Henriques, P. F.

Lucas Pinto, J.

Oliveira, Daniel P. S. de

Sousa, P. J. O.

Repositorio da Universidade da Coruña

Caderno Lab. Xeolóxico de LaxeCoruña. 2004. Vol. 29, pp. 237-246Will the compass go the way of the dinosaurin Traverse lay out for regional explorationprogrammes?¿Le pasará a la brújula como al dinosaurioen las descripciones geológicas de los programasde exploración regional?DE OLIVEIRA, D. P. S.1; SOUSA, P. J. O.2; HENRIQUES, P. F.3;LUCAS PINTO, J.4AbstractAn investigation of the methodologies of using compass laid-out andGPSr laid-out traverses for regional exploration programmes isinvestigated in this work. Both advantages and disadvantages of bothmethods are discussed and a case study is presented. We conclude thatin all likelihood that the compass will become obsolete in regionalexploration programmes.Key words: Compass, handheld GPS station, regional exploration.CAD. LAB. XEOL. LAXE 29 (2004)Daniel P. S. de Oliveira et al.238(1) Instituto Geológico e Mineiro; (Departamento de Prospecção de Minérios Metálicos), Apartado 7586,2721-866, Alfragide; Portugal(2) Instituto Geológico e Mineiro; (Departamento de Prospecção de Minérios Metálicos), Apartado 104,7801-902 Beja, Portugal(3) Instituto Geológico e Mineiro; (Departamento de Prospecção de Rochas e Minérios Não Metálicos),Apartado 7586, 2721-866 Alfragide, Portugal(4) Instituto Geológico e Mineiro; (Departamento de Prospecção de Minérios Metálicos), Apartado 7586,2721-866 Alfragide, PortugalCAD. LAB. XEOL. LAXE 29 (2004) Will the compass 2391. INTRODUCTIONThe Instituto Geológico e Mineiro (IGM)and some precursor institutions, namelythe Direcção Geral de Geologia e Minas, areclosely linked to a rich history of mineralexploration both nationally and in the formercolonies.Generally, the start of regionalexploration programmes for metallicminerals involves the collection of streamsediment, rock chip, water and soil sam-ples where previous geochemical datais not available. This may well be lin-ked to geophysical data gathering de-pending on the terrain and nature of orebodies in question (e.g. Iberian PyriteBelt).The location of stream sediment, rockand water samples is largely dictated byexisting topographic and geomorphologicterrain features. However, soil samples canbe collected anywhere where a reasonablesoil profile is developed in regions of pooroutcrop. Soil sampling has, therefore, to becarried out in a systematic pattern so as totest the area in question as well as test theunderlying lithologies. Therefore, the bestway to undertake this is to carry out soilsampling traverses, in single lines, to testpotential areas generally or grids to testareas in more detail.This paper briefly outlines the methodo-logy used in general regional explorationwith compass laid out traverses or grids andcontrasts that same methodology with usingGPS receiver that makes use of the U.S.Global Positioning System to lay outtraverses or grids. The advantages anddisadvantages of each method are discussed,and finally a case study is presented.2. WHAT IS GPS?The Global Positioning System (GPS) isa Global Navigation Satellite System (GNSS)made up of a network of 24 satellites placedinto an approximately 20 000 m-high orbitabove the earth by the U.S. Department ofDefence. GPS was originally intended formilitary applications, but in the 1980’s, thegovernment made the system available forcivilian use. GPS works in any weatherconditions, anywhere in the world, 24 hoursa day. There are no subscription fees or setupcharges to use GPS (www.garmin.com/aboutGPS/).Today there are two GNSS’s in operation;the previously referred to GPS (U.S. GlobalPositioning System) and the RussianGLONASS (GLObal NAvigation SatelliteSystem), both of which are military systems.These systems are constantly being upgradedto meet higher standards of reliability. Athird GNSS, a civil system named GALI-LEO, is currently being developed in Europeto specifically provide a higher standard ofintegrity and reliability, required to ensurethe safety of lives during transport by air,land and sea. This system is scheduled tocome on line between 2006-2008 (http://europa.eu.int/comm/dgs/energy_transport/galileo/index_en.htm).2.1 How it worksGPS satellites circle the earth twice a dayin a very precise orbit and transmit signalinformation to earth. GPS receivers (GPSr’s)take this information and use triangulationto calculate the user’s exact location.Essentially, the GPSr compares the time asignal was transmitted by a satellite withthe time it was received. The time differenceCAD. LAB. XEOL. LAXE 29 (2004)Daniel P. S. de Oliveira et al.240tells the GPSr how far away the satellite is.With distance measurements from moresatellites, the receiver can determine theuser’s position and display it on the unit’selectronic map.A GPSr must be locked on to the signalof at least three satellites to calculate a 2Dposition (latitude and longitude) and trackmovement. With four or more satellites inview, the receiver can determine the user’s3D position (latitude, longitude