Environmental State in S. Domingos Mine

Environmental State in the Portuguese Test Site: S. Domingos Mine: Past and Present Portugal – May 2000

MĂŠrtola

Environmental State:Past and present MINEO Project

INDEX

1. INTRODUCTION

2

2. S. DOMINGOS MINING HISTORY

3

3. IMPACT OF MINING ACTIVITY IN S. DOMINGOS REGION: POPULATION, LOCAL AND NACIONAL ECONOMY

6

4. EVOLUTION IN EXPLOITATION PLAN DURING MASON & BARRY LABOUR

9

5. S. DOMINGOS MINE GEOLOGY

11

6. ENVIRONMENTAL PROBLEMS CAUSED BY MINING EXPLOITATION

16

7. SUMMARY CHARACTERISATION OF S. DOMINGOS DRAINAGE SYSTEM

26

8. PREVIOUS STUDIES OF ENVIRONMENTAL AND CHARACTERISATION PROBLEMS

29

9. AVAILABLE INFORMATION PRODUCED DURING EXPLORATION WORKS SINCE 1960 10. REFERENCES

38 39

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Environmental State:Past and present MINEO Project

1. INTRODUCTION

In the Alentejo, Portugal, mining tradition originates from pre-roman and roman times. This activity is marked by numerous mining occurrences that deserve special care from local and central authorities and a special effort to transform them into museum attractions.

S. Domingos Mine, located in the Southeast part of Portugal in the Baixo Alentejo Province, approximately 60 Km SE from Beja, is one of those historical mining centres that date from pre- and roman times. Its particular features lies in the unusual characteristics of the area, showing a unique beautiful landscape. All the recent historical mining past during the last 150 years is an important part of the Portuguese cultural assets. The large area covered by the mine, resulting from the more than 25 MT tons of ore that have been extracted during mining works,

make

it

one

of

the

most

interesting

abandoned

mines

in

Portugal

(CARVALHO,1971 in GASPAR, 1996).

The main activity of the mine was copper concentrate production. Aside from this, 9.9 Mt of cupriferous pyrite were processed as an elementary source of sulphur (REGO, 2000).

The Mine is located in an eroded peneplain, dipping gently to the NW and SSE. The climate is Mediterranean type with Atlantic and/or Continental influences, characterised by long dry summers and short winters. Most of the area is covered with thin soils. Natural rock outcrops are abundant in the SĂŁo Domingos region. The population density is low and their main activity was dedicated to mining of sulphide deposits during exploitation activity (until 1966).

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Environmental State:Past and present MINEO Project

2. S. DOMINGOS MINING HISTORY

Pre-roman period Almost every archaeological study in VMS mines in the Iberian Pyrite Belt (IPB) show evidence of pre-roman exploitations of precious metals and copper in surficial ores, as a result of their concentration by supergene alteration.

Through time the mine rejects showed that the metal underwent alterations such that different periods of mining can be recognised. Analytical studies of copper objects in the III millennium a.C. shows Ag while objects from the II millennium do not.

The studies of waste piles with different colours and different grain sizes also shows variations in metallurgical processes as well as stand-still periods.

While at S. Domingos there were few studies carried out, other areas in the IPB showed that there was pre-Roman mining activity.

There is still doubt among several authors about the age of the exploitations and civilisations that existed in the Mediterranean basin. The presence of stone hammers used in mining works near the ancient explorations, as well as different colours of smelted materials (slag) are present in such quantities that they cannot be explained only by roman works alone. Also, objects similar of the one's used in Mesopotamia during the Copper and Bronze Ages and megalithic monuments are found near mining areas in the Southern Iberian Peninsula (GASPAR, 1998).

Roman period The calculation of exploitation during the Roman period has been estimated by several authors from the volumes of ancient waste piles and the respective chemical composition phases. The existent literature is few but very clear and shows that at S. Domingos during this period the underground works went below the hydrostatic level. The volumes of exploration were calculated in more then 150 000 m3 of ore. Roman works are also found in Chanรงa (GASPAR, 1998).

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Environmental State:Past and present MINEO Project

Romans exploited the mine for gold from the iron cap and small galleries that probably date from that time can be recognised. These ancient mining activities were largely confined to the oxidised ore near the surface (WEBB, 1958).

Post- roman period Since the roman expulsion by the Visigoths c.a. 405 a.C., there followed a period of almost no mining activity in IPB except maybe at Aljustrel and one or two mines in Spain until 1492 during the Islamic occupation of the Iberian Peninsula.

XIX Century exploitation A temporary exploitation concession of S. Domingos Mine was awarded in 1858 to Ernest DĂŠligny, Luis Decazes and Eugenio Leclere as concessionaires of Nicolau Biava and permanent license was given in 1859 when Diogo Mason took charge.

Mason & Barry, Ltd., the mining explorers since 1859, carried out the construction of a typical mining village, whose typology characterises the classical industrial period. They created rigorous urban planning and the village was almost autonomous with farms, orchards and even with its own police force (ALVES, 1997).

The mining plan began in 1859 but the underground and surface mining only began in 1863.

Because the copper values were fluctuating, only the richest ones were sent to England where incineration processes were used to extract sulphuric acid. This extraction process was experimental in closed ovens, in order to avoid environmental problems similar to the one that occurred in Rio Tinto (near SĂŁo Domingos in the Spanish IPB) as well as the heavy recompensations that were paid to the owners of polluted lands. This process in open environment produced gases rich in SO2, As, Sb and Tl that provoked disastrous effects in fauna and flora of the region of Rio Tinto where there is no fauna and flora until today.

In S. Domingos the first products extracted by incineration processes were separated and the richest nodules were submitted to a fusion process. The leaching of the poor products was carried out in cementation tanks but this process was abandoned in 1868 because of technical difficulties and high costs. When copper prices went down, the mine management decided to leach the material in a raw state, making the recovery more efficient.

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Environmental State:Past and present MINEO Project

Summary of method utilised: 1 - separation of Cu>2% from Cu <2% in four piles, fines and poor material; 2 - crushing of the richest and course grained material to pieces of more or less 5 cm; 3 - accumulation of Cu<2% in piles with interior channels made of gravel material for easy circulation of the air, sandstone chimneys to control temperature of the process as this process was strongly exothermic; 4 - the leaching of the piles with water controlling the temperature to avoid spontaneous combustion of the mined material and excessive formation of sulphuric acid that could make a poor cement and raise the iron consumption (GASPAR, 1998).

The Cu 0,4-0,7 % was exported to produce sulphuric acid, the leaching products had 14% of Cu and were lidded to the tanks to decant particles and sent to cementation tanks. The iron used in the process was about 20 000t a year. From the 4 Mt of copper mineralization extracted since 1870 until 1887, 334 575 t were transported to the treatment factory in Achada do Gamo and 378 320 t of washed product and 85 046t of copper cement were exported. In Swansea, England, part of the material was to obtain copper and part was to obtain gold and silver (GASPAR, 1998).

