AU7895398A - Analysis of auriferous ore - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: De Beers Consolidated Mines Limited Actual Inventor(s): Ulf Anders Staffan Tapper Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: ANALYSIS OF AURIFEROUS ORE Our Ref 538959 POF Code: 1503/304551 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1lI (y2 6" 2 BACKGROUND TO THE INVENTION THIS invention relates to the analysis of auriferous ore.

It is known that gold concentration in a sample of auriferous ore can be measured using a nuclear analytical technique referred to as fast neutron activation analysis. The technique, which is described inter alia in University of Witwatersrand Report No SRCNS 86/03, employs a fast, i.e. high energy neutron beam with an energy level of the order of a few mega electron volts (MeV). The interaction between the neutron beam and the gold nuclei results in a gamma ray emission which can be detected by a gamma ray spectroscope.

The report referred to above proposes a neutron beam with an energy level in the range 2MeV to 4MeV for high speed analysis of the sample. The gamma ray emission from the gold nuclei has a component with an energy of 228keV and a half-life of 7,8 seconds. This relatively long half-life allows the activation process, i.e. the actual gamma ray emission, to be separated physically from the gamma ray detection apparatus. This is important because it would otherwise be difficult to measure the gamma ray emission in the high radiation environment created by the neutron source. In general, the gamma ray emission is proportional to the neutron flux in the activating beam and the concentration of gold in the sample. However the detection apparatus must be calibrated to take account of attenuation of the neutron beam and the ganma ray emission taking place in the ore sample where the gold is embedded.

-3 SUMMARY OF THE INVENTION According to the present invention there is provided an on-line- method of analysing auriferous ore, the method comprising the steps of: moving a streamn of ore particles which are to be analysed lengthwise relative to an elongate neutron emitter which emits neutrons transversely at an appropriate energy level, so that the ore particles are h-radiated by transversely emitted neutrons at that energy level, at a position downstream of the neutron emitter, measuring gamma radiation emitted by the particles, and from the measurement of gamma radiation, assessing the gold concentration of the ore particle stream.

The method may furthermore include the step of sort*n the ore particles into a concentrate fraction and a discard fraction on the basis of the gold concentration of the ore stream.

Preferably, the irradiating neutrons have a well-defined energy in the range 2MeV to 4MeV, most preferably in the range 2,4MeV to 2,6Mev. Preferably a]lso, the neutrons are generated by d-d reactions resulting from impingement of a deuteron beam on a deuterium gas target by a deuteTon beam. The deuteron beam typically has an energy of I Me"M to 3MeV.

-4 In one embodiment, the ore particle stream is conveyed linearly by a conveyor and is irr-adiated by neutrons emitted by two or more elongate neutron generators extending in the direction in which the ore stream is conveyed. The ore stream may, for instance, be conveyed linearly by a conveyor belt with deuterium gas targets of the neutron generator arranged above and below the belt so as to irradiate the ore particles, as they are conveyed by the belt, with radially emitted neutrons.

In another embodiment, the ore particle stream is conveyed along a spiral path extending about an elongate neutron beam generator arranged on the axis of the spiral path so that, as the particles move spirally in a longitudinal direction they are irradiated by neutrons emitted radially by the neutron beam generator.

The invention also extends to apparatus for on-line analysis of auriferous ore, the apparatus comprising: a protective enclosure, an elongate neutron emitter in the enclosure which is arranged to emit neutrons transversely, means in the enclosure for moving a stream of ore particles which are to be analysed lengthwise relative to the neutron emitter so that the particles are irradiated, in the enclosure, by the transversely emitted neutrons, means for moving the irradiated particle stream out of the enclosure, and means outside the enclosure for measuring gamma radiation emitted by the particles and for assessing the gold concentration of the ore particle stream from the gamma radiation measurement.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 diagrammatically illustrates a first embodiment of the invention; and Figure 2 diagrammatically illustrates a second embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS In Figure 1, which illustrates a first embodiment of the invention, a fast neutron generator is indicated generally with the reference numeral 10. The generator 10 includes a high current, small particle accelerator 12 for accelerating a charged particle beam, in this case a deuteron beam, produced by an ion source 14.

