Origin and Chemical Characteristics of Tourmaline in Kahang Porphyry Copper Deposit, NE Isfahan, Central Province of Iran

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1 Origin and Chemical Characteristics of Tourmaline in Kahang Porphyry Copper Deposit, NE Isfahan, Central Province of Iran Pezhman Rasekh 1 (P.rasekh@ut.ac.ir), Mirsaleh Mirmohammadi 2, Mahin Mansouri Esfahani 1 1 Isfahan University of Technology, Department of Mining Engineering, Isfahan, Iran 2 School of Mining Engineering, College of Engineering, University of Tehran, Iran Abstract: Kahang porphyry copper deposit lies in the central part of Urumieh-Dokhtar magmatic belt which is the main volcanic belt of Iran. The porphyry phases of the complex consist of a diorite porphyry, quartz monzonite and a dacite porphyry phase associating with tourmaline-bearing quartz veins. Electron microprobe analysis indicated that the tourmalines from quartz veins display schorl-dravite solid solution. Plotting of chemical data in Ca-X site vacancy-na+(k) ternary diagram, it is found that the tourmalines are categorized as alkali group. The studied tourmalines are plotted in (R 1+ +R 2+ ) versus R 3+ diagram which show that most of the tourmaline samples reflect extent of substitution toward proton-deficient. According to Al-Fe(tot)-Mg and Ca-Fe(tot)-Mg diagrams, the tourmalines from the quartz veins are related to ferric iron-rich quartz tourmaline rocks, calc-silicate rocks, and metapelites, as well as, Ca-poor metapelites and metapsammites. Considering the petrographic observation and geochemical investigations, the tourmalines of the Kahang area are classified as hydrothermal origin. BSE image and chemical zoning of this mineral confirm its hydrothermal origin. The tourmalines from quartz veins, with average Fe # values of 0.58 (Fe # <0.6) are represented as distal. Keywords: (Kahang Copper Deposit, Urumieh Dokhtar magmatic belt, Hydrothermal Tourmaline, Mineral Chemistry) Introduction Tourmaline is one of the most important boron silicate minerals which is more common in acidic igneous rocks and known as a frequent mineral in different magmatic-hydrothermal deposits. (Harraz et al, 2001). Because of its refractory nature and occurrence in a wide verity of geological environments, tourmaline has received great interest in recent years and is believed to be a useful petrogenetic indicator and a potential exploration tool for ore genesis (Henry & Guidotti, 1985, Henry & Dutrow, 1996; Slack, 1996; Jiang, 2001, Yu and Jiang, 2003; Miyanarczyk and Williams-Jones 2006; Neiva et al. 2007) and more recently, has been recognized as a medium

2 for recording geologic information, not like a DVD (Barbara L. Dutrow et al, 2011). Iron-rich tourmaline has been regarded as a typical mineral of pegmatite and is a common accessory in granites, while magnesian varieties are associated with metamorphic or metasomatic assemblages (Ethier and Campbell 1977). In igneous rocks boron is enriched via three primary processed that can lead to the formation (1): partial melting of boron-bearing protoliths, (2): fractional crystallization of igneous melts, and (3): generation of hydrothermal fluids in association with boron-bearing melts. (Barbara L. Dutrow et al, 2011). As study of the quartz veins would be useful toward understanding magmatic-hydrothermal evolution of a mineralization complex and formation of various types of quartz veins in a porphyry system is associated with ore mineralization (Azadi et al, 2014), the third primary process is going to be investigated through this article. Fracture filling quartzvein tourmalines are the most abundant vein types of the Kahang area and are going to be focused through the present study to illustrate chemical composition and probable genesis of tourmaline. Geological Setting This deposit is located in the central part of Cenozoic Urumieh-Dokhtar magmatic belt which was formed during the successive stages of Tethyan ocean closure during the Cretaceous- Oligocene subduction and late Paleogene continent-continent collision (Bernerian and King 1981; Pourhosseini 1982, Hezarkhani 2006a). This zone comprised of quite all of the large porphyry copper deposits of Iran such as Sarcheshmeh, Meiduk, Sungon and Kahang (Fig. 1). Fig. 1: Modified geological map of Kahang porphyry copper deposit (Azadi et al, 2014).

