Mineral Exploration in the Iberian Pyrite Belt and the Story of the Aguas Teñidas Massive Sulphide Discovery
First Steps – with Riofinex in Portugal
Lead up to Neves Corvo
A Report on Geology and Difficult Metallurgy
Riofinex’s Portuguese Exploration Programme
A Detour to Holland
Second Helpings – with Billiton in Spain
The Set Up
Articulating and Implementing a Strategy
Teamwork and Personalities
Programme at Aguas Teñidas
Discovery of, and Subsequent Events at, Aguas Teñidas
Notes and References
I don’t really remember when I first became aware of the Iberian Pyrite Belt. In a way it sorted of drifted up on me from the time that I got my first job out of university in 1969 when I began work for a company called Rio Tinto Finance and Exploration Limited – Riofinex for short. I learned that the foreign-sounding name originated about one hundred years earlier when an English company had been formed to exploit large ancient ore bodies, at a place in Spain called ‘Rio Tinto’, to provide copper and sulphuric acid for England’s booming industrial economy. The name means ‘Red River’, just as ‘Vino Tinto’ means ‘Red Wine’, and the name came from the red-coloured pollution of the main stream draining the area of several great mineral deposits.
The deposits were originally worked for silver and gold by contemporaries of the Phoenicians, and there are several Old Testament references to the goings-on in the area. Later the Romans took over and left the greatest pile of ancient smelter slag found anywhere on earth. The English company’s fortunes waned until they sold most of their interest for £8 million in 1954, using the cash to get into more profitable mining ventures, for example into uranium mining at Elliott Lake in Canada. Later the Rio Tinto company merged with the Anglo-Australian Zinc Corporation to form The Rio Tinto-Zinc Corporation – RTZ for short. Riofinex drifted on, a small, comfortable company, patiently supported by its large parent but seemingly unable to find an ore body capable of producing a successful new mine.
My work with Riofinex started in Scotland, then took me, courtesy of the parent company, to the United States, to South Africa and then – literally – round the world examining goldfields, gold mines and gold prospects. After that I was deposited in Brazil for five fascinating years where I was involved in gold, zinc/lead, and diamond exploration. However, towards the end of 1979 I was asked to move to Portugal to set up a new Riofinex exploration office. One of the tasks would be to carry out a programme in the part of the Pyrite Belt that extended from Spain into its smaller neighbour.
I first set foot in the Pyrite Belt at the end of the following January, starting with a visit to Rio Tinto, where I was privileged to be received by the mines’ geological staff under the leadership of Felix Garcia Palomero, with geologist José (Pepe) Malave and geophysicist Nestavo Centeno Diaz. We visited all parts of the mine complex, including the San Dionisio body in an impressive open pit known as Corta Atalaya, the Cerro Colorado copper-rich stockwork and the Planes-San Antonio deposit, examining the geology, the geochemistry and the geophysical responses of the mineralization. Nestavo could understand English, but could not speak it so I spent hours talking to him slowly in English while he replied carefully in Spanish – which I did not then speak but found I could understand based on my knowledge of Portuguese. My brain felt bruised! The Rio Tinto geologists also arranged for me to visit the similar but very distinct mineralization at Tharsis, where I was most generously received by Kenneth Gray.
After about ten days of such invaluable visits and conversation I was ready to move to the Lisbon area of Portugal, where I would be based. RTZ at that time owned an aluminium extrusion company called Pilar Portuguesa SARL – Portalex for short. The General Manager, Nuno Cabral, and Finance Manger, Tony Starte, were both extremely helpful in facilitating the establishment of Riofinex in Portugal, and in guiding me as I began to make contacts at the Ministry of Mines, the DGGM (Departamento Geral de Geologia e Minas) and the SFM (Serviço de Fomento Minero). Vitor Oliveira was the principal geologist at the SFM and was always generous with his time and his extensive knowledge of the Pyrite Belt.
Much of the Portuguese part of the Pyrite Belt is buried under a surface covering of sand, gravel and similar deposits, but the SFM had carried out basic geological mapping and geophysics surveying, especially gravity, over a lot of the prospective part of the country, and had done a limited amount of drilling in areas deemed to be anomalous. This led to one or two new mineralized prospects, and to discoveries at Aljustrel, but nothing of significant economic importance was found away from the traditional mining areas. A joint venture was set up in 1972 between the Portuguese state and a mixed private/state French entity, and they spent several years working with the SMF data. Their efforts resulted in the discovery in 1977, at the substantial depth of 350 metres below surface, of what became the hugely important Neves Corvo deposits. By 1980 it was known that Neves Corvo contained exceptionally rich mineralization at grades of 6% copper and 5-6% zinc, and evaluation drilling was continuing, but the scale and true significance of the deposits was not public knowledge.
By the end of February 1980, based on the information so generously shared by personnel from Rio Tinto, Tharsis and representatives of Portuguese interests, I was able to compile a report for Riofinex that explained the then status of the mining industry in both the Spanish and Portuguese parts of the Pyrite Belt. There were four main types of ore. At Rio Tinto about 3,000 kg of gold and 27,000 kg of silver were being recovered annually from what remained of the oxidised cappings (‘gossan’) that had covered the central parts of the deposits. About 13,000 tonnes of copper was being produced annually from stockwork sulphide ore at Cerro Colorado, also at Rio Tinto. Sulphuric acid was being produced in several places (Rio Tinto and Tharsis in Spain and Lousal and Aljustrel in Portugal), destined for the chemical and fertilizer industries. So-called ‘complex ore’ was in the process of going into production at Aznalcollar in Spain, but the operation was reported to be ‘experiencing difficulties in its differential flotation circuits’.
The mineralization of the Pyrite Belt is about 350 million years old and is of the type known as ‘volcanogenic massive sulphide’ (‘VMS’). Such deposits form by submarine exhalation of hot sulphide-rich muds near to centres of active volcanism, and accumulate in topographic depressions. Depending on the style of exhalation the deposits can be composed overwhelmingly of sulphide (‘massive sulphide), or can be inter-layered with marine or volcanic-derived sediment (‘safrão’ in Portugal, ‘azufrones’ in Spain); a feeder-zone or ‘stockwork’ may cut the underlying rocks, marking the zone of passage of the sulphide-bearing fluids on their ascent to the seabed.
