AU2007209544B2

AU2007209544B2 - Sub-surface analysis of particulate substrates

Info

Publication number: AU2007209544B2
Application number: AU2007209544A
Authority: AU
Inventors: Soeren Lund Jensen; Henrik Sabra
Original assignee: SCANDINAVIAN HIGHLANDS HOLDING AS
Current assignee: SCANDINAVIAN HIGHLANDS HOLDING AS
Priority date: 2006-01-26
Filing date: 2007-01-25
Publication date: 2010-12-02
Anticipated expiration: 2027-01-25
Also published as: CA2640137A1; WO2007085462A1; GB0601634D0; ZA200806495B; AU2007209544A1; EP1977221A1

Description

CANRPonbl\DCC\MKA\326MX33 1 DOC4/11/2010 Sub-Surface Analysis of Particulate Substrates Technical Field The invention relates to methods of spatial analysis of large-scale particulate substrates such as regolith-forming material, for instance various types 5 of soil, or waste material from industrial processes. The invention also concerns an apparatus suitable for use in such methods. The invention is useful in a wide range of applications, in particular mineral exploration and production, geological surveying, environmental and pollution surveying, both of raw and waste materials. In nature, minerals of economic value are often found in ores of volcanic, 10 hydrothermal, igneous or sedimentary origins which have a variable overburden of consolidated or partly consolidated particulate material which can be clay, silt, sand, gravel or a mixture thereof forming various types of soil such as that formed from glacial, fluvial, alluvial, aeolian deposits or chemical deposits such as evaporate deposits like limestone. 15 Although the geochemistry of the overburden is not normally identical with the source rock, it can give an indicative idea of the composition of the source rock, given knowledge of physical and chemical decomposition as well as the repositional history of the overburden. However, analysis purely of the surface of the overburden will often give an 20 erroneous result, leading in the best case to an underestimate of the economic potential and in the worse case leading to the potential ores in the rock being missed altogether. Therefore it would be desirable to be able to establish with greater accuracy the chemical analysis of the overburden in such a way that this can be related with 25 some confidence to the chemical analysis of the underlying rock formation. It is desirable to determine the characteristics of the bulk mineral and of trace elements found therein, some of which are indicative of the presence of precious metals. Separately, there are also concerns which lead to a need for assessing the 30 chemical analysis (e.g. content of heavy metals) of soil and the consequent likely C :NRPonblDCCMKA\326K33_ 1. DOC-1/ I/2010 -2 content in ground water. In order to do this it is important to be able to provide accurate chemical analysis of the sub-surface soil. Traditional sub-surface soil characterisation techniques for these purposes include collection of field samples and subsequent analysis in the laboratory. 5 Expensive, time consuming, time-delayed testing of this sort is unsuitable for examining large land areas where soil or fluid contamination has occurred and is also unsuitable for obtaining a detailed analysis of the distribution of the relevant materials through the soil. It is known to assess soil for pollutants and other chemicals using devices 10 which work by the laser induced breakdown spectroscopy (LIBS) technique, as for instance described in US 5,757,484, US 6,147,754 and US 5,847,825. All of these techniques are based upon use of a penetrometer device, which is pushed vertically downwards through the soil. Results can be obtained in real time but these are limited to analysis of variation of the relevant materials as the depth 15 increases. If it is desired to establish the extent of the presence of the polluting material over a large area of land, it is necessary to apply the penetrometer device in a large number of different positions and use it to bore vertically down in those different positions. This is time consuming and still only results in measurements for discrete points over the surface of the land. Interpolation is required to produce 20 data showing information over the surface in the form of a map. It would also be desirable to provide a method and apparatus which can provide sub-surface characterisation of the properties of soil under these circumstances, which can be rapid, continuous and cost effective. In view of the above, it is therefore desired to provide a method of spatial 25 analysis of a mass of particulate mineral-containing substrate applied in mineral exploration and production and used in the assessment of the positioning or concentration of ores, or use for mineral exploration and production of apparatus for the spatial analysis of a mass of particulate mineral-containing substrate that alleviate one or more of the above difficulties, or at least provide a useful 30 alternative.

