Genesis of Tozlou Pb-Zn Occurrence (South of Zanjan): Evidence from Geology, Mineralization, and Geochemistry

زمین شناسی اقتصادی

Volume 15, Issue 4 - Serial Number 39, 2023, Pages 1-30   

Document Type: Research Article

DOI: 10.22067/econg.2023.82203.1076

Authors

Hamed Daneshvar¹; Hossein Kouhestani^{* 2}; Mir Ali Asghar Mokhtari²; Afshin Zohdi²

¹M.Sc., Department of Geology, University of Zanjan, Zanjan, Iran

²Associate Professor, Department of Geology, University of Zanjan, Zanjan, Iran

Abstract

Tozlou Pb-Zn mineralization, ~250-300m long, and ~50m thick, is hosted by limestone units of the Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Mineralization at Tozlou can be divided into five stages. Stage 1 is the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is categorized with dolomitization processes along with minor pyrite. Stage 3 occurred as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 includes late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes. Hydrothermal alterations include decarbonatization, carbonatization ± silicification, and late carbonatization. Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements pattern of ore samples, fresh and altered limestones is similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Characteristics of Tozlou occurrence are comparable with intermediate-sulfidation type of epithermal deposits.
 
Introduction
Epithermal deposits are a group of base/precious-metal deposits that are formed by hydrothermal fluids in shallow environments under pressure/temperature changes and fluid-rock interactions (Hedenquist et al., 2000). Based on the host rock, epithermal deposits are divided into volcanic-hosted deposits and sedimentary-hosted deposits. According to the tectonic setting and magma type, they are divided into calc-alkaline magmas (including three subcategories of high-, intermediate-, and low-sulfidation) and alkaline magmas (White and Hedenquist, 1990; Cooke and Simmons, 2000; Hedenquist et al., 2000; Simmons et al., 2005). These types of deposits include a continuous range of deposits formed by magmatic/meteoric fluids and show different geometry, but have the same formation mechanism, especially the hydrothermal fluids circulation (Sillitoe and Hedenquist, 2003; Simmons et al., 2005).
Sedimentary rock-hosted deposits are divided into two groups: Carlin-type and sediment-hosted disseminated deposits. Carlin-type deposits are often formed as strata-bound or replacements at the boundary of rock units and are controlled by faults. They are distinguished by invisible Au in As-rich pyrite and arsenopyrite and do not show compatible spatial relationships to magmatic centers (Kuehn and Rose, 1992). Sediment-hosted disseminated deposits occurred as disseminated ore in sedimentary rocks (Hofstra and Cline, 2000). These deposits are physically and chemically comparable to Carlin-type deposits, but spatially and temporally are related to sub-volcanic porphyry intrusions (Theodore et al., 2000; Hofstra and Cline, 2000).
Tozlou Pb-Zn occurrence is 50km south of Qeydar in Zanjan province. This occurrence was first discovered/explored in 2017. Although general geological characteristics of Tozlou occurrence have been determined (Majidifard and Shafei, 2006), the mineralogy and origin of Tozlou occurrence have not been studied in detail. Here, detailed geology, mineralogy, alteration styles, and geochemistry of Tozlou occurrence are investigated to constrain the genetic model and type of its mineralization system. These results may have implications for future exploration of base-metal mineralization in this region and nearby areas.
 
Materials and methods
Comprehensive field and laboratory works have been carried out on Tozlou area. During the fieldwork, a detailed stratigraphic section of limestone units of Qom Formation was measured, sampled, and described. Fifty samples were collected from ore zones and limestone host rocks for laboratory analysis. Then, 34 thin and 15 polished-thin sections were prepared for mineralogical studies in the laboratory at the University of Zanjan, Iran. Fourteen typical samples from the ore zones and fresh/altered host limestone were analyzed for geochemical analysis using ICP–MS in Zarazma Analytical Laboratories, Tehran, Iran.
 
