فصلنامه زمین شناسی ایران
پیاپی 17 (بهار 1390)

This article attempts to investigate the relation between mineralization and structural evolution of elements، while it is using field surveys and satellite image analysis in NE Shahr-e- Babak، which is part of Urmie-Dokhtar volcanic belt. Structural analysis indicates a close relationship presents between mineralization and structural evolution of elements in the region. T1، T2، R' and R fractures are the most important fracture types in the area which are resulted from the large scale folding and right- lateral faulting in the region. Analysis indicates riedel that the T2 extended fractures with an E-W trend are the oldest fractures in the area which are dependent to the folding and have been filled by magma forming dike swarms. At the second stage، R' fractures have formed which are dependent on the movement of faults in the area having NE-SW trends and left- lateral with normal kinematic component cutting the T2 fractural and porphyry copper deposit have formed at their intersection. Some other extended fractures in the area include T1 that is extended fractures with N-S trends in which valuable veins with isolated dikes have been emplaced. Riedel fractures dependent on anti-riedel shear fracture with NW-SE process lack filling and bare mineralization has been done in them. Structural analysis and offset fractures indicate that anti-riedel fractures have been formed before riedel fractures in right lateral transpression system which itself a reason for the uplift in the region. Hence، structural elements have had a direct impact on the mineralization in the region.

Sanandaj-Sirjan structural zone contains complexes of sedimentary and magmatic rocks، which have been subjected to numerous deformation and metamorphic phases during different times. Nevertheless، there are disagreements about the structural phases affecting this zone. Kuh-e Sefid Tootak Anticline، in southern part of Sanandaj-Sirjan zone، has units with a Paleozoic age. Sourian complex with the age of Upper Carboniferous to Permian and with degree of metamorphism of lower green schist sits at the top of Tootak complex with age of Silurian to Lower Carboniferous and with degree of metamorphism of upper green schist to lower amphibolite. A monzo-granite body intruded at the bottom of Tootak complex. Based on this study، this monzo-granite body with an alumina-rich calc-alkaline nature is the product of partial melting of continental crust، and concurrent to a plastic shear tectonic regime which is penetrated into metamorphic rocks of the area. The Uranium Lead dating method suggests an age of 173± 9 Ma for this intrusive body. According to structural and metamorphic evidence as well as geological relationships، it can be concluded that the Hercynian and Early and Middle Cimmerian occurrences played significant role in transformation of the study area as part of southern Sanandaj-Sirjan zone.

One of the stratigraphic units of the Kopet-Dagh Basin is Aitamir Formation. This formation has been studied at four locations including Sheikh and Sorkhezoo in the Sheikh Syncline and Gadganloo and Paskooh in the Bibahreh syncline. The Aitamir Formation consists of fine glauconitic sandstone، siltstone، shale and carbonate rocks. This formation in studied area contains shell beds or shell concentrations. Three types of shell concentrations can be distinguished according to differences in stratigraphic، sedimentologic، palaeoecological، and taphonomic features. These three types of shell concentrations are found in distinct positions within the depositional sequence. Ammonite-dominated concentration (S3) in the early TST has a distinct basal erosional surface (ravinement surface)، and the shells are completely disarticulated، fragmented and abraded with a chaotic orientation، suggesting reworking of previous deposited sediments، and redeposition in a semi-restricted lagoon environment. Shell concentration at the end of the TST is a hiatus type or condensed back lap shell bed. It is characterized by (S1 S2 G1G3 G4P2P4 and P5) high percentage of whole shell، low abrasion and fragmentation، poorly sorted and diversity of fauna. This concentration was accumulated during periods of high rates of production of biogenic hard parts and low sedimentation rates، in an offshore environment. Shell concentrations at the top of the HST (top lap shell bed) (G2، P3) are multiple-event type. Taphonomic features of this concentration are very similar to the early TST concentrations. One distinct difference in characteristic of these two types is lateral extension، so that TST concentration is commonly seen as a bed، whereas the late HST concentration is a lenticular، patchy or pavement form.

