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Trace Element Concentrations in Porphyry Copper Deposits from Metaliferi Mountains, Romania: a Reconnaissance Study

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Trace Element Concentrations in Porphyry Copper Deposits from Metaliferi Mountains, Romania: a Reconnaissance Study Ore Geology Reviews 63 (2014) 22–39 Contents lists available at ScienceDirect Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev Trace element concentrations in porphyry copper deposits from Metaliferi Mountains, Romania: A reconnaissance study Mihaela Elena Cioacă a,⁎, Marian Munteanu a,b, Liang Qi c,GeluCostind a Geological Institute of Romania, Department of Regional and Economic Geology, 1 Caransebeş St., 01271 Bucharest, Romania b University of the Witwatersrand, School of Geosciences, 1 Ian Smuts St., Braamfontein 2000, Johannesburg, South Africa c State Key Lab of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China d Rhodes University, Department of Geology, Artillery Road, 6140 Grahamstown, South Africa article info abstract Article history: There are fifteen Miocene intrusions with porphyry copper mineralization in the Metaliferi Mountains, Romania; Received 18 September 2013 most are associated with epithermal Au–Ag (±Te, Bi, Se, Ge) vein systems. The investigation of fifty samples from Received in revised form 9 April 2014 six deposits (Roşia Poieni, Bucium–Tarniţa, Colnic, Rovina, Valea Morii and Bolcana) indicated bulk rock mean Accepted 24 April 2014 values of 0.16–0.88 ppm Au, b50 ppm Mo, 0.02–0.35 ppm Re, 0.06–0.6 ppm In, 1.3–3.3 ppm Ag, 0.23– Available online 2 May 2014 1.17 ppm Bi, 3.2–5.5 ppm Se, 2.4–3.3 ppm Ge, and 2.6–18 ppm Te. Trace element analyses by electron microprobe suggest that part of the Au, Ag, As, Te and Se may occur as fine-particle inclusions hosted within common sulfide Keywords: Porphyry copper minerals (pyrite, chalcopyrite and bornite). Measured concentrations range from below the minimum limit of Trace elements detection to as much as 1430 ppm Au, 530 ppm Ag, 1920 ppm Te, 10,500 ppm As and 2620 ppm Se in pyrite, Metaliferi Mountains 970 ppm Au, 1180 ppm Ag, 1000 ppm Te, 410 ppm As and 420 ppm Se in chalcopyrite, and 920 ppm Au, Romania 4830 ppm Ag, 1470 ppm Te, 4230 ppm Se and 1540 ppm Bi in bornite. Gold is concentrated preferentially in py- rite, while silver is consistently high (N1000 ppm) in bornite. In the porphyry-type mineralization, galena forms microinclusions in pyrite, chalcopyrite and bornite, and contains up to 3750 ppm Ag, 17,380 ppm Se, 1570 ppm Ge and 780 ppm Te. Galena and pyrite from the epithermal mineralization in the Măgura–Bolcana–Troiţa system contain concentrations of Ag and Se ten times lower than in the same minerals from the porphyry copper min- eralization. The present data show that Te is a significant trace element in the potassic zone of the investigated porphyry systems. The data also shows that this does not correlate with the presence or absence of ophiolitic basement, or with variation in the chemistry of the host intrusions. Tellurium enrichment in porphyry-type de- posits of the Metaliferi Mountains supports their genetic relationship with the spatially associated epithermal systems. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The Metaliferi Mountains (South Apuseni Mountains) in Romania (Fig. 1) host a dense concentration of ore deposits related to Miocene Copper, Au and Mo are the principal commodities in porphyry-style calc-alkaline magmatism (Ghiţulescu and Socolescu, 1941; Ianovici ores, but other metals, notably Ag and platinum group elements (PGEs), et al., 1976; Roşu et al., 2001, 2004; Neubauer et al., 2005). Mineraliza- may be recoverable from some porphyry Cu (–Au, –Ag) deposits. Ele- tion occurs as veins (Au–Ag ± Te and base metal), epithermal breccia ments such as In, Re, Sn, W, Bi, Zn, Te, Se and Ge can also be present in pipes and replacement bodies, and in several subjacent porphyry Cu- porphyry Cu–(Mo–W–Sn) systems at elevated concentrations (Berger type systems. Some of these deposits are ranked as large or very large et al., 2008; Sinclair, 2007) and can potentially be extracted as by- (Borcoş et al., 1998; Milu et al., 2004; UdubaşaandUdubaşa, 2004; products (Ayres et al., 2002). Although data for porphyry systems is lim- Vlad and Orlandea, 2004; Tămaş et al., 2006). The largest of these, the ited, these trace elements are commonly concentrated within the com- Roşia Poieni porphyry Cu deposit contains 431 Mt ore at 0.55% Cu and mon sulfides, notably gold within pyrite (e.g., Cook and Chryssoulis, 0.25 g/t Au (Kouzmanov et al., 2005b). According to Vlad and 1990; Deditius et al., 2011; Reich et al., 2005, 2013a), silver in chalcocite Orlandea (2004), historical gold production in the district totals 630 t or bornite (e.g., Cook et al., 2011; Reich et al., 2013b), indium in sphal- at Roşia Montană, 380 t at Barza–Brad, 330 t at Baia de Arieş and 250 t erite (e.g., Cook et al., 2009a) or rhenium in molybdenite (e.g., at Stănija; all these deposits are of epithermal type. The Săcărâmb Aminzadeh et al., 2011; Ciobanu et al., 2013; Golden et al., 2013). epithermal deposit produced ca. 30 t Au, 55 t Ag and 60 t Te (Udubaşa and Udubaşa, 2004). ⁎ Corresponding author. Tel.: +40 21 3060491; fax: +40 21 31 81 326. The results of substantial research have been published on individu- E-mail address: mihaela.cioaca@igr.ro (M.E. Cioacă). al porphyry Cu deposits. These include accounts of the systems at Roşia http://dx.doi.org/10.1016/j.oregeorev.2014.04.016 0169-1368/© 2014 Elsevier B.V. All rights reserved. M.E. Cioacă et al. / Ore Geology Reviews 63 (2014) 22–39 23 Fig. 1. Location of the porphyry copper deposits in the “Golden Quadrangle”—Metaliferi Mountains (modified after Cioflica et al., 1973). 1. Valea Tisei, 2. Trâmpoiele, 3. Muncăceasca, 4. Măgura Poienii, 5. Tălagiu, 6. Cireşata, 7. Musariu, 8. Voia, 9. Deva. Poieni (André-Mayer and Sausse, 2012; Iatan, 2009; Kouzmanov et al., the trace element contents in porphyry-type mineralization. This com- 2005c, 2010; Milu et al., 2004; Popescu et al., 2006); Valea Morii parison is used to show that the well-documented trace element signa- (André-Mayer et al., 2001; Borcoş et al., 1978), Bolcana (Cardon et al., ture of the epithermal assemblages (enrichment in Au, Ag and Te) can 2005, 2008; Cioacă, 2008, 2011; Cioacă et al., 2010; Milu et al., 2003; also be recognized in higher temperature assemblages within the por- Popescu and Cioacă, 2006), Rovina, Colnic and Cireşata (Halga et al., phyry type mineralization, thus further supporting a genetic relation- 2010). Attention has also been given to several of the larger epithermal ship between the two styles of mineralization. deposits, including Roşia Montană (Bailly et al., 2005; Kouzmanov et al., 2005c; Tămaş et al., 2006, 2014), Săcărâmb (Alderton and Fallick, 2000; 2. Geological setting Ciobanu et al., 2008; Cook and Ciobanu, 2005; Popescu et al., 2010, 2013), and Larga (Cook and Ciobanu, 2004, 2005). These articles and a Miocene (14–7 Ma) volcanic-hydrothermal activity in the Metaliferi number of regional studies (Berbeleac, 1985; Borcoş et al., 1998; Mountains was controlled by the regional geodynamic evolution of the Boştinescu, 1984; Harris et al., 2013; Marcoux et al., 2002; Neubauer Carpathian orogen and Pannonian basin during the Cenozoic. This evo- et al., 2005; Popescu and Neacşu, 2007; Roşu et al., 2001, 2004; lution comprised subduction and collision of the European and Moesian Udubaşa and Udubaşa, 2004; Udubaşa et al., 2001; Vlad and Orlandea, plates with the Intracarpathian Alcapa and Tisia blocks, resulting in a 2004) have documented the spatial and genetic relationships between subsequent extensional regime, driven by the translation and clockwise the porphyry Cu deposits and epithermal mineralization. rotation of Tisia block (Neubauer et al., 2005; Roşu et al., 2004). Rotation Remarkably few publications (Cheşu, 1983; Cioacă et al., 2010; Cook of the Tisia block in excess of 60° at 14–12 Ma produced deep and Ciobanu, 2004) deal, however, with the trace element geochemistry transtensional faults and NW–SE-trending graben-like pull-apart ba- of the porphyry copper deposits in the Metaliferi Mountains. Consider- sins, which favored a rapid magma ascent, generating numerous volca- ing this, the research reported here is, in many respects, a reconnais- nic–subvolcanic systems. Although the geochemical studies indicate sance study, aimed at identifying geochemical features and trends that that Miocene magmas from the Metaliferi Mountains have a “subduc- can serve as premises for more detailed investigation. We provide tion signature”, they were generated by decompressional melting of a new trace element geochemical data on bulk rock samples and on sul- heterogeneous source situated at the crust–lithosphere mantle bound- fide grains from mineralization in six porphyry deposits that were ac- ary (Neubauer et al., 2005; Roşu et al., 2001, 2004; Seghedi et al., cessible for sampling: Roşia Poieni, Bucium–Tarniţa, Colnic, Rovina, 2007). Variable and higher Nb and Nb/Y ratio in younger rocks Valea Morii and Bolcana. Our aim is to establish any similarities or dif- (10–7 Ma) suggest the generation of the magma by a mixing of astheno- ferences between these deposits regarding the distribution of the spheric melts (Roşu et al., 2001, 2004). Petrochemical studies indicate a trace elements of potential economic interest, and to document the normal calc-alkaline character for the early magmatic products role of the main sulfide minerals in concentration of trace elements. (14–12 Ma), and an adakite-like calc-alkaline signature for the younger We also provide trace element concentrations in sulfides from the (12–7Ma)rocks(Roşu et al., 2004). This magmatism generated amphi- Măgura–Bolcana–Troiţa epithermal system and compare them with bole andesites with pyroxene ± biotite (particularly well represented 24 M.E.
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