07 Mining Apuseni

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Romania Field Trip SEG Student Chapters Uni Geneva - ETH Zürich - Uni Budapest - Uni Cluj 05.09-14.09.2006

Mining history of the Apuseni Mountains

IntroductionThe Golden Quadrilateral in the Metaliferi Mountains (South Apuseni Mountains) includes gold and silver deposits which, without doubt, constitute the most productive gold area in Europe (Fig. 1a). The Golden Quadrilateral covers an area of approximately 500 km2 within the Apuseni Mountains immediately to the north of the city of Deva ad the limits are marked by the Săcărâmb (Nagyág, Gross-Astdorf), Baia de

Ampelum, an administrative center for gold mining by the Empire. Traces of ancient workings of placer and lode deposits are known not only from Roşia Montană (Alburnus Maior, Verespatak, Goldbach), but also from districts such as Căraci, Ruda-Brad, Ţebea, Baia de Criş (Körösbánya), and Vulcoi Corabia, among others (Fig. 1b). The district is considered to have reached maximum development and peak gold production during the Austro-Hungarian Empire period from the end of the 18th century to 1918. Mining was generally done by hand, with pit ponies or man carried wicker basket transport to surface. Processing of ore was by means of water powered

Past and present mining in the Apuseni MountainsAttila TÓTH (Eötvös Lóránd University, Budapest), Aurélie QUIQUEREZ (University

of Lausanne), István MÁRTON (University of Geneva)

Romania

Hungary

Slovakia

Ukraine

Croatia

Bulgaria

TurkeyGreece

Macedonia

Albania

Moldova

Serbia-Montenegro

Bosnia - Herzegovina

GoldenQuadrilateral

> 10 Moz Au

5-10 Moz Au

1 Moz Au Deva

Zlatna(Ampulum)

Sãcãrâmb(Nagyág)

The “Golden Quadrilateral”

Mures

Cris

Aries

Baia de Aries(Offenb )ánya

Stanija

Almasu Mare

Vulcoi Corabia

Rosia Montana(Alburnus Maior)

APUSENI MOUNTAINS

Caraci

Baia de Cris(Körösbánya)

Tebea

Ruda-Brad

Cainel

Craciunesti

N

Arieş (Offenbánya, Offenburg), Căraci-Brad (Karács) and Zlatna (Ampelum, Zalatna, Goldmarkt) districts (Fig. 1b).

The Golden Quadrilateral continuously produced gold since discovery. But the historic gold district in the last 30 years also became an interesting copper-prospecting area, when also 12 important porphyry copper systems were discovered using combined geophysical and geochemical prospecting methods. Consequently the Golden Quadrilateral is in fact actually the Golden-Copper Quadrilateral.

Figure 1a: The position of the Golden Quadrilateral within the Eastern European gold “anomaly map” after Márton et al. (2006); Figure 1b: Major historical mining districts in the Golden Quadrilateral (Apuseni Mountains). In comma former mining locality names were included (Latin, Hungarian or German), updated from Manske et al. (2006).

Several well preserved mining works and many archaeological findings confirm the very early gold extraction. The Apuseni Mountains have been inhabited since the Stone Age. It is known that Apuseni gold was used by the Mycenaeans and the Trojans, and is believed to have been used also by the Pharaohs. The region was known as Dacia and inhabited by the Dacs. The Romans conquered this area and carried out tonnes of gold and silver. Trajan’s Column in Rome commemorates the importance of the conquest. It was calculated that the Romans had extracted about 150,000 kg of gold from Dacia. The modern town of Zlatna was known in Roman times as

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stamp batteries and gold was collected on woollen fleeces. Private mining continued during the period between the world wars and re-commenced after the Second World War. From the end of the 19th century besides the gold, important quantities of Cu, Pb and Zn have been extracted. Some old mines are still in operation, or are preserved as outdoor underground museums (e.g. at Roşia Montană and Brad). “The road of gold” to Deva and then to Vienna followed the route through Geoagiu (Algyógy) passing through Săcărâmb Forest. Today this road is 50 km shorter than the national road. Scientific research done parallel with exploitation led to the discovery, for the first time in the world, of the element tellurium (Te, described by Müller von Reichenstein in 1778 from Fata Băii samples) as well as of a large number of new minerals.