XX Century exploitation At the beginning of the XX Century the evolution of the sulphuric acid industry favoured of sulphuric acid extraction from pyrite and the increase of exportations resulted in the mining out of some ores, e.g. in Sicily. This resulted in an increase in exploitation of pyrite in the S. Domingos Mine. From 1913 until 1932 SĂŁo Domingos produced 3 445 533 t of copper ore and between 1923 to 1932, 3616 t of Cu cement with average values of 72,33%.

At the end of 1960, a new crisis caused by native sulphur market concurrence extracted by sulphur ores of low degree in deep ores (by hot water pressure) and the external market gave place to internal consumption of sulphides to the sulphur acid factories. As an example, as much as 430 000 t of acid were produced in factories like QUIMIGAL and SAPEC, being most of it used to produce fertilisers.

From the beginning of pre-roman times until 1968, according to CARVALHO (1971) the Mine produced 25 Mt of ore (GASPAR, 1998).

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Environmental State:Past and present MINEO Project

Some doubts remain (unresolved) about the mining out of the ore. V. OLIVEIRA (pers. com., 1999), thinks that is possible that the ore continues deeper but not laterally. It’s the only mine where there is only one known orebody.

The landscape in São Domingos is now a remarkable example of the deep alterations that were produced by industrial exploitations during more than 100 years; the mining exploitation carried out for 107 years. The Mine was closed in 1966, due to exhaustion of the ore.

3. IMPACT OF MINING ACTIVITY IN S. DOMINGOS REGION: POPULATION, LOCAL AND NACIONAL ECONOMY

Implantation of a mining industry in a region, through times, always forced the fixation of population in the vicinity of the mining activity. The richness and duration of the exploitation leads to autonomy of the population in question, which had remained for some time after the exploitation period finished.

São Domingos is the only and more complete example of a big autonomous population exclusively built by a mining company in the south of the country. Mason & Barry allied with La Sabina, with French and Spanish capital, began the colonial implantation in 1854 by Spanish and other contract workers.

With the evolution of the industrial complex more people were needed for underground mining, open pits and the construction of Pomarão harbour. The answer from local authorities was insufficient as it was considered that they were needed for agricultural works. People were contracted from the Beiras and Algarve regions, and the restrictions submitted in the mine to avoid fights were applied to the regional villages during non-work periods.

With a very low density population this particular area became an industrial populated region and an influent force in regional government and at the same time an increasing problem.

Urban planning and architectural structures were needed, also in here began the hierarchical structure of the constructions and cultural differences between English and miners.

Geographical occupation meant social differences and social revolt was expected, so law enforcement had to be implemented.

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Environmental State:Past and present MINEO Project

On the other hand, with the evolution of exploitation and mineral treatment the beginning of expropriation

(Achada do Gamo to the factory and railway construction to Pomarão)

predicted in government mining law had to be applied which corresponded in large investments of the company to the landowners. Also the environmental problems with damage in agriculture resulted in a decrease in production already poor. But also primary activities benefited from the mining industry due to the use of local artisans (blacksmiths, cereals farmers, etc.) e.g. construction of the railway line and the animals consumed cereals produced by the farmers.

The marked development reached by this isolated area was the construction, in 1858, of the (second in Portugal) railway, 15km long, connecting the S. Domingos Mine to the Pomarão Harbour, in the Guadiana River, from where the ore was transported to the Atlantic Ocean. A well preserved railway track without the tracks, is shown below in Figure 1.

Figure 1- Present day remains of the trackless railway line. Along the full extent of the line remains of the sleepers can be seen.

Economic, social and political changes in the 60’s and 70’s induced a “desertification” in the area, progressively erasing past industrial events, and revealing the socio-economic changes in the village (ALVES, 1997).

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Environmental State:Past and present MINEO Project

Present day Scenario Presently, the most striking feature is the large open pit left by the extraction works (Figure 2A). From the primitive mining nuclei, there still remains the primitive hospital and the English graveyard (Figure 2B) (ALVES, 1997). The co-existence of two different cultures is reflected in the entire urban planning layout, with the english administration facilities located away from those belonging to local miners – there were even two different graveyards for the two different religions.

(A)

(B)

Figure 2A) - Open pit flooded; 2B) English cemetery.

Presently, there is a plan for the full urban recovery of S. Domingos Mine area and Pomarão, including the 15km railway from the Mine to the Pomarão Harbour, and the transformation of the area into a mining museum. The transformation of the village includes, not only urban space planning, but also the adoption of rules for land use and building construction (Law Decree nº 186/98). The Pomarão Harbour will also be modernised and used for recreational purposes. Figure 3 shows the urbanisation general plan “Plano Geral de Urbanização” of S. Domingos Mine village, that has already been approved by the Central Administration.

8

Environmental State:Past and present MINEO Project

Figure 3 â&#x20AC;&#x201C; General Urbanisation Plan of S. Domingos Mine village.

It shows the open pit that resulted from ore extraction (adapted after REGO, 1996).

4. EVOLUTION IN EXPLOITATION PLAN DURING THE MASON & BARRY PERIOD

The first plan dates from 19 September 1858 and plans for the underground exploitation of the orebody in all itâ&#x20AC;&#x2122;s extension following old workings with longitudinal galleries (parallel to the orebody axis) and cross cuts, distributed by several levels with connecting wells and supporting rock piles in the exploitation areas.

In 1863-65 there were already built 27 vertical holes to mining circulation and sewage waste (REGO, 1996).

9

Environmental State:Past and present MINEO Project

Following this period, was constructed the construction railway to transport the mining product from the mine to Guadiana River in 1860 and PomarĂŁo harbour and later the sulphur smelting factory in Achada do Gamo in 1863-65.

In 1866-67 the second exploitation plan was made in a copper price downturn scenario that predicted the open pit exploitation with lower costs and continuing the extration method of underground in the untouched ore.

The first exploitation of the open pit started in 1868, causing a progressively strong impact in the landscape until 122 m deep, when the open pit extraction was abandoned, continuing only the underground works. Urban infrastructures e.g. a church, had to be destroyed for the advance of surface exploitation and the population was relocated to other parts of the concession.

Dikes were constructed to support the mining works and the water supply of populations in 1871-73.

Underground work continued and in 1945 reached 300m deep. In 1966 the exploitation reached 390 m where presumably the orebody finished. The cross section of the orebody profile drawn in 1945 in REGO (1996) is shown (Fig. 4).

Figure 4 â&#x20AC;&#x201C; Cross section of mining exploitation drawn in 1945 in grey colour pyrite mass (adapted after REGO,1996).

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Environmental State:Past and present MINEO Project

In 1873 a forestation project of the Serra was implemented, following governmental law, in order to restore environmental conditions in the region (REGO, 1996).

5. S. DOMINGOS MINE GEOLOGY

S. Domingos Mine belongs to Metallogenetic Province of Iberian Pyrite Belt (IPB), which extends from Spain along the south area of Portugal, in Baixo Alentejo Province.

