Perante os erros, as omissões e sobretudo o desrespeito pela verdade patenteados neste artigo, não resisti a reagir, embora não competisse a mim tomar a atitude de defesa do Organismo, cujos dirigentes que sucederam ao malogrado Engenheiro António Bernardo Ferreira, tão mal me tinham tratado.
Conhecendo as características dos dirigentes e dos técnicos da 1.ª Brigada de Prospecção que à data se encontravam em funções, não esperaria senão passividade ou até uma certa subserviência para com a arrogância assumidas pelos técnicos estrangeiros.
Extasiado com os elogios de que estava a ser alvo, Xavier Leca esquecera totalmente as suas afirmações no telefonema de 25 de Maio de 1977, em que me denominara “pai do jazigo”.
A minha reacção, publicada a páginas B45 e B46 do Volume 100 (Janeiro – Abril de 1991) da mesma Revista foi a que a seguir transcrevo:
“Despite my great admiration for the French state organization, the Bureau de Recherches Géologiques et Minières (BRGM), I find myself in strong disagreement with the version of the Neves – Corvo discovery that has been presented by Xavier Leca. Amicus Plato, sed magis amica veritas.
It is not my intention to belittle the achievements of the association formed by the Sociedade Mineira de Santiago (SMS), the Société d’Études, de Rcherches et d’Exploitation Minieres (SEREM) and the Sociedade Mineira e Metalúrgica de Peñarroya Portuguesa (SMMPP).
No one could deny that it was the Association that first struck the deposit. However, it is ethically remiss of the author to minimize the role of previous exploration by the Portuguese state organization, the Serviço de Fomento Mineiro (SFM), in the discovery.
Having granted the Association access to material on the Pyrite Belt of Alentejo held in its technical archives, the SFM does not receive adequate credit for the enormous amount of work represented by the documents that were consulted.
For example, no reference was made to a paper published in 1955 of which I was the main author(1).This described a major prospecting programme, which I implemented systematically in subsequent years. The discovery of the Neves – Corvo target was a natural outcome of the programme – Just as the Estação and Gavião orebodies, in the Aljustrel area, had been before. Furthermore, the Almodôvar area was characterized in the paper as especially prospective for copper deposits.
I have no hesitation in stating that without the benefit of almost 30 years of systematic investigations by the SFM of the entire Pyrite Belt of Alentejo, the Neves – Corvo discovery could not have made in the time frame that it was. In fact, there is no question that the SFM can be credited not only with the identification of the Castro Verde - Almodôvar area as one with potential for massive sulphide deposits (the area had not previously even been considered part of the Pyrite Belt!) but also with the definition of the gravity anomaly that led to the discovery of the Neves – Corvo deposit itself.
Had the activity of the SFM in the Castro Verde area not been interrupted as a result of the Portuguese Government’s decision to transfer prospecting rights to a private entity, the Neves – Corvo deposit would have been discovered at least five years earlier than it was.
The SFM would have ascribed considerably more weight to the gravity anomaly than to the interpretative geological model concerning the siting of massive – sulphide bodies in the stratigraphic sequence.
Moreover, as in identical circunstances that have been encountered on several previous occasions, the SFM would not have stopped the investigation of the gravity anomaly before determining its cause.
Leca is perhaps aware that, early on, I drew the Association’s attention to the fact that borehole Nr. 1 had failed to supply information that would explain the gravity anomaly that it was designed to test. He may also recall that he and other geologists of the Association mentioned, in a paper published in 1981, that the SFM had drawn their attention to the Neves anomaly, emphasizing its importance (2).
His claim that that the SFM regarded Algaré as the main target around which to base its prospecting programme is totally incorrect.
Numerous internal documents and the practice of many years demonstrate clearly that the SFM’s intention was to cover the whole Pyrite Belt of Alentejo with a series of gravity surveys. Priorities were established according to potentiality grades that were defined on the basis of results obtained as the programme progressed.
At Algaré – Neves the SFM begun to investigate an area of 28 km2 (fig. 1). Following its usual practice, the next step would have been to survey adjoining areas to delimit the Neves gravity anomaly, which was still open to the southeast, and to allow a clear distinction of the regional and residual components. It was at precisely that stage, however, that, on instructions from the government, the SFM was obliged to interrupt its prospecting operations.