VMS deposits are known from some of the oldest rocks on earth, are common in the geological record, and are still being formed, especially at submarine spreading centres, today. All are rich in sulphides, but the composition of the sulphides varies. Iron sulphides usually predominate, mainly pyrite, and there are often minor, but economically valuable, quantities of copper, zinc and lead sulphides, with economically significant traces of gold and silver. An array of other minor metals may occur, many of which are considered deleterious, notably bismuth, cadmium, arsenic, antimony and mercury.
The terminology for the massive sulphides of the Pyrite Belt includes ‘pyritite’ for the extraordinarily heavy, massive, mineralization composed of well over 90 % pyrite, and ‘complex ore’ for banded mineralization with significant grades of copper, zinc and lead (the ‘base metals’) admixed with pyrite in a rock with a layered or banded appearance. Often the stockworks are enriched in copper. The banded ore may carry rich grades, usually made up primarily of a mixture of lead and zinc minerals, although there are also rare rich banded copper ores. Often the copper and lead/zinc minerals are closely mixed together. Surrounding and/or overlying the deposits, a more oxidised type of mineralization may occur, including barite, oxidised iron or manganese minerals including hematite, and perhaps gypsum.
The rocks containing the mineralization are usually referred to as the mineralized sequence. Those below the mineralization, often acid volcanic rocks, are referred to as the footwall sequence and those above it, typically consisting of fine-grained sediments such as shales and fine volcanic-derived sediment, sometimes of purple colour, are usually called the ‘hanging-wall sequence’.
VMS deposits have been hugely important contributors to world supplies of copper, lead, zinc gold and silver, most obviously in Canada where deposits such as Kidd Creek and the Horne mine at Noranda were extremely profitable. However, the attractive characteristics of the Canadian ores critically include coarse granularity, induced by high-temperature metamorphic processes that affected the mineral deposits long after their initial formation. During metamorphism the original fine-grained minerals tended to coalesce and anneal into larger grains that proved amenable to modern mineral separation processes, especially flotation. As a result it is relatively easy to make ‘clean’ concentrates that cause few problems in smelting. The ‘copper’ concentrate, for example, contains only low, and acceptable, values in zinc.
In the case of the Pyrite Belt, although the rocks have been severely deformed during movement of Africa northwards against the European landmass, they have never been subjected to the high temperatures needed to anneal the fine sulphide minerals into large grains. As a consequence the potentially valuable mineralization does not respond well to conventional mineral processing techniques. For example, grains of the zinc mineral sphalerite of 1 to 3 microns size commonly occur trapped within larger grains of the copper mineral chalcopyrite. This means that even after fine grinding, for example to 20 microns, some zinc is inevitably carried through into the copper concentrate, contaminating it and potentially incurring penalties from the smelters which then have to deal with it. Fine grinding is expensive and may produce technical problems such as ‘sliming’.
My report of February 1980 noted the following known resources in the Pyrite Belt.
San Guillermo/Filon Norte/Sierra Bulhoes
About 60 million tons at similar grades to Tharsis
Believed to contain about 40 million tons in three adjacent orebodies,
including massive pyritite and complex ore with good values in at least copper, lead and zinc
Almost no reserves remaining
About 250 million tons in various orebodies, notably Moinho and Feitais (both of which were in production), Estação and Gavião (see below).
About 50 million tons were officially admitted, although it was believed that there might easily be 80 to 100 million tons, in at least two deposits, one very rich in copper (perhaps 6 %) the other in zinc (perhaps 5-6 %) as complex ore, plus potential for other ore bodies. Not all of the admitted 50 million tons contained the high grades of copper and zinc mentioned, but probably at least 10 million tons did.
In Canada, a 10 million ton VMS mineral deposit would be considered an important economic asset and this puts into context the immense size of some of the Pyrite Belt deposits. The greatest VMS deposit known in the world would have been the original vast Rio Tinto deposit, including San Dionisio, Cerro Colorado and Planes-San Antonio, before parts of it were lost by erosion. It is thought to have originally contained about 1,000 million tons of sulphide mineralization.
The consequence of the metallurgical difficulties presented by the Pyrite Belt deposits was that huge quantities of mineralization rarely constituted ‘ore’ – mineralization that can be worked at a profit. Since economic geology as applied to mining is all about trying to make a profit, these were important considerations indeed. What would be the point of finding a new body of pyritite or complex mineralization to add to the uneconomic inventory of known deposits? Clearly there were issues that needed addressing before money was spent on an exploration programme.
All of these considerations were noted in my report of February 1980, and I also presented an evaluation of potential opportunities for RTZ to join with existing operators in the Pyrite Belt to carry out additional research that might turn some of the known unecomomic complex mineralization into ore. I was struck by the fact that:
‘Annually, some 80,000 tons of base metals, 2 million oz. of Au, 80 million oz. Ag and about 1 million tons of iron is not recovered from the ores mined. At present prices this represents 80% of the ore’s value, the recovered sulphur making up the other 20%.
I don’t know what the impact was of this report by a geologist that dealt so largely with mineral processing and economics, probably very little because Riofinex decided to press ahead with exploration expenditure. It felt that the SMF’s data might quickly provide leads to other prospects and visualized a programme of re-evaluation of gravity data to highlight anomalies in favourable geological settings, followed by detailed surface investigation and drilling. With luck, high-grade copper or lead/zinc mineralization might be found, perhaps with useful gold and silver credits, as was rumoured at Neves Corvo.
Riofinex enlisted the help of Rod Woolham, an experienced geophysicist who worked for one of RTZ’s associated companies in Canada and had a good knowledge of the important Canadian VMS deposits. Together we identified a number of interesting target areas over which, in November 1980, we requested exploration rights from the DGGM. Unfortunately, because the rumours about Neves Corvo were circulating in the mining world, other companies began showing an interest in the SFM data and just as it appeared that the DGGM was on the point of awarding Riofinex rights over the target areas that had been identified, it stalled. Instead of allowing us to ‘cherry-pick’ targets, it determined that any interested company must take on much larger areas over which they would be required to commit minimum expenditures and later deliver their data to the state.
In January 1981 Riofinex’s original submittal was formally rejected and it was asked to make a new proposal. In April the company was granted two licences, near Albernoa in the north and Rosario in the south. These were not the most attractive areas and there was a feeling that we had been fobbed-off with what was scathingly referred to as ‘moose pasture’ by our Canadian colleagues. Nevertheless, there was some potential and the company dutifully complied with the terms of the agreement, carried out evaluations of the SFM data, did some new gravity and some electromagnetic surveys, and conducted geological mapping and geochemical sampling. This led to the definition of drill targets and several holes were completed. Unfortunately nothing of any interest was found.