The general geology of the mine consists of the Volcano-Sedimentary Complex with acid and basic rocks from Tournaisian age. WEBB (1958) described the area as being underlain by Palaeozoic sediments, “comprised mainly of clay-slates with interbedded grits, quartzites and occasional tuffaceous horizons”. More recently, mapping identified these Palaeozoic sediments as: in the northern part, older formations from Pulo do Lobo Antiform [Gafo Fm. (schists, silts, greywackes acid and basic volcanism) and Represa Fm. (schists, silts, greywackes and quartzwackes)] from the Upper Devonian age, to south in the mine area Phylito-Quartzitica Fm. (phyllites, silts, quartzites and quartzwackes) and Barrranco do Homem Fm. (phyllites, silts and greywackes) of same age (OLIVEIRA & BRANDÃO, 1990). With the Hercynian compression the sedimentary assemblage was intensely folded and the more incompetent beds marked with a strong flow cleavage, dipping at steep angles to the NNE, the strike direction of both cleavage and bedding is 110-125º. Locally quartzites occur in large extents. At intervals along regional strike, sediments are intruded by dykes ranging from acid (porphyries) to basic (diabases) in composition, more recently mapped as Volcano-Sedimentary Complex of Lower Carboniferous age (OLIVEIRA & BRANDÃO, 1990). To the south is a big area covered by the Mértola Fm. of Lower Carboniferous age consisting of a turbiditic sequence of pelites and greywackes (Flysch). The VolcanoSedimentary Complex, orientated WNW-ESE, is represented by the alignment of the S. Domingos and Pomarão anticline. In the flanks of this structure representative IPB rocks are exposed and marked by three volcanic acid episodes, separated by sedimentary episodes. The Tharsis orebody near Puebla de Guzman (Spain) is related to the first of these volcanic episodes to the E of Pomarão. Within the anticline outcrops the Eira do Garcia Member (silts and pelites and greywackes (PQ) and Nascedios Member (grey pelites and thin interbedded limestones) of Upper Devonian. A geological map of the S. Domingos mining area to the Pomarão Harbour is shown in appendix I (extracted from 46-D-Mértola).

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Environmental State:Past and present MINEO Project

The S. Domingos mine lies at the eastern end of one these Volcano-Sedimentary belts.

Mapping evidenced intensive faulting, most, along vertical NW shear-planes and along bedding strike, some of those faults clearly post-date the igneous rocks. Although jasper, hematite, manganese oxides and minor sulphide disseminations occur at several points, the known orebody is the only evidence of significant metal concentration (WEBB, 1958).

An irregular tract of surficial iron-staining and gossan extends southeast from the orebody and lies in part on the slopes of a shallow to moderately incised valley which drains southeast from a point about 500 m from the mine.

The volcanic sequence in the mine is not well exposed and the structure is complicated. The upper volcanic levels are covered by a thick turbiditic sequence and the Phylite Quartzite (PQ) group in an allochthonous position covers the volcanic pile. The outcropping area was formed by a unique vertical mass of cupriferous pyrite associated with zinc and lead sulphides, elongated in an E-W direction. It was an open pit mine, exploited to a depth of 120 m below the topographic surface. From this depth down to a depth of 420m, mining accesses consisted on wells and galleries. Figure 5 shows the mapping of level 240m and geological section of the massive sulphide.

Figure 5 â&#x20AC;&#x201C; Mapping of level 240 m and geological section of the massive sulphide (adapted after WEBB, 1958).

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Environmental State:Past and present MINEO Project

Average grades of the exploited material range from 1.25% Cu (10% Cu maximum), 2-3% Zn and Pb (14% Zn and Pb, maximum). Massive pyrite grades average in the range from 4548% in sulphur, and in addition to pyrite there are subordinate amounts of chalcopyrite, sphalerite, galena and other rarer sulphides (WEBB, 1958).

The intense wall-rock alteration surrounding the ore body is typically hydrotermal, and comprises argilisation (kaolin and allunite), sericitisation, chloritisation and silicification.

The reddish-brown gossan cap extending southeast from the orebody is probably an erosional relic of transported iron oxides and hydroxides that accumulated during the original weathering of the ore which is almost completely eroded. The deep residual gossan results from a weathering process of the exposed orebody, due to, eventual uplift and peneplanation.

Figure 6 illustrates the northern side of the open pit mining walls where the ancient roman galleries exploited, in the past from the superficial gossan body for gold, silver and copper can be seen.

Figure 6 â&#x20AC;&#x201C; View of the northern part of the cast open pit of the S. Domingos Mine.

From W to E, along the open pit wall levels, there can be clearly identified the white coloured alteration zones of the black shales, the extremely silicified felsic tuffs, host rocks of the stockwork feeders, and the basic lithotype, represented by green coloured rocks due a possible hydrothermal alteration below the stockwork, chloritisation (SILVA et al.,1997).

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Environmental State:Past and present MINEO Project

It can also be seen is Fig (2B) that the open pit mine is partially filled with water. This water, as a consequence of the pyrite oxidation, is extremely acidic, and represents one among others environmental problems associated with the S. Domingos mine.

Anastomosing veinlets, vein networks (feeder channels) and disseminations of sulphides that grade into massive sulphide lenses

composes

the

stockwork

mineralisation by coalescence of veins and replacements. Generally stockworks occur mainly in highly silicified and chloritised footwall volcanic rocks (BARRIGA & CARVALHO, 1983, in SILVA et al., 1997).

During exploitation, mined raw material was crushed in a mill located near the open cast pit. Three kilometres South of the mining area (at Achada do Gamo place), the crushed material was smelted to obtain high level grades of copper ore and sulphur Figure 7 – Detail of the oxidised mineralisation, stockwork – Ore feeder composed by felsic rocks and weathered pyrite veinlets, an example of the stockwork local ore fedeers.

products (which was largely used in the chemical industry, until the 50’s).There

still remain the ruins of the important smelting plant. Enormous dark dumps of slag (figure 8), called “Black Dunes” have replaced the natural landscape in this place.

14

Environmental State:Past and present MINEO Project

Figure 8 – Example of the “Black Dunes”, from deposition of slag resulting from the pyrite smelting processes.

After in situ ore refinement, copper material was delivered in railway cars to Pomarão Harbour, 15 km south of the mine site, near the Guadiana river, from where it was transported, by boat, to the final consumers. Figure 9 shows a view of some ruins of the Pomarão Harbour, where the copper ore was delivered from Guadiana River to Atlantic Ocean.

Figure 9 – Ruins of infrastructures at Pomarão Harbour.

15

Environmental State:Past and present MINEO Project

Due to good outcrops and the relatively simple geological structure. This fact allowed the identification of three volcanic episodes and definition of a coherent and complete lithostratigraphic sequence

for

the

whole

IPB

metallogenic province (BOOGART, 1967) shown in figure 10.

Figure 10– Composite stratigraphic column for the Pyrite Belt in the Pomarão Anticline. (adapted after Silva et al, 1993).

6. ENVIRONMENTAL PROBLEMS CAUSED BY MINING EXPLORATION

As the S. Domingos mining area contains presently several features that may result in important chemical impact, e.g. an open pit and tailings dump, it is important to give an idea of how the chemical alterations and processes may have occurred from the last mining works in the 60’s.

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Environmental State:Past and present MINEO Project

Characterisation of mine waste in a sulphide deposit mine The following flow chart shows the process of waste management where a proper characterisation of the ore body is crucial to evaluate the problem and this is based on: \ Background data review like mineralogy/geochemistry of the ore at it was mined in time, data and reports of tailings operation (production and disposable), chemical process of mineral treatment; \ Detailed geological and hydrogeological investigation; \ Mineralogical and geochemical evaluations;

Figure 11- Waste characterisation flow chart (adapted after SARB, 1997).

