WO2007108707A1

WO2007108707A1 - Mining apparatus and method

Info

Publication number: WO2007108707A1
Application number: PCT/NZ2007/000057
Authority: WO
Inventors: Peter Lewis Hilton
Original assignee: Peter Lewis Hilton
Priority date: 2006-03-22
Filing date: 2007-03-22
Publication date: 2007-09-27
Also published as: WO2007108707A8; NZ546071A

Abstract

A gold recovery apparatus having at least one flow path through which a slurry can be passed. At least a portion of the lower part of the interior of each flow path has a non-smooth surface. Each flow path is configured to promote a substantially non-turbulent or laminar flow in any slurry passing through it except adjacent to the non-smooth surface. The non smooth surface is preferably a ribbed surface having ribs aligned perpendicular to the flow path and with a pitch of about two millimetres. The non-surface can be a lightly brushed ribbed fabric. The light pile of the lightly brushed fabric can help to retain the gold.

Description

Mining Apparatus and Method

FIELD OF THE INVENTION

This invention relates to apparatus and method for the recovery of gold and other minerals, and/or to apparatus suitable for screening slurry or grading metal etc, and/or to a vacuum nozzle, all being suitable for use in a mining apparatus or gold recovery plant.

BACKGROUND

In previous times gold was often discovered on the surface of the ground. However, as these supplies have largely been exploited, it has been necessary to mine further into the ground to find gold.

In the past and in some parts of the world gold miners have used the wind to separate gold particles from the soil they are mixed with. In this method, the soil is tossed upwards and the heavier gold particles drop down and are caught while the lighter soil is blown away.

However, it is more common to mix the soil, or pulverised rock, etc with water to form a light slurry and then to separate the gold from the slurry. Again, because the gold particles are usually the heaviest, they can be caught while the rest of the soil etc is washed away. A sluice box typically includes a number of traps in which the gold particles collect and the remainder of the soil or ore is washed past. Some soil or ore contains black sand or other relatively heavy particles which also tend to collect in these traps, meaning that the traps fill up too quickly, and if they are not cleaned out then subsequent gold particles tend to wash over the traps and are lost.

The sources of gold are becoming increasingly sparse and these days it is often necessary to process many tons of soil to obtain even a small quantity of gold. This means that to recover the gold economically, it is increasingly important to find efficient ways to convert the ground into a slurry, and to separate the often fine gold particles from the huge quantities of soil.

Depending on the locality, much of the gold present in the ore that is mined is in the form of small nuggets or flakes or relatively fine dust. These types of gold are often the most difficult to recover and many recovery systems are not able to recover the dust efficiently meaning that a significant proportion of the potential gold yield from an area is not realised. In a competitive environment this wastage can mean the difference between an economically viable mining operation and one that is not.

OBJECT

It is therefore an object of the present invention to provide a gold recovery apparatus or method which will at least go some way towards overcoming the above mentioned problems, or at least provide the public with a useful choice.

STATEMENTS OF THE INVENTION

Accordingly, in a first aspect, the invention may broadly be said to consist in a gold recovery apparatus having at least one flow path through which a slurry can be passed, and at least a portion of the lower part of the interior of the or each flow path having a non- smooth surface, the or each flow path being configured to promote a substantially non- turbulent or laminar flow in any slurry passing through it except adjacent to the non-smooth surface.

Preferably the or each flow path is an enclosed flow path.

Preferably the lower part of the interior of the or each flow path is generally flat, albeit having a non-smooth surface.

Preferably the or each flow path has a substantially rectangular cross section.

Preferably the rectangular cross section has a substantially constant width and depth.

Preferably the or each flow path has a width to depth ratio greater than eight to one.

Preferably the non-smooth surface is adapted to produce localised non-laminar flow in any flow of slurry adjacent to the non-smooth surface.

Preferably the non-smooth surface is a ribbed surface with the ribs aligned at an angle to the direction of flow of the slurry through the flow path. More preferably the ribs are aligned substantially perpendicular to the direction of flow of any slurry through the flow path.

Preferably the pitch of the ribs is in the range of one to three millimetres.

Preferably the height of each rib is in the range of 0.2 to 1.0 millimetres.