C:\RPonbl\DCC\KA\326K833_ DOC-3/1l/20 10 -2A According to the invention we provide a method of spatial analysis of a mass of particulate mineral-containing substrate applied in mineral exploration and production and used in the assessment of the positioning or concentration of ores, the method comprising: 5 providing a probe, wherein the probe is adapted to generate a plasma from the substrate material by emitting a beam of laser light which contacts the substrate material and the probe comprises a light collector; positioning the probe below the surface of the mass of substrate; causing the probe to pass through the mass of substrate below the surface 10 of the mass of substrate between a first position and at least one second position, wherein the first position and the at least one second position are separated in the horizontal direction; taking a chemical analysis measurement at the first position by using the probe to generate a plasma at the first position, collecting light from the plasma 15 with the light collector, transmitting it to a spectrometer and determining a chemical analysis of the substrate at the first position; taking at least one further chemical analysis measurement at the at least one second position. Thus, according to some embodiments of the invention, the probe passes 20 through the mass of substrate between positions which have horizontal separation and chemical analysis measurements are taken at these positions. Usually measurements are taken at many horizontally separated positions so as to give a series of measurements which can be used to generate a substantially continuous 25 WO 2007/085462 PCT/EP2007/000665 3 map of chemical analysis properties of the substrate. For instance, the probe can be caused to pass through the mass of substrate along a predetermined line, chemical analysis measurements being taken at many positions along the line. In preferred embodiments the method also comprises subsequently causing the probe to pass 5 through the mass of substrate along further lines, often several of these. The lines are generally substantially parallel but can be positioned having horizontal separation between them. Alternatively or additionally the lines can be separated by vertical distance, that is they are at different depths below the surface of the mass of substrate. Thus the map of chemical analysis properties can be two-dimensional or 10 even three-dimensional. In preferred embodiments, the method also incorporates taking sub-surface measurements of properties other than chemical analysis. It is particularly preferred that the method is carried out using a system whereby the probe is fixed to a cleaving device adapted to cleave the mass of 15 substrate so as to enable the probe to pass through the mass of substrate. This cleaving device can then be attached to a vehicle which can move across the surface of the mass of substrate. The substrate analysed in the method is particulate mineral-containing substrate. That is, it is not solid rock. However, it may be formed predominantly or 20 wholly of rock material. For instance it can be regolith, that is loose, heterogeneous material covering solid rock, or regolith-forming material. If the substrate contains a significant proportion of organic material it is more conventionally referred to as soil. When the method is applied in mineral exploration and mining or geological surveying the substrate is often a soil, for instance clay, residual soil, glacial soil, 25 fluvial soil, alluvial soil, aeolian soil, evaporate deposits, gravity transported soil or chemical precipitated soil. In these cases the method can be used in the assessment of the positioning or concentration of ores such as sulphite ores, for example those containing copper, lead and zinc, oxide ores, for example those containing aluminium, chromium, 30 vanadium, iron, titanium and manganese or metallic alloy ores, for example those containing silver, gold and platinum group metals. Often the substrate enriched with the relevant mineral is glacial, fluvial, alluvial , aeolian or evaporate deposits. It is important to determine the chemical analysis of the bulk of the substrate to characterise the dominant mineral as this is 35 indicative of the presence of ores of interest. However, it is also important to determine the presence, concentration and identity of trace elements in the minerals as these are also indicative of the presence of materials of interest. For example, a C:\NRPorbl\DCC\MKAU26XX31_ DOC-3/Il/2010 -4 gold deposit is often associated with the presence of traces of barium, antimony or arsenic. The substrate may also be soil or waste material in the case of the method being applied for pollution and environmental control. 5 The method also has benefits when applied in other areas, such as methods of drilling for sub-surface materials such as hydrocarbon accumulations, ground water aquifers, mineral deposits or other accumulations of economic interest. In these circumstances it is also important to be able to analyse changes in chemical parameters (markers). This allows evaluation and grading of zones 10 already penetrated and to forecast when a zone which is likely to be valuable is being approached or even a zone which is likely to be potentially hazardous. Drilling methods of this type generally generate cuttings which are transported to the surface mechanically, by gravity or by suspension in drilling fluids, water, foam or air. The term "cuttings" includes dusts, slurries and foams. 15 The recovered particulate material, in solid or fluid form, represents the penetrated material. The invention allows the real time analysis of the composition and chemical parameters of the flow of recovered cutting material from the bore hole. Prior to the invention this kind of analysis would normally be carried out by taking samples, preparing these and having them analysed externally in a 20 laboratory, thus leading to significant time delay (hours, days or even weeks) from the production of the sample. In the majority of cases, especially in the applications for mineral exploration and mining, geological, pollution and environmental surveying, the probe is caused to pass through the mass of substrate by moving the probe whilst 25 the substrate remains stationary. Alternatively, it can be valuable to ensure that the probe is maintained stationary, whilst the substrate is passed by the probe so that the probe moves through the mass of substrate material in that way. Analysis of a liquid, gaseous or solid mass of substrate in motion relative to a stationary probe could be performed 30 directly on the cleaved surface when appropriate or in a sealed or open flowcell. In C \NRPortbl\DCCMKA\126M#33_1 DOC-1/1 l/2010 -5 the case of a flowcell, partial or complete control over the analyte level in the flowcell can be achieved by means of a transparent analysis window, a continuous direct flow, an overflow, a mechanical riser/transportation, a restricted inlet relative to output capacity or back-pressure control via an electrical, mechanical, hydraulic 5 or pneumatic pressure or substrate level regulator. This latter method can be applied for analysis of drill cuttings, waste material or a flow of raw material. Typically the material would be positioned on a conveyer belt passing past the probe. A further application for the method is in input and output control in 10 industries, such as the chemical or manufacturing industry or in mining. It is in some circumstances necessary to analyse the chemical content of large masses of particulate raw material for chemical processes, and this is normally done by single sample analysis either on the process line itself or on input or output materials. The method allows the analysis of a large mass of raw material in a 15 continuous and rapid manner. Of particular interest is the analysis of by-products and waste products. In the chemical industry such materials are often simply dumped and accumulate over a period of, in some cases, years. The chemical analysis of the mass of dumped material can thus vary considerably through that mass. This causes 20 difficulties when it is decided to attempt either to re-use or store or deposit the by product or waste product. Examples include ash from power plants, which may be contaminated with heavy metals such as lead or cadmium. The level of contamination affects what can be done with the ash. The method allows the convenient and rapid analysis of such a mass and 25 aids the consequent process of assessing what must be done with it. The probe is set up so that it can emit a beam of laser light which contacts the substrate material so as to generate a plasma from the substrate material. The light emitted by the plasma is then collected and passed to a spectrometer so as to determine the chemical analysis of the substrate.

