JOURNAL OF ECONOMIC GEOLOGY
Year:2012 | Volume:4 | Issue:1|Papers Count:10

Tertiary intrusive granitoids within the Lut block in the Khorasan Razavi and South Khorasan provinces are mainly sub-volcanic with porphyry texture and their composition varies from granite to diorite but monzonite is dominant. With the exception of Hired, these are classified as belonging to the magnetite-series of I-type granitoids. Chemically, these rocks are meta-aluminous. Those with mineralization are K-rich and those without mineralization such as Najmabad are Na-rich. All intrusive rocks plot in the field of calcalkaline to adakite except Najmabad that plot in the adakite field. Based on low content of Nb (<5 ppm), high ratio of Zr/Nb (>30), low initial 87Sr/86Sr (<0.705), and high initial eNd value (+5.2), Najmabad magma originated from a subduction zone and is less contaminated with continental crust. In contrast, based on high content of Nb (>17 ppm), low ratio of Zr/Nb (<2), high initial 87Sr/86Sr (>0.707) and low initial εNd value (-3), magmas in the Kaybar-Kuh were more contaminated in the continental crust. Based on depletion in HREE and high ratio of (La/Yb)N (17-23), magma in Najmabad originated in the deep region in which garnet was present. Based on REE pattern and ration of Eu/Eu* (0.8-1), intrusive rocks within Maherabad, Khoopik, Chah-Shaljami, Kuh Shah and Dehsalm are calc-alkaline and their magma formed in an oxidant condition whereas Kaybar Kuh magma with low ratio of Eu/Eu* (<0.8) was contaminated in the continental crust under reduced conditions.The age of these granitoids is between Middle Eocene and Lower Oligocene. Kaybar-Kuh (43.3 Ma) is situated in the north and Chah-Shaljami (33.3 Ma) in the south. The initial 87Sr/86Sr ratios decrease from north (0.7077) to south (0.7047) as the age decreases.eNd of Maherabad, Khoopik, Dehsalm, and Chah-Shaljami granitoids is between +0.5 and +2.49 and the initial87Sr/86Sr ratio is less than 0.7055. The age of the source rock (TDM, which was calculated based on Sm-Nd isotopes) indicates that these magma originated from oceanic crust with different ages. Kaybar-Kuh originated from the oldest oceanic crust (840 Ma) and was contaminated more in continental crust, but Najmabad originated from a younger oceanic crust (360 Ma) with minor contamination. Dehsalm and Chah-Shaljami magma which had some differences with Maherabad and Khoopik, originated from oceanic crust of 200 Ma.The period between 42 and 33 Ma (Middle Eocene to Lower Oligocene) is the most important stage of mineralization in eastern Iran especially in South Khorasan. Some of the major systems, which are identified so far are: porphyry Cu-Au, reduced intrusive related Au, high sulfidation Au, Fe- skarn, Pb-Zn-Sb vein and IOCG deposits. Granitoid rocks formed between 42 and 33 Ma within the Lut block and northern area has great potential for exploring porphyry Cu-Au, IOCG, Fe, Pb-Zn, Au etc.

The Gheshlagh bauxite deposit is located 110 km southeast of Gorgan. The deposit has been developed as a strati form horizon with more than 2 km length and a thickness of about 25 m along the contact of Ruteh and Elika carbonate formations. Textural analysis indicates both allochthonous and autochtonous origins for the bauxites. Bohemite, diaspore, anatase, rutile, hematite, goethite, kaolinite, svanbergite, pyrite, and quartz were identified in the ore paragenesis. Based on textural and mineralogical evidence, the deposit can be divided into five distinct units including upper bauxite, upper kaolinite, hard bauxite, lower kaolinite and lower bauxite. Accumulation coefficients of trace elements and geochemical indices such as Ti/Cr, TiO2/Al2O3, Zr/Ti and Nb/Y, combined with the geological evidence suggest the basaltic rocks of the Soltanmeidan Formation as the main source of bauxite materials. Combination of mineralogical and geochemical data shows that the deposit formed in two main stages. First, bauxite materials, Fe and Ti oxides and clay minerals developed as authigenic bauxitization processes of basaltic parent rock. Then, these materials were transported to karst depressions and were accumulated as a bauxite horizon.

