Iranian Journal of Geology
Year:2021 | Volume:14 | Issue:56|Papers Count:7

The study area is located about 8 km south of Bandar Abbas in Hormozgan Province. This area is in the south of the Zagros folded zone and part of the Hormuz series. The late Precambrian-early Cambrian rocks comprise intercalations of rhyolite-rhyodacite lava and tuff, crystal tuff, tuffaceous shale, sandstone and evaporite layers. Iron mineralization along with apatite are found as dike, massive, vein-veinlets and disseminated forms in tuffaceous shale and crystalline tuff rock units. Based on iron oxides and apatite contents, mineralization can be divided into iron-oxides (mainly magnetite), iron oxides-apatite and apatite types. The main ore-forming minerals include magnetite, oligist, hematite, goethite and limonite, apatite, and gangue minerals are calcite, quartz and clay minerals. The Hormuz Island ores have a high concentration of rare earth elements (REE) and the total amount of REE in apatite-rich ores is up to 3%. The geochemical studies show that a strong positive correlation between P and REE. Comparison of the chondrite-normalized REE pattern of the Hormuz magnetite-apatite ores with those from the Bafq-Posht-e-Badam block and the Kiruna type iron ore deposits represent genetic similarity of mineralization. The homogenization temperature in the two-phased liquid and vapor (L+V) fluids in apatite minerals vary from 309 to 565° C (average 388° C), and salinity varies between 14. 16 to 33. 87 (20/80) wt. % NaCl. Finally, based on the field geology, mineralogy, geochemistry and fluid inclusion features, the Hormuz magnetite-apatite mineralization is classified in the Kiruna-type magnetite-apatite deposits group with magmatic-hydrothermal origin.

The study area in the south of Deh Tah, Lut Block comprise Oligocene volcanic rocks which are composed of andesite, trachyandesite, dacite and rhyolite. These lavas have porphyric to porphyritic textures with abundant amphibole phenocrysts. Most of the Oligocene lavas display calck alkaline to high-K calck alkaline magmatic affinities. In the binary diagrams, the andesitic to trachyandesitic samples cluster far away from the trachydacitic, dacitic and rhyolitic samples suggesting that they were not afftected only by magmatic differentiation. The REE patterns and spider diagrams show enrichement in light ion litophile element (LILE) and hight field strength element (HFSE) depletion. The normalized patterns of the andesite to trachyandsite have a reliable overlap with oceanic island basalt (OIB). The patterns of the acidic lavas are correlated with the patterns of continental crust. These geochemical evidence indicate that the andesitic to trachyandesitic lavas are generated from partial melting of lithospheric mantle which previously metasomatized by subduction components (melt-fluids). Partial melting of the continental crust has an important role in generation of the acidic lavas. Based on geological setting and geochemical data, it seems that the Oligocene volcanic rocks formed in a post-collision zone, due to thinning of the continental lithosphere in Lut Block. This process is probably related to lithospheric delamination which occurs in a post-collisional zone in Lut Block, as a part of the Alpine-Hymalaya orogenic belt.

In this research, Saveh North-Narbaghi copper deposit was evaluated by using linear and nonlinear geostatistical methods and their results were compared. To achieve the goal, in the first step, average grade and ore reserve were calculated using log-kriging and indicator kriging with cut off grades of 1000, 1500, 2000, and 2500 (ppm) by SGeMS2. Then the deposit was simulated by Datamine software and the average grade and ore reserve were estimated through ordinary kriging method. The results of the research show that the differences between log-Kriging and ordinary Kriging with applied cut off grades for the ore reserve are 0. 96%, 19. 18%, 9. 81% and 10. 44% respectively. Also, the discrepancy between indicator Kriging and ordinary kriging methods with applied cut off grades are 13. 45%, 9. 29%, 14. 73% and 11. 63% respectively. In general, the accuracy of the results and research performance are understood from the proximity of the results of average grade and amount of ore reserve estimation employed by all three methods. However, the average grade with different cut off grades by multiple indicator Kriging method is higher than the other methods due to lower blending ore and gangue in this method and high degree of purity of ore blocks compared with the other methods. Also, the reason of overestimation obtained by ordinary block kriging using Datamine software is related to the user's intervention in determining the mineralized intervals in the boreholes on the basis of experience and recognition of the deposit condition.

Qareh-Dash rhyolites from the Shahindej area are peraluminous rocks with high SiO2 and K2O contents. These rocks are mainly composed of quartz, K-feldspar and rare plagioclase phenocrysts in a fine-grained K-feldspar rich matrix. Geochemically, Qareh-Dash rhyolites show enrichment in LREEs and LILEs and depletion in HREEs. Field studies, textural and petrographical relations, along with whole rock geochemistry, demonstrate that the parental magma of the Qareh-Dash rhyolites was originated from the crust. The composition of the parental magma was modified due to fractional crystallization of plagioclase and titanomagnetite evidenced by negative Eu, Sr and Ti anomalies in multielement diagrams. The chemical characteristics of Qareh-Dash rhyolites such as Rb/Nb, K/Rb, Rb/Sr, Rb/Ba and Ga/Al ratios are similar to A-Type granites/ rhyolites associated with post-collision tectonic settings. According to Precambrian age for the Qareh-Dash rhyolites, formation of these rocks might be related to extensional phases which were probably taken place after closure of proto-Thetys Ocean.