C\NRPonbl\DCC\MKA\3268833_ I DOC-/1 1/2010 -6 Thus, the method uses laser induced breakdown spectroscopy (LIBS) to measure a chemical analysis of the substrate. This technique is well known and is also known as laser induced plasma spectroscopy (LIPS). As mentioned above, the LIBS technique is known in some methods of analysing soil for pollution and is 5 also described in our co-pending application PCT/EP2005/007931 for the analysis of heterogeneous rock surfaces. The LIBS technique uses a pulsed laser to generate a laser spark which rapidly heats a sample causing vaporization, dissociation into atomic species, and ionisation, which produces a plasma. As the plasma cools, the excited species 10 relax and emit spectral energy at characteristic wavelengths. The emission can be spectrally resolved to identify the elemental species that are present in the sample based on the presence of characteristic spectral lines. The concentration of the elemental species present may be proportional to the intensity of the spectral lines produced or, if it is not proportional, may be calculated by descent calibration. 15 More details of the construction and operation of the probe are given below. In the method the probe passes through the mass of substrate. Since in preferred embodiments the substrate is partly or largely consolidated, force is required in order to cleave the substrate sufficiently to allow the probe to pass through it. Preferably this is done by means of a cleaving device which can cleave 20 the mass of substrate so as to enable the probe to pass through it. Generally the cleaving device is a blade, such as a ripper, or a plough. The cleaving device can be made of any appropriately hard material but is generally metallic. Generally the probe is affixed to the cleaving device. Preferably the cleaving device has at least one hollow portion having outer walls and the probe is 25 positioned within the hollow portion between the outer walls. This gives protection to the probe and cables. In this case at least one of the outer walls of the cleaving device is provided with an opening through which the beam of laser light can pass from the probe and through which the light collected from the plasma can pass back into the probe. 30 In the method the LIBS method is used to measure a chemical analysis.

C :\RPotbl\DCC\MKA\3268X33 1 DOC-3/lI/2010 -6A By chemical analysis we mean the obtaining of information about the presence (qualitative) or amount, absolute or relative (quantitative), of one or more chemical elements. For instance, the presence of a single element can be detected, or the ratio(s) between two (or more) elements, or the amount of one or 5 more elements. For instance, in the method the chemical analysis can be for a single element or it can be for a single main element and additional trace elements. In the method a chemical analysis measurement is taken at at least two positions below the surface of the mass of substrate. These positions are 10 separated in the horizontal direction. The probe is moved through the substrate at a certain depth and travels substantially parallel to the surface of the substrate. The probe takes measurements at points which are separated in the horizontal direction, but the points will not be due horizontal with respect to one another unless the surface of 15 the substrate is, itself, flat and horizontal. Substrates being analysed are typically not entirely flat and horizontal but can be, for example, the side of a hill. The surface of the substrate can be sloped at an angle of up to 60 degrees to the horizontal, but, preferably, is sloped at below 30 degrees to the horizontal. As the measurements are taken parallel to the 20 surface, where the surface of the slope is not horizontal, the measurements will not be on a particular horizontal line but, as the invention is not concerned with analysing vertical surface, the measurements will always have some horizontal separation between them. The method preferably involves positioning the probe below the surface of 25 the mass of substrate and causing the probe to pass through the mass of substrate WO 2007/085462 PCT/EP2007/000665 7 oelow its surface from the first position to multiple further positions along a line which is usually predetermined. A chemical analysis measurement is taken at each of the multiple further positions. Where a detailed analysis of the area is required, the distance between these further positions is preferably not more than 50 meters, more 5 preferably not more than 5 meters and most preferably not more than 50 centimetres. If the horizontal distance between the positions at which chemical analysis measurements are taken is short then a substantially continuous map of the chemical analysis measurement along the line through the substrate can be generated. Where it is desired to make an initial survey of a large areas, to "scan" it for 10 areas of potential interest where further investigations can be concentrated, the distance between the further positions can be from 1km, to 10 km or even up to 100km. In this case, a map is not made. . It is possible for the probe to move from the first position to a further position, stop and take the chemical analysis measurement and then continue moving, but 15 preferably the probe is caused to move continuously throughout the method. This is possible because the LIBS method allows the analysis time to be so short that it is not necessary to stop the probe moving every time a chemical analysis measurement is to be taken. In this case, the speed of movement of the probe through the mass of substrate is preferably at least 0.1 to 1 meters per second, more preferably around or 20 above 5 meters per second. In the method, as the probe moves through the mass of substrate, preferably a chemical analysis measurement is taken at least once every sixty seconds, more preferably at least once every ten seconds and most preferably at least once every second. 25 In the method, the probe is positioned below the surface of the mass of the particulate substrate and usually remains at the same depth below the surface of the particulate substrate. As the probe passes through the mass of substrate along any predetermined line it usually remains at substantially the same depth below the surface. 30 Measurements are generally taken at depths below the surface of the mass of substrate of from 5 to 300 centimetres. The method can additionally comprise subsequently or simultaneously causing a probe to pass along second and optionally further predetermined lines through the mass of substrate. 35 For instance, the further lines may be horizontally separated from the first predetermined line, for example on a grid. Often they are substantially parallel with one another and are generally straight. However, where it is convenient to tailor the survey lines to the surroundings, for example where there are surface obstructions CANRPonbl\DCC\MKA\326K8333I DOC-311l/2,11 -8 on the land, the lines can be any desired shape. Preferably they are at substantially the same depth below the surface of the mass of substrate. The horizontal distance between such lines is preferably not more than 5 meters, more preferably not more than 1 meter, most preferably not more than 50 5 centimetres. Where there is a small distance between the horizontal lines, the cleavers containing the probes can be mounted on the same frame. The predetermined lines may alternatively be vertically separated and again are often substantially parallel with one another. Thus they can be at different depths below the surface of the mass of particulate substrate. Measurements at 10 different depths can be taken simultaneously or at different times. Preferably the difference between the depths at which measurements are taken is less than 2.5 meters, preferably less than 1 meter, most preferably less than 50 centimetres. One way of taking two or more chemical analysis measurements simultaneously at different depths is to provide two or more probes fixed to the 15 same cleaving device, thus maintaining the same fixed vertical separation. Commonly the surface of the mass of particulate substrate is undulating and so a line which maintains the same depth below the surface will generally not itself be horizontal but points along the line will be separated by horizontal distance. Commonly the lines along which the probe moves and on which 20 measurements are taken are substantially parallel to the surface. Preferably the probe is associated with a positioning system which allows the recordal of the position at which each measurement of chemical analysis is taken so that this can be used to generate a two-dimensional or three-dimensional map of the distribution of the chemical analysis features of interest. 25 It is important that the position of the probes is accurately monitored so that an accurate map can be constructed from the data obtained. Any appropriate positioning system can be used, provided its accuracy is appropriate for the relevant application. Examples include DGPS, GPS and other satellite navigation systems. It is also possible to use decca, radio, radar, optical, fixed point or other 30 navigation systems.

