2.1 General Considerations 2 WOLLOMAI PROSPECT 1:1000 SCALE-OUTCROP MAPPING ed-brow Red-beo n小y 100M GRANITE SHALE SANDSTONE LATERITE QUARTZ FLOA WOLLOMAI PROSPECT 1:5000 SCALE-DETAILED REGIONAL MAPPING 0 50 Fig.2.2 How the scale chosen affects the style and content of geological maps of the same are Generalisation is required at all scales.There is no such thing as a"fact"map.However.the component of field observation is greatest in large-scale maps explorationists in most cases cannot obtain a sufficiently large tenement holding to this kind of mappingorth whil Maps wit油 te-range scal es between 1:25,000 and 1:5.000 can be described as detailed regional maps.These are appropriate scales for the first- pass mapping of large tenement holdings.They are also ideal scales to use when
2.1 General Considerations 21 GRANITE SHALE GOSSAN SANDSTONE BASALT LATERITE DOLERITE QUARTZ COLLUVIUM ALLUVIUM QUARTZ FLOAT WOLLOMAI PROSPECT 1:1000 SCALE - OUTCROP MAPPING WOLLOMAI PROSPECT 1: 5000 SCALE - DETAILED REGIONAL MAPPING 100 M Red-brown soils Red-brown soils Red-brown soils sandy soil sandy soil sandy soil sandy soil sandy soil sandy soil spring 60 48 60 55 58 56 85 80 83 80 sandy soil Red-brown soils 1:1000 map area Gossan 65 60 48 52 8 5 8 40 5 10 50 10 48 0 meters 500 N Conglomerate N Fig. 2.2 How the scale chosen affects the style and content of geological maps of the same area. Generalisation is required at all scales. There is no such thing as a “fact” map. However, the component of field observation is greatest in large-scale maps explorationists in most cases cannot obtain a sufficiently large tenement holding to make this kind of mapping worth while. Maps with intermediate-range scales between 1:25,000 and 1:5,000 can be described as detailed regional maps. These are appropriate scales for the firstpass mapping of large tenement holdings. They are also ideal scales to use when
22 2 Geological Mapping in Exploration combining geological mapping with regional prospecting or regional geochemistry (such as stream sediment sampling).At scales in this range,some of the larger features which might have had an effect on the localization of ore are capable of being shown.although the outline of an ore deposit itself could not generally be shown.The intermediate range of map scales is therefore suitable for the control and developr On on of signific ant areas of min tion can be These scales are appropriate for showing the features that directly contro and local ize ore.Maps at these scales are often called outcrop maps and the need to make them generally arises after a prospect has been defined.The purpose of such maps is to identify the size,shape and other characteristics of the potential ore body.The map is then used to help specify,control and evaluate all subsequent programmes of detailed prospect exploration including geophysics.geochemistry and drilling. 2.1.6 Measuring and Recording Structures To fully define and understand the attitude of a planar surface such as a bedding plane,cleavage,joint,vein etc.a geologist needs to know its strike,its dip and the direction of the dip towards one of the principal compass quadrants.Of these measurements,the strike is usually the most important,because it is that which defines the potential continuity of the surface in the horizontal plane of a geological tions rded digit of a drilling program When ed to nalo xxx(the strike)is a 3-digit compass bearing (000-360).yy (the dip)a two digit number representing the angle from the horizontal(00-90)and A is the direction of dip towards a principal compass direction or quadrant(i.e.N.NE,E.SE,S,SW. W or NW).As an example:042/23 NW is a surface with strike of 42 that dips at 23 to the northwest because this method reauires three data fields (strike dir and dip direction)the advent of computer-based databases has lead to a variety of other ways,utilising only two data fields,being employed for digital recording of mea nes.Thes g attitude as dip or as a simple strike and dip with the dip direction qualifier recorded by means of a convention in the way the strike number is expressed.The most common of these conventions is the so-called "right-hand rule.This rule can be explained thus:imagine grasping a strike/dip map symbol with the right hand,palm down and fingers pointing in the direction of dip.The thumb then indicates the strike direction to be recorded.For example:an east-west strike (090-270)with a 60 dip to the north would be recorded as 270/60.A record of 090/60 would indicate the same strike but a dip of 60 to the south. These diff ent methods of recording the attitude of planes are described and e and ve rncombe(1998)
