Mineralogy, geochemistry, fluid inclusions and genesis of Fe-Cu-Au mineralization associated with Ahmadabad intrusions, Semnan

زمین شناسی اقتصادی

Article 4, Volume 14, Issue 2 - Serial Number 33, 2022, Pages 65-91   

Document Type: Research Article

DOI: 10.22067/econg.2021.70627.1025

Authors

Fariba Tayefi^{* 1}; Behzad Mehrabi²; Majid Ghasemi Siani³

¹M.Sc., Department of Geochemistry, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran

²Professor, Department of Geochemistry, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran

³Assistant Professor, Department of Geochemistry, Faculty of Earth Sciences, Kharazmi University, Tehran, Iran

Abstract

 
Introduction
Hydrothermal iron ore deposits are formed at various depth, from shallow to deep environments mainly as veins, veinlets and stockworks (Guilbert and Park, 1997). Ahmadabad deposit is located in 30 km northeast of the Semnan province, between the Alborz and Central Iran sedimentary-tectonic structural zones. According to the previous studies in the Ahmadabad ore deposit (Haji Babaei and Ganji, 2018; Ketabforoush, 2016), there are major uncertainties on origin of mineralization and involved hydrothermal process. In previous studies, based on fluid inclusions data, Ahmadabad hematite-barite ore deposit is considered as a low-temperature hydrothermal barite ore deposit, and also considered as Ahmadabad barite-iron oxide ore deposit as a veins-type hydrothermal-magmatic ore deposit (Haji Babaei and Ganji, 2018). Ketabforoush (2016) based on lithological, mineralogical and alteration assemblage characteristics of the Ahmadabad iron ore mineralization, regarded it as an Iron Oxide-Copper-Gold (IOCG) type hydrothermal mineralization. This study attempts to use mineralogy, geochemistry and microthermometry of fluid inclusions data in quartz and barite for investigating the genesis of Fe-Cu-Au mineralization and possible style of mineralization at the Ahmadabad deposit.
 
Material and methods
During the field work, 54 samples were collected from the host rocks and alteration and mineralization zones. For petrography, mineralogy and paragenetic sequence studies, 48 thin-polished sections were prepared and studied by ZEISS Axioplan2 polarized microscope at Kharazmi University Tehran branch. After ore petrography 10 suitable ore samples were selected for chemical analysis. Preparation, crushing and pulverizing of the samples were carried out in Kharazmi University and samples were analyzed in the Zarazma and Iranian Mineral Processing Research Center (IMPRC) labs. for major, minor and rare earth elements by using WD-XRF and ICP-MS methods. Geochemical analyses results are presented in Tables 1 and 2. Microthermometric analyses were carried out on 3 doubly polished thin section from quartz and barite minerals using a Linkam THMS 600 freezing-heating stage, mounted on a ZEISS Axioplan2 research microscope at the IMPRC.
 
Discussion
The formation and associated process of iron ore deposition has been much debated and discussed, with the focus on hydrothermal and magmatic origin (Naslund et al., 2000). In Ahmadabad deposit, it seems that monzonite and monzodiorite subvolcanic intrusions has been emplaced through a volcanic sequence. During magma emplacement and crystallization, magmatic fluids due to lower density, rising to the upper part of the intrusions and penetrated into the volcanic host rocks causing vein-type iron mineralization. On the basis of mineralogical and microthermometric studies of fluid inclusions, the mineralizing fluid was possibly of magmatic origin; cooled and diluted by mixing with meteoritic fluids. Temperature and pressure drop following the migration of the magmatic fluid to the shallow depths may changes the nature of mineralizing fluids from reduced to oxidant state and deposition of iron as hematite after sulfide (pyrite and chalcopyrite) and sulfate (barite) precipitation. Salinity and homogenization temperature of fluid inclusions show that high temperature-salinity fluid mixed with low temperature-salinity fluid and by decrease in temperature and salinity, followed by cooling and dilution, provided the favorable condition for iron oxide deposition. Based on current studies, Ahmadabad deposit formed in following stages:
- Intrusion’s emplacement in the shallower depth, caused migration and circulation of mineralized fluid in fractures and faults act as fluid channeling conduits.
- Circulation of these fluids through fractured systems may also cause some metal leaching from the wall rocks.
- Moderate to high temperature and salinity magmatic fluid, while approaching the shallow depth were mixed with meteoric fluids and by cooling and dilution process, and possibly transition from the reduction-oxidation boundary, ore bearing fluid nature changed resulted in hematite deposition after sulfide and sulfate phases.
 
