فصلنامه زمین شناسی اقتصادی
سال پنجم شماره 1 (پیاپی 8، بهار و تابستان 1392)

Arghash – Ghasem-Abad area in NE Iran is located in the rim of the Sabzevar structural zone. Tertiary outcrops include granite and quartz monzodiorite porphyry associated with dacite and andesite volcanic rocks. In the study area، quartz gabbro and quartz monzodiorite dykes intruded the older rocks. Granite and volcanic rocks host Au-Sb-bearing quartz-calcite veins. Mineralized veins are mainly located around the dykes in the southern part of the area. According to geochemical studies، granites have high-K calc-alkaline affinity with transitional I/A-type features. The volcanic rocks with adakitic composition contain high abundances of Sr and Ba. The dykes in the area show characteristics of lamprophyric rocks. U-Pb zircon dating of granite yielded an age of 55. 4±2. 2 Ma (Lower Eocene). Initial 87Sr/86Sr and εNd values for the granites are 0. 704142 and +5. 84، respectively. Initial 87Sr/86Sr ratios strongly suggest a depleted mantle source for the magma. This dating demonstrates that the Au-Sb mineralization occurred later than Lower Eocene. Based on field observation، the mineralization is more related to the lamprophyric dykes than to the adakitic rocks.

Isotopic and microthermometry results from Sheikh-Darabad Cu-Au indices in Mianeh region, East-Azarbaijan province, indicate Cenozoic post-magmatic activities with developed adularia facies through an extended and Neogene related alteration that is given rise to occurring silica vein systems as the main hosting locations for epithermal mineralization. The research evidence also has been coincided with Queensland textural zoning conclusions which confirm a success case of silica textural variations associated with Sheikh-Darabad gold and copper bearing locations based on paragenesis of quartz-pyrite-chalcopyrite. As a new result, fractal-based geometry has been used for assessing the nonlinear distribution of siliceous components and subsequently for prognosis of gold mineralization potential in Sheikh-Darabad region. In practice, most of quartzitic occurrences and related textural variations have been precisely studied and realized by satisfying to silica power law statement in order to obtain the self-similar peculiarities of individual textures. Therefore, using a textural pattern for evaluating and correlating between silica zonal variations and its ordinary textural evolutions in post-magmatic environments, is a new criterion for prospecting precious metals with finally emphasizing on gold exploration priorities in Sheikh-Darabad region.

The Nasirabad manganese deposit is located 5 km south of Nasirabad، 8 km SW of Neyriz in the Fars province. Structurally، the area is placed in the southeastern part of Zagros thrust belt. In this area، the manganese mineralization occurred as ore layers and nodules، interlayered with Pichakun radiolarite chert deposits. In this study، mineralogy and geochemistry of uranium، thorium and lead isotopes were used to investigate the primary and secondary processes. In this way، in addition to petrographic and XRD studies، ICP-MS analysis was carried out in order to measure the U، Th and Pb isotopes. The strong fractionation of Fe and Mn phases and also the absence of Fe-bearing minerals in the XRD results، presence of syngenetic todorokite and quartz crystals، high U/Th ratios in some samples and Th versus U diagrams، all indicate entrance of Mn-bearing hydrothermal fluids into the sedimentary basin of the Nasirabad manganese deposit. The pyrolusites in radiolarites tests as replacement textures، host rock space filling and fracture filling pyrolusites، indicates the influence of secondary exogenic processes on primary hydrothermal mineralization. Non-homogenous 206Pb/Pb204، 207Pb/Pb204 and 208Pb/Pb204 values show non-steady hydrothermal processes in the sedimentary basin and indicate mixing of hydrothermal lead isotopes with another secondary source. Strong positive correlation between absolute values of radiogenic lead isotopes and insoluble High Field Strength Elements (HFSE) such as 207Pb vs Nb (r=0. 81)، 207Pb vs TiO2 (r=0. 93)، 207Pb vs Th (r=0. 79) and strong correlation between these elements and some mafic components like 208Pb vs Fe2O3 (r=0. 94) and Th vs MgO (r=0. 86) represent entrance of radiogenic lead with mafic detrital materials into the sedimentary basin. Similar linear trend among 206Pb/Pb204 vs 208Pb/Pb204 and 207Pb/Pb204 ratios in nodules and manganese layers show the same geochemical condition in Mn-nodules and layers formation and indicate that isotopic ratios were unaffected by secondary processes including leaching and redeposition of manganese.