andaltitude). Once the user’s position has beendetermined, the GPS unit can calculateother information, such as speed, bearing,track, trip distance, distance to destination,sunrise and sunset time and more(www.garmin.com/aboutGPS/).2.2 How accurate is GPS?GPSrs are extremely accurate, thanks totheir parallel multi-channel design. Thenow common 12 parallel channel receiversare quick to lock onto satellites when firstturned on, and they maintain strong locks,even in dense foliage or urban settings withtall buildings. Certain atmospheric factorsand other sources of error can affect theaccuracy of GPSr’s. On average, the availableGPSr’s are accurate to within 15 meters.Satellite-Based Augmentation SystemsNewer GPSr models with Satellite-BasedAugmentation Systems (SBAS) capabilitycan improve accuracy to less than threemeters on average. While the GNSSnetworks are being developed to achievemaximum performance, SBAS have beenestablished to provide improved accuracy,providing differential signal corrections forGPS and GLONASS transmissions.SBAS are networks of ground relaystations and geostatic satellites designed toreceive satellite navigation signals andtransmit corrected time and distance mea-surements that greatly improve accuracy.Observation and relay stations have been setat known positions all over the world, whiletheir geostatic satellites continuouslymaintain a fixed position above the Earth.Using these known values for distance, SBAScorrects satellite navigation signals foratmospheric delays, incorrect satellitepositioning and poor geometry, sometimescaused by inline or close alignment ofsatellites, increasing accuracy in specificregions. Using the same signal frequenciesas satellite navigation, SBAS-enabledreceivers are inter-compatible.Three augmentation systems arecurrently in varying stages of operation anddevelopment covering North America(WAAS - Wide Area AugmentationSystem), Europe (EGNOS - EuropeanGeostationary Navigation Overlay System)and Asia (MSAS - Multifunctional TransportSatellite-based Augmentation System). Theincredibly accurate positioning capabilitiesof SBAS are already being used in mining,agriculture, development and many otherindustries as well as hiking, boating,hunting, travel and an expanse of otherleisure and business activities in NorthAmerica. The European system, EGNOS, isscheduled for full operation in 2004 andrepresents the first step toward Europe’sGALILEO global satellite navigationsystem. MSAS is scheduled for full operationin 2005 and will expand safety and air-traffic capacity in the Asia pacific regions(http://www.thalesnavigation.com/en/products/aboutgps /augmentation.asp).CAD. LAB. XEOL. LAXE 29 (2004) Will the compass 241Differential Global Positioning SystemUsers can also get better accuracy withDifferential Global Positioning System(DGPS), which is a system designed toimprove the accuracy of Global NavigationSatellite Systems by measuring infinitesimalchanges in variables to provide satellitepositioning corrections.Two or more receivers observe the sameset of satellites, taking similar measure-ments that produce similar errors whenpositioned closely together. A referencereceiver, placed at a known location,calculates its theoretical position and com-pares it to the measurements provided bythe navigation satellite signals. Thedifference between the two values revealsthe measurement error. The referencereceiver then transmits a corrected signal toany number of receivers at unknownpositions within the area covered by theDGPS. Accuracy of global satellitepositioning is thereby increased from 15meters to within a few meters. This techniquecompensates for errors in the satellitenavigation system itself but may not alwayscorrect errors caused by the localenvironment when satellite navigationsignals are reflected off of tall buildings ornearby mountains, creating multi-pathsignals. The accuracy of DGPS decreaseswith asynchronous measurement caused byspatial and temporal error decorelation whenthe system receivers are set at greaterdistances apart.The most sophisticated DGPS techni-ques can increase positioning accuracy towithin a few millimeters. Raw measure-ments recorded by the reference receiverand one or more roving receivers can beprocessed using specially designed softwarethat calculates the errors. The correctionsmay then be transmitted in real time or afterthe fact (post-processing). By applying thecorrections and recalculating the position,accuracy from within several meters to withina few millimeters is achieved, depending onthe specific methodology used and thequality of the real-time data link (http://www.thalesnavigation.com/en/products/aboutgps/dgps.asp).3. METHODOLOGY FOR REGIONALEXPLORATIONGenerally, any exploration programmestarts with a target area and very clearobjectives for that area as well as a reasonablygood understanding of the geologicalconditions of the area.Once these parameters are known andtarget areas delimited, the best way to testthe area in question is to undertake soilsampling traverses over large