Results
Ahmadabad iron ores mineralization based on field geology, mineralogy, geochemistry and microthermometry data is similar to epigenetic deposits formed by magmatic-meteoric fluids due to fluid mixing. Mineralization in the Ahmadabad deposit be divided into two stages of mineralization: 1) primary hydrothermal mineralization stage (hypogene), and 2) secondary stage (supergene). The main iron ore mineralization in Ahmadabad is hematite (specularite) which is mainly formed later than sulphides including pyrite and chalcopyrite, as open space-filling, vein-veinlet, massive and disseminated style of deposition. Barite, calcite and quartz are the main gangue minerals, though in some place’s barite has economic potential. Based on field data and mineralogical studies, the subvolcanic intrusions of the Early Eocene age, after emplacement within the volcanic units controlled by fault and fracture zones, have caused extensive low-grade alterations and limited mineralization in intrusion and volcanic host rocks. Microthermometric studies of fluid inclusions show that the best possible model for formation of the Ahmadabad ore deposit, is mixing of hot and high-salinity magmatic fluid with cold and low-salinity meteoric water.
Although iron ore grade changes greatly with variation in the silica contents, high grade Fe mineralization mainly occurred in the fault and fractured zones away from widespread intensive silicification which is mainly associated with Cu±Au mineralization. These features are the key exploration criteria for future exploration program in the region.

Keywords

Subvolcanic intrusion; Hematite; Mixing fluids; Hydrothermal iron; Alborz and Central Iran; Ahmadabad

References

Alderton, D. M. H., Pearce, J. A., and Potts, P. J., 1980. Rare earth element mobility during granite alteration: evidence from Southwest England. Earth Planet Scientific Letters, 49(1): 149-165. https://doi.org/10.1016/0012-821x(80)90157-0

Barnes, H.L., 1979. Solubilities of ore minerals. In: H.L. Barnes (Editor), Geochemistry of hydrothermal ore deposits. John Wiley and sons, New York, pp. 406-460. Retrieved October 17, 2021 from https://scholar.google.com

Bean, R.E., 1983. The Magmatic-Meteoric Transition. Geothermal Resources Council, California, Report 13, 253 pp.

Boynton, W.W., 1984. Cosmochemistry of the rare earth elements: meteorite studies. In: P. Henderson (Editor), Rare earth element geochemistry. Elsevier, New York, pp. 63-114. https://doi.org/10.1016/B978-0-444-42148-7.50008-3

Dickin, A. P., 1988. Evidence for limited REE leaching from the Roffna Gneiss, Switzerland. Contributions to Mineralogy and Petrology, 99(2): 273-275. Retrieved Sep 5, 2021 from https://scholar.google.com

Ferkous, K., and Leblanc, M., 1995. Gold mineralization in the west Hoggar shear zone, Algeria. Mineral Deposita, 30(3): 211-224. Retrieved Sep 5, 2021 from https://scholar.google.com

Frietsch, R. and Perdahl, J.A., 1995. Rare earth elements in apatite and Magnetite in Kiruna-type iron ores and some other iron ore type. Ore Geology Reviews, 9(6): 489-510. https://doi.org/10.1016/0169-1368(94)00015-G

Ghorbani, M., 2003. Introduction to the economic geology of Iran. Geological Survey of Iran, Tehran, 695 pp.

Groves, D.I. and Bierlein, F.P., 2007. Geodynamic setting of mineral deposit system. Journal of the Geological Society, 164(1): 19-30. https://doi.org/10.1144/0016-76492006-065

Groves, D.I., Bierlein, F.P., Meinert, L.D. and Hitzman, M.W., 2010. Iron Oxide Copper- Gold (IOCG) Deposits through earth History: Implications for Origin, Lithospheric Setting, and Distiniction from other epigenetic iron oxide deposits. Economic Geology, 105(3): 641-654. https://doi.org/10.2113/gsecongeo.105.3.641

Guilbert, J.M. and Park, C.F., 1997. The Geology of Ore Deposits. New York, American, 985pp.

