TIMING OF MIOCENE-QUATERNARY MAGMATISM AND METALLOGENY IN THE SOUTH APUSENI MOUNTAINS, ROMANIA

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1 TIMING OF MIOCENE-QUATERNARY MAGMATISM AND METALLOGENY IN THE SOUTH APUSENI MOUNTAINS, ROMANIA ROSU 1 Emilian, UDUBASA 1 Gheorghe, PÉCSKAY 2 Zoltan, PANAIOTU 3 Cristian, PANAIOTU 3 Cristina Emilia 1 Geological Institute of Romania, 1 Caransebes Street, RO-78344, Bucharest 32, Romania. rosu@igr.ro; 2 Institute of Nuclear Research of the Hungarian Academy of Sciences, P.O. Box 51, Bem ter 18/c, H-4001 Debrecen, Hungary; 3 University of Bucharest, Paleomagnetism Laboratory, Bălcescu 1, Bucharest, Romania In the South Apuseni Mountains (SAM), the Miocene-Quaternary volcanic activity evolved in three episodes. The first volcanic products are represented by poorly developed rhyodacite tuffs, hosted by Globigerina bearing marls (Langhian), followed by main and complicated magmatic activity in Kossovian-Pannonian. The last episode (Early Pleistocene) displays an alkaline character and occurs on a different geostructural context only in Uroiu Hill (1.6 Ma), after a gap of about 6 Ma. At regional scale this areal display specific features with regard to space-time evolution of volcanic activity, association of elements, type of mineral deposits and age of deposits. In this paper, we present the whole available data regarding the K-Ar ages included in our different papers (a few of them being re-analysed and corrected afterwards) and on this basis to estimate the age of main mineralizing processes in different areas according to spatial-temporal evolution of Neogene magmatism. Based on detailed field observations combined with K-Ar ages, geochemical analyses, and paleomagnetic data the scenario for Neogene magmatic evolution of SAM is as follows: an early volcanogenic sedimentation in newly created pull-apart basins, followed by two magmatic activity events. The first event (calc-alkaline medium-k quartz andesites with amphibole, pyroxene ± biotite), between Ma, is spatially restricted to Zarand-Barza-Zlatna-Rosia Montana-Bucium areas and shows a progressive clockwise rotation, around 70º between 14.5 Ma and 12 Ma. The second event, represented by calc-alkaline medium to high-k quartz andesites with amphiboles, biotite ± pyroxene, developed between Ma, covers a larger areas in the Deva-Sacaramb- Hartagani and Baia de Aries-Rosia Montana zones, is free of paleomagnetic rotations, and the main products here are "adakite-like" calc-alkaline rocks. Small bodies (10.5 Ma) with alkaline features (trachyandesites, microdiorites)(sacaramb-hartagani area) and basaltic andesites (7.4 Ma) (Rosia Montana-Bucium area), with distinct geochemical signature, are the latest products in the respective districts. 33

2 Sample Locality Lithology Rock type K (%) 40 Ar rad (%) 40 Ar rad (ccstp/g) K-Ar ages ZARAND 117 Tălagiu α am px neck x ± Dieci α am px neck x ± Camna α px lava flow x ± Chişindia α px neck x ± Vârfuri α px lava flow x ± Minisulde Sus α px lava flow x ±0.7 1 BRAD 2352 Curechi α am px sub-volcanic x ± Cireşata α q am bi±px neck x ± Dl. Caraciu α am px neck x ± Barza α am px neck x ± Caracel α px neck x ± Valea Arsului α am px neck x ± Plesa-Brad α q am bi neck x ± Brad -v. Steau α q am bi±px intrusive breccia? x ± Bratisa α q am bi±px volcanoclastic rocks x ± ZLATNA 6922* Trâmpoiele mδ am px sub-volcanic x ±0.5 2, 590 Stanija α am px neck x ± Stanija α am px neck x ± Almasu Mare α am px neck x ± BUCIUM - ROSIA MONTANA 6912 Bucium S mδ am px sub-volcanic x ± Bucium S mδ am px sub-volcanic x ± Bucium-Citera α am px neck x ± * Dl. Carnic υ sub-volcanic x ± 0.63 # 795 Taul din Brazi υ sub-volcanic x ± Dl. Contu υ sub-volcanic x ± 1 # 84 Rotunda