3 Methods Optical petrography was utilized to initially characterize polished thin sections of the samples; About 100 polished thin sections of Kahang porphyry copper deposit were studied using an Olympus microscope at mineralogy and petrology laboratory of University of Tehran. Two sections are then selected as representative samples and analyzed for almost 60 spots using microprobe analyzer JXA-8900R_WD/ED housed in the Department of Geosciences at University of Tubingen/ Germany. The thin sections were, first, scanned w/ the 10X objective, plane polarized light (PPL), then, selected areas on the thin section were examined through EPMA analysis. A Microsoft Visual Basic program, WinTcac, is used to calculate chemical composition of tourmaline as well as plotting descriptive compositional diagrams. Petrography Detailed core logging and petrographic studies of thin sections indicated that igneous rocks in Kahang porrphyry deposit are divided into three types (Azadi et al, 2014). The first rock suites are Eocene volcanic host rocks including mainly andesite, trachy-andesite, tuff, basalt and quartz-andesite. Oligo-Miocene quartz-diorite-granodiorite and late dacite are the quartztourmaline units, classified into the second group (Fig. 2A). The last and third rock types are post-mineralization dacitic and andesitic dikes, injected into the older unites. Tourmalines of Kahang porphyry copper deposit are generally divided into 3 types (1): fracture filling quartz-tourmaline veins along with quartz-diorite-granodiorite and late dacite rock type, (2): near surface tourmaline-bearing breccia pipes, (3): Crystals of disseminated tourmalines in diorite and granodiorites (Rasekh, 2014). Fracture filling quartz-tourmaline veins are the most abundant vein types of the Kahang area which are clearly visible (Fig. 2A). Within the veins, tourmaline is surrounded by pyrite, anhydrite and quartz (Fig. 2B). BSE images represent fine scale compositional zoning resulting from compositional variation within individual tourmaline grains (Fig. 2C).

4 Fig. 2: (A). Drilled core of the studied area as the representative sample; (B). Radiated tourmalines in vicinity of quartz, pyrite and anhydrite (PPL); (C). BSE image of the zoned tourmalines; Mineral abbreviations have been taken from Whitney et al. (2010). Mineral Chemistry of Tourmaline The general formula for the tourmaline group is (R1)(R2)3(R3)6 (BO3)3Si6O18(OH,F)4, where common site consists of: R1 = Na, Ca, K or vacant; R2 = Mg, Fe 2+, Mn 2+, Fe 3+, Cr 3+, V 3+, Ti 4+, Al or Li ( when coupled with Al); R3 =Al, Fe 3+, Mg 2+ (when coupled with Ca in R1); or 1.33Ti 4+ (London and Manning, 1995). London and Manning (1995), believed that tourmalines with magmatic origin are essentially unzoned and may be distinguished by high Fe/Mg, high F, high Al in the R2 site and high