Another company that had shown an interest in the Pyrite Belt, both in Spain and Portugal, was Billiton – a minerals company then owned by the Shell oil group and based out of The Hague in Holland. Billiton established an office in Beja and I was able to make a visit there because the geologist in charge, Ross Buckland, an Australian, had been my colleague in Brazil. Riofinex always seemed to operate on a shoestring, and by comparison Billiton’s Beja office was well provided with both creature comforts and technology. I felt jealous! This was one of the reasons that, about October 1981, when an advert appeared in Mining Journal for a geologist to work for Billiton in The Hague, I applied for the post. The appointments process was slow and bureaucratic.
My attempts to gather intelligence about the Pyrite Belt and its mineralization were ongoing. In Portugal I made visits to Aljustrel, São Domingos, Montinho, Caveira and Lousal, and in Spain I returned to Tharsis and Rio Tinto.
I was also very fortunate to be allowed access to drill logs of Neves Corvo in September 1980, including some assay results, from which I was able to construct a cross section of the main part of the orebodies, data that I immediately sent back to the Riofinex office in London. I think this was the first technical information that RTZ received about the deposits in which it would later invest. At that time it was officially admitted that there were 15 million tons with an average grade of 5.76 % copper. In fact, Neves Corvo turned out to be an exceptional deposit that inaugurated production in 1988 and became Europe’s most important copper mine and, I understand, produced zinc, lead and – surprisingly – tin. Mining peaked at 2.3 million tons of ore in 1998 and annual copper production is currently stated to be 90,000 tons.
A geological report of 1991 noted:
‘These deposits include the Neves, Corvo, Graça and Zambujal orebodies, which have more than 150 million tons of polymetallic massive sulphides, of which 31 million metric tons average 8 percent copper ore. About 3 million metric tons average 2.5 percent tin.’
At the end of 1981 I sent Riofinex a report that reviewed the company’s involvement in the Pyrite Belt programme in Portugal and made strategic and technical proposals for its continuation. I pointed out ‘the specific objective of the exploration programme has never been clearly defined’ but by this time I had plenty of technical data available and had evaluated a great deal of information on VMS deposits from the Canadian literature. Rod Woolham and I had developed parameters for the likely surface expression in terms of gravity or electromagnetic response for model orebodies of different sizes at different depths, and I had then a much better idea of the type of orebody that might make a viable mine.
The exploration techniques being used by Riofinex were most likely to locate deposits larger than 10 million tons, but I proposed that a well-mineralized body of 5 to 10 million tons might be an attractive target, particularly if it were a stockwork, a small high-grade sulphide body such as Sierracilla in Spain, or ‘Corvo-type’ high-grade copper mineralization. I also reminded the company that ‘complex ores’ with significant base metal values were ‘normally economically untreatable’ at that time, a clear indication of my continuing concern that a technical exploration success (discovery of a substantial sulphide body) might not translate into a profitable mining enterprise.
After reviewing the history of exploration in the Pyrite Belt, a new approach for work on the Riofinex license areas was proposed. ‘The best approach is likely to be an integrated one …' combining geology, geophysics and geochemistry. In terms of geophysics, data then available suggested that the ‘standard’ technique of gravity surveys with stations on a 100 m square grid over areas of favourable geology would miss a 5 to 10 million ton mineralized body. On the other hand, tests carried out at Rio Tinto over the Planes-San Antonio body with pulse electromagnetic (EM) surveys suggested that these might be able to ‘see’ down to a depth of 300 m in the Pyrite Belt. Riofinex had already started to apply pulse EM in its license areas and it was proposed that such work be continued and drill holes be lined with plastic tubing to permit down-the-hole pulse EM surveys to be conducted after drilling was completed. This was all pretty new stuff at the time.
In terms of geology, the report noted that:
‘An improved knowledge of rock types, stratigraphy, structure and facies variations together with an always continuing study of known mineralization is indicated. Only by examining mineralization in place, in hand specimens, in section and in the existing literature can an improved knowledge of types and models be achieved. Geology must be the basis for geophysical interpretation and geochemical sampling.’
I was much less clear on the contribution that geochemistry might make to a new discovery, and the geological staff at Rio Tinto were very negative about any potentially useful role for it at all, on the basis that there was much widespread contamination from over 2,000 years of mining activities across the Pyrite Belt. They felt that spillages during ore transport, fumes spread across the landscape from old smelters and roasting units, and widespread disseminated pyrite throughout the system would make standard application of geochemical methods meaningless. I suggested that soil geochemistry, mercury sniffing and multi-element lithogeochemistry might have roles to play.
At the end of 1981 I was not very enthusiastic about Riofinex’s exploration programme. The company’s license areas did not seem to me to be very promising and even if we were to find a deposit it appeared more likely than not that it would be either pyritite or complex sulphides that would only add to the inventory of untreatable mineralization scattered across the Pyrite Belt.
One of my last acts was to take my London-based boss, Dr. Chris Morrissey, and his boss, Jack Gunter, a mining engineer, on a visit to Neves Corvo. Jack had been in charge of Riofinex and of RTZ Consultants from 1974 and continued in those posts until 1989. I believe this was his first visit to the Pyrite Belt and just over two years later RTZ was negotiating a 49 % interest in Neves Corvo. I occasionally wonder if the report I sent to London in September 1980 and the visit Jack made in March 1982 were the catalysts to RTZ’s later investment.
I did not see Riofinex’s Pyrite Belt programme through to a conclusion, because in about February 1982 Billiton offered me work and I left Portugal and moved to The Hague.
Billiton was founded by Dutch interests in about 1860 to mine tin in what were then the Dutch East Indies, now Indonesia. In 1970 it was bought by the Shell oil group as a vehicle to expand into mining. Plenty of money was pushed by Shell into Billiton such that by about 1982 it had an annual exploration budget of some US$ 54 millions and was active in twenty countries. There were some good people in Billiton, but the very limited success it experienced with such an enormous effort is probably testimony to the difficulties of achieving growth by ‘throwing money’ at a business rather than allowing growth through evolution. It took time for Shell to realize that the ‘synergies’ it imagined between oil and mining did not exist, at which time it sold Billiton to a South African mining group called Gencor. Billiton was divested from Gencor in 1997 and merged with BHP of Australia to form BHP Billiton, now billed as the world’s largest mining company.