Results and Discussion
The main rock units exposed in Tozlou occurrence belong to Eocene sequence, Lower Red Formation, Qom Formation, and Quaternary units. Small outcrops of gabbro-gabbro diorite (gb) can also be seen in this region. Eocene strata include brown thin-bedded sandstone (Unit E^s), alternating tuff and shale (Unit E^tsh), and thin- to medium-bedded tuffs (Unit E^t). Lower Red Formation includes a polygenetic conglomerate (Unit Ol^lrc) of Oligocene age. Qom Formation consists of massive- to medium-bedded cream-to-grey limestones (Unit OM_q^l) and alternating marl and thin-bedded grey limestone (Unit OM_q^ml). Quaternary units include terrigenous sediments.
Pb-Zn mineralization at Tozlou has ~250-300 m leng and ~50 m thick and is hosted by limestone units of Qom Formation. The main mineralization zone occurred as vein-veinlets and vug infill textures, where mineralization is observed as Pb-Zn-bearing barite veins or supergene minerals (cerussite and smithsonite). Decarbonatization, carbonatization±silicic, dolomitization, and late carbonatization are hydrothermal alterations in Tozlou area. Mineralization processes at Tozlou can be divided into five stages. Stage 1 comprises the decarbonatization of the limestone host rock, which is characterized by the increased porosity and permeability of the host rock. Stage 2 is represented by the dolomitization of the limestone host rock, which is accompanied by minor pyrite. Stage 3 occurs as Pb-Zn-bearing barite and calcite (calcite II) veins. Stage 4 is characterized by late-stage calcite (calcite III) veins. Stage 5 is related to supergene processes.
Ore minerals include galena and pyrite along with minor sphalerite. Calcite, barite, and quartz are gangue minerals. Smithsonite, cerussite, and goethite are formed by supergene processes. The ore minerals show vein-veinlets, brecciated, disseminated, vug infill, colloform, cockade, replacement, and residual textures. The Chondrite-normalized rare earth elements patterns of ore samples, fresh and altered limestones, are similar, which can indicate the major role of host rocks in the concentration of ore-forming elements. This pattern is almost similar for different ore samples, which can indicate that they have been formed by the same mineralization system. Despite carbonate host rock, we think that mineralization at Tozlou is similar to the intermediate-sulfidation style of epithermal base metal deposits.
 

Keywords

Pb-Zn mineralization; Intermediate-sulfidation Epithermal; Qom Formation; Tozlou; Zanjan

References

Albinson, T., Norman, D.I., Cole, D. and Chomiak, B., 2001. Controls on formation of low-sulfidation epithermal deposits in Mexico: Constraints from fluid inclusion and stable isotope data. In: T. Albinson and C.E. Nelson (Editors), New Mines and Discoveries in Mexico and Central America. Society of Economic Geologists, Littleton, pp. 1–32. https://doi.org/10.5382/SP.08.01

Andreeva, E., Matsueda, H., Okrugin, V.M., Takahashi, R. and One, S., 2013. Au-Ag-Te mineralization of the low-sulfidation epithermal Aginskoe deposit, Central Kamchatka, Russia. Resource Geology, 63(4): 337–349. https://doi.org/10.1111/rge.12013

Bagherpour, H., Mokhtari, M.A.A., Kouhestani, H., Nabatian, Gh. and Mehdikhani, B., 2020. Intermediate-sulfidation style of epithermal base metal (Ag) mineralization at the Qoyjeh Yeylaq deposit, SW Zanjan, Iran. Journal of Economic Geology, 11(4): 545–564 (in Persian with extended English abstract).https://doi.org/10.22067/econg.v11i4.71615

Bienvenu, P., Bougault, H., Joron, J.L., Treuil, M. and Dmitriev, L. 1990. MORB alteration: Rare earth element/non-rare hydromagmaphile element fractionation. Chemical Geology, 82: 1–14. https://doi.org/10.1016/0009-2541(90)90070-N

Cooke, D.R. and Simmons, S.F., 2000. Characteristics and genesis of epithermal gold deposits. In: S.G. Hagemann and P.E. Brown (Editors), Gold in 2000. Society of Economic Geologists, Littleton. pp. 221–244. https://doi.org/10.5382/Rev.13.06

Daneshvar, H., 2023. Geology, geochemistry, and genesis of the Tozlou Zn-Pb occurrence, south of Zanjan. Unpublished M.Sc. Thesis, University of Zanjan, Zanjan, Iran, 70 pp. (in Persian with English abstract)

Einaudi, M.T., Hedenquist, J.W. and Inan, E.E., 2003. Sulfidation state of fluids in active and extinct hydrothermal systems: Transitions from porphyry to epithermal environments. In: S.F. Simmons and I. Graham (Editors.), Volcanic, geothermal, and ore-forming fluids: rulers and witnesses of processes within the earth. Society of Economic Geologists, Littleton, pp. 285–313. https://doi.org/10.5382/SP.10.15

Gemmell, J. B., 2004. Low- and intermediate-sulfidation epithermal deposits. In: D.R. Cooke, C.L. Deyel and J. Pongratz (Editors), 24 Ct Gold Workshop. University of Tasmania, Hobart, Australia, pp. 57–63. Retrieved August 16, 2023, from https://catalogobiblioteca.ingemmet.gob.pe/cgi-bin/koha/opac-detail.pl?biblionumber=40250&shelfbrowse_itemnumber=40250

