نوع مقاله: مقاله پژوهشی
نویسندگان
1 دانشجوی دکترا، دانشگاه آزاد اسلامی، واحد علوم و تحقیقات، تهران، ایران
2 دانشیار، گروه زمین‌شناسی، دانشگاه گلستان، گرگان، ایران
3 استادیار، گروه زمین‌شناسی، دانشگاه صنعتی شاهرود، شاهرود ایران
چکیده
کلیدواژه‌ها
عنوان مقاله [English]
نویسندگان [English]
Lead and zinc mineralization occurs in limestones of the Upper Jurassic Lar Formation at Pichamto, which is located 38 km northwest of Shahroud city in East Alborz structural zone. Lead and zinc mineralization emplaced in host rocks as lens- and vein-shaped bodies due to replacement, and open-space and fracture fillings. Petrographical and mineralogical studies indicate that smithsonite, calamine, galena, and cerrusite make the main ore minerals, whereas calcite, dolomite, aragonite, iron oxides, quartz and clay minerals are the gangue minerals. Wall-rock alteration includes carbonate recrystallization, dolomitization and brecciation. Fluid inclusion studies indicate two-phase (L+V) liquid- and gas-rich types. Final ice melting temperatures measured in inclusions rage from -19.8 to -8.3 °C. The salinity of fluid inclusions vary between 12 and 22.22 wt.% NaCl equivalent with an average value of 15.41 wt.% NaCl equivalent. Homogenization temperatures for fluid inclusions temperature range between 70 °C and 220 °C, with 176 °C as the average homogenization temperature. The salinity and homogenization temperature ranges for fluid inclusions in the Pichamto deposit suggest that ore-forming fluid derived from basinal brines, similar to hydrothermal solutions in MVT-type Pb-Zn deposits. The δ34S values for two galena samples from Pichamto deposit are +15.6 and +16.2 ‰. These values reveal that the seawater sulfate is the most probable source of sulfur. The reduced sulfur was most likely supplied through thermochemical sulfate reduction. The δ13C values of hydrothermal calcite samples are −4.16 ‰ and -9.17 ‰. The δ18O values in calcite samples are 2.6 ‰ and 0.8 ‰. The δ18O values in calcite overlap with the oxygen isotopic composition of Phanerozoic seawater, indicating possible important participation of Phanerozoic seawater in the ore-forming fluid. The negative δ13C values of calcite samples indicate that the organic materials within the host rocks contributed significantly to the hydrothermal fluid. The δ13C and δ18O values in smithsonite are -7.21 ‰ and -3.41 ‰, respectively. The light carbon isotopic composition of smithsonite reveal the secondary origin of the mineral, and the contribution of meteoric waters and waters containing CO2 derived from decomposition of organic materials in its formation.The Pichamto deposit is comparable to MVT-type Pb-Zn deposits from several points of view including tectonic setting, host rock, wall rock alteration and the source of ore-forming fluids and materials, and have formed during two primary (sulfides formation) and supergene (carbonates and silicates formation) stages.
آقانباتی، ع.، 1383- زمین‌شناسی ایران، انتشارات سازمان زمین‌شناسی و اکتشافات معدنی کشور، 586 ص.
زمانی پدرام، م.، کریمی، ح. ر. و حسینی، ح.، 1385- نقشه زمین‌شناسی 100000/1 علی آباد، سازمان زمین‌شناسی و اکتشافات معدنی کشور.
فردوست، ف.، 1385- گزارش زمین‌شناسی نقشه 1000/1 معدن تاش- مجن، دانشگاه صنعتی شاهرود.
قربانی، م.، 1381- دیباچهای بر زمین‌شناسی اقتصادی ایران، انتشارات سازمان زمین‌شناسی و اکتشافات معدنی کشور، 695 ص.
محمدی، ز.، عربامیری، ع.، کامکار روحانی، ا. و ابراهیمی، س.، 1392- مطالعات زمین‌شناسی و ژئوشیمی کانسار سرب و روی چمتو در شمال غرب شاهرود. اولین کنفرانس ملی مهندسی اکتشاف منابع زیرزمینی.
مهدیزاده، ی.، 1389- تلفیق داده های اکتشافی منطقه پیچمتو با دادههای حاصل از اندازهگیریهای مقاومت ویژه الکتریکی و قبطش القایی به منظور ارائه مدل سهبعدی کانسار، پایان‌نامه کارشناسی ارشد، دانشگاه صنعتی شاهرود.
References
Alavi, M., 1991- Sedimentary and Structural Characteristics of the Paleo-Tethys Remnants in northeastern Iran, Geological Society of American Bulletin, 103: 983-992.
Bodnar, R. J., 1993- Revised equation and table for determining the freezing point depression of H2O-NaCl solutions, Geochimica et Cosmochimica Acta, Vol.: 57, 683-684.
Bodnar, R. J., 1999- Hydrothermal Solutions.in Encyclopedia of Geochemistry, C.P. Marshall and Fairbridge eds., Kluwer Academic Publishers, Lancaster, 333-337.
