GEOCHEMISTRY
Year:2015 | Volume:4 | Issue:1|Papers Count:7

Shanjan barite ore is located on the southern slopes of Mishow mountains in Shabestar. Mineralization here is found as several disrupted lenticular veins, hosted by shale and schist rocks of Kahar Formation. The ore mineral is crystalline, with an average BaO grade of about 54.73%. The size of euhedral and semi-euhedral and tabular barite crystals reaches up to 2 cm. The main barite veins are about 1m thick, while the thickness of other veins in higher elevations, ranges between 10 and 20 cm. These are cross-cut by thin medium- to fine-grained quartz veinlets. Furthermore, there are disseminations and veinlets of sulfide minerals cross-cutting barite veins, which are mainly composed of chalcopyrite with lesser amounts of pyrite and galena. Fluid inclusions within the barite veins are mainly 2-phase with degree of fillings higher than 80%, which indicates the low temperature of the ore-bearing fluids. Sulfur isotope composition of barite and chalcopyrite (37.81-39.11 and 21.46-22.52 ‰, respectively) shows that sulfur was most likely originated from basinal waters confined within the shale units of Kahar Formation, which also contain framboidal pyrite and organic materials, as the d34S of barite is very close to the isotopic composition of Late-Precambrian sea-water sulfates. Meanwhile, analyses carried out on the rhyolitic rocks and shale units of Kahar Formation indicate high Ba content of these rocks, so these rocks may have acted as the possible source of barite ore.

Mazayjan with an area of 170 km2 is located at longitudes 53o 45’-53o 55’ E and latitudes 30 o 15’-30 o 23’ N, southeast of Sourian City, Fars Province in the Sanandaj-Sirjan Zone. The sedimentary and metamorphic with minor igneous rocks of Silurian to Lower Cretaceous, overlain by Quaternary deposits occurred in the study area. Iron, copper, manganese, lead and zinc hydrothermal mineralization of different origins controlled by structural features were reported from the study area. Stream sediment media is widely used as efficient and cost-effective method in prospecting of metallic deposits at district scale. Statistical analysis of geochemical data on stream sediments by using fractal concentration-area method was used to achieve this goal. This method considers the spatial position and distribution pattern of the geochemical data. Among geostatistic groups, those of Cu, Fe and Mn in 195 stream sediment samples have irrevocable potential and adaptability to litho-structure in Mazayejan. The target areas for Cu-Fe and Mn-Fe are located in the southwestern and northern parts of the study area with remarkable relationship to detrital limestone accompanied by pyrite-chalcopyrite bearing metatuff and detrital spary limestone containing Fe-Mn lenses respectively. Intensity of the geochemical anomalies increases close to structural features such as faults and brecciated zones. Field evidence confirms high mineralization potential for Cu, Fe and Mn in the target areas.

Mineralization of sedimentary copper has been observed in Iran associated with clastic sedimentary formations during the Late Triassic, Late Jurassic, Early lower cretaceous and Miocene or with salt domes in the Zagros zone. In Chehrabad area, Oligomiocene to recent formations are observed. The main mineralization of copper, lead and zinc are found in certain sandstone bands of Upper Red Formation. Development of mineralization in reduced green sandstons and also accumulation and enrichment of copper minerals around the plant remains that indicates the role of organic compounds and reductive environment in the concentration of metallic elements. In order to study the petrography, mineralogy and geochemical characteristics, 71 samples were taken for thin and polish sections and chemical analysis by ICP-OES, XRD and Fire Assay methods. According to these studies, in Chehrabad mineral deposit, host rock sandstones are sublitharenite to subarkose. The most aboundant mineral is malachite and carbonate and oxide minerals are more important than sulfide minerals. Chemical analysis showed the presence of some elements with economic values such as copper, lead, zinc and silver. Sedimentary copper mineralization of Chehrabad is comparable to sedimentary copper deposits of Red Bed Type in lithology, stratigraphy, mineralogy and controlling factors and like these deposits, mineralization is concentrated in a detrital sedimentary sequence of red beds and selectively in reduced green sandstone bands.

