Petrogenesis of the Khaku pegmatites corundum-bearing in the margin of Alvand granite complex, and its comparison with important worldwide ruby and sapphire deposits

Document Type : Research Article

Authors

• Hadis Sadeghi ¹
• Shahryar Mahmoudi ²
• Mohammad Reza Jafari ³
• Mohammad Ali Arian ⁴

¹ Ph.D. Student, Department of Geology, Faculty of Basic Sciences, Tehran North Branch, Islamic Azad University, Tehran, Iran

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

³ Assistant Professor, Department of Geology, Faculty of Basic Sciences, Tehran North Branch, Islamic Azad University, Tehran, Iran

⁴ Associate Professor, Department of Geology, Faculty of Basic Sciences, Tehran North Branch, Islamic Azad University, Tehran, Iran

10.22067/econg.2022.77895.1050

Abstract

Blue-colored corundum (sapphire) is found in syenitic pegmatites in Alvand igneous complex in the Khako area. From the petrographic point of view, the host rock is composed of feldspar and small amounts of quartz, which includes corundum crystals of transparent to translucent blue color, 1 to 6 cm long, covered with a sheath of mica with a composition of muscovite to phengite. It seems that the core of corundum crystals crystallized in the magmatic stage in equilibrium with mica + aluminosilicate + feldspar ± perthite, and in the next metasomatic stage, corundum crystals grew from the reaction of plagioclase and mica. The chemical composition of the main minerals in pegmatite rocks indicates the magmatic origin of these rocks, which were formed during the magmatic differentiation process. In the continuation of the metasomatic cycle, the geochemical conditions for formation of new corundum crystals and regrowth of primary corundum have been prepared by reducing the silica content (de-silicification) and increasing the Al/Si ratio. These processes during post-magmatic cycles in granite masses, are known as Plumasite processes. The classifications done in pegmatites, based on abundance of rare elements and phosphorus content in feldspar crystals, indicate fertility of these rocks from rare elements. These pegmatites are included in the group rich in lithium and beryllium. Moreover, comparison of the chemical composition of corundum crystals with famous corundum deposits in other parts of the world shows that these rocks have a special similarity with magmatic corundum deposits in connection with synthetic intrusive masses. In addition, these rocks show a composition similar to magmatic deposits created by metasomatic processes.
 
Introduction
The corundum crystals found in the southern part of Alvand's intrusive mass have been introduced as the most important sapphire gem potential in Iran (Sadeghi et al., 2022; Sajjadi Alehashem et al., 2021). The corundum crystals in this area have been reported in preliminary studies conducted by different researchers (Beharifar, 2012). Although it is not possible to determine certain criteria for the gem value of a mineral., characteristics such as transparency, color, hardness, refractive index, reflection, and absorption of light are among the most important factors in determining the quality of colored gems. The crystallized oxide of pure corundum is colorless However, corundum has five main coloring elements, including Cr3+, Fe3+, Fe2+, Ti4+ and V3+. Geochemical factors in the formation of corundum are usually magmatic or high-grade metamorphic processes that cause formation of aluminum oxide crystals from a magma with a low silica content (Černý, 1991; Černý and Ercit, 2005) or a differentiated pegmatite magma (Sánchez-Muñoz et al., 2017). These rocks can provide special conditions to produce corundum with the help of fluids originating from magmatic fractionation and metamorphic processes (Zwaan et al., 2015; Peucat et al., 2007). Many studies have been done on classification and genesis of corundum deposits (Sutherland et al., 2009, Schmetzer and Peretti, 1999; Simonet et al., 2004). Classification of corundum reserves is essential in choosing detailed prospecting and exploration methods and prospecting for new reserves in similar structural zones.
 
Materials and methods
25 thin sections were prepared from the collected samples. 5 thin polished sections have been used in electron microscope studies and electron probe microanalysis (EPMA). 5 samples of pegmatites containing corundum crystals found in the Khaku deposit Index and 10 single crystals of separated corundum crystals, have been chemically analyzed by XRF and ICP-MS methods in Zarazma Company of Tehran under standard conditions for major elements and trace elements. Also, EPMA analysis of accompanying minerals and corundum crystals was performed by a Cameca-SX-100 device with a beam diameter of 5 microns and accelerating voltage of 2400 mA at the Iranian Mineral Materials Processing Research Center in Karaj.
 
