Investigation of the rare elements from the porphyry copper deposits in Romania

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1 Investigation of the rare elements from the porphyry copper deposits in Romania Project PN-II-RU-PD Scientific report (abstract) Project Director, Dr. Mihaela Cioacă

2 I. Introduction Porphyry copper deposits are the world's most important source of Cu but other elements such as Mo, Au, Ag, Re, Sn, W, PGE, In, Se, Te, Bi could be recovered from these deposits as subproducts or co-products of Cu extraction (Berger et al., 2008; Sinclair, 2007). In this project, the main focus is on the trace elements contents in porphyry copper deposits from Romania. Other geological aspects studied concern: the host minerals, the spatial distribution of the selected trace elements in the studied deposits, the preferential association between these elements with the type of host rock and type of hydrothermal alterations and the geochemical conditions of transport and precipitation. Seven deposits were investigated in this study: six from the Metallogenetic Subprovince of South Apuseni Mts. (Roşia Poieni, Bucium-Tarniţa, Valea Morii, Colnic, Rovina, Bolcana) and one (Moldova Nouă from the Laramian magmatism of the Banatite province in the Southern Carpathians. Several investigation methods were used in this project in order to perform the targeted objectives: optical microscopy, electron micro probe analyses (EMPA), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorbtion spectrometry (AAS), Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS), microthermometry on fluid inclusions. II. Geological background Metaliferi Mts are caracterized by the existence of numerous types of ore deposits and occurences, including porphyry copper, hydrothermal veins and intrusive breccia types. All these are associated with volcanic and subvolcanic complexes, developed during the Neogene magmatism. Fifteen porphyry copper deposits are known in this area. Most of them are classified by Boştinescu (1984) as Cu-Au type (Valea Morii, Musariu, Bolcana, Rovina, Voia, Tălagiu, Larga, Trâmpoiele, Valea Tisei, Muncăceasca, and Bucium-Tarniţa) and Cu-Mo (Au) (Deva, Roşia Poieni). Halga et al. (2010) classified the Colnic and Cireșata ore deposits as Au-Cu type. Two main petrographic types of host rocks are known: amphibole-bearing microdioritic/andesitic rocks, at Roşia Poieni, Tarnita, Bolcana and Colnic, and amphibolepyroxene-bearing quartz-dioritic/microdioritic rocks, at Valea Morii and Rovina. The alteration-mineralization zonality is in accordance with the diorite type model (Borcoș et al., 1998). The ore mineral assemblage from all deposits include magnetite, 2

3 chalcopyrite, pyrite, gold and subordinate bornite, rarely molybdenite (Roşia Poieni, Bolcana, Rovina, Colnic, Bucium-Tarniţa), pyrrothite (Bucium-Tarniţa, Colnic, Bolcana), rutile (Valea Mori) etc. (Borcoş et al., 1984; Milu et al., 2004, Vlad, 1983; Berbeleac, 1985, Halga et al., 2010, André-Mayer et al., 2001) in the inner part of the deposit, characterized by potassic alteration. Phyllic alteration, with pyrite as the main metallic mineral, overprints the margin of the potassic zone of all deposits. Polymetallic Au-Ag veins cross most of the investigated porphyry copper deposits (Roşia Poieni, Bucium-Tarniţa, Bolcana, Valea Mori), forming a system of veins with pyrite, sphalerite, galena, tennantite-tetrahedrite, chalcopyrite, native gold and others in the mineral assemblage. The porphyry copper deposits from Metaliferi Mountains are associated with the Miocene magmatism. The geochemical signatures of magmatic-volcanic products reflects a gradual evolution, from normal calc-alkaline for Ma products and adakitic-like calc-alkaline geochemistry for Ma products. The latest magmatic products apears as few small bodies with alkaline features. (Roşu et al., 2004). The genesis of the magma is related to decompresional melting of a heterogenous source, placed at the crust-lithospheric mantle boundary, but mixing with asthenospheric melts is not excluded (Roşu et al., 2004). Some porphyry Cu mineralized bodies (Moldova Nouă, Ciclova, Şopot, Teregova- Lăpuşnicel) are known in Banat Mts., part of the Banatitic Magmatic and Metallogenetic Belt (Vlad, 1983; Ciobanu et al, 2002). Moldova Nouă deposit (72 Ma) is one of the largest Cu deposit from Romania with 500 Mt at 0,35% Cu (USGS report, 2013). This deposit is located in Sasca-Moldova Nouă metallogenic district (Vlad, 1983) and is related to the Suvorov calc-alkaline quartz-dioritic subvolcanic body (2.5 km in length and m in width). Copper mineralization of Moldova Nouă consists of magnetite, chalcopyrite and pyrite in the potassic alteration zone and pyrite, chalcopyrite, molibdenite, subordinate tetrahedrite, sphalerite and anhydrite, in the phyllic alteration zone from the upermost part of deposit (Vlad, 1983). A supergene alteration (with covellite, bornite, chalcocite malachite, azurite, melanterite and crysocole) was described by Vlad (1983). III. Trace elements geochemistry One hundred bulk mineralized samples were analyzed in order to obtain information about the mineralogy, petrography and geochemistry of the investigated porpphyry type deposits. The samples show different degrees of hydrothermal alteration, from potassic to 3

