECHNICAL GEOLOGY (APPLIED GEOLOGY)
Year:2009 | Volume:4 | Issue:4|Papers Count:9

A complete study including field geology, petrography, fluid inclusions, and trace- and rare-earth element geochemistry, and lead and sulfur isotope studies has been carried out on the Baba Gholleh Pb-Zn prospect located in the Sanandaj-Sirjan tectonic zone of western Iran. Ore-host rock relationships and petrographic studies show that Baba Gholleh Pb-Zn prospect is a vein-type deposit in which ore minerals occur predominantly with quartz veins and flat lenses, interbedded in the metamorphic host rocks. Galena and sphalerite are dominant ore minerals accompanied by quartz and calcite gangue minerals.Fluid inclusion studies suggest that ore-forming fluid has a low to moderate salinity. The temperatures of homogenization range mostly between 135 °C and 200 °C, corresponding well with the metamorphic temperatures of the host rocks. This temperature range also occurs in the temperature range of the basinal fluids, but the salinity of the ore-forming fluid is slightly less than that of basinal fluids, resulting from interference of meteoric waters.Geochemistry of trace elements points out that the host rocks are anomalously enriched in Zn and Pb, hence they could provide ore constituent metals. REE profile in mineral sphalerite reveals that these elements were leached from host rocks in low temperature conditions through fluid-rock interaction.Sulfur isotope composition of coexisting galena and sphalerite indicates that deposition of these minerals occurred in disequilibrium conditions, resulting from low total concentration of H 2 S in ore-forming fluid and rapid rates of sulfide deposition. Sulfur in sulfide minerals derived possibly from metamorphic host rocks. Lead isotopic studies indicate that the lead in galena was derived from an upper crustal source with higher 238 U/ 204 Pb ratio than the average for continental crust. The Pb-isotope model ages for mineralization, range from 270 to 472 Ma (average value is 371±100 Ma), indicate a Middle Ordovician to Lower Permian age. These Pb isotope model ages are not in accordance with the geological data which indicate a Post-Middle Jurassic age for mineralization.

The Zahedan granitoids, which pertain to an arid to semiarid region, have been studied. Those granite rocks without a cover of Quaternary sediments are exposed directly to dry and warm climate. The characteristic conditions of southeastern Iran perform a major role in the amount of rock demolition and weathering and in the formation of special morphologic forms. Samples have been taken from the granite massive. Hand samples and microscopic thin sections show that they have relatively medium grain size and are of bright color. The major minerals are well-formed biotite, abundant quartz and zonal plagioclase. Dykes and stock intrusion are the main characteristics of these rocks. Due to the contact with intrusions and granitoids, most of the host rocks have been changed into hornfels and schists. The green schists are contact concordant and as host rocks have an excessive spread. All stages of weathering processes, i.e. physical, chemical and down to soil building, can be observed here. Another specific feature is the existence of dark and fine- grained enclaves in rocks. The rocks show signs of granoporphyrit-microgranular structures in microscopic thin sections. There is plentiful biotite in rocks.Part of the Zahedan granite is under the influence of wind erosion. Xenolith discharge from the granite massive causes the creation of manifold spin holes in rocks. In this way it bestows to rocks a karstic facade and cavernous forms.The biomechanical weathering, as growth of tree roots in joints and cracks of granite, expedites the demolition of rocks. The splitter activity of wild pistachio tree roots, like a wedge, has been attributed to mechanical weathering. Another kind of physical erosion is the stone surface exfoliation, known as exfoliation domes. The released pressure on the stone surface creates fractures followed by the erosion of rock and formation of numerous blocks. Most of the available joints in granite are subsequently filled with quartz.

Zarab region situated in south of Baft city and Northern Boundary of Sanandaj-Sirjan zone. Petrographical studies indicate Rock units get moderately green schist facies metamorphism grade and contain of: orthogenesis, Marble and abundance schist's in Zarab region.We can see flow structures in marble and various microstructures as like S-C structures, and structures Mica Fishes and et… in schist' s. We could recognize dextral shear sense, which caused Microstructures. The amounts of tension strains in normal section that prepared from oriented samples indicate prolate form strain ellipsoid parallel to schistosity fabrics. Field studies show, which the thrust faults, have a dextral movement (co orientation with microstructures shear sense), similar orientation, slip movement and absence of fault plan erosion. Varieties between faulting deformation (brittle deformation) and shear sense of microstructures (ductile deformation), reveal two deformation phase with a nonconcurring deformation time and brittle deformation took place in second stage.