Each year Billiton conducted programme and budget meetings at the head office in The Hague, when representatives from each country presented their plans and requested financing for them. It was a bureaucratic system, modelled on one that apparently worked well in the oil industry. As mentioned previously, Billiton was active in the Pyrite Belt, in both Portugal and Spain, and I was therefore invited to attend the meetings when the two representatives of these countries made their programme and budget pitches. I tried to table the concerns that I had about complex ores and the difficult metallurgy they represent, and the effects of these factors on the exploration models and techniques that should be applied in the field, but my comments attracted little interest.
Nevertheless, I enjoyed my time in The Hague, and benefited from working alongside mining engineers, mineral processing engineers, project evaluation personnel, and other professionals. It seemed that, after a period of a year or two, I was destined to return to South America, perhaps to take part in a porphyry copper project at La Granja in Peru, or to run the company’s substantial exploration effort in Brazil. Business conditions were increasingly difficult, however, and Shell decided to make telling reductions in Billiton’s exploration budget. Fear of redundancy began to stalk the corridors of the company, and it was against this background that my boss, Peter Verwoerd, invited me into his office to ask if I’d like to go to Spain to manage the Pyrite Belt programme there. Peru or Brazil seemed to me to be better bets, so I gently reminded Peter, whom I very much liked and respected, of my negative comments during the programme and budget meetings about Pyrite Belt exploration. After due consideration, he took the view that it would not be in the company’s best interests to send me to Spain.
The world economic situation did not improve, however, and as the months passed by actual cuts and redundancies began to thin the ranks of the company. Any hope of work in Peru or Brazil was dashed and I began to make contingency plans in case I were to be among those put on notice. This was the background against which, at the end of 1983, Peter again invited me to run the Spanish Pyrite Belt programme. I told him, enthusiastically, how splendid I thought his idea was, and how much I would enjoy the opportunity to work in such an interesting area! My boots were on the ground in Spain early in February of the following year.
Activities in Spain were run out of Shell’s head office in Madrid, where Amado Ahmed Anda, an Argentinian of Arab descent, was the Exploration Manager. He had a series of programmes in northwest Spain, operating out of an office at Salamanca, and the Pyrite Belt programme based out of an office at San Telmo. The Pyrite Belt programme was a joint venture (JV) set up in 1980 between PRN (Promotora de Recursos Naturales), a subsidiary of Banco de Bilbão, with 49 %, and BESA (Billiton Española S. A.), the operator. Up to that point the programme was run by Kees Windt, a Dutch geologist supported by a team of five other geologists. I liked Kees and, so far as I could tell, he had been doing a good job. However, for reasons I never understood, it had been decided to make wholesale changes, hence the invitation for me to take over.
After a brief visit to Madrid office I travelled on to the Pyrite Belt and began taking over the exploration office. By the end of February the staff changes on the programme were pretty much complete. I was to have with me three geologists, a German called Heinz Groepper and two Spaniards, Pedro Rodriquez and Javier Gonzalez Más. Pedro was the only survivor from the previous team and was a huge asset. There was also a geophysical technician called Javier Vasquez, an office manager called José Manuel Mora and a number of experienced field workers.
The licence areas controlled by the joint venture were excellent, in that they contained several abandoned mines and prospects. These included the Carpio, Cruzadillo, Confesionarios and Aguas Teñidas mines. The licence areas also surrounded the active San Telmo mine, an open pit then producing pyrite for the manufacture of sulphuric acid (with a little by-product copper) and the old Lomero-Poyatos mine.
All the mines in the area had been essentially pyritic, but Carpio had produced some copper ore, possibly supergene, Lomero-Poyatos was unusually rich in gold and Aguas Teñidas was noted for high values in copper, lead, zinc and silver. Clearly there was excellent potential for finding new mineralization – but if we found any, would it be treatable at a profit? Given the insights about the metallurgy that I had obtained with Riofinex, and expressed at Billiton’s programme and budget meetings, I decided to do what I could to maximise the chances. The plan was to prioritize activity around base or precious metal potential rather than simply looking for a mineralized pyritic body.
My first monthly report, for February, stated:
“The objective is to find an economically attractive volcanogenic base and/or precious metals mineral deposit in ground controlled by the PRN/BESA joint venture in the Pyrite Belt.”
“At this time there appear to be six identifiable types of deposit which might satisfy the above objective. … It is important to differentiate these sub-types of volcanogenic deposit as it may require different geological, geochemical and geophysical strategies for their discovery. Ongoing data collection of the characteristics of the sub-types (dimensions, physical and chemical attributes, geological settings, geographical distribution, inter-relationships) should, of course, continue.”
The “six identifiable types of deposit” were listed as:
Hanging wall ribbon ore
Chalcopyrite in black shale in stratigraphic hanging wall
Fracture- and open-space-filling, non-massive pyrite, chalcopyrite ore in stratigraphic footwall
Cerro Colorado, San Dionisio, Corvo, San Miguel
Supergene-enriched Fe cappings at surface
Rio Tinto (part), Tharsis (part)
Zn, Pb, (Cu)
Within or adjacent to pyritite bodies. About 6 % base metals, plus precious metals
San Dionisio, Planes-San Antonio, Neves, Aznalcollar, Sotiel
Minor complex ore
Zn, Pb, Cu
Very high grade smaller bodies, long and narrow, not associated with massive pyrite bodies
Sierracilla, Monte Romero, Rio Corumbel
Stratabound precious metals
Gossanous or primary stratabound precious metal mineralization
This was at least a start to deciding how best to order target priorities, to identify exploration strategies and to promote more acute observation at known mines and deposits when the team had the opportunity to make visits. In short, it was a more responsible way to spend the companies’ money.
The 1984 budget catered for 3,500 metres of diamond drilling. When I arrived on site two difficult holes were nearing completion at Cruzadillo, but no other target had been developed for drilling – I wondered if this might have been one of the reasons that the JV partners had insisted on changes in personnel.
The programme information was filed by mineral title area, and I decided to re-order it into prospect files in two categories: Target Evaluation and Target Generation. This, I felt, would allow us to focus on potential drill targets. Two months later I was able to list under ‘Target Evaluation’ eight Category One, fifteen Category Two and twenty Category Three targets.
Each of the more important target areas was assigned to one of the geologists, to review the work carried out and identify the additional work – geological, geophysical or geochemical – needed to bring each prospect to the point at which it would be possible to propose drill targets. I think this gave our work great focus.