C:\NRPonb\DCC\MKA\326xN13 1 DOC-3/1l 2010 -9 The positioning system preferably has accuracy to less than 10 meters, preferably less than 1 meter, more preferably less than 10 centimetres, both horizontally and vertically. There are many advantages to the use of LIBS for carrying out the chemical 5 analysis. In particular, the method allows real-time analysis, meaning that the time between operating the laser and obtaining the analysis of the composition of the substrate at the measurement point is less than 60 minutes, usually less than 30 minutes and can be below 15 minutes or 5 minutes but is most preferably below 10 minutes, more preferably below 30 seconds and may even be as low as 1 10 second. Using the LIBS technology under the surface of the substrate is advantageous as the laser beam will not shine above the surface, thereby avoiding the hazards usually associated with working with laser, such as the danger of blindness or damage to the eyes. Keeping the laser beam under the 15 surface also means that the method can be used in the presence of combustible gases as the risk of the laser causing the gases to combust is substantially eliminated. The method does not require any specific type of LIBS, meaning that any suitable type of laser, duration of laser pulse, type of detector or spectrometer to 20 resolve the emitted energy, etc. can be used. The plasma can be generated using repetitive single spark laser pulses or repetitive double spark laser pulses. Double or multi-pulse lasers, as well as an array of delayed single shot lasers, are used in the preferred embodiment of the invention. In this case, the analyte is excited by several pulses, rather than one pulse, to generate the desired 25 plasma. An advantage of using double or multi-pulse lasers is the lower demand for energy of each laser pulse. This allows a stronger plasma to be created using a less powerful laser. Furthermore with a lower energy laser pulse, the risk of damaging the optical fibres or optical system used to transmit the laser pulses from the laser to the analyte, is reduced.