5 Fe/(Fe+Mg) ratios with predominantly schorl in component. In contrast, tourmalines of hydrothermal origin can be considered by petrographical and chemical fine-scale zonation (Fig. 2B) with compositions close to the schorl-dravite solid solution and they have little or no Al in the R2 site. The calculated X-site cation totals (Na+Ca+K) for the studied quartz veins samples ranges from to apfu which compared with the ideal value of 1.0 apfu for tourmalines of the schorl-dravite solid solution (Harraz and Sharkawy 2001). These values show the existence of vacancies in the X-site, ranging for quartz vein tourmalines from to apfu. Plotting of the data in (Na+X-vacancy) vs. Mg/(Fe+Mg) diagram shows compositional range from schorl to dravite (Fig. 3A). Plotting Ca-X site vacancy-na+(k) ternary diagram, it is found that the tourmalines are categorized as alkali group (Fig. 3B). The studied tourmalines are plotted in (R 1+ +R 2+ ) versus R 3+ diagram which show that the most tourmaline samples reflect extent of substitution toward proton- deficient and according to (Henry and Dutrow 1990); this is consistent with tourmalines of quartz veins (Fig. 4). When the data plotted on Al-Fe(tot)-Mg and Ca-Fe (tot) -Mg ternary diagrams indicated that quartz-tourmaline veins of the study area are derived from a probable origin as iron-rich quartz-tourmaline rocks, calc-silicate rocks, Ca-poor metapelites and metapsammites (Fig. 5A and B). The FeO/(FeO+MgO) ratio can be used to discriminate tourmalines formed in different host lithologies. This ratio for the tourmaline from the quartz veins is less than 0.6 (Henry and Dutrow 1996). Thus, it appears that the range in the FeO/(FeO+MgO) ratios for the investigated tourmalines of kahang area (ave. 0.58) correlated better with those of ferric iron-rich quartztourmaline rocks. Plotting of data on ternary diagram Ca X-Vacancy (Na+K) it is claimed that the tourmalines from Kahang area belongs to the Alkali group domain (Fig. 3B).

6 A B Fig.3: (A). (Na+X-vacancy) vs. Mg/(Fe+Mg) diagram shows compositional range from schorl to dravite end members (Yavuz et al, 2008); (B). Showing the tourmalines from the Kahang in the alkali group domain (from Hawthorne and Henry, 1999). Fig. 4: R 3+ vs. (R 1+ +R 2+ ) (apfu) diagram (Modified from Yavuz, 2008).

7 Fig.5: Microprobe compositions of tourmaline from the Kahang area, plotted on the (A) Al Fe (tot) Mg and (B) Ca Fe (tot) Mg diagrams of Henry and Guidotti (1985). 1: Li-rich granitoid pegmatites and aplites, 2: Li-poor granitoids and their associated pegmatites and aplites, 3: Ferric iron-rich quartz tourmaline rocks (hydrothermally altered granites), 4: Metapelites and metapsammites coexisting with an Al-saturating phase, 5: Metapelites and metapsammites not coexisting with an Al-saturating phase, 6: Ferric iron-rich quartz tourmaline rocks, calc-silicate rocks, and metapelites, 7: Low-Ca metaultramafics and Cr, V-rich metasediments, 8: Metacarbonates and metapyroxenites, 8: Metacarbonates and meta-pyroxenites, 9: Ca-rich metapelites, metapsammites and calc-silicate rocks, 10: Ca-poor metapelites, metapsammites and quartz-tourmaline rocks, 11: Metacarbonates, 12: Metaultramafics. Fig.6: Tourmaline composition from granite related deposits in the MgO (wt%) vs. FeO/(FeO+MgO) diagram from Pirajno and Smithies, Pirajno and Smithies (1992) proposed that the Fe # [Fe # =FeO/(FeO+MgO)] of tourmaline is as an indicator of proximity indicator. For tourmalines associated with granite related may be

8 considered as proximal to distal due to the distance from the inferred granitic source. Tourmalines from granites and metasedimentary environments have Fe # values ranging from 0.86 to 0.96 and 0.41 to 0.67, respectively (Henry and Dutrow 1996). Tourmalines with Fe # values, higher than 0.8 correspond to an endogranitic to proximal setting, between 0.8 and 0.6 are indicative of proximal to intermediate deposits, and those with Fe # values lower than 0.6, just same as the investigated samples of this study (Fig. 5B) are considered as distal (Pirajno and Smithies 1992). Conclusions Tourmalines of the porphyry-copper deposits are characterized by several generations and complexly zoned individual crystals. Tourmalines from quartz veins in Kahang deposit display schorl-dravite component and are considered as alkali group. The results of the chemical data show that most of the tourmalines reflect extent of substitution toward proton- deficient. Al- Fe (tot) -Mg and Ca Fe(tot) Mg diagrams indicate that the tourmalines from Kahang area fall within a field related to ferric iron-rich quartz-tourmaline rocks, calc-silicate rocks, metapelites, Capoor metapelites and metapsammites. The tourmalines from quartz veins, with average Fe # values of 0.58 are represented as distal. According to the petrographic observations as well as geochemical signatures, the investigated tourmalines are classified as hydrothermal origin and can be used in geochemical prospecting for further prospectivity mapping of copper mineralization.