The first target in Category One was Aguas Teñidas, which I assigned to Heinz, and by April its listing noted:
“3 possible drill targets defined. Geophysical interpretation pending. EM-37 to be carried out. Old mine notably rich in Cu and Zn.”
It was a fact that I had seen many more Pyrite Belt mines and deposits than the other members of the team, and there’s only so much you can understand from books, reports and what people tell you. Therefore, to broaden our collective experience of real Pyrite Belt mineralization, I initiated a series of visits for all the geologists to active and abandoned mines in the area. We were splendidly received at Aznalcollar, Sotiel, La Zarza and Concepción. At each, we examined the mineralization, and the variations within it; we looked carefully at the rocks that contained it; we listened to explanations from the resident mine geologists who lived with the deposits on a daily basis; we asked lots of questions. We gave particular attention to the surface manifestation of each deposit in terms of visible evidence in the geology and in the geochemical or geophysical signature. Several times the resident geologists told us that they had found our visit stimulating.
We also collected suites of samples from each mine we visited, took them back to our office, described them in detail, labelled them, compared them with those we had collected from other deposits, and those in our own areas, and discussed the similarities and differences. Geophysical work was supervised by George Reynolds, a company geophysicist based in Madrid, and we constantly discussed George’s results with him and tried to put them into a geological context. George’s input was absolutely essential. We read widely both about the Pyrite Belt and also about other VMS deposits from around the world. I think everyone felt that we were team building and that each had an important contribution to make. We felt we were becoming ‘knowledgeable’.
By June we were able to call up our first drill rig and after that we had drills operating continuously until we ran out of money in mid-December. The programme eventually completed nineteen holes on nine prospects for 3,215 metres with thirteen sulphide intersections – an excellent ‘hit’ rate. Although none contained enough copper or other useful metals to be economic, it was not a bad effort. By October we could already identify drill targets for a further 4,050 m drilling to be carried out in 1985, which showed we had plenty of ideas.
From time to time we received visitors at our office at San Telmo, and I also had to go to meetings in Madrid. I thought it curious that each time I set off, Heinz, Pedro and Javier all made a point of wishing me ‘good luck’. I felt confident that we were working well and was never apprehensive about the reception I might expect in head office. Eventually, however, I learned the reason for my colleagues’ concern. Anda, it turned out, could be very unpredictable and the day came when he ranted at me in his office. It was suddenly unsettling. He also relied very much on the opinions of an administrator who, I was informed, was noted for extreme Fascist views, and who seemed determined to find conspiracies among the staff where there were none.
Working under Anda in Madrid as Chief Geologist was Dr. Chris Wheatley, a pleasant fellow who, I understood, did his Ph.D. on something to do with VMS deposits. Unfortunately, as far as I could tell, Chris went in fear of Anda and the office politics, and fretted about losing his job. He was therefore unable to stand up for himself and, when in contact with the field geologists, appeared to merely transmit whatever Anda said. On top of that, when visiting the project he seemed lost with the rocks and mineralization we were dealing with. The situation would have become impossible for me had I not had the solid support of the San Telmo team. Peter Verwoerd noted the team spirit on a visit he made in October and ‘…complimented the staff on its motivation’.
George Reynolds, based in Madrid, was also subjected to its corrosive regime and in 1988 he wrote me a letter describing how he was eventually forced out of the company. He found the politics very difficult, and noted that Anda and his administrator ‘brought much hardship upon almost every member of the Billiton staff’. He mentioned the ‘numerous policy and staff changes’ and said: ‘We had to fight him [Anda] to succeed, but unfortunately we also [had] to fight each other to survive’. I wonder if the explanation for Kees’ transfer was that he fell foul of Madrid office politics – it seems that sooner or later Anda had a go at all comers. I thanked my lucky stars that I was based far away in the Pyrite Belt.
Years later, David Whitehead, Anda’s boss at Billiton in The Hague, told me that Anda was a real problem and quite a lot of time had been spent trying to work out how best to deal with him. I wished I had known that at the time because, although I thought Anda neurotic, I had to assume that he had the full support of management. If William Shakespeare had been around, he might have taken inspiration from the scheming in Madrid office to have penned a new tragedy.
Without doubt the area of the old Aguas Teñidas mine was one of the most interesting prospects in our license areas. In 1963 a mining engineer, Isidoro Pinedo Vara, published a weighty tome filled with valuable information about the Pyrite Belt, and I had consulted a copy of it at Rio Tinto while working for Riofinex. The book was out of print and although everyone knew of it almost no-one had a copy. In the entry for Aguas Teñidas Pinedo noted that the mine had been active from about 1886 to 1900, and again from 1916 to about 1934, closing each time because it was considered worked out. From 1917 to 1933 Pinedo recorded a production of 584,000 tons of ore at copper grades varying between 3 and 8 %, average about 6 %. Not bad! He described the deposit not as a ‘mass’ but as a long, narrow, irregular vein and estimated the total size as 0.9 million tons. There had been a main shaft with a number of levels, and an internal shaft. The average width was said to be about 5 metres.
I coveted a copy of Pinedo’s book, ‘Piritas de Huelva’, and made enquires about the publishing house, ‘Editorial Summa’, in Madrid. It transpired that the company had gone bust, but I was put in contact with a gentleman who had run the business and who, it turned out, had a number of copies of ‘Piritas de Huelva’ tucked away at his home. I arranged to buy twenty of them, at my own expense, and sold them on, at cost, and to huge delight, round the geologists at all the mines we visited. I also learned that Sr. Pinedo was still alive, living quietly in southern Spain, now more interested in horticulture than mining. In October, with Javier Gonzalez Mas, I was able to spend an evening with Sr. Pinedo and, after listening to my enthusiastic appreciation of his book and learning of my efforts to put it back into circulation, he kindly signed my copy:
After the 1930s, Aguas Teñidas continued to attract attention from time to time. On 15th June 1971 Gil Fernandez Alvarez wrote a report of work carried out by a 50:50 joint venture between Asturiana de Zinc and Sociedad Francesa de Piritas de Huelva. They had used mise-a-la-mass and resistivity geophysical techniques round the old mine, and drilled three diamond drillholes, two of which intersected mineralization with locally interesting values in Cu, Pb or Zn. Two samples from the old dumps contained over 10 % Zn, with some Pb, Cu and Ag. The JV concluded that the mineralization cut by their drillholes was too deep to be detected by the geophysical methods employed and no further work was done. It was considered at the time that any mineralization at the old mine was effectively exhausted and we paid no great attention to it while I was on the programme.
