Sulfur isotopic properties and its relationship with TOC in sedimentary copper deposits of the Nahand- Ivand area, NW Iran

Document Type : Research Article

Authors

• Seyedeh Narges Sadati ¹
• Mohammad Yazdi ²
• Zahra Nourian Ramsheh ²

¹ Mohaghegh Ardabili

² Shahid Beheshti

10.22067/econg.v10i1.56795

Abstract

Introduction
The Tabriz basin is an intra-mountain basin (Reichenbacher et al., 2011), which includes the Qom Red Bed Formation along with the Miocene Upper Red Formation. The lower unit of the Upper Red formation, M2mg unit, which hosts copper deposits includes an alternation of green grey sandstone and red marl with the interlayer of gypsiferous and saltiferous sediments (Sadati et al., 2013). Based on paleontological evidence, this unit is middle Miocene in age and is overlain by red sandstone, marl, shale (M3ms, M4sm) and locally up to red conglomerate (M5sc). In addition, this unit has considerable evaporitic layers, such as gypsum and salt.
On the basis of field study all mineralization is distributed in the light-colored layers of the red sedimentary sequence, especially at the boundary between a red layer and a light-colored layer and is mostly restricted to within palaeo channels which consist of greenish-grey, well-sorted coarse- to very coarse-grained sandstones to microconglomerates.
Both pyrite and copper-bearing minerals usually occur in the stratification of the organic matter- bearing host rocks which are mainly composed of gray sandstone.
The size of organic matter varies from a few millimeters to 5-10 cm in length; almost all fragments are flattened and oriented conformably to bedding planes of host sedimentary rocks. Also,
fine-grained sulfides are disseminated along the bedding planes in the sandstone. Copper precipitation in these places was possibly promoted by reduction from such organic materials.

Sampling and analytical methods
Investigations on mineralized samples showed that pyrite is the first sulfide mineral precipitated in the selected samples, followed by chalcopyrite, bornite, chalcocite, digenit, and covellite. The intergrown nature of sulphur-bearing minerals, along with their small grain size and their inter locking with detrital grains and calcite cement, make physical separation extremely difficult, although microdrilling techniques can achieve spatial resolutions for these samples. In the laboratory 25 to 100 µg (weight depends on the mineral analyzed) of the samples derived from microdrilling was combusted in a Eurovector 3000 elemental analyzer, yielding sulfur dioxide that was delivered to an Isoprime mass spectrometer using continuous-flow techniques, with helium as the carrier gas.
Also, sulfide mineral powder was analyzed for the sulfur isotope compositions. Some samples were crushed to 40 to 60 meshes and the sulfide mineral separates were handpicked under a binocular microscope. The sulfur isotopes were analyzed at the Stable Isotope Laboratory, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing. The isotopic data are reported using the δ notation in units of per mil, relative to the Cañón Diablo troilite (CDT) standard.
Organic carbon (TOC) was determined by treating powdered samples with 6 M HCl to remove the carbonate. The sample was then rinsed to remove the acid. The mass difference between the original sample and the acid-treated residue was used to determine the carbonate content.
The dried sample was then combusted and the evolved CO2 was analyzed on the mass spectrometer. During the mass spectrometric analysis the sample peak height was calibrated against organic carbon standards to estimate the organic carbon content.

Result and Discussion
Framboidal pyrite is the most common typical byproduct of bacterial sulfate reduction (BSR), a process that occurs at temperatures from 0°C up to about 60–80°C (Donahue et al., 2008).
The metabolic activity of the sulfate reducing bacteria generally depletes (or fractionates) the resulting sulfide in 34S, by up to 70% (Kalender, 2011).
The availability of S content is consistent with controlling δ34Ssulfide in some portions of this study area, but not all. Total organic carbon (TOC) is above 4% for one mineralized sample of the Upper red Formation.
Sulfide sulphur and organic carbon distribution shows that pyrite-rich sandstones are the copper ore precursor, and that mineralizing the processes provoked the depletion of both reduced S and organic C as a consequence of interaction with an oxidized Cu-bearing fluid. On the other hand, lowed 34S values are consistent with bacteriogenic derivation of sulphur.

