AU2009225366A1 - Opal sorting multi-apparatus assembly - Google Patents

Description

11445AU(2)DIVDIV ORIGINAL Complete Specification Applicant: Opdetech Pty Ltd Title: Opal sorting multi-apparatus assembly Address for Service: LESICAR PERRIN, 49 Wright Street, Adelaide, South Australia 5000, Australia The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 Opal sorting multi-apparatus assembly The present invention relates to an opal sorting multi-apparatus or table assembly and in particular to an assembly that can first separate mined material into a range of sizes, and subsequently separate the opal-bearing material from the from the mined material. BACKGROUND OF THE INVENTION Opal sorting machines are known and rely on the fact that opal absorbs electromagnetic radiation in the ultra-violet part of the spectrum that is then re-radiated as visible light at a wavelength typically around 470 nm. The half-life time of this re-radiation is some 4 seconds. This property is currently exploited whereby mined ore containing opal and other material including dust and rocks are placed on a moving belt in a dark room where the ore is exposed to ultraviolet radiation. As the belt moves out of the ultraviolet irradiating zone it emits radiation in the visible spectrum where human operators then pick out the opal. Typically, an opal-sorting table includes a number of human operators located around the belt whose task is to handpick the radiating opal. This procedure is commonly referred to as noodling. As a consequence of the use of human operators it is well accepted that the efficiency of noodling, in terms of the opal that is collected is of the order of some 60%. There are a number of limitations to this well-known method. Not only is the cost of human operators relatively high, but also people tend to make mistakes and do get tired, resulting in the efficiency of picking out the opal unreliable over time. Further still, in cases where there may be a range of sizes of opal or opal slivers moving down the belt, human operators will typically collect the larger fragments, resulting in the smaller fragments not being collected. In addition at times where there may be a large number of opal stones and slivers moving down the belt, human operators may simply not be able to pick up all the radiating stones. Automatic sorting tables have been proposed where optical detectors are used to discriminate between the opal and other material. The light detection means in these tables are not able to localise any existing stones, the optical detection means having a large field of view. Other problems of using such tables also includes the fact that the optical detectors are not extremely sensitive, this exacerbated by the conditions under which these tables may be required to operate, including high temperatures and vibrations. Furthermore, contaminating elements such as light, dust and other particles affect the detection area.

3 Once a stone has been detected an air pulse is used as the detected stone falls of the belt to force the stone into a collection bin. There are numerous problems with the use of such a table. One of the more common ones is the fact that the use of an air pulse causes dust and other light particles to be raised into the air. Further, use of an air pulse not only separates the opal stones and slivers but other particulates since the air pulse has a certain minimum depth or length. A solution to the problems arising from the use of an air pulse to sort the opals is offered in a co pending application and is also referred to in the following description. A further difficulty with current noodling methods is the fact that mullock, the by-product of opal mining within which is still to be found a fair percentage of opal, comes in a range of sizes. Using one table to sort out opal from different size other materials is not optimal for different sized materials requires different tuning of optical detection techniques as well as different means to physically separate the opal from the rest of the material. It is an object of the present invention to provide an opal detection assembly that overcomes at least some of the abovementioned problems, or provides the public with a useful alternative. SUMMARY OF THE INVENTION Therefore in one form of the invention there is proposed an opal detection assembly for detecting opal in mined ore, said assembly including: - a transport means adapted to carry said mined ore; - a source of ultraviolet light located at a first section of said transport means adapted to scatter ultraviolet radiation onto said mined ore; - an optical detection means located at a pre-determined distance after said first section of said transport means and adapted to detect visible light re-radiated from opal in said mined ore; a first shield that seeks to minimise the amount of ultraviolet radiation scattered outside of said first section; and a second shield that seeks to minimise the amount of contaminating visible light that is detected by the optical detection means.