Exploration area of Barmolk is located in the northwest of the country, East Azarbaijan province and northeast of the Varzeghan county. Northern outcrops of the area consist of Eocene volcanic and volcanoclastic rocks and Oligocene porphyry quartzmonzonite intrusion bodies, which are cut off by first and second generation non-mineralized dikes. Towards to the north, this mass is in contact with upper Cretaceous-Paleocene carbonate-flysch deposits. In addition, Plio-Quaternary injection of dacite subvolcanic domes and eruption of alkaline basalt in the studied area have taken place. Kighal porphyry extends to the southwest of Barmolk area. Phyllic, propylitic and argillic hydrothermal alterations were identified in this mass, but potassic alteration was not observed. This indicates that the Barmolk porphyry is not an independent mass and is the margin of Kighal porphyry mass. The main texture in this mass is porphyritic with fine-graind matrix. Mineralization appears to be disseminated, vein-veinlet and fracture surface filling including chalcopyrite, galena, sphalerite and pyrite. Pyrite content in this mass is low, and this is one of the reasons for the lack of supergene enrichment zone. Due to the presence of lead and zinc mineralization mostly in the form of vein-veinlet in the first-generation quartzdiorite dikes (DK1) and with regards to the injection of these dikes into Sungun after supergene zone formation, the mineralization of lead and zinc can be attributed to the epithermal processes, related to the Barmolk intrusive mass. Consequently, the latter mineralization occurred after the injection of first-generation quartzdiorite dikes.

Siahjangal ophiolite is located in the North and Northeastern part of Taftan volcano in the Sistan Suture Zone (SSZ). This ophiolite (Upper Cretaceous) is exposed in the Flysch rocks (Eocene). Harzburgite, lherzolite, serpentine, spilite and gabbro are major rocks in this ophiolite. Ultramafic units have olivine, orthopyroxene and clinopyroxene minerals. Mafic units have clinopyroxene and plagioclase. Ultramafic rocks have mainly granular and gabbro rocks have ophitic, sub-ophitic and granular textures. Geochemical verities of major, minor and rare earth elements in the Siahjangal ophiolite revealed that the ultrabasic and basic rocks were formed due to partial melting than crystal differentiation. REE elements diagrams normalized to the Chondrite and MORB and their comparison with the normal and enriched MORBs, chemical differentiation diagrams, the ratios of accessory elements and changes of Zr, Nb, Y, U, Ti elements against Zr / Nb ratio all indicates the similarity to N-MORB. Transition elements diagrams (V, Co, Cr, Ni) against La / Ce ratio and the ratio of (La / Yb) N, La / Yb, La / Ce versus (La / Sm) N, show that these ratios compared with N-MORB and E-MORB represent enrichment and geochemical similarities to N-MORB. Tectonomagmatic diagrams show Siahjangal ophiolite belongs to supra-subduction zone.

Rapid sea-level rise and drowning of carbonate platforms is one of the important geological events in the Late Cretaceous and after the Turonian global unconformity. This transgression in central and western Zagros Basin is represented as shaley sediments of the Laffan Member, which were deposited over the Sarvak Formation. The stratigraphic position and the occurrence of the Charophytes-Ostracods biozone indicate the late Cretaceous, Coniacian age for the Laffan Member, which is stratigraphically equivalent to the Surgah Formation in Lurestan area in the west of Iran. The Laffan Member is mainly shaley in lithology with intercalations of thin-bedded argillaceous limestones and is the caprock over the reservoir of the Sarvak Formation in some oil fields in SW Zagros. Microfacies, sedimentary environments, biostratigraphy and sequence stratigraphy of the Laffan Member in two wells of Azadegan Oil Field located in Abadan Plain were investigated. Petrographic data revealed the presence of a shaley facies and two carbonate microfacies including charophitic mudstone-wackestone to bioclastic planktonic foraminiferal wackestone. These microfacies were deposited in transitional-brackish to deep marine environments. Marine transgression over the eroded palaeotopography of the Cenomanian-Toronian carbonates resulted in estuaries as channels and transitional environments. In these estuaries, mixture of the fresh and marine waters resulted in deposition of the lower parts of the Laffan Member and graded upward into the marine deposits of the upper parts of this Member. The sudden change of shallow-transitional facies to deep marine sediments in the Laffan Member indicates drowning of the carbonate platform of central Zagros Basin in Coniacian. The evidence like erosional base, deepening-upward sequences, frequency of mudstone facies (shale) and continuity with marine carbonates confirm this conclusion. Investigation of vertical changes of the microfacies with gama-ray well log data indicate the Laffan Member is part of a sequence as lowstand deposits (LST), transgressive deposits (TST) which grade upwards into maximum flooding surface (MFS) and high-stand deposits (HST) which comprise a third-order sequence. This sequence begins with an erosional unconformity and follows up with the formation of the estuary and deep sea sediments. The latter package is covered with the carbonate sediments of the lower part of the Ilam Formation (Santonian) which represents carbonate platform deposits of high-stand system track (HST).