EP1779095A1 - Analyse de formations rocheuses par spectroscopie par plasma produit par laser - Google Patents

Analyse de formations rocheuses par spectroscopie par plasma produit par laser

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Publication number
EP1779095A1
EP1779095A1 EP05788676A EP05788676A EP1779095A1 EP 1779095 A1 EP1779095 A1 EP 1779095A1 EP 05788676 A EP05788676 A EP 05788676A EP 05788676 A EP05788676 A EP 05788676A EP 1779095 A1 EP1779095 A1 EP 1779095A1
Authority
EP
European Patent Office
Prior art keywords
outer housing
point
plasma
laser
light
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05788676A
Other languages
German (de)
English (en)
Inventor
Soeren Lund Jensen
Thomas MT-Teknik STEENBERG
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Scandinavian Highlands AS
Original Assignee
Scandinavian Highlands AS
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Filing date
Publication date
Application filed by Scandinavian Highlands AS filed Critical Scandinavian Highlands AS
Publication of EP1779095A1 publication Critical patent/EP1779095A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/71—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light thermally excited
    • G01N21/718—Laser microanalysis, i.e. with formation of sample plasma
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells

Definitions

  • the invention relates to methods of chemical analysis of chemically heterogeneous rock formations, for instance in the course of exploration or mining operations, comprising determining a chemical analysis of a man-made surface in the rock formation.
  • the invention also relates to devices which are adapted for use in such methods .
  • ores such as sulphide ores (for example copper, lead and zinc) , oxide ores (for example aluminum, chromium, vanadium, iron, titanium or manganese) or metallic alloy ores (for example silver, gold, platinum group metals) .
  • sulphide ores for example copper, lead and zinc
  • oxide ores for example aluminum, chromium, vanadium, iron, titanium or manganese
  • metallic alloy ores for example silver, gold, platinum group metals
  • the concentrations of minerals are often heterogeneous. That is, the concentration of mineral varies significantly in different regions of the formation.
  • the mineral may be found in very high or very low concentrations and may even be absent from some regions.
  • minerals often comprise grains or crystallites or crystals with varying chemical compositions and the average chemical composition of the ore varies with position in the mineralisation.
  • One option is to take samples from positions within the removed material that are very close together, which can lead to an accurate determination of the composition of the surface but is very lengthy and costly. It is also inefficient because the ore could be completely absent from a large proportion of the sampled surface.
  • X-ray fluorescence X-ray fluorescence
  • AAS X-ray fluorescence
  • ICP X-ray fluorescence
  • neutron activation X-ray fluorescence
  • none of these methods can provide reliable quantitative in-situ analysis because of the need for sample preparation. Relatively long return times also limit the use of these analytical methods.
  • the apparatus used in methods involving XRF is large and can not be used in typical holes .
  • the invention aims to provide a method of chemical analysis which is adapted for use in analysis of chemically heterogeneous rock formations and which can be used in-situ to determine efficiently and in real time the location, distribution and concentration of a mineral in a rock formation.
  • the invention provides, in a first aspect, a method of spatial analysis of a chemically heterogeneous rock formation, comprising determining a chemical analysis of a man-made surface of the rock formation, the method comprising the steps of : providing the man-made surface; providing a device which is adapted to emit a beam of laser light so as to generate a plasma at a first point on the surface, and a light collector; taking a first measurement by generating a plasma at the first point, collecting light from the plasma with the light collector, transmitting it to a spectrophotometer and determining a chemical analysis of the surface at the first point.
  • a second aspect of the invention provides an apparatus for use in carrying out spatial analysis of a chemically heterogeneous rock formation, the apparatus comprising: (a) a laser which is adapted to generate a beam of laser light;
  • a device adapted to emit a beam of laser light and comprising (i) a focus means adapted to focus the laser light before emission so that a plasma is generated at a surface adjacent the device, (ii) a light collector positioned so as to collect light from the plasma, (iii) an outer housing containing the focus means and the light collector,
  • the device which is the part of the apparatus which emits the laser light is a third aspect of the invention.
  • the invention uses laser induced plasma spectroscopy (LIPS) to carry out chemical analysis.
