Mineralogy, chemistry of magnetite and genesis of Korkora-1 iron deposit, east of Takab, NW Iran

زمین شناسی اقتصادی

Article 6, Volume 6, Issue 2 - Serial Number 11, January 2015, Pages 355-374   

Document Type: Research Article

DOI: 10.22067/econg.v6i2.22650

Authors

Mohammad Maanijou^* ; Rahimeh Salemi

Bu-Ali Sina

Abstract

Introduction
There is an iron mining complex called Shahrak 60 km east of Takab town, NW Iran. The exploration in the Shahrak deposit (general name for all iron deposits of the area) started in 1992 by Foolad Saba Noor Co. and continued in several periods until 2008. The Shahrak deposit comprising 10 ore deposits including Korkora-1, Korkora-2, Shahrak-1, Shahrak-2, Shahrak-3, Cheshmeh, Golezar, Sarab-1, Sarab-2, and Sarab-3 deposits )Sheikhi, 1995) with total 60 million tons of proved ore reserves. The Fe grade ranges from 45 to 65% (average 50%). The ore reserves of these deposits vary and the largest one is Korkora-1 with 15 million tons of 55% Fe and 0.64% S. The Korkora-1 ore deposit is located in western Azarbaijan and Urumieh-Dokhtar volcanic zone, at the latitude of 36°21.8´, and longitude of 47°32´.

Materials and methods
Six thin-polished sections were made on magnetite, garnet, and amphibole for EPMA (Electron Probe Micro Analysis). EPMA was performed using a JEOL JXA-733 electron microprobe at the University of New Brunswick, Canada, with wavelength-dispersive spectrometers.

Results and discussion
Outcropped units of the area are calc-alkaline volcanics of rhyolite, andesite and dacite and carbonate rocks of Qom Formation in which intrusion of diorite to granodiorite and quartzdoirite caused contact metamorphism, alteration plus skarnization and formation of actinolite, talc, chlorite, phlogopite, quartz, calcite, epidote and marblization in the vicinity of the ore deposit.
Iron mineralization formed at the contacts of andesite and dacite with carbonates in Oligo-Miocene. The study area consists of skarn, metamorphic rocks, and iron ore zones. The shape of the deposit is lentoid to horizontal with some alteration halos. The ore occurred as replacement, massive, disseminated, open-space filling and breccia. The ore minerals of the deposit include low Ti-magnetite (0.04 to 0.2 wt % Ti), minor apatite, and sulfide minerals such as pyrite and chalcopyrite. Magnetite is the most important mineral and has 0.2 to 4 mm grain size and partly transformed into hematite, limonite and goethite. In some places, magnetite can be seen as euhedral grains in hand specimen. Supergene minerals such as chalcocite, malachite, azurite, and covellite are also present. Hematite formed as primary and secondary types in which primary type occurred in deeper parts of the ore body along with magnetite and has lamellar texture with up to 0.2 mm grain size. Meanwhile, secondary type of hematite formed from martitization along magnetite grain boundaries and fractures. In the surface area of the deposit, ore minerals strongly altered to mixtures of oxide and hydroxide minerals (ochre) like goethite, hematite, limonite and lepidochrocite which changed the color of the ore body to yellow, deep orange, red and brown. Pyrite is the most important sulfide mineral and formed in three stages. In the first stage, pyrite occurred with magnetite and has 0.1 to 0.3 mm subhedral to anhedral grains which altered to oxide and hydroxide minerals. At the second stage, pyrite has 0.2 to 1 mm euhedral grains, occurred between the magnetite and gangue minerals and converting to chalcopyrite. At the third stage, pyrite with magnetite, calcite and quartz filled fractures as open-space fillings and are pretty unaltered.
The skarn zone includes garnet, pyroxene, secondary calcite, epidote, and chlorite and the metamorphic zone includes marble. Sericitization, silicification, calcitization, chloritization-epidotization, argilitization, propylitization and actinolitizion are the important alterations in the area from which chloritization-epidotization and calcitization in the ore and propylitic alteration in the volcanics are dominant.
The EPMA analytical results on 30 points on magnetite and hematite suggest that the amount of Ti and V (0.004 wt % and 0.002 wt % in average, respectively) are low in contrary to Mn and Al (0.33 wt % and 5.32 wt % in average, respectively). Therefore, it fits in the skarn ore deposit domain in Ni/(Cr + Mn) versus Ti + V and Ca + Al + Mn versus Ti + V discrimination diagrams of iron ore deposits (Beaudoin et al., 2007). High Mn in the rock samples of Korkora-1 can be resulted from substitution of Fe+2 by Mn+2 in magnetite structure that can be a sign of hydrothermal skarn. Titanium, Mn, V and Zn show a positive correlation and Al, Cu, Mg, P, Si, Ca, Ni and Cr show a negative correlation with Fe. According to the chemistry of magnetite and plotting them on V2O5 versus TiO2 and V2O5 versus Cr2O3 diagrams, it can be recognized that the samples of Korkora-1 deposit resemble exoskarn magnetite of Goto deposit. The analysis of goethite of Korkora-1 show the amount of 2.5 to 4 wt % SiO2, 76 wt % Fe, and Ni (110 ppm) without Ti and Cr in its structure.
Mineralographical and geochemical evidence from ore, occurrence of iron in contact with carbonates and skarn mineralogy such as garnet, pyroxene, secondary calcite, epidote and chlorite suggest iron skarn genesis for Korkora-1 deposit. Fluids generated from intrusive bodies like diorite and quartz-diorite with variations in physicochemical conditions, produced skarn in contact with carbonates and volcanic rocks. The heat from intrusive bodies caused recrystallization of carbonates and formed marbles in the footwall of the deposit. Meteoric water has also less important contribution in the ore-forming fluids. Fluid inclusion studies show existing of two types of fluids, a low salinity (10 wt % NaCl equiv.) and a medium salinity (25 to 30 wt % NaCl equiv.) fluid. Mixing magmatic and meteoric waters makes decreasing in the temperatures and deposition of ore fluids. The Korkora-1 deposit formed in four stages: 1) intruding the intrusive bodies, 2) entering Fe and SiO2 into Qom carbonates and forming calc-silicates, 3) mixing magmatic and meteoric fluids, hydrolysis of calc-silicates, consuming H+, instability of Fe complexes and deposition of iron oxides, 4) retrograde alterations of hydrous and non-hydrous calc-silicates with low temperature and high fO2 fluids and forming chlorite, calcite, clay minerals and hematite.

