فصلنامه زمین شناسی اقتصادی
سال پنجم شماره 2 (پیاپی 9، پاییز و زمستان 1392)

Sangan magnetite skarn mine is located 300 km southeast of Mashhad، along the eastern part of Khaf-Drouneh volcanic-plutonic belt. Granitoids from three areas within the Sangan mine A، C-North and Dardvay were studied. Within the study area، three intrusive rocks including biotite-hornblende monzonite porphyry، biotite syenite and syenogranite were recognized. Based on field cross cutting، absence of garnet-magnetite skarn around the contact، and alteration by younger hydrothermal fluids، these granitoids are older than the magnetite skarn. U-Pb zircon age of the granitoid is 42 Ma (Middle Eocene). Magnetic susceptibility of the granitoids are 310-900 × 10-5 (SI units) and therefore، they are classified as belonging to the magnetite-series (oxidant type) I-type. Chemically، these granitoids are metaluminous، alkali-calcic to alkali and shoshonite to ultrapotassic. Enrichment of LREE، relative to HREE and enrichment of LILE (Sr، Cs، Rb، K and Ba) relative to HFSE (Nb، Ta، Ti، Hf and Zr) indicate that the magma formed in island arc setting. This magma originated from low partial melting

Sarcheshmeh porphyry copper deposit is located 65 km southwest of Rafsanjan in Kerman province. The Sarcheshmeh deposit belongs to the southeastern part of Urumieh-Dokhtar magmatic assemblage (i. e.، Dehaj-Sarduyeh zone). Intrusion of Sarcheshmeh granodiorite stock in faulted and thrusted early-Tertiary volcano-sedimentary deposits، led to mineralization in Miocene. In this research، the mass changes and element mobilities during hydrothermal process of potassic alteration were studied relative to fresh rock from the deeper parts of the plutonic body، phyllic relative to potassic، argillic relative to phyllic and propylitic alteration relative to fresh andesites surrounding the deposit. In the potassic zone، enrichment in Fe2O3 and K2O is so clear، because of increasing Fe coming from biotite alteration and presence of K-feldspar، respectively. Copper and molybdenum enrichments resulted from presence of chalcopyrite، bornite and molybdenite mineralization in this zone. Enrichment of SiO2 and depletion of CaO، MgO، Na2O and K2O in the phyllic zone resulted from leaching of sodium، calcium and magnesium from the aluminosilicate rocks and alteration of K-feldspar to sericite and quartz. In the argillic zone، Al2O3، CaO، MgO، Na2O and MnO have also been enriched in which increasing Al2O3 may be from kaolinite and illite formation. Also، enrichment in SiO2، Al2O3 and CaO in propylitic alteration zone can be attributed to the formation of chlorite، epidote and calcite as indicative minerals of this zone.

Manganese ore deposits occurred in various types of syngenetic، diagenetic and epigenetic mineralization in association with radiolarian cherts in colored melange of Neyriz ophiolite in Abadeh Tashk area، eastern Fars Province. Microscopic study and XRD analyses show a simple mineralogy for manganese compounds in all types. Psylomelane and braunite are the primary manganese compounds in syngenetic type that are found as alternative bands with amorphous silica and quartz in a sedimentary environment. Braunite and bixbite occur in lens shape deposits، showing diagenetic type of mineralization that formed in fold hinges during diagenesis process. Pyrolusite، auororite and rancieite are major minerals of epigenetic type that formed during remobilization and reprecipitation of manganese compounds in radiolarian cherts from upper horizons as open space fillings by supergene processes. Manganese ores show low values of TiO2 (0. 012-0. 13 %)، Fe/Mn (0. 02-5. 45) and Al2O3 (0. 019-2. 13) and high values of Si/Al (21. 84-427. 46). The ores contain low contents of Co (31-131 ppm)، Cu (17-277 ppm) and Ni (12-193 ppm) and have negative anomalies of Ce and positive Eu، low total REE and enriched LREE compared to HREE، indicating that primary manganese compounds and host cherts formed close to mid oceanic ridges above seafloor hydrothermal fluid channels.

Misho intrusions outcrop in the southern part of North Tabriz fault، east Misho Mountains، NW Tabriz. Filed studies، petrological and geochemical data show that both mafic and felsic rock types occur in the area. Mafic rocks include gabbro consisting of plagioclase، clinopyroxene، olivine and opaque minerals and felsic bodies consist of alkali granite with K-feldspar، quartz، plagioclase and a few grains of biotite and amphibole. Mafic rocks have higher enrichment in LREEs than in HREEs. Also، the mafic rocks are rich in LILEs and poor in HFSEs. Geochemical characteristics of the gabbros show that they formed as a result of interplay between a depleted asthenospheric mantle and an upwelling mantle plume، while granitic rocks are alkaline and metaluminous to peraluminous rich in LILEs especially Rb and Th and poor in Nb، Sr، Eu، Ba،Ti. Geochemical characteristics of the granites belong to A-type granites and A2 subgroup that formed in an extensional tectonic setting of the post collision in active continental margin by lower crustal melts.