4 Conveniently, the optical detection means are housed in a cover and may include a focal lens adapted to limit or expand the area of detection. The second shield may additionally contain a transparent screen below the optical detection means, and be adapted to protect the optical detection means from dust or unwanted material. The screen is, preferably, removable for cleaning and may include filters adapted to filter ultraviolet light, Further, the second shield may contain at least one curtain, and possibly up to four curtain, that extend substantially downwards to said transport means in a configuration that further seeks to minimise the amount of contaminating visible light detected by the optical detection means. Curtains used in the screen, preferably, include a first layer constructed of a resiliently flexible material adapted to strengthen said curtain and a second layer including ultraviolet light absorption means said second layer facing toward the optical detection means. Preferably, said detection means is in communication with a control means adapted to control a sorting assembly. The detection means, in a preferred embodiment includes at least one photomultiplier tube and at least one control system. Photomultiplier tubes are conveniently housed in a duct through which air is allowed to pass thereby cooling said tubes and furthermore may include an access and visual inspection means. Preferably, the opal detection assembly further includes a sorting assembly adapted to controllably move sorted material between a first position thereby allowing at least one object to move through a first trajectory and at least one second position thereby allowing said object to move through at least one second trajectory. The control means may be connected to both the sensor and the detection means said control means adapted to control the position of said sorting assemebly according to both the pre determined characteristic as well as the speed of the transport means. Preferably, the opal detection assembly further includes a hopper adapted to receive mullock said mullock then transported to a dust trommel to separate mullock from dust, said dusted mullock further transported to a sorting trommel including a plurality of sorting means to separate the dusted mullock into different size range, each sorting means connected to a chute to feed the particular size range to said transport means. The sorting trommel preferably includes a hollow rotating cylinder having an outer skin having multiple apertures, said trommel having several different sized apertures extending 5 longitudinally across said trommel and adapted to allow for different size particles of the mullock falling therethrough. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several implementations of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings, Figure 1 is a perspective schematic view of a table discrimination apparatus incorporating the opal detection assembly of the present invention; Figure 2 is a cross-sectional view of the apparatus of Figure 1; Figure 3 is a partial perspective view of a table discrimination system detailing the light detection and shielding system of the apparatus of the present invention; Figure 4 is a schematic perspective view illustrating the relative orientation of two adjoining tables containing the opal detection assembly as well as means to cool, protect and inspect the control means. Figure 5 is a partial schematic view illustrating mechanical mechanism embodying the present invention; Figure 5 is a perspective schematic view of the assembly embodying the present invention; Figure 6 is a perspective schematic view of the assembly further embodying the present invention; and Figure 7 is a perspective view of the assembly as in Figure 6 detailing some of the internal construction . DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and 6 scope of the invention. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. The present invention discloses an improved assembly 10 for the detection of opal in mined ore 12. Mined ore 12 is first irradiated with ultraviolet light 14 so that any opal existing within will re radiate light 16 in the visible spectrum. The visible light 16 is detected by optical sensing devices 18 which in order to detect effectively, must be shielded against any contaminating elements such as exterior light and dust. The invention proposes the use of a first shield 20 to minimise any ultraviolet light 14 from escaping a section of the transport area, together with the use of a second shield 22 which seeks to minimise the amount of contaminating light reaching the optical sensing devices 18 and to further minimise this light, and a series of light- absorbing curtains 24 and 26. Furthermore, any dust and other particles are shielded by a protective cover 28 and below the sensing devices 18, a removable transparent screen 30, A control means 32 also exists to control a flipper 34 and are cooled and protected from contaminating particles thereby further improving opal detection. Referring firstly to Figures I to 4 there is shown an opal-sorting table 36 including a frame 38 and four supporting legs 40, support beams 42 extending between each adjacent leg 40 for stability of the table 36. Feet 42 on each leg 40 help to distribute the weight of the table 36 on a floor. A conveyor belt 44 extends along the table 36 and is supported by rollers 46 and 48 at either end, one of the rollers coupled to and rotatably driven by a motor (not shown) to drive the belt 44. Typically, the motor is a hydraulic motor although it may equally well be an electric motor. Located above and extending perpendicularly above one end of the belt 44 is a longitudinal hopper 50 that is loaded with material 12 to be sorted. A third roller 52 extends longitudinally with the hopper 50 and is in contact with the material 12. A gap 54 in between the roller 52 and the hopper 50 allows material 12 to pass from the hopper 50 and drop onto the belt 44. By controlling the speed of the roller 52 the operator is able to control the rate of material 12 that drops onto the belt 44. As with the conveyor belt 44, the roller 52 is driven by a suitable motor. In operation the conveyor belt 44 typically moves at a speed of some 1.4 to 2.7 metres per second, the speed limited to the operation of the flippers 34 by solenoids as discussed below. At times the speed of the main belt may by synchronised with the speed of the hopper roller 52. However, at times it may be desirable to vary the speed between the two, that depending on the type of material that is being sorted. For that reason the speed of the rollers is controlled independently.