C:\NRPonbl\DCCMKA\126F833 J DOC-1/l /2)10 - 10 A further advantage of double or multi-pulse lasers is that the use of mutible pulse lasers in LIBS will increase the Signal to Noise and Signal to Background ratio significantly. This leads to, amongst other advantages, reduced requirements for the resolution and bandwidth of the spectrometer used. 5 Yet another advantage of double or multi-pulse lasers is that they can improve detection of weak spectral lines or higher order lines in air, especially in the near UV interval, for example Sulfur. Examples of such pulsed lasers are Nd:YAG and Excimer lasers. Typically a Nd:YAG laser is used with 532 or 1064nm wavelength, but the wavelength can 10 be even higher, for example between 1500 and 1700 nm. In the preferred embodiment, a 532nm (commonly known as a green laser) is used. This is advantageous as decreasing the wavelength of the laser, for example reducing the wavelength from 1064 to 532nm, means that less laser pulse energy is needed for exciting of the analyte and plasma formation. A further 15 advantage is that a plasma can more easily be generated with lower wavelengths, particularly when the substance being analysed is highly reflective, for example is quartzsand or carbonates. Laser pulse duration can range from femtosecond laser pulses to 50 nanoseconds. Pulse energy can be from 5 mJ upward, for instance up to around 20 250 mJ and is preferably 20 to 50 mJ. Pulse frequency can be from 1 Hz but is typically from 5 Hz upwards, for instance up to about 50 Hz, can be even up to 1000 Hz or 500 Hz but is preferably between 10 and 50 Hz, most preferably about 20 Hz. LIBS can be used both as a quantitative and qualitative analytical method 25 for chemical analysis. Entire spectra can be analysed in order to make a quantitative chemical analysis. Alternatively only a narrow part of the spectrum can be analysed in order to gain qualitative information about the presence of a single component, a selection of components, ratio between components or combinations thereof.

C:NRPonblDCC\MKA\326X33I DOC-3/l/W2W - 11 The analysis involves taking a measurement by generating a plasma at a point, collecting light from the plasma with the light collector, transmitting it to a spectrometer and determining a chemical analysis of the substrate at the measurement point. 5 The laser beam is generated by a laser. The beam of laser light is emitted from the device which is adjacent the surface. The laser may form part of the probe. Alternatively, it may be positioned away from the substrate being analysed and connected to the probe by light guidance means which transmit the laser light to the device. Examples include optical fibres. 10 A beam homogenizer is used in the preferred embodiment of the invention. This allows the maximum total laser pulse energy launched into an optical lens or fibre to be increased without exceeding the damage threshold limit. Suitable beam homogenizers are known from literature such as "New simplified coupling scheme for the delivery of 20 MW Nd:YAG laser pulses by large core optical fibers, 15 Schmidt-Uhlig T., Karlitschek P., Marowsky G., Sano Y., Appl. Phys. B vol. 73, pp. 183-186, 2001". A beam homogenizer causes a more uniform distribution of laser pulse energy into the fibre end leading to a higher total single laser pulse energy transmission into the optical fibre. Furthermore, by using a beam homogenizer it is also possible, to a certain degree, to control the mode of the pulse in the fibre as 20 well as the numerical aperture during input and output in the fibre. Generally the probe comprises a focus means which focuses the laser light. The focused light is emitted from the device and generates a plasma from the substrate material. The probe that is used can, in one embodiment, include a single optical 25 fibre solution. In this embodiment there is only one optical fibre between the laser and the probe. Hence, the laser light travelling towards the probe and the light collected from the plasma travelling back from the probe to the spectrometer are both transmitted though the same optical fibre. In this embodiment a beam splitting unit is mounted on the laser to split and transmit the returning spectral light from 30 the plasma to the spectrometer, between the laser and the beam homogenizer.

C:\RPonblDCC\MKA\326803 I.DOC.3/1I1/2010 - 12 Alternatively, a dual optical fibre solution can be used which uses two or more optical fibres, so that the laser light is transmitted to the probe in one fibre, and the spectral light collected from the plasma is transmitted back to the spectrometer in another. This means that the beam-splitting unit mentioned above 5 does not need to be used, which results in lower laser pulse energy loss due transmission. This also means that a green laser (532 um) can be used without the omission of wavelengths near 532 um in the returning spectral light, as would be the case with a single optical fibre. In this embodiment, optimal focusing of the laser pulse on the mineral-containing substance, as well as optimal focussing of 10 the returning spectral light onto spectrometer inlet, can be obtained. Finally when using two or more optical fibres, it is possible to use optical fibres with different properties, (for example different numerical apertures, and different diameters) for the laser pulse transmission and the returning spectral light transmission. The method requires collecting the light generated by relaxation of the 15 species in the plasma. Generally the light collector is a lens and the collected light is transmitted to the spectrometer by light guidance means, such as optical fibres. The LIBS technique uses a spectrometer as a means of analysing the light from the plasma. The spectrometer can be any suitable type. Preferably an Echelle spectrograph is used. 20 It is possible to use one or more multi element spectrometers or one or more narrow wavelength spectrometers for single or a specific range of elements. Generally the spectrometer is located away from the substrate to be analysed, and generally also uses a detector such as a CCD or ICCD (intensified CCD). 25 The data from the spectrometer should be translated into a chemical analysis by using suitable software, for example provided in a PC. The spectrometer may have an input into a user-interface or a feedback system. The detector is positioned between the spectrometer and the analysis software. The detector transmits the data from the spectrometer to the software and can store 30 information from the spectrometer.