Mining in the Certej- Săcărâmb areaOver the two and a half centuries there were big volumes written about Săcărâmb. In the 19th century mining specialists from Europe, North America and even Brazil had come to study the strangest chemical formation created in the mountain which has the same name as the former name of Săcărâmb town (Nagyágite). Săcărâmb is the second ranking mineral occurrence in the Apuseni Mountains, as a whole. Officially the gold mining in Certej, Hondol, Măgura Topliţei and Săcărâmb started when Maria Teresa had decided to encourage the gold mining in Transylvania. First gallery - Maria Gallery - was dug in 1746. It has been estimated that the Săcărâmb Mine has yielded 85,000 kg of gold during nearly 250 years of mining activity. More than 300 km of mine shafts and tunnels, on 5 main levels, were dug in an area of no more than 1 km by 1 km. The ore found in the Săcărâmb and the altered host rocks contain more than 100 mineral species. Săcărâmb is the type locality for nagyágite, rhodochrosite, krennerite, alabandite, petzite, stuzite, muthmannite, and krautite, as well as one still unnamed new mineral (the arsenian nagyágite; Papp 2004).

The records indicate that during two centuries (18th and 19th century) the entire mining complex was the most profitable in whole Europe. The town has been developed at the same time with the mine. In 1835 the first Mining School in Southeastern Europe had been founded (Fig. 2). In 1862 the school became Sub-engineer’s Institute, also first of its kind in that region, where number of students and specialists from Hungary, Germany, Austria, Russia, England, Holland, Sweden, Turkey, Brazil, Japan and North America have studied.

Between 1920 and 1930 Săcărâmb had 14,000-15,000 inhabitants (at the same time Deva had only 8,000). In Săcărâmb were running banks, workshops, 3 slaughter houses, a beer manufacture, shops also. There was running even a casino. Later the mining came to decline. From over 2000 houses today only 10% are still holding on. First gold foundry

was opened in 1763 in Certej and it had worked over 119 years. The skills of the miners from Certej and Săcărâmb were well known all over the world (Fig. 3).

Fortunately, starting at the beginning of the last century the most interesting gold specimens were collected and preserved by geologists of the Brad Mining Company. These became later the collection of the Gold Museum in Brad – the centre of the gold extraction in the area. The best represented is the Roşia Montană ore deposit, besides other traditional mining areas in the Golden Quadrilateral of the Apuseni Mountains (Bucium, Baia de Arieş, Brad-Săcărâmb, Zlatna-Stănija, etc) and the Baia Mare

Figure 2: The building of the Mining School in Săcărâmb.

Figure 3: Gold underground exploitation method used in the 18th century. Engraving placed inside the Museum of SM Certej.

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region (Cavnic). Most of these deposits were mined since antiquity. Gold flakes and nuggets panned from the river placers are exhibited.

Mining in the Baia de Arieş areaBaia de Arieş is a mining centre extracting mainly base metals but also arsenopyrite and pyrite-rich concentrate containing gold. The first writing about it is in a document of Charles I of Hungary from 1325. In the beginning of the 15th century it was declared free town. It lost this status later, but regained it in 1798. Baia de Arieş is the type locality for sylvanite, which was first discovered by Müller von Reichenstein in 1785.

Mining in the Roşia Montana areaGold mining at Roşia Montană dates back over 2000 years ago to Geto-Dacian times, prior to the first century AD. Subsequently the Roman Empire seized control of the area in 106 AD, primarily to control the production of gold, in what was termed the Golden Quadrilateral. Roşia Montană was known as Alburnus Maior by the Romans, and mined by them during the years 106 to 273 AD. Several wooden and waxen tablets written in Latin or Greek were recovered from mine workings during the 18th and 19th centuries. These tablets, dating back to 131 AD, record details of mining contracts, real estate transactions, and other commercial activity during the early Roman Empire. Mining has attracted immigrants to the region from Germany, Italy, Hungary, and Austria, who formed a significant fraction of the population (Fig. 4). Seven different religious denominations are represented in the area, the principal denomination being Romanian Orthodox.