Zafarabad iron deposit is located northwest of Divandareh، in the northern margin of Sanandaj-Sirjan plutonic-metamorphic zone. The deposit is in lentoid to tubular shape، within a shear zone and occrrued in host rocks of calc-schist and limestone. Magnetite with massive، cataclastic and replacement textures are the main phases، while pyrite and other sulfide minerals are found. Major and trace elements are measured by ICP-MS and ICP-AES methods. Based on some ratios of trace elements in the ore samples and (Ti+V vs. Cal+Al+Mn and Ti+V vs. Ni/(Cr+Mn)) diagrams which are used for classification of iron deposit types، Zafarabad iron deposit fall in the range of skarn deposits. Spider diagrams show a steady decline from LREE to HREE elements with Eu (mean value of 0. 06 ppm) and Ce (mean value of 0. 94 ppm) negative anomalies. Comparing the distribution patterns of REE for the Zafarabad magnetites with those of various types of iron deposits shows that the REE pattern for Zafarabad is similar to these deposits. Analysis of calculated parameters for REE shows that the hydrothermal fluids responsible for mineralization are mainly of magmatic origin through fractionation and crystallization processes of a deep iron rich fluid phase and its emplacement within the carbonate rocks، forming iron skarn.

Determining the promising area for ore deposits is one of the most important steps of prospecting in regional scales. There are many different methods for identifying these areas including geochemical and geophysical methods، remote sensing and sophisticated statistical methods. Based on the theory of spatial relations between the dispersion pattern of ore deposits and metallogenic provinces، mineralization belts، faults and structural factors، some new interpretative methods can be proposed in the preliminary exploration phase of the potential areas. In this study، the geostatistical methods were used، where the spatial location of faults and known metallic deposits were considered as the primary source of data to obtain their correlation (case study of metallic deposits in Yazd province). The research was performed on 807 major and minor faults and 76 metallic deposits، mainly from hydrothermal origins. The data was arranged in ArcViewGIS software environment. The geostatistical analysis was performed by defining the regionalized variable (distance between faults and deposits) in a Mathematica subroutine. Variography operations، in order to find the spatial structure، were performed on regionalized variable using Surpac software. It was also shown that the theory of spatial correlation was valid for the defined variable. In this work، the variography operation was used to find the direction and the range of the effect of faults and deposits. Variograms indicated that the possibility of ore deposits existence in an area could depend on the direction of the faults. By drawing the directional variogram and variogram map، the best stretches for more exploratory studies is shown to be parallel along the Azimuth 130◦ and 64 km distance. By revealing the spatial structure in different directions، the area of mineralization related to the faults and the number of ore deposits associated with major faults have been marked.

Kalateh Ahani is located 27 km southeast of Gonabad within the Khorasan Razavi province. The area is part of Lut Block. Sub-volcanic monzonitic rocks intruded regional metamorphosed Shemshak Formation (Jurassic age). Magnetic susceptibility of less altered monzonitic rocks is < 25 ×10-5 SI، therefore they belong to reduced type ilmenite granitoid series. Both intrusive and metamorphic rocks are altered to argillic، propylitic، silicification and some iron oxides. Argillic alteration is dominant within the intrusive rocks. Two major quartz sulfide (sulfides are oxidized) veins trending NW-SE are recognized within the study area. Based on core logging، both disseminated and veinlet mineralization types are recognized within the intrusive and metamorphic rocks. Eight types of veinlet and vein are identified within the intrusive rocks. Maximum density of the veinlets is about 35 per meter within the biotite monzonite porphyry. Hypogene minerals include pyrite، chalcopyrite، sphalerite، galena and quartz. Secondary minerals comprise malachite، hematite، chrysocolla، goethite and gangue minerals are quartz and siderite. Rock geochemistry shows high anomalies of Cu، Pb، Zn، Sn، As، and Au both in the surface and within the mineralized core. Cu > 0. 6%.، As، Pb and Zn > 1%، Au up to 150 ppb and Sn = 133 ppm. The Sn content of vein in the northern part of Kalateh Ahani (Rud Gaz) is > 1%. Based on mineralization، alteration and geochemistry، it seems that Sn mineralization is associated with the Cretaceous monzonitic rocks. Zircon U–Pb dating indicates that the age of the monzonitic rocks associated with mineralization is 109 Ma (Lower Cretaceous). Based on (87Sr/86Sr) i = 0. 71089-0. 710647 and (143Nd/144Nd) i = 0. 512113-0. 51227 of the monzonitic rocks، the magma for these rocks were originated from the continental crust. This research has opened new window with respect to Sn-Cu mineralization and exploration within the Lut Block which is associated with Cretaceous granitoid rocks (reduced type، ilmenite series) originated from the continental crust.

