JOURNAL OF ECONOMIC GEOLOGY
Year:2014 | Volume:6 | Issue:1|Papers Count:12

The base (Cu–Pb–Zn) and precious metals (Ag±Au) mineralization at the No. 4 anomaly of Golojeh deposit occurred in volcanic and sub–volcanic Eocene–Oligocene host rocks, in the central part of the Tarom– Hashtjin zone. Basic to intermediate volcanic, volcaniclastic and sub–volcanic rocks are dominated in the area and include andesite, basaltic andesite, trachy-andesite, dacite and tuff with affinity to sub–alkaline to high–potassic calc–alkaline series. The mineralization in the area with average grade of Au (0.15 ppm), Ag (0.24%), Cu (0.6%), Zn (4%) and Pb (6%) occurred in two major NW–SE trending quartz–sulfide veins (A and B) with crustiform, breccia, vein–veinlet and open-space filling structure and texture. The sulfide content varies from 5 to 60% and is dominated by galena, sphalerite, chalcopyrite and pyrite. SEM studies indicated presence of Ag (0.47 to 0.66 wt.%) and Cd (0.33 to 0.72 wt.%) in galena and Fe (0.23 wt.%) in sphalerite. Hydrothermal alteration of phyllic (quartz–sericite–pyrite), argillic (quartz–illite/muscovite) and silicification are related to mineralization. Correlation coefficient of metal pairs of Cd–Zn (0.86), Cd–Pb (0.82), Pb–Ag (0.80), Au–Ag (0.75), Pb–Zn (0.70) and Cd–Bi (0.74) was recorded in the quartz–sulfide ore–bearing veins. Microthermometric studies on two phases liquid–vapor fluid inclusions in ore–bearing veins, shows homogenization temperature to liquid (Thlv→l) in the range of 223 to 287°C and salinity of 6.5 to 17 wt.% NaCl eq. (quartz-hosted) and homogenization temperature ranging from 175 to 244°C and salinity from 1.5 to 12 wt.% NaCl eq. (sphaerite-hosted). First ice–melting temperature (Tmf) ranges of fluid inclusion in sphalerite-hosted of quartz–sulfide ore–bearing veins were recorded between −23 and −18°C in NaCl–H2O system.Vein–breccia and crustified structure and texture, presence of illite/muscovite alteration assemblage accompanied by high contents of galena, sphalerite and minor chalcopyrite and tennantite, low to moderate temperature and salinity of ore-bearing fluid, low depth of mineralization and Fe–bearing sphalerite features at the No. 4 anomaly of Golojeh deposit, are similar to those of intermediate sulfidation (IS) epithermal base and precious metals vein–type deposit that probably might be related to Cu–Au porphyry system in depth.

The Halak Abad prospect occurs in the northeastern part of Central Iran zone (Sabzevar structural zone). In this investigation, geochemical evolution, age and source of part of northeastern Iran magmatic arc (intrusive bodies) in Halak Abad area in the Khorasan Razavi province has been studied. The exposed rocks consist of volcanic rocks with andesite and dacite nature, limestone, plutonic rocks mostly diorite, quartz diorite, monzodiorite, quartz monzonite, granodiorite and granite and sedimentary rocks such as limestone, sandstone and conglomerate. Magnetic susceptibility of intrusive rocks is >100 ´ 10-5 SI, so they belong to the magnetite-series (oxidized). This magmatism is mainly low-K (tholeiite series) and meta-aluminous. The amounts of Zr, Th, Nb and Ti show depletion compared to N-MORB. Trace elements behavior shows a nearly flat pattern. Age of granodiorite body based on U-Pb zircon dating is 99.7±1.8 Ma (Mid-Cretaceous) and 87Sr/86Sr initial ratio is 0.7047. The geochemical signature and 87Sr/86Sr initial ratio in the area suggest volcanic arc magmatism in subduction zone. This magmatism has characteristic such as high Na2O (3-7 %), low K2O (0.12-1 %), high CaO (4-5.7%), low Rb (1-20 ppm), low total REE (<40 ppm), high Ba/Nb, Sm/Yb<2, (La/Yb)N<5, 87Sr/86Sr initial ratio < 0.7045 and eNd: +4.5 show differences with normal granitoids in subduction zones. Geochemical and petrological characteristics indicate melting in relatively low pressure (shallow depth). The lines of evidence demonstrate that formation of this granitoid needs a suprasubduction zone.