Historical mining activity peaked during the Austro-Hungarian period in the 1800s, when the area was known as Verespatak, meaning “Red River.” State control of all mining activities followed the Second World War with extensive underground development to outline reserves and gain access for pillar and stope mining. Underground operations continued until 1970, when open-pit mining commenced, which still continues. In 1959 all gold mining at

Roşia Montană was brought under the control of the state and the state mining company, who continued underground mining and development. In 1970 an open pit operation was initiated on the Cetate deposit concurrent with underground development, which continued until 1975. The Minvest operated open pit was designed to operate at a rate of 400,000 tones per year. Production to date, calculated from the original topography indicates that a total of approximately 6.8 Mt of material or 130m of topography has been mined to date from the Cetate open pit producing approximately 10,000 to 12,000 ounces of gold per year. More than 2000 years of underground mining and exploration has resulted in the development of over 110 km of underground drives. These drives and cross-cuts as well as room and pillar development in addition to “glory” holes have been surveyed and included in the block model and it is calculated that 3.7 Mt of material has been removed from underground to date. Earlier underground mining was focused on development along high grade “veins” whereas recent (post-1959) underground development was designed as delineation style orthogonal grid pattern workings with some room and pillar exploitation. Development was conducted on levels at a spacing of approximately 15-40 m over a vertical relief of over 400 m. Current mining and production is by means of an open pit at Cetate and production is estimated at a rate of 200,000 tones per year. The present operation is subsidised by the state, but prior to Romania’s joining the European Union these subsidies from the central government will be terminated. The subsidiary of Gabriel Resources Ltd., Roşia Montană Gold Corporation, has completed feasibility studies including compliance with Romanian and international requirements for environmental, cultural, and archaeological impact assessments. Recent exploration of the deposit by Gabriel Resources has outlined a global resource of 344.07 Mt at an average grade of 1.3 g/t Au and 6.0 g/t Ag for a total (measured, indicated and inferred) contained resource of 14.3 Moz Au and 67.0 Moz Ag.

The Golden Quadrilateral: key to the renaissance of mining in EuropeThe present mining operations (Roşia Montana, Certej, Musariu, Bolcana) are subsidised by the state, but prior to Romania’s joining the European Union these subsidies from the central government will be terminated.

Gabriel’s success at Roşia Montană has lured other juniors to Romania’s historic mining camps, particularly the Golden Quadrilateral. Among them is London-based European Goldfields (EGU-V), which holds several properties in the region. European Goldfields was created in 2000 through the acquisition of four mineral concessions from Gabriel Resources Ltd, one of which was relinquished in January 2005. The European Goldfields LTD in joint venture with the state owned Minvest SA now holds three concessions Figure 4: Ancient photo with miners, Rosia Montana.

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in Romania, including the prospecting Certej area.Recently, other Toronto-based junior

company; the Carpathian Gold Inc. has reported significant gold and copper grades from their Colnic-Rovina porphyry copper-gold prospect.

In the last few years there has been a sustained increase in exploration activity across the region with most of the major companies having a presence (e.g. the Newmont owns 20% of shares at Gabriel). The good economical environment with high metal prices establish a new exploration rush in the region, concluding a question: the Golden Quadrilateral region is a key to the renaissance of mining in Europe?

Environmental aspects of the mining: AMD, heavy metal contamination of the River Arieş and catchments

The Abrud-Arieş catchments systemThe Abrud–Aries river system, western

Romania, is subject to ongoing mining activity associated with Au, Cu, Pb and Zn ore extraction. The catchment contains what is believed to be Europe’s largest unutilized Au deposit at Rosia Montana which is planned to be exploited by open-cast mining techniques. The magnitude and environmental significance of metal (Cd, Cu, Pb, and Zn) concentrations in surface water and river channel sediment have been investigated along a 140 km reach of the Rivers Abrud and Arieş and 9 tributaries affected by mining (Forray and Hallbauer 2000, Bird et al. 2005). The Arieş Valley is an example of a center of pollution because many mines are located on his hydrographical basin like Masca-Baisoara, Rosia Montana, Bucium, Baia de Arieş and Roşia Poieni (Fig. 5).

The causes of pollutionThe main cause of pollution is the acid

mine drainage (AMD). The pH of the surface waters becomes very acid with the oxidation of pyrite and other sulphides. These acid waters can carry large amounts of heavy metals. The first treatment is using calcium hydroxide to make the pH raising.