Haji Babaei, A. and Ganji, A., 2018. Characteristics of the Ahmadabad Hematite/Barite deposit, Iran- studies of mineralogy, geochemistry and fluid inclusions. Geologos, 24(1): 55-68. https://doi.org/10.2478/logos-2018-0004

Hart, C.J.R., Mair, J.L., Goldfarb, R.J. and Groves, D.I., 2004. Source and redox controls on metallogenic variations in intrusion-related ore systems, Tombstone-Tungsten Belt, Yukon Territory, Canada. Earth and Environmental Science Transactions of The Royal Society of Edinburgh, 95(1-2): 339-356. Retrieved June 29, 2021 from https://scholar.google.com

Hitzman, M.W., 2000. Iron Oxide-Cu-Au deposits: what, where, when, and why. In: T.M. Porter (Editor), Hydrothermal Iron Oxide Copper-Gold and Related deposits: A global Perspective, Adelaide, Australia, pp. 9-25.

Hitzman, M.W., Oreskes, N. and Einaudi, M.T., 1992. Geological characteristics and tectonic setting of Proterozoic iron oxide (Cu-U-Au-REE) deposits. Precambrian Research, 58(1-4): 241-287. https://doi.org/10.1016/0301-9268(92)90121-4

Jiang, S.Y. and Zhao, K.D., 2007. Rare earth element and yttrium analyses of sulfides from the Dachang Sn-polymetallic ore field, Guangxi Province, China: Implication for ore genesis. Geochemical Journal, 41(2): 121-134. https://doi.org/10.2343/geochemj.41.121

Ketabforoush, Sh., 2016. Investigation of mineralization in Ahmadabad, Semnan region on the basis of petrological, mineralogical and alteration evidence. M.Sc. Thesis, Damghan University, Semnan, Iran, 132 pp.

Kikawada, Y., 2001. Experimental studies on the mobility of lanthanides accompanying alteration of andesite by acidic hot spring water. Chemical Geology, 176(1-4): 137-149. https://doi.org/10.1016/s0009-2541(00)00375-2

Kordian, Sh., Mokhtari, M.A.A., Kouhestani, H., and Veiseh, S., 2020. Geology, mineralogy, structure and texture, geochemistry and genesis of the Golestan Abad iron oxide-apatite deposit (east of Zanjan). Journal of Economic Geology, 12(3): 229-335. (in Persian with English abstract). https://doi.org/10.22067/econg.v12i3.79628

Large, R.R., 1975. Zonation of hydrothermal minerals at the Juno mine, Tennant Creek goldfield, Central Australia. Economic Geology, 70(8): 1387-1413. https://doi.org/10.2113/gsecongeo.70.8.1387

Mason, B. and Moore, C.B., 1982. Principles of Geochemistry. John Wiley and Sons, New York, 350 pp.

Monteiro, L.V.S., Xavier, R.P., Hitzman, M.W., Juliani, C., Filho, C.R.S. and Carvalho, E.R., 2008. Mineral chemistry of ore and hydrothermal alteration at the Sossego iron oxide-copper-gold deposit. Carajas Mineral Province, Brazil. Ore geology Reviews, 34(3): 317-336. https://doi.org/10.1016/j.oregeorev.2008.01.003

Nakhaei, M., and Mohammadi, S.S., 2021. Petrography, geochemistry and tectonic setting of adakitic bodies in the Tighanab area and their relationship with iron skarn mineralization (southeast of Sarbisheh-east of Iran). Journal of Economic Geology, 12(4): 449-470. (in Persian with English abstract). https://doi.org/10.22067/econg.v12i4.81783

Naslund, H.R., Aguirre, R., Dobbs, F.M., Henriquez, F. and Nystrom, J.O., 2000. The origin, emplacement and eruption of ore magmas. Actas IX Congreso Geologico Chileno (Puerto Varas) 24(2): 135-139. Retrieved June 29, 2021 from https://scholar.google.com

Nezafati, N. 2006. Au-Sn-W-Cu-Mineralization in the Astaneh-Sarband Area, West Central Iran, including a comparison of the ores with ancient bronze artifacts from Western Asia Unpublished Ph.D. Thesis, University of Tuebingen, Tuebingen, Germany, 114 pp.