7 It should be understood that the method described above for feeding mined ore onto the transport means is by no means the only method of achieving this and the present invention is not intended to be limited to only this method. The material that passes through the gap 54 and drops into belt 44 is exposed to ultraviolet radiation 14 by the use of longitudinal ultraviolet lamps 56 located above the belt 44. A shield 20 extends over the lamps 56 to minimise the amount of radiation 14 that is scattered outside of the shielded area, the lamps 56 and the shield 20 held in place by the use of arms 58 that are attached to frame 38. Any opal then absorbs the ultraviolet radiation 14 and re-radiates it in the visible part of the spectrum. The shield 20 is positioned in a way that prevents scattered ultraviolet light 14 from escaping the work area thereby providing a much more efficient process. Located above and towards the other end of the belt 44 are optical sensing devices 18 extending longitudinally across the belt 44. The devices typically include optical detectors 18 that collect radiated light 16 and feed it into an optical to electrical signal converter, such as a photomultiplier tube 60. The optical sensing device 18 is in fact an optical fibre cable. Any detected signal from the photomultiplier 60 is assessed by a suitable control device 62, supplied power from source 64 that is operatively connected to a mechanical flipper 34 by control cable 66. Each optical sensing device 18 includes its own photomultiplier tube 60 that in turns controls its own mechanical flipper 34. The photo multiplier tubes 60 may be separately cooled to improve their sensitivity and this will be discussed below. Furthermore, the use of the optical fibre cable allows them to be separated from the rest of the table 36 thereby removing any unwanted vibrations. To avoid any contaminating light from being detected by the photomultipliers 60 through fibres 18, a shield 22 covers the detection area and the optical componentry 18 extends into shield 22 though aperture or slit 66. The optical componentry 18, typically the ends of the optical fibres are housed in a cover 28 having a transparent glass or plastic screen 30 that protects the optical componentry 18 from any dust or unwanted material and is typically adapted to be easily removable for cleaning. One typical way to be able to do this is to have the screen 30 longitudinally slidable within a housing 68, the end of the screen 30 reachable through a slot on the side of the shield 22 where it is covered by plate 70. The screen 30 may also include filters adapted to filter out the ultraviolet light 14 that is used to excite the opal in the first instance. It is obviously quite integral to the operation of the whole of the table 36 that the light that is sensed reaching each optical detector 18 be localised to allow for the fine control of each flipper 8 34. For that reason inside the shield 22 that extends towards the centre of the belt 44 are curtains 24 and 26 that further ensure that no other light reaches the optical detector 18. Although the curtains 24 and 26 are designed to extend downwardly they are very light and can easily be swayed to ensure that they do not cause material 12 to be held back on the belt 44. The curtains 24 and 26 are typically constructed of two layers of material, the first layer 72 being of a resiliently flexible material to provide for the strength of the curtain, the second layer 74 providing for the required absorption characteristics, as illustrated in Figure 3. At times up to four curtains may be used to cut out intrusive light. Illustrated in Figure 4 is a schematic diagram illustrating two opal-sorting tables 36 both of which contain the opal detection assembly of the present invention, positioned next to each other to accommodate for different particle sizes. This process is described further on. Located above and extending longitudinally along the trailer is main duct 76 in which are mounted photomultiplier tubes 60. The main duct 76 allows for the passage of air therethrough providing cooling for the photomultiplier tubes 60 from an air-conditioning means (not shown). Ducts 78 connect cavities 80 located below the duct 76 within which are located the control systems 62 associated with each photomultiplier tube 60 and flipper 34. Both the main duct 76 and the cavities 80 include transparent doors 82 enabling visual inspection and access to the tubes 60 and control systems 62. Typically there are some twenty flippers 34 extending below and across the front of the belt 44. The flippers 34 are adjacent to each other so that there is a minute gap there in-between, typically of the order of 1-2 millimetres. The flippers 34 are designed to very quickly pivot around pivot point 84. Their position is chosen so that when the flipper 34 has not been activated material transported on belt 44 is caused to fall in trajectory 86 whilst when the flipper 34 has been activated it rotates inwardly and upwardly to deflect material into trajectory path 88. Those skilled in the art will now appreciate that when one of the optical sensing devices sense optical radiation with the aid of the opal detection assembly of the present invention, the signal is collected and amplified by the photomultiplier tube 60 before it is fed into the control device 62. The device is semi-intelligent and can calculate, based upon the speed of the belt 44 that it is typically able to measure by the use of an appropriate sensor or timing pulse 90, precisely when it needs to activate the flipper 34 to cause that material 92 that the optical detector 18 has detected to radiate visible light, to be ejected into path 88 where it is then collected in bin 94. Deflection plates 96 and 98 help to collect the flipped or ejected material 92 into the bin 94.