Acknowledgements
We gratefully thank Mr. Reza Sheikhi from Saba Noor Co. who kindly helped us during the research. We also thank Professor David Lentz from University of New Brunswick for advising and supporting the research.

References
Sheikhi, R., 1995. Economic geology study of Shahrak Fe deposit, east of Takab. M.Sc. Thesis, Shahid Beheshti University, Tehran, Iran, 161 pp. (in Persian with English abstract)
Beaudoin, G., Dupuis, C., Gosselin, P. and Jebrak, M., 2007. Mineral chemistry of iron oxides: application to mineral exploration. In: C.J. Andrew (Editor), Ninth Biennial SGA meeting, SGA, Dublin, pp. 497−500.

Keywords

Mineralogy; magnetite chemistry; iron deposit; skarn; Korkora-1; Takab

References

Azizi Shotorkheft, H., 2003. Petrogenesis of contact metamorphic rocks and related Fe skarn in Shahrak area, east of Takab. M.Sc. Thesis, University of Tehran, Tehran, Iran, 134 pp. (in Persian with English abstract)

Barton, M.D. and Johnson, D.A., 1996. An evaporitic-source model for igneous- related Fe- oxide (REE- Cu- Au- U) mineralization. Geology, 24(3): 259−262.

Barton, M.D. and Johnson, D.A., 2000. Alternative brine sources for Fe- oxide (-Cu- Au) systems: Implications for hydrothermal alteration and metals. In: T. M. Porter (Editor), Hydrothermal Iron Oxide Copper-gold and Related Deposits: A Global Perspective. V. 1, Australian Mineral Foundation Inc, Adelaide, pp. 43−60.

Beaudoin, G., Dupuis, C., Gosselin, P. and Jebrak, M., 2007. Mineral chemistry of iron oxides: application to mineral exploration. In: C.J. Andrew (Editor), Ninth Biennial SGA meeting, SGA, Dublin, pp. 497−500.

Bonyadi, Z., Davison, G.J., Mahrabi, B., Meffre, S. and Ghazban, F., 2011. Significance of apatite REE depletion and monazite inclusion in the brecciaed Se-Chahun iron oxids-apatite deposit, Bafq district, Iran: Insights from par agenesis and geochemistry. Chemical Geology, 281(3-4): 253−269.

Deer, W.A., Howie, R.A. and Zussman, J., 1992. An introduction to rock forming minerals. 2 nd edition, Longman, Harlow, Wiley, New York, 712 pp.

