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Rosia Montana

Romania

Main commodities: Au Ag
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The Rosia Montana low- to intermediate-sulphidation, epithermal gold deposits lie 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 and fall within the Carpatho-Balkan province of the Tethyan-Eurasian metallogenic belt.

The earliest recorded mining in the region that embraces 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 which falls within the Apuseni and Metaliferi Mountains, north of the regional centre of Deva.  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 most intense development and exploitation was under the Austro-Hungarian Empire between the late 17th century and 1918.   Hard rock gold production from Rosia Montana is estimated to have totalled around 28 tonnes (0.9 Moz), augmented by colluvial and alluvial production.

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 Montana 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 Frasin and Rodu epithermal gold deposits and the Rosia Poieni and Bucium-Tarnit porphyry copper-gold deposits.

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 of Rosia Montana, 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 Montana comprise north vergent Cretaceous thrust sheets of shallow marine to terrigenous flysch-type sedimentary units.  These sedimentary units are the host to igneous activity and mineralisation in the Rosia Montana area.

The Rosia Montana deposit is associated with, and hosted by, a Miocene age polymict "vent breccia" of a maar-diatreme complex, emplaced into the Cretaceous flysch-type sedimentary rocks and intruded by rhyodacite to dacite domes. These intrusive domes follow the lateral and vertical contact between the Cretaceous sediments and the vent breccias.   Mineralisation in the breccia occurs as a series of relatively flat-lying zones which may be up to 200 m thick, while structurally controlled mineralisation is also found within Cretaceous sediments beyond the edges of the maar.

The deposit is interpreted to have been generated during episodic fracturing and brecciation events taking place over a period of several hundred thousand years, with mineralisation being punctuated by the eruptive events as indicated by crosscutting and overprinting relations of different breccia bodies in the maar-diatreme complex and age dating of gangue adularia and juvenile magmatic phases.

The bulk of the known reserves are hosted within two adjacent dacite bodies, namely Cetate to the west and and Cirnic to the east. Surrounding breccia units host the Igre Orlea and Cirnicel deposits.

At Cetate, the dacite body is surrounded by peripheral and internal phreato-magmatic breccias composed of dominant dacite clasts grading out into mixed volcanoclastic breccias. Mineralisation is present over an 800 m long by up to 500 m wide, north to NE trending zone as disseminations within the dacite and breccias as well as late carbonate-quartz-clay-sulphide veins.

The Cirnic dome complex is "mushroom shaped" in section which at depth forms a sub-vertical, approximately circular plug. Gold and silver mineralisation is found in two main zones, i). the larger within a NE-SW corridor on the western margin of the dacite plug; and ii). a roughly east-west trending zone on the southern margin of the same intrusive. The precious metal mineralisation occurs as disseminations associated with pervasive quartz-adularia-trace pyrite alteration overprinted by carbonate-quartz-clay-trace sulphide veining.

The epithermal low- to intermediate-sulphidation system is characterised by magnetite-destructive alteration with a paragenesis that comprises earlier stages of adularia, quartz (silicification), illitic clay and pyrite, generally disseminated in quartz-pyrite veinlets and silicified breccias.  The late-stage mineralisation is associated with carbonate-quartz ± base-metal sulphide veins and disseminations and clays.   Most of the gold deposition is related to the quartz-adularia-pyrite zones.   The presence of silicification is the best field guide to gold mineralisation.   Carbonate, with rhodochrosite and base metal sulphides, which accompany (often high grade) gold in narrow late-stage veins, was the focus of early mining, although this style of mineralisation does not constitute the bulk of the gold resource.

Most of the gold mineralisation occurs as disseminations. The major gold mineral is electrum, associated with pyrite, base-metal sulphides, and a variety of Au-Ag sulphosalts with minor tellurides. The overall aspect of the gangue and alteration mineral assemblages, as well as the sulphide assemblage, is characteristic of intermediate sulphidation-state epithermal deposits.

A feasibility study completed in 2001 delineated a measured + indicated resource of 302 Mt @ 1.3 g/t Au and 6 g/t Ag for a total resource of 395 tonnes (12.77 Moz) of gold and 1900 tonnes (61 Moz) of silver.

The same study also defined total proven + probable reserves of 225.7 Mt @ 1.4 g/t Au and 7.5 g/t Ag for 325 tonnes (10.5 Moz) Au and 1700 tonnes (54.6 Moz) Ag.

Leary, et al., 2004 quote a total measured + indicated + inferred resource of 400 Mt @ 1.3 g/t Au, 6 g/t Ag.

The most recent source geological information used to prepare this summary was dated: 2001.    
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:
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.
Manske S L, Hedenquist J W, OConnor G, Tamas C, Cauuet B, Leary S and Minut A,  2006 - Rosia Montana, Romania: Europes largest gold deposit: in    SEG Newsletter   no. 64 pp 1, 9-15
Wallier S, Rey R, Kouzmanov K, Pettke T, Heinrich C A, Leary S, O Connor G, Tamas C G, Vennemann T and Ullrich T,  2006 - Magmatic Fluids in the Breccia-Hosted Epithermal Au-Ag Deposit of Rosia Montana, Romania: in    Econ. Geol.   v101 pp 923-954
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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