Remote sensing and mineral exploration

Remote sensing and mineral exploration


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Du 12 au 14 mai 1982, un colloque a ete conjointement organise a Montreal (Canada) par 1’Association Quebecoise de tel&l&ection et la So&e Francaise de Photogrammetrie et de Ttl&lCtection, sur les perspectives d’avenir que laisse entrevoir le lancement prochain en 1984 du satellite francais d’observation de la Terre, SPOT. Plus prttcisement, les objectifs Ctaient d’une part, de sensibiliser les communautes scientifiques canadiennes et francaises aux possibilites des satellites d’observation de la Terre de la deuxieme generation, d’autre part, d’amener les utilisateurs potentiels dcs donnees transmises par ces satellites a debattre de leurs apports et de leurs limitations a partir des premiers resultats des programmes de simulations realisb tant en France qu’au Canada. Ces debats se sont d&rot&s dam le cadre de quatre ateliers consacres a la cartographic, a la for&, a l’agriculture a la vegetation et a l’hydrologie. Cette manifestation a reuni une centaine de participants. Pour beaucoup d’entre eux elle a permis la poursuite d’echanges outre atlantique amorces un an plus tot a Montreal od s’ttait egalement derouli: un premier colloque sur l’utilisation de la prochaine generation de satellites d’observation de la Terre. La publication (315 pages dont 42 pages d’illustrations noir et blanc et 8 pages couleur) reunissant les communications et les comptes rendus des ateliers, est disponible aupres de la SociCtCFrancaise de PhotogrammCtrie et de Tel&detection, 2 avenue Pasteur, 94160 Saint-Mande. Prix 250 F.


COSPAR Conference, Ottawa, Canada, 17 May-2 June 1982 by S. Ringrose (with additions by W. D. Carter and L. C. Rowan) Over 1000 scientists involved in all aspects of space research gathered in Ottawa in late May and early June 1982 to attend the 24th Plenary Meeting of COSPAR, the ICSU Committee on Space Research. Among the many technical sessions was a 4% day symposium entitled “Remote Sensing and Mineral Exploration: National Case Histories based on IGCP Project 143”. This was cosponsored by IGCP, COSPAR, URSI, AGID and IUGS, and marked the termination of IGCP Project 143. It was attended by nearly 100 scientists from 18 countries. (“Extract from La Lettre du CNES No. 83 of 25 October 1982. “‘Extract from Episodes, Volume No. 3 of October 1982.


The symposium was opened by C. C. Weber, IUGS Secretary General, who congratulate the project co-leaders and s~~siurn organizers, W. D. Carter and L. C. Rowan. He referred to the project as one of the “most fruitful” of IGCP, and noted the similarity between the aims of the project and those of IUGS. Dr. Weber pointed out that although remote sensing techniques are in routine use in many geological research and exploration programmes, they are clearly not the geological exploration panacea of the early literature. No one now assumes that the use of multispectral imagery will automatically lead to the discovery of oil, gold or copper. “Geological remote sensing has grown up”, he said, and has taken its proper place among other t~h~qu~ for geological mapping and exploration. Dr. Weber stated that “the most important evolution in the geological use of remote sensing belongs to the immediate future” when new higher resolution satellites are to be launched. Landsat D, with a r~olution of 30-40 m, was put into orbit on 16 July 1982, and in 1984 the French Space Agency will launch SPOT with a resolution of lo-20 m and stereoscopic coverage. During the symposium there was much discussion on the structural relationships of ore and petroleum deposits. J. Kutina (USA) in a discussion of deep crustal fractures, showed how he had discovered a polymetallic deposit in Nevada. Other contributions dealt with regional structure mapping, and the recognition of continental-scale linear and circular features in North America, India, China, Eurasia, Spain, Nepal and Bulgaria. Although considerable headway has been made in the area of regional structural mapping, the significance of these features is only vaguely understood. In considering spectral m~uremen~ of rocks and alteration zones, M. H. Podwysocki, D. B. Segal and 0. D. Jones (USA) evaluated data from NASA’s airborne Thematic Mapper Simulator, designed to simulate the bands obtained from Landsat D. Three band ratios have proved particularly useful in identifying terrestrial features: 1.65/2.22 pm for alunite and kaolinite, as well as minerals with a high water content and foliage; 1.65/0.49 for limonitic minerals, and 066’0.83 for vegetated areas because of high chorophyll absorption. M. Settle and J. V. Taranik (USA) described NASA’s current and planned research. A project mission known as Gravsat/Mag~t, scheduled to be launched in the late 198Os,will be the first satellite mission to perform a simultaneous survey of the earth’s gravity and magnetic fields at low orbital altitudes, It will measure the gravity field strength to an accuracy of one milligal and the magnetic field strength to 2-5 gammas over a distance of about 100 km. D. Hastings from the EROS Data Center (USA) described the synthesis of remotely sensed geophysical and terrain data by manual and digital techniques. The fatter require the establishment of an entire database in digital format. Data elements may be derived from topo~aphic, geologic and soils maps, as well as from aeromagnetic, radiometric, electromagnetic, geochemical and Landsat surveys. These can be computer adjusted,, registered and compared in any 4

