Classifying – separating – and assorting solids – Sorting special items – and certain methods and apparatus for... – Condition responsive means controls separating means
Patent
1995-01-25
1997-02-18
Dayoan, D. Glenn
Classifying, separating, and assorting solids
Sorting special items, and certain methods and apparatus for...
Condition responsive means controls separating means
209589, B07C 500
Patent
active
056034148
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of and apparatus for detecting diamonds in a rock sample, and can be used when prospecting for diamonds to locate microdiamonds in particulate mineral material.
When prospecting for diamonds, samples of rock, e.g. drill cores, are taken and are reduced to powder particles (particle size generally in the range from 50 to 300 micrometers ), e.g. by chemical treatment and grinding. This mineral powder is analyzed by taking samples and spreading the samples on microscope slides, which are then observed under a microscope by a skilled operator.
The rock samples may contain diamonds, usually in a very low concentration, and these will give rise to small diamonds or fragments of diamond--microdiamonds--in the powdered mineral sample. Thus diamondiferous rock may be identifiable by the presence of microdiamonds in the mineral powder samples.
Detecting microdiamonds in mineral powder samples is a very skilled job and very time consuming. The microdiamonds themselves may be graphite covered and very difficult to recognize. In most cases, there will be no microdiamonds in a sample, and a very large number of samples has to be processed as part of the prospecting process.
It is an object of the present invention to provide a method of and apparatus for detecting diamonds in a rock sample whereby diamond can be identified uniquely. It is also an object of the present invention to provide a method of and apparatus for detecting diamonds in a rock sample which can be carried out automatically by a machine.
SUMMARY OF THE INVENTION
The present invention provides a method of and apparatus for ascertaining whether diamonds (ie., particles comprising diamond material) are present in a layer of powder particles obtained by reducing a rock sample and placing (normally depositing) the powder particles on a substrate.
The invention exploits the relative transparency of diamond material to soft (i.e. relatively low energy) X-radiation compared with other material. Powder particles which transmit X-radiation, or only absorb a small amount of X-radiation are identified as probably diamond. The location of the diamonds in the sample may also be identified, and the weight of the diamonds present may be estimated. The powder particles may be identified as being diamond or not.
Diamond is found to have relatively high transparency to soft X-radiation compared with all other minerals with which diamonds are likely to be associated. This is due to the low atomic number of carbon, from which diamond is formed. All the other minerals present in the sample will contain a significant proportion of higher atomic number elements, such as aluminjure or silicon, which have significantly higher absorptions than diamond. The energy of X-rays used depends on the particle size, but will usually be about 8 keV.
Preferably, the layer of powdered mineral material is mounted on a standard soft X-ray transparent microscope slide, which forms said substrate.
Mineral powder may be prepared by crushing rock samples and treating the resulting powder in a similar process to that used in normal prospecting.
Although for convenience, the small particles are referred to herein as powder, the particles can be of a size normally considered to be grit rather than powder. The particles can typically be in the size range about 20 micrometers to about 600 micrometers, preferably about 50 micrometers to about 300 micrometers, but nonetheless the particles may have a size of up to about 1 mm or about 2 mm or more and could mainly be in the range about 1 mm to about 2 mm.
The apparatus of the invention may be set up to indicate which samples have microdiamonds, to give an indication of the location of the microdiamonds in the layer and, possibly, to indicate the size and weight of the diamonds identified. In order to do this, the image of X-radiation transmitted by the layer will have to be analyzed by an image processing technique. For example, the powder may be set up on a slide with defined corn
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Cooper Martin
Rooney Marie-Line
Smith James G. C.
Smith Martin P.
Dayoan D. Glenn
Gersan Establishment
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