GEOCHEMISTRY
Year:2015 | Volume:4 | Issue:2|Papers Count:7

The Cu-bearing veins of the Nesen Formation are part of the Central Alborz Zone, located 100 km southwest of Amol city. The veins hosted by a sequence of dolomitic limestone of the Elika Formation. Mineralization mostly occurs as open space fillings, taking place as veins and hydrothermal breccias. Chalcopyrite, pyrite, tetrahedrite, quartz, calcite and barite are the main ore minerals which occur during three main stages. The first stage is characterized by the presence of calcite, dolomite, quartz and chalcopyrite. Wall rock dolomitization and silicification occurred in this stage. The second stage, the main mineralization stage in the study area, contains the most intense of sulfide mineralization. The third stage is characterized by the presence of quartz veins and veinlets that cross cut the mineralogical assemblages of the first and second stages. Colloform chalcedony and barite are the gangue minerals in this stage. Chalcocite, azurite, malachite, goethite and cuprite are the supergene products in the study area. Dolomitization and silicification are the main hydrothermal alterations which increased in the vicinity of the veins. Evaluation of the geochemical data set using different multivariate statistical methods has led to make useful prediction of the high grade regions. The geochemical investigations indicate the same distribution pattern of Cu, Zn, Sb, Ba and Sr which have most concentration in the hydrothermal alteration zones. Combinations of geology, mineralogy and geochemical results show the rule of basinal saline hydrothermal solutions in the formation of the Nesen veins. These results suggest that boiling, cooling and dilution were the main ore deposition processes in the area.

The study area is a part of the anomaly 5 of Saghand Uranium deposit which is located in 180 km NE of Yazd. The petrology of this area consists Granite, Quartzdiorite, Gabbro, Diabase & Altered rocks. Among the rocks units in the area, granite rocks have suffered the least alteration and metasomatism while basic rocks such as gabbro and diabase rocks have suffered the most severe alteration processes and hydrothermal activities. During this processes, albite and Na-amphibole formed from the hydrothermal sodic fluids. Based on the geochemical studies, the rocks with higher radioactivity in the anomaly 5 of Saghand, shows an enrichment or positive anomaly for U, Th, La, Ce and Pb while the elements P and Sr show negative anomalies. Bivariate diagrams show positive correlation between U and Rare Earth Elements. REE plots indiate a moderately Eu anomaly, and also the enrichment of LREE in comparison to HREE.

Geochemical characteristics of the petroleum play an important role in oil field development. This study tends to investigate oil geochemical characteristics of the Bangestan reservoir in Ahvaz oil field. A total of 4 oil samples from Ahvaz oil field (49, 368, 375, 455) were subjected to SARA test and GC-MS analyses. The results of oil fractions indicate the presence of high saturation fractions which are ascribed to paraffinic oils. The high saturation/aromatic ratio may be related to long migration distance or high relative maturity. In these samples high ratios of tricyclic C22/C21 terpane to low values of C24/C23, and low tricyclic C26/C25 vs. high values of C31R/C30 Hopane are indicators of carbonate-marl source rocks for the studied crude oils. The plot of C25/C26 to C25/C24 tet. ratio exhibits a marine environment during deposition of the source rocks. The variation plot of C32-22S/ (22S+22R) against C29-20S/(20S+20R) presents medium-high maturity for the oils under study. The calculated C28/C29 sterane ratios vary from 0.9 to 1 which reflects that source rock was deposited in early Cretaceous (Gadvan and Kazhdumi formations). Increasing maturity trend in Ahvaz oil field can be related to a rising thermal regime towards the east enhanced by dominance of fracture systems.

Hezar volcanic complex is the latest Eocene volcanic phase in the Kerman province, comprising of lavas (basalt, trachy-basalt, basaltic-trachy-andesite, trachy-andesite), pyroclastic and sedimentary rocks (in the western area). Petrographically, the lavas contain plagioclase, pyroxene, olivine, minor, and secondary minerals, with porphyritic and trachytic textures. Plagioclases and pyroxenes have a lesser degree of alteration and often show seriate texture, zoning and resorption and they are occasionally crushed. These evidence show disequilibrium condition as a result of pressure decrease during ascent to the surface. Large plagioclase crystals could be formed in the magma chambers and during the ascent of magma in the conduit. Geochemical investigations indicate that the lavas belong to calc-alkaline magmatic series characterizing a volcanic arc setting. The origin of the lavas is partial melting of mantle in the garnet stability range.