Preferably the crest of each rib is curved having an average radius of curvature in the range of 0.7 to 1.4 millimetres.

Preferably the valley between adjacent ribs is curved having a radius of curvature in the range of 0.1 to 0.6 millimetres.

Preferably the non-smooth surface is the upper surface of a fabric connected to, or forming, at least a part of the lower part of the interior of the or each flow path.

Optionally the non-smooth surface is a surface texture or an undulating pattern on a surface.

Preferably the fabric is a ribbed fabric.

Preferably the fabric is a brushed fabric or has a fine or microscopic pile.

Preferably the average length of the pile of the fabric is in the range of 0.05 to 1.0 millimetres.

More preferably the average length of the pile of the fabric is in the range of 0.1 to 0.5 millimetres.

Preferably the diameter of the fibre used in the fabric is in the range of eight to twenty five micrometres.

Preferably the flow path is configured to allow a depth of flow of slurry over the non- smooth surface in the range of 5 to 15 millimetres.

Yet more preferably the flow path is configured to allow a depth of flow of slurry over the non-smooth surface in the range of 6 to 12 millimetres. Preferably the flow path is oriented such that slurry can flow through the flow path in a substantially horizontal direction.

In a second aspect, the invention may broadly be said to consist in a gold recovery plant incorporating at least one gold recovery apparatus substantially as specified herein.

Preferably the plant is adapted to supply slurry through the or each flow path at an average flow velocity in the range of 0.2 to 1.0 metres per second.

Yet more preferably the plant is adapted to supply slurry through the or each flow path at an average flow velocity in the range of 0.4 to 0.8 metres per second.

Preferably the plant is mounted on a raft and is suitable for operation whilst water-borne.

Preferably the gold recovery apparatus is situated below the water line of the raft.

In a third aspect, the invention may broadly be said to consist in a method of recovering gold from the ground or an ore, including the steps of;

mixing the ground or ore with water to produce a slurry,

producing a substantially non-turbulent or laminar flow in the slurry while passing the slurry over a non-smooth surface, the non-smooth surface being adapted to promote a non-linear flow in the slurry adjacent to the non-smooth surface, and

recovering any gold that is retained by the non-smooth surface.

Preferably the method includes passing the slurry over the non-smooth surface with an average flow rate in the range of 0.2 and 1.0 metres per second.

Yet more preferably the method includes passing the slurry over the non-smooth with an average flow rate in the range of 0.4 and 0.8 metres per second.

Preferably the plane of the non-smooth surface is aligned substantially horizontally when the slurry is passed over it.

Preferably the non-smooth surface is a ribbed surface. Preferably the non-smooth surface is a fabric surface.

Preferably the fabric surface is a ribbed fabric surface.

Preferably the gold is recovered from the non-smooth surface by inverting the non-smooth surface to allow the gold to drop out, and/or by washing it out.

Preferably the method includes the use of a gold recovery apparatus substantially as described herein.

In a fourth aspect the invention may broadly be said to consist in a screening separator, wherein the separator includes a main chamber in which a slurry can swirl, a liner through which slurry can pass which separates an inner part of the chamber from an outer part of the chamber, an inlet communicating with the inner part of the chamber and an outlet communicating with the outer part of the chamber.

Preferably the liner through which slurry can pass is a mesh screen material.

Preferably the separator includes vanes or paddles situated within the inner part of the chamber and adapted to rotate about a substantially vertical axis that is situated at or adj acent a centre of the chamber.

Preferably the inlet is aligned such that slurry that enters the main chamber is caused to rotate about the main chamber about a substantially vertical axis.

In a fifth aspect the invention may broadly be said to consist in a vacuum head for a gold recovery plant, wherein the vacuum head includes a first nozzle or set of nozzles which are connectable to a pressurised supply of water and which can be directed towards a surface to be eroded, and a second nozzle or set of nozzles which are connectable to a vacuum source and through which a slurry can pass.

Preferably the first nozzle or set of nozzles is/are arranged to direct a jet(s) of water in a substantially downward direction.

The invention may also broadly be said to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of the parts, elements or features, and where specific integers are mentioned herein which have known equivalents, such equivalents are incorporated herein as if they were