"Massive sulphides" are defined generally as accumulations of sulphides plus gangue minerals in which ore and waste rock comprises at least 60 wt % of sulphides (FRANKLIN et al., 1981 in SARB, 1997). However, for geochemical considerations, this discussion considers massive sulphide deposits to consist of any rock mass in which the ratio sulphide:silicate is greater than unity on a volume:volume basis.

The reason for this simplified definition involves the ability of sulphides to generate acidic solutions, and the inability of silicates associated with massive sulphide ores to neutralise low-pH, sulphate-bearing solutions. Hence, the discussions presented here are also applicable to vein and replacement ores having low neutralising capacity gangue.

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Environmental State:Past and present MINEO Project

Because iron sulphide, always as pyrite and/or pyrrhotite, is an ubiquitous component of all massive sulphide deposits, and because such pyrite is usually not recovered during mineral processing, this sulphide generally comprises the most environmentally-significant constituent of massive sulphide wastes.

The base metal sulphides, comprising economic massive sulphide ores, are generally limited to those containing Fe, Cu, Zn, and Pb. Only scant amounts of other metals are present, although tin may occur in economic quantities in some systems (e.g. Neves-Corvo, Portugal; parts of the Kidd Creek orebody Timmins; Ontario, Canada). Au and Ag are also present in most massive sulphide systems, gold occurring, as the native metal and silver associated with sulfosalts or sulphides, especially sphalerite or galena.

Mn, Cd, As, Bi, Hg and Sb are present as geochemically minor but locally important elements. Non-metallic minerals include quartz, several carbonates, sericite, chlorite and barium usually is present in variable amounts, as barite (SCHUSTER et al. in SARB, 1997).

Mineral zonation is usually chalcopyrite, chlorite and sericite concentrated towards the footwall (and stockwork), spharelite, galena and barite are abundant near the hanging wall and in peripheral zones, and pyrite, arsenopyrite, quartz and carbonates scattered throughout (BARRIGA & CARVALHO, 1983).

Since stockwork ores are hosted in footwall rocks and are intensely hydrothermally altered, often to such a degrees that the original texture and mineralogy are lost and the rocks become aggregates of alteration minerals like quartz, chlorite and sulphides (chalcopyrite, pyrite, pyrrhotite, sphalerite) sometimes with significant sericite and/or carbonates (BARRIGA & CARVALHO, 1983).

Several geochemical aspects of massive sulphide ores makes them especially sensitive to weathering and the subsequent generation of Acid Rock Drainage(ARD):

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Environmental State:Past and present MINEO Project

Acid Rock Drainage, also referred to as Acid Mine Drainage (AMD), is the process in which sulphide minerals oxidise in a weathering environment giving rise to sulphuric acid. Other processes taking place, either due to the acid generation or simultaneously with the acid generation, are often considered part of the ARD process. These processes may increase the weathering by dissolution of minerals and increasing the mobility of metals. Pyrite is the sulphide mineral commonly thought to generate sulphuric acid. With sulphuric acid, the mobility of many metals is increased.

The ARD process is a natural occurring process that has been known to economic geologists for a long time and labelled, in some settings, as supergene process. At the surface, traces of ARD may be seen as red iron oxide/hydroxide staining or low pH ochre coloured surface drainage (GLADER et al., 1996 in SARB,1997). Evidence of ARD can also be seen in sulphide ore bodies where oxidation of the primary ore has taken place.

As indicated in Figure 12, supergene enrichment is where iron is released from sulphides previously occupying the leached zone. lron is released and precipitated in the gossan. Other metals may be transported downwards below the water table, in the enriched zone and precipitated (SCHUSTER et al. in SARB, 1997)

Figure 12 - Supergene enrichment process (after EVANS, 1980 in SARB, 1997)

Increased exposure of sulphide containing mine waste occurs due to mining activity. The following is a list of environment where ARD may occur:

19

Environmental State:Past and present MINEO Project \ Drainage from underground workings; \ Surface run-off from open-pit faces and pit workings; \ Waste-rock dumps metal mines; \ Mine soil piles from coal mining (high sulphur coal); \ Tailings deposits; \ Spent ore piles from leaching (dump, heap, etc.); \ Natural exposure of sulphide containing rocks.

This section will focus on the processes that take place when rock surfaces are exposed to weathering, due to mining activity. Acid generating reactions, acid neutralizing reactions, and rate of such reactions will also be discussed.

Evolution in open pit water/rock reaction since the end of mining exploitation During mining and if minable ore is below the water table, pumping will have to take place to keep the pit dry. With time a cone of depression develops which may lower the water table near the pit. The aspect of the mine at ending time with the remaining ore rocks exposed to oxygen is represented in figure 13A). When the mine closes, groundwater diverted surface water, and rainwater will enter the pit creating a pit-lake. The groundwater inflow will be high in the beginning and slow down when the water in the pit approaches an equilibrium level. In addiction to the inflow rate, this level is controlled by evaporation, surface discharge to creeks, and groundwater recharge. The example of this second scenario is in figure 13B).

(A)

(B)

Figure 13 - A) Open pit when the mine reaches the end; B) After filling with water (adapted after SARB,1997).

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Environmental State:Past and present MINEO Project

Lakes are commonly not considered steady state systems due to the dynamic effect input and output. This input and output varies seasonally and on daily bases, temperature may also vary on seasonal or daily bases. Trace element distribution varies greatly from lake to lake depending upon their difference in input water quality (MILLER et al., 1996 in SARB, 1997) and variable physical parameters: depth, temperature, sediment chemistry, and rainfall.

The S. Domingos open pit (Fig. 2B) is permanently filled with water, with seasonal variations, due to high temperatures in summer, consequently high evaporation rate, and low precipitation rate. In a general case of this nature, in the open pit, most elements are affected by redox processes (SCHUSTER et al. in SARB, 1997). They either undergo redox reactions themselves (e.g. Fe and Mn) or their distribution is affected by the elements that undergo redox reactions (e.g. adsorption and co-precipitation).

The major mechanisms driving the redox cycle are: 1. Plankton synthesis in surface water, elements may be adsorbed or assimilated by plankton and released at depth in a different oxidation stage, or directly as an electron acceptor in biodegradation (SCHUSTER et al. in SARB, 1997); 2. Bacteriological degradation in subsurface water, where metal reduction Fe (III) and Mn (IV) take place to reduce free energy. Iron and manganese will be in their higher oxidation state in well-oxygenated water. They will be present as hydrolysed oxides, colloids or particles with typical concentrations of 0.4-2 Âľmol/liter. In seasonal or permanently stratified lakes, the bottom becomes anoxic Fe (II) and Mn (II). The more stable forms of these two minerals can exist there, and accumulate to high concentrations.

Figure 14 represents the diagrams of oxidation evolution in a waste pile, if oxidation is taking place in a waste dump, it will take place in a narrow zone where oxygen is consumed.