9 Each flipper 34 is activated by the use of an air solenoid 96 fed air by the use of hoses 98 and 100 that control the air solenoid 96 to extend and retract as desirable. An air supply is provided though regulator 102 as is well known in the art. Those skilled in the art will appreciate that with a row of flippers extending across the belt 44,, different flippers 34 will be caused to operate to ensure that any detected material is collected into bin 94. Other material 104 that is non-radiating then drops onto a further conveyor belt 106 supported at one end by roller 108 to be transported away from the table 38, typically to an area that is some distance away. Since each optical detector 18 and its own control device 62 operate each flipper 34 independently, even small opals or slivers of opal are detected and sorted from the rest of the material. In cases where there may be a relatively large piece of opal that is detected, adjoining flippers may equally well be activated. The control means 32 can be programmed to allow for different working scenarios. For example if an optical detector 18 has detected two stones very close to each other, the control system 62 may very well instruct the flipper 34 to remain in the flipped position until both stones have been directed into bin 94. In addition, the flipper 34 will remain in the flip or open position depending on the length of the light pulse that has been detected, as would be the case where a long piece of opal has been detected. The size of the flippers 34 can also be varied to allow different material to be sorted. For example, the flippers may very well be wider and longer. However, any lengthening of the flipper will affect the material collected for a longer flipper will sweep through a greater path of the ejected material. The actual relative sizes and length of the flippers is therefore to be determined on the physical material to be sorted and the stroke length of the flipper that is required. Typically the optimal stroke of the flipper is some 25 millimetres. illustrated in Figure 5 is a flipper 34 in more detail. Thus the flipper 34 pivots around pivot point 84, in this case being a rod 110 along which are pivotable all of the flippers 34. The tension on the flippers can be adjusted by the use of suitable nuts 112 and 114 on spring or biasing means 116. The flippers 34 are mounted in a suitable frame including side arms 118 and rear support beam 120. It is to be understood that the method of sorting the opals using a flipper 34 and control means 32 as described above, forms part of a co-pending application and the present invention need not be limited to this type of sorting means.