Cheshmeh-Konan area is located ~15 km northwest of Tasuj، East-Azarbaidjan province. The most important lithologic units of the area are red sandstones، green-gray sandstones، shale، and marl (Miocene). Based on field evidence and petrographical investigations، the host sediments were deposited in a peritidal setting associated with a sabkha-type environment. Copper mineralization in the area occurred as stratiform within the green-gray coarse-grained sandstones and includes minerals such as chalcocite، covellite، bornite، chalcopyrite، malachite، and azurite. Considering the obtained results، control of the mineralization in the area is in relation to sandstone sedimentary facies and concentration of organic matters. Combination of the obtained results from field، petrographical and mineralographical investigations indicate that factors such as accessibility to chloride ligands، presence of high quantities of organic matters، diagenetic processes، function of marls and shales as geochemical barriers، and the existence of fault systems have played a major role in copper mineralization at Chesmeh-Konan area. The obtained results show that copper mineralization in the area is mostly similar to Red Bed type sedimentary copper deposits.

The Eocene volcanic rocks from the southwest of the Jandaq (Kuh-e-Godar-e-Siah، Central-East Iran micro-continent) are andesitic basalt and andesite in composition. These rocks contain xenoliths with granulitic mineralogy. Mineral assemblage of these xenoliths is plagioclase + phlogopite + corundum + sillimanite + chlorite + phengite with granublastic، poiklioblastic and foliated textures in the pick metamorphic condition. Thermometry of phlogopite in these xenoliths suggests the average temperature 782oC. The characteristics of the xenoliths are consistent with the granolitic facies metamorphism of the Al-saturated Si-undersaturated crustal sediments at the lower crust condition. Melting of these granulites forms the magma which crystallized the S-type granitoids. Differentiation and crystallization of this magma causes the S-type granite formation. Therefore، the S-type granites in the study area are probably generated from melting of the granulites parts of which brought to the surface as xenoliths by Eocene magmatism in south of the Jandaq (Kuh-e-Godar-e-Siah). S-type granites in the study area are located along the Doruneh، Chupanan and Aeirakan faults in the Aeirakan area and Jandaq ophiolite. These granites are the source of uranium، thorium and uranium ore in southwest of the Aeirakan mountain.

In this study، principal components analysis was used to investigate lithological characteristics of Jahani salt dome، Firouzabad. The spectral curves of rocks in the study area show that the evaporate rocks have the highest reflectance at specified wavelengths. The highest reflection has been seen in gypsum and white salt، while minimal reflection can be observed in the igneous rocks from the region. The results show that PCs have significantly low information. It is clear that PC1 shows more information in the highest variance while PC2 has less information. Regional geological map and field controls show compatibility between the enhanced zones and outcrops in the field.

Jian Cu deposit is hosted by Surian volcano-sedimentary complex of Permo-Triassic age on the eastern edge of the Sanandaj-Sirjan metamorphic zone at a distance of 195 km from Shiraz، southwestern Iran. The complex consists mainly of metabasalt، chlorite-quartz schist، chlorite-muscovite schist، mica schist and graphite schist. Pyrite is the most important sulfide and chalcopyrite is the major Cu-bearing mineral occurring as disseminated grains and veinlets in host chlorite-quartz schist and chlorite-muscovite schist. Chondrite-normalized REE pattern of metabasalt with La/LuN=2/9 indicates mantle tholeiitic basalt as the source of metamorphosed igneous rocks. Geochemical data on the metabasalts، especially the content of immobile elements (e. g.، Ti) and High Field Strength Elements (HFSE) (e. g.، Zr، Nb and Y)، show low degree of partial melting for parental magma with E-MORB affinity. Chloritic، silicification and minor sericitic assemblages are the main alteration types associated with the Jian Cu deposit. The Y/Ho ratio of Cu ores varies from 29. 9 to 32. 5، indicating the important role of sea water in the mineralizing system. Petrographical and geochemical data indicate that the Jian Cu deposit was formed as volcano-sedimentary hosted massive sulfide. The Ishikawa alteration index (AI) in association with chlorite-carbonate-pyrite index (CCP) is useful for the geochemical exploration of Cu deposits in the study area.