The Nain and Ashin ophiolites are located in northeastern Isfahan province, in western Central-East Iranian Microplate. Pillow lavas are one of the most significant Cretaceous rock units. The lower partial melting degree in mantle peridotites of Ashin ophiolite, and the derived melt by melting their clinopyroxene caused a more basic (basalt) and enriched nature for the Ashin pillow lavas, whereas higher partial melting degree and consequently incongruent melting of orthopyroxene and increment of silica in the ascending melt, together with aqueous fluids led to formation of more acidic (andesite – basaltic andesite) and depleted melts (in trace elements) in Nain ophiolite. The REE content of Nain samples have IAT chemical affinity, but the samples from Ashin show MORB characteristics. Based on petrograhic observations, lower Eu/Eu* of clinopyroxene phenocrystals of Ashin, calculated Kd of clinopyroxene together with HREE enrichment in the melt in equilibrium with clinopyroxene (especially in Ashin when compared with Nain), the plagioclase crystallization was primer and higher in comparison with clinopyroxene, especially in Ashin compared with Nain. The melt in equilibrium with clinopyroxene in Ashin was similar to MORB composition, whereas it is similar to IAT in Nain. Thus, despite the proximity of these two ophiolitic series and some field and petrographic similarities, pillow lavas from them are different from each other in both primary melt composition and the processes of differentiation and the tectonic setting.

The study area is located about 3 km southwest of the Hormoz Island in the Hormozgan province, in the Persian Gulf. The main rock units in the region consist of a highly altered acidic pluton cratophyre, which is responsible for apatite formation, diabasic dike, marl and altered basalt.Apatite is the only phosphate mineral in the Hormoz Island, which has accumulated REE in its crystal structure. The amount of Na2O and SiO2 oxides in apatite are high and the average content of the main elements Fe, Mg, Al, Ca are 7.5 ppm, 365 ppm, 2880 ppm and 27.8%, respectively. The Y, Mn, Rb contents increase and Sr decreases with increasing magmatic differentiation. It shows that a moderate magmatic differentiation occurred during the crystallization of apatite. The total REE content in the Hormoz apatite is high (1.22-2.25%). LREE/HREE ratio is also high. This means that Hormoz apatites are enriched in light rare earth elements. The REE normalized pattern shows a negative slope with a negative Eu anomaly. According to various diagrams based on apatite composition, it is deduced that the Hormoz apatites belong to mafic I-type granitoids with high oxidation state (Fe2O3/FeO>1).

Mafic and ultramafic plutonic igneous bodies, with small and big outcrops, between Shemshak rock units (Jurassic) are observed in east of Imam Zadeh Hashem, in southern Guilan province. Ultramafic cumulates consist of clinopyroxenite, and plagiofer clinopyroxenite, olivine clinopyroxenite, and mafic rocks, based on mineralogy consist of gabbros, olivine gabbros, biotite gabbros and amphibole gabbros. According to geochemical data, studied rocks have tholeiitic nature and in the tectonic setting diagrams, display arc characteristic. The chondrite normalized REE patterns show low enrichment in LREEs relative to HREEs. The negative Nb and Ti anomalies in primitive mantle and MORB-normalized multi-element diagrams of the rocks are characteristic of island arc magmas. Also, enrichment in LILE and depletion of HFSE may indicate a subduction-related tectonic setting. According to geological and geochemical evidence, Imam-Zadeh Hashem ultramafic and sub-alkaline gabbro rocks can be as a part of the Southern Caspian Sea Ophiolite sequence (SCO) that formed in a suprasubduction tectonic system.

Granitoid rocks of Kaje area, northwest Ferdows, with the composition of diorite, monzodiorite, monzonite, monzogranite, syenogranite and granite, with calk-alkaline and high potassium affinities, have trace and rare earth element geochemical characteristics similar to those from subduction zones, belonging to I-type granitoid rocks. Most of these rocks are oxidized (magnetite series), while one suite is reduced (ilmenite series) showing S-type characteristics. Three samples of granitoid rocks were dated using zircon U-Pb method. Granitoid rocks belong to upper Cretaceous epoch. A Granite porphyry with the age of 84.2±1.3 Ma (Santonian stage) is the oldest body followed by a biotite hornblende monzogranite of 70.8±1.4 Ma (Campanian stage) and the youngest body is a hornblende quartz diorite with the age of 67.9±1 Ma (Maastrichtian stage). Initial 87Sr/86Sr and 143Nd/144Nd ratios as well as eNdi for the granite porphyry are 0.708080, 0.512129 and -7.81, respectively. Those ratios for the biotite hornblende monzogranite are 0.706125, 0.512416 and -2.55, respectively; and for the hornblende quartz diorite are 0.707491, 0.512221 and -6.43, respectively. Based on geochemical and isotopic data, three types of granitoid can be distinguished having three different sources and characteristics. The first and oldest one is the granite porphyry of continental crust source, the second one is the monzonite and monzodiorite and the third group is the diorite of mantle source which originated and emplaced in different depths with various rates of contamination. These rocks have higher (87Sr/86Sr)i values compared with the other upper Cretaceous rocks in Bazman and Gazu areas, and lower (87Sr/86Sr)i values in comparison with the Bejestan rocks. Petrochemistry of the granite group is similar to the Bejestan rocks, but these are 10 m.y. younger and the other two groups have similar geochemistry and source to Bazman and Gazu with more contamination by the crust.