  • LIPS laser induced plasma spectroscopy
  • the invention has many advantages, especially in a mining or exploration operation. For instance, no sample removal from the rock formation is required and thus minimal or no sample preparation is needed and there are no special requirements as to the state of the sample surface (in particular porosity, whether the surface is wet or dry) . In some cases it may be advantageous to remove dust or mud from the surface before taking measurements but no other special preparation is required. In addition, there is no need for provision of a special atmosphere such as inert gas, a vacuum or dry air.
  • the ability to analyse without removing samples from the surface greatly increases the accuracy of determining the distribution of the ore mineral within the formation and further facilitates spatial analysis
  • LIPS can give real-time analysis meaning that the time between operating the laser and analysing the composition of the rock surface is less than 60 minutes, usually less than 30 minutes and can be below 15 minutes or 5 minutes but is most preferably between 30 seconds and 1 minute.
  • the device, apparatus and methods of analysis of the invention are advantageous in the mining industry as they are particularly adapted for use in relatively narrow openings having high length to diameter ratio
  • the invention allows determination of the chemical analysis of the inner surfaces of drilled holes in rock formations.
  • LIPS has been used in the past with respect to analysis of soil (which is rather soft in comparison with rock formations, and in which mobility of elements is generally greater than in rocks) , in particular to determine the level of contamination of soil (see US Department of Defense Environmental Security Technology Certification Program published April 2003) .
  • LIPS may also have been used for exploration methods but only for rather homogeneous rock faces and not in such a manner as to generate a spatial analysis .
  • rock formations which have hard surfaces .
  • the rock is generally consolidated sedimentary rock or igneous rock.
  • the man-made surface can be made by grinding, drilling, sawing, ploughing, blasting, hammering or by fracturing caused by man-made explosions or tensions .
  • the invention is particularly useful for analysis of openings with relatively high ratio of length to diameter, as it is particularly difficult to analyse these accurately and efficiently using conventional methods.
  • openings are: holes used for pre- extraction exploration and prospecting of metals or minerals, where the depth is usually 0.1 to 1000 meters but can be up to 1500m and the diameter is 1 to 70 cm at the narrowest point; holes used for blasting in the mining industry, where the depth of the hole is usually 0.1 to 50 meters and the diameter at the narrowest point is 1 to 20 cm,- and channels made by sawing or grinding the surface of a rock formation used for pre-extraction exploration and prospecting of metals or minerals, where the depth of the channel is usually 1 to 100 centimetres and the width at the narrowest point is 0.1 to 10 centimetres.
  • the depth of the opening is preferably between 0.1 - and 1000m and the width of the opening at the narrowest point is preferably between 1 and 100cm, more preferably 1.5 and 50cm, most preferably 1.5 and 16cm.
  • the opening in the rock formation has a diameter which is not more than 200% of the diameter of the device.
  • the invention makes use of the known laser induced plasma spectroscopy (LIPS) technique for chemical analysis.
  • LIPS laser induced plasma spectroscopy
  • 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 more elements .
  • the LIPS 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 relax and emit optical 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.
  • the invention does not require any specific type of LIPS, meaning that any suitable type of laser, duration of laser pulse, type of detector or spectrophotometer to 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.
  • pulsed lasers are Nd:YAG and Excimer lasers.
  • a Nd:YAG laser is used with 532 or 1054nm wavelength.
  • 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 25OmJ 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 and is preferably between 10 and 50 Hz, most preferably about 20 Hz.
  • LIPS can be used both as a quantitative and qualitative analytical method 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.
  • 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 spectrophotometer and determining a chemical analysis of the rock at the point on the surface.
  • 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 device. Alternatively, it may be positioned away from the rock surface being analysed and connected to the device by light guidance means which transmit the laser light to the device. Examples include optical fibres.
  • the device comprises a focus means which focuses the laser light.
  • the focused light is emitted from the device and generates a plasma at the surface.
  • the focus point of the laser beam may be at or slightly behind the surface.
  • the invention requires collecting the light generated by relaxation of the species in the plasma.
  • the light collector is a lens and the collected light is transmitted to the spectrophotometer by light guidance means, such as optical fibres.