4 phyllic and argillic. The mineralization in the potassic zone of all investigated deposits is dominated by the assemblage chalcopyrite-pyrite-magnetite (hematite) ± bornite (covellite). Other identified minerals are: gold (at Colnic, Rovina, Bolcana, Moldova Nouă), molybdenite (Colnic, Rovina, Moldova Nouă), unidentified REE minerals (Moldova Nouă). The trace elements concentrations in whole rock samples were determined using AAS, for gold, and ICP-MS, for the other elements (Mo, Re, Ag, Te, Se, In, Ge, PGE). The AAS measurements were performed at SC Prospecțiuni SA, Bucharest with pre-concentration by fire assay method. The detection limit for gold is 0,01 ppm. The ICP-MS measurements were performed at Guizhou Tuopu Resource and Environmental Analysis Center, using a Bruker Aurora M90 spectrometer and the method from Qi et al. (2000) for sample preparation. Rare elements in bulk rock The mean bulk rock values of the main trace elements that are generally recovered from porphyry copper type deposits (Au, Ag, Mo, Re) are: ppm Au, ca. 2 ppm Ag, <50 ppm Mo, ppm Re, ppm Te, 3-5 ppm Se, ppm Ge and <1 ppm In. The pyrite concentrates from Moldova Nouă have 206 ppm Te. PGE are < 2,1 ppm in bulk rock samples and 6.5 ppb in pyrite concentrates from Moldova Nouă. There is a good to very good positive correlation between Cu, Au and Ag in the potassic alteration zones of all deposits excepting Colnic. In, Se and Te show positive correlations with Cu at Bolcana. A positive correlation of Cu with Se and In is indicated at Bucium-Tarniţa and Roşia Poieni. Au exhibits a good positive correlation with Te at Colnic (in the potassic alteration zone) and Roşia Poieni (in the sericitized samples) and a good positive correlation with Se, at Valea Morii and Bucium-Tarniţa. Trace elements in minerals The investigated metals and semimetals could be present in porphyry copper type mineralization as own minerals (such as gold, molybdenite), but also as trace elements in the network of some sulfides and sulfosalts such as pyrite, chalcopyrite, bornite, tetrahedritetennantite etc. The trace elements signatures of main minerals were determined using EMPA and LA-ICPMS. EMPA analyses were performed at Rhodes University, Grahamstown (South Africa). LA-ICP-MS study of minerals (chalcopyrite, pyrite, bornite) and fluid inclusions was performed at Institute of Geochemistry and Petrology, ETH Zurich. 4