Boni, M. and Mondillo, N., 2015- The Calamines and the Others: The great family of supergene nonsulfide zinc ores. Ore Geology Reviews 67, 208–233
Boni, M., Gilg, H. A., Aversa, G. and Balassone, G., 2003- The “Calamine” of SW Sardinia (Italy): geology, mineralogy and stable isotope geochemistry of a supergene Zn-mineralization. Econ. Geol. 98, 731–748.
Criss, R. E., 1995- Stable isotope distribution, variations from temperature, organic and water rock interactions. In T.J. Ahrens, ed., Global Earth Physics: A Handbook of Physical Constants, 1, p. 92-307, American Geophysical Union, Washington, D.C.
Daliran, F. and Borg, G., 2005- Characterisation of the nonsulphide zinc ore at Angouran, Northwestern Iran, and its genetic aspects. In: Mao, J. and Bierlein, F.P. (Eds.) Mineral Deposit Research: Meeting the Global Challenge. v. 2, 913-916.
Ghazanfari, F., 1999- Zn–Pb Mines and Deposits in Iran, unpublished report.
Ghorbani, M., 2013- The economic geology of Iran, mineral deposits and natural resources, Springer Geology, doi:10.1007/978-94-007-5625-0, Dordrecht.
Gilg, H. A., Allen, C., Balassone, G., Boni, M., Moore, F., 2003- The 3-stage evolution of the Angouran Zn “oxide”-sulfide deposit, Iran. In: Eliopoulos, D. G. et al. (Eds.) Mineral exploration and sustainable development. Millpress, Rotterdam, p. 77–80
Gilg, H. A., Boni, M., Hochleitner, R. and Struck, U., 2008- Stable isotope geochemistry of carbonate minerals in supergene oxidation zones of Zn–Pb deposits. Ore Geol. Rev. 33, 117–133.
Guilbert, J. M., Park, Jr. C. F., 1997- The Geology of ore deposits, Freaman and company, New York.
Hitzman, M. W., Reynolds, N. A., Sangster, D. F., Allen, C. R. and Carman, C., 2003- Clasification, genesis and exploration guides for non-sulphide zinc deposits. Economic Geology, v.98 (4), p. 685-714
Hoefs, J., 2009- Stable isotope geochemistry, 6th edn. Springer-Verlag, Berlin, 285 P
Leach, D. L., Sangster, D. F., Kelley, K. D., Large, R. R., Garven, G., Allen, C.R., Gutzmer, J. and Walters, S., 2005- Sediment-hosted lead–zinc deposits: a global perspective. In: Econ Geol 100th Anniv, pp. 561–608
Leach, D. L., Taylor, R. D., Fey, D. L., Diehl, S. F. and Saltus, R. W., 2010- A deposit model for Mississippi Valley-Type lead-zinc ores, chap. A of Mineral deposit models for resource assessment: U.S. Geological Survey Scientific Investigations Report 2010–5070–A, 52 p.
Ohmoto, H. and Goldhaber, M. B., 1997- Sulphur and carbon isotopes. In: Barnes HL (ed.), Geochemistry of hydrothermal ore deposits, 3rd edition. Wiley and Sons, 517–611
Ohmoto, H., 1986- Stable isotope geochemistry of ore deposits. Rev Miner 16, Stable isotopes in high-temperature systems, 491–559
Ohmoto, H., Rye, R. O., 1979- Isotopes of sulphur and carbon. In: Barnes HL (ed) Geochemistry of hydrothermal ore deposits, 2nd edn. Wiley and Sons, New York, pp 509–567
Reichert, J. and Borg, G., 2008- Numerical simulation and a geochemical model of supergene carbonate-hosted nonsulphide zinc deposits. Ore Geol. Rev. 33, 134–151.
Reichert, J., 2007- A metallogenetic model for carbonate-hosted non-sulphide zinc deposits based on observations of Mehdi Abad and Irankuh, Central and Southwestern Iran. Ph.D Thesis, Martin Luther University, Halle Wittenberg.
Sangster, D. F., 1990- Mississippi Valley-type and sedex lead-zinc deposits: a comparative examination. Trans Inst Mining Metall B: B21-B42
Sangster, D. F., Outridge, P. M. and Davis, W. J., 2000- Stable lead isotope characteristics of lead ore deposits of environmental significance, Environ. Rev. 8, 115-147.
Sasaki, A. and Krouse, H. R., 1969- Sulfur isotopes and the pine point lead–zinc mineralization. Economic Geology 64, 718–730.
Seal, R. R., 2006- Sulfur isotope geochemistry of sulfide minerals. Reviews in Mineralogy and Geochemistry 61, 633–677.
Van der Kerkhof, A. M. and Hein U. F., 2001- Fluid inclusion petrography, Lithos 55, pp. 27-47.
Veizer, J., Ala, D., Azmy, K., Bruckschen, P., Buhl, D., Bruhn, F., Carden, G. A. F., Diener, A., Ebneth, S., Godderis, Y., Jasper, T., Korte, C., Pawellek, F., Podlaha, O. G. and Strauss, H., 1999- 87Sr/86Sr, δ13C and δ18O evolution of phanerozoic seawater. Chem Geol 161:59–88
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