minerals Article Major and Trace Element Geochemistry of Pyrite and Pyrrhotite from Stratiform and Lamellar Orebodies: Implications for the Ore Genesis of the Dongguashan Copper (Gold) Deposit, Eastern China Zhongfa Liu 1, Yongjun Shao 1, Haodi Zhou 2, Nan Liu 3, Kuanxin Huang 1, Qingquan Liu 1,4,* ID , Jiandong Zhang 1 and Cheng Wang 1 1 Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring (Central South University), Ministry of Education, Changsha 410083, China; [email protected] (Z.L.); [email protected] (Y.S.); [email protected] (K.H.); [email protected] (J.Z.); [email protected] (C.W.) 2 Hunan Key Laboratory of Land and Resources Evaluation and Utilization, Changsha 410007, China; [email protected] 3 Hunan Institute of Geological Survey, Changsha 410116, China; [email protected] 4 School of Resources and safety engineering, Central South University, Changsha 410083, China * Correspondence: [email protected]; Tel.: +86-731-888-30616 Received: 28 May 2018; Accepted: 24 August 2018; Published: 1 September 2018 Abstract: The Dongguashan copper (gold) deposit in Anhui Province is one of the largest copper (gold) deposits in the Tongling ore district, which is the most important region in the Middle–Lower Yangtze River Metallogenic Belt, Eastern China. Stratiform and lamellar orebodies are the major deposit types. Pyrite and pyrrhotite from the stratiform deposit type (Py I, Po I) and lamellar deposit type (Py II, Po II) are investigated using Electron-probe Microanalyses (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Py I, Py II, Po I and Po II have high contents of Cu, Co, Au and Se, low contents of As, Pb and Zn, with Co/Ni ratios of 0.50−48.00, 4.00−45.00, 1.55−14.45 and 1.02−1.36, respectively, most of which are greater than 1 and vary widely; these characteristics are consistent with those of pyrite with a magmatic–hydrothermal origin. The higher Au/Ag and Fe/(S + As) ratios of pyrite and crystallization temperatures (286–387 ◦C) of hexagonal pyrrhotite indicate that the mineralization occurrs in environments with medium- to high-temperatures, high sulfur fugacity and medium-shallow depths. Therefore, we suggest that the Dongguashan copper (gold) deposit is a stratabound skarn-type ore deposit associated with magma intrusion activity during the Yanshanian Period. Keywords: EPMA and LA-ICP-MS; major and trace elements; pyrite and pyrrhotite; Dongguashan copper (gold) deposit; Tongling ore district 1. Introduction As minerals represent the most basic units of rocks and/or ore, their chemical composition and type are of great significance when discussing the origins of rocks and/or ore, as well as the ore genesis and the ore-forming environment [1,2]. Due to the influence of factors, such as the purity of single minerals and the interference associated with solid solutions, the data obtained using traditional chemical analyses for single phases have large errors. The rapid development of Electron-Probe Microanalyses (EPMA) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) has realized in situ analysis of single minerals at the nanoscale, which has Minerals 2018, 8, 380; doi:10.3390/min8090380 www.mdpi.com/journal/minerals Minerals 2018, 8, x FOR PEER REVIEW 2 of 20 Minerals 2018, 8, 380 2 of 20 Spectrometry (LA-ICP-MS) has realized in situ analysis of single minerals at the nanoscale, which has solved the problem of the large errors in traditional analytical methods. So far, these in situ solved the problem of the large errors in traditional analytical methods. So far, these in situ analytical analytical methods have been widely applied to study on the ore-forming environments, methods have been widely applied to study on the ore-forming environments, ore-forming material ore-forming material source, ore-forming processes, and ore genesis [1,3–10]. source, ore-forming processes, and ore genesis [1,3–10]. The Tongling ore district in Anhui Province, which is enriched in Cu, Fe, and Au, is one of the The Tongling ore district in Anhui Province, which is enriched in Cu, Fe, and Au, is one of most important regions in the Middle–Lower Yangtze River Metallogenic Belt, Eastern China the most important regions in the Middle–Lower Yangtze River Metallogenic Belt, Eastern China (Figure 1). Five major deposits have been discovered in this ore district, including the Dongguashan (Figure1). Five major deposits have been discovered in this ore district, including the Dongguashan Cu-Au, Shizishan Cu-Au, Tongguanshan Cu-Fe, Fenghuangshan Cu-Fe and Xinqiao Cu-S-Fe Cu-Au, Shizishan Cu-Au, Tongguanshan Cu-Fe, Fenghuangshan Cu-Fe and Xinqiao Cu-S-Fe deposits. deposits. In the last few years, researchers have carried out many in-depth studies of these deposits In the last few years, researchers have carried out many in-depth studies of these deposits in the in the Tongling ore district. Different ore genetic models have been established, which mainly Tongling ore district. Different ore genetic models have been established, which mainly include include the stratabound–skarn model [11], the “multi-story building”-type model [12,13], the the stratabound–skarn model [11], the “multi-story building”-type model [12,13], the generalized generalized skarn–porphyry-type hydrothermal model [14] and the porphyry–skarn–manto-type skarn–porphyry-type hydrothermal model [14] and the porphyry–skarn–manto-type model [15]. model [15]. Figure 1. Geological map showing the location of the Tongling ore district, and related porphyry– Figure 1. Geological map showing the location of the Tongling ore district, and related skarn–stratabound Cu-Au-Mo (>135 Ma) deposits along the Middle–Lower Yangtze River Valley porphyry–skarn–stratabound Cu-Au-Mo (>135 Ma) deposits along the Middle–Lower Yangtze River Metallogenic Belt [16]. Faults: TLF—Tancheng–Lujiang fault, XGF—Xiangfan–Guangji fault, Valley Metallogenic Belt [16]. Faults: TLF—Tancheng–Lujiang fault, XGF—Xiangfan–Guangji fault, YCF—Yangxing–Changzhou fault. YCF—Yangxing–Changzhou fault. The Dongguashan copper (gold) ore deposit is one of the largest copper (gold) deposits in the TonglingThe Dongguashanore district, and copper it is located (gold) ore approximately deposit is one 7 ofkm the to largestthe east copper of Tongling (gold) depositscity (Figure in the2), TonglingAnhui Province, ore district, Eastern and itChina. is located It approximatelyis controlled by 7 km stratigraphic to the east ofhorizons, Tongling anticlines, city (Figure and2), Anhuiinterlayered Province, structures. Eastern The China. major It is stratiform controlled and by stratigraphic lamellar orebodies horizons, in anticlines,the Dongguashan and interlayered deposit structures.are distributed The along major the stratiform northern and core lamellar and limbs orebodies of the in Qingshan the Dongguashan anticline, depositand they are are distributed hosted in alongthe limestones the northern of the core Middle and limbsand Upper of the Carbonif Qingshanerous anticline, Huanglong and they and areChuanshan hosted in formations. the limestones The ofDongguashan the Middle andcopper Upper (gold) Carboniferous deposit, with Huanglong its unique andgeological Chuanshan characteristics, formations. has The attracted Dongguashan a lot of copperattention (gold) to geologists deposit, withfor a its long unique time. geological A great characteristics, deal of scientific has attractedprogress ahas lot been of attention made toin geologistsidentifying for the a longsource time. of Aore-forming great deal of materials scientific progressand fluids, has rock- been madeand ore-forming in identifying ages, the sourceand ore of ore-forminggenesis [17–26]. materials However, and fluids, as far rock- as the and ore ore-forming genesis of ages, the Dongguashan and ore genesis copper [17–26 ].(gold) However, deposit as far is asconcerned, the ore genesis questions of the remain, Dongguashan as this deposit copper (gold)has been deposit proposed is concerned, to be a questionsstratabound remain, skarn-type as this deposit[15,23,25,27–29], has been proposedexhalative to sedimentary be a stratabound and hydr skarn-typeothermal [15 ,superimposition-type23,25,27–29], exhalative [21,22,30–36], sedimentary and hydrothermalexhalative sedimentary-type superimposition-type deposit [21 [19,37–39].,22,30–36 ], and exhalative sedimentary-type deposit [19,37–39]. Minerals 2018, 8, 380 3 of 20 Minerals 2018, 8, x FOR PEER REVIEW 3 of 20 Figure 2. Geological map of the Tongling ore district [27,40]. Figure 2. Geological map of the Tongling ore district [27,40]. Questions regarding deposit genesis is mainly focused on stratiform and lamellar orebodies. It willQuestions be helpful regarding for us to understand deposit genesis the ore is genesi mainlys by focused determining on stratiform their geneses. and In lamellar this paper, orebodies. we It willare begoing helpful to study for usthe tomajor understand and trace the element ore genesis compos byitions determining of pyrite and their pyrrhotite geneses. in Instratiform this paper, we areand goinglamellar to studyorebodies the by major using and EPMA trace and element LA-ICP-MS compositions and to constrain of pyrite the and ore pyrrhotite genesis. in stratiform and lamellar orebodies by using EPMA and LA-ICP-MS and to constrain the ore genesis. 2. Geological Setting 2. GeologicalThe Tongling Setting ore district is located in the northeastern section of the Lower Yangtze area, in theThe junction Tongling between oredistrict North China is located and inthe theYangtze northeastern Block. This section ore district of the is Lower bounded Yangtze by the area, in theXiangfan–Guangji junction between fault North to the north, China the and Tanlu the fa Yangtzeult to the Block. northeast, This and ore the district Yangxing–Changzhou is bounded by the fault to the south (Figure 1). A three-stage tectonic evolution of the Lower Yangtze area has been Xiangfan–Guangji fault to the north, the Tanlu fault to the northeast, and the Yangxing–Changzhou proposed, i.e., the formation of Pre-Sinian (Late Neoproterozoic) basement, the development of fault to the south (Figure1).