However, the geology along the trend of the old mine was clearly favourable and Heinz soon produced a geological map of the area, carried out soil and rock sampling and checked out old pits and prospect shafts. Numerous anomalous geochemical values were encountered, including some with more than average gold.
I have mentioned geophysics a number of times in this account, and it has long had an important role in Pyrite Belt exploration. In Portugal, Turam, an early electromagnetic method, detected an anomaly at Carrasco at Aljustrel in 1950-53, drilling of which lead to discovery of the much larger Moinho body nearby. Resistivity and self-potential methods were tried, but no further discoveries were made. In general, Turam was baffled by shallow formational conductors in hanging-wall schists. In 1962 the Planes body at Rio Tinto was discovered by drilling EM and gravity anomalies, and in 1963 the very large (more than 70 Mt) Feitais body at Aljustrel was discovered at a depth of 100 m by drilling a gravity anomaly. In 1965-67 the Nueva Almagrera body at Tharsis (2.5 Mt) was found by resistivity, Turam and gravity methods, and five other gravity anomalies at Tharsis have also been successfully drilled. At Aljustrel a second gravity discovery came in 1968 with the drilling of the Estação body (more than 60 Mt) at a depth of 250 metres. In 1977 the discovery of Neves Corvo at a depth of 350 metres was in large part due to gravity surveying.
Most developments in geophysical methods of exploration have taken place in Canada, and electromagnetic methods were given impetus there by their success in detecting conductive massive sulphide deposits below glacial cover, and lakes. However, as mentioned previously, the conductivity of Canadian VMS deposits is significantly better than those of the Pyrite Belt, probably because the sulphides have been annealed by high-temperature metamorphism. On the other hand, in Canada metamorphism has also produced graphitic horizons from what were originally organic-rich shales. This does not occur in the Pyrite Belt, but there are conductive fault zones and other conductive horizons, often black shales, that not only confuse interpretation of the electromagnetic anomalies but interact with each other in ways that can make interpretation of data a difficult task for geophysicists.
In the 1970s increasingly sophisticated electronics allowed development of ‘pulse’ or ‘transient’ electromagnetic methods in Canada, in which an electrical pulse creates an electromagnetic field that is then abruptly switched off. Any conductive body is energized during the pulse and produces a secondary field that decays when the pulse is switched off. Decay of the secondary field can be detected by a receiver at surface. Pulsing and measurement of the decay curve from conductors continues until sufficient data have been accumulated for interpretation. Electromagnetic energy is usually generated by a large wire loop laid out on surface and the receiver moves from station to station across the area of interest taking readings which are plotted on maps and profiles for interpretation. However, a receiver can also be lowered down a drillhole in an attempt to detect mineralization at depth, and this was rapidly recognized as a potentially powerful method of improving the efficiency of exploration.
One of the first methods of pulse EM to be applied in the Pyrite Belt was by the Canadian company Crone. Rod Woolham promoted the use of Crone EM in the Pyrite Belt and the method was shown capable of detecting the deep San Antonio body at Rio Tinto. Thereafter it was used on Riofinex’s programme in 1982 and in 1984. BESA/PRN opted for a pulse EM system known as EM-37 using Geoconsult, a French contractor who also carried out gravity surveying for us. In February 1984 Madrid office was urged to firm up an EM-37 contract and surveying of the Herreritos-Aguas Teñidas area started. My May monthly report noted:
‘A series of parallel conductors was located by EM-37 in the Herreritos-Aguas Teñidas area. These appear mostly formational and correlate well with HLEM conductors. The survey is continuing.’
BESA/PRN used other geophysical techniques, especially induced polarisation (IP). It was generally the case that geological mapping and sampling, geochemical sampling of soils and rock-chips, and gravity profiling, IP and EM-37 were all carried out over prospects in the process of deciding on drill targets. Interpretation of the geophysical results was done either by or under the supervision of George Reynolds working with the contractors and generally in consultation with the geologist in charge of the prospect.
Geological input into interpretation of geophysical data was important on several counts. Obviously it was the geologist who was best able to provide input on lithologies and structure, and on the location of geochemical anomalies, but geology also provided information on the potential shape and physical characteristics of the target. For example, the geologist could inform the geophysicist about the characteristics of stockworks, of massive pyritite bodies, or of banded complex ores that might have better conductivity. In fact, tests were carried out by the geologists at San Telmo on hand specimens to measure the range of conductivities and densities of different types of sulphide and formational lithologies to help the geophysicists calibrate their computer-assisted modelling. In spite of all the science, though, geophysical interpretation of data in such complex natural systems was always likely to be imprecise.
By July 1984 geological mapping and sampling showed favourable geology extended to the east of the old Aguas Teñidas mine, marked by anomalous base and precious metal values. Although the EM conductors looked rather ‘formational’ i.e. as though they might be caused by conductive lithological horizons or structures, George Reynolds recommended that the best part of each conductor should nevertheless be drilled. On this basis a drill target was defined and given the name of ‘Aguas Teñidas Este’ (‘East’), and two diamond drillholes were planned, to be called ‘AE-1’ and ‘AE-2’. Each was to be 300 meters long and inclined towards the south, designed to cut through the centre of the interpreted EM conductors and supported by possible small gravity anomalies. Initially the holes would start in the fine-grained sediments typical of hanging-wall lithologies and they were planned to find mineralization down-dip of a gossanized acid volcanic sequence of footwall-type that was exposed on surface.
AE-1 was drilled between 27th July and 21st August and reached 298.39 metres in length. AE-2 started on 23rd August and ended at 296.93 metres on 7th September. Neither hole detected the targeted EM conductor, and neither encountered any massive sulphide, or even the interface between the fine-grained sediments and the acid volcanic lithologies. Both stayed in hanging-wall lithologies and produced 600 metres of fine-grained shales and epiclastic tuffs. It was disappointing, perplexing and embarrassing; diamond drilling does not come cheap.
Neither hole had much sulphide in it – indeed surprisingly little for typical Pyrite Belt rocks – but Heinz noted that the ratio of chalcopyrite to pyrite in the minor disseminations that did exist seemed unusually high. I spent a weekend re-logging AE-2 in detail for my own education and wrote a report in which I noted three facies in the epiclastic sequence, defined, apparently, by their state of oxidation. There was a purple oxide facies with trace hematite and specularite, a green silicate facies with iron as chlorite, and a dark grey reduced facies with iron reporting as sulphide. No sulphide existed in the oxide or silicate facies. The ratio of chalcopyrite to pyrite in the reduced facies was similar to AE-1 and approached 1:1.