  • the LIPS technique uses a spectrophotometer as a means of analysing the light from the plasma.
  • the spectrophotometer can be any suitable type. Preferably an Echelle spectrograph is used.
  • the spectrophotometer is located away from the surface to be analysed.
  • the invention generally also uses a detector such as a CCD or ICCD (intensified CCD) .
  • the data from the spectrophotometer should be translated into a chemical analysis by using suitable software provided, for example provided in a PC.
  • the spectrophotometer may have an input into a user- interface or a feedback system.
  • the detector is positioned between the spectrophotometer and the • analysis software. The detector transmits the data from the spectrophotometer to the software and can store information from the spectrophotometer.
  • the invention provides spatial analysis of the chemical content of the rock formation. That is, it provides a determination of the variation of the chemical analysis over a region of the rock formation. To achieve this, the method requires that measurements are taken at at least two different points on the man- made surface, and preferably at least 10, more preferably at least 100 points and usually even more.
  • the apparatus used in the invention includes a movement control system which moves the point at which the plasma is generated relative to the rock surface.
  • the chemical analysis of the surface can be made along the length direction of openings such as holes, cores or tracks in order to describe features of the chemical composition and variations thereof. Alternatively a number of spots within an area, around the perimeter of an opening or at the edge of a track can be analysed in order to establish features of the chemical composition at a certain position.
  • the movement control system is used to move the device to enable measurements to be taken at different points on the surface.
  • the device usually includes an outer housing so that the point at which the plasma is generated is adjacent to the outer housing.
  • the movement control system moves the outer housing relative to the rock surface. This is particularly useful when the device is carrying out a scanning operation (as discussed below) .
  • the movement control system moves the point at which the plasma is generated relative to the outer housing. This is a fine movement and can be used during a more detailed analysis of the surface. This allows the point at which the plasma is generated to be moved without moving the outer housing of the device itself.
  • the movement control system can be any suitable design, for instance using a spindle to achieve movement of the point at which the plasma is generated relative to the outer housing.
  • the movement controller includes control software which can be operated by a user distant from the device and the surface to be analysed.
  • the device preferably comprises an outer housing which is preferably made of plastic, metal, ox any material which is rigid and strong enough to withstand any accidental knocks against the surface. Examples are stainless steel, Inconel ® , bronze and titanium.
  • the outer housing usually has an opening or window through which the laser beam can be emitted from the device.
  • the outer housing is preferably an inner housing which is typically made of a plastic or metal material .
  • the inner housing also usually has an opening or window in it through which the laser beam can pass.
  • the laser is generally located within the inner housing, preferably in a fixed position relative to the inner housing.
  • the inner housing is moveable relative to the outer housing. This is typically achieved by use of the movement control system.
  • the outer housing and the inner housing can each be pressurised in order to prevent dust from entering the device.
  • the windows in the inner and outer housing can be covered in glass through which the laser'beam can pass, to prevent and debris evtering the housing.
  • the glass is usually spherical.
  • the device may contain an air nozzle or vent to blow away dust from the point to be analysed.
  • the device preferably includes a positioner which is adapted to maintain a predetermined distance between the outer housing and a rock surface.
  • the positioner is preferably one or more spacers which are connected to the outer housing and which maintain a predetermined distance between the outer housing and the rock surface.
  • the device preferably includes at least two spacers.
  • the device has a longitudinal axis and longitudinal sides substantially parallel to the longitudinal axis.
  • At least one spacer can be resiliently biased so as to create a force holding the device against the inner surface of an opening in a rock formation.
  • the hole can be of a size predetermined to be of diameter slightly greater than that of the device, so that there is no need for spacers.
  • the spacers can be made of any suitable material which is capable of withstanding handling and possible impact on a rock surface.
  • the device When the device is in use, it preferably moves across the rock surface in a direction parallel to its longitudinal axis.
  • the point at which the plasma is generated also moves in a direction parallel to the longitudinal axis of the device.
  • the point at which the plasma is generated can be moved so that it rotates about the longitudinal axis of the device. This latter option is particularly useful when the surface is a drilled hole.