Oxygen flows towards this zone because of a chemical gradient. Behind the zone, oxidation is not taking place, and the waste will be in a reducing environment. This narrow zone where oxidation takes place is called the oxidation zone. Various flow rates can be modelled to generate best-case and worst-case oxidation front scenarios.

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Environmental State:Past and present MINEO Project

Fig. 14 - Example of evolution of the oxidation front in a waste pile (adapted after SARB, 1997).

In Achada do Gamo the process is already probably complete as can be observed in Figure 15. Achada do Gamo is a waste pile which formed an accidental lake since sulphuric acid factory was closed, and the remaining pyrite was left near by. Observing the picture gives a first impression that the oxidation process is in the final state, pH reported values are about 1.

Fig. 15 - Achada do Gamo waste pile lake near the remaining old sulphuric acid factory

Pyrite oxidation Iron-disulphide occurs in two forms, pyrite and marcasite (FeS). crystallographically isometric, while marcasite is orthorhombic.

Pyrite is

Marcasite is known to

weather more easily than pyrite (MASON AND BARRY, 1968, in SARB,1997).

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Environmental State:Past and present MINEO Project

Under weathering conditions, pyrite may oxidise to form sulphuric acid and ferrous ion as exemplifying by the following chemical equation: 2 FeS2(s) + 2H2O + 702 = 4H+ + 4SO42-+ 2Fe 2+ The ferrous ion may oxidise to form ferric ion and precipitate as ferrihydrate (or goethite, jarosite, schwertsmannite) following the reactions: 4Fe2+ +O2 + 4H+ = 4Fe3++ 2H2O Fe3++ 3H2O = Fe (OH)3(s) + 3H+

The overall pyrite oxidation reaction can then be written as follows: FeS2(s) + 15/4O2 + 7/2H20 = Fe (OH)3(s) + 4H++ 2SO42Processes SINGER AND STUMM (l970) proposed the following visualisation of the overall reactions in pyrite oxidation (Figure 16).

Figure 16 - General scheme pyrite oxidation (adapted after SARB, 1997).

Pyrite Oxidation Rate As shown before, there are at least two known pyrite oxidation agents available in nature: oxygen and ferric ion (Fe3+). If pH is less than 3.5, significant quantities of Fe3+can exist in solution. At pH>2.5, precipitation of ion ferrihydrate will remove Fe3+ from solution.

23

Environmental State:Past and present MINEO Project

If the sulphate concentration is sufficiently high, ferric ion may also be removed from acidic solutions by precipitation of iron-sulphate minerals like jarosite, coquimbite, and kornelite, however, these iron-sulphate minerals have high solubility.

There are many factors that affect the oxidation rate of pyrite, and hence, control acid generation: \ specific surface area exposed; \ pH & oxygen concentration (in water and gas phase); \ ferric iron concentration; \ temperature and chemical activation energy (required to initiate acid generation); \ bacteriological activity.

Surface Area Exposed.

The exposed specific surface area of pyrite is one of the most important variables controlling the oxidation rate (NICHOLSON, 1994, in SARB, 1997). Grain size is related with the area exposed because in a certain area decreased grain size per unit weight increases the reaction rate. There is a linear relation between grain size and reaction rate. pH and Oxygen Concentration Oxygen concentration affects the pyrite oxidation. (WILLIAMSON & RIMSTIDT, 1992 in SARB, 1997) suggested the following empirical relation of pyrite oxidation rate: Rate=10-8.19(O2)0.5/(H+)0.11 where (O2) and (H+) are concentrations of oxygen and hydrogen ions in the solution.

Ferric Iron Concentration The rate of pyrite oxidation by Fe high Fe

3+

3+

depends on the presence of oxygen in solution. With

/Fe2+ and the presence of oxygen, the oxidation rate increases (WILLIAMSON &

RIMSTIDT, 1992, in SARB, 1997). However, under low Fe3+/Fe2+ the rates are faster with low oxygen concentration than with high. Ferric iron is more effective in oxidising pyrite than oxygen. This may be due to the fact that ferric iron can bind directly to the pyrite surface making electron transfer easier (LUTHER, 1987, in SARB, 1997).

24

Environmental State:Past and present MINEO Project In addition, the intermediate sulphur oxidising species, sulfoxy ion (S2O3 2-), is more readily oxidised by ferric iron than oxygen (LUTHER, 1987, in SARB, 1997).

Temperature and Chemical Activation Energy The activation energy for pyrite oxidation with oxygen is about 60-80 kj/mol. This is important to remember, since pyrite oxidation is a strong exothermic reaction.

Bacteriological Activity The bacteria niobacillus and Ferrobacilius Ferrooxidans utilises energy from oxidising sulphide to sulphate and ferrous to ferric iron in their metabolism. This sulphur and iron oxidation may increase the pyrite oxidation rate considerably (Fig. 18).

Figure 18 Pyrite oxidation rate: represented by suphate production versus time for the sulphide mine waste at 21ยบC and pH=3 in the presence and absence of bacteria (after SCHARER et al.,1991, in SARB,1997)

According to STUMM and MORGAN (l981), bacteria do not oxidise the pyrite directly, but remove the reduced sulphur species and ferrous iron by oxidation.

The following

bacteriological sulphur oxidising reaction has been suggested (TORMA, 1988; SILVER, 1978 in SARB, 1997): S22- + 4O2 -> 2SO42The Thiobacillus Ferrooxidans require oxygen. This bacteria accelerates oxidation of Sb, Ga, Mo, As, Cu, Cd, Co, Ni and Zn sulphides by enhancing the sulphide oxidation rate.

Bacteria can also reduce sulphate to sulphide, slowing down the acid generation.

25

Environmental State:Past and present MINEO Project

The bacterial population depends upon nutrient concentrations of phosphate, nitrate, carbon dioxide, and pollutants (as heavy metals).

7.

SUMMARY CHARACTERISATION OF THE S. DOMINGOS DRAINAGE

SYSTEM

The mine is located in the hydrographic basin of Guadiana River, and the drainage of the mining area occurs along several kilometres until the Mosteirão River, a Chança River tributary, where Chança Dam is located.

The Chança River has its headwaters in the Aracena Mountains in Spain. The river flows for 96 km, until its confluence with Guadiana River in Pomarão. The last 60 km define the border between Portugal and Spain. Of the total drainage area of 2229 km2, just 24% is located in Portugal.

In 1985 the Spanish Government immediately upstream of the confluence, creating a new reservoir built a large dam, and possible entrapment basin of the metals mobilised from the mining tailings and reservoir deposits. This reservoir as a maximum volume of 386x106 m3, a maximum waters depth of 63 m, and a surface area of 19.4x106 m2. The Chança Reservoir is used above all to supply water for municipal and agriculture uses.

Besides the referred water courses, at least 30 streams were identified, the most important are, apart from Chança and Ribeira Mosteirão: Barranco das Mulheres; Barranco de Umbelina and Barranco do Serro do Urso, most of the other streams are perennial.

Both Tapada Grande and Tapada Pequena reservoirs, were built by the mining company to provide water for their operations. These reservoirs are the main source of water flowing through the mine basin except, of course, during large rainfall events. Both reservoirs are important quality reference sites (PEREIRA et al., 1995).

