Mineralogy, Geochemistry, and Origin of Buyukmahal Manganese Mineralization in the Artova Ophiolitic Complex, Yozgat, Turkey
The Artova ophiolite complex (AOC) is exposed along the northwestern and eastern margins of Yozgat area in Turkey. The Mn-deposit in the Buyukmahal area is part of this ophiolite complex. The deposit is in banded and lenticular forms and hosted by a radiolarite unit overlying the volcanics. Pyrolusite and magnetite are the main minerals of the manganese ore in the Buyukmahal (Yozgat) area. The gang minerals in the deposit are composed only of quartz and calcite. In this study, mineralogy, major oxide, trace element and REE contents of Buyukmahal manganese mineralization are evaluated. The geochemical data indicate that Buyukmahal mineralization does not originate from a pure hydrothermal or pure hydrogenous source but from a system consisting of both sources. It is also asserted that the mineralization was first developed on a sea floor spreading center within the Alpine Ophiolite System and then obducted as part of the AOC.
The Alpine Ophiolite System (AOC) is exposed along the northwestern and eastern margins of the Yozgat region in Turkey. The Mn mineralization in the Buyukmahal is a part of this ophiolite complex. The mineralization in this area is highly firm and generally fractured and folded, developed in banded and lenticular shape, and syngenetic with radiolarite cherts. Mineralizations are chiefly NW-SW trending and small anticline structures are observed in some parts. Although mineralization in the Buyukmahal area has not been studied, Derbent and Eymir manganese deposits within the AOC were investigated recently by Öksüz [1, 2]. These deposits were operated from time to time by local miners, but lately none of the deposits is mined out due to low reserve potential. The Eymir manganese deposit which is genetically linked to Buyukmahal mineralization occurs within radiolarite cherts of the lower Cretaceous ophiolite complex . Major and trace element contents of the Eymir ore indicate that the deposit is of a hydrothermal-hydrogenous type volcano sedimentary mineralization and both oxic and anoxic sedimentation conditions prevailed. The Derbent manganese mineralization, another manganese deposit in the Yozgat region, occurs as two separate ore bodies . Chemical data yield that hydrothermal and hydrogenous-diagenetic processes played important role in formation of Derbent mineralization. The geochemical characteristics of these deposits are consistent with those of several other manganese mineralizations such as Waziristan, Hazara , Baby Bare , Baft Ophiolitic melange Kerman (Iran) , Wakasa , Çayırlı , and Kasımağa  deposits. Particularly Waziristan (Pakistan) and Çayırlı (Turkey) deposits are regarded as hydrothermal exhalative manganese deposits occurring on seafloor spreading centers associated with ophiolite units [9, 10]. The Buyukmahal deposit under investigation is also thought to be a hydrothermal exhalative manganese mineralization. The aim of this study is to discuss the mineralogical and geochemical mechanisms responsible for development of manganese ore in the Buyukmahal area.
2. Geological Setting
Turkey comprising the border between Eurasia at the north and Gondwana at the south is an E-W elongating component of the Alpine-Himalayan Orogenic zone. The Alpine Orogenic system is formed by the closure of a different branch of the Tethys Ocean. During the closure of Tethys Ocean, continental parts of the Gondwana and Laurasia continents collided. Turkey as an orogenic mosaic (orogenic collage) is a part of these continental parts including remnant materials between these continentals . The AOC is included to the Alpine Orogenic system. The AOC of Upper Cretaceous age shows a wide distribution and hosts several ore mineralizations.
Darmik formation of Upper Cretaceous age consists of Boyalik limestone, Akcadag sandstone, and a radiolarite member. Sarimbey volcanic assemblage (spilitic basalt, andesite unit), Artova ophiolite complex (serpentine, harzburgite, dunite, gabbro, diabase, chert), and Cretaceous limestone blocks are also observed in the area. Artova ophiolite complex is unconformably overlain by conglomerate, sandstone, mudstone, and gypsum levels of the Incik formation of terrestrial character  (Figure 1).
Ore bodies in the study area occur as laminated, banded and lenticular forms (Figures 2(a), 2(b), 2(c) and 2(d)). The mineralization is entirely associated with radiolarite cherts and thickness of lamina and bands is in the range of 1 to 90 cm. Manganese ores are quite fractured and fissured and show an irregular structure (Figure 2(a)). Polished section determinations indicate that ore assemblage is composed of hematite and pyrolusite, whilst quartz and calcite are the gangue minerals. Pyrolusite and magnetite are the main minerals in the Buyukmahal deposit. Hematite peaks were recorded in XRD analysis but it could not be observed in ore microscopy and Raman spectroscopy determinations.