  • the rock surface comprises sulphide minerals, oxide minerals or metallic alloys.
  • the method of the invention is particularly useful when the mineral and/or the ore is invisible with the naked eye. This is often the case for precious metals such as gold and platinum group elements. The need for chemical analysis and in particular accurately and efficiently targeted chemical analysis increases if the mineral and/or ore is not visible to the naked eye.
  • the invention is also particularly useful when the concentration of the mineral in the rock is low.
  • the invention is particularly useful when the mineral forms less than 50% of the composition of the rock, preferably less than 20%, more preferably less than 10% and most preferably less than 1%.
  • the invention is suitable for use in mining in a rock formation in which there is a heterogeneous (non- continuous) distribution of elements to be analysed.
  • the invention is particularly useful for mining and exploration activities related to platinum group metals, gold, silver, zinc, copper, vanadium, nickel, chromium, cobalt, titanium, lead, niobium, molybdenum, tantalum, tungsten, tin, antimony, bismuth and rare earth elements (and combinations thereof) .
  • the invention is particularly useful for precious metals, for example platinum group metals, gold and silver, because these precious metals are very high in value.
  • the invention is also useful in diamond mining or exploration as diamonds are known to be associated with certain mineral compositions.
  • the most common mineral compositions indicating a higher possibility of the presence of diamonds are, olivine (Fe/Mg) where the iron to magnesium ratio is important, ilmenite (Fe/Ti) the iron to titanium ratio is important and garnet (Cr, Mg, Ca, Fe) where the content and ratios are also important.
  • the invention is useful in exploration methods These include searching for deposits of useful minerals and in establishing the nature of a known mineral deposit, preparatory to development. It may also be used during mining operations, that is processes of extracting mineral deposits from rock formations.
  • the invention can also be useful in oil exploration and drilling.
  • the size of a spot analysed using LIPS can have a volume of approximately 1 ⁇ m 3 but may have a much larger volume, of between 0.05 and 0.2 mm , preferably around 0.1mm . This is typically smaller than a grain or crystallite in a mineral.
  • an average must be taken from a number of measurements to get an accurate result .
  • the average should be taken from a large number of measurements (over 100) from a small area (of about 100 cm 2 ) to give a very accurate reading. Over a large surface, this can be very slow.
  • the heterogeneous distribution of rock formations generally means that the distance between grains, inclusions and/or crystallites is typically between 10 and 10000 times higher than the size of the plasma generated by LIPS.
  • the apparatus and the method of the invention allow for inclusion of a feedback system. This can be used in conjunction with the movement controller to determine the movement of the device over the surface . Measurements can then be taken at points along the surface.
  • the feedback system also allows for analysis to be done in stages of increasing accuracy so that detailed analysis of the entire surface is not necessarily carried out . A scanning stage can be used to identify areas likely to contain the ore and then subsequent stages concentrate the analysis to determine the concentration of the ore and mineral in these areas. Hence, the efficiency can be greatly improved.
  • the apparatus and device of the invention preferably comprise a feedback system which is adapted to control the movement controller- in accordance with input from the spectrophotometer.
  • the input is produced using the information obtained from the spectrophotometer when its signal has been processed.
  • the feedback system of the invention ensures efficiency and quality of the chemical analysis .
  • the feedback system can determine the speed of the device relative to the surface of the sample, the number of points to be analysed, the position of the points and the number of measurements to be taken at each point.
  • the aim of this system is to identify areas where the ore is present by making a highly reduced number of measurements as compared to a detailed analysis of the chemical compositions with high spatial resolution along the length of the surface.
  • the feedback system can also make use of conventional statistical methods for geological exploration and sampling such as semi-variogram and Kriging or the use of an optical system for visual inspection of the sample surface or the use of a reduced number of measurements combined with conventional statistical methods or the use of knowledge obtained from pre-exploration studies and geology in general or combinations thereof.
  • a preferred method involves the device being used to analyse features of the composition of the surface in a number of stages.
