Journal of Economic Geology

1-27

Authors: Mohammad Hassan Karimpour; Azadeh Malekzadeh Shafaroudi; Lang Farmer; Chak Stern

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 calc-alkaline to adakite except Najmabad that plot in the adakite field. Based on low content of Nb (30), low initial 87Sr/86Sr (17 ppm), low ratio of Zr/Nb (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* (

47-58

Authors: Rasool Ferdowsi; Ali Asghar Calagari; Ghader Hosseinzadeh; Ghahraman Sohrabi

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 420-550°C and ¦O2=10-22-10-25. Retrograde stage was accompanied by some physicochemical changes (decrease in temperature to <420°C and increase in ¦S2) which caused the alteration of pre-existing anhydrous calc-silicates to hydrous calc-silicates (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.

77-107

Authors: Maryam Abdi; Mohammad Hassan Karimpour

The Kuh Shah prospecting area is located in Tertiary volcano-plutonic belt of the Lut Block. More than seventeen subvolcanic 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 stockwork veinlets. Intrusive rocks are metaluminous, 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 εNd) and geochemical data suggest that the Kuh Shah granitoid rocks formed from depleted mantle in a subduction-related 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-stockwork-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.

123-134

Authors: Adel Saki; Hoshang Purkaseb

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 THERMOCALC® 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.

155-168

Authors: Babak Talaei; Ali Abedini

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.