26

Environmental State:Past and present MINEO Project

There are still some old channels and reservoirs with a total volume of 2.2x106 m3 and total surface area of 97x104 m2, however sedimentation resulting from mining operations has decreased those values considerably.

These old reservoirs still affect the present effluent flow and, because extensive deposition and possible reactions with the sediment, the ultimate effluent composition as well. Large tailing mounds are still present in the mine area close to the old reservoirs and channels.

During mining treatment in leaching and cementation of copper products large quantities of water were needed. Therefore, small dikes were built to reserve acid water that after would circulate through the mining piles and the remaining water was evaporated or infiltrated in a considerably large surface of evaporation (2 hm3 / year of contaminated water was released in this process) this peripheral channels extended downstream of Chumbeiro Dam. These channels presently have different coloured ferrous waters (COBA, 2000).

In the mine drainage system is observed the Tapadinha and Portela de S. Bento dikes also with extremely acidic waters. The last reservoir is Chumbeiro. A system of surrounding channels to deviate pluvial waters from the central valley so they would not join the contaminated waters. These channels are still preserved until today, some of these are made by natural terrain with some signs of erosion and others are covered with stones.

During long periods of about 3-5 years the precipitation is very low so the water flow in most streams that drain the mine is practically null, but this conclusion is only based on median values so, can be false because of seasonal precipitation variation, with high amplitude values (COBA, 2000).

Hydrogeological conditions The lithostratigraphy in IPB classifies these rocks as "hard rocks" or fractured rocks generally with low permeability and porosity. The hydraulic conductivity is dependent of fractures and their filling. The permeability by principal and transverse fractures is important because the mobility of water can be significant. These "hard rocks" have considerable heterogeneity and anisotropy (COBA, 2000). Three different zones are considered in these rocks: 27

Environmental State:Past and present MINEO Project

1. Surficial altered and some times porous corresponding to alluvial deposits that varies from few meters to several tens of metres.

2. Secondary fissure zones where permeability and porosity is controlled by fractures with considerable depth, from half a metre to one hundred metres.

3. Deepest zone where fracture density is low.

The model based in fracturation is based in the one proposed in Neves Corvo by FERNANDEZ-RUBIO et al., 1985 in VINCENTE, 1999 (COBA, 2000) before mining exploitation. This consists in three systems: Surficial, (CC), Medium (CI) and Depth (SP).

To the hydraulic zonation follow an hydrochemical zonation, where the fossil water sodic chlorated located in the depth system (SP) in medium system lesser chlorated then the previous are more bicarbonate and sulphate, in surficial system are bicarbonate and richer in sulphates and chlorates (COBA, 2000).

The conceptual flux model concluded by COBA consists in: a) A small hydraulic basin with orientation NNE-SSW implanted in the IPB formations and Flysch of Baixo Alentejo Formations. b) Drainage net to facilitate the surrounding flows that lead the water to MosteirĂŁo stream. c) Tailing dumps and alluvial deposits with porous behaviour. d) "Hard rocks" covered or not by thin soils with irrelevant porosity. e) Presence of dikes that facilitate infiltration. f) Water that flows from the valley margins to the centre, and other part can circulate through deeper fractures that can be transported elsewhere. g) The fault system oriented NE-SW helps circulation of water in a longitudinal direction. h) The tailings deposits can be: either in favour of local infiltration; receptor of lateral waters from the surrounding channels or local infiltration in "hard rocks" or emergency escape from bedrock through faults.

28

Environmental State:Past and present MINEO Project

8

PREVIOUS STUDIES AND CHARACTERISATION OF ENVIRONMENTAL PROBLEMS

Hydrogeochemistry based on previous studies Parameters measured in water collected in the stream that came from S. Domingos mine to Mosteirão River in April 1997, have shown a pH of 3.55 and fluid conductivity of 2182 µS/cm (MATOSO, 1998). A general aspect of the water in the small river from S. Domingos Mine to Mosteirão River is shown in figure 19. Old retaining dikes containing acidic water, favour the infiltration of surface water (MATOSO, 1998). Also the permeability of the dumps, higher than the local geological formations, increase the infiltration of contaminated water and consequently leaching of this material.

Figure 19 – General aspect of the water in the small river from S. Domingos Mine to the Mosteirão River.

29

Environmental State:Past and present MINEO Project

COBA Consulting reported periodic results collected by Regional Environmental Department of Environmental Ministry from Tapada Grande Reservoir and these results are shown in Tables 1 and 2.

Table 1 Periodic data from 1998 from Tapada Grande (after COBA, 2000) Date

Oxidibility

Transparency

Air Temp.

Water Temp

pH

mg/L

m

ยบC

ยบC

esc.Sorensen

Cond. 20ยบC N amoniac. microS/cm

mg/L NH4

98/01/20

4,7

0,15

13,2

13,0

7,5

116

0,03

98/02/17

4,7

0,19

16,6

14,4

7,2

109

0,33

98/03/17

4,9

0,36

23,0

19,5

7,3

133

0,03

98/04/21

4,7

0,42

18,0

20,0

7,5

133

0,03

98/05/19

4,4

0,40

24,0

23,3

7,8

127

0,03

98/06/23

4,5

0,65

26,2

26,7

7,9

128

0,26

98/07/21

4,2

1,20

28,5

27,5

7,8

185

0,03

98/08/18

4,3

0,90

24,0

26,5

7,6

153

0,03

98/09/15

3,7

19,5

23,6

7,3

158

0,03

98/10/20

3,6

1,18

20,0

19,6

7,6

153

0,08

98/11/17

3,6

0,80

21,0

18,7

7,5

160

0,28

98/12/15

3,7

0,80

18,0

12,0

7,7

159

0,04

Average

4,3

21,0

20,4

7,6

143

0,10

Minimum

3,6

13,2

12,0

7,2

109

0,03

Maximum

4,9

28,5

27,5

7,9

185

0,33

Table 2- Periodic data from 1998 from Tapada Grande (after COBA, 2000) Date

SST CBO5(20gC)

CQO

Phosphates

Nitrates

mg/L O2 mg/L P2O5 mg/L NO3

Diss. O2 Diss. O2

Mn

Total coll.

Faecal coll.