Qareh Qeshlaq marble quarry as one of the valuable resources of ornamental stones in West Azarbaijan province formed through thermal carbonate springs while its mineral deposit thickness is limited in comparison with surface extension. In the present research, geological and blocky modeling of the marble deposit was carried out in order to develop a production planning for this quarry, identifying the position of single-marketable-block extracted from it and increasing its economical aspects for exploitation. During the study, in addition to preparing a geological and blocky model for the quarry, firstly the optimum dimensions of its extractable single marketable-block were quantified and then through representing the confining surfaces equation of marble strata in the computer, the optimal maximum dimension and the number and exact location of the single marketable-blocks were determined and presented to the operating team. Based on the findings of these studies and according to the existing 83 exploratory boreholes data, it is possible to extract 183 single marketable-block pink marble and 103 single marketable-block malachite both with 1.5 ´ 2.5 ´ 2.5 m raw dimensions while only 2 single marketable-block alabaster layer with 1.3 ´ 2.5 ´ 2.5 m dimensions. The results also show that with applying extraction consideration, regarding the productivity coefficient of the layers, and removing the gradual color changes zone, the maximum thickness of the single marketable-blocks for the pink marble, malachite, and alabaster will become 1.65, 1.65 and 1.4 m, respectively.

Volcanic rocks of interest are situated in the middle part of the Urumieh-Dokhtar Magmatic Arc (UDMA). They are parts of a vast magmatic province located in the north of Bitlis-Zagros suture zone. Having a prevailing porphyritic texture, these rocks include phenocrysts of plagioclase, amphibole and biotite in a matrix composed of feldspar, quartz, opaque, glass and microlite and mineralogically show composition of dacite to andesite. Minerals are mostly fresh. Effects of alteration are limited to weak chloritization and saussuritization in some amphiboles and rim of plagioclases, respectively.All of the analyzed biotites in the Miocene-Pliocene volcanic rocks in the east of Kamu are of Mg-biotite. According to a widespread classification of micas to 6 general end-members, biotites of interest are averagely composed of 55.45% phlogopite, 15.90% talc, 12.72% Ti-phlogopite, 11.44% eastonite, 3.71% ferri-eastonite and 0.78% muscovite. Chemical composition of biotites indicates a calk-alkaline magmatic series for the magma from which biotites are crystallized. Estimation of the oxygen fugacity of magma, based on chemical composition and Fe3+ content of biotite, shows that the oxygen fugacity was limited to FMQ buffer in quality and was about 10-15 bar in quantity. This value accords the oxygen fugacity for intermediate-acidic volcanic rocks.

The Jajarm karst bauxite deposit is located about 175 km southwest of Bojnourd. The deposit has been developed as a stratiform horizon along the contact of Triassic dolomites and the Jurassic shales and sandstone. In this study, the textural elements of the Jajarm bauxites are classified into matrix and separated textures based on morphological and genetic criteria. Pelitomorphic and microgranular textures are the most abundant matrix textural elements and ooids, pisoids, pelletsand secondary occurrences are the main separated textural elements. Textural analyses indicated both allochthonous and autochtonous origins for the Jajarm bauxites. Detailed petrographic studies allowed the recognition of two types of ooids and pisoids based on morphological features and laminations. Type A is characterized by thin, regular and continuous lamination, whereas type B has thick, irregular and discontinuous lamination. Ooids and pisoids are mainly composed of alternating kaolinite-hemetite and diaspore-geothite laminae in which Al2O3 concentration increases towards the outer laminae. Fine-scale alternation of these laminae in the ooids and pisoids implies the climatic fluctuations of wet and dry seasons. Secondary textural elements are mainly observed as veins enriched in SiO2 and Al2O3.

The Darreh-Zar porphyry copper deposit, located in the Urumieh – Dokhtar magmatic belt, lies about 10 km southeast of Sar-Cheshmeh porphyry copper deposit. The ore body with hydrothermally altered zones including potassic, chlorite-sericite, sericite, argillic and propylitic all related to the Darreh-Zar porphyry stock intruded the Eocene volcanic rocks. Pyrite, chalcopyrite, molybdenite, with different textures as disseminated and veinlet, are the major sulfide minerals and chalcocite and covellite are considered as the secondary minerals. Sulfur isotopic composition of the sulfates and sulfides studied fall on the magmatic values. Two different origins may be suggested for the gypsums studied: 1- hydration of anhydrite and 2- oxidation of pyrite during supergene enrichment. The stable isotopic data calculated on couple minerals (pyrite-anhydrite) point to the formation temperature of about 485-515οC for the fluids involved in mineralization. The fluid responsible for mineralization suggests magmatic sources for all sulfide phases and reduced aqueous sulfur species. Isotopic zoning, based on the δ34S pyrite values, divided the area into the east and the west parts with negative and positive correlation against the depth, respectively. Also, a negative correlation is observed between the Cu and the δ34S in the eastern portion of the area.