فصلنامه زمین شناسی اقتصادی
سال سوم شماره 2 (پیاپی 5، پاییز و زمستان 1390)

Most skarn deposits are directly related to magmatic activity، and there is a systematic correlation between composition of causative plutons and the metal contents of the related skarns. Darreh Zerreshk deposit is located in southwest of Yazd. Petrological and geochemical studies show that Darreh Zerreshk granitoid ranges in composition from granite through quartz monzodiorite and has subalkaline، calc-alkaline and metaluminous to prealuminous characteristics like most worldwide skarn granitoids. This study shows that geochemical characteristics of the Darreh Zerreshk granotoid rocks are similar to granitoids of Millstream Cu-Fe skarn deposit in Canada، Fe skarns in British Columbia and Au-Cu skarns in the RioNarcea gold belt in Spain. The similarity between REE patterns in Darreh Zerreshk intrusion and skarns also confirms the strong petrogenetic relationship between magmatic and skarnization processes.

Nain ophiolite melange is located 140 Km east of Isfahan. Based on the geological studies، this area belongs to Mesozoic ophiolite of Urumieh – Dokhtar zone، west of central Iran. Country rocks are pridotite and serpentinized pridotite. The pridotite rocks are composed of Harzburgite، Lherzolite and replacement Dunite which is belong to spinel pridotite facies. Paragenesis of ore minerals are Chromite، Irarsite، Magnetite، Hematite، Pentlandite، Millerite، Chalcopyrite، Pyrite، and Covelline. Geochemical surveys of host rock and chromite show tholeiite series of magma and alpine type chromite. PGE (Ir، Pt، Pd، and Os) are enriched in chromite. REE spider diagram pattern show the processes of boninitic magma and partial melting.

The study area is located south of Ghonabad in Eastern Iran. This area is situated between two major faults، Darouneh to the north and Dashtbyaz to the south. The movements of these faults cased major dislocation of this block. Najmabad granodiorite to granite batholith is elongated trending east-west 2×8 Km2. Mineralization is associated with granite and monzonite. Alteration zones are: propylitic، sericitic، argillic and silicification. Chemically، granite-granodiorite is met-aluminous،، spider diagram normalized to lower continental crust show enrichment of LILE such as Rb، Cs، K and LREE (La، Ce)، depletion of Ti، Sr، Ta، Nb، Ba، Cs. Based on low values of magnetic susceptibility [(5 to 11) × 10-5 SI]، therefore it is classified as belonging to the ilmenite-series (reduced type). The result of U-Pb zircon age dating of granodiorite is 161. 85 Ma (Middle Jurassic، Callovian time). Based on Initial εNd isotope values for granodiorite is -6. 51، initial 87Sr/86Sr and 143Nd/144Nd ratios for granodiorite is (0. 70913 and 0. 512095)، the magma for granite and granodiorite originated from the continental crust. During Middle Jurassic (Callovian) due to continental collision، Upper Triassic to Lower Jurassic rocks is regionally metamorphosed. During the continental collision، Middle Jurassic (164-162Ma) reduced type granitoid magma (Ilmenite series، continental crust melting) formed and intruded these regional metamorphosed rock in Najmabad، Shah Kuh and Sorkh Kuh area.

Groundwaters hydrochemistry of Ayrakan and Cheshmeh Shotori areas and geochemistry of rare earth elements، indicate Ayrakan alkali granite as the origin of uranium and other dissolved elements in groundwaters of these areas. Geochemical and hydrogeochemical studies as well as the trend of uranium and thorium transition and mobility in aqueous environments of these areas indicate uranium adsorption by iron hydroxide (goethite) as the deterrent agent against uranium transition and mobility from depth to surface. Gamma-ray spectroscopic study of sediments from Cheshmeh Shotori area by HPGe detector indicates the presence of 226Ra in high contents and as the radioactive nuclide that is the reason for high activity of these sediments. Production of 226Ra from 238U decay، shorter half-life of 226Ra compared to 238U، radium transition by groundwaters from depth to surface as well as hydrogeochemical evidences، all suggest the possibility of existence of hidden uranium deposit and uranium mineralization in depth and the distance between Ayrakan and Cheshmeh Shotori areas.