3. Material and Methods
Twenty ore samples (500 g each) were collected from the Buyukmahal manganese deposit. The whole section of the ore from top to bottom was sampled systematically. Samples were taken at 30 cm intervals.
Powders of 12 samples under 200 mesh were analyzed at ACME Laboratories. Major oxide and trace element contents were determined with ICP-ES and REEs were analyzed with the ICP-MS method. 30 g sample was powdered into 100 μm for geochemical analysis. 0.5 g sample was processed in HCl-HNO3-H2O solution at ~95°C for 1 hour and then the amount of sample was increased 10 mL for the final filtering. Results of analysis are given in Tables 1, 2, and 3. In addition, in order to determine paragenesis and textural characteristics of mineralization, 10 polished sections were studied with ore microscopy. XRD analysis for six samples was done at TPAO (Turkish Petroleum Corporation) laboratories. A Rigaku DMAX IIIC model X-Ray diffractometer with a Cu target (2–70° 2θ) was used in the analyses. Ore minerals were also studied with Thermo Scientific DXR Raman Microscope at the Geological Department of the Ankara University. The Raman spectrums obtained were evaluated with Crystal Sleuth program to determine the mineral paragenesis. Chemical composition of pyrolusite was determined with microprobe analysis conducted at Montan Universität in Leoben (Austria). The results are shown in Table 4.
Mineral paragenesis in the study area was investigated with ore microscopy studies as well as XRD, Raman spectroscopy, and microprobe analysis for pyrolusite. Results show that pyrolusite and magnetite are the main ore minerals in the Buyukmahal area accompanied by little amount of hematite. Gangue minerals are quartz and calcite. Results of microprobe analysis performed on four points in a pyrolusite crystal are shown in Table 4.
4.1. Pyrolusite (MnO2)
It is mostly precipitated from low-temperature hydrothermal fluids. Pyrolusite is a common alternation mineral in oxidized marine environments. Pyrolusite and magnetite, forming the main components of the Buyukmahal area, with a whitish yellow color, are distinct with their strong anisotropic character. Pyrolusite minerals develop in small veins and characteristic with anhedral and subhedral cutaways. Ore microscopy and Raman spectroscopy images of pyrolusite are shown in Figure 3. Using the results of microprobe analysis, the structural formula of pyrolusite (on the basis of two oxygen) is calculated as Mn1.69-Fe0.07-Si0.09-Al0.02-Ca0.01O2 (Table 4).
4.2. Magnetite (Fe3O4)
Magnetite occurs as small scattered crystals or veins. Vein magnetite is observed cutting the pyrolusite (Figure 4). In single nicol magnetite is seen in brown and gray colors and in the crossed nicols it is in anisotropic character. Samples are slightly magnetic. Ore microscopy and Raman spectroscopy images of magnetite are shown in Figure 4.
Geochemical data are used to determine the origin of mineralization (e.g., hydrothermal, hydrogenous, and diagenetic). The chemical composition of Buyukmahal deposit is SiO2: 85.40 to 10.32 wt%, MnO2: 68.54 to 6.79 wt%, and Fe2O3: 16.73 to 2.31 wt%. Fe and Mn are characteristically fractionated on precipitation from a hydrothermal solution, producing high or low Mn/Fe rations in exhalative sediments . Mn/Fe rations of the deposit range from 25.89 to 0.90 wt% (Table 1). These values are conformable with those of hydrothermal exhalative manganese deposits in ophiolitic regions and recent submarine spreading centers [1, 14, 15].
The Si-Al discrimination diagram, proposed by Peters , is used to distinguish hydrothermal from hydrogenous Mn-oxide deposits. Buyukmahal ore samples are almost within the field of hydrothermal field, with only one sample within the field of hydrogenous deposits (Figure 5).
Ba contents of Waziristan , Hazara (Pakistan) , Binkılıç , Çayırlı , and Kasımağa (Turkey)  regions are very high (415, 6304, 6892, 1229, and 2719, resp.) indicating a sedimentary contribution. High Ba content of the Buyukmahal deposit (ave. 3659) is also indicative of sedimentary origin. Modern submarine hydrothermal Mn-oxide deposits are more enriched in Cu, Zn, Ni, and Co contents in comparison to pelagic sediments. However, they are lower than hydrogenous deposits [13, 18]. Choi and Hariya  discriminated hydrogeneous deposits and submarine hydrothermal Mn-deposits on a Ni-Zn-Co ternary diagram. On this diagram, five samples are plotted near hydrogenous fields and seven samples are close to hydrogenous field (Figure 6). In Fe-(Ni + Co + Cu) * 10-Mn triangular diagram [9, 10, 19], all samples are plotted in hydrothermal and diagenetic fields (Figure 7). Correlation data on major oxide and some trace elements contents of ore samples are given in Table 5.