Conclusion
Taking into account the sedimentary environment, the abundant presence of the former evaporit layers in the host rock, the presence of evaporit layers below and above the mineralized rocks, and the absence of a widespread magmatic sulfur source, it is concluded that the Cu-Co sulfides of the Nahand-Ivand deposits obtained their sulfur by either bacterial or thermochemical reduction of sedimentary sulfate. The examined samples preserved original sedimentary textures (i.e. immature organic matter and sedimentary bedding). These geological evidences point to the fact that a biological (thermochemical) sulfate reduction is unlikely. Therefore, the sulfate-reducing bacteria were responsible for pyrite formation in the examined sample.
The S isotope composition of pyrite in this study is related to organic C abundance. Most of the samples show a correlation between S and C, but mineralized samples are relatively enriched in S and TOC content.

References
Donahue, M.A., Werne, J.P., Meile, C. and Lyons, T.W., 2008. .Modeling sulfur isotope fractionation and differential diffusion during sulfate reduction in sediments of the Cariaco Basin. Geochimica et Cosmochimica Acta, 72(9): 2287–2297.
Kalender, L., 2011. Oxygen, carbon and sulphur isotope studies in the KebanPb–Zn deposits, eastern Turkey: An approach on the origin of hydrothermal fluids. Journal of African Earth Sciences, 59(4–5): 341–348.
Reichenbacher, B., Alimohammadian, H., Sabouri, J., Haghfarshi, E., Faridi, M., Abbasi, S., Matzke-Karasz, R., Fellin, M., Carnevale, G., Schiller, W., Vasilyan, D. and Scharrer, S., 2011. Late Miocene stratigraphy, palaeoecology and palaeogeography of the Tabriz Basin (NW Iran, Eastern Paratethys). Palaeogeography, Palaeoclimatology, Palaeoecology, 311(1–2): 1–18.
Sadati, N., Yazdi, M., Behzadi, M., Adabi, M.H. and Mokhtari, A.A, 2013. The role of organic matter in genesis of sedimentary-hosted stratiform copper deposits in Nahand-Ivand area, NW Iran. Goldschmidt Conference, Firenze Fiera Congress and Exhibition Centre, Florence, Italy.

Keywords

• Sulfur isotope
• Organic matter
• Copper mineralization
• gray sandstone
• bacterial sulfate reduction

20.1001.1.20087306.1397.10.1.13.6

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References

Aghazadeh, M. and Badrzadeh, Z., 2012. Sediment-hosted Cu mineralization in Iran: main metallogenic basins and mineralization periods. 34th International geological congress, Geological Survey of Queensland, Brisban, Australia.

Alirezaei, 2009. Stable isotope geochemistry. University Publication, Tehran, 340 pp.

Asadian, 1993. Geological map of Tabriz, Scale 1:100,000. Geological Survey of Iran.

Bendall, C., Lahaye, Y., Fiebig, J., Weyer, S. and Brey, G.P., 2006. In situ sulfur isotope analysis by laser ablation MC-ICPMS. Applied Geochemistry, 21(5): 782–787.

Brown, A.C., 2013. Low-Temperature Sediment-Hosted Copper Deposits. In: K. Turekian and H. Holland (Editors), Treatise on Geochemistry: Geochemistry of mineral despite. Elsievier, Amsterdam, pp. 251-271.

Dewaele, S., Muchez, Ph., Vets, J., Fernandez-Alonzo, M. and Tack, L., 2006. Multiphase origin of the Cu–Co ore deposits in the western part of the Lufilian fold-and-thrust belt, Katanga (Democratic Republic of Congo). Journal of African Earth Sciences, 46(5): 455–469.