  • the method additionally uses a feedback system which controls the movement of the device in accordance with input from the information obtained from the spectrophotometer and wherein the method additionally comprises the steps of; scanning by moving the point at which the plasma is generated over the surface and taking measurements at predetermined scan points; using the feedback system to compare the chemical analysis at the scan points with predetermined criteria, selecting a number of sample areas on the surface where the chemical meets predetermined criteria, and within each- sample area; moving the point at which the plasma is generated over the surface within the sample area, and taking measurements at predetermined fine measurement points.
  • the first step is typically scanning. This involves moving the device over a macroscopic area and taking measurements at scan points to identify the types of minerals that are present in the rock.
  • the scan points are preferably between 0.1 and 1 m from each other.
  • main mineral phases of the rock can be identified, for example whether the rock comprises carbonate, quartz, feldspar, amphibole etc.
  • the results are then compared by the feedback system with predetermined criteria, for example, if the mineral is associated with a sulphide phase the feedback system will ""choose ' ' sample areas which comprise a sulphide phase to undergo subsequent more detailed analysis.
  • the aim is to determine the general type of the rock rather than accurate levels of particular elements. Therefore, the detection limit does not need to be particularly ' high compared to later analytical stages and a smaller number of measurements
  • the sample area chosen varies according to the nature of the mineralization. However, a typical width is between 0.01 and 1 m. The sample area is significantly larger than the typical size of grains or crystals .
  • the next stage typically is a more detailed analysis or fine measurement within each sample area.
  • a number of measurements on a microscopic scale are carried out at fine measurement points on the surface. This means that the fine measurement points are between 0.5 and 1000 ⁇ m from each other, preferably between 1 and 50 ⁇ m from each other.
  • the fine measurement points should be spaced throughout the sample area to ensure that the measurements are made on a large number of different crystals. This enables an accurate result to be obtained.
  • the feedback system works by taking an average of a number of measurements at the fine measurement points to get an accurate determination of the overall chemical analysis within each sample area.
  • the detection limit of the device typically many measurements or spectra are taken at each fine measurement point. This allows taking into account the background noise in the spectra and to ensure that the spectrophotometer can pick up a low level of the mineral.
  • the detection limit should be below lOOppm, preferably below 50ppm. To achieve this, typically more than 100, preferably more then 200, most preferably more than 300 measurements are taken at each fine measurement point .
  • analytic techniques can be used in combination with LIPS, for example an optical system for ' visual inspection of the sample surface.
  • Other suitable techniques include geophysical methods such as magnetic field measurements (eg Fluxgate magnetometer) , inclination sensor (accelerometer) , electrical resistance measurements, acoustic methods and radiation detection devices.
  • Figure 1 shows a cross section through a device according to a preferred embodiment of the present invention.
  • Figure 2 shows a device according to a preferred embodiment of the present invention.
  • the Figures both show a device (21) within a man- made hole drilled in a rock formation (20) .
  • the device is adjacent to the inner surface (1) of the hole.
  • the device has outer housing (2) with spacers (4) attached to it .
  • the spacers are located above and below the opening (3) in the outer housing (2) through which the laser beam is emitted.
  • the spacers (4) maintain a predetermined distance between the outer housing (2) and the rock surface (1) .
  • the spacers (4) on the opposite side of the housing have a bias mechanism (5) . This ensures that the spacers on the opposite side of the housing from the opening (3) are in contact with the surface of the hole.
  • the device comprises an inner housing (6) in which the laser (8) is located. The inner housing can be moved with respect to the outer housing by means of one aspect of the movement controller (7) .
  • the device comprises an optical system (11) and a lens (10) which directs the laser beam through an opening . (12) in the inner housing (6) and the opening (3) in the outer housing (2) .
  • windows rather than openings are present in both the inner and the outer housing through which the laser beam can pass.
  • the laser beam is directed at the rock surface (1) and the optical system (11) , lens (10) , laser (8) and outer housing (2) are positioned so that the focus point of the laser beam is at or behind the surface.
  • the device also comprises a light collector (9) which, in this case, is an optical fibre and is positioned so that it can collect light from the plasma generated by the laser at the surface.
  • the device includes a sealing means (14) which prevents dust from entering the space between the inner and outer housing.
  • the device includes a power cord (15) which supplies power to the parts of the device that need it such as the laser (8) and the fine movement controller (7) .