Kajal kaolin deposit is located ~20 km northwest of Hashtjin، Ardebil province. Field evidence and laboratory investigations show that the deposit is an alteration product of ignimbrites، tuffs، and trachy-andesites of Eocene age. According to mineralogical data، the major rock-forming minerals include kaolinite، montmorillonite، polygorskite، orthoclase، zeolite (stilbite)، quartz، and chalcedony. Mass change calculations of elements، with assumption of Ti as immobile monitor element، indicate that leaching and fixation are two prominent regulators for concentration of major، minor، trace، and rare earth elements in the deposit. The distribution pattern of REEs، normalized to ignimbrite، in kaolin samples illustrates a weak fractionation of LREEs from HREEs coupled with strong negative Eu anomaly during the evolution of the deposit. Calculations of correlation coefficients among elements show that there is a high intrinsic correlation between HREEs in the studied samples. According to geochemical indices، it can be inferred that the hypogene alterations are superimposed by supergene ones in the course of evolution of the deposit. In accordance with the mode of distribution of elements in the deposit، it appears that the behavior of elements during kaolinization of ignimbrites was affected by the function of factors such as pH، redox potential، temperature variations، high fluid to rock ratio، preferential adsorption by clays and iron oxides، discrepancies in the stability rate of minerals، abundance of complex-forming ions (CO32-، F־، Cl־، PO43-، and SO42-)، and isomorphic substitution. The obtained results indicate that epithermal acid-sulfate solutions along with acidic supergene solutions originated from oxidation of hypogene pyrites played an important role in development of the deposit. Further geochemical considerations show that clay minerals along with secondary phosphates like monazite، rabdophane، and xenotime are the potential hosts for REEs in the deposit.

Mercury mineralization has occurred in relation with a listwaenitic type hydrothermal alteration system in Tavreh area located northwest of Khoy. Mercury-bearing alteration zone which has an area about 0. 4 km2 is situated in one of Aland river upstreams. The only mercury compound found in this district is mercury sulfide (cinnabar) deposited as vein and veinlet forms. Geochemical investigations indicate that mercury distribution has variable values which vary between 0. 36-10500 ppm. Its average in alteration zone is 300 ppm، although its average reaches to 0. 35 percent in the mineralized veins. Considering the Clarke amount of mercury، it has increased more than 3750 times in overall alteration zone and more than 46000 times in mineralized veins. Based on the stream sediment heavy mineral geochemistry، distribution of cinnabar under physical weathering and transportation processes has occurred at least 7 km far away from the altered zone in downstream sediments. Mercury concentrations in samples taken from surface and underground waters are less than 0. 1µg/L. In comparison with mercury concentrations، data obtained from other world’s ore fields and considering the maximum permissible contaminant level in drinking waters، it can be concluded that the waters of this region have not been contaminated in mercury. Therefore، despite the extent of anomalous zone in Tavreh region، this zone cannot play a role as the contaminant source of environment. It is seemed that due to presence of mercury as stable mercury sulfide compound، the possibility of its leakage could not been obtained due to decomposition of this mineral.