Haghighi Bardineh, S.N., Zarei Sahamieh, R., Zamanian, H. and Ahmadi Khalaji, A., 2017. Geochemical, Sr-Nd isotopic investigations and U-Pb zircon chronology of the Takht granodiorite, west Iran: Evidence for post-collisional magmatism in the northern part of the Urumieh-Dokhtar magmatic assemblage. Journal of African Earth Sciences, 139: 354–366. https://doi.org/10.1016/j.jafrearsci.2017.12.030

Hassani Soughi, F., Calagari, A.A. and Sohrabi, G., 2021. Consideration of mineralization and characterization of fluid inclusions in the Gharehkand sediment-hosted gold-bearing vein-veinlets, southeast of Maragheh, East Azarbaidjan. Journal of Economic Geology, 13(2): 387–409. (in Persian with extended English abstract) https://dx.doi.org/10.22067/econg.v13i2.87317

Hedenquist, J.W., Arribas, A. and Gonzalez-Urien, E., 2000. Exploration for epithermal gold deposits. In: S.G. Hagemann and P.E. Brown (Editors), Gold in 2000. Society of Economic Geologists, Littleton, pp. 245–277. https://doi.org/10.5382/Rev.13.07

Hofstra, A.H. and Cline, J.S., 2000. Characteristics and models for Carlin-type gold deposits. In: S.G. Hagemann and P.E. Brown (Editors), Gold in 2000. Society of Economic Geologists, Littleton. pp. 163–220. https://doi.org/10.5382/Rev.13.05

Humphris, S.E., 1984. The mobility of the rare earth elements in the crust. In: P. Henderson (Editor), Developments in Geochemistry. Elsevier, Amsterdam, pp. 317–342. https://doi.org/10.1016/B978-0-444-42148-7.50014-9

John, D.A., 2001. Miocene and early Pliocene epithermal gold-silver deposits in the northern Great Basin, western USA: Characteristics, distribution, and relationship to magmatism. Economic Geology 96(8): 1827–1853. https://doi.org/10.2113/gsecongeo.96.8.1827

Johnston, M.K., 2003. Geology of the Cove Mine, Lander County, Nevada, and a genetic model for the McCoy-Cove magmatic-hydrothermal system. Unpublished Ph.D. Thesis, University of Nevada, Reno, Nevada, USA, 353 pp.

Kuehn, C.A. and Rose, A.R., 1992. Geology and geochemistry of wall-rock alteration at the Carlin gold deposit, Nevada. Economic Geology, 87(7): 1697–1721. https://doi.org/10.2113/gsecongeo.87.7.1697

Lottermoser, B.G., 1992. Rare earth elements and hydrothermal ore formation processes. Ore Geology Reviews, 7(1): 25–41. https://doi.org/10.1016/0169-1368(92)90017-F

Majidifard, M.R. and Shafei, A., 2006. Geological map of Marzban, scale 1:100,000. Geological Survey of Iran.

Mansouri, S., Aliani, F., Maanijou, M., Sepahi Gerow, A.A. and Mostaghimi, M., 2015. Mineralogy and geochemistry of granitoids and associated iron skarn of Takht (north of Kaboodar Ahang). Journal of Petrology, 21: 157–176. (in Persian with English abstract) Retrieved April 24, 2023, from https://ijp.ui.ac.ir/article_16197_5c6b8fe4ee86f4b580496929cfce37f9.pdf

McDonough, W.F. and Sun, S.S., 1995. The composition of the Earth. Chemical Geology, 120(3-4): 223–253. https://doi.org/10.1016/0009-2541(94)00140-4

Mohammadi, E., Hasanzadeh-Dastgerdi, M., Ghaedi, M., Dehghan, R., Safari, A., Vaziri-Moghaddam, H., Baizidi, Ch., Vaziri, M.R. and Sfidari, E., 2013. The Tethyan Seaway Iranian Plate Oligo-Miocene deposits (the Qom Formation): distribution of Rupelian (Early Oligocene) and evaporate deposits as evidences for timing and trending of opening and closure of the Tethyan Seaway. Carbonates and Evaporites, 28(3): 321–345. https://doi.org/10.1007/s13146-012-0120-7

Mohammadi Niaei, R., Daliran, F., Nezafati, N., Ghorbani, M., Sheikh Zakariaei, J. and Kouhestani, H., 2015. The Ay Qalasi deposit: An epithermal Pb-Zn (Ag) mineralization in the Urumieh–Dokhtar volcanic belt of northwestern Iran. Neues Jahrbuch für Mineralogie-Abhandlungen (Journal of Mineralogy and Geochemistry), 192(3): 263–74.  https://doi.org/10.1127/njma/2015/0284

