Rosia Poieni


Main commodities: Cu Au
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The Rosia Poieni porphyry copper-gold and overprinting high sulphidation epithermal deposit lies within the Apuseni Mountains of the Transylvanian region of Romania, approximately 40 km north-west of the city of AlbaIulia and immediately to the north of the city of Deva.  It falls within the Carpatho-Balkan province of the Tethyan-Eurasian metallogenic belt and is approximately 4 km ENE of the Rosia Montana intermediate sulphidation Au-Ag deposit.

The earliest recorded mining in the region that embraces Rosia Poieni and Rosia Montana dates from the first century AD, prior to the siezure of production by the Roman Empire in 106 AD.   The area, which extends over an area of around 500 sq km was known as the Golden Quadrilateral and falls within the Apuseni and Metaliferi Mountains.  Production from the area, which has been virtually continuous over the last almost 2000 years, is thought to have been as much as 1300 tonnes (42 Moz) of gold.

The Apuseni Mountains region was subjected to clockwise rotation during early Tertiary time and was subsequently deformed by a major E-W to ESE-trending strike-slip fault systems.  Major transtensional faults are interpreted to have generated pull-apart basins that acted as the structural loci for Tertiary epizonal intrusions and related hydrothermal systems.  The Rosia Poieni deposit lies within a generally NNW-trending structural corridor associated with strike slip faulting due to the easterly movement and rotation during the collision and northerly migration of the African continental plate into the European continent during the Miocene.  A number of deposits and mineral occurrences occur within this 15 km-long corridor, including the Rosia Montana, Frasin and Rodu epithermal gold deposits and the Bucium-Tarnit porphyry copper-gold deposit.

The Apuseni Mountains encompass a number of Tertiary calc-alkaline volcanic centres representing three main episodes of activity between about 14.8 and 1.6 Ma.  Numerous epithermal and mesothermal Au-Ag, Cu-Au and Cu deposits are known within the district, associated with these mid-Miocene-Pliocene (Neogene) andesitic-dacitic volcanic and sub-volcanic bodies, which intrude a variety of lithologies.   To the south, mafic bodies, which may represent mid-Jurassic oceanic crust basalts, are overlain by late-Jurassic to Cretaceous marine to deltaic sediments, including thick limestones.  The country rocks at Rosia Poieni comprise north vergent Cretaceous thrust sheets of shallow marine to terrigenous flysch-type sedimentary units.

Hydrothermal alteration and mineralisation at the Rosia Poieni porphyry Cu-Au deposit, which is in the northern part of the Apuseni Mountains, is apparently related to a single magmatic pulse of andesite porphyry intrusion, the Middle Miocene subvolcanic, the Fundoaia microdiorite. The deposit exhibits a transition from porphyry Cu-Au mineralisation with associated potassic alteration, minor dykes, and overprinting pyrite-sericite into high-sulphidation epithermal veins with advanced argillic alteration zones over vertical interval of 300 m. Several successive magmatic, breccia and hydrothermal events have been discriminated.

The transition from porphyry to epithermal style mineralisation is characterised by overprinting, fluid-assisted brecciation of the host rocks and the formation of breecia- and pebble-dykes which form the main channels that focused the epithermal fluids and host the high sulphidation epithermal quartz-pyrite-enargite veins. These veins, which are typically of vuggy silica with advanced argillic alteration haloes, are cut by late quartz-sphalerite-galena polymetallic veins associated with phyllic alteration.

Zonation of alteration within the porphyry copper/epithermal gold deposit extends outwards from the deep and central part of the porphyritic intrusion towards shallower and outer peripheries, with four alteration types having been recognised, namely:
i). Potassic - which mainly affects the Fundoaia subvolcanic body, with the andesitic country rocks only being altered in the immediate contact zone with the intrusion. Mg-biotite and K-feldspar are the dominant alteration minerals, accompanied by ubiquitous quartz; chlorite and anhydrite. Magnetite, pyrite, chalcopyrite and minor bornite are associated with this alteration. The early, extensive, potassic zone in the central part of the mineralised system originally passed laterally outwards into a propylitic zone.
ii). Propylitic - was developed peripheral to the early, extensive, potassic zone which represents the central part of the mineralised system, passing laterally outwards into the propylitic zone, which is charactyerised by an assemblage of chlorite, epidote, albite and carbonates. iii). Phyllic - is peripheral to, and overprints the outer margin of the potassic zone and the inner parts of the propylitic zone. It replaces almost all early minerals with abundant quartz, phengite, illite, variable amounts of illite-smectite mixed-layer minerals, minor smectite and kaolinite. Abundant pyrite is the main sulphide in this alteration zone.
iv). Advanced argillic - is developed in the upper epithermal parts of the volcanic structure, with an assemblage of alunite, kaolinite, dickite, pyrophyllite, diaspore, aluminium-phosphate-sulphate minerals (woodhouseite-svanbergite series), zunyite, minamyite, pyrite and enargite (luzonite). Veins containing enargite (luzonite) and pyrite occur in a gangue of quartz, pyrophyllite and diaspore, and are found within and surrounding the subvolcanic intrusion, partially controlled by fractures. A zonal pattern of alteration is observed from the centre of fractures outwards with: a). vuggy quartz; b). quartz + alunite; c). quartz + kaolinite ±alunite and, in the deeper part of the argillic zone, quartz + pyrophyllite + diaspore; d). illite + illite-smectite mixed-layer minerals ±kaolinite ±alunite, and e).  chlorite + albite + epidote.

Koneev, 2004 quotes a total measured+indicated+inferred resource of 350 Mt @ 0.36% Cu, 0.29 g/t Au.

The most recent source geological information used to prepare this summary was dated: 2004.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Andre-Mayer A S and Sausse J,  2007 - Thickness and spatial distribution of veins in a porphyry copper deposit, Rosia Poieni, Romania: in    J. of Structural Geology   v29 pp 1695-1708
Ianovici, V and Borcos, M.,  1982 - Romania: in Dunning, F.W., Mykura, W. and Woolley, A.R., 1982 Mineral Deposits of Europe, v. 2: Southeast Europe The Mineralogical Society, The Institution of Mining and Metallurgy, London,    pp. 55-142.
Zimmerman, A., Stein, H.J., Hannah, J.L., Kozelj, D., Bogdanov, K. and Berza, T.,  2008 - Tectonic configuration of the Apuseni-Banat-Timok-Srednogorie belt, Balkans-South Carpathians, constrained by high precision Re-Os molybdenite ages: in    Mineralium Deposita   v.43, pp. 1-21.

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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