10 The belt 44 illustrated in Figure 1 is a V -shaped belt that in some circumstances may have the advantage of ensuring that any material is linearly aligned as it travels down the belt. However, the optical devices 18 as used in the present invention are capable of detecting the opal across a flat belt without requiring the use of a grooved belt. Those skilled in the art will now appreciate that the use of the table incorporating the opal detection assembly of the present invention overcomes the problems of separating out opal from the rest of the material even where the relative sizes and amounts of the opal vary greatly across the belt. The optical devices 18 may further include a focal lens (not shown) that can be adjusted to vary the diameter of the area from which optical light is collected, The table 36 as proposed in the present invention has increased the efficiency of noodling to levels well above 90% and even close to 98%. This has great economic advantages in that it enables mullock heaps from current opal mining to be thoroughly processed. It also enables mullock that has already been noodled by human operators to be re-noodled to collect any opal that has been missed. With the speed of the belt operating at metres per second, a typical table that has a belt some 1 metre in width can process up to I tonne of mullock per minute. Removing the use of human operators increases the total operating time of such a table without concern of operator fatigue and efficiency. It should therefore now be apparent that the present invention including the provision of light shields, curtains and a UV filter means that the photomultiplier tube can detect even a small amount of light. Further isolation and cooling of the photomultiplier tubes increase their sensitivity. This provides for a much more accurate detection as tests have shown. As mentioned above, the optical detectors field of view and size of the flippers need to be able to accommodate different sizes of mullock that passes through the table. In the case where there are a variety of sizes of mullock the efficiency of opal detection may not be as high as it could be if the mullock was more uniform in size, Illustrated in Figures 6 and 7 is an assembly embodying the present invention and including a plurality of opal-sorting tables all of which incorporate the opal detection assembly of the present invention. The tables are set in series, wherein each table is pre-set to be able to detect opal from mullock of a certain uniform size. The assembly further includes means to separate the mullock into separate sizes as well as to separate the mullock from dust. Finally, the assembly is mounted on a drivable platform and can thus be transported to a desired location where it can be used to sort opal from general mullock.