22 2 Geological Mapping in Exploration combining geological mapping with regional prospecting or regional geochemistry (such as stream sediment sampling). At scales in this range, some of the larger features which might have had an effect on the localization of ore are capable of being shown, although the outline of an ore deposit itself could not generally be shown. The intermediate range of map scales is therefore suitable for the control and development of new prospect generation. On maps at scales more detailed than 1:5,000, individual outcrops or outcrop areas and the surface expression of significant areas of mineralization can be shown. These scales are appropriate for showing the features that directly control and localize ore. Maps at these scales are often called outcrop maps and the need to make them generally arises after a prospect has been defined. The purpose of such maps is to identify the size, shape and other characteristics of the potential ore body. The map is then used to help specify, control and evaluate all subsequent programmes of detailed prospect exploration including geophysics, geochemistry and drilling. 2.1.6 Measuring and Recording Structures To fully define and understand the attitude of a planar surface such as a bedding plane, cleavage, joint, vein etc., a geologist needs to know its strike, its dip and the direction of the dip towards one of the principal compass quadrants. Of these measurements, the strike is usually the most important, because it is that which defines the potential continuity of the surface in the horizontal plane of a geological map, or between the adjacent sections of a drilling program. When measurements are recorded digitally (as opposed to analog recording as a strike and dip symbol on a map) the most common traditional way has been in the form of xxx/yy/A, where xxx (the strike) is a 3-digit compass bearing (000–360◦), yy (the dip) a two digit number representing the angle from the horizontal (00–90◦) and A is the direction of dip towards a principal compass direction or quadrant (i.e. N, NE, E, SE, S, SW, W or NW). As an example: 042/23 NW is a surface with strike of 42◦ that dips at 23◦ to the northwest. Because this method requires three data fields (strike, dip and dip direction) the advent of computer-based databases has lead to a variety of other ways, utilising only two data fields, being employed for digital recording of the measured attitude of planes. These involve recording attitude as dip and dip direction, or as a simple strike and dip with the dip direction qualifier recorded by means of a convention in the way the strike number is expressed. The most common of these conventions is the so-called “right-hand rule”. This rule can be explained thus: imagine grasping a strike/dip map symbol with the right hand, palm down and fingers pointing in the direction of dip. The thumb then indicates the strike direction to be recorded. For example: an east-west strike (090–270◦) with a 60◦ dip to the north would be recorded as 270/60. A record of 090/60 would indicate the same strike but a dip of 60◦ to the south. These different methods of recording the attitude of planes are described and discussed in detail in Vearncombe and Vearncombe (1998)
21 General Considerations 3 The attitude of linear structure is measured and recorded as its trend and plunge (see fig.e4).Trend is defined as the horizontal direction or strike of a vertical plan passing thr rough the lin measured in the direction of plur It ing b etween 000 360op vertical plane.A measurement of 76/06 represents a plunge of 76 towards 067.If a lineation lies in a plane,then it can be measured as its pitch on that plane.A pitch is the angle that a lineation makes with the horizontal,measured in the plane that contains the lineation.If the attitude of the plane is also known,then knowing the pitch enables the trend and plunge to be calculated.The simplest way to do this is by means of a stereonet (Fig.D.2). Any computer software used should be capable of accepting and presenting data in all the above formats. 2.1.7 Using Satellite Navigation(GPS) Small,battery-operated,man-portable instruments have been available since the late 1980s to make eof the satellite-based global p ng sy em GPS)Theya on t ny as of field location data n latitude/ongtd gy.Sin ce th or regional me grid co f mo tvalue for fi are marked. ing positio hed map sheet on which these coordinates This makes GPS ideal for regional geological mapping onto pub lished map bases or for regional prospecting and regional and detailed geochemical and geophysical data collection.Observations and sample locations can be quickly recorded against location coordinates and the position of each data point readily found again should that become necessary.In addition,the explorationist can roam aro nd the cou on foo t,by vehicle o or plane,follow evolvin dea nd of the day,the GP S instrument will provide a direct route bac base camp Some limitations in the operation of GPS instruments should be noted however For the most accurate location signal,GPS devices need an unobstructed line of sight to the satellites.At least four widely spaced satellites must be"seen for ar accurate triangulated fix to be computed.This means that GPS will not work well in heavily we oded or forested ar except where large clearings can be found. opraed by the US Depatment of Defence andbe rell cAt C e available GPS system ate coverag oyused grid ct.10.5 se Mercator metrie grid (UTM).A 12H GPS is a hoo ped off in a clearing nle need n fear that the helicopter pilot will not be able to find that particular hole in the canopy again