  • a cable (17) is shown in Figure 1 which is part of a movement controller and moves the device relative to the rock surface.
  • Signal wire (16) is a part of the feedback system and relays information about the location of the device relative to the surface and the location of the point at which the plasma is generated.
  • the spectrophotometer (23) is located, in this embodiment, on the ground outside the hole.
  • the movement controller (24) is located above the hole and a user interface (22) is located above the hole and the feedback system can be controlled from here.
  • the movement controller can also be controlled from the user interface and the results of the chemical analysis from the spectrophotometer can be reviewed via the user interface.
  • Example 1 The method of the invention is used in the investigation of a mineralisation of platinum in chromite present in pyroxenite. The platinum is known to be located in a sulphide phase in the chromite .
  • the sulphide content in the chromite is known to be between 0 and 5% and the sulphide phase typically contains 0 to 100 ppm platinum.
  • a minimum average concentration of 1 ppm platinum is required for a profitable mining operation in this location.
  • the presence of chromium, magnesium, aluminium and silicon indicate a pyroxenite mineral.
  • a hole which is 500 meters long is made in the rock formation by grinding.
  • the information relating to the hole, the mineral and ore and feasible concentrations is fed into the feedback system via the user-interface.
  • the inner surface of this hole is analysed by a method of the invention.
  • the surface is divided into 1 meter segments along the length to give a total of 500 segments.
  • a reasonably accurate determination of the concentration of chromium, magnesium, aluminium and silicon is achieved by taking 200 measurements per segment (i.e. having scan points every 0.5 cm) . One measurement per scan point is taken.
  • a 10 Hz pulsed laser is used which takes 10 measurements per second and the device has a speed of 5 cm/s relative to the sample surface.
  • the scanning operation has a duration of approx. 3 hours.
  • the next step is the positioning of a number of sample areas within the chromite-containing phase is such way that the results of the measurements in these positions results in a meaningful description of the phase.
  • the feedback system will often position a number of sample areas equidistantly over the phase of interest. In this case 10 sample areas with a length of 10 cm and a width of 10 cm are positioned equidistantly over the 50 meters of the pyroxenite phase.
  • the size of the sample area is significant larger than the size of the grains or crystals on the surface to ensure that the fine measurement points within the sample area hit a high number of different grains or crystals (a high number of fine measurement points on the same grain or crystal would not result in the average chemical analysis within that sample area) .
  • the number of fine measurement points that should be analysed within each sample area depends on the required accuracy. In this case 150 fine measurement points are analysed within each sample area and the fine measurement points are positioned equidistantly within the sample area.
  • the 200 plasma are created at each fine point to give a detection limit below 50 ppm.
  • the detector creates a spectra from the 200 measurements which has. a very high level of accuracy.
  • the average chemical composition within the sample area is calculated from the results from the 150 fine measurement points analysed.
  • the results from one sample area are 1 fine measurement point with 80 ppm platinum, 1 fine measurement point with 60 ppm platinum, 1 fine measurement point with 50 ppm platinum, 1 fine measurement point with 40 ppm platinum, and 146 fine measurement points with no platinum (or a platinum content below the detection limit) .
  • Example 2 In this example a method of the invention is used to investigate the spatial concentration of platinum from example 1. This example additionally involves use of an optical feedback system.
  • the presence and position of the sulphide within the pyroxenite is investigated using an optical system.
  • a system consists of a source of light with a wavelength that is mainly reflected by the sulphide phase and not by the pyroxenite. This reflection is used to direct the device to the sulphide phase and is a very efficient way to clarify whether the sulphide phase is present and if it contains any platinum.
  • Example 3 In this example a method according to the invention including a feedback system is used in the investigation of the spatial concentration of gold in a blasting hole in a mining operation.
  • a minimum concentration of 2 ppm gold is required for a profitable mining operation in this location.
  • the aim of the investigation is to ensure that only rocks with a gold content of minimum 2 ppm are released at the blasting.
  • the blasting hole in this example is 3 meters deep and it is thought to be possible that the gold content drops below 2 ppm at a certain depth within the hole.