Results
In the newest pegmatite classification (Černý, 1991; Černý and Ercit, 2005), which is most widely used by researchers nowadays, a combination of factors, including depth of establishment, metamorphic degree, and rare element contents are considered. This classification has 4 main categories or classes including 2 Abyssal classes (high grade, high pressure to low), Muscovite (high pressure, low temperature), and Miarolitic (shallow level of rare element with low temperature and pressure). The class of pegmatites with rare elements is divided into LCT and NYF types based on abundance of rare elements: LCT Type is rich in lithium, cesium, and NYF type tantalum and rich in niobium, yttrium, and fluorine. Descriptions of sub-groups by Pezzotta Corundum-bearing pegmatites are included in the Abyssal sub-group. This group is of high pressure and temperature type and is formed at a temperature between 700 and 800 degrees Celsius and a pressure of 4 to 6 kbar (Černý and Ercit, 2005). The mineral abundance of muscovite and biotite shows that Alvand pegmatite shows few characteristics of the muscovite subgroup (high pressure, low temperature). This indicates formation of these rocks at temperatures lower than 700 degrees Celsius. A mineralogical classification is based on the latest classification done in pegmatites (Müller et al., 2022). The pegmatites of the Khaku area are in the corundum pegmatites, a product of magmatism, and are affected by the processes of subsolidus fluids. This group of pegmatites are mostly rich in rare elements and aluminum. Chlorite is the most abundant secondary mineral in corundum-bearing rocks. The chemical composition shows that chlorites of the region are rich in iron and poor in titanium and calcium, their XMg varies from 0.23 to 0.37 (Table 3), and in the classification of chlorites, they are in the range of pycnochlorite to diabenitite (Fig 4-A). The 8 samples of biotite and muscovite from the Khaku region were analyzed by EPMA (Tab 4). There were four biotite crystals in sample SH-1, and four other muscovite crystals in sample SH-3. The structural formula of micas has been calculated based on 11 oxygen atoms and 8 cations (Deer et al., 2013). The lowest amount of X_Mg in sample SH-1 is equal to 0.46, and the highest amount of X_Mg in sample SH-3 is equal to 0.56. According to Al versus Fe/Fe+Mg variations (Deer et al., 2013). These biotites are a compositional variety between polar siderophyllite and anite (Fig 3-B). The chemical composition of feldspars in the Khaku region shows a relatively uniform chemical composition rich in albite and a major part that is rich in an orthosis in pegmatites such that X_Ab is equal to 0.90 to 0.95. Most of the feldspars have a composition of orthosis type X_Or 85 % to 90% (Tab 5). In the ternary diagram of albite-anorthite-orthoses (Deer et al., 2013), feldspars in pegmatites are located in the orthosis zone and in the zone of pure albite and oligoclase (Fig 3-C). The results obtained from chemical analysis of corundum crystals show that they all contain 86% to 97% aluminum oxide (Al₂O₃). In all the samples analyzed by theSiO₂ method as the second main oxide, there is more than one percent in the crystal., and it varies in the range 1.01%-1.46% to.
 
Discussion
The geochemical and geotectonic characteristics of pegmatites in the Khaku area are like those of group II and III pegmatites of the classification of Sánchez-Muñoz et al., (2017), indicating that they are the result of primary crystallization from magmatic melts After those subsolidus reactions during exhumation and cooling rock mass has caused crystallization of corundum and condensation of rare elements (Fig 5). The samples of Khaku are in the range of corundums of magmatic origin and along the dividing line of the magmatic and metamorphic region. These crystals have significant similarities with blue sapphires from the Bo Phloi mine in Thailand (Bo Phloi/Thailand), which are magmatic-metasomatic corundums rich in titanium and magnesium (Fig 6-A). Chromium is also an important tracer in corundum with metamorphic genesis, especially corundum crystallized in alumina-rich marbles and under severe metasomatism. From this point of view, the corundums of the Hamedan Khaku deposit have relatively low amounts of chromium and vanadium and are among the metasomatic magmatic deposits. They are comparable to the sapphires of the Mogok mine in Myanmar (Mogok/Myanmar) (Fig 6-B). This mine is of the metamorphic magmatic type containing ruby in alumina-rich marbles with intense metasomatism (Peucat et al., 2007).