2.1 General Considerations 23 The attitude of linear structure is measured and recorded as its trend and plunge (see Fig. E.4). Trend is defined as the horizontal direction or strike of a vertical plane passing through the lineation, measured in the direction of plunge. It is recorded as a compass bearing between 000 and 360◦. Plunge is the angle that the lineation makes with the horizontal, measured in the vertical plane. A measurement of 76/067 represents a plunge of 76◦ towards 067◦. If a lineation lies in a plane, then it can be measured as its pitch on that plane. A pitch is the angle that a lineation makes with the horizontal, measured in the plane that contains the lineation. If the attitude of the plane is also known, then knowing the pitch enables the trend and plunge to be calculated. The simplest way to do this is by means of a stereonet (Fig. D.2). Any computer software used should be capable of accepting and presenting data in all the above formats. 2.1.7 Using Satellite Navigation (GPS) Small, battery-operated, man-portable instruments have been available since the late 1980s to make use of the satellite-based global positioning system GPS).10 They are a boon to many aspects of field geology. Since the GPS provides location data based on latitude/longitude or regional metric grid coordinates, it is of most value for fixing position or navigating on a published map sheet on which these coordinates are marked.11 This makes GPS ideal for regional geological mapping onto published map bases or for regional prospecting and regional and detailed geochemical and geophysical data collection. Observations and sample locations can be quickly recorded against location coordinates and the position of each data point readily found again should that become necessary. In addition, the explorationist can roam around the country on foot, by vehicle or plane, following outcrop, evolving ideas or hunches, confident that anything interesting found can be easily located again, and, at the end of the day, the GPS instrument will provide a direct route back to base camp. Some limitations in the operation of GPS instruments should be noted however: • For the most accurate location signal, GPS devices need an unobstructed line of sight to the satellites. At least four widely spaced satellites must be “seen” for an accurate triangulated fix to be computed. This means that GPS will not work well in heavily wooded or forested areas except where large clearings can be found.12 10GPS is operated by the US Department of Defence and is available free to all civilian users. At the time of writing (2010) it is currently the only commercially-available available GPS system. From 2013, on current estimates, the European Galileo satellites will provide an alternate coverage. 11The most commonly used grid is Universal Transverse Mercator metric grid (UTM). A description of coordinate systems will be found in Sect. 10.5. 12However, in forested areas, GPS is a boon for airplane or helicopter operations. The geologist dropped off in a clearing in the rain forest to collect a stream sediment sample need never again fear that the helicopter pilot will not be able to find that particular hole in the canopy again
24 2 Geological Mapping in Exploration The presence of adjacent cliffs or rock faces(such as might be encountered in a mine open cut)can also seriously degrade the satellite signal and lead to lower levels of accuracy,or even a complete absence of signal. .At the time of writing(2010)the GPS system only provides a maximum consis- tent accuracy from small hand-held units of 10-15m in the horizontal direction alyslightly gre ter That uld lie within circle 2030 iameter held GPS hand controlled mapping can be employed.A posi on erro of 30 m at 10,000 scale is 3 mm.This might be acceptable,but at 1,000 scale the equivalent potential 30 mm error in plotting a point on a map would not. Better GPS accuracy can be provided by averaging a number of fixes over a period (some GPS units can do this automatically)but this process takes time High accuracies of the order of+3 m can be achieved by the use of two time ordinated GPS units,the location of one of which is fixed.This is known differer tial GPS (DGPS).For it to pr vide fix eal time there short-wave radio link bet the mo le and fixe ed GPS units tively,dat from the can b sub y downlo ade d to computer,and an accu rate position calculated.The highest GPS accuracies(maximum errors around 1 m)are obtainable by making use of special GPS correction radio signals.These systems make use of signals from geostationary satellites to calculate a correc tion map for their area of coverage.DGPS equipped receivers can then make use of this data to correct their position fix.However.at the time of writing these signals are only available in some areas of the developed world.in the United States n is called the WAASs A i vice).in Europe EGNOS(Euro G and in Japan as MSAS( Navigatio ultifun ional Satellit