The Shahabad gabbroic intrusion، with NW-SE trend cropped out at the boundary of Zagros and Sanandaj-Sirjan zones is composed of olivine gabbro، orthogabbro and troctolite. Plagioclase، clinopyroxene and olivine are the main minerals; and magnetite، titanomagnetite and serpentine are minor and secondary minerals. Microprobe analyses of the minerals show that plagioclase is labradorite، pyroxene diopsidic augite and olivine، chrysolite. The rocks appear to have calc-alkaline and metaluminous nature. The plots of some trace elements and composition of clinopyroxenes in the tectonic discrimination diagrams indicate a volcanic arc environment. In addition، spider diagram pattern of elements shows Sr enrichment and Ti، Nb، Zr and P depletion، typical characteristics of volcanic arc subduction related magmas. Furthermore، close similarity between the patterns of spider diagram for the Shahabad pluton with those of Andean basic rocks suggests that the Shahabad calc-alkaline basic magma may have formed in a subduction environment. Based on geological، geochemical and mineralogical features، formation of the gabbros، as a part of ophiolite mélange، is attributed to a suprasubduction system.

Alteration of ophiolitic ultramafic rocks، formation of listwaenite and associated mineralization are interesting phenomena of metallogeny of Khoy ophiolite. It seems that the hydrothermal circulations responsible for mercury mineralization were derived from geothermal systems caused by intermediate to acidic magmatism in Neogene-Pleistocene time. Reactivation of brecciated serpentinite with hydrothermal solutions led to the silica-carbonate hydrothermal alteration and formation of listwaenite. The importance of these alteration types is due to associated Hg-Au mineralization. Based on the microscopic mineralogical studies، XRD analysis، geochemical characteristics and field relationships، three types of listwaenite including silica، silica-carbonate and carbonate have been recognized. Tavreh mercury occurrence has formed in relation with silica type listwaenite which also named as birbirite. Alteration zones have structural controls and are restricted to shale (marl) /serpentinite fault type contacts. Mineralogically، silica type listwaenite mainly consists of quartz، chalcedony، opal and secondary iron hydroxides. Magnesite، dolomite، calcite and clay minerals are the minor phases. Toward silica-carbonate and carbonate listwaenites، silica minerals decrease while carbonate minerals increase. Geological field relations and existence of residual chrome spinel in the listwaenite of Tavreh area confirmed the ultrabasic host rock. Based on geochemical studies، average values of SiO2، Fe2O3، MgO and L. O. I as the main components of silica listwaenite are 82. 6، 6. 99، 1. 02 and 3. 74 wt %، respectively. Among rare elements، average values of Hg، Pb، As and S have been obtained as 646. 2 ppm، 517. 7 ppm، 329. 1 ppm and 281 ppm، respectively. Mass changes (gains and losses) of major and minor elements during the alteration process in the Tavreh area have considered، using Gresens’ equation in this study. Cinabar-bearing silica listwaenite is enriched in SiO2، Al2O3، K2O and Hg components and is depleted in MgO and MnO. Silica-carbonate type shows enrichment in CaO، Na2O، Al2O3، K2O and TiO2 and deplection in MgO، MnO P2O5، SiO2، Cr2O3 and Fe2O3. Carbonate type shows increase in CaO and Sr and reduction in SiO2، Na2O، MgO، Al2O3، Fe2O3، TiO2 and MnO.

The Tajroud vein system is located 190 km southwest of Mashhad، and in the southern part of the Sabzevar zone. The vein host rocks consist of Eocene intermediate to silicic volcanic rocks. The mineralization occurs as open space filling، taking place as veins، veinlets and hydrothermal breccias. Based on field geology and textural evidence، three main stages of mineralization were identified. Stage I mainly contains quartz، pyrite، chalcopyrite and magnetite. Stage II، which has the same mineral assemblage as stage I، is the most important stage in terms of volume. Finally، stage III is characterized by repetitive quartz and calcite banding with negligible amounts of sulfide minerals. Hydrothermal alteration is developed around the veins and tends to be more intense in the vicinity of the veins. The plot of the Ishikawa alteration index (AI) versus chlorite-carbonate-pyrite index (CCPI)، known as alteration box plot، displays three main alteration trends. The hydrothermal alteration assemblage of quartz، adularia، chlorite، illite، calcite، and epidote that envelops the Tajroud vein system formed from the upwelling of near-neutral to weakly alkaline hydrothermal solutions. The mineralogic، alteration and geochemical characteristics of the studied area and comparison with epithermal ore deposits indicate that the Tajroud vein system represents an epithermal system of low-sulfidation type.