Murphy, J.B. and Hynes, A.J., 1986. Contrasting secondary mobility of Ti, P, Zr, Nb and Y in two meta-basaltic suites in the Appalachians. Canadian Journal of Earth Sciences, 23(8): 1138–1144. https://doi.org/10.1139/e86-112

Pirajno, F., 2009. Hydrothermal processes and mineral systems. Springer, Berlin, 1250 pp. http://dx.doi.org/10.1007/978-1-4020-8613-7

Rahimsouri, Y., Mehrabi, B. and Alipour, Sh., 2018. Mineralogy, geochemistry and fluid inclusion studies

of Dagh-Daali Zn-Pb (±Au) deposit (northern Takab, northwest Iran). Journal of Petrology, 9(3): 217–244. (in Persian with English abstract) https://doi.org/10.22108/ijp.2019.114335.1110

Rudnick, R.L. and Gao, S., 2003. Composition of the continental crust. In: H.D. Holland and K.K. Turekian (Editors) Treatise on Geochemistry. Elsevier-Pergamon, Oxford, England, pp. 1–64. http://dx.doi.org/10.1016/b0-08-043751-6/03016-4

Salehi, T., Ghaderi, M. and Rashidnejad-Omran, N., 2011. Mineralogy and geochemistry of rare earth elements in Qomish Tappeh Zn–Pb–Cu (Ag) deposit, southwest of Zanjan. Journal of Economic Geology, 2(2): 235–254. (in Persian with English abstract) https://doi.org/10.22067/ECONG.V2I2.7853

Salehi, T., Ghaderi, M. and Rashidnejad-Omran, N., 2015. Epithermal base metal-silver mineralization at Qomish Tappeh deposit, southwest of Zanjan. Scientific Quarterly Journal, Geosciences, 25(97): 329–346. (in Persian with English abstract) https://doi.org/10.22071/GSJ.2015.41519

Saunders, J.A., Hofstra, A.H., Goldfarb, R.J. and Reed, M.H., 2014. Geochemistry of hydrothermal gold deposits. In: H.D. Holland and K.K. Turekian (Editors) Treatise on Geochemistry. Elsevier-Pergamon, Oxford, England, pp. 33–424. http://dx.doi.org/10.1016/B978-0-08-095975-7.01117-7

Shirkhani, M., 2007. Mineralogy, geochemistry and genesis of Ay Qalasi Pb-Zn deposit, SE Takab. Unpublished M.Sc. Thesis, Tarbiat Modares University, Tehran, Iran, 143 pp. (in Persian with English abstract)

Sillitoe, R.H. and Hedenquist, J.W., 2003. Linkages between volcano-tectonic settings, ore fluid compositions, and epithermal precious-metal deposits. In: S.F. Simmons and I. Graham (Editors), Volcanic, geothermal, and ore-forming fluids: Rulers and witnesses of processes within the Earth. Economic Geology Special Publication 10, Littleton, pp. 315–343. Retrieved April 24, 2023, from https://www.researchgate.net/publication/285488888

Simmons, S.F., White, N.C. and John, D.A., 2005. Geological characteristics of epithermal precious and base metal deposits. In: J.W. Hedenquist, J.F.H. Thompson, R.J. Goldfarb and J.P. Richards (Editors),

One Hundredth Anniversary Volume. Society of Economic Geologists, Littleton, pp. 485–522. https://doi.org/10.5382/AV100.16

Theodore, T.G., Kotlyar, B.B., Berger, V.I., Moring, B.C. and Singer, D.A., 2000. Implications of stream-sediment geochemistry in the northern Carlin trend, Nevada. U.S. Geological Survey, Menlo Park, Report 94025, 45 pp.

Wang, L., Qin, K.Z., Song, G.Y. and Li, G.M., 2019. A review of intermediate sulfidation epithermal deposits and subclassification. Ore Geology Reviews, 107: 434–456. https://doi.org/10.1016/j.oregeorev.2019.02.023

White, N.C. and Hedenquist, J.W., 1990. Epithermal environments and styles of mineralization:

Variations and their causes, and guidelines for exploration. Journal of Geochemical Exploration 36(1–3): 445–474. https://doi.org/10.1016/0375-6742(90)90063-G

Whitford, D.J., Korsch, M.J., Porritt, P.M. and Craven, S.J., 1988. Rare earth element mobility around the volcanogenic polymetallic massive sulfide deposit at Que River, Tasmania, Australia. Chemical Geology, 68(1–2): 105–119. https://doi.org/10.1016/0009-2541(88)90090-3

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