The correlation coefficients indicate the presence of strong positive relations between major oxides and various trace elements (Al2O3-Fe2O3: ; Al2O3-TiO2: ; TiO2-Fe2O3: ) and the contribution of mafic terrigenous material to the deposition environment.
Major oxide, trace, and REE geochemistry are very useful for understanding the formation conditions of ore deposits. REE contents of 12 samples collected from the Buyukmahal manganese mineralization are shown in Table 6.
REE contents of the hydrothermal and hydrogenous ferromanganese and manganese deposits differ considerably and thus can provide great information on the genetic processes involved in the formation of submarine manganese and ferromanganese ores [20–23]. REE patterns of the studied deposit (Figure 8(a)) are compared with those of other hydrogenous and hydrothermal manganese deposits (Figure 8(b)). Results indicate that hydrogenous ferromanganese deposits are more enriched in REEs than their hydrothermal equivalents. Hydrogenous ferromanganese deposits show positive Ce anomaly but hydrothermal ferromanganese deposits are characteristic with negative Ce anomaly [22–24]. All samples of the Buyukmahal manganese mineralization show strong negative Ce anomalies which resemble the pattern of typical submarine hydrothermal deposits (Figure 8(a)). However, the Ce anomaly depends on the temperature of the fluid, the proximity to the hydrothermal source, and redox conditions [23, 25, 26]. Eu also shows negative anomaly in all samples, indicating contamination from the continental crust and/or sediment contribution via dehydration .
In hydrothermal solutions LaN/NdN ratio is 3.0–7.4 (average 4.5) and DyN/YbN ratio is 0.6–2.1 (average 1.2). These ratios in Mn-oxide crusts are 2.7–4.3 and 0.4–1.2, respectively . These rations in hydrogenous deposits are 0.90–1.50 and 0.3–1.91, respectively . The ranges of LaN/NdN and DyN/YbN ratios for the Buyukmahal manganese mineralization are 1.41–2.34 (average 1.82) and 0.90–1.44 (average 1.18) (Table 6). These values imply that Buyukmahal mineralization might be a hydrogenous deposit.
Y/Ho ratios in the area range from 13.06 to 31.54 (average 25.05). High Y/Ho ratios are indicative of multienvironments for the mineral deposition. In this respect, both deep marine environments and terrigenous materials may be effective for precipitation .
Data computed with the formula of Ceanom = log [3 × CeN/(2 × LaN + NdN)] also yield information on the origin of mineralization. For example, in the case of Ceanom > −0.1, Ce is said to be enriched, which reflects an anoxic character for the water body of sedimentation. If Ceanom < −0.1, there is a negative Ce anomaly which indicates an oxic nature for the water body of sedimentation . Ce anomalies in all samples at Buyukmahal are found to be Ceanom < −0.1, indicating an oxic character for the sedimentation environment.
6. Discussions and Conclusions
The AOC of Upper Cretaceous age is located along the northwestern and eastern margins in Yozgat (Turkey) and is included to the Alpine Orogenic system. Mineralization in the Buyukmahal area, observed in banded and lenticular forms, occurs in a close association with radiolarite cherts and is intensely affected by the tectonism.
Based on the results of major and trace element data, mineralization in the study area was probably formed from hydrothermal solutions associated with a sea floor spreading center. However, ore minerals at Buyukmahal were not precipitated entirely from a purely hydrothermal or purely hydrogenous fluid, but certainly from a mixture of these two. For instance, Ti is generally immobile in hydrothermal solutions and could be a measure of clastic input . The good correlation observed between Al2O3 and TiO2 () can be attributed to the mixing of detrital materials during precipitation .
Fe compounds (less stable than Mn) precipitate proximal parts, whilst Mn compounds precipitate distal parts of hydrothermal vents along the sea floor spreading centers [33, 34]. Eh and/or pH of the hydrothermal solution also exert controls on the precipitation of Mn and Fe and their compounds [34–37]. Mn is more mobile relative to Fe during low Eh and/or pH conditions. The fractionation of Mn compounds from Fe compounds suggests a spatial variation in Eh and/or pH . Considering Fe and Mn concentrations of the mineralization in the study area, it can be asserted that Buyukmahal deposit was formed from a hydrothermal source; in addition, considering the high Fe content, mineralization might be formed in a proximal site of the hydrothermal vent.