The second source of pollution is represented by the water dumps which are usually placed near the river. The rainwater flow through the dumps and enter in the phreatic level and in the case of heavy rain, the water can make the dumps overflow directly into the river and affect the stability of the settling ponds. In addition to that, the host rocks and gangue which compose these waste dumps and ponds contain large quantities of sulphides because of the ancient low-efficiency extraction methods.

There is another source of pollution which comes indirectly from the mine. This is an organic pollution coming from ore dressing plants such as the flocculants and frothers.

With TEM analysis on the fine fraction of the tailings, we can see the presence of silica, illite and jarosite, which contains heavy metals like (Cr, Co, Cu, Zn, As, Cd, Pb, Hg). At the Valea Sartasului for example there are jarosite with ~2000 ppm As and 1100 ppm Pb, which is very high. The most toxic elements are: As, Cd and Hg. The presence of arsenic is well known within ores from Baia de Arieş, Roşia Poieni and Roşia Montana with high concentration (50-2000 ppm As), but there is no study about the impact on the environment and the risk for the population. The amorphous iron hydroxides and hydroxyl-sulphates have a large specific surface and can adsorb many metals, like Cu and As.

Major mining activities along the Arieş catchment (Fig. 5)

1. Băişoara area: the ores are usually hosted by Mg-rich skarns, pyroxene skarns and metasomatic bodies. The mining activities take place in underground. The waste is deposited in dumps or settling ponds on the surface. The leached waters of the dumps are alkaline (pH = 8.02) and do not contribute to the pollution of the Arieş River.

2. Baia de Arieş: the mining is now confined underground with waste dumps on the surface, but because of the intense oxidation of the sulphides, leaching waters (both underground and on the surface) are acidic. The hydrothermal mineralisation is with high amounts of pyrite hosted by limestone. The pH is locally very different depending on the type of the original host rock: the limestone could prevent the AMD. But carbonates are

Figure 5: Map of River Arieş cathment showing the location of rivers, tailings and mines (Bird et al. 2005).

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in general not sufficient and AMD of this area is one of the sources of pollution of the Arieş River. In the Baia de Arieş mining area, the electric conductivity (EC) is high (425 μS/cm), SO4 distribution along the Arieş River can be connected to the location of mining works (Forray 2002, Fig. 6b).

3. Roşia Poieni: porphyry copper-gold deposit exploited by open pit mining, with around 0.4% de Cu. Because of the big and opened quarry, considerable amounts of mineralised rock are exposed to rainfall, leaving large amounts of pyrite for intense oxidation and decomposition. This process gives birth to very acidic, leaching waters (pH 2.03) that

cannot be buffered because of the very low neutralisation capacities of the rocks in the vicinity of Roşia Poieni (Forray 2002). These acidic waters flow into the Arieş River leading to a marked increase in pollution.

4. Roşia Montana: world-class epithermal breccia-hosted Au-Ag (and some base metal veins) deposit: two main shallow dacitic domes, Cetate and Cârnic, are intruded within maar-diatreme breccia. Currently a complex monitoring system was developed by the RMGC for a better understanding of the water quality situation around Roşia Montana.

Figure 6: Ternary diagrams showing variations and relative concentrations of waters from the Arieş River and selected European rivers.

Geochemical variations in the water compositions

Surface waters in the Arieş Valley are mostly sulphide type waters because of the direct influence of the mining and sulphur content of the tailing and dumps, but with the flow the water type evolves to a carbonate type (Table 1, Fig. 6). This shows the interaction between water and lithology. During this evolution we can normally observe an evolution of the pH which tends to be neutral, and a precipitation of heavy metals as iron hydroxides. The decrease of SO4 concentration is mainly caused by the dilution and not by the chemical reactions between SO4 and Ca2+, which could lead to the formation of CaSO4 and precipitation of gypsum.

The metal concentration variations were summarised based on Bird et al. (2005) and Forray and Hallbauer (2000):

Cu: The increase in Cu concentration (Fig. 7) is related to the presence of a settling pond in Harmaneasa Valley. Under normal circumstances, Cu2+ is adsorbed onto iron hydroxides, which are present in small quantities in the streambed. Adsorption starts at a pH of 5, whereas at neutral pH values, Cu2+ concentrations in solution are very low. Cu precipitates as hydroxide at a pH of 7.2 Because

of the relatively low pH of the Arieş River in places, the main process, which is responsible for the decrease of Cu concentration, could be adsorption. The presence of iron hydroxides precipitated from AMD by oxygenation can significantly modify the amount of Cu2+ in solution. Cu concentrations decrease rapidly along the river from the source of pollution because it is strongly associated with the Fe/Mn hydroxides which precipitate first. In addition to that, Cu tends to adsorb to organic matter.