-6- The accelerated deuteron beam is split into two components which are transported by guides 16 which direct the respective components at respective deuterium gas targets 18 located above and below an endless conveyor belt 20 which moves around pulleys 22. As illustrated, the gas targets I8 are elongate in shape and are aligned linearly with the direction of belt movement.

The guides 16, gas targets 18 and conveyor belt 20 are located inside a protective enclosure 26.

Ore particles 28 which are to be analysed are fed in succession into the enclosure 26 by a feeder 30 which deposits the particles onto the upper run of the conveyor belt 20. The conveyor belt conveys the particles in the direction of the arrow 32 and eventually discharges them as shown.

The impingement of the accelerated deuteron beam on the deuterium gas targets generates neutrons through the so-called d-d reaction. It is known that the neutrons which are generated by the d-d reaction and emitted at an angle of approximately 900 to the direction of the accelerated deuteron beam have a we]l-defined energy which is typically in the range 2,4MeV to 2,6MeV for a range of deuteron beam energies- The range of deuteron beam energies may, for instance, be 1MeV to 3MeV for generation of a neutron beam having this well-defined energy which is within the optimal range mentioned previously.

With the apparatus illustrated in Figure 1, the radially emitted neutrons, i.e.

neutrons emitted at approximately 90' to the longitudinal axes of the gas targels 18, irradiate and interact with the ore particles transported in the direction of the arrow 32 by the conveyor belt 20. The nuclear interaction with gold nuclei in the particles gives rise to the emission of gamma rays as explained previously.

After neutron irradiation, the particles 28 are discharged from the conveyor belt 20 under gravity and fall through a guide 36 which drops them onto another conveyor belt 38.

The latter conveyor belt 38 transports the particles out of the enclosure 26 to an analysis station at which gamma ray spectroscopes 40 measure gamma ray emissions from the ore particle stream at positions above and below the belt. Outputs from the spectroscopes 40 are fed to a computer 42 which analyses the signals presented to it and derives, on-line, a value for gold concentration in the ore particle stream.

Knowledge of the gold concentration of the ore particle stream may usefully be employed to provide assay information which can be used to optimise the underground gold mining operation generating the ore stream. Alternatively, information concerning gold concentration can be used downstream to trigger a sorting apparatus to separate the ore particle stream into a concentrate fraction and a discard fraction.

In this embodiment, the essence of the invention is the use, in the neutron beam generator, of an elongate gas target which can generate generally mono-energetic, radially directed neutrons that irradiate the ore particles as the latter are transported in the longitudinal direction of the targets 18. With a view to compensating for the natural inhomogeneities of the individual particles and resultant variations in attenuation of the neutrons and gamma 8 rays, it is considered preferable to irradiate the particles, and also to measure their gamma ray emissions, from two sides simultaneously. It will be appreciated that further neutron beam irradiation and gamma ray detection positions may also be used to provide for further compensation for natural inhomogeneities in the ore particles.

Figure 2 diagrammatically illustrates another embodiment of the invention- Components corresponding those in Figure 1 are indicated with the same reference numerals. In this case, there is a single, elongate, vertically orientated deuterium gas target 50 aligned axially with the deuteron beam accelerator 12. The target 50 is located on the axis of a vertically extending spiral elevator 52 which conveys the ore particles upwardly, as indicated by the arrows 54, and which surrounds the target within the protective enclosure 26. After the particles leave the enclosure, i.e. after neutron irradiation, gamma ray emissions are measured by one or more gamma ray spectroscopes (not shown) located in appropriate positions relative to the spiralling ore stream.