C:NRPonblDCC\MKA\326813..DOC-3I 112010 - 13 Preferably the probe is caused to pass through the mass of substrate using a transportation device, such as a tractor, a truck, a crawler, an all terrain vehicle (ATV) a car, or even a boat. Alternatively, the transportation device can be airborne, such as a helicopter, fixed wing plane or other airborne vehicle. When an 5 airborne transportation device is used, it is connected physically to the probe and movement of the airborne device causes the probe to pass through the mass of the substrate. For example, the probe, optionally in a cleaving device, is mounted on the airborne device and trailing from it through the air to the substrate. In this case elements of the apparatus not included in the probe are located 10 in or on the vehicle. Thus this includes the laser and the spectrometer. If convenient, the probe can be remote from the transportation device, but connected to it, for example by a wire. The power can also be supplied from a power supply on the transportation device, e.g. a battery source, a solar cell source. It is preferably supplied by a 15 generated located on or remote from the transportation device. Similarly, a positioning system can be included in the transportation device. Preferably, data is stored and processed in real-time and is preferably stored and processed so that results are available on site to the operator at the time of operation. 20 The method also includes the possibility of post-processing of stored data. Data obtained from the method is preferably stored in a conventional manner in a storage device, usually on the transportation device. The results of the chemical analysis are preferably presented as a graphical presentation, which, for three dimensional data, is usually represented by a map, 25 which can include survey lines and way points. The two dimensional data can also be represented in a graphical format, in a diagram. The data obtained by the method can be transmitted to a central or a local database for further analysis by any known means. This can be by wireless communication or by wire, fibre or other optical/electrical/magnetic device, in 30 known manner.

C.\NRPorbl\DCC\MKA\326833 I.DOC-3/ Il2UN10 -13A Similarly, data can be processed in the remote location and further information passed back to the operator at the location at which measurements are taken. The communications between the device and the operator are preferably 5 two way, thereby allowing the operator to make adjustments to the device, such as to calibrate it. In the method of the invention it is also preferred that measurements are taken of other parameters. These include direct or indirect geophysical measurements. The 10 parameters can be physical, mechanical or other chemical parameters (measured other than by LIBS). These include resistivity, density, radiation level, acoustic velocity, reflectivity, pH, mechanical strain (as the probe passes through the substrate), grain size of the particulate substrate, homogeneity of the substrate. Measurements can be taken by x-ray fluorescence. 15 These additional measurements can be taken for instance using a geo electrode device, a magnetometer, TEM, VLF, seismic apparatus, geo-radar or gravimetric analyser. These additional parameters can also be incorporated into any profile or map generated from the LIBS measurements. 20 It is also possible to collect samples from the points at which the chemical analysis measurements are taken, so that the results obtained from the LIBS method can be combined with other data obtained at a later stage on these retrieved samples. The present invention also provides use for mineral exploration and 25 production of apparatus for the spatial analysis of a mass of particulate mineral containing substrate, the apparatus comprising a probe which is adapted to emit a beam of laser light and which comprises (a) a focus means adapted to focus the laser light before emission so that a plasma can be generated from substrate material adjacent the probe, (b) a light collector positioned so as to collect light 30 from the generated plasma and (c) an outer housing containing the focus means CANRPonb\DCC\MKA\3268X33 I.DOC-4/Il/2010 - 13B and the light collector, the housing being fixed to a cleaving device adapted to cut through the mass of substrate in a substantially horizontal direction so that the probe can pass through the substrate between first and second positions having horizontal separation. 5 In some embodiments, the apparatus includes a source of pressurised air. The air is channelled to the window where it is used to ensure that the area of the substrate being analysed is not covered with water. Alternatively, a vacuum can be used to suck water away from the spot being analysed. In the case where the probe is located on a cleaving device which is itself 10 fixed to a transportation device, it is often preferred to mount the cleaving device on the transportation device in such a way that limited horizontal movement of the cleaving device is permitted. This reduces the extent and number of stoppages caused by obstacles in the mass of substrate. It is preferred to include with the other elements for use in the method a 15 mechanical-acoustic device for grain size analysis of samples removed from the substrate. It is also preferred to include, either in the probe or fixed to a cleaving device, a device for measuring mechanical strain by measuring the resistance of the bypassing substrate using a pressure sensor mounted on a strain probe. 20 Preferred embodiments of the present invention are hereinafter described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 shows a cross-section through apparatus according to preferred embodiments of the present invention, when in use. Figure 2 shows a cross-section through a preferred probe according to 25 some embodiments of the present invention. Figure 3 shows an example of a 3D continuous survey carried out by an embodiment of the method of the present invention. Figure 4 shows a two-dimensional cross-section through the three dimensional survey of Figure 3.