Talezang Formation sediments Outcropped in an extensive area specially in southwest of Lorestan. It is lying conformably on Amiran clastic formation and it is upper boundary is confined to the Kashkan red siltstone formation. In the type section it is dated upper Paleocene to middle Eocene which is composed of limestone with moderate bedding to massive form.Limestone of the selected sections are mostly sandy with sandstone and shale interbeds. Miscellanea Miscella, Miscellanea Minauta, Kathina sp., Lockhartia sp., Gavelinella sp., are the typical fossils are defined in the selected sections from this formation, then the proposed age for the formation in the Upper Paleocene – Ibersian.

The Asmari Formation was studied from biostratigraphy and depositional environment point of view in well No.25, Gachsaran oil field. The thickness of Asmari Formation in well No.25 is 632meters.The study of 220 thin sections taken from the studied well led to the identification of 47 genera and 48 species of benthonic foraminifera. According of the index foraminifera such as Eulipidina sp., Nepherolepidina sp., Borelis melo curdica, Miogipsinoides complanatus, The age of the Asmari Formation in the subsurface studied is Oligocene (Rupelian-Chattian) - Early Miocene (Aquitania- Burdigalian).10 Carbonate microfacies were also identified within the Asmari Formation, well No.25. The microfacies belong to the shallow open marine, barrier, restricted lagoon and lagoon environment.

The Fahliyan Formation of the upper Khami Group (Lower Cretaceous) composed of carbonate Rocks. In order to study facies, depositional environment and sequence stratigraphy of the Fahliyan Formation in the southwest of Fars Basin, surface sections (Bidkhon in Assaluyeh Anticline and Khartang) and subsurface sections (Nar-2 and West Aghar) have been studied. Field observations and Petrographic studies indicate that the Fahliyan Formation deposited in four facies belts: Tidal Flat (A), Lagoon (B), Barrier (C) and Open marine (D). Study of Facies, their Vertical and Lateral changes and comparison with modern and ancient environments indicate that the Fahliyan Formation deposited in a Shelf carbonate platform with shallow environments. Sequence stratigraphy of the Fahliyan Formation in the area indicates on the existence of two depositional sequences (3rd-order cycles). In studied sections, lower boundary and top boundary of the first sequence and top boundary of the second sequence are type 1 unconformity (SB1).

Nannofossils are good for biostratigraphy, since they are abundant, planktonic, rapidly evolving and largely cosmopolitan especially in the late Cretaceous. With respect to this reality and due to the lack of any precise paleontological study, the nannofossils of Gurpi formation were investigated in the Dare-Shahr. This formation consists of marl and shale and two members (Lopha and Emam Hassan limestones). In this study, for the first time, 24 genera and 48 species of nannofossils were identified. According to the stratigraphic distribution of calcareous nannoplanktons the study section is Late Santonian to Early Danian age corresponding to CC16-CC26 (Sissingh 1977) and NP1-NP2 (Martini 1971). The presence of Biantolithus sparsus, Cruciplacolithus primus, Micula prinsii, indicate that the K/T boundary is continues and within Gurpi Formation in Dare-Shahr section.

To study the Bryozoa and the stratigraphy of Permian rocks in the Bazman region an east-west stratigraphic section was studied. The Sarab section, which takes its name from the Sarab River, is located on the southern slope of the Bazman Volcano. The rocks of this section with a thickness of 202 m. are divided into 7 informal rock units, where the lower boundary has discordance with carboniferous sediments, and the upper boundary is faulted. Based on the microfossils and the Bryozoa, the age of the lower part of the Jamal Formation is Bolorian. In this study, three genera and species were identified, one of which has been reported for the first time in Iran.Fistulipora timorensis (Bassler 1929), * Strablascopora cf. germana (Bassler 1929)* Filiramoporina sp., Streblotrypa (Streblascopora) marmionensis (Etheridge 1926).