It would appear from errors of geophysical interpretation that the author’s expertise is not in geophysical prospecting. I have not seen the reports of the geophysicists who worked for the Association, but it is difficult to believe that they could have been responsible for the mistakes in the paper.
Space does not permit me to comment on all of them, but two are particularly illuminating.
The first concerns the amplitude of the gravity anomaly at Neves. Although the gravity map accompanying the paper retains the regional component, it is not difficult to see that the residual anomaly exceeds 1.4 mgal – much higher than the 0.4 or 0.6 mgal stated by Leca.
The second concerns the interpretation of this anomaly. Any elementary textbook of geophysical prospecting emphasizes the interpretative ambiguity inherent in the gravity method and the consequent impossibility of determining, without information from other techniques, the depth to the top of the body responsible for a given gravity anomaly. I t is only possible to establish a limit to the depth (in the case, much greater than the true value) beyond which a given anomaly cannot be generated (3).
All the author statements about calculations of the depth of the orebody on the basis of gravity results are, thus, without foundation – and if, indeed, one geophysicist suggested that the depth to the too of the orebody was 80 m, his conclusion was certainly based on data supplied by the geological department.
I wish to add that it is highly unlikely that the presence of tin minerals in the Neves – Corvo ore would have remained undetected by the SFM for so long: any mineral capable of causing a significant change in the expected density of the cores would have been detected almost immediately.
Cassiterite – with its abundance and high density – is a case in point. In fact, the SFM had long been aware of the considerable advantages.
of determining core densities as a matter of routine. It was the practice of the SFM to measure the density of all cores, not only to provide explanations for gravity anomalies but also to detect minerals of potential interest that may occur as fine disseminations, mainly within dark matrices, and which might be difficult to identify macroscopically. This approach proved to be very successful.
I would also like to inform Dr. C.J. Morrissey that political events in Portugal in 1974 and some subsequent years did not significantly influence tha attitudes of foreign companies involved in exploration programmes under contract to the Portuguese Government. No Company left Portugal on account of the course political events were taking. On the contrary, other foreign companies - Riofinex among them – showed strong interest in coming to Portugal, although it must be admitted that such interest was not welcomed by the Government.
On the other hand, if the country’s political evolution had little effect on the attitude taken by foreign companies to prospecting in Portugal, it certainly had very adverse consequences for the efficiency of the SFM. Indeed, it is because of the notorious weakening of the SFM after the Revolution that articles like Leca’s are possible, not to mention several others that contain serious distortions of the history of the Neves – Corvo discovery.
In summary, I must say that I concur fully with the emphasis given by the author to the fundamental role played by geology to the Neves – Corvo discovery. I am referring, of course, to the SFM’s geological surveys,. which provided the original justification for its own gravity surveys and for the drilling later carried out by the Association. So far as the Association’s geological surveys are concerned, without impugning their quality it has to be said that the highly regrettable dogmatism evident in their interpretation (on which see, for instance, Joralemon, quoted by Mc Kinstry (4) delayed the eventual discovery by at least five years. Such a conclusion emerges very clearly from a reading of the account that Leca has given.
References:
1 – Rocha Gomes A. A. and José da Silva F. Prospecção de pirites no Baixo Alentejo. Estudos Notas e Trabalhos Serv. Fom. Min. 10, n.º 1-2 1955, 32 -77
2 – Albouy L. et al Le gisement de sulfures massifs polyméttaliques de Neves . Corvo (Baixo Alentejo), Sud Portugal. Chron. Rech. Minière n.º 460, May-June 1981, 5-27.
3 – SMITH R A. Some depth formulae for local magnetic and gravity anomalies.; some formulae for interpreting local gravity anomalies. Geophys. Prospect.,7, 1959, 55-63, 1960, 607-13.
4 – Mc Kinstry H. E. Mining Geology (Englewood Cliffs, N.J. Prentice- Hall, 1948), 203
No próximo post, incluirei a reacção de Leca a estes comentários.
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