Study of planktonic foraminifera of the Gurpi Formation in southwest of Firouzabad area led to recognition of 13 genera and 29 species of the planktonic foraminifera. Eight biozones were determined in the Gurpi Formation including Dicarinella asymetrica Zone (Santonian to Earliest Campanian), Globotruncanita elevata Zone (Early Campanian), Globotruncana ventricosa Zone (Mid to Late Campanian), Radotruncana calcarata Zone (Late Campanian), Globotruncanella havanensis Zone (Late Campanian), Globotruncana aegyptiaca Zone (Late to Latest Campanian), Gansserina gansseri Zone (Latest Campanian to Early Maastrichtian), Contusotruncana contusa and Racemiguemblina fructicosa Zone (Early to Late Maastrichtian). These biozones are comparable with the newest biozones that are proposed for Tethys realm. The study of planktonic foraminifera led to recognition of three groups of morphotypes indicating that the Gurpi Formation was deposited in deep water environments.

The study area is located about 40 km southwest of Yazd in eastern Shir-Kuh range. Intrusive bodies occur as dike and small stocks. Chemical composition of intrusive bodies is in the range of granodiorite، diorite، and gabbro. The nature of magmatism is clac-alkaline، generated in orogenic setting. Cretaceous carbonate rocks in vicinity of those intrusions are transformed into various marbles and skarns. The following mineral assemblages include: Forsterite + serpentine + talc + brucite + hydromagnesite + calcite + dolomite. Brucite porphyroblasts are only the most widespread mineral in marbles. The peak of metamorphism is begun with periclase and forsterite (>700 ºC) formation. Then low temperature paragenesis like carbonate and hydrous minerals form at 25 ºC. There are several stages in the marble evolution which imply the polygenic genesis of the marbles.

Khuni mining area is located about 50 km northeast of Anarak city (Isfahan Province)، central Iran structural zone. Geologically، the study area is covered by the Upper Proterozoic metamorphic rocks and Eocene volcanics. Cheshmeh Khuni، the most important mineralization in this area، occurs in eastern part of Khuni area. This deposit occurs as veins and is composed of magnetite، hematite and trace amounts of goethite. Gold mineralization occurs in Eocene volcanic rocks. Based on geochemical analysis of 34 volcanic rocks samples (44 elements) from Cheshmeh Khuni mineralization، the minimum، maximum and average Au grades are 2 ppb، 4810 ppb and 475. 70 ppb respectively. The maximum grades of Tl، Mo and Mn are 2. 3 ppm، 813 ppm and 5290 ppm respectively. The average grades of the later elements are 1. 17، 27ppm and 1356 ppm respectively. Fluid inclusions were mainly liquid dominant، two- phase (L+V) inclusions. Fluid inclusions were homogenized to liquid at temperatures between 200 and 320°C with a well defined mode at about 290 and 320 C. Final ice melting temperatures ranged between -1 to -7. 1ºC which correspond to 1. 65 to 10. 61 NaCl equivalent wt% respectively، with a mode of about 4-5 NaCl equivalent wt%. The evidence collected from the ore mineralization and fluid inclusion studies in this area indicate the epithermal origin for the Khuni mineralization. NaCl، MgCl2 and CaCl2 were probably the major salts of the fluid inclusions، studied.

The Shurijeh Formation forms a gas reservoir in the eastern Kopet Dagh basin. Terrigenous and evaporite sediments of this formation have been deposited, due to tectonic phase of the Late Cimmerian in a vast area in the eastern Kopet Dagh basin, in continental and rarely marine environments in the Late Jurassic- Early Cretaceous time. In order to study the depositional environments and presenting a model for this formation, a stratigraphic section was measured and studied in the south-southwest of Hamam Ghaleh village. Shurijeh Formation has a thickness of 953.5 m in the studied area and in contrast to other known sections, is composed of five lithological units. In addition to terrigenous and evaporite deposits, there are two carbonate units with a high thickness. Petrographic study of 402 thin sections shows that these sediments were deposited in a shelf platform in four facies belts, including tidal flat, lagoon, shoal and shallow open marine

In northeast region of Birjand، two distinct groups of volcanic rocks are exposed. Paleogene andesitic، dacitic and rhyolitic rocks as the major formation and younger mogearites، andesitic basalts and basalts that have erupted in the paleogene intermediate to acidic extrusive rocks background with the main trend of northwest – southeast. Investigations show that these two lithological complexes are the results of two different petrogenetical phenomenas and they have different genetic and geochemical characteristics. Intermediate to acidic volcanic rocks belong to active continental margin calcoalkaline rocks and they have formed from differentiation of a primary andesitic magma that are affected from crustal contamination at least in its rhyolitic and dacitic terms. The major nature of basaltic volcanic rocks is alkaline and they belong to intraplate basalts with mantle magmatic source that has erupted to the surface through extensional systems as the right lateral fault zones revenue.