9 References Azadi, M., Mirmohammadi, M., Rasekh, P., "Geometric-Genetic and Mineralogic Classification of Veinlets and Breccias in Kahang Porphyry Copper Deposit, Northern East Isfahan, Iran", 21 th Symposium of Mineralogy and Crystallography Association of Iran. Rasekh, P., "Chemical characteristics of Tourmaline in various hydrothermal deposits of Iran", (Unpublished BSc. Thesis). University of Tehran, Tehran, Iran. Berberian, M., King, G. C., "Towards a paleogeography and tectonics evolution of Iran", Canadian Journal of Earth Sciences. 18: Burianek, D., Hanzl P., Hrdlickova, K., "Pegmatite dykes and quartz veins with tourmaline: an example of partial melting in the contact aureole of the Chandman Massif Intrusion, SW Mongolia", J. Geoscience, 56, p Buriánek, D., Novák, M., "Compositional evolution and substitutions in disseminated and nodular tourmaline from leucocratic granites: examples from the Bohemian Massif, Czech Republic", Lithos, 95, p Azadi, M., Mirmohammadi, M., Hezarkhani, A., "Aspects of magmatic hydrothermal evolution of Kahang porphyry copper deposit, Central Iran", J. Geoscience. Harraz, HZ., Sharkawy, FEL., "Origin of tourmaline in the metamorphosed Sikait pelitic belt, South Eastern Desert Egypt", J. African Earth Sci, 33: Dutrow, B., Henry, D., "Tourmaline: A Gelogic DVD", Gselements, p Hawthorne, FC., Henry, DJ., "Classification of the minerals of the tourmaline group", Eur. J. mineral. 11: Yavuz, F., Karakaya, N., Yıldırım, D.K., Karakaya, M.C., Kurmal, M., "A Windows program for calculation and classification of tourmaline-supergroup (IMA-2011)", Computers & Geosciences, 63: London, D., Morgan, GB., VI Wolf, MB., "Boron in granitic rocks and their contact aureoles", Mineral. 33: London, D., Manning, DAC., "Chemical variation and significance of tourmaline from SW England", Economic Geology 90: Medaris, LG., Fournelle, JH., Henry, DJ., "Tourmaline-bearing quartz veins in the Baraboo Quartzite, Wisconsin: Occurrence and significance of foitite and oxy-foitite ", Can. Mineral. 41: Pesquera, A., Torres-Ruiz, J., Gil-Crespo, PP., Velilla, N., "Chemistry and genetic implications of tourmaline and Li-F-Cs micas from the Valdeflores area (Caceres, Spain)", Am. Mineral. 84:

10 Whitney, DL., "Abbreviations for names of rock-forming minerals", American Mineralogist, Volume 95, p Hawthorne FC, Henry DJ., "Classification of the minerals of the tourmaline group", Eur J Mineral, 11: Pirajno, F., Smithies, RH., "The FeO/(FeO+MgO) ratio of tourmaline: a useful indicator of spatial variations in granite-related hydrothermal mineral deposits", J. Geochem. Explor. 42: Henry, DJ., Guidotti, CV., "Tourmaline as a petrogenetic indicator mineral: An example from the staurolite-grade metapelites of NW Maine", Am Mineral p.70:1 15. Henry, DJ., Dutrow, BL., "Metamorphic tourmaline and its petrologic applications", Am Mineral 70:1 15. Mineralogy, Petrology and Geochemistry, Rev Mineral p.33:

Geochemistry and genesis of Darb-e-Behesht porphyric copper index, South Kerman, Iran

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