In September a down-the-hole EM survey was carried out on AE-1 using two loop positions and the response indicated a probable conductor below the drillhole, but also the possibility of a conductor above it. George Reynolds recommended a third loop position and this was done in October. Interpretation of the results by Geoconsult was evidently difficult and had still not been completed by December. By then, however, I had spoken to Vitor Oliveira, still with the SFM in Portugal and one of the most knowledgeable Pyrite Belt geologists, about the trace sulphides in AE-1 and AE-2, in particular about the high chalcopyrite/pyrite ratio. His response was both thoughtful and immediate: black shales with persistent trace chalcopyrite, as found in AE1 and 2, could well be the aureole of stratabound VMS mineralization.
By this time the drilling budget for the year was exhausted and drilling was not scheduled to recommence until April 1985. A new drillhole was recommended at Aguas Teñidas East with geological, geochemical and geophysical support:
- We had failed to encounter the favourable geological horizon targeted by AE-1 and AE-2 but we believed it had to pass through the area and it was the expected location of any mineralization there might be.
- The persistently high chalcopyrite/pyrite ratio in the dark shales intersected in both drillholes might be a geochemical halo of weak copper values leaking from a potential ore body.
- The original geophysical target, represented by a dense and electrically conductive mass, was not cut and had been reinterpreted as lying below the first two drill holes.
- There were strongly anomalous geochemical responses in the area, in soils and rocks.
The new hole was supported by both George and Heinz and would be called AE-3. Its target would be 75 m deeper than the AE-1 target, indicating a DDH of 400 m length. The recommended collar coordinates, shown in my monthly report for March 1985, were 690.800E/4.183.430N.
AE-3 as recommended
AE-3 as drilled
* Later extended to 456.30 m
In the event, AE-3 was drilled in September 1985 between AE-1 and AE-2, aimed below both of them. It cut about 17 metres of massive sulphides containing 0.8% copper, 7.1% zinc, 1.5% lead, 40 g/t silver and 0.8 g/t gold on an acid volcanic footwall. The intersection was at a vertical depth of 315 metres, but about 400 metres along the length of the inclined borehole.
It was a good discovery, but I wasn’t there to see it because in April Billiton moved me on to pastures new.
Once the initial discovery was made it was decided to deepen AE-1 to 456.3 m and the hole intersected massive sulphides at a depth of about 400 m over about an 8 m length of the hole. Further drilling and other activity continued to outline the mineralization such that by May 1987 it was estimated that there was at least 25 million tonnes with average grades as shown below. Within this was 7 Mt of cupriferous mineralization and a further 7 Mt of ‘polymetallic’ mineralization (enriched in zinc and lead). Aguas Teñidas East was an important discovery both in the context of the Pyrite Belt and as a volcanogenic massive sulphide deposit on a world scale.
including 7 at
and 7 at
Later published data, from about 2006, states that the deposit comprises 41 million tonnes with 1.3 % Cu, 3.1 % Zn and 0.9 % Pb.
According to a report by a mining consultant in 2007, the deposit scheduled for mining is some 1,400 m long, extending from about 689.500E to 691.100E. It varies in its north-south dimensions mostly between 100 and 200 m and in some places it is more than 50 m thick. Available information states that it does not link up with the old Aguas Teñidas orebody, the main shaft of which was at about 688.900E.
A company presentation from 2007 shows additional inferred ore in a western continuation, based on a small number of drill intersections, that extends as far as 688.500E. This suggests that the overall length of the body is at least 2,600 m.
In 1990 it was announced that the Billiton/PRN joint venture would carry out a feasibility study at Aguas Teñidas that included driving an inclined tunnel into the deposit and performing a detailed programme of underground drilling. The study, to test the economic viability of the body, was expected to take two years and cost US$ 6 million. However Billiton then relinquished its interest in favour of Placer Dome, a Canadian company, who carried out additional drilling. Navan Mining, for whom I understand Pedro Rodriguez was the project geologist, took over in 1995 and in 1997 began construction of an inclined tunnel of the type proposed by Billiton/PRN. It also acquired the mineral processing plant at the Sotiel mine, 28 kilometres away by road. Between 1999 and 2001 nearly 900,000 tonnes mainly of ‘polymetallic’ ore (with zinc, lead and silver), but with some copper ore, was mined and processed. Unfortunately Navan Mining got into financial difficulties and production ended.
However, in a world that seems increasingly short of mineral resources and where metals prices have risen strongly in recent years, Aguas Teñidas continued to attract attention and in 2004 new owners, a Canadian company called Iberian Minerals Corporation (IMC), developed a plan to bring the property back into production. In April 2008 there were five drills operating at the deposit to investigate a copper-rich ‘stockwork’ zone that lies beneath the main mineralization. A financing facility of US$ 210 millions was secured to implement a full mining operation. In February 2009 IMC’s website reported that they were building a ‘completely new processing facility’ and sinking ‘a second underground ramp to facilitate the commissioning in the 4th quarter of 2009’. Commercial production was officially declared on October 26th 2009.
At June 30th 2009 IMC reported a Combined Resource of 27.5 million tonnes, comprising 11.72 Mt of Measured ore and 15.78 Mt of Indicated ore. The three main ore types are as in the following table.
In addition, Inferred Resources, mostly in the Western Extension, totalled 10.62 Mt, of which 7.59 Mt was Cupriferous. Total resources were therefore over 38 million tonnes.
Millions of tonnes
Polymetallic (Cu, Zn, Pb)
The current production schedule for Aguas Teñidas runs from 2009 to 2018 and foresees mining and processing of 19.2 Mt of ore at an annual rate of 2.2 Mt. Both Cupriferous and Polymetallic ore will be mined, but the emphasis until 2013 will be on the former. Many details of the operation, including the production schedule, can be examined in an IMC presentation available online. By way of example, forecast metal production for the year 2011 is 29,975 tonnes of copper, 49,165 tonnes of zinc and 7,175 tonnes of lead. Figures for other years are available in the IMC presentation on slide 28.