Although mineralization at Buyukmahal is of a hydrothermal type, it does not originate from a pure hydrothermal or pure hydrogenous source. Geochemical data support a system contributed from both sources. The mineralization was developed on a sea floor spreading center within the Alpin Ophiolite system and then obducted as part of the AOC.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
This study constitutes a part of M.S. degree thesis of Neslihan Okuyucu. The Scientific and Technical Research Council of Turkey (TUBITAK Project no. 109Y167) and the Bozok University (Grant no. B.F.F.M/2009-06) are greatly acknowledged for financial support. Dr. Ibrahim Uysal is kindly appreciated for his help in EMP analysis. The authors also thank Professor Yusuf K. Kadıoğlu and Cumhur Ö. Kılıç for the Raman spectroscopy analysis.
N. Öksüz, “Geochemistry and the origin of manganese mineralizations in Derbent (Yozgat) Region,” Bulletin of the Earth Sciences Application and Research Centre of Hacettepe Universit, vol. 32, no. 3, pp. 213–234, 2011.View at: Google Scholar
K. Heshmatbehzadi and J. Shahabpour, “Metallogeny of manganese and ferromanganese ores in baft ophiolitic Mélange, Kerman, Iran,” Australian Journal of Basic and Applied Sciences, vol. 4, no. 2, pp. 302–313, 2010.View at: Google Scholar
J. H. Choi and Y. Hariya, “Geochemistry and depositional environment of Mn oxide deposits in the Tokoro Belt, northeastern Hokkaido, Japan,” Economic Geology, vol. 87, no. 5, pp. 1265–1274, 1992.View at: Google Scholar
S. Koç, Ö. Özmen, and N. Öksüz, “Geochemistry characteristic of kasimaga (Keskin-Kırıkkale) manganese oxide mineralizations,” Mineral Research and Exploration Magazine, vol. 122, p. 107, 2000.View at: Google Scholar
E. Bonatti, T. Kraemer, and H. Rydell, “Classification and genesis of submarine iron-manganese deposits,” in Ferromanganese Deposits on the Ocean Flor: International Decade on Ocean Exploration, D. Horn, Ed., pp. 149–166, National Science Foundation, Washington, DC, USA, 1972.View at: Google Scholar
D. A. Crerar, J. Namson, M. S. Chyi, L. Williams, and I. M. Feigenson, “Manganiferous cherts of the Fransiscan assemblage: I. General geology, ancient and modern analogues, and implications for hydrothermal convection at oceanic spreading centers,” Economic Geology, vol. 77, pp. 519–540, 1982.View at: Google Scholar
A. Okay and O. Tuysuz, “Tethyan sutures of northern Turkey,” in The Mediterranean Basins: Tertiary Extension Within the Alpine Orogen, B. Durand, L. Jolivet, F. Horvath, and M. Serrane, Eds., vol. 156, pp. 475–515, Geological Society, London, UK, 1999.View at: Google Scholar
A. E. Akcay, M. Dönmez, H. Kara, A. F. Yergök, and K. Esentürk, “1/100 000 scale geological maps of Turkey, Yozgat-İ33 threader,” MTA Ankara, vol. 80, pp. 1–16, 2007.View at: Google Scholar
X. Jiancheng, S. Weidong, D. Jianguo et al., “Geochemical studies on Permian manganese deposits in Guichi, eastern China. Implications for their origin and formative environments,” Journal of Asian Earth Science, vol. 74, pp. 155–166, 2013.View at: Google Scholar
A. Sasmaz, B. Turkyilmaz, N. Ozturk et al., “Geology and geochemistry of middle eocene maden complex ferromanganese deposits from Elazığ-Malatya Region, Eastern, Turkey,” Ore Geology Reviews, vol. 56, pp. 352–372, 2014.View at: Google Scholar
T. Peters, “Geochemistry of manganese-bearing cherts associated with Alpine ophiolites and the Hawasina formations in Oman,” Marine Geology, vol. 84, no. 3-4, pp. 229–238, 1988.View at: Google Scholar
A. H. Gültekin, “Geochemistry and origin of the Oligocene Binkılıç manganese deposit, Thrace basin, Turkey,” Turkish Journal of Earth Sciences, vol. 7, p. 11, 1998.View at: Google Scholar
D. S. Cronan, “Underwater minerals,” Academic Press, London, UK, 1980.View at: Google Scholar