The aim of the present study is to delineation of geochemical anomalies by using rubost principal components analysis with log-ratio transformations, classic principal components analysis, concentration-area fractal model (C-A model) and finally present the useful methods which have the better coincide with geological features in the Zarshuran district. The applied methods were compared using geological features, occupied area of anomalies respect to the total study area and field observations. Robust principal components analysis (RPCA) couple with isometric logratio (ilr) transformations were utilized to open the geochemical data in order to reduce the effects of the data closure problem. The 20-quantile intervals decomposed anomaly maps from PC1 were obtained from the robust and classical PCA. Results indicated that the upper quintile (>80%) of robust and classical PCA cover 32.54% and 18.6% of area of anomaly, respectively. As a result, the robust PCA with smaller area of anomaly has good spatial associations with outcrops of Zarshuran former mining area (ore filed), Zarshuran unit, Chaldagh silicified limestone and newly explored works confirmed by field observations. Although the C-A model show a smaller area of anomaly (8.06%), the anomaly locations are limited to Zarshuran old mining area without new exploration targets. Comparison of the models indicates that the RPCA model with deletion the closure problem of geochemical data is more beneficial to further Au exploration in the Zarshuran mining district.

The study area is located in the NW of Iran. Based on structural-sedimentary map of Iran, this region is part of the Alborz-Azarbaijan zone. The oldest rock units in the area are volcanic and sedimentary rocks of upper Cretaceous and volcanic rocks of Eocene. The impure carbonate rock units are intruded by Oligocene intrusive bodies, which have produced numerous skarn deposits and hydrothermal alterations along with Cu and Au mineralization. This paper aims to detect the anomalous zones for Au, As and Sb in the Ahar quadrangle, using secondary distribution haloes (by using stream-sediment geochemical samples). In this regard, by taking into account factors such as stratigraphy, lithology, tectonics and topological center of streams, 620 stream sediment samples were collected and after preparation, their Au content was determined by fire assay method, while the As and Sb contents were analyzed by using ICP-MS method. Based on the results of this investigation, four anomalous zones were recognized for Au in the Ahar region, located at the east of Ahar city, NE section of Ahar quadrangle and in the vicinity of Sonajil and Injeh villages and finally at the SW of Ahar quadrangle. Additionally, the anomalous zones of Au were found to show good correlation with anomalous zones of As and Sb. By integrating the obtained data for Au, As and Sb it was revealed that these anomalies are mainly related to alkali-granitic to hornblende-biotite granitic intrusions of Oligocene age and the related hydrothermal alteration zones.

In order to evaluate the source rock potentiality of the Garau Formation, 14 outcrop samples were collected and subjected to preliminary geochemical assessment, from Tange-Shanak valley south of Aligoodarz city. Primary results from Rock-Eval II pyrolysis, indicate that; this formation contains sufficient TOC values. TOC contents range between 0.88 to 5.71%. The quality of organic matter in terms of hydrogen index (HI) between 298 up to 610 (mg HC/g Total Organic Carbon), with mainly kerogen type II, with small contribution of type I kerogen. Maturity level of organic matter in this Formation is based on (Tmax), is between 421 to 443 °C. This formation exhibits a good source rock potential that has entered Oil windows stage, with capabilities of producing liquid (crude oil) hydrocarbons. Based on HI vs OI plot, the origin of organic matter of the Formation is marine, which is deposited in reducing environments. With help of pyrolysis results and comparison of hydrogen and oxygen contents of samples, organic facies and depositional environment were determined. Based on HI and OI indices, the organic matter of the Garau Formation originated from marine algae is composed by organic matters with terrestrial origin. The studies on the Biomarkers of examined samples show that the origin of the organic matter of this Formation usually belongs to open marine, however sometimes the trace of organic matter with deltaic origin is observed by entrance of some terrestrial organic matter. The studied samples have been evaluated by using the GC-MS technique with comparing C29/C30 against C34/C35 Hopanes, the type of the lithilogy of formation is clastic (shale) lithology and the rest little amount of them is carbonate type.