11 Referring to Figures 6 and 7 in detail there is shown a truck trailer 122 mounted at the front on a dolly 124 including wheeled axles 126 with a plurality of wheels 128. The trailer 122 further includes a wheeled axle 130 at the rear end for supporting the trailer 122. Mounted at the front of the trailer is a grizzly hopper 132 into which can be loaded mullock 134 using typically a front end loader 136. The hopper 132 includes a grid 138 commonly known as a grizzly gird that oily allows passageway therethrough of particles less than a certain size, typically 75 millimetres and less. The mullock 134 is then transported by a conveyor belt 140 located at the bottom of the V-shaped hopper 132, the conveyor belt 140 supported by the use of rollers 142. Typically an electric motor is used to drive the conveyor belt although other motors, such as hydraulic motors, could very well be used. Conveyer belt 140 feeds the mullock 134 from the hopper 132 into a dust trommel 144, the dust trommel 144 including a cylindrical mesh 146 of a fine size through which passes fine and small particles to be discarded from the rest of the mullock 134. Typically the size of the mesh in the dust trommel 144 is of the order of some 7 to 7.5 millimetres. The dust trommel 144 includes a plurality of ribs 148 for structural integrity and is adapted to rotate on a central shaft 150 rotatably driven by an appropriate motor at a speed of up to several revolutions per second. Any particles and dust that fallout of the dust trommel 144 are collected on a dust conveyor belt 152, shield 154 assisting to direct the fine particles onto the conveyor belt 152. The conveyor belt 152 then passes through the rest of the trailer 122 until it emerges at the rear end thereof, where it is dropped onto a cross-over conveyor 156 to the tailing conveyor 158 to be disposed of as a sorted mullock heap 160. The dust trommel 144 angles downwardly and other particles that are larger than the mesh size on the dust trommel 144 fall under gravity into bin 162, bucket elevator 164 then raising the dusted mullock to a sorting trommel 166. The sorting trommel 166 is of a cylindrical configuration and includes different sized meshes extending around the outer circumference of the sorting trommel 144, the sizes of the meshes increasing down the trommel 166. The first mesh 168 typically is a grid with spacings some 10 millimetres in size enabling particles from around 7 to 10 mm to fall through. Second mesh 170 is typically some 16 mm grid spacings allowing particles up to 16 mm to fall through. Third mesh 172 has grid spacings some 25 mm apart allowing particles of up to that size to fall through whilst fourth mesh 174 has grid spacings up to 50 mm allowing particles up to that size to fall through. The different meshes are mounted on a central shaft 176 and are separated by wheels 12 178 that are attached to the shaft 176 to provide the structural support for attaching the mesh to the shaft 176. It is to be understood that it is not the intention to limit the present invention to the particular sizes of mesh as detailed above. The mesh sizes are used as a general guide only. Furthermore, it is not intended to limit the invention to four mesh sizes. In fact, the assembly may include more or less different mesh sizes to aid in the separation of the mullock into particular size ranges. Located below and coupled with each mesh size is an opal-sorting table 38. Thus mesh 168 feeds particles of sizes up to 10 mm to table 180, mesh 170 to table 182, mesh 172 to table 184 and mesh 174 to table 186. The tables are all located in a dark room 188 ensuring that no outside light can enter the room, a door providing access (not shown). Each table has a hopper fed material through chute 190 to ensure that material passing through the mesh is fed into the table hopper 50 only as discussed earlier. Mullock that is more than 50 mm in size can either fall into a separate bin to be later sorted by hand or alternatively to yet another table adapted for sorting out such large stones (not shown). Any other material that has not passed though any of the grids then passes out of the sorting trommel to chute 192 where it then falls onto the cross-belt 156 to be removed from the trailer assembly. Those skilled in the art will now appreciate that the present invention provides for an assembly that can sort opal from other material regardless of the size of the other material by sorting out the material into separate size ranges before it reaches an opal-sorting table. Since the relative range of particles sizes for each table is known beforehand, the configuration of the table can be optimised for that particular size range. Some of the factors that can then be optimised include the field of view of the optical detectors. Larger particles will require a larger field of view than smaller ones. The width and length of the mechanical flippers may also be varied to suit different particle sizes. The mullock that has had opal removed from it then falls onto a central conveyor belt 194 25 (equal to the conveyor belt 76 in Figure 1-4) that then conveys the mullock to the crossover belt 156 for disposal as discussed above. In the above embodiment there were shown four tables within a sealed room 188 that separate opal from mullock. Each table may have different size flippers to separate opal in a range of particle sizes. For example, the very first table that separates particles whose size is up to 10 13 mm uses flippers that are some 110mm in length and 48 mm wide, a total of twenty flippers extending across the table. The second table that separates particles up to 16 mm in size typically uses flippers that are the same size as the first table. The third table separates particles up to 25 mm in size typically uses flippers that are 120 mm in length and 54 mm in width, there being some 18 flippers across the table. The fourth table separates particles up to 50 mm in ' size uses flippers that are 140 mm in length and some 65 mm in width, there being 16 flippers across one table. Finally, although not shown in the embodiment above there may very well be a further table designed to separate particles that are up to 75 mm in size. Such a table may include flippers that are some 140 mm in length and are some 550 mm in width there being only some two flippers across the table. It is to be understood that the particular operation of the tables may vary. For example, instead of using mechanical flippers one may equally well employ an air pulse. Other features that may be changed is the configuration of the flippers as well as the optical detection means. The primary advantage of the present invention is that it improves upon the efficiency of opal separation by using tables that are configured for different size particles by the use of the dust and sorting trommel. The use of multiple tables improves the total amount of mullock that can be passed through the assembly per any given hour. Common use of cooling means that the tables can all operate under optimal conditions. Mounting of the assembly on a trailer means that it can be easily transportable to different sites and especially ones where the mullock has already been rudimentary sorted and where the use of current hand-techniques is no longer economically feasible. In summary, the opal detection assembly which is incorporated into the opal sorting table described above provides for the effective detection of opal in mullock prior to sorting. The inclusion of various components in the assembly such as the shields, the curtains and the transparent screen provide for a very accurate detection of visible light from the opals. Furthermore, the present invention provides a means for sorting the objects into various size groups prior to being fed to individual tables containing the detection assembly. Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