In this embodiment natural inhomogeneities of the ore particles, and resulting variable attenuation of the irradiating neutrons and emitted gamma rays are compensated for by the fact that the particles are continuously reorientated relative to the neutron source as they are moved spirally by the conveyor.

Claims (15)

1. An on-line method of analysing auriferous ore, the method including the steps of: moving a stream of ore particles which are to be analysed lengthwise relative to an elongate neutron emitter which emits neutrons transversely at an appropriate energy level, so that the ore particles are irradiated by transversely emitted neutrons at that energy level, at a position downstream of the neutron emitter, measuring gamma radiation emitted by the particles, and from the measurement of gamma radiation, assessing the gold concentration of the ore particle stream.

2. A method according to claim 1 wherein the ore particle stream is sorted into a concentrate fraction and a discard fraction on the basis of the assessed gold concentration.

3. A method according to claim 1 or claim 2 wherein the neutron emitter emits fast neutrons with an energy in the range 2MeV to 4MeV. 10

4. A method according to clahn 3 wherein the neutron emitter emits fast neutrons with an energy in the range 2,4MeV to 2,6MeV. A method according to any one of the preceding claims wherein the neutron emitter is an elongate deuterium gas target and is caused to emit neutrons by impinging a deuteron beam thereon.

6. A method according to claim 5 wherein the deuteron beam has an energy in the range 1MeV to 3MeV.

7. A method according to any one of the preceding claims wherein the ore particle stream is conveyed linearly by a conveyor between two or more elongate neutron emitters extending in the direction in which the ore stream is conveyed.

8. A method according to any one of claims I to 6 wherein tie ore particle stream is conveyed along a spi-ral path extending about an elongate neutron emitter arranged on the axis of the spiral path. 11

9. Amethod according to any one of the preceding, claims wherein the ore particle st-earn is irradiated, within a protective enclosure, by neutrons emitted by a neutron emitter within the enclosure and the ore particle stream is then mnoved out of the protective enclosure for measurement of gamma radiation emitted by the particles. An apparatus for on-line analysis of auriferous ore, the apparatus including: a protective enclosure, an elongate neutron emitter in the enclosure which is arrange~d to emit neutrons transversely, means in the enclosure for moving a stream of ore particles which are to he analysed lengthwise relative to the neutron emitter so that the particles are irradiated, in the enclosure, by the transversely emitted neutrons, means for moving the i-radiated particle stream out of the enclosure, and means outside the enclosure for measuring gamma radiation emitted by the particles and for assessing the gold concentration of the ore particle stream from the gamnma. radiation measurement- 12

11. An apparatus according to claim 10 wherein the neutron emitter is arranged to emit fast neutrons with an energy in the range 2MeV to 4MeV.

12. An apparatus according to claim 12 wherein the neutron emitter is arranged to emit fast neutrons with an energy in the range 2,4MeV to 2,6MeV.

13. An apparatus according to any one of claims 10 to 12 wherein the neutron emitter is an elongate deuterium gas target and the apparatus includes means to produce a deuteron beam and cause the deuteron beam to impinge on the target.

14. An apparatus according to claim 13 wherein the means to produce the deuteron beam is arranged to produce a deuteron beam having an energy in the range 1MeV to 3MeV. An apparatus according to any one of claims 10 to 14 and including a plurality of parallel elongate neutron emitters in the enclosure and a conveyor in the enclosure to convey the ore particle stream linearly between the neutron emitters in their lengthwise direction. 13

16. An apparatus according to any one of claims 10 to 14 and including a spiral conveyor for conveying the ore particle stream along a spiral path extending about the neutron emitter.

17. An on-line method of analysing auriferous ore substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings.

18. An apparatus for on-line analysis of auriferous ore substantially as herein described with reference to Figure 1 or Figure 2 of the accompanying drawings. DATED: 7th August, 1998 PHILLIPS ORMONDE FITZPATRICK Attorneys for: DE BEERS CONSOLIDATED MINES LIMITED ^u^^^^tfc