erlay Se Augmentation System).High accuracy DGPS systems are normally employed for accurate surveying applica tions (such as for aircraft navigation systems.accurate land surveving (i.e.claim boundaries)or levelling gravity stations),but at present have limited application for a geologist trying to create a large scale geological map in the field. Relying exclusively on GPS for navigation can create problems(potentially seri- ous)should the unit become inoperative.Never rely on GPS to the point where if the inetru ent stops working for whatever reas on,you cannot find your way safely back to bas GPS can not be used to provide accurate positioning on air photographs sinc these lack coordinates and contain scale and angle distortions.However,it is still useful to approximately locate oneself on a photo by using the GPS to provide a distance and bearing to a known feature of the photo scene.That feature has been previously entered as a waypoint in the GPS instrument's memory.In most cases knowing an approximate position on an air photo will enable an exact fix to be quickly obtained by means of feature matching.Ground-located photo features for entering as waypoints should ideally be located in the central two-thirds of the photo cene,wh distortion of the image is minimal
24 2 Geological Mapping in Exploration The presence of adjacent cliffs or rock faces (such as might be encountered in a mine open cut) can also seriously degrade the satellite signal and lead to lower levels of accuracy, or even a complete absence of signal. • At the time of writing (2010) the GPS system only provides a maximum consistent accuracy from small hand-held units of 10–15 m in the horizontal direction. Maximum potential errors in altitude are generally slightly greater. That means that a GPS position plotted onto a map could lie anywhere within a circle of 20–30 m diameter. This provides a practical limit to the scales at which handheld GPS-controlled mapping can be employed. A position error of 30 m at 10,000 scale is 3 mm. This might be acceptable, but at 1,000 scale the equivalent potential 30 mm error in plotting a point on a map would not. Better GPS accuracy can be provided by averaging a number of fixes over a period (some GPS units can do this automatically) but this process takes time. High accuracies of the order of ±3 m can be achieved by the use of two timecoordinated GPS units, the location of one of which is fixed. This is known as differential GPS (DGPS). For it to provide fixes in real time there has to be a short-wave radio link between the mobile and fixed GPS units. Alternatively, data from the two units can be subsequently downloaded to computer, and an accurate position calculated. The highest GPS accuracies (maximum errors around 1 m) are obtainable by making use of special GPS correction radio signals. These systems make use of signals from geostationary satellites to calculate a correction map for their area of coverage. DGPS equipped receivers can then make use of this data to correct their position fix. However, at the time of writing, these signals are only available in some areas of the developed world. In the United States the system is called the WAAS system (Wide Area Augmentation Service), in Europe as EGNOS (Euro Geostationary Navigation Overlay Service) and in Japan as MSAS (Multifunctional Satellite Augmentation System). High accuracy DGPS systems are normally employed for accurate surveying applications (such as for aircraft navigation systems, accurate land surveying (i.e. claim boundaries) or levelling gravity stations), but at present have limited application for a geologist trying to create a large scale geological map in the field. • Relying exclusively on GPS for navigation can create problems (potentially serious) should the unit become inoperative. Never rely on GPS to the point where, if the instrument stops working for whatever reason, you cannot find your way safely back to base. • GPS cannot be used to provide accurate positioning on air photographs since these lack coordinates and contain scale and angle distortions. However, it is still useful to approximately locate oneself on a photo by using the GPS to provide a distance and bearing to a known feature of the photo scene. That feature has been previously entered as a waypoint in the GPS instrument’s memory. In most cases, knowing an approximate position on an air photo will enable an exact fix to be quickly obtained by means of feature matching. Ground-located photo features for entering as waypoints should ideally be located in the central two-thirds of the photo scene, where distortion of the image is minimal