5 EMPA results Some grains of pyrite, chalcopyrite, bornite, galena, gold, enargite and tetrahedritetennantite were analysed for trace elements concentration (Au, Ag, Se, Te, Cd, Ge and In). In the porphyry-type mineralization from Metaliferi Mts, but also at Moldova Nouă, the pyrite has Au, Ag and Te concentrations in a wide range of values, from below detection limit to 1000 ppm for Au and Te and between 250 ppm and 860 ppm for Ag. Se has values < 70 ppm at Moldova Nouă, but in the range of ppm in approx. 50% of samples from the deposits of Metaliferi Mts. The chalcopyrite presents detectable values for Ag, Au, Te, Se and In: up to 950 ppm Au, ppm Te, ppm Ag, < ppm Se. In is detected in few gains and Ge is constantly below detection limits. The bornite from Roşia Poieni and Bolcana porphyry Cu deposits shows values up to 920 ppm Au, 1400 ppm Te, 4,830 ppm Ag in some grains, although other grains have contents of these elements below detection limits. Se presents a mean value of 216 ppm at Roşia Poieni and 560 ppm at Bolcana. In and Ge were not detected. In addition, minerals from associated base-metal veins-type mineralization were investigated at Moldova Nouă (pyrite, tetrahedrite, enargite, galena, and sphalerite). LA-ICP-MS results The smooth LA-ICP-MS profiles outline the existence of some microinclusions containing high concentrations in trace elements. For example, high Te, Au and Ag microinclusions were identified in pyrite at Moldova Nouă (hessite?), while microminerals with Pb and Te (altaite?) are included in chalcopyrite from Bolcana. Gold microinclusions in pyrite, chalcopyrite or bornite were founded in all deposits. Excluding the measurements that indicate the presence of microinclusions, all results show low concentrations in trace elements. Quantitative LA-ICP-MS data on chalcopyite show large range of values ( ppm Au, ppm Te, 5-92 ppm Ag, ppm Se etc.). The higher values in trace elements such as Au, Ag, Te, were measured on the samples from Colnic. Chalcopyrite from Moldova Nouă presents lower Zn and Se, but higher As relative to the chalcopyrite in the porphyry copper deposits from Metaliferi Mts. The pyrite is more inhomogeneous showing broad compositional variations in the same deposit. For example, at Colnic, some elements vary by one order of magnitude or more from one sample to onother (Au: 0.27->10 ppm, Zn: >1000 ppm). In the case of pyrite 5

6 from Moldova Nouă, Cu and Zn have smooth spectrums that indicate zonality in their distribution. LA-ICPMS investigations on bornite were done only for Moldova Nouă and Roşia Poieni deposits. Bornite from Roşia Poieni is enriched in Ag, Te, Bi and Se compared with bornite from Moldova Nouă, the latter having higher concentrations of As, Sb, Ge, In and Sn. Gold is detected only in the bornite from Roşia Poieni (0.35 ppm). PGE (Pd and Pt) are below detection limits in all measured sulfide grains. V. Fluid inclusions analysis. Case study: Moldova Nouă In this project, fluid inclusions study was focused on Moldova Nouă porphyry type deposit. Micropetrographic study shows the presence of numerous types of brine inclusions and vapor inclusions, forming a boiling assemblage. Most of the inclusions present a negative crystal shape, ca. 10µm in size, rarely larger. Only halite is present as a transparent solid phase and occupies 20-40% vol. in brine inclusions. Chalcopyrite has been found in most brine inclusions, as daughter mineral. The salinity of brine inclusions ranged between 34% and 48% NaCl eqv., and was estimated using the final dissolution temperature of halite ( C) (method of Bodnar and Vityk, 1994). Chemical composition of brine inclusions was analysed using LA-ICPMS method. The equivalent salinity (NaCl+KCl+FeCl 2 ), was considered as an internal standard. Preliminary results showed high values of Cu, Fe, Zn and Pb (hundreds ppm). Bi, Mo, Ag and Te are detected in some inclusions ( ppm Bi, ppm Mo, ppm Ag, ppm Te). VI. Disscutions and conclusions All investigated deposits have Au-rich porphyry copper geochemical signature (> 0.2 g/t Au, ~ 1-2 ppm Ag, < 0.005% Mo). Most trace elements concentrations (Au, Ag, Te, Bi, In) show significant enrichment. Platinum group elements (PGE) record very low values in all deposits, commonly < 1 ppb, occasionally higher (1.6 ppb Pd at Moldova Nouă and 1.21 ppb Pd at Bucium-Tarniţa). 6

