نوع مقاله: مقاله پژوهشی
نویسندگان
1 گروه زمینشناسی، دانشکده علوم زمین، دانشگاه شهید بهشتی، تهران.
2 گروه زمینشناسی، دانشگاه نیو برونزویک، کانادا.
چکیده
کلیدواژه‌ها
عنوان مقاله [English]
نویسندگان [English]
Chehelkureh copper deposit is located in Kuh-e-Lunka area, 120 km NW of Zahedan (SE of Iran). The host rocks of mineralization are intercalated Eocene turbiditic greywackes, siltstones, and shales (flysch). They are folded with N-S trend and the eastern limb of this fold has been drag folded. Several stocks and dykes of granodiorite to quartz monzodiorite and granite compositions intruded the turbidites, converting them locally to hornfels. These intrusions are oriented parallel to the major NW-SE fault set. The Chehelkureh ore field comprises numerous irregular lenses and veins. The ore field extends for 1500m in N23°W direction, and is displaced by late brittle faults striking roughly E-W. The fault and fracture filling ores include quartz, dolomite, ankerite, siderite, calcite, and lesser amounts of pyrrhotite, arsenopyrite, pyrite, chalcopyrite, sphalerite, galena, Se-rich galena, marcasite, molybdenite, ilmenite, and rutile. Assay data from 39 drill holes show high contents of base metals, with an average of 1.48% Cu, 1.77% Zn, 0.85% Pb (4.1% Cu+Zn+Pb), and silver (average 22 ppm in 45 samples). The ores are not so enriched in gold (0.14 ppm on average in 45 samples).
A composite sample of least-altered greywackes and shales (host rocks) is used for comparison with mineralized samples. Mass-balance calculations were carried out to quantify chemical changes resulting from different alteration episodes. With the low solubility and low variance of Al (Al2O3) in moderately altered sedimentary country rocks compared with many other immobile trace components, Al2O3 is used as an immobile component for mass-balance calculations. There is a net mass increase in Fe2O3T, and MgO and a net mass decrease in Na2O, CaO, K2O, and SiO2 with chloritization. Carbonatization shows Fe2O3T, and MgO enrichment and SiO2 and Na2O depletion, implying that ankerite, siderite and dolomite are predominant phases. SiO2 is enriched in silicified samples and depleted in other alteration types. There is no mass change in Cu, Pb and Zn with kaolinization, but these elements are enriched in other alteration types. Hg is enriched in all alteration types except kaolinization, which may even show a slight depletion. Samples from gossan with silicification showed an increase in SiO2, Fe2O3T, Cu, Pb, Hg, and Zn and a decrease in MgO, Na2O, CaO, and K2O. Some trace and major elements have high variance in different alterations and are more complicated to interpret, such as P2O5, MnO, Ni, Co, and Rb.
The REE contents of the composite host rock sample are enriched in the LREE relative to the HREE and moderately depleted in Eu and Ho. As a whole, samples with kaolinization and carbonatization (ankerite and siderite) have been enriched in REE contents and other wallrock alteration, including chloritization, dolomitization, kaolinization, minor sericitization, and silicification, are depleted in REE. SEM-EDS evidence indicates that enrichment of REE-bearing phosphates, such as monazite, occurred with carbonatization and kaolinization assemblages.
کلیدواژه‌ها [English]
سعیدی، ا.، 1365- گزارش زمینشناسی و سنگشناسی منطقه چهلکوره (شمال باختر زاهدان)، سازمان زمینشناسی کشور، 51 صفحه.
واله، ن. و سعیدی، ا.، 1367- نقشه زمینشناسی چهلکوره، سازمان زمینشناسی ایران، برگه 8050.
References
Alderton, D.H.M., Pearce, J.A. & Potts, P.J., 1980- Rare earth element mobility during granite alteration: Evidence from southeast England, Earth Planet Sci. Lett., 49: 149-165.
Bierlien, F.B., Waldron, H.M. & Anne, D.C., 1999- Behaviour of rare earth and high field strength elements during hydrothermal alteration of meta-turbidites associated with mesothermal gold mineralization in central Victoria, Australia, J. Geochemical Exploration, 67: 109-125.
Cail, T.L. & Cline, J.S., 2001- Alteration associated with gold deposition at the Getchell Carlin-type gold deposit, North-central Nevada, Economic Geology, 96: 1343–1359.
Cetiner, Z.C., Wood, S. & Gammons, C.H., 2005- The aqueous geochemistry of the rare earth elements. Part XIV. The solubility of rare earth element phosphates from 23 to 150°C, Chemical Geology, 217: 147-169.
Delaloye, M. & Desmons, J., 1980- Ophiolites and melange terranes in Iran: a geochronological study and its paleotectonic implications. Tectonophysics, 68: 83–111.
Fedikow, M.A.F. & Amor, S.D., 1990- Evaluation of a mercury-vapour detection system in base- and precious-metal exploration, northern Manitoba, Journal of Geochemical Exploration, 38: 351-374.