  • This information is entered into the feedback system. No information about the distribution or grain size is- available. In this case it is important to minimise the standard deviation of the calculated gold content .
  • a sufficiently high number of fine measurement points need to be analysed within each sample area. Only 20 spectra are taken at each fine measurement point, as gold is most often located in grains with a fairly high gold content. The number of fine measurement points is chosen to be 1000 and the size of the sample area is 4 cm by 10 cm (width by length) . The analysis of each sample area takes approx. 35 minutes when the 10 Hz pulsed laser is used.
  • the feedback system is used to evaluate whether 1000 fine scan points within a sample area results in a sufficiently accurate determination of the gold content within that area.
  • the first sample area is positioned at the bottom of the hole (i.e. at a depth of 3 meters) . If the result showed a gold content above 2 ppm no further analysis is needed and the explosives can be positioned at the bottom of the blasting hole. If the gold content is found to be 1.0 ppm at the bottom of the hole, the next sample area is positioned 1 meter from the bottom (i.e. at a depth of 2 meters) .
  • the gold content is 1.8 ppm, in this case one can assume a linear variation in the gold content and use linear extrapolation and estimate that the gold content should be above 2 ppm at a depth of 1.75 meters
  • the bottom 1.25 meters of the blasting hole could then be closed (e.g. by a solid stick made from wood) and the explosives positioned at a depth of 1.75 meters.
  • the sample area is positioned at a depth of 1.75 meters in order to verify that the gold content is above 2 ppm.
  • the results are compared with other nearby blasting holes in order to evaluate whether the results seem reasonable. If one blasting hole showing a gold content of 2 ppm at a depth of 3 meters is surrounded by blasting holes showing no gold at a depth of 3 meters, then the result showing 2 ppm is likely a faulty measurement, and is repeated.
  • This example relates to the investigation of the concentration of platinum in an exploration hole in relation to an ""invisible ore 1 ' type of mineralisation. This means that the ore is not visible to the naked eye.
  • the platinum content is related to the ratio between cobalt and nickel.
  • a scanning stage has been carried out and it is known that the cobalt and- nickel are uniformly distributed within the sample and the concentration is 0 to 100 ppm.
  • An atomic cobalt/nickel-ratio > 2.5 indicates a platinum content above 1 ppm.
  • the sample areas are positioned at 1 meter intervals. Each sample area is analysed at 20 fine measurement points and 200 spectra are taken at each fine measurement point to have a sufficiently low detection limit for cobalt and nickel. Using 10 Hz laser pulses (i.e. 10 spectra measured per second) , the time for analysing each sample area is

Abstract

Cette invention concerne des procédés d'analyse chimique de formations rocheuses hétérogènes, par exemple au cours d'opérations minières ou de prospection. Les procédés consistent à déterminer une analyse chimique d'une surface créée par l'homme dans la formation rocheuse. On décrit en outre des dispositifs conçus pour être utilisés avec lesdits procédés, lesquels procédés mettent en oeuvre une spectroscopie par plasma produit par laser (LIPS) pour effectuer ladite analyse chimique.
EP05788676A 2004-07-23 2005-07-21 Analyse de formations rocheuses par spectroscopie par plasma produit par laser Withdrawn EP1779095A1 (fr)

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GB0416512A GB0416512D0 (en) 2004-07-23 2004-07-23 Analysis of rock formations
PCT/EP2005/007931 WO2006008155A1 (fr) 2004-07-23 2005-07-21 Analyse de formations rocheuses par spectroscopie par plasma produit par laser

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EP1779095A1 true EP1779095A1 (fr) 2007-05-02

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AU (1) AU2005263614B9 (fr)
CA (1) CA2574867A1 (fr)
GB (1) GB0416512D0 (fr)
WO (1) WO2006008155A1 (fr)
ZA (1) ZA200701442B (fr)

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AU2005263614A1 (en) 2006-01-26
CA2574867A1 (fr) 2006-01-26
AU2005263614B2 (en) 2009-01-15
GB0416512D0 (en) 2004-08-25
ZA200701442B (en) 2009-03-25
WO2006008155A1 (fr) 2006-01-26
AU2005263614B9 (en) 2009-03-05

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