α am px lava flow x ± Geamăna W α am px sub-volcanic x ± Detunata αβ neck x ±0.3 1 BAIA DE ARIES 801 Valea Lacului α am bi sub-volcanic x ± Dl.Bulzu α am px neck x ± Poeniţa α q am bi sub-volcanic x ± Poeniţa α q am bi sub-volcanic x ± Şurligata α am±px sub-volcanic x ±0.9 2 SACARAMB - HARTAGANI 388 Valea Draica α am bi±px blocks in bedded rocks x ± The paleomagnetic data show also, that: (1) the clockwise rotation within Tisia block started after collision of the northern part of Alcapa block with the European continental margin at about 16 Ma (Panaiotu, 1998); (2) most of the Tertiary clockwise rotations were very fast: (around 70º between 14.5 Ma and 12 Ma) and (3) the Miocene volcanism from the Apuseni Mountains took place in a very dynamic rotational setting. All the data regarding K-Ar ages for Neogene magmatic- Quaternary rocks in Apuseni Mountains are presented in Table 1. Table 1 Sample location, rock type, lithology and K-Ar ages (whole rocks) for Neogene- Quaternary magmatic rocks in Apuseni Mountains. Source

3 567 Dealul Paua-N α q am bi±px neck x ± Cetraş α q am bi±px neck x ± Voia α am neck x ± Dealul Padina α q am bi±px neck x ± 0.62 # 192 Dl. Duba α q am bi±px neck x ± Goruniste α q am bi±px neck x ± Valea Draica α q am bi±px blocks in bedded rocks x ± Zuckerhut α q am bi±px neck x ± Hondol α am neck x ± Pr. lui Toader mδ am px±bi sub-volcanic x ± Zâmbriţa tα neck x ± Hondol α q am bi±px neck x ± Dl. Paua S α q am bi±px neck x ± Faerag-Certej α am neck x ± 0.93 # DEVA 6920 Serhediu α am sub-volcanic x ± Nocet α am bi sub-volcanic x ± * Mina Deva mδ am bi sub-volcanic x ± Cetate α am bi neck x ± UROI MM29 Uroi tα neck x ±0.1 1 Abbreviations: α=andesite, αβ=basaltic andesite, tα=trachyandesite, mδ=microdiorite, υ=dacite, am=amphibole, bi=biotite, px=pyroxene, q=quartz. Sources of K-Ar ages are from: (1) Pécskay at al., 1995; (2) Roşu et al., 1997; (3), Roşu et al., 2001, 2004; new data ( # ); rocks hosting ore deposits (*). The Neogene ore-deposits of the South Apuseni Mountains (SAM) are related to "normal" and "adakite-like" (or rather "high Sr" andesite) calc-alkaline intermediate magmatic complex structures generated under extensional and rotational regime in a non-subduction setting. A possible scenario, according to geotectonic, geochemical and paleomagnetic data, involves a transtensional tectonic regime directed by contemporaneous eastward translation and clockwise rotation of Tisia- Getia terrane, in area of South Apuseni Mts., on a relatively thin lithosphere. Expression of this are the deep-seated transtensional fault systems generating graben like small pull-apart aligned basins, which represent the structural control for magma uprising. The mechanism of magmagenesis is considered to be related to decompressional melting of a heterogeneous source (subcontinental mantle affected by metasomatic process related to earlier subduction events and /or lower crust) situated at the crust-lithosphere mantle boundary. Mixing with asthenospheric melts generated during the extension-related attenuation of the lithosphere may also be implied (Rosu et al., 2001,2004). The Neogene ore-deposits of the SAM are represented by porphyry copper-gold deposits, base metal, world-class gold deposits and rich smaller deposits showing an uncommon density of ore bodies (Udubaşa et al., 2001). A detailed analysis of each zone shows that only some magmatic structures are productive, showing peculiar structural patterns. Despite of some mineralogical and geochemical differences existing between "normal" and "adakite-like" calcalkaline andesites, the whole area of SAM is characterized by numerous porphyry copper systems (Cu ± Au, Mo) (although many of sub-economic class), base metal-gold and telluride epithermal ores: veins (low-sulfidation and sporadically high-sulfidation types), breccia pipes or replacement 35