Nยบ100ml

Nยบ100ml

1000

169

0,030

886

31

0,040

775

4

mg/L O2

98/01/20

31,3

5,0

98/02/17

27,0

2,0

8,8

0,14

3,44

94

9,5

0,92

98/03/17

13,5

2,0

11,4

0,15

3,29

104

9,8

0,21

98/04/21

6,3

2,5

12,1

0,17

2,85

106

9,8

0,33

0,100

565

1

98/05/19

6,7

3,0

12,4

0,02

2,23

97

8,3

0,21

0,020

32900

62

98/06/23

5,0

4,0

16,1

0,03

1,30

76

6,0

0,30

0,030

4900

11

98/07/21

7,0

3,0

17,5

0,04

0,46

105

8,4

0,20

0,040

11200

18

98/08/18

1,0

3,5

15,2

0,023

0,09

94

7,9

0,35

0,080

21800

134

98/09/15

4,7

4,0

17,7

0,03

0,09

73

6,6

0,18

0,090

8250

91

98/10/20

6,5

1,0

15,6

0,01

0,31

84

7,7

0,14

0,130

113500

4000

98/11/17

4,5

3,0

14,9

0,02

0,21

55

5,2

0,02

0,610

14467

1

98/12/15

6,7

2,0

13,2

0,04

0,43

72

7,8

0,06

0,260

2350

1

13,0

0,10

4,74

% sat

Fe

mg/L

70

mg/L O2 mg/L Fe mg/L Mn 7,4

0,44

0,093

Average

10,0

2,9

14,0

0,06

1,62

86

7,9

0,28

0,127

17716

377

Minimum

1,0

1,0

8,8

0,01

0,09

55

5,2

0,02

0,020

565

1

Maximum

31,3

5,0

17,7

0,17

4,74

106

9,8

0,92

0,610

113500

4000

30

Environmental State:Past and present MINEO Project

These waters are monitored by the government with the objective to serve the local needs and sampling is made every month in this case the quality according to legislation (83º article of DL nº 236/98), parameters like pH, temperature, conductivity, NH4, CBO5, P2O5, nitrates, Fe, Mn, are below the law maximum permitted values. Parameters like: dissolved oxygen, total and faecal coliforms are above the regulated values but possible to be treated.

COBA made sampling in 59 points in April 2000 in a rain season 15 in wells and 44 at surface streams in contaminated areas and non-contaminated areas. Chemical results are not available yet, but parameters like pH, temperature, condutivity are available and the results shows in open pit, (pH=2.8, cond.=6253 µS/cm, Eh=448 mV at 18.2ºC); some points of Mosteirão River (pH = 6.51, 6.63, cond.= 337, 654 µS/cm) upstream from Tapadinha Dam (pH=2.76, cond. = 3615 µS/cm) Tapadinha reservoir (pH=2.81, cond=3680 µS/cm; Serro da Mina Dam in principal valley (pH=2.62, cond=5173.3 µS/cm); near hydraulic passage (pH=2.92, cond=2570 µS/cm) surrounding channel near (ph=2.9, cond=2623.3 µS/cm); Portela de S. Bento (pH=2.82, cond=3273.3 µS/cm) stream after confluence of previous site mentioned (pH=2.88, cond=2640 µS/cm). Points like Montes Altos have high conductivity and not very low pH, can be a case where sulphides are not acid water productive. According to this study groundwater at the influence of this drainage, despite faulting considerations, seems not being affected by anomalous values of these two parameters.

COBA also made samplings in open pit, near sulphur factory dam and drainage near tailings and the values are in table 3.

Table 3 - Chemical results in the highly contaminated water bodies (after COBA,2000) Parameter(mg/L)

Open pit

S Factory dike Dumping drainage

(SO4)2-

5000

114000

2000

Al

124

4480

54

Mn

91

108

5,4

Pb

<0,4

1

5,4

Cu

46

2080

21,5

Zn

108

1880

22

According to a study about the relation between the metal content in the water column of Chança Reservoir and sediments from the mine downstream until Chança River Basin.

31

Environmental State:Past and present MINEO Project

The high content of heavy metals are in the sediments and waters from the streams, values in the water column of Chança Reservoir seems to be normal. Changes in water in the water regime, oxidation of heavy metals from tailings sulphides etc. may alter the established equilibrium. (PEREIRA et al, 1995).

Figure 20 â&#x20AC;&#x201C; Heavy metals distribution in stream sediments collected in the small river. (after SANTOS OLIVEIRA, 1998).

Geochemistry based on previous studies Geochemical analyses carried out in samples collected in stream sediments (5 samples) and dumps (3 samples) from S. Domingos Mine gives a roof idea of the values in the area, by the time of sampling (SANTOS OLIVEIRA, 1998). The location of these sampling points is shown in Figure 20. The results are presented in Table 4.

32

Environmental State:Past and present MINEO Project

Table 4 – Average concentrations determined for heavy metals and other elements in the S. Domingos Mine, from expedite and exploratory sampling (after SANTOS OLIVEIRA, 1998).

Streamline sediments

Cu

Pb

Zn

Ag

As

Sb

Cd

Ba

P

Mn

Fe

ppm

ppm

ppm

ppm

ppm

Ppm

ppm

Ppm

ppm

ppm

%

841

8975

361

1.5

1412

361

3

368

495

318

12.2

181

5400

239

8

2070

239

2

38

222

10

17.0

(5 samples) Dumps (3 samples)

Biogeochemistry An investigation was developed in the S. Domingos mining area to see in what level of contamination the biotic communities live. As it has been proven in the past, the acidic alteration in natural environment can be influenced by bacteria and other biotic organisms with bigger size. This study tries to relate the high values of heavy metals and acid conditions with these communities.

The vegetation communities present in the area reflect the arid conditions and are dominated

by Citus ssp. and Lavandula sp. in the schists of basin margins. Trees are dominantly Quercus ilex. Citus ladanifer reflects acid soils non carbonated and very degraded, pour and dry, near water streams Juncus sp.

The sampling was based on three criteria: proximity of contamination, representativitly, accessibility by land. Samples were collected in 9 point sites in water profile of Chança Dam, Malagon Dam, English Dam, water samples in the streams selected and sediments in all points except in Tapada Grande and Tapada Pequena and Mosteirão River, living organisms were collected in all points except in the Chança reservoir.

The maps shown in figures 21, 22, 23 show the metal content in stream sediments and living organisms identified in those sites (field data are refers to September 1992).

33

Environmental State:Past and present MINEO Project

Chanรงa River

Malagon English

River

Dike

Chanรงa Dam

Guadiana River

Figure 21- Concentrations of copper, zinc and chromium in mg/kg of dry sediments (adapted after CANTEIRO,1994).

From Fig. 21 it is possible to observe that when the Cu content is high the Zn is equally high but and that occurs near the English Dike, i.e. that, when the water column is higher the concentrations are attenuated.

34

Environmental State:Past and present MINEO Project

Figure 22- Concentrations of nickel, cobalt, cadmium in mg/kg of dry sediments (adapted after CANTEIRO, 1994).

Nickel reflects a different behaviour having higher content in sediments, when the water volume is higher and consequently, the water column is also higher.

35

Environmental State:Past and present MINEO Project

Figure 23. Biotic communities found in these sampling sites (adapted after CANTEIRO, 1994).

This study concluded that, once the pyrite decomposition processes begin, there is no return without the action of neutralising agents. This happens because, grains of pyrite, iron, and sulphate, existing in the sediment, in the mining drainage system and slags, continue to stimulate the production of H+ ions, although the drainage systems support biotic communities present, such as, algae and aquatic macro-invertebrates.

36

Environmental State:Past and present MINEO Project

How do these organisms survive in these extreme acidic conditions? It is not uncommon to find life in these environments (many studies reported biodiversity in this situations), in addition, the species found in these environments are common species and no particular fauna is associated in to the effluents. The stability of the water drainage regime and the lengthy period of exploitation made those organisms develop defence mechanisms that gave them gradual tolerance to such extreme environments. Along with that, interaction of variables that compound the biotic habitat and availability of food and predators contributes to a successful colonisation. The defence mechanisms developed by these organisms consist in the production of specific enzymes (CANTEIRO, 1994).