J. R. Hein, S. S. Marjorie, and L. M. Gein, “Central Pasific cobalt rich ferromanganese crusts. Historical perspective and regional variability,” in Geology and Offshore Mineral Resources of the Central Pasific Basin, Sircum Pasific Council for Energy and Mineral Resources, B. H. Keating and B. R. Balton, Eds., vol. 14 of Earth science series, Springer, New York, NY, USA, 1992.View at: Google Scholar
J. R. Toth, “Deposition of submarine crusts rich in manganese and iron,” Geological Society of America Bulletin, vol. 91, no. 1, pp. 44–54, 1980.View at: Google Scholar
D. E. Ruhlin and R. M. Owen, “The rare earth element geochemistry of hydrothermal sediments from the East Pacific Rise: examination of a seawater scavenging mechanism,” Geochimica et Cosmochimica Acta, vol. 50, no. 3, pp. 393–400, 1986.View at: Google Scholar
J. D. Wonder, P. G. Spry, and K. E. Windom, “Geochemistry and origin of manganese-rich rocks related to iron-formation and sulfide deposits, western Georgia,” Economic Geology, vol. 83, no. 5, pp. 1070–1081, 1988.View at: Google Scholar
J. R. Hein, A. Kochinsky, P. Halbach et al., “Iron and manganese oxide mineralization in the Pacific,” in Manganese Mineralization: Geochemistry and Mineralogy of Terrestrial and Marine Deposits, K. Nicholson, J. R. Hein, B. Buhn, and S. Dasgupta, Eds., vol. 119, pp. 123–138, Geological Society, London, UK, 1997.View at: Google Scholar
H. Elderfield, C. J. Hawkesworth, M. J. Greaves, and S. E. Calvert, “Rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments,” Geochimica et Cosmochimica Acta, vol. 45, no. 4, pp. 513–528, 1981.View at: Google Scholar
J. R. Hein, Y. Hsueh-Wen, S. H. Gunn, A. E. Gibbs, and W. Chung-ho, “Composition and origin of hydrothermal ironstones from central Pacific seamounts,” Geochimica et Cosmochimica Acta, vol. 58, no. 1, pp. 179–189, 1994.View at: Google Scholar
S. S. Sun and W. F. McDonough, “Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes,” in Magmatism in Ocean Basins, A. D. Saunders and M. J. Norry, Eds., pp. 313–345, Geological Society, London, UK, 1989.View at: Google Scholar
N. M. Evensen, P. J. Hamilton, and R. K. O'Nions, “Rare-earth abundances in chondritic meteorites,” Geochimica et Cosmochimica Acta, vol. 42, no. 8, pp. 1199–1212, 1978.View at: Google Scholar
J. Nayan, J. Rongfen, and W. Ziyu, Permain Palaeogeography and Geochemical Environment in Lower Yangtze Region, Petroleum Industry Press, Beijing, China, 1994.
J. Wright, H. Schrader, and W. T. Holser, “Paleoredox variations in ancient oceans recorded by rare earth elements in fossil apatite,” Geochimica et Cosmochimica Acta, vol. 51, no. 3, pp. 631–644, 1987.View at: Google Scholar
R. Sugisaki, “Relation between chemical composition and sedimentation rate of Pacific ocean-floor sediments deposited since the middle Cretaceous: basic evidence for chemical constraints on depositional environments of ancient sediments (plate tectonic orogenic model),” Journal of Geology, vol. 92, no. 3, pp. 235–259, 1984.View at: Google Scholar
A. G. Panagos and S. P. Varanavas, “On the genesis of some manganese deposits from eastern Greece,” Syngenesis and Epigenesis in the Formation of Mineral Deposits, pp. 553–561, 1984.View at: Google Scholar
S. Roy, “Environments and processes of manganese deposition,” Economic Geology, vol. 87, no. 5, pp. 1218–1236, 1992.View at: Google Scholar
K. B. Krauskopf, “Separation of manganese from iron in sedimentary processes,” Geochimica et Cosmochimica Acta, vol. 12, no. 1-2, pp. 61–84, 1957.View at: Google Scholar
J. D. Hem, “Chemical factors that influence that influence the availability of iron and manganese in aqueous systems,” Geological Society of America Bulletin, vol. 83, pp. 443–450, 1972.View at: Google Scholar
L. Frakes and B. Bolton, “Effects of ocean chemistry, sea level, and climate on the formation of primary sedimentary manganese ore deposits,” Economic Geology, vol. 87, no. 5, pp. 1207–1217, 1992.View at: Google Scholar