Because of the intrusion of leuco-gabbro intrusions into the mantle peridotites of the Naein ophiolite, a chemical potential gradient has established and new metasomatic rocks were formed in their contact zone. The rocks that are produced by this special type of contact metamorphism, are wehrlite, olivine clinopyroxenite and clinopyroxenite, ranging from mantle peridotite to gabbro. These rocks are formed at the expense of peridotitic part of the contact zone. Clinopyroxene composition in terms of major elements and trace elements in wehrlite and clinopyroxenite are completely different from peridotite and gabbro revealing that the new clinopyroxenes were formed by contribution of host peridotite and gabbroic melt.

The purpose of this study is the geochemical evaluation of some shale-bearing horizons from Jurassic carbonaceous deposits in central Iran and eastern Alborz areas. The studied samples were taken from Tabas, Pabdana (Kerman), Khomroud (Kerman) and Takht Tonnel (Minoodasht) areas that were comparatively studied from hydrocarbon generation potential aspects. Consequently, sample analysis, were done including extraction of organic matter, separation to different fractions, preparation of gas chromatograms and isolation and fingerprints determination. Preliminary pyrolysis investigation on the samples showed that kerogen was mainly of type III and II and the level of maturity of organic matter in different areas was different. The amounts of hydrocarbon and non-hydrocarbon fractions in Kerman Pabdana samples indicated that saturated compounds (Paraffin’s) were abundant, while the organic material of Tabas samples have properties of aromatic specifications. Additional information from the biomarker analysis (Hopanes) from extracted bitumens, showed that the source rock for Minoodasht was a shale deposited in a relatively shallow marine reducing environment. The samples of Kerman (Pabdana) were relatively carbonate with a reducing environments. Using the maturity parameters of Hopanes and Steranes families the organic matter mtuarity of Minoodasht samples were in the beginning of oil window (catagenesis stage), the Kerman samples, mid to late oil generation window (end of catagenesis) and kerogen of Tabas samples in advanced stages of maturity in the generation window (methagenesis). The Richness of organic matter and the hydrocarbon generation potential, Minoodasht deposits were, good to average (oil potential), the Kerman area (Pabdana and Khorood) were good to very good (oil and Gas potential), and the Tabas samples are moderate to good (gas prone).

The Dopolan bauxite deposit is located in 110km southwest Shahr-e-Kord city, at the Chaharmahal and Bakhtiari province. This deposit is belonging to Zagros thrust zone. Dopolan bauxite deposit is hosted by dolomite with interbeded clay Khanekat formation. Khanekat formation overlaid by thin bedded clay bearing dolomite and limestone of Nyriz formation. The bauxite horizons consist of 5 separate layer bauxite, respectively from bottom to top including, iron rich bauxite, clay bauxite, oolitic bauxite, pisolitic bauxite and organic matter enriched bauxite. The XRD results of analysis show that the main mineral constituents of Dopolan deposit are diaspore, boehmite, kaolinite, nacrite, and pyrite. Oolitic, pisolitic, pleomorphic, breccias and collomorphic are the most important textures in this deposit. These textures are evidence for autogenic origin of bauxite deposit. The most enrichment REEs content of bauxite horizons are iron-rich and clay bauxite that is nearest to bed rock (Khanekat dolomite). Rhythmic increment of REE values in bauxite layers approaching to the bedrocks shows occurrence of karst bauxite. REEs pattern of bauxites exhibit LREE enrichment relative to HREE, positive Ce anomaly and negative Eu anomaly imply that to antigenic origin of these layers. Correlation coefficients between REEs and some of the major elements such as Si, P, Fe suggest that distribution of REEs controlled by clay minerals, Fe oxy-hydroxides and secondary phosphate minerals. So, parent rock for bauxitization, according to similarity between REE pattern of bauxite horizons and Khan-e-Kat dolomite, is clay bearing dolomites of Khan-e-Kat formation.

The Alout gold occurrence is located in the Kurdistan province, in the Sanandaj-Sirjan Zone. Because of the geological framework, this area is very important for gold mineralization prospects related to shear zones. In this study, orogenic gold mineralization was studied in terms of geochemical features by analysis of stream sediments and lithogeochemical studies of surficial, trench and borehole samples. In each phase of study, potential zones of mineralization and geochemical features, related to orogenic gold mineralization, were characterized, and these results were validated by the results of the detailed exploration. According to the surveys, host rock was thick to medium green schist and thin dark gray slate. The gold mineralization occurred in the contact zone. The results, in different scales, approved the association of arsenic and silver with gold. Furthermore, the results revealed a marginal antimony, zinc and cadmium orogenic gold mineralization.