Keywords

• Pegmatite
• Corundum
• Feldspar
• Sapphire
• Khako
• Alvand

20.1001.1.20087306.1401.14.3.5.0

---

References

Aliani, F., Maanijou, M., Sabouri, Z. and Sepahi, A.A., 2012. Petrology, geochemistry and geotectonic environment of the Alvand Intrusive Complex, Hamedan, Iran. Geochemistry, 72(4): 363–383. https://doi.org/10.1016/j.chemer.2012.05.001

Ayers, J.C. and Watson, E.B., 1991. Solubility of apatite, monazite, zircon, and rutile in supercritical aqueous fluids with implications for subduction zone geochemistry. Philosophical Transactions of the Royal Society, 335(1638): 365–375. https://doi.org/10.1098/rsta.1991.0052

Barth, T., 1929. Zur Genese der Pegmatite im Urgebirge. 1. Die Geologie und Petrographie der granitischen Pegmatite im südlichsten Norwegen. Geologiska Föreningen i Stockholm Förhandlingar, 51(1): 125–128. https://doi.org/10.1080/11035892909447064

Beharifar, A.A., 2012. Fabric of migmatites. In: F. Masoudi (Editor), Migmatites. Tarbiat Moalem University Press, Tehran, pp. 37–72. (in Persian with English abstract)

Bonazzi, M., Langone, A., Tumiati, S., Dellarole, E., Mazzucchelli, M., Giovanardi, T. and Zanetti, A., 2020. Mantle-Derived Corundum-Bearing Felsic Dykes May Survive Only within the Lower (Refractory/Inert) Crust: Evidence from Zircon Geochemistry and Geochronology (Ivrea–Verbano Zone, Southern Alps, Italy). Geosciences, 10(8): 1–32. https://doi.org/10.3390/geosciences10080281

Černý, P., 1991. Rare-element granitic pegmatites. Part I: Anatomy and internal evolution of pegmatite deposits. Part II: Regional and global environments and petrogenesis. Geoscience Canada, 18(2): 49–81. Retrieved Octuber 25, 2022 from https://journals.lib.unb.ca/index.php/GC/article/view/3722

Černý, P. and Ercit, S., 2005. The classification of granitic pegmatites revisited. The Canadian mineralogist, 43(6): 2005–2026. https://doi.org/10.2113/gscanmin.43.6.2005

Černý, P., Meintzer, R.E. and Anderson, A.J., 1985. Extreme fractionation in rare-element granitic pegmatites; selected examples of data and mechanisms. Canadian Mineralogist, 23(3): 381–421. Retrieved, 2 March 2017 from https://pubs.geoscienceworld.org/canmin/article-abstract/23/3/381/11780/Extreme-fractionation-in-rare-element-granitic

Deer, W., Howie, R. and Zussman, J., 2013. An introduction to the rock-forming minerals. Mineralogical Society of Great Britain and Ireland, 506 pp. https://doi.org/10.1180/DHZ

Dokukinaa, K.A., Konilova, A.N., Vanb, K.V. and Mintsa, M.V., 2017. Dumortierite- and Corundum-Bearing Quartz–Feldspar–Mica Rocks of the Belomorian Eclogite Province: An Example of Melting of Phengite + Quartz. Doklady Earth Sciences, 477(1): 1353–1357. https://doi.org/10.1134/S1028334X17110204

Eghlimi, B., 2000. Geologcal map of Hamdan, scale 1:100000. Geological Survey and Mineral Exploration of Iran.