Zn: Increase in Zn2+ content is registered because of the input of the metal from the settling pond from Harmaneasei Valley (Fig. 7). Zn2+ is caused by the input of effluents that originate in the settling ponds of Brezesti and Sartesului Valley. At pH values between 6 and 8, the main chemical species of Zn is the 2+ cation in solution. At pH values of 6, the adsorption of Zn2+ onto the surface of iron hydroxides is very low, but at higher values the process begins. That is mostly why the concentration stays quite high till 35 km. The waters of the Arieş River, by comparison, contain concentrations of Cu2+ and Zn2+ that are up to 100 times higher than those of unpolluted river water. Zn like Cd has also a better potential or remobilisation than Cu in solution, and there are mostly in the exchangeable phase of the sediments.

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Pb: Lead in both rivers Abrud and Arieş is largely associated with the Fe/Mn oxides and residual phases. Organic matter and sulphides account for only a minority of sediment associated Pb speciation, particularly in the River Abrud, although relatively more Pb (34– 50%) reports to this phase in the River Arieş.

Metals associated with the residual phase are generally incorporated into the lattice structure of resistant minerals and are likely to be generally unavailable for chemical or biochemical interaction within the aquatic environment.

Oxides of Fe and Mn are ubiquitous in fluvial sedimentary environments and act as important sorbers of metals due to their high specific surface areas. They are very important for Pb speciation, particularly as a coating to sediment particles.

Fe, Al: Fe2+ and Al3+ are quite common in water polluted by mining activities. In primary sulphide ores, the elements in minerals are present mainly in the reduced form. When minerals get in contact with the atmosphere they become oxidised. Thus Fe2+, which is unstable in solution, is oxidized to Fe3+. It then becomes unstable under higher pH conditions and precipitates as iron hydroxide. The critical pH values are 4.3 for Fe3+ and 5.2 for Al3+. In the Baia de Arieş mining area, the brown crust, which covers the

pebbles on the riversides, indicates the presence of iron hydroxides. Because of pH values higher than the critical ones, Fe3+ and Al3+ precipitate.

As: The main source of As is arsenopyrite, pyrite and arsenic sulphosalts. The arsenic concentration in water is controlled by anion exchange reactions, co-precipitation with Fe/Mn hydroxides and by pH and Eh. Arsenic mobility is controlled by the sorption on Fe/Mn hydroxides and on carbonates. Fe3+ precipitation may reduce the amount of arsenic in the water with 99%. Arsenic is mobilized at very low pH (AMD). The arsenic may be adsorbed on iron- rich particles like goethite and ferrihydrite in the water can be transported as suspension and then can be remobilised afterwards.

Pollution of Abrud and Arieş riversTo quantify the river pollutions we use Tables

2a and 2b including also target values for different elements (Bird et al 2005). With the exception of Pb, metal concentrations in the River Abrud are highest immediately downstream of the EM Bucium mine, with Cd, Cu and Zn exceeding EU imperative values. Cadmium and Cu concentrations are elevated above imperative values downstream of the Rivers Izbitza, Abrudului and Rosia, whilst Zn exceeds the target values downstream of the Rivers Izbitza and

Figure 7: Variation of concentration for Cu2+ and Zn2+ in waters along the Arieş Valley (Forray 2000).

Table 1: Chemical composition of waters from the Arieş River (Forray and Hallbauer 2000).

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Rosia. Statistically significant (a =0.05) correlation coefficients exist for the relationships between solute concentrations of Cd/Zn (r2=0.99), Cd/Cu (r2=0.91) and Cu/Zn (r2=0.92) in the River Abrud. Cu and Zn are closely associated in sulphide ores such as sphalerite, where Cd is a trace element.

The Bucium mine grossly pollutes the River Abrud but within 2.5 km downstream metal concentrations decline by 98.9%. Correlation relationships between pH and metal concentrations in the River Abrud are statistically significant for Cd and Zn, but not for Cu and Pb.