Kamtal skarn is located 15 km northeast of Kharvana, East-Azarbaijan. A quartz-monzonitic stock of Oligocene age intruded the upper Cretaceous sedimentary sequence (claystone, limestone, marl, and siltstone) developing noticeable metamorphic (marble, hornfels) and metasomatic (skarn) alteration zones along the contact. Kamtal skarn is of calcic type and consists of both endoskarn and exoskarn zones.Exoskarn includes two zones of garnet skarn and epidote skarn. Skarnification processes are divided mainly in two major stages(1) prograde and (2) retrograde. During prograde stage, the emplacement of intrusive body caused isochemical metamorphism of the wall rocks and developed marble and hornfels units in enclosing rocks. Crystallization of intrusive body led to evolvement of hydrothermal fluid phase which infiltrated into enclosing rocks. Reaction of these fluids with the early-formed metamorphosed wall rocks brought about extensive progressive metasomatic alteration characterized by the formation of anhydrous calc-silicate minerals such as garnets and pyroxenes at a temperature range of 420-550oC and ¦O2=10-22-10-25. Retrograde stage was accompanied by some physicochemical changes (decrease in temperature to<420oC and increase in ¦S2) which caused the alteration of pre-existing anhydrous calc-silicates to hydrous calcsilicates (epidote, and tremolite-actinolite), silicates (quartz, chlorites, and other clay minerals), oxides (magnetite and hematite), sulfides (pyrite, chalcopyrite, and tetrahedrite), and carbonate (calcite).Comparison of Kamtal skarn with some other ones of corresponding type from Iran and other countries shows that Kamtal skarn well resembles to Anjerd and Pahnavar skarns in East-Azarbaijan.

The study area is located at northwest of Sarbisheh in South Khorasan province and eastern border of Lut block. In this area, Tertiary (Eocene-Oligocene to Pliocene) volcanic rocks consisting of basaltic andesite, dacite, rhyodacite, vitreous rhyolite (perlitic in some parts), tuff and ignimbrite are exposed. In the Daghar Mountain, A, B and C perlite layers with thicknesses of 102, 7 and 58 meters respectively, occur alternatively with volcanic-pyroclastic rocks. Zoning, sieve texture and embayment of plagioclase and roundness of minerals in the lavas indicate disequilibrium conditions during magma crystallization.Chemically, these are meta-aluminous, medium to high-K calc-alkaline, enriched in LILE and negative anomaly for Nb and Ti. Chondrite-normalized Rare Earth Elements (REE) plots indicate enrichment of light REE in comparison with heavy REE, (La/Yb)N of 9.14-12.64, low negative anomaly for Eu in basaltic andesite (Eu/Eu*=0.91) and dacite (Eu/Eu*=0.78-0.87) and strong negative anomaly for Eu in the rhyolites (Eu/Eu*=0.18-0.35). Negative anomaly for Eu indicates calc-alkaline nature for these rocks. On the basis of chemical characteristics and magnetic susceptibility, these are I-type. Tectonically, the rocks belong to subduction zone and active continental margin and their parental magma originated from partial melting of enriched mantle and then crustal contamination during differentiation process. Dacites have an initial 87Sr/86Sr between 0.7048 and 0.7050 (average 0.7049) that confirm mantle source for the magma. Volcanic glasses of rhyolitic composition altered by hydration (likely meteoric water) and formed perlite. Physical tests and chemical analyses show that perlite of Sarbisheh is suitable as raw material for production of expanded perlite.

The Kuh Shah prospecting area is located in Tertiary volcano-plutonic belt of the Lut Block. More than seventeen sub volcanic intermediate to acidic intrusive rocks, diorite to syenite in composition, were identified in the study area. The intrusions are related to hydrothermal alteration zones and contain argillic, propylitic, advanced argillic, silicified, quartz-sericite-pyrite, gossan and hydrothermal breccia which overprinted to each other and are accompanied by weathering which made it complicated to distinguish zoning. Mineralization is observed as sulfide (pyrite and rare chalcopyrite), disseminated Fe-oxides and quartz-Fe-oxide stock work veinlets. Intrusive rocks are met aluminous, calc-alkaline with shoshonitic affinity with high values of magnetic susceptibility. The Kuh Shah intrusive rocks are classified as magnetite-series of oxidant I-type granitoids. Based on zircon U–Pb age dating, the age of these granitoid rocks is 39.7±0.7 Ma (Middle Eocene). The radioisotope data (initial 87Sr/86Sr and 143Nd/144Nd ratios as well as eNd) and geochemical data suggest that the Kuh Shah granitoid rocks formed from depleted mantle in a subductionrelated magmatic arc setting. Geochemical anomalies of elements such as Cu, Au, Fe, Pb, Zn, As, Sb, Mo, Bi, Hg and also Mn, Ba, Te and Se, correlated with quartz-sericite-pyrite, gossan-stock work-hydrothermal breccias, irregular silicified bodies and advanced argillic hydrothermal alteration zones. Geophysical anomalies correlated with hydrothermal alteration and mineralization zones. The interpretation of the results represents complex patterns of sub-circular to ellipsoid shape with north-east to south-west direction. These evidences are similar to the other for known Cu-Au porphyry and Au-epithermal systems in Iran and worldwide.

