Em fins de 1991, foi-me chamada a atenção para novo artigo de Delfim de Carvalho, intitulado “A CASE HISTORY OF THE NEVES – CORVO MASSIVE SULFIDE DEPOSIT, PORTUGAL, AND IMPLICATIONS FOR FUTURE DISCOVERIES”, desta vez, publicado em “Economic Geology Monograph 8 – Historical Perspectives of Genetic Concepts and Case Histories of Famous Discoveries”.
Grande foi a minha decepção por ver novamente apresentado, em terra estranha, e agora, por um português investido em elevado cargo na Administração Pública, um raro caso de prospecção mineira, sem o respeito que era devido aos seus principais promotores.
Além de omissões e deturpações que se me afiguram intencionais, há erros que, embora indesculpáveis, são apenas fruto de escassa preparação do autor em matéria de prospecção mineira, mormente no âmbito das técnicas geofísicas.
Acerca deste artigo que motivou expressivo louvor ao seu autor, com publicação no Diário da República N.º 257 – II série, de 8-11-1991, fiz os seguintes comentários, que enviei a “Economic Geology” para publicação, em 15 de Janeiro de 1992:
“The discovery of Neves – Corvo deposit has originated a great interest to the international mining community, owing not only to the huge reserves that are being revealed, as the exploration work proceed, but also to the high contents of copper, tin, lead and zinc, in important parts of the deposit, with emphasis to the unforeseen presence of tin.
It is regrettable, however, that the history of the discovery is being described with the omission of essential achievements and without care about the reliability of the consulted information.
Very recently, I felt obliged to make corrections to a paper by Xavier Leca, published in Vol. 99 of “Transactions of the Institution of Mining and Metallurgy, Applied Earth Section, September – December 1990 B 139-52”. Most of what I wrote, then, adjusts well to this paper by Delfim de Carvalho. Leca and Delfim de Carvalho, although quoting the activity of Serviço de Fomento Mineiro (SFM), i.e., the Portuguese State Department responsible for the actions towards the inventory of the country mineral resources, deliberately belittled its contribution for the discovery.
THE TRUTH, WHICH OUGHT NOT TO BE CONCEALED. IS THAT THE DISCOVERY IS DUE ALMOST EXCLUSIVELY TO THIS PORTUGUESE STATE DEPARTMENT.
THE INTERVENTION OF THE ASSOCIATION FORMED BY THE “SOCIEDADE MIMEIRA DE SANTIAGO (SMS), THE “SOCIÉTÉ D’ÉTUDES, DE RECHERCHES ET D’EXPLOITAFIONS MINIÈRES” (SEREM) AND BY THE “SOCIEDADE MINEIRA E METALÚRGICA DE PEÑARROYA PORTUGUESA (SMMPP) WHICH WAS BROUGHT ABOUT BY THE INOPPORTUNE ADJUDICATION MADE BY THE PORTUGUESE GOVERNMENT OF THE AREA IN WHICH THE DEPOSIT IS SITUATED, HAD THE CONSEQUENCE OF A MINIMUM OF FIVE YEARS DELAY IN THE DISCOVERY. MOREOVER, THIS ADJUDICATION WAS MADE WITHOUT PREVIOUS CONSULTATION TO SFM AND WHEN THE GRAVITY ANOMALY, WHICH IS THE SIGNATURE OF THE DEPOSIT, HAD ALREADY BEEN PUT IN EVIDENCE AND HAD EVEN BEGUN TO BE INVESTGATED.
The Association demonstrated lack of experience in mineral prospecting and some of its technicians have been misleading the international community, by transforming, what I consider, serious errors into geologic successes.
The history of this discovery is extremely simple and it is not necessary to appeal to profound geological lucubrations or to sophisticated geophysical methods to describe it.
The geological surveys of SFM, supported on maps at a scale 1:5.000, notwithstanding its preliminary character, were sufficient to classify the Almodôvar zone, where the discovery happened, as a top priority target area. That was the reason why, within an area of about 4.000 sq. km, SFM selected a portion of 28 sq. km for investigation by the gravity method, as soon as that area became available for its actuation. As a result of this gravity survey, a very extensive anomaly of an amplitude higher than 1.4 mgal (not 0.4 or 0.6 mgal, as erroneously is being described). It would have been enough to investigate the cause of this anomaly to immediately find the deposit! Leaving such a remarkable anomaly without explanation, for more than five years, was a mistake that the Association ought to have recognized.
By reading this paper, I became aware that the Association has even put in doubt the reliability of the gravity surveys, because the results did not fit its geological interpretation ( pág 327 …During these discussions, the reliability of the gravity data was debated …).