distances, withwidely spaced samples (e.g. 100 m), to testlarger areas or grids to test in greater detaila smaller area.Traverses or grids are initially sited giventhe local geological and geomorphologicalconditions of the terrain and are initiallyplotted on a map. These lines have tosubsequently be transferred from the mapinto the field.For the purpose of discussion and me-thodology, we will no longer distinguishbetween traverses and grids since the one isa composite of the other, and the methodo-logy of carrying out a traverse or a grid in thefield is simply that one has more traverses atright angles to each other.CAD. LAB. XEOL. LAXE 29 (2004)Daniel P. S. de Oliveira et al.2423.1. Traditional compass methodo-logyThe start point of the traverse has to befound in the field using map data coupledwith visual characteristics of the terrain.Once this point is found, set up of a sightingcompass, preferably tripod-mounted forstability, can now begin. Azimuth of traverseis taken with the compass and traverse layout can begin. From the start point a memberof the team will walk out a measured distanceand plant a sighting staff. The placement ofthis sighting staff is determined by thecompass operator that will direct thedirection the traverse given the deviation tothe left or right of the sighted azimuth. Asecond member of the team with a secondsighting staff will then leapfrog the firstsighting staff and line the second staff up ata measured distance until the desired secondpoint of sampling/measurement is reached.This leapfrogging action continues untilthe whole traverse is marked in the field. Inthe case of grids, the use of an optical squareis required to sight traverses at right anglesto each other. If this is not available, thenfield personnel must resort to thePythagorean Theorem to resolve traverselines.This method works well in flat and clearterrain but problems arise in hilly, heavilyvegetated or woody terrain. In the case ofhilly terrain, measurement between pointsor sighting staffs has to be carried out in aline projected above the terrain on a flatsurface and not parallel to terrain dip so thataccurate distances are measured. In terrainwith dense vegetation, the vegetation has tobe cut so that visual contact can bemaintained between compass and successivesighting staffs. However, in terrains whereobstacles are present in the line of traverse,the traverse line has to be deviated to the leftor to the right of the obstacle and thenbrought back to the original line (Fig.1).Fig. 1. Hypothetical soil sample grid lay out. Shown in grey are the offsets characteristics of aconventional compass-laid grid pattern to overcome line-of-sight obstacles.CAD. LAB. XEOL. LAXE 29 (2004) Will the compass 243Advantages of the compass method:1. Relative accuracy in flat, obstacle-free terrains with easily recognisablelandmarks;2. Ease of use.Disadvantages of this method:1. The set up of the starting point in thefield can be out by as much as a 100 m dueto comparison of map and terrainsgeomorphology;2. Time consuming and expensive;3. Labour intensive since one memberis always needed to sight the compass and atleast two to leapfrog each other with sightingstaffs;4. Errors in measurement betweensampling points can be induced due touneven terrain;5. Poor accuracy in flat, obstacle-freeterrains with no easily recognisablelandmarks;6. Measurements using tape measureshave to be carried out in short intervals toprevent tapes becoming concave andinducing in measurement errors;7. Equipment intensive (compass,tripod, sighting staffs, tape measure/s, ma-chetes + sampling equipment).3.2 GPSr methodology-In this section the use of handheld GPSstations with waypoint and navigatecapabilities are investigated. These types ofGPS stations/receivers are ideal for traverselay out in the field.This methodology needs the same carefulplanning and selection of target areas as theprevious method. When traverses are plottedon a map, the starting point and end pointcoordinates of these must be obtained forevery traverse to be carried out.Once in the field, the starting point ofthe traverse can be accurately determinedusing the GPS station by walking the gene-ral area of the start point until map-extractedcoordinates and field obtained coordinatesmatch, or navigating to the start point froma random, close by point. Once the startingpoint is found, the GPS can be programmedto follow a specific route that will follow thetraverse line. This is done by entering theend point coordinates and selecting thenavigate function on the GPS station. TheGPS will compute distance and directionbased on the two sets of start and endcoordinates. Measurement is taken as aprojected horizontal line above the terrain,and distances are simply read off as onewalks the traverse. The GPS will warn ofdeviations from the intended traverse andcorrections can be carried out systematicallyin the field with little trouble. With the useof the GPS it is far easier to overcomeobstacles some of which may be walked overor simply contoured since there