Engel, A.E.J., Engel, C.G.,  Chodos, A.A. and  Godijn, E., 1958. Progressive metamorphism and granitization of the major paragneiss, northwest Adirondack Mountains. Gological Survey Aamrica Bulletin, 69(11): 1369–1414. https://doi.org/10.1130/0016-7606(1958)69[1369:PMAGOT]2.0.CO;2

Giuliani, G., Ohnenstetter, D., Fallick, A.E., Groat, L. and Fagan, A.J., 2014. The geology and genesis of gem corundum deposits. In: L.A. Groat (Editor), Gem corundum. Mineralogical Association of Canada, Tucson, pp. 22–112. Retrieved July 11, 2018 from http://eprints.gla.ac.uk/89825/

Gordiyenko, V.V., 1971. Concentration of Li, Rb and Cs in potash feldspar and muscovite as criteria for pegmatites. International Geology Review, 13‌(2):134–142. https://doi.org/10.1080/00206817109475411

Hey, M., 1954. A new review of the chlorites. Mineralogical Magazine and Journal of the Mineralogical Society, 30(224): 277–292. https://doi.org/10.1180/minmag.1954.030.224.01

Khodorevskaya, L.‌I. and Varlamov, D.A., 2018. High-Temperature Metasomatism of the Layered Mafic-Ultramafic Massif in Kiy Island, Belomorian Mobile Belt. Geochemistry internasional., 56(6): 535–553. https://doi.org/10.1134/S001670291806006X

Linnen, R.L., Van Lichtervelde, M. and Černý, P., 2012. Granitic Pegmatites as Sources of Strategic Metals. Elements, 8(4): 275–280. https://doi.org/10.2113/gselements.8.4.275

Mahmoudi, S., Corfu, F., Masoudi, F., Mehrabi, B. and Mohajjel, M., 2011. U–Pb dating and emplacement history of granitoid plutons in the northern Sanandaj–Sirjan Zone, Iran. Journal of Asian Earth Sciences, 41(3): 238–249. https://doi.org/10.1016/j.jseaes.2011.03.006

Monfaredi, B., Hauzenberger, C.A., Neubauer, F., Schulz, B., Genser, J., Shakerardakani, F. and Halama, R., 2020. Deciphering the Jurassic-Cretaceous evolution of the Hamadan metamorphic complex during Neotethys subduction, western Iran. Internasional Journal of Earth Sciences (Geolgy Rundsch), 109(3): 2135–2168. https://doi.org/10.1007/s00531-020-01893-x

Müller, A., Simmons, W., Beurlen, H., Thomas, R., Ihlen, P.M., Wise, M., Roda-Robles, E., Neiva, A.M.R. and Zagorsky, V., 2022. A proposed new mineralogical classification system for granitic pegmatites – Part I: History and the need for a new classification. The Canadian Mineralogist, 60(2): 203–227. https://doi.org/10.3749/canmin.1700088

Ndikumana, J.d.D., Bolarinwa, A.T., Adeyemi, G.O., Olajide-Kayode, J. and Nambaje, C., 2020. Geochemistry of feldspar and muscovite from pegmatite of the Gatumba area, Karagwe Ankole Belt: implications for Nb–Ta–Sn mineralisation and associated alterations. SN Applied Sciences, 2(1568): 1–12. https://doi.org/10.1007/s42452-020-03370-1

Peucat, J.‌J., Ruffaut, P., Fritsch, E., Bouhnik-Le, E., Simonet, C. and Lasnier, B., 2007. Ga/Mg ratio as new geochemical tool to differentiate magmatic from metamorphic blue sapphire. Lithos, 98(1–4): 261–271. https://doi.org/10.1016/j.lithos.2007.05.001

Rakotondrazafy, A.F.M., Giuliani, G., Ohnenstetter, D., Fallick, A.E., Rakotosamizanany, S., Andriamamonjy, A., Ralantoarison, T., Razanatseheno, M., Offant, Y. and Garnier V., 2008. Gem corundum deposits of Madagascar: A review. Ore Geology Reviews, 34(1–2): 134–154. https://doi.org/10.1016/j.oregeorev.2007.05.001