C:WRPonb\DCC\MIKA1268833 I DOC-3/1l112010 - 13C Figure 1 shows a detailed cross-section of one version of the apparatus according to preferred embodiments of the present invention in soil. The apparatus has two probes positioned beneath the soil 19, which, in this case, is the mass of particulate mineral containing substrate which is being analysed. 5 WO 2007/085462 PCT/EP2007/000665 14 The apparatus comprises an upper three point hitch 1 which can be attached to a vehicle to move across the surface of the substrate. The apparatus comprises an upper sub-surface probe, 11, having supplementary sensors, 12, and a sapphire glass analysis window, 13, through which the beam of laser light is emitted to contact 5 the substrate 19. The second probe is the lower sub-surface probe, 15, which takes measurements at a second depth below the surface of the substrate. To protect the probes and to allow the probes to cleave through the substrate, the probes are within housing 18, which at its distal end has upper cast wear shin 14 and a heal cast wear 10 shin 17 with lower cast wear shin 16 in between the upper cast wear and heal cast wear. The probes 11 and 15 are attached to cables and optical fibres having various purposes as follows. Cable 5 is a single or dual core fibre optics cable which runs from the laser and spectrometer (not shown) to the probes. Cable 4 is a multi core 15 cable which carries information regarding supplementary chemical and physical measurements taken under the surface of the substrate. Cable 3 carries information regarding supplementary surface measurements. Cable 6 is a pressurised air or vacuum supply which is used at the surface being analysed to remove excess water. The cables pass through internal slot 10 in the housing 18. 20 The upper three point hitch 1 is part of the ripper frame 2. The frame also has a lower ripper hitch, a survey depth control 8 and a hydraulic rod for angle adjustment or obstacle evator 9. The frame is attached to the housing 18 which houses the probes 11 and 15 which carry out LIBS chemical analysis of the soil, with the laser light and information 25 being transmitted through the cables to the necessary laser and spectrometer (not shown). Figure 2 shows a larger scale section through a probe situated in the substrate 19. The outer housing comprises of side wall 20 with adjustable upper seating flange 21 and adjustable lower seating flange 32. The probe has an upper 30 cable connector 22 and when in a series of probes, a lower cable connector 33. The multi core cable 4 is connected to supplementary internal or external chemical and physical sensors 12 in the probe where the single or dual core fibre optics which leads to the sensor and spectrometer, 5, is connected directly to the LIBS apparatus. The LIBS apparatus comprises a plasma light fibre optics connector 23 and 35 laser pulse fibre optics connector 24. Light from these connectors (23 and 24) shines through a focus lens 25 a collimate lens 26 respectively and onto reflecting prism 28 or decoupling mirror 29. The light passes through lens 34 which focuses the laser WO 2007/085462 PCT/EP2007/000665 15 julse and collimate light from the plasma and is emitted and collected through sapphire glass 13. The intensity of the laser pulse is determined by sensor 31. On the exterior of the housing is an over pressure or vacuum zone flange 30. The pressurised air 5 supply, 6, leads to a sealed zone inside the flange of the housing 27. Figure 3 shows a 3D continuous survey in plan view made using the method of the present invention. The method has been carried out to detect the levels of gold, by detecting arsenious, which is a mineral associated with gold, in the substrate over a horizontal distance of 6 kilometres. 10 The result of the chemical analysis are shown in regions of different colours representing different concentrations of arsenious detected in the substrate. The darkest colour A represents areas having a level of more than 15 parts per million arsenious. The correspondingly less dark regions B, C, D and E represent levels having 10 to 15 parts per million arsenious, 7.5 to 10 parts per million arsenious, 5 to 15 7.5 parts per million arsenious, and 2.5 to 5 parts per million arsenious respectively. The areas in white, F, have been found to contain less than 2.5 parts per million of arsenious. Hence, the results of the survey give a very clear indication of the quantities and distribution of arsenious over the area surveyed. Figure 4 is a two dimensional cross-section through the plan view of Figure 3 20 along to the survey line. The survey was done with three probes at different depths, probes I, I and Ill as can be seen in Figure 4. The area shown with the darkest shading A represents an area of considerable interest as it has a high level of arsenious as clearly shown in both Figures 3 and 4. Methodology for carrying out the survey is, in general, the same as that used 25 in previous methods for carrying out geochemical analysis of soils. The previous methods involved taking samples from the soil, whereas in the present invention the analysis is carried out in-situ. The survey described in an article (found at http://www.appliedqeochemists.orq/tmp/seq abst/hall.pdf ) entitled "Secondary geochemical signatures in glaciated terrain" by Gwendy E. M. Hall (Geological 30 Survey of Canada, GSC), Stew M. Hamilton (Ontario Geological Survey OGS), Beth McClenaghan (Geological Survey of Canada, GSC), and Eion M. Cameron (Eion Cameron Geochemical Inc.) C:NRPonbl\DCC\MKA\3268)33 I.DOC-3/11/2010 - 15A Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or 5 group of integers or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the 10 common general knowledge in the field of endeavour to which this specification relates.

Claims

1. A method of spatial analysis of a mass of particulate mineral-containing substrate applied in mineral exploration and production and used in the 5 assessment of the positioning or concentration of ores, the method comprising: providing a probe, wherein the probe is adapted to generate a plasma from the substrate material by emitting a beam of laser light which contacts the substrate material and the probe comprises a light collector; positioning the probe below the surface of the mass of substrate; 10 causing the probe to pass through the mass of substrate below the surface of the mass of substrate between a first position and at least one second position, wherein the first position and the at least one second position are separated in the horizontal direction; taking a chemical analysis measurement at the first position by using the 15 probe to generate a plasma at the first position, collecting light from the plasma with the light collector, transmitting it to a spectrometer and determining a chemical analysis of the substrate at the first position; taking at least one further chemical analysis measurement at the at least one second position. 20

2. A method according to claim 1 in which the probe is caused to pass through the mass of substrate by moving the probe whilst the mass of substrate remains stationary. 25

3. A method according to claim 1 or 2 in which the substrate is unconsolidated or part consolidated regolith forming material, preferably clay, silt, sand gravel or a mixture thereof, residual soil, glacial soil, fluvial soil, alluvial soil, aeolial soil, evaporite deposits, gravity transported soil or chemical deposited soil. 30

4. A method according to any preceding claim, comprising moving the probe along a first predetermined line through the mass of substrate and taking chemical CANRPonbl\DCCMKA\3262263_1 DOC-2W0/2010 , - 17 analysis measurements in at least 10 horizontally separated positions along the line.