Neyshabour turquoise mine is located in northwest of Neyshabour، southern Quchan volcanic belt. Eocene andesite and dacite forming as lava and pyroclastic rocks cover most of the area. Subvolcanic diorite to syenite porphyry (granitoids of magnetite series) intruded the volcanic rocks. Both volcanic and subvolcanic rocks are highly altered. Four types of alteration are recognized including: silicification، argillic، calcification and propylitic. Silicification is dominant followed by argillic alteration. Mineralization is present as stockwork، disseminated and hydrothermal breccia. Hypogene minerals are pyrite، magnetite، specularite، chalcopyrite، and bornite. Secondary minerals are turquoise، chalcocite، covellite، and iron oxides. A broad zone of gossan has developed in the area. Oxidized zone has a thickness of about 80 m. Mineralized samples show high anomalies of Cu، Au، Zn، As، Mo، Co، U، LREE، Nb، and Th. Both aeromagnetic and radiometric (U and Th) maps show very strong anomalies (10 × 5km) within the mineralized area. Based on geology، alteration، mineralization، geochemistry، and geophysics، Neyshabour turquoise mine is a large Iron oxide Cu-Au-U-LREE (IOCG) mineralized system. In comparison with other IOCG deposits، it has some similarities with Olympic Dam (Australia) and Candelaria (Chile). In comparison with Qaleh Zari and Kuh Zar mines، Neyshabour turquoise mine is the first Iron oxide Cu-Au-U-LREE (IOCG) mineralized system discovered in Iran

The Dehbid magnetite deposit is located in northeastern part of Fars province، in the southern border of Sanandaj-Sirjan metamorphic zone. The mineralization occurred as veins and lenses along NW-SE faults. The ores are mainly hosted in silicified dolomite of early Mesozoic (Triassic). Mineralogical studies show that the ores are dominated by magnetite and minor hematite with massive texture occurring as cement of angular remnants of silicified host dolomite. According to geochemical data، Fe2O3 content in the mineralized zones show extensive variation between 34 to 75 wt %. The P، Ti، Cr and V contents of the iron ores are remarkably low and Co/Ni، Cr/V and LREE/HREE ratios، positive Eu anomalies، negative Ce anomalies، Eu/Sm = 1، along with field and textural observations of Dehbid ores indicate that the deposit belongs to the class of hydrothermal iron ores. At Dehbid، the magnetite ores are formed as open space fillings. The sparse rhyolites and basalts in the area may be regarded as the origin of iron and heat in the hydrothermal system. A decrease in temperature and likely pressure due to fluid mixing are the major causes of iron oxide deposition.

The Zonouz kaolin deposit is located ~15 km northeast of Marand، East-Azarbaidjan province. Based on physical features in field investigations، such as color، five distinct kaolin types including (1) white، (2) lemon، (3) gray، (4) brown، and (5) yellow are distinguished in the deposit. Field evidence and petrographic studies indicate that the deposit is genetically close to trachy-andesite rocks. According to mineralogical data، the deposit contains quartz، kaolinite، montmorillonite، calcite، pyrophyllite، chlorite، muscovite-illite، dolomite، hematite، and anatase minerals. Geochemical data indicate that function of alteration processes on trachy-andesite rocks during development of Zonouz ore deposit was accompanied by leaching of elements such as Al، Na، K، Rb، Ba، V، Hf، Cu، Zr، Tm، Yb، and Lu، enrichment of elements such as U، Nb، and Ta، and leaching-fixation of elements such as Si، Fe، Ca، Mg، Ti، Mn، P، Cs، Sr، Th، Co، Cr، Ni، Y، Ga، LREE، Tb، Dy، Ho، and Er. Incorporation of obtained results from mineralogical and geochemical studies show that physico-chemical conditions of alteration environment، the relative stability of primary minerals، surface adsorption، preferential sorption by metallic oxides، existing of organic matters، scavenging and concentration processes، and fixation in neomorphic mineralogical phases played important role in distribution of elements in the deposit. Geochemical studies show that development of the deposit is relative to two types of processes، (1) hypogene and (2) supergene. The distribution pattern of REEs indicates that differentiation degree of LREEs from HREEs in supergene kaolins is more than hypogene kaolins. Geochemical studies indicate that minerals such as Mn-oxides، zircon، anatase، hematite، cerianite، and secondary phosphates (monazite، rhabdophane، churchite، and zenotime) are the potential hosts for rare earth elements in this deposit.