Ohmoto, H. and Goldhaber, M.B., 1997. Sulfur and Carbon isotopes. In: H.L. Barnes (Editor), Geochemistry of hydrothermal ore deposits. John Wiley and Sons, New York, pp. 517-612. Retrieved Oct 17, 2021 from https://scholar.google.com

Palacios, C. M., Hein, U. F., and Dulski, P., 1986. Behaviour of rare earth elements during hydrothermal alteration at the Buena Esperanza copper-silver deposit, Northern Chile. Earth Planet Scientific Letters, 80(3-4): 208-216. https://doi.org/10.1016/0012-821x(86)90105-6

Pollard, P.J., 2006. An intrusion-related origin for Cu-Au mineralization in iron oxide-copper-gold (IOCG) provinces. Mineralium Deposita, 41(2): 179-187. https://doi.org/10.1007/s00126-006-0054-x

Roedder, E., 1984. Fluid inclusions. Mineralogical Society of America, United States, 644 pp.

Rolland, Y., Pillard, F. and Klapouzczak, A., 2007. Exercise program fornursing home resident with Alzheimer’s disease: A 1-year randomized, controlled trial. Journal of the American Geriatrics Society, 55(2): 158-165.https://doi.org/10.1111/j.1532-5415.2007.01035.x

Rollinson, H.R., 1993. Using geochemical data: evaluation. presentation, interpretation. Longman Scientific and Technical, Essex, 352 pp.

Rosiere, C.A., Siemes, H., Quade, H., Brokmeier, H.G. and Jensen, E.M., 2001. Microstructures, texture and deformation mechanisms in hematite. Journal of Structural Geology, 23(9): 1429-1440. https://doi.org/10.1016/S0191-8141(01)00009-8

Selverstone, J., Morteani, G., and Stuade, J.M., 1991. Fluid channelling during ductile shearing: transformation of granodiorite into aluminous schist in the Tauern Window, eastern Alps. Journal of Metamorphic Geology, 9(4): 419-431. http://doi.org/10.1111/j.1525-1314.1991.tb00536.x

Shepherd, T.J., Rankin, A.H. and Alderton, D.H.M. 1985. A partical guied to Fluid inclusion studies. Blackie, London, 239 pp.

Stocklin, J., 1968. Structure history and tectonics of Iran: A review. The American Association of Petroleum Geologists Bulletin, 52(7): 1229-1258. https://doi.org/10.1306/5D25C4A5-16C1-11D7-8645000102C1865D

Tayefi, F. 2021 Mineralogy, geochemistry and microthermometry of siliceous Fe-Cu bearing veins associated with Ahmadabad intrusion, Semnan. M.Sc. Thesis, Kharazmi University, Tehran, Iran, 194 pp.

Whitney, D.L. and Evans, B.W., 2010. Abbreviations for names of rock-forming minerals. American Mineralogist, 95(1): 185-187. https://doi.org/10.2138/am.2010.3371

Wilkinson, J.J., 2001. Fluid inclusions in hydrothermal ore deposits. Lithos, 55(1-4): 229-272. https://doi.org/10.1016/S0024-4937(00)00047-5

Williams, P.J., Barton, M.D., Johnson, D.A., Fontbote, L., DeHaller, A., Mark, G., Oliver, N.H.S. and Marschik, R., 2005. Iron oxide copper-gold deposits: geology, space-time distribution and possible modes of origin. In: J.W. Hedenquist, J.F.H. Thompson, R.J. Goldfarb, and J.P. Richards (Editors), Economic Geology 100^th anniversary volume. Society of Economic Geologist, USA, pp. 371-405. Retrieved June 29, 2021 from https://www.segweb.org

Yari, F., Zarrinkoub, M.H., and Mohammadi, S.S., 2021. Geology, petrography, mineral chemistry and fluid inclusion of the Kalate Shab iron skarn (East of Sarbisheh, Southern Khorasan). Journal of Economic Geology, 12(4): 563-584. (in Persian with English abstract). https://doi.org/10.22067/econg.v12i4.77836