When I read the astonishing statement that “on the evening before the mineralisation was encountered, the geologist at the drill site, in despair, nearly decided to terminate the drill hole”, I am induced to believe that, even at the terminal phase of its activity, the Association persisted ascribing a very low weight to the gravity results.
From the history narrated by Delfim de Carvalho, one could thus arrive at the conclusion that the discovery of Neves – Corvo deposit was accidental, and that if the Association had not achieved it, the deposit would still remain untouched.
Depths of 300 m, which are now surprising Delfim de Carvalho, because they proved to be of economic interest and accessible to the prospecting techniques, did not intimidate SFM, since long ago. Delfim de Carvalho, who belonged to the group of technicians headed by myself, although he had a small participation in the activities within the Pyrite Belt of Alentejo, with the exception of Cercal – Odemira Region, where according to my instructions he was supposed to improve geological surveys executed much before he joined SFM, ought to remember, at least, the success of Estação, achieved in due time, in circumstances somewhat similar to those of Neves – Corvo, with the difference that in this case we did not loose 5 years. Estação orebody was discovered, in February 1968, at a depth of 350 m, after great technical difficulties, which caused strong pressures from headquarters in Lisbon to terminate the drill hole before reaching the projected depth. In this case, persistence was rewarded. We never accepted to terminate the drill hole, before an explanation was obtained for the gravity anomaly which was being investigated, although it reached, at its maximum, only the value of 0.4 mgal.
Delfim de Carvalho should not have forgotten bore hole n.r 1 of Salgadinho, drilled by SFM, in Cercal – Odemira region, mainly on the grounds of a gravity anomaly and not of hydrothermal alterations, as he erroneously has been affirming, reached, by August 1974, the depth of 573 m, i. e. the limit of the drill-rig, without supplying an explanation for the anomaly being investigated. The fact that I was dismissed in January 1975, at the light of the revolutionary turmoil, from the mineral prospecting activities in Southern Portugal, of which I have been the main promoter, rendered it impossible for me to resume the work.
I could quote other examples, but I do not want to leave without comment that this conclusion by Delfim de Carvalho, following Neves – Corvo discovery, is in full disagreement with what he wrote in another paper, see page 20 of GEONOVAS – Vol. 1 – Nr. 3 Pirites – Novos rumos para a prospecção).
Delfim de Carvalho demonstrates full disrespect for elementary ethics. Not having participated either in the works of SFM in Almodôvar Region, or in the subsequent activities of the Association, he was not qualified to write about the subject. I wonder whether he had the legal authority to write this paper, since it was supported almost exclusively on studies, published or not, by other authors. He should, at a minimum, have been much more careful in the reproduction of the data he managed to consult.
Besides the errors already mentioned, I am going to refer several others also present in the paper.
1 – The importance of the Pyrite Belt of Alentejo was not duly appreciated, only after Neves – Corvo discovery! It is a great injustice and even an outrage to the memory of SFM founders, not to recognize that this Institution always had full perception of the Pyrite Belt potential. SFM dedicated to the Belt a constant attention, since early the 40’s and not since the end of this decade, as Delfim de Carvalho writes. Delfim de Carvalho did not read carefully the paper of which I am the main author, entitled “Prospecção de Pirites no Baixo Alentejo”, published in 1955 in “Estudos, Notas e Trabalhos do Serviço de Fomento Mineiro,Vol. 10, Fasc. 1 e 2”. Furthermore, Delfim de Carvalho only now begins to quote it in the bibliography, though he largely used the information there contained and also claimed to be the author of some studies included in this paper. In fact, in previous papers on the same matter, he forgot to mention it. Had he read it carefully, he would not be so much surprised with Neves – Corvo success and would interpret it as a logical consequence of the methodical accomplishment of the prospecting program there explained, rewarding the efforts developed during several decades. Even the richness in copper was foreseen! (see pages 67 and 68 of the paper).
Estação and Gavião orebodies had already been previous consequences of the same program and I take this opportunity to correct the affirmation that Gavião orebodies were discovered by SMS. In reality, SMS only had to investigate with bore-holes the gravity anomaly detected by SFM and already interpreted as corresponding to the part of Aljustrel deposit displaced by the great tectonic accident known as the Messejana Fault. Even Albouy, L. N. Conde , F. Foglierini, X. Leca, A. Morikis, L. Callier, P. Carvalho and J. G. Songy knew this! (See page 10 of the paper by these authors published in nr. 460 – 1981 of “ Chronique de la Recherche Minière”, under the title “ Le gisement de sulfures massifs pollymétaliques de Neves – Corvo.
Os comentários N.ºs 2 a 8 serão objecto do próximo post.
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