Implementation of production by IMC at Aguas Teñidas has not been straightforward, as described in an article from Northern Miner following a visit of November 2009. The processing plant was set up with two circuits, copper and polymetallic. While the copper circuit worked well, the polymetallic did not. The original plan for the polymetallic circuit was to sequentially separate pyrite, then copper, lead and zinc. In June 2009 the circuit had to be shut down because it was not producing consistent saleable copper and lead concentrates and recoveries were low. It was reconfigured to produce a bulk copper-lead concentrate, followed by a zinc concentrate. The plan envisaged later producing separate copper and lead concentrates. The metallurgical problems resulted in a cash shortfall of US$20-30 million, but fortunately Trafigura, a financially strong Dutch metals trading group, owns over 40 % of IMC’s shares and supported the company.
IMC noted in its first quarter 2010 report: ‘The copper circuit operated on target while the poly-metallic circuit was below target on throughput and zinc recovery’.
Incidentally, one of IMC’s directors is Jack Gunter – the mining engineer I took to visit Neves Corvo in 1981. Jack was head of Riofinex from 1974 to 1989, and was also head of RTZ Consultants, whose software was used to estimate the Neves Corvo reserve. In 1984 RTZ took a 49 % interest in Neves Corvo and it seems likely that Jack’s knowledge of Pyrite Belt mineralization must have been enhanced by these activities.
The time I spent in the Spanish Pyrite Belt was one of the most rewarding periods of my career as a minerals exploration geologist. Spain is such a fascinating country, the geology of our licence areas was extremely interesting and the team of Heinz, Pedro, Javier and our supporting workers was a joy to be with. The discovery drill hole was made essentially as recommended in my final monthly report written on March 25th 1985, but I am sorry I was not there for the excitement of seeing the first mineralization come out of AE-3. Heinz, the prospect geologist all along, was then in charge and he certainly deserved all the satisfaction he must have felt. One may ask if the Aguas Teñidas East mineral deposit would have been discovered if I’d never set foot in the Pyrite Belt. Probably it would, but no-one can really know and I certainly felt that I’d had an important role in the success that it represented.
What is certain is that Aguas Teñidas and everything leading up to it contributed richly to my professional life as a geologist, not least the priceless experience of working in a close-knit, hard-working, focussed team in one of the world’s great mineral belts.
A minerals exploration programme is a funny thing. It comprises a series of quite expensive activities aimed at finding a mineral deposit in the three dimensions of a block of mineral title, and yet there may be no mineral deposit to find! Until the moment of discovery, all is unfulfilled hope, or doubt. Once a discovery is made, it turns out that everyone knew all along what the outcome would be, and all the data leading up to the discovery was logical and the result inevitable.
Various accounts of the discovery of Aguas Teñidas East have appeared – three to my knowledge besides this one of mine. Chris Wheatley wrote a report, on which I commented by letter on May 25th 1987, and which George Reynolds referred to as a ‘paint job’. In 1994 Dave Hopgood, the geophysicist who took over from George Reynolds, co-authored a paper about geophysical aspects of the discovery, to which George replied, giving his version of events as the resident geophysicist when the actual discovery was made and during the subsequent exploration until 1987. The geophysicists don’t really seem to agree with each other and all think that Geoconsult, the EM-37 contractors, got it wrong, and none of them seem to think the geologists got much right!
My view is that a good exploration programme working in a complicated natural system successfully detected a large mineral deposit at very considerable depth, in spite of misleading indications from both geology and geophysics. Much dedication was shown by all the technical staff involved, such that setbacks were successfully overcome as further information was gathered. Chris Wheatley stated that the success was ‘underpinned by total management commitment’, but that was not how it seemed during my tenure in San Telmo. Instead I have a good deal of empathy with George Reynolds view: ‘Perhaps the most remarkable aspect of the Aguas Teñidas discovery was that it was made in spite of [Anda] and his numerous policy and staff changes’.
The mine that is now in operation has a projected life of eleven years, but may go on longer. I wish IMC well in their immense endeavours and hope they are fortunate to enjoy favourable metal prices and go on to recoup their investment and to make good profits. Aguas Teñidas was a superb technical discovery (at the exceptional depth of more than 300 metres, much like Neves Corvo), but it is twenty-five years since it was first found and so far, for its owners, it has only incurred expenses.
Nevertheless, many people have already benefited greatly. They include all those who have worked on the project and in doing so earned wages and salaries and gathered experience. They also include all the businesses that have contributed to the mine – the drilling and engineering contracting companies, the chemical analytical laboratories, equipment manufacturers, technical consultants, the airlines who have flown innumerable executives to and from the area, promoters of the shares of Navan and IMC and all those who have worked to raise finance for the project. Indeed, one could go on for a long time listing the beneficiaries who have put ‘cash in the bank’ as a result of the discovery of Aguas Teñidas. But a solid return on shareholders’ funds has yet to materialise and I am left wondering whether my early misgivings about ‘the problems of the recovery of metals from the sulphide ores of the Pyrite Belt’, and as expressed at Billiton’s programme and budget meetings in The Hague, should not have been heeded. In the Pyrite Belt, be careful what you wish for.
It puts me in mind of the old joke about a man who caught a bear and it wouldn’t let him go! But mineral exploration is a fine game.
 For example, flotation testwork on mineralization from Moinho at Aljustrel was carried out by grinding the ore to 20 microns.
 Incidentally, the report euphemistically described these as ‘reserves’, but in 1980 there was less rigour in the terminology used in relation to mineral bodies than there is now.
 Carvalho, Delfim de, ‘A Case History of the Neves-Corvo Massive Sulfide Deposit, Portugal, and Implications for Future Discoveries’, Economic Geology, Monograph 8, 1991, pp 314-334.
 To the agreeable Mr. Philip M. Dunkerley, wishing him much success in the mining investigation of the Onubian Basin, with best wishes, Isidoro Pinedo, October 1984.
 HLEM – Horizontal loop EM, another, portable, EM system then in use by PRN/BESA.
 Case History of the Aguas Teñidas East Cu-Zn-Pb-Ag-Au Sulphide Discovery, May 1987, C. J. Wheatley, internal report for PRN/BESA.
 Personal communication, 29th April, 1988.
 Hopgood, J. D. and N. Hungerford, ‘Geophysical Case History of the Discovery of the Aguas Teñidas Massive Sulphide Deposit, SW Spain’, Exploration Geophysics 25 (1) 1-17, and http://www.publish.csiro.au/?paper=EG994001
 Idem ‘Case History…’
 Personal communication, 29th April, 1988.