Grant, J. A., 1986- The isocon diagram- a simple solution to Gresens’ equation for metasomatic alteration, Economic Geology, 81: 1976-1982.
Grant, J. A., 2005- Isocon analysis: A brief review of the method and applications, Physics and Chemistry of the Earh, 30: 997-1004.
Gresens, R. L. 1967- Composition-volume relationships of metasomatism, Chemical Geology, 2: 47-65.
Haskin, L.A., Haskin, M.A., Frey, F.A. & Wildeman, T.R., 1968- Relative and absolute terrestrial abundances of the rare earths. In: L.H. Ahrens (Editor), Origin and Distribution of the Elements, Pergamon, Oxford, p. 889-912.
Henderson, P., 1984- Rare earth element geochemistry, Elsevier Science Publishers, 510 p.
Leitch, C.H.B. & Lentz, D.R., 1994- The Gresens approach to mass balance constraints of alteration systems: Methods, pitfalls, examples. In Alteration processes associated with ore-forming systems, Edited by D. R. Lentz, Geological Assocciation of Canada, Short Course Notes, 11: 161-192.
Lentz, D.R., 2005- Mercury as a lithogeochemical exploration vectoring technique: a review of methodologies and applications, with selected VMS case histories, The Gangue, 85: 1-11.
Maanijou, M., Lentz, D., Rasa, I. & Aletaha, B., 2006a- Geology, mineralogy and alteration of Chehelkureh polymetallic ore deposit, Southeast Iran. Atlantic Geoscience Society, Wolfville, Nova Scotia, Canada.
Maanijou, M., Lentz, D., Rasa, I. & Aletaha, B., 2006b- Petrology, geochemistry and geotectonic environment of arc-related granitoids in the Chehelkureh area, Southeast Iran: Implications for the formation of the polymetallic ore deposit in the region, Proceedings of 12th Quadrennial IAGOD Symposium, Moscow, Russia.
Montel, J.-M., Foret, S., Veschambre, M., Nicollete, C. & Provost, A., 1996- Electron microprobe dating of monazite, Chem. Geo., 131: 37-53.
Mori, Y., Nishiyama, T. & Yanagi, T., 2003- Mass transfer paths in alteration zones around carbonate veins in the Nishisonogi Metamorphic Rocks, southwest Japan, American Mineralogist, 88: 611–623.
Movahhed Aval, M., 1974- Report on exploration of copper-lead-zinc deposits of Chehel-Kureh and Nasagh-e-Pourchangy Kuh-e-Lunka area, GSI report, 80 p.
Samson, I.M. & Wood, S.A., 2004- The rare earth elements: Behavior in hydrothermal fluids and concentration in hydrothermal mineral deposits, exclusive of alkaline settings, in Linnen, R.L. and Samson, I.M., eds., Rare-Element Geochemistry and Ore Deposits. Geological Association of Canada, Short Course Notes.
Sun, S.S., 1982- Chemical composition and origin of the Earth's primitive mantle, Geochim. Cosmochim. Acta, 46: 179-192.
Taylor, S.R. & McLennan, S.M., 1985- The Continental Crust: Its Composition and Evolution, Blackwell, Oxford, 312 p.
Vielreicher, N.M., Groves, D.I., Fletcher, I.R., McNaughton, N.J. & Rasmussen, B., 2003- Hydrothermal monazite and xenotime geochronology: a new direction for precise dating of orogenic gold mineralization. Soc. Econ. Geol. Newsl. 53: 1-15.
Walther, J. V. & Woodland, A. B., 1993- Experimental determination and interpretation of the solubility of the assemblage microcline, muscovite and quartz in supercritical H2O. Geochim. Cosmochim. Acta, 57: 2431-2438.
Walther, J. V., 1997- Experimental determination and interpretation of solubility of corundum in H2O between 350 and 600 from 0.5 to 2.2 kbar, Geochim. Cosmochim. Acta, 61: 4955-4964.
Watika, H., Rey, P. & Schmitt, R.A., 1971- Abundances of other rare elements in Apollo 12 samples: five igneous and one breccia rocks and four soils. Proc. 2nd Lunar Sci. Conf., Geochim. Cosmochim. Acta, Suppl. 2, 2: 1319-1329.
Wood, S.A., 2003- The geochemistry of rare earth elements and yittrium in geothermal waters, in Simmons, S.F., and Graham, I., eds., Volcanic, Geothermal, and Ore-Forming Fluids: Rulers and Witnesses of Processes within the Earth. Society of Economic Geologists, Special Publication 10: 133-158.
Wood, S.A., 2004- The hydrothermal geochemistry of the Rare Earth Elements, The Gangue, 8: 1-7.
Wood, S.A., 2006- Rare Earth Element systematics of acidic geothermal waters from the Taupo Volcanic Zone, New Zealand, Journal of Geochemical Exploration, 89: 424-427.
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