7 Some of the detected trace elements were probably present in the crystal networks of their host minerals, but some were also identified as mineral microinclusions in chalcopyrite, pyrite and bornite. The gold concentration in sulfide network is low (< 1 ppm), excepting Colnic. In the case of Colnic, the porous pyrite presents higher concentrations of Au, Te, Ag, Zn, As etc., probably because of its rapid cristalization. Positive correlation of Cu with Au, Ag, In, Bi in most ore deposits, especially in the potassic zone, suggests a common magmatic source of these elements. Sericitization and argilization processes contributed to the redistribution of the trace elements (enrichment of Mo, Re and Te and depletion of Cu respectively). The trace element distribution in the main sulfide minerals shows no significant difference between the deposits in the Metaliferi Mountains (Miocene province) and Moldova Nouă (Banatite/Laramian province). At Moldova Nouă, fluid inclusions study shows that the trace elements were transported as chlorides in hypersaline fluids and the precipitation of metals was controlled by the boiling processes at C. EMPA results evidenced a preference of Au for pyrite, while Ag, Bi and Se show values of hundreds ppm in bornite. Very high concentration of Te in bulk rock (hundreds ppm in some samples from the sericitized samples from Moldova Nouă and Roşia Poieni) could indicate the presence of tellurides in these samples. Bulk rock results on the investigated samples from the porphyry Cu deposits in Romania, suggest depletion in PGEs relative to mantle and some modest enrichments in Ir and Pd relative to upper crust. Chemical composition and microtermometry measurements of the fluid inclusions in samples from Moldova Nouă indicate a salinity of 34-48% NaCl eqv. and significant concentrations of some metals (Cu, Mo, Ag, Pb, Zn, Mn, Pb, Cs, Ba) and, occasionally, Te and Au. References Berbeleac I Gold ore deposits (in Romanian). Editura Tehnică Bucureşti. 315p Berger B.R., Ayuso R.A., Wynn J.C., Seal R., Preliminary Model of Porphyry Copper Deposits. USGS Open-File Report. Borcoș M., Vlad S., Udubașa G., Găbudeanu B Qualitative and quantitative metallogenetic analysis of the ore genetic units in Romania. Romanian Journal of Mineral Deposits 78, Special Issue, Pages

8 Borcoş M., Krautner H.G., Udubaşa G., Săndulescu M., Năstăseanu S., Biţoianu C., Map of the mineral resources, 2 nd edition. Explanatory note. Institute of Geology and Geophysics, Bucharest Boştinescu S., Porphyry copper systems in the South Apuseni Mountains Romania. Anuarul Institutului de Geologie şi Geofizică LXIV, Ciobanu C., Cook N. J. Stein C. H Regional setting and geochronology of the Late Cretaceous Banatitic Magmatic and Metallogenetic Belt. Mineralium Deposita (2002) 37: Halga S., Ruff R., Stefanini B., Nicolici A., The Rovina Valley Project, Apuseni Mts., Romania. Gold copper porphyry discoveries in a historic mining district. Romanian Journal of Mineral Deposits 84, Milu V., Milesi J.P., Leroy J.L., Roşia Poieni copper deposit, Apuseni Mountains, România: advanced argillic overprint of a porphyry system. Mineralium Deposita 39, Roşu E., Szakacs A., Downes H., Seghedi I., Peckskay Z., Timing of Miocene- Quaternary magmatism and metallogeny in the South Apuseni Mountains, Romania. Romanian Journal of Mineral Deposit 81, special issue, Sinclair W.D., Porphyry deposits, in Goodfellow, W.D., ed., Mineral Deposits of Canada: A Synthesis of Major Deposit-Types, District Metallogeny, the Evolution of Geological Provinces, and Exploration Methods. Geological Association of Canada, Mineral Deposits Division, Special Publication, Vlad S.N., Geology of porphyry copper deposits (in Romanian). Editura Academiei, Bucharest 8

MINERALOGY OF VIVIANITE FROM ROSIA POIENI; METALLOGENETIC SIGNIFICANCE

MINERALOGY OF VIVIANITE FROM ROSIA POIENI; METALLOGENETIC SIGNIFICANCE Prof.univ.dr. GHEORGHE C. POPESCU, conf.univ.dr. GHEORGHE ILINCA, conf.univ.dr. ANTONELA NEACŞU University of Bucharest, Faculty of