Einaudi, M.T., Meinert, L.D. and Newberry, R.J., 1981. Skarn deposits. Economic Geology, 75th Anniversary, 1987: 317−391.

Frietsch, R., 1973. The origin of the Kiruna iron ores. Geology. Foren, Stockholm Fort, 95(4): 375−380.

Frietsch, R., 1984. On the magmatic origin of iron ores of Kiruna type: discussion. Economic Geology, 79(8): 1949−1951.

Frost, R.B., 1991. Stability of oxide minerals in metamorphic rocks. Reviews in Mineralogy , 25(1991): 469–487.

Geijer, P., 1931. The iron ores of the Kiruna type: Geological distribution, geological characters, and orgin. Sveriges geologiska undersökning, Serie C, Avhandlingar och uppsatser 367, Gen.-stab. lit. anst. i distr, Stockholm, 39 pp.

Gosselin, P., Beaudoin, G. and Jebrak, M., 2007. Application of the geochemical signature of iron oxides to mineral exploration. GAC-MAC Annual Meeting Program with Abstract [CD-ROM].

Guilbert, J.M. and Park, C.F., 1986 . The Geology of Ore Deposits. W.H. Freeman and Company, Oxford and New York, 985 pp.

Hallaji, A., 1991. Study of REE mineralogy and origin of Golgohar Fe deposit (Sirjan-Kerman), M.Sc. Thesis, Tarbiat Moalem University, Tehran, Iran, 183 pp.

Jami, M., 2005. Geology, geochemistry and evolution of the Esfordi phosphate—iron deposit, Bafq Area, central Iran. Unpublished Ph.D. thesis, University of New South Wales, Australia, 355 pp.

Kwak, T.A., 1994. Hydrothermal alteration in carbonate-replacement deposits, ore skarns and distal equivalents. In: D.R. Lentz (Editor), Alteration and Alteration Processes Associated with Ore-Forming Systems. Geological Association of Canada, Short Course Notes, St. Johns, Newfoundland, 11: 381−402.

Loberg, B.E. and Horndahl, A.K., 1983. Ferried geochemistry of Swedish Precambrian iron ores. Mineralium Deposita, 18(3): 487–504.

Marschik, R. and Spikings, R., 2008. Geochronology and stable isotope signature of alteration related to hydrothermal magnetite ores in Central Anatolia, Turkey. Mineralium Deposita, 43(1): 111−124.

Miri, M., 2011. Petrological and geochemical studies of igneous rocks of Tekyeh Bala (southeastern Kordestan) with special view on Fe mineralization. M.Sc. Thesis, Bu-Ali Sina University, Hamedan, Iran, 142 pp.

Murray, J.W., 1979. Iron oxides. In: R.G. Burns (Editor), Reviews in Mineralogy 6, Marine Minerals. Mineralogical Society of America, Washington, D.C., pp. 47−98.

Nystrom, J.O. and Henriquez, F., 1994. Magmatic features of iron ores of the Kiruna type in Chile and Sweden: Ore textures and magnetite geochemistry. Economic Geology, 89: 820−839.

Pournik, P., 2007. Geological-Mining and Evaluation report on Fe deposit of Shahrak. 350 pp. (in Persian)

Rahgoshay, M., Mackizadeh, M.E., Amooei Ardakani, T. and Shafaei Moghaddam, H., 2008. Study of geochemistry of garnet-vesuvianite-wollastonite-pyroxene assemblages in Hosh skarns, west of Taft (Yazd province). Crystallography and Mineralogy Magazine of Iran, 16(1): 31−48. (in Persian with English abstract)

Ray G.E., Lefebure D.V., 2000. A synopsis of iron oxide ± Cu ± Au ± P ± REE deposits of the Candelaria-Kiruna-Olympic Dam family. British Columbia Ministry of Energy and Mines, Geological Fieldwork 1999, Paper 2000-1: 267−272.

Razjigaeva, N.G. and Naumova, V.V., 1992. Trace element composition of detrital magnetite from coastal sediments of Northwestern Japan Sea for provenance study. Journal of Sedimentary and Petrology, 62(5): 802−809.

Schwartz, M.O. and Melcher, F., 2004. The Faleme iron district, Senegal. Economic Geology, 99(5): 917–939.

Sheikhi, R., 1995. Economic geology study of Shahrak Fe deposit, east of Takab. M.Sc. Thesis, Shahid Beheshti University, Tehran, Iran, 161 pp. (in Persian with English abstract)

Whitney, D.L. and Evans, B.V., 2010. Abbreviations for names of rock-forming minerals. American Mineralogist, 95(1): 185−187.