Ecotoxicity revealed to be a useful tool in the study of these biologic systems, this experiment shows the impact (especially biologic) of the effluent in neutral pH stream systems. It also can isolate potential toxic sites in different locations of mining area. The difficulty noted was the poor previous information available about the behaviour of these communities (CANTEIRO,1994).

Slag and tailings mapping CONASA is a spanish company who investigated the area for precious metals in the tailings.

They made a 1/1000 scale mapping of the tailings and classify them in three types: a) gossan rock tailings; b) gossan rock mixed with altered rock; c) slag tailings.

This mapping is archived in the IGM Reports at the Beja Office. Eleven tailing sites were delimited according to grain size, composition, colour and different mixture of materials and gold content, the others were not considered important from an economic point of view.

37

Environmental State:Past and present MINEO Project

The tailings were drilled and different grain size materials were divided in >40 mm, 40-9 mm, 9-5 mm and < 5 mm and by chemical analysis concluded that the higher grade in tailing material was the one in higher grain sizes.

Chemical analyses were made for Cu, S, Pb, Zn, Au and Ag in this tailing to see the economic potential. These results are archived in the IGM Reports.

9. AVAILABLE INFORMATION PRODUCED DURING EXPLORARION WORKS SINCE 1960

Indirect geophysical and geochemical exploration methods were widely used in the S. Domingos Mine – Pomarão area. The area is covered with gravity, magnetic, airborne spectrometry and electrical surveys.

Numerous geochemical analyses (geochemistry from soils and sediments) are also available, mainly in an analogical format.

Geological and Mine Mapping, since 1970, at scales 1:5 000, 1:10 000, 1:25 000, 1: 50 000 and 1: 200 000 are available for the area.

Direct prospecting data since 1960 from drill cores and geological logs are also available.

Geochemical Exploration Database mainly from Iberian Pyrite Belt since 60’s.

GEOMIST- GIS organised information of geological, mining, geophysical, drilling data from Iberian Piryte Belt.

38

Environmental State:Past and present MINEO Project

10. REFERENCES

ALVES, H. (1997) – Mina de S. Domingos: um caso de tipologia industrial mineira. Arquivo de Beja, Vol. IV, Série III, Abril 97, pp.7-17.

BARRIGA, F. (1983) – Hydrothermal metamorphysm and ore genesis at Aljustrel, Portugal.

PhD Thesis, University of Western Ontario, 368p..

BARRIGA, F. (1990) – Metallogenesis in the Iberian Pyrite Belt. In: Dallmeyer R. D. and Garcia E. M., Eds., Pre-Mesozoic Geology of Iberia, Springer-Verlag, pp.369-379.

BARRIGA, F. and CARVALHO, D. (1983) – Carboniferous volcanogenic sulfide mineralizations in South Portugal (Iberian Pyrite Belt). In: Sousa M. J. L., Oliveira, J. T., Eds., The Carboniferous of Portugal. Memórias dos Serviços Geológicos de Portugal, v. 29, pp.99-113.

BRITO, M.G.A.; RAMALHO, E.(1999) "Guide and Notes for S. Domingos Portuguese Mine Visit" Fourth ERSTN Meeting.

BOOGARD, M. (1967) – Geology of the Pomarão region, Southern Portugal, Thesis, Grafish Centrum Deltro, Rotterdam, 113p.

CANTEIRO,M.H.S.F (1994) – Mina de S. Domingos:um caso de estudo de contaminação histórica. Tese de Mestrado do Departamento de Zoologia, Faculdade de Ciências e Tecnologia da Universidade de Coimbra.178 pp.

CARVALHO, D. (1976) – Considerações sobre o vulcanismo de Cercal-Odemira. Suas relações com a Faixa Piritosa. Com. Serv. Geol. Portugal, Lisboa. T. 65, pp.169-191.

CARVALHO, D. (1979) – Geologia, metalogenia e metodologia da investigação de sulfuretos polimetálicos do sul de Portugal. Comunicações dos Serviços Geológicos de Portugal, t. 65, pp.169-191.

CARVALHO, D. BARRIGA, F. & MUNHÁ, J. (1997) – The Iberian Pyrite Belt of Portugal and Spain. Examples of bimodal – siliciclastic systems. In: Barrie T. and Hannington M. eds. Volcanic-Associated Sulfide Deposits: Processes and Examples in Modern and Ancient Settings, Reviews in Economic Geology.

COBA Consultores de Engenharia e Ambiente (2000), 1º Relatório de Progresso - Estudo de Controlo Ambiental na área mineira de S. Domingos CONASA Companhia Nacinal de Pirites S. A. Report (1990-1994) - Trabalhos de investigação realizados na zona da Mina de S. Domingos.

39

Environmental State:Past and present MINEO Project

GASPAR, O (1998) "História da Mineração dos Depósitos de Sulfuretos Maciços Vulcanogénicos da Faixa Piritosa Portuguesa". Boletim de Minas Vol.35 Nº4 Lisboa.

GONÇALVES PEREIRA, E; MOURA, I, RIBEIRO DA COSTA, J.; MAHONY, J. D. and THOMANN, R. (1995)- The S. Domingos Mine: A study of heavy metal contamination in the water column and sediments of the Chança River basin by discharge from an ancient cupriferous pyrite mine (Portugal). Mar Freshwater Res. 1995, 46, 145-151 pp.

MATOSO, A. (1998) – Impacte ambiental de antigas minas de sulfuretos localizadas no Alentejo. IV Simpósio Internacional dos Sulfuretos Polimetálicos da Faixa Piritosa Ibérica, Lisboa.

OLIVEIRA, J. T. (1990) – South Portuguese Zone, in Pre-Mesozoic Geology of Iberia, Editions R. D. Dallmeyer e E. Martinez Garcia, Springer-Verlag, pp.333-346.

OLIVEIRA, J. T. & SILVA, J. B. (1990) – Notícia Explicativa da Carta Geológica à escala 1:50000. Folha 46-D-Mértola. Serviços Geológicos de Portugal.

OLIVEIRA, J. T., HORN, M. & PAPROTH, E. (1979) – Preliminary note on the stratigraphic of the Baixo Alentejo Flysh Group, Carboniferous of Portugal, and on the palaeogeographic development compared to corresponding units in northwest Germany.

Comunicações dos Serviços Geológicos de Portugal, v. 65, pp.151-168.

Portaria nº 186/98 (1998) – Legislação. Diário da República, 1ª Série-B, de 19 de Março de 1998. Boletim de Minas, nº 35, pp.81-89.

REGO, M. (1996). Mineração no Baixo Alentejo. Câmara Municipal de Castro Verde.

Santos Oliveira, J. M. (1998) – Algumas reflexões com enfoque na problemática dos riscos ambientais associados à actividade mineira. Estudos, Notas e Trabalhos do Instituto Geológico e Mineiro, T. 39, pp. 3-25.

SARB

(1997).

SARB

Consulting,

Inc.,

Environmental

Scientists

Environmental

geochemistry of ore deposits and mining activities- Short Course (1997) Oslo, Norway.

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