Claims (19)

1. An opal detection assembly for detecting opal in mined ore, said assembly including: - a transport means adapted to carry said mined ore; - a source of ultraviolet light located at a first section of said transport means adapted to scatter ultraviolet radiation onto said mined ore; - an optical detection means located at a pre-determined distance after said first section of said transport means and adapted to detect visible light re-radiated from opal in said mined ore; a first shield that seeks to minimise the amount of ultraviolet radiation scattered outside of said first section; and a second shield that seeks to minimise the amount of contaminating visible light that is detected by the optical detection means.

2. An opal detection assembly for detecting opal in mined ore according claim 1, wherein said optical detection means are housed in a cover.

3. An opal detection assembly for detecting opal in mined ore according to claim 1 or claim 2, wherein said optical detection means includes a focal lens adapted to limit or expand the area of detection.

4. An opal detection assembly as in anyone of the above claims wherein said second shield contains a transparent screen below the optical detection means and is adapted to protect the optical detection means from dust or unwanted material.

5. An opal detection assembly as in anyone of the above claims wherein said transparent screen is housed so as to be removable for cleaning.

6. An opal detection assembly as in anyone of the above claims wherein said transparent screen includes filters adapted to filter ultraviolet light.

7. An opal detection assembly as in anyone of the above claims wherein said second shield contains at least one curtain which extends substantially downwards to said transport means in a configuration that further seeks to minimise the amount of contaminating visible light detected by the optical detection means. 15

8. An opal detection assembly as in anyone of the above claims wherein the second shield contains up to 4 curtains.

9. An opal detection assembly as in anyone of the above claims wherein said curtain includes a first layer constructed of a resiliently flexible material adapted to strengthen said curtain and a second layer including ultraviolet light absorption means said second layer facing toward the optical detection means.

10. An opal detection assembly as in anyone of the above claims wherein said detection means is in communication with a control means adapted to control a sorting assembly.

11. An opal detection assembly as in claim 10 wherein said control means includes at least one photomultiplier tube and at least one control system.

12. An opal detection assembly as in claim 11 wherein said photomultiplier tubes are housed in a duct through which air is allowed to pass thereby cooling said tubes.

13. An opal detection assembly as in anyone of the above claims wherein said control system and said photomultiplier tubes include an access and visual inspection means.

14. An opal detection assembly as in anyone of the above claims wherein said opal detection assembly further includes at least sorting assembly adapted to controllably separate sorted material between a first position thereby allowing at least one object to move through a first trajectory and at least one second position thereby allowing said object to move through at least one second trajectory.

15. An opal detection assembly as in anyone of the above claims wherein said opal detection assembly further includes a control means in connection with both the sensor and the detection means said control means adapted to control the position of said sorting assembly according to both the pre-determined characteristic as well as the speed of the transport means.

16. An opal detection assembly as in anyone of the above claims wherein said transport means is a conveyor belt.

18. An opal detection assembly as in anyone of the above claims wherein said opal detection assembly further includes a hopper adapted to receive mullock said bullock then transported to a dust trommel to separate mullock from dust, said dusted mullock further transported to a sorting trommel including a plurality of sorting means to separate the dusted bullock into 16 different size range, each sorting means connected to a chute to feed the particular size range to said transport means.

19. An opal detection assembly as in claim 18 wherein said hopper includes a grizzly, optionally having parallel bars 75mm apart.

20. An opal detection assembly as in claim 19 wherein said sorting trommel includes a hollow rotating cylinder having an outer skin having multiple apertures, said trommel having several different sized apertures extending longitudinally across said trommel and adapted to allow for different size particles of the mullock falling therethrough.