Tashtab Mountain is located 25 km from the city of Khur in northeastern Isfahan province. Several bentonite mines formed in this area as a result of the Eocene volcanic alteration. These mines are classified as the Khur bentonite horizon. Studies on trace elements in parent rock and clays show that the studied bentonites formed from andesite-basaltic parent rocks. The XRD analysis shows that studied clay minerals consist of Namontmorillonite with a low amount of kaolinite. In addition, there are quartz, calcite and crystobalite. The alteration process leached most of major and trace elements. Most of removing in major elements happens in alkaline elements, and in trace elements LILEs show most of depletions. Al and Ti are immobile elements and show lower amount of changes. Cu is the metal that shows most depletion among other metal elements in contrast Ni, Cr and Zn shows a little enrichment also, the trend of REEs is similar to parent rock with a difference. HREEs are more depleted than LREEs. It may happen because of leaching of HREEs as complexes and absorbing of LREES into the clay minerals structure.

The Cheshin meta-calcareous rocks (Permo Triassic) in southeast Hamedan outcrop in association with a variety of pelitic schists and hornfels rocks. The intrusion of the Alvand Batholith (Jurassic age) into pelitic and calcareous host rocks has produced metamorphic rocks in the Hamedan area (Cheshin village). On the basis of the dominance of calcite/dolomite, silicate and ore minerals, the calcareous rocks can be divided into two groups: a) marbles and calc-silicates; b) skarn rocks. The ore bodies occur in a contact zone between sillimanite-hornfels and calc-silicate rocks and formed the skarn rocks. Based on mineralogy, skarn rocks in the studied area consist mainly of diopside, garnet, tremolite, vesuvianite, epidote and ore minerals (magnetite and hematite). The skarnification processes occurred at two stages: (1) prograde metamorphism, and (2) retrograde metamorphism. The first stage involved prograde metasomatism and anhydrous minerals such as garnet and pyroxene formed. Second stage of retrograde skarn development is also recognized. In addition to Fe, Si and Mg, substantial amounts of Fe, along with volatile components were added to the skarn system. Consequently, considerable amounts of hydrous minerals, oxides and carbonates replaced the anhydrous minerals in the host rocks and hydrous minerals such as epidote+chlorite+amphibole formed.Using multiple equilibria by THERMOCALCÒ program, temperature (~630 oC), pressure (~4 kbar), and fluid composition (XCO2 as low as 0.17) have been calculated for the formation of the calc-silicate rocks.Skarn mineralogy shows good agreement with these calculations.

The study area is located in southeastern Iran, about 110 km southwest of Kerman. Geologically, the area is composed of ophiolitic rocks, volcanic rocks, intrusive bodies and sedimentary rocks. Vein mineralization within andesite, andesitic basalt, andesitic tuffs occurred along the Chahar Gonbad fault. Sulfide mineralization in the ore deposit has taken place as dissemination, veins and veinlets in which pyrite and chalcopyrite are the most important ores. In this area, argillic, phyllic and propylitic alteration types are observed. Such elements as Au, Bi, Cu, S and Se are more enriched than others and the enrichment factors for these elements in comparison with background concentration are 321, 503, 393, 703 and 208, and with respect to Clark concentration are 401, 222, 532, 101 and 156, respectively. According to multivariate analysis, three major mineralization phases are recognized in the deposit. During the first phase, hydrothermal calcite veins are enriched in As, Cd, Pb, Zn and Ca, the second phase is manifested by the enrichment of sulfide veins in Cu, Au, Ag, Bi, Fe and S and the third phase mineralization includes Ni, Mn, Se and Sb as an intermediate level between the two previous phases.

Qahr-abad fluorite deposit is located 58 km southeast of Saqqez, in northwestern Kordestan province and in northern end of Sanandaj-Sirjan Zone. The factors such as change in physicochemical conditions of mineralization environment (pH and Eh), variation in pressure and temperature, alteration, metamorphism, oxidation of organic matters, adsorption, activity and solubility of associated anions, residual enrichment, and leaching of clay minerals have played important roles in distribution of major, trace and rare earth elements as well as development of the deposit. Further geochemical consideration using distribution of rare earth elements indicates that the bulk contents of REE in the samples are few and violet fluorites formed in early-stage mineralization along with enrichment of LREE (as a result of assimilation and replacement of wall rock) and blue and colorless fluorites in the late-stage mineralization along with enrichment of MREE and HREE (as a result of recrystallization and remobilization). The mineralization of violet fluorites in the deposit occurred in a relatively oxidizing-basic condition, while colorless to light yellow and blue to greenish blue fluorites occurred in a relatively reducing-acidic condition. Using Tb/Ca vs. Tb/La diagram, it can be deduced that fluorites are from hydrothermal types and the genetic model for the deposit is as replacement in carbonate rocks.