A combination of elements is usually used in reconnaissance geochemical exploration and distribution maps are drawn to identify probable anomalies. In this study، 102 stream sediment samples from the arid environment of Mesgaran area، eastern Iran، were investigated using R-mode factor analysis. A four-factor model with a cumulative variance of 75. 90% clearly indicated group associations of the elements coinciding precisely with the lithology and the mineralization present in the study area. Factor scores were calculated and mapped in order to evaluate the anomalous locations of the relevant associations across the whole area. Mineralization factor had strong positive loadings for the elements Au، Cu، Zn، and S and clearly delineated the known mineralization present in the study area.

Roudgaz prospect area is a Cu، Sn، Pb، Zn، and Au polymetal vein system located to the southeast of Gonabad and in the northeast of Lut block. Oxidan subvolcanic Tertiary rocks with monzonite to monzodiorite porphyry composition intruded the metamorphic rocks of middle Jurassic. The majority of intrusive bodies are affected by carbonation، argillic، sericitic، and silicification-tourmaline alteration. Mineralization in the area is controlled by fault and is present as vein with domination of NW-SE direction and 85-90º dip. Primary minerals are quartz، tourmaline، chalcopyrite، pyrite، and secondary minerals are malachite، azurite، and goethite. Geochemical sampling using chip composite method indicated high anomalies of Cu، Sn، Pb، and As (up to 10000 ppm)، Zn (up to 5527 ppm)، and Au (up to 325 ppb). Broad gossan zone is present in the area and is related to the oxidation of sulfide minerals. IP/RS survey was performed over the geochemical anomalies for identification of the location and extension of sulfide mineralization at depth. Generally، chargeability increases in gossan zones، veins، old workings and geochemical anomalies. Resistivity over the quartzite unit and also in locations where mineralized vein is associated with quartz has a high anomaly of up to 425 ohm-m. Due to high geochemical anomaly of Sn and its relation with reduced subvolcanic intrusives، ground magnetic survey was performed to identify the location of magnetite (oxidant) and ilmenite (reduced) series at depth. Variation of Total Magnetic Intensity (TMI) is 335. 1 Gamma in the TMI map. The highest magnetic anomalies in the RTP map are located to the north of the survey area which is related to magnetite series (hornblende biotite monzodiorite porphyry) and extend to the south at depth. The lowest magnetic anomaly is located to the center of the survey area and particularly to the east of the Roudgaz village correlating the highest chargeability and geochemical anomaly. Based on coincidence of geochemical and chargeability anomalies، two holes were drilled in the area and 24 samples were collected from the core drills for geochemical analyses. The highest anomalies are accompanied by silicification and chlorite alteration and locations of extension of secondary Fe oxides.

The Dehdasht bauxite deposits are located 40 km northeast of Dehdasht in Kohgilouye and Boyer-Ahmad Province. It is a part of the Irano-Hymalayan karstic bauxite belt located in the upper part of karstic depressions of Santonian-Turonian Sarvak carbonate formation. The aim of this study is to determine various geneses of pisoliths and prevalent processes in bauxitization. For this purpose، laboratory experiments were carried out including qualitative mineralogical investigation by X-Ray Diffraction (XRD) and petrographic study of thin section. Bauxitization processes led to the formation of bohemite، diaspore، calcite، kaolinite، anatase، rutile، goethite، hematite and chlorite in these deposits. Bauxitization was developed by destruction of kaolinite and deferruginization and caused aluminium concentration in the deposits. Mineralogically، these deposits vary based on the presence of pyrite in the gray horizon in some deposits such as Mandan. Minerals were formed due to three stages of weathering، diagenetic and epigenetic processes. Based on quantitative mineralogical results of the bauxite horizons، depositional/diagenetic environments of the study area vary from vadose to phreatic. Micromorphological investigations show pisoliths with simple، vitreous، complex and oolithic cores and also discolored and broken pisoliths. Therefore، the deposits can be divided into three types: autochthonous، allochthonous and para-autochtonous. Dissolution features and kaolinization، deferruginization and diaspore formation in fractures demonstrate diagenetic and epigenetic processes that occurred after the formation of the deposits. Investigation of encrust particles frequency shows that particles with 50-200 micron in diameter، have the most frequency and simple fabric of ooliths shows short-term formation. Comparison of the frequency of encrust particles as well as TiO2/Al2O3 variation diagrams، indicates that some deposits such as Mandan had lengthier bauxitization time.