Journal of Economic Geology (Jun 2019)
Geology, mineralogy, geochemistry, and geophysical investigation of the Agh Ziarat polymetallic deposit, northern Urmia, northwestern Sanandaj-Sirjan Zone
Abstract
Introduction The Agh Ziarat (Au±Cu±Mo) Polymetallic deposit is located at 75 north of Urmia, northwestern part of the Sanandaj-Sirjan Zone. Several studies have been carried out on chemical composition, geochemistry, petrology, and petrogenesis of intrusive bodies of the Qushchi area, north of Urmia (Jahangiri, 1993; Behnia, 1996; Asadpour, 2001; Azimi, 2011; Shahabi, 2013; Sarjoughian and Kananian, 2015). However, the mineralization potential of the intrusion rocks and volcano-sedimentary sequences has not been investigated yet. The present investigation provides an overview of the geological framework, mineralogy of orebodies and gangue, geochemical, and geophysical characteristics of the Agh Ziarat deposit. Therefore, identification of mineralization style and potential in the study area can be used as an exploration guide in the regional scale in the Sanandaj-Sirjan zone and elsewhere. Materials and methods Petrography and ore mineralogy studies were carried out on 15 thin, 20 polished, 10 polished thin sections, and 11 XRD analyses to identify the alteration and ore mineral textures and mineral paragenesis at the Department of Mining Engineering, the Urmia University of Technology. X-Ray Fluorescence (XRF), SEM, ICP-MS analyses were performed on 6, 13, and 70 samples collected from different altered and mineralized host units including metamorphosed volcanic rocks, intrusive bodies, and aplitic dikes in the Kansaran Binaloud Laboratory, respectively. Mineralogical composition of ore minerals was examined by Electron Probe Micro Analysis (EPMA) on six selected samples in the Iran Mineral Processing Research Center. Structural controls, depth, and vertical distribution or mineralized zones investigated by Induced Polarization-Resistivity (IP/RS) geophysical exploration surveys on 10 east-west-trending profiles. Result The host rocks are Neoproterozoic to lower Plaeozoic volcano-sedimentary sequences consisting of gneissic granite, amphibolite, schist, and pyroxenite, which are metamorphosed to greenschist facies. The intrusion of Cretaceous syenite, granite, and aplitic dikes within host rocks caused are caused by hydrothermal alteration and gold (copper±molybdenum) mineralization. Hydrothermal alteration zones are predominantly including argillic, silicified and sulfide alterations, which have mainly occurred in granite gneiss, amphibolite, schist, and intrusive rocks, respectively. Gold (copper±molybenum) mineralization occurred as vein and veinlets consisting of replacement, disseminated, and open space filling textures. The mineralogy of orebodies comprises of native gold, pyrite, chalcopyrite, molybdenite, magnetite, galena, sphalerite, and Hg, Nd, Ag, Se, and Ba-bearing sulfosalt minerals together with supergene and oxidation mineral phases including chalcocite, covellite, malachite, azurite, hematite, and goethite. The EPMA micro analysis on pyrite, chalcopyrite, and molybdenite showed that these minerals are characterized by high abundance of S, Mo, Fe, and Au (41.26, 52.33, 23.03, 0.04 wt. %, respectively) and low contents of Pb, W, Cu, Zn, and As (1.12, 0.46, 0.19, 0.08, 0.03 wt. %, respectively). The multivariate measurement of geochemical data using the Spearman's Rank correlation method indicated by positive relationship of Cu, Co, Ni, As, Pb, and in particularly Mo. Copper displays a positive and strong correlation with Co, Ni, Au, As, Pb, Mo, and W in ore-bearing zones. Furthermore, the ore-related elements are distinguished by the presence of Au, As, Cu, Mo, Ni, and Co in factor I, Cu in factor II, and Zn in factor III using the factor analysis method. In addition, an important geochemical behavior was observed among altered Au, As, Mo, and Cu and mineralized zones. Therefore, ore elements and in particularly Au, Mo, and Cu elements are classified in the same cluster. The positive correlation of ore elements with most other elements is indicated by distribution of Au±Cu±Mo orebodies in the area. The positive and relatively strong correlation of Au and As can be inferred from the cogenetic nature of those elements. The IP/RS geophysical investigation is distinguished by low abundances of induced polarization (IP) and high resistivity (RS) values in most profiles. Consideration of IP and RS pseudo profiles indicate the distribution of anomalous zones toward southern part of the area together with vertical zoning pattern similar to other alteration zones. Integration of the obtained results from geology, which reflects relatively extensive magmatic activity related to active tectonism and extensional structures, together with exploration geochemistry and geophysics resulted in the identification of two main potential areas in both northern and southern parts of the study area. Discussion The main altered and mineralized zones in the study area are characterized by vein and veinlet textures of ore mineralization together with geochemical and geophysical anomalies. The supergene mineralization of some sulfide and oxide minerals (e.g., malachite, azurite, chalcocite, covellite, hematite, and goethite) resulted in the low abundances of chargeability (10-40 ml/v) in most IP-RS profiles in the area. The geological, geochemical, and geochpysical data are integrated to recognize the mineralized and promising zones. Acknowledgements The author gratefully acknowledges the management of the Kansar Bakhtar Azarbaijan Company for their logistic support to carry out filed works, access and sampling of drill cores. Journal of Economic Geology Reviewers and editor are also thanked for their constructive and valuable comments. References Asadpour, M., 2001. Petrology and geochemistry of ultramafic to intermediate rocks of the Qushchi area (Urmia). M.Sc. Thesis, Shahid Beheshti University, Tehran, Iran, 255 pp. Azimi, M.S., 2011. Investigation of geological evidence of magma mixing between gabbrodiorite and alkali granite in the Qushchi area (north of Urmia). Ph.D. Thesis, University of Tehran, Tehran, Iran, 139 pp. Behnia, P., 1996. Petrogenesis of granitoids in the Qushchi area: process of alkaline metasomatism. M.Sc. Thesis, University of Tehran, Tehran, Iran, 150 pp. Jahangiri, M., 1993. Petrology and petrogenesis of the Qushchi granitoide complex, north of Urmia. Ph.D. Thesis, Shahid Beheshti University, Tehran, Iran, 160 pp. Sarjoughian, F. and Kananian, A., 2015. Magma mixing process in the Qushchi intrusion: using mineral chemistry. Journal of Earth Science Researches, 5(1): 1–17. (in Persian) Shahabi, Sh., 2013. Geochemistry, petrology, and geochronology of the alkaline granite (A-type) and gabbro in the Qushchi area, northwest of Urmia. M.Sc. Thesis, University of Damghan, Damghan, Iran, 135 pp.
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