In the River Arieş, despite generally higher solute metal concentrations in its mining-affected tributary streams, Cd, Pb, and Zn concentrations all comply with EU directive 75/440/EEC and are generally similar to those measured in the upper Arieş, which is not affected by mining activity. In the River Abrud, peak Cd, Cu, and Zn concentrations in river sediment (similar to metal levels in surface waters) occur downstream of the Bucium mine. Widespread Cu pollution in river sediments also occurs in the River Arieş with 67% of sites exceeding the Dutch imperative value. Channel sediments in the River Arieş are more polluted with Cd, Cu, Pb and Zn than surface waters.

In addition, rivers in northwest Romania are underlain more extensively by igneous bedrock which has a lower buffering capacity than the bedrock found in the Arieş catchment; this promotes more widespread solute contamination of surface waters.

Seasonal variations in metal concentrations

Cu concentrations are generally higher in July, under lower discharge conditions, than they are in March. That demonstrates the dilution effect of the snow melt waters. On the other hand, under higher discharge, solute Cu and Zn concentrations were higher in March 2004 at a number of sites - these sites were generally situated in the River Arieş and generally Cur and Zn concentrations in river channel sediment at a majority of sites were lower during March 2004, under bankfull discharge. That demonstrates the influence of the temperature on the activity of the elements in solution and on the precipitation. Higher solute metal concentrations were associated with a reduction in the mean values of pH measured in

the Arieş catchments during bankfull discharge. A reduction of the pH at high flow suggests that some mining point sources have been activated.

Comparison between Arieş and Abrud pollution

Arieş River seems to be chemically much less polluted than Abrud River for some reasons: Large number of non-mined tributaries

streams within the Arieş basin delivers uncontaminated water to the river and dilute contaminants from active mine sites.

The natural buffering capacity of the local bedrock creates higher pH in the River Arieş system (7.3–8.7), promoting dissolution and adsorption of solute metals.

Finally, a number of ore deposits within the Arieş system, such as Baia de Arieş and Iara, have been shown to contain appreciable amounts of carbonate gangue, limiting widespread production of metal-rich AMD.

ReferencesBird, G. T, Brewer, P. A., Macklin, M. G., Serban, M.,

Balteanu, D., Driga B. (2005) Heavy metal contamination in the Arieş river catchment, western Romania: Implications for development of the Rosia Montana gold deposit. Journal of Geochemical Exploration, 86: 26-48.

European Goldfields, Annual Report and Company Presentation, 2004.

Forray, F.L., Hallbauer, D.K., (2000) A study of the pollution of the Arieş River (Romania) using capillary electrophoresis as analytical technique. Environmental Geology 39: 1372– 1384.

Forray, F.L. (2002) Geochemistry of the environment in the areas of mining works from the Arieş Valley (Apuseni Mountains). PhD thesis, University of Babes-Bolyai, Cluj-Napoca.

Gabriel Resources Ltd, Annual Report and Company Presentation, 2004.

Manske, S. L., Hedenquist, J. W., O’Connor, G., Tamas, C., Cauuet, B., Leary, B. & Minut, A. (2006) Rosia Montana, Romania: Europe’s largest gold deposit. SEG Newsletter 64: 1-15.

Márton, I., Kovács, A., Tomas, R. (2006) Overview on the Metal Exploration and Mining in South

Table 2: Target values concerning the quality of surface waters (Bird et al 2005).

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Eastern Europe, Mining-Metalurgist-Geologist Conference of EMT, Sfantu-Gheorghe, abstract.

Ciobanu, C., Bogdan, G., Cook, N. (2004) Neogene ore deposits and metallogeny of the golden quadrilateral, South Apuseni Mts., Romania, IGCP 486 Proceedings - IAGOD Guidebook. Series 12: 23-89.

Papp, G. (2004) History of Minerals, Rocks and Fossil Resins Discovered in the Carpathian Region, Hungarian Natural History Museum, Budapest.

Udubaşa, G., Ďud’a, R., Szakáll, S., Kvasnytsya, V., Koszowszka, E., Novák, M. (2002) Minerals of the Carpathians. Prague: Granit.

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07 Mining Apuseni

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