Citation: Dinc˘ a, G.; Apopei, A.I.; Szabo, R.; Maftei, A.E. The Effect of Mn Substitution on Natural Sphalerites by Means of Raman Spectroscopy: A Case Study of the Săcărâmb Au–Ag–Te Ore Deposit, Apuseni Mountains, Romania. Minerals 2022, 12, 885. https:// doi.org/10.3390/min12070885 Academic Editor: Panagiotis Voudouris Received: 3 June 2022 Accepted: 13 July 2022 Published: 14 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). minerals Article The Effect of Mn Substitution on Natural Sphalerites by Means of Raman Spectroscopy: A Case Study of the Săcărâmb Au–Ag–Te Ore Deposit, Apuseni Mountains, Romania George Dincă 1,2 , Andrei Ionut , Apopei 3, * , Robert Szabo 1 and Andreea Elena Maftei 4 1 GeoEcolab Laboratory, Geological Institute of Romania, Str. Caransebes , Nr. 1, 012271 Bucharest, Romania; georgedinca@rocketmail.com (G.D.); robert21szabo@gmail.com (R.S.) 2 Research Center for Ecological Services (CESEC), University of Bucharest, 050663 Bucharest, Romania 3 Department of Geology, Faculty of Geography and Geology, “Alexandru Ioan Cuza” University of Ias , i, 700505 Ias , i, Romania 4 Institute for Interdisciplinary Research, Department of Exact and Natural Sciences, “Alexandru Ioan Cuza” University of Ias , i, Alexandru Lăpus , neanu Str., No. 26, 700057 Ias , i, Romania; andreea.maftei@uaic.ro * Correspondence: andrei.apopei@uaic.ro Abstract: Natural samples of sphalerites containing Mn in the range 0 ≤ x ≤ 0.25 apfu from the Săcărâmb Au–Ag–Te ore deposit, found in the Apuseni Mountains, Romania, were investigated using Raman spectroscopy to determine its capability to provide estimates of Mn content. Raman data for the natural Mn-rich sphalerite have not been published so far, with the largest concentration of Mn in sphalerites being from Romanian territory (i.e., 14.1 wt.%). The results are in good agreement with SEM-EDS data. In this study, three genetic types of sphalerites were identified: from ferroan (Zn 0.87 Fe 0.16 ) ∑=1.03 S 0.97 to manganoferroan (Zn 0.77 Mn 0.14 Fe 0.06 ) ∑=0.97 S 1.03 , as well as mangan-rich (Zn 0.8 Mn 0.25 ) ∑=1.05 S 0.95 compositions. Sphalerites with a high content of Mn (up to 14.1 wt.%) were strongly connected to the presence of alabandite in the mineralized assemblages. The formation of several types of sphalerites in the Săcărâmb Au–Ag–Te ore deposit was caused by the succession of different types of hydrothermal fluids and the interaction between the fluids and the host materials (host rocks and earlier mineralized stages). Keywords: manganoan sphalerite; alabandite; hydrothermal; Raman spectroscopy; Apuseni Mountains 1. Introduction Sphalerite is well known as the main source of zinc and is a common mineral in base-metal hydrothermal mineralization. Common substitutions in the cubic polytype of the ZnS structure ( β-ZnS, sphalerite) include Fe 2+ , Mn 2+ , and Cd 2+ for Zn 2+ in tetrahedral sites. Common substitutions for Zn 2+ in the tetrahedral sites of the cubic polytype (β-ZnS, sphalerite) include Fe 2+ , Mn 2+ , and Cd 2+ . Besides these major divalent cations, other minor and trace elements are found in the crystal lattice of natural sphalerites, involving coupled substitution [1,2]. ZnS polytypes, especially sphalerite and wurtzite (hexagonal α-ZnS polymorph), have been the subject of several studies dealing with geological (e.g., geobarometer [3]) and economic implications (e.g., [1]) due to the numerous substitutions that can occur in the ZnS lattice. Furthermore, ZnS is one of the most important II-VI compound semiconductors used in various domains: light-emitting or laser diodes in the Near-UV region, photocatalysis, solar energy conversion, etc. [4,5]. In recent decades, Raman spectroscopy has been used extensively for the structural and chemical characterization of sphalerites. Zigone et al. [6] reported vibrational changes in the synthetic crystals of ZnS doped with relatively small amounts of Fe, Mn, Co, or Cr. Several authors have shown the efficiency of Raman spectroscopy in quantifying Minerals 2022, 12, 885. https://doi.org/10.3390/min12070885 https://www.mdpi.com/journal/minerals