Rieder, M., Cavazzini, G., D'yakonov, Y.S., Frank-Kamenetskii, V.A., Gottardi, G., Guggenheim, S., Koval., EV., Mfiller, G., Nieva, M.R., Radoslovich, E.W., Robert, J.L., Sassi, ER, Takeda, H., Weiss, Z. and Wones, D.R., 1998. Nomenclature of the micas. Clays and Clay Minerals, 46(5): 586–595. https://doi.org/10.1346/ccmn.1998.0460513

Robb, L.J. and Robb, V.M., 1979. The nature of Archean pegmatite deposits in the North-Eastern Transvaal University of the Witwatersrand, Economic Geology Research Unit, 30 pp. Retrieved Jun 15, 2010 from https://books.google.com/books/about/The_Nature_of_Archaean_Pegmatite_Deposit.html?id=isUKAQAAMAAJ

Sadeghi, H., Mahmoudi, S., Aryan, M. and Ghafari, M., 2022. Geochemistry and gemology characteristics of corundum in the Khakoo pegmatites in the southeast of Alvand batholith (west Iran). Iranian Journal of Crystallography and Mineralogy, 30(3): 474–459. (in Persian with English abstract) https://doi.org/10.52547/ijcm.30.3.459 

Sajjadi Alehashem, F., Moazzen, M. and Jahangiri, A., 2021. Introducing semi-gem quality blue corundum from the Alvand complex, Hamedan, west Iran. Periodico di Mineralogia, 90(2): 195–209. https://doi.org/10.13133/2239-1002/17315

Sánchez-Muñoz, L., Müller, A., Andrés, S.L., Martin, R.F., Modreski, P.J. and de Moura, O.J.M., 2017. The P-Fe diagram for K-feldspars: a preliminary approach in the discrimination of pegmatites. Lithos, 272–273: 116–127. https://doi.org/10.1016/j.lithos.2016.10.030

Schmetzer, K. and Peretti, A., 1999. Some Diagnostic Features of Russian Hydrothermal Synthetic Rubies and Sapphires. Gems and Gemology, 35(1): 17–28. https//doi.org/10.5741/GEMS.35.1.17  

Schwarz, D., Pardieu, V., Saul, J.M., Schmetzer, K., Laurs, B.M., Giuliani, G., Klemm, L., Malsy, A.K., Erel, E., Hauzenberger, Ch., Du Toit, G., Fallick, A.E. and Ohnenstetter, D., 2008. Rubies and sapphires from Winza, Central Tanzania. Gems and Gemology, 44(4): 322–347. http://dx.doi.org/10.5741/GEMS.44.4.322

Sepahi, A., Jafari S.R. and Mani-Kashani, S., 2006. The study of chemical composition and evolution of minerals during various metamorphic events in the Hamadan region. Iranian Journal of Crystallography and Mineralogy 14(2): 431–454. (in Persian) Retrieved October 10, 2022 from http://ijcm.ir/article-1-687-fa.html

Sepahi, A.A., Jafari, S.R., Osanai, Y., Shahbazi, H. and Moazzen, M., 2018. Age, petrologic significance and provenance analysis of the Hamedan low-pressure migmatites Sanandaj-Sirjan zone, west Iran. International Geology Review, 61(12): 1446–1461. https://doi.org/10.1080/00206814.2018.1517392

Sepahi, A.A., Vahidpour, H., Lentz, D.R., McFarlane, C.R.M, Maanijou, M., Salami, S., Miri, M., Mansouri, M. and Mohammadi, R., 2020. Rare sapphire-bearing syenitoid pegmatites and associated granitoids of the Hamedan region, Sanandaj-Sirjan zone, Iran: analysis of petrology, lithogeochemistry, and zircon geochronology/trace element geochemistry. Geological Magazine, 157(9): 1499–1525. https://doi.org/10.1017/S0016756820000023