Donahue, M.A., Werne, J.P., Meile, C. and Lyons, T.W., 2008. .Modeling sulfur isotope fractionation and differential diffusion during sulfate reduction in sediments of the Cariaco Basin. Geochimica et Cosmochimica Acta, 72(9): 2287–2297.

EI Desouky, H. and Muchez, P., 2009. Two Cu–Co sulfide phases and contrastingfluid systems in the Katanga Copperbelt, Democratic Republic of Congo. Ore Geology Reviews, 36(4): 315–332.

Ghorbani, M.R., 2013. The economic geology of Iran: Mineral deposits and natural resources. Springer, Heidelberg, 572 pp.

Kakegawa, T. and Nanri, H., 2006. Sulfur and carbon isotope analyses of 2.7 Gastromatolites, cherts and sandstones in the Jeerinah Formation, Western Australia. Precambrian Research, 148(1): 115–124.

Kalender, L., 2011. Oxygen, carbon and sulphur isotope studies in the KebanPb–Zn deposits, eastern Turkey: An approach on the origin of hydrothermal fluids. Journal of African Earth Sciences, 59(4–5): 341–348.

Karimzadeh Somarin, A., 2004. Marano volcanic rocks and associated Fe mineralisation, East Azarbaijan Province, Iran. Journal of Asian Earth Sciences, 24(1): 11–23.

Nabavi, M., 1976. An Introduction to Geology of Iran. Geological Survey of Iran, Tehran, 109 pp. (in Persian with English abstract)

Rajabpour, Sh., Abedini, A., Alipour, S. and Zakeri, L., 2013. Investigation on mineralization and genesis of stratiform copper in Cheshmeh-Konan area of Tasuj, East-Azarbaijan province. Journal of Economic Geology, 5(1): 49–63. (in Persian with English abstract)

Reichenbacher, B., Alimohammadian, H., Sabouri, J., Haghfarshi, E., Faridi, M., Abbasi, S., Matzke-Karasz, R., Fellin, M., Carnevale, G., Schiller, W., Vasilyan, D. and Scharrer, S., 2011. Late Miocene stratigraphy, palaeoecology and palaeogeography of the Tabriz Basin (NW Iran, Eastern Paratethys). Palaeogeography, Palaeoclimatology, Palaeoecology, 311(1–2): 1–18.

Sadati, N., 2014. Genesis and Mineralogy of Copper Mineralizationin sedimentary rocks in Nahand- Ivand area (North of Tabriz). Ph.D. thesis, Shahid Beheshti University, Tehran, Iran, 264 pp. (in Persian with English abstract)

Sadati, N., Mao, J., Yazdi, M., Behzadi, M., Adabi, M.H., Xu, L. and Mokhtari, A.A, 2014. Diagenetic alterations of copper sulfides in sedimentary copper deposit in Nahand –Ivand area, NW Iran. The 14th international mineral processing symposium program, Pine Bay Resort Hotel, Kuşadası, Turkey.

Sadati, N., Mao, J., Yazdi, M., Behzadi, M., Adabi, M.H., Xu, L., Zhenyu, Ch. and Mokhtari, A.A., 2016. Sulfide mineral chemistry investigation of sediment-hosted stratiform copper deposits, Nahand-Ivand area, NW Iran. Ore Geology Reviews, 72(1): 760–776.

Sadati, N., Yazdi, M., Behzadi, M., Adabi, M.H. and Mokhtari, A.A, 2013. The role of organic matter in genesis of sedimentary-hosted stratiform copper deposits in Nahand-Ivand area, NW Iran. Goldschmidt Conference, Firenze Fiera Congress and Exhibition Centre, Florence, Italy.

Sen, S. and Purabrishemi, Z., 2010. First porcupine fossils (Mammalia, Rodentia) from the late Miocene of NW Iran, with notes on late Miocene–Pliocene dispersal of porcupines. Paläontologische Zeitschrift, (84): 239–248.

Yazdi, M., 2003.Conventional methods in geochemical explorations. Shahid Beheshti University, Tehran, 180 pp. (in Persian)