4 bodies. Further on, there is a typical feature of many magmatic-metallogenetic structures: either porphyry systems enveloped by epithermal vein arrays (Bolcana-Troita, Valea Morii etc.) or productive subvolcanic bodies enveloped by barren volcanic structures (e.g. Sacaramb)(Rosu et al., 2003). There are a few data regarding the timing of mineralization but based on these and on detailed field observations (pre-, host rocks, syn- and post mineralization), combined with K-Ar ages, geochemical analyses, and paleomagnetic data (Fig. 1) we can remark the following: the oldest mineralisation is the gold mineralization from Rosia Montana (13.6 Ma); in Zlatna area, the timing of mineralization developed between 12.6 Ma (porphyry copper) and probably 10.5 for epithermal ore deposits; the age of microdiorites with porphyry copper mineralization from Deva according with our data is 12.1 Ma. On the same criteria, we can estimate the intervals of mineralization processes from Sacaramb -Hondol-Voia area (porphyry and epithermal ore deposits) between Ma, Ma for porphyry and epithermal from Bucium Rosia Poieni area and Ma from Baia de Aries. In Barza area, the mineralized fragments of andesite-microdiorites are present in andesites from Ciresata Hill (12.81±1.27 Ma); estimative interval of mineralization is between 12.8 (possible younger, cca 12.5 Ma) and 10 Ma, according to preliminary data obtained by A. Lips on the Valea Morii samples (personal communication) Our data suggest three main time intervals for mineralization processes: the first, at the boundary Badenian/Sarmatian (13.6 Ma) in Rosia Montana area, the second, largely developed at regional scale between Ma (Middle Sarmatian-Upper Pannonian) and the third, between Ma at the Baia de Aries (Pannonian). According to these data, with a few exceptions (e.g.rosia Montana and probably Bucium Rodu), all the productive structures was emplaced after the cessation of the large clockwise rotation. This period, at regional scale and especially at the scale of complex magmatic structures ("volcanoplutonic structures") was favourable to intrusion and emplacement of shallow-columnar small sized subvolcanic bodies connected with deep sources rich in vapour-like fluid of low density and more saline liquid (brine) at this moment of evolution. This "shallow-columnar " subvolcanic bodies were the main "way" to transport this products and were in their upper part the place of segregation of ore -forming elements by separation of vapour and brine in accord with processes of crystallisation and physico-chemical parameters of magmatic-hydrothermal systems. In the SAM area, the porphyry copper mineralizations show a primary character, or with only local subsequent convective copper enrichment processes, being rich in fluid inclusions with very high salinity; in most the cases, the epithermal veins and/or breccias spatially related to porphyry copper or shallow subvolcanic bodies are rich in fluid inclusions with very high salinity, too (e.g.brad area, Bocsa-Sacaramb, Hanes- Larga, Baia de Aries area)(nedelcu et al., 1999, 2001) 36