Sepahi, A.A., Whitney, D.L. and Baharifar, A.A., 2004. Petrogenesis of andalusite-kyanite-sillimanite veins and host rocks, Sanandaj-Sirjan metamorphic belt, Hamadan, Iran. Journal of Metamorphic Geology, 22(2): 119–134. https://doi.org/10.1111/j.1525-1314.2004.00502.x

Shahbazi, H., Salami, S. and Siebel, W., 2014. Genetic classification of magmatic rocks from the Alvand plutoniccomplex, Hamedan, western Iran, based on zircon crystal morphology, Geochemistry, 74(4): 577–584. http://dx.doi.org/10.1016/j.chemer.2013.11.001

 

Shahbazi, H., Siebel, W., Pourmoafee, M., Ghorbani, M., Sepahi, A.A., Shang, C.J. and Vousoughi Abedini, M., 2010. Geochemistry and U–Pb zircon geochoronology of Alvand plutonic complex in Sanandaj-Sirjan Zone (Iran): New evidence forJurassic magmatism. Journal of Asian earth sciences, 39(6): 668–683. https://doi.org/10.1016/j.jseaes.2010.04.014

Sheikhi Gheshlaghi, R., Ghorbani, M., Sepahi, A.A., Deevsalar, R. and Shinjo, R., 2020. Petrogenesis of gem sapphire in a pegmatite-aplite vein from the Alvand batholith, Western Iran. Mineralogy and Petrology, 114(8): 501–513. https://doi.org/10.1007/s00710-020-00716-w

Simonet, C., Fritsch, E. and Lasnier, B.A., 2008. A Classification of gem corundum deposits aimed towards gem exploration. Ore Geology Reviews, 34(1–2): 127–133. https://doi.org/10.1016/j.oregeorev.2007.09.002

Simonet, C., Paquette, J.L., Pin, C., Lasnier, B. and Fritsch, E., 2004. The Dusi (Garba Tula) sapphire deposit, Central Kenya—A unique Pan-African corundum-bearing monzonite. Journal of Asian earth sciences. 38(4): 401–410. https://doi.org/10.1016/j.jafrearsci.2004.02.002

Smeds, S.A., 1992. Trace elements in potassium-feldspar and muscovite as a guide in the prospecting for lithium- and tin-bearing pegmatites in Sweden. Journal of Geochemical Exploration, 42(2–3): 351–369. http://dx.doi.org/10.1016/0375-6742(92)90032-4

Smite, I.V., 1974. Feldspar Minerals. Crystal Structure and Physical Properties. Springer Berlin, Heidelberg, 625 pp. https://doi.org/10.1007/978-3-642-96173-1

Stocklin, J., 1968. Structural history and tectonics of Iran: a review. AAPG Bulletin, 52(7): 1258–1229. https://doi.org/10.1306/5D25C4A5-16C1-11D7-8645000102C1865D

Sutherland, L.F., Meffre, S. Giuliani, G., Fallick, E.‌A. Graham, T.I. and Webb, B.G., 2009. Gem corundum megacrysts from east Australia basaltic fields: trace elements, oxygen isotopes and origin. Australian Journal of Earth Sciences, 56(7): 1003–1022. https://doi.org/10.1080/08120090903112109

Van Long, P., Quang Vinh, H., Garnier, V., Giuliani, G., Ohnenstetter, D., Lhomme, T., Schwarz, D., Fallick, A.E., Dubessy, J. and Trong Trinh, P., 2004. Gem corundum deposits in Vietnam. Journal of Gemmology, 29(3): 129–147. Retrieved October 25, 2022 from http://eprints.gla.ac.uk/931/1/Jo_Gemm_29%283%29_129-147.pdf

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

Zwaan, J.C., (Hanco), Buter, E., Mertz-Kraus, R. and Kane, R.E. 2015. The Origin of Montana’s Alluvial Sapphires: Inclusions, Geochemistry, and Indications of a Metasmatic Origin. Gems & Gemology, 51(4): 370–391. Retrieved September  10, 2019 from https://www.gia.edu/doc/GG-WN15-Zwaan.pdf