combination, but the value of such information to mineral exploration has yet to be widely tested in North America. Similar studies in Australia by J. Huntingdon and G. O’Sullivan show that this technique has considerable promise as an exploration tool. W. D. Carter reviewed the digital method of producing Landsat mosaics and provided some justification for going ahead with a digital image mosaic of the North American Plate as part of the DNAG project. Whether this will be constructed is still in doubt in the face of increasing costs and declining budgets. In a session devoted to vegetation, geochemistry and ore discovery, D. N. H. Horler, J. P. Barber, J. P. Darth, D. C. Ferns and A. R. Bar-ringer (UK) reported that reflectance measurements of plants treated with various concentrations of metals (Cd, Cu, As, Sn, Pb) were closely correlated with a blue shift in the wavelength of the observed spectrum edge of chlorophyll absorption. They suggest that such measurements may be able to distinguish subtle environmental effects better than other forms of spectral reflectance. M. M. Cole (UK) reported on the enhancement of Landsat data (contrast stretch and rotation) for mapping of mineralized zones in Australia and China. Landsat interpretation led to the recognition of “dark areas” which were found upon field examination to contain lead gossans and banded ironstones with varying amounts of Fe, Zn, Cu and MO. Other “dark areas” were associated with laterite and serpentinite outcrops. His research underlined the value of Landsat imagery for locating prospective targets for mineral exploration. J. R. Belanger and A. N. Rencz (Canada) integrated airborne and Landsat multispectral scanner data to map the glacially related mineral dispersal train of the Thetford Mines area in Quebec, Canada. They were able to correlate anomalous reflectance of vegetation with the enrichment of heavy metals in soils. An unsupervised enhancement of Landsat imagery showed tonal discontinuity caused by vegetation differences related to metal-enriched soils. The symposium had one major omission, namely the lack of speakers or representatives from the Third World with the main exception of India. In a few cases, Third World areas were discussed, but little work has been done in areas where rapid inventories of mineral and other resources are urgently required. Landsat imagery can readily provide the tools for basic mapping, mineral location, and to a certain extent mineral identification. Yet it appears that this kind of effort is not being made at the present time. Instead, large areas of North America and the USSR are being mapped, compiled and recompiled, overlaid and digitized, while much of the Third World goes unnoticed. Yet there are available several years of Landsat data stored in the EROS Data Center and elsewhere, covering all parts of the Earth, including the Third World. The extent and quality of these data will shortly be improved as satellites capable of producing higher resolution imagery are sent into space. It is incumbent upon resource-oriented scientists everywhere to use as much of this information as possible so that inventories of resources, terrain conditions and land use change can be made as effectively and expeditiously as possible. 5

At the close of the symposium there was a brief discussion on the possible follow-up to IGCP Project 143 due to terminate at the end of 1982. As W, D. Carter said in his closing remarks, “this project has really been about communication”. Suggestions were made for an institute of global metallogeny, for a link with the Geosat programme, and for a new IGCP project under new leadership. Although no one ~ohmteered immediately to play such a role, several participants indicated they would consult their national IGCP committees. Another alternative would be to seek a semi-permanent home for the project under COSPAR, This possibility is now being considered as COSPAR is anxious to increase participation by deveIoping countries in its research activities. 1.3. COMPTE-RENDWDU COLLOQUE INTERNATIONAL



Toulouse, 30 aoBt-2 septembre 1982 Du 30 aofit au 2 septembre 1982 s’est term au CNES B Toulouse un colloque international sur les anneaux des plan&es, r&missant une centaine de participants parmi lesquels les plus grands sp&cialistes dans ce domaine. Cette r&mion, organist% sous la responsabilitt scientifique de A. Brahic, astronome $t l’observatoire de Meudon et de plusieurs autres scientifiques franeais et &rangers, avait pour but de presenter une synthese des r&&&s scientifiques les plus marquants de l’exploration in sitts des anneaux de Jupiter et de Saturne par les sondes Voyager I et 2 en 1979 et 1981, ainsi que des observations faites depuis la Terre des anneaux d’uranus. Outre de nombre~s~ presentations sur les r&ultats des observations, une session complete a et& consacree B la dynamique des anneaux, en particulier & la structure complexe des anneaux de Saturne. On comprend bien &present certains mecanismes physiques qui agissent dam ces systemes, tels que l’effet gravitationnel des petits satellites ‘“gardiens”, l’effet de la v&co&e et des ondes de densite decouverttes au sein de ces armeaux par les sondes Voyager. On explique ainsi de faGon satisfaisante le confinement des anneaux minces comme ceux d’uranus ou de l’anneau F de Saturne, les curieuses torsades observees le long de ce [email protected] anneau, l’existenee de bords nets, etc. Cependant, malgre Ies progres theoriques r&&b ces deux demi&es arm&s par les chercheurs, la structure des anneaux de Satume demeure largement incomprise, en particulier le “dkoupage” en milliers de zones claires et de zones sombres. Les travaux se ~u~uivent pour tenter de r&soudre ces en&mea. De l’avis unanime, ce colloque s’est revel& d’un tres haut niveau et a permis de presenter des r&&.&.s particulierement interessants et inedits. Les actes de ce colloque seront publies par le Departement des Affaires U~ve~~~r~ du CRIES dans le courant du premier trimestre 1983. “‘Extract from La Lettre du CNES No. 83 of 25 October 1982.