2.2 Mapping Using Reflectance Imagery as a Map Base 子 Plotting latitude and longitude coordinates in the field is difficult.Metric grid coordinates such as UTM(Universal Transverse Mercator,for a detailed descrip tio tion see Sect.10.5)are much easier to use.Make sure yor our GPS unit can provide nd ront operate vatlab published maps are often based on poor-quality photogrammetry with little or no ground checking.Such maps can be highly inaccurate.Even where photogrammetry-based maps have been made with care,in heavily forested coun- try the map-maker has often been unable to accurately position smaller streams. roads or villages because of the obscuring tree canopy.In these areas,the GPS fix,being more accurate than the map,can be very misleading when it comes to feature. 2.2 Mapping Using Reflectance Imagery as a Map Base 2.2.1 General Light from the sun reflects from the earth's surface and radiates in all directions vided it is not blocked by clouds)back int which nd wave of th ed .Any system ce the data as an imag nown as refle ance agery. The instrument tha t does t can be mounted on either an aircraft or satellite.The word photograph is specif ically used for images recorded onto photographic film by a camera lens system This section deals primarily with air photographs-i.e.photographs taken look ing vertically down from an aircraft-but most of the comments apply equally to the handling and use of hard copy satellite images.Details about how satellite images are acquired and presented,and how they can be used as a remote sensing nysical tool (sr ectral gy),will be found in Chap.8. ted in a ft tak a se eries of phe graphs s the plar el passes over terrain. ave ad antage of being r eap to collect and,since they are tak raphs tude,can show great detail.Overlapping adjacent photographs along the fli ght path (Fig.2.3)enables subsequent stereoscopic(3-dimensional)viewing(Fig.2.5).Air photographs typically offer a resolution of ground features that range in size from a few centimetres upwards,depending on the height of the aircraft above the ground and the quality of the camera optics used.Film is an analog method of recording data that offers exceptionally high resolution that is ultimately limited only by the cal e ulsi on the film.The lution of the film used fo graphs an ord electronic recording meth e greater that is able with Air pu raphs are typica lected f or normal viewing at scales of from 1:500to 1:100.000,but,unlike digital images,they can be enlarged many times without losing resolution
2.2 Mapping Using Reflectance Imagery as a Map Base 25 • Plotting latitude and longitude coordinates in the field is difficult. Metric grid coordinates such as UTM (Universal Transverse Mercator, for a detailed description see Sect. 10.5) are much easier to use. Make sure your GPS unit can provide a fix in latitude/longitude and regional metric grid coordinates. • In many parts of the Third World where explorationists operate, available published maps are often based on poor-quality photogrammetry with little or no ground checking. Such maps can be highly inaccurate. Even where photogrammetry-based maps have been made with care, in heavily forested country the map-maker has often been unable to accurately position smaller streams, roads or villages because of the obscuring tree canopy. In these areas, the GPS fix, being more accurate than the map, can be very misleading when it comes to trying to locate a particular feature. 2.2 Mapping Using Reflectance Imagery as a Map Base 2.2.1 General Light from the sun reflects from the earth’s surface and radiates in all directions, including (provided it is not blocked by clouds) back into space. Any system which can record the intensity and wavelengths of the reflected light and reproduce the data as an image, is known as reflectance imagery. The instrument that does this can be mounted on either an aircraft or satellite. The word photograph is specifically used for images recorded onto photographic film by a camera lens system. This section deals primarily with air photographs – i.e. photographs taken looking vertically down from an aircraft – but most of the comments apply equally to the handling and use of hard copy satellite images. Details about how satellite images are acquired and presented, and how they can be used as a remote sensing geophysical tool (spectral geology), will be found in Chap. 8. In air photography, a camera mounted in an aircraft takes a series of photographs as the plane flies in regular parallel passes over the terrain. Air photographs have the advantage of being relatively cheap to collect and, since they are taken at low altitude, can show great detail. Overlapping adjacent photographs along the flight path (Fig. 2.3) enables subsequent stereoscopic (3-dimensional) viewing (Fig. 2.5). Air photographs typically offer a resolution of ground features that range in size from a few centimetres upwards, depending on the height of the aircraft above the ground and the quality of the camera optics used. Film is an analog method of recording data that offers exceptionally high resolution that is ultimately limited only by the grain size of the chemical emulsion on the film. The resolution of the film used for air photographs is an order of magnitude greater that is currently achievable with electronic recording methods. Air photographs are typically collected for normal viewing at scales of from 1:500 to 1:100,000, but, unlike digital images, they can be enlarged many times without losing resolution