5 The processes of mineralization were influenced by regional frame but as much important were the control at local scale, where this special moment of emplacement of shallow subvolcanic bodies connected with tectonically control and the permissive spaces created in the upper part in neighborhood of porphyry Cu ± Au, Mo, base metal and gold mineralization. The spatial-time evolution and the distribution of complex magmatic structures ( "volcanoplutonic structures") at regional scale, what usually are associated with mineralized structures is a good argument in sustaining this idea. BA Z B S B D RM Fig. 1. Time evolution of volcanic and metallogenetic activity in the Southern Apuseni Mountains. For metallogenetic activity the time intervals are estimative. Symbols for rock types (black symbols are normal calc-alkaline rocks, open symbols are adakite-like calc-alkaline rocks): squares=dacites; circles=andesites; diamond=basalts andesites; triangle=alkaline rocks. Areas acronyms: ZB-B-Z = Zarand Basin Brad Zlatna; RM-BA-B = Roşia Montană Baia de Arieş Bucium; S = Săcărâmb; D-U = Deva Uroi (see Table. 1 for their locations). K-Ar ages from Pécskay at al., 1995; Roşu et al., 1997, 2001, 2004 and this study. Time evolution of volcanic activity diagram after Roşu et al., Thick bars represent presumed age of mineralization for specific areas. 37

6 References Nedelcu L., Rosu E., Costea C. (1999) The complexes chlorides related to some Neogene ore deposits of the Metaliferi Mountains, Romania, In: Mineral Deposits: Processes to Processing, Stanley et al. (eds.), Balkema, Rotterdam Nedelcu L., Rosu E., Costea C. (2001) Mineral microinclusions hosted in sulfides of main Neogene porphyry copper and epithermal ore deposits of the South Apuseni Mountains, Romania. Rom. Jour. Min Dep.79, suppl. 2, Special Issue, Geodynamics and Ore Deposits Evolutions of the Alpine-Balkan-Carpathian-Dinaride province, ABCD-GEODE WORKSHOP 2001 Vata Bai, Romania, 8-12 June 2001, Abstracts Volum, Panaiotu, C. (1998): Paleomagnetic constraints on the geodynamic history of Romania. In: Sledzinski J (Ed.) Monograph of Southern Carpathians. Warsaw Institute of Technology, Institute of Geodesy and Geodetic Astronomy, Warsaw. Reports on Geodesy 7(37), Pécskay Z., Edelstein O., Seghedi I., Szakacs A., Kovacs M., Crihan M. & Bernad A. (1995): K-Ar datings of the Neogene-Quaternary calc-alkaline volcanic rocks in Romania. Acta Vulcanologica 7 (2), Rosu E., Pecskay Z., Stefan A., Popescu G., Panaiotu C., Panaiotu C. E. (1997) The evolution of the Neogene Volcanism in the Apuseni Mountains (Romania): constraints from new K Ar data. Geologica Carpatica, 48, 6, , Bratislava. Roşu E., Szakács A., Downes, H., Seghedi I., Pécskay Z., Panaiotu C. (2001) The origin of Neogene calc-alkaline and alkaline magmas in the Apuseni Mountains, Romania: the adakite connection. Rom. Jour. Min Dep.79, Suppl. 2, Special Issue, Geodynamics and Ore Deposits Evolutions of the Alpine-Balkan-Carpathian-Dinaride province, ABCD-GEODE WORKSHOP 2001 Vata Bai, România,, 8-12 June 2001, Abstracts Volume, 3-23, Bucharest. Rosu E., Udubasa G., Nedelcu L., Pecskay Z., Panaiotu C., Panaiotu C.E., Ivascanu M.P.(2003) Why is the Neogene Mining district of the South Apuseni Mountains (Romania) unique in the Carpathians? In: Geodynamics and Ore Deposit Evolution of the Alpine-Balkan- Carpathian-Dinaride Province, Final GEODE-ABCD (2003) Workshop, Programme and Abstracts, Seggauberg, Austria, March 22-24, 2003, p 49. Roşu, E., Seghedi, I., Downes, H., Alderton, D.H.M., Szakács, A., Pécskay, Z., Panaiotu, C., Panaiotu, C.E., Nedelcu, L. (2004) Extension-related Miocene calc-alkaline magmatism in the Apuseni Mountains, Romania: origin of magmas. Swiss Bulletin of Mineralogy and Petrology, Special Issue 84/1, Editors A. von Quadt, T. Driesner and C. Heinrich (in press) Udubaşa G., Roşu E., Seghedi I., Ivăşcanu M.P. (2001) The Golden quadrangle in the Metaliferi Mts. Romania: what does this really mean? Rom. Jour. Min Dep.79, Suppl. 2, Special Issue, Geodynamics and Ore Deposits Evolutions of the Alpine-Balkan-Carpathian- Dinaride province, ABCD-GEODE WORKSHOP 2001 Vata Bai, România, 8-12 June 2001, Abstract Volume, 24-34, Bucharest. 38