is no need tokeep the starting or intermediate points invisual contact.Advantages of the GPSr method:1. Ease of use;2. Fast and cheap;3. Relatively precise depending on mapscale at which the work is carried out;4. Not labour intensive;5. Ease of use in the way of obstacles;6. Not equipment intensive;elimination of the compass, tripod, sightingstaffs and tape measures;CAD. LAB. XEOL. LAXE 29 (2004)Daniel P. S. de Oliveira et al.2447. Very accurate to determine thestarting point of the traverse;8. Ease of integration in GIS softwarepackages.Disadvantages of the GPSr method:1. Large trees with extensive foliagewill hinder communication between theGPS station and satellites;2. Relative precision of GPS stationscan induce in errors less than 15 m. However,on a 1:25000 map scale even this error isinsignificant. This error can be substantiallyreduced if two GPS stations are used inconjunction, one stationary and the othermobile (Differential GPS).4. A CASE STUDYDuring the course of a regionalexploration programme for gold associatedFig. 2. Simplified excerpt of the 1:25000 Military Topographic sheet 79 (Morais) showing the soilsampling grid undertaken south of Izeda in the Morais Massif. Shown is the close correlation obtainedbetween projected sampling points and GPS obtained sampling point. Deviations from this correlationare observed occasionally due to natural geological and geomorphological occurrences.CAD. LAB. XEOL. LAXE 29 (2004) Will the compass 245with platinoids in the Trás-os-Montes region(de Oliveira, 2003), more specifically 4 kmS of Izeda in the Intermediate AllochthonousOphiolitic Complex (Pereira et al., 1998;2000), of the Morais Massif (NE Portugal),a 100x100 m soil sampling grid was set upusing a handheld GPS station. In thenorthern part of this grid, this distance washalved (Fig. 2) to obtain greater resolutionnear thrust planes.Here the terrain is gently undulating inthe north and hilly in the south of the gridand characterised by dense 1 to 2 m highbrush throughout as well as clumps of treesin the north.A total of 290 samples were collected inthis region. Total time of collection, over24500 m of traverses, totalled 12.5 workingdays (8 working hours/day) using a handheldGPS station. In contrast, it is estimated thatusing compass laid out traverses, each 1500m traverse would take 5 working days tocomplete given the terrain and vegetationcover characteristics. Therefore, the 24500m of traverses laid out in the Izeda areawould have taken an estimated 82 workingdays given no setbacks, i.e. a time saving of85% has been obtained by using thehandheld GPS station. Furthermore, thelocation of the GPS laid out sampling pointsare centred within a 20 m circle of theprojected sampling point (large circles inFig. 2). Deviations from this pattern occurnot due to errors in GPS-obtainedcoordinates but due to geological andgeomorphological terrain characteristics,e.g. outcrops, sub outcrops and flood plainsof streams.5. FINAL NOTESWe have shown that the use of the GPSrin the lay out of a grid used for a regionalexploration programme was undertaken andcompleted in a fraction of the time that itwould have taken using conventionalcompass methods. Time and, mostimportantly, money were saved. As theGNSS technology becomes ever moreaccurate, cheaper and GPSr’s are easier touse, it is our opinion that with respect to theoriginal question asked in the title of thiswork, the answer is a resounding YES!6. ACKNOWLEDGEMENTSThis work was a spin off from the CYTED(Ciencia y Tecnologia para el Desarrollo)Project XIII.1 “Desenvolvimento de Guias deProspecção de Metais Preciosos em ComplexosOfiolíticos” and has benefited from manydiscussions with friends, colleagues andformer colleagues that are and were involvedin exploration programmes. Our thanks goto all of them.Recibido: 22-3-2004Aceptado: 10-7-2004CAD. LAB. XEOL. LAXE 29 (2004)Daniel P. S. de Oliveira et al.2467. REFERENCESDE OLIVEIRA, D. P. S., 2003. Development ofexploration guides for precious metals in ophiolitecomplexes: Final report on the work carried out inthe Morais ophiolite complex (Trás-os-Montes),NE Portugal. Instituto Geológico e Mineirointernal report, 84p.http://www.garmin.com/aboutGPS/http://www.thalesnavigation.com/en/products/aboutgps/http://www.thalesnavigation.com/en/products/aboutgps/augmentation.asphttp://www.thalesnavigation.com/en/products/aboutgps/dgps.aspGALILEU: http://europa.eu.int/comm/dgs/energy_transport/galileo/index_en.htmPEREIRA, E., RIBEIRO., A. e SILVA, N., 1998.Carta Geológica de Portugal, Folha 7-D (Macedode Cavaleiros), Instituto Geológico e Mineiro.PEREIRA, E., RIBEIRO, A. e CASTRO, P., 2000.Notícia Explicativa da Folha 7-D Macedo deCavaleiros, Instituto Geológico e Mineiro, 63p.

Will the compass go the way of the dinosaur in Traverse lay out for regional exploration programmes?

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Will the compass go the way of the dinosaur in Traverse lay out for regional exploration programmes?

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