5. A method according to claim 4 in which the horizontal distance between the 5 positions at which chemical analysis measurements are taken is not more than 50 m, preferably not more than 5 m and preferably not more than 50 cm.

6. A method according to claim 4 or 5 wherein consecutive measurements are taken within not more than 60 seconds, preferably not more than 10 seconds, 10 more preferably not more than 1 second.

7. A method according to any preceding claim in which the first position and the second position are at substantially the same depth below the surface of the mass of substrate and the method also comprises taking at least two further 15 measurements at third and fourth positions, the third and fourth positions being at a second depth below the surface of the mass of substrate.

8. A method according to claim 7, comprising providing at least two probes, wherein the first probe is positioned substantially vertically above the second 20 probe so that the first probe takes a measurement at a first depth below the surface of the mass of substrate and the second probe takes a measurement at a second depth below the surface of the mass of substrate.

9. The method according the claim 7 or claim 8 in which the difference 25 between the first and second depths below the mass of substrate is less than 25m, preferably less than 1m, most preferably less than 50cm.

10. A method according to claim 5, further comprising subsequently moving the probe along a second predetermined line through the mass of substrate, the 30 second line being horizontally separated from the first predetermined line and at substantially the same depth below the surface of the mass of substrate. - 18

11. A method according to claim 10, in which the horizontal distance between the first and second predetermined lines is not more than 100cm, preferably not more than 50m, more preferably not more than 5m. 5

12. A method according to any preceding claim in which measurements are taken at a depth from 5cm to 300cm below the surface of the mass of substrate.

13. A method according to claim 5 in which the probe is moved through the 10 mass of substrate at a speed of at least 0.5 metres per second, preferably at least 1 metres per second, more preferably at least 5 meters per second.

14. A method according to any preceding claim in which the probe is fixed to a cleaving device adapted to cleave the mass of substrate so as to enable the probe 15 to move through the mass of substrate, preferably the cleaving device being a blade, more preferably a ripper or plough.

15. A method according to any preceding claim additionally comprising taking, at the same positions as the measurement of chemical analysis, measurements of 20 additional parameters of the substrate, preferably selected from resistivity, density, radiation, acoustic velocity, reflectivity, pH and homogeneity.

16. A method according to any preceding claim in which the probe and optional cleaving device are mounted on a vehicle adapted to travel over the surface of the 25 mass of substrate or an airborne transportation device.

17. A method according to any preceding claim wherein the position of the probe is monitored using a satellite positioning system. 30

18. Use for mineral exploration and production of apparatus for the spatial analysis of a mass of particulate mineral-containing substrate, the apparatus C VNRPoflbIDCC\MKA\362263_ DOC.2&101O201( - 19 comprising a probe which is adapted to emit a beam of laser light and which comprises (a) a focus means adapted to focus the laser light before emission so that a plasma can be generated from substrate material adjacent the probe, (b) a light collector positioned so as to collect light from the generated plasma and (c) 5 an outer housing containing the focus means and the light collector, the housing being fixed to a cleaving device adapted to cut through the mass of substrate in a substantially horizontal direction so that the probe can pass through the substrate between first and second positions having horizontal separation. 10

19. Use according to claim 18, in which the cleaving device is fixed to a vehicle or to an airborne transportation device adapted to move the cleaving device across the surface of a mass of particulate mineral-containing substrate.

20. Use according to claim 18 or claim 19, in which the cleaving device is a 15 blade, preferably a ripper or plough.

21. Use according to any of claims 18 to 20, comprising two of said probes attached to a single cleaving device and positioned such that when the cleaving device passes through the mass of substrate the probes will be at two different 20 depths below the surface of the mass of substrate.

22. Use according to any of claims 18 to 21 additionally comprising means for processing data in real-time, storing the data, transmitting the data and/or presenting the data. 25

23. Use according to any of claims 18 to 22 additionally comprising means for measuring properties of the bedrock or overburden, in particular geo-radar resistivity, magnetic susceptibility or seismic apparatus. 30

24. Use according to any of claims 18 to 23 additionally comprising means for collecting samples of the particulate mineral-containing substrate. C:\NRPortbl\DCC\MKA\32622631 .DOC-2/I1/200 - 20

25. Use according to any of claims 18 to 24 additionally comprising means for real-time analysis of particulate mineral-containing substrate sample collection and bagging in several depths for further lab or field analysis. 5

26. A method of spatial analysis of a mass of particulate mineral-containing substrate applied in mineral exploration and production and used in the assessment of the positioning or concentration of ores, or use for mineral exploration and production of apparatus for the spatial analysis of a mass of 10 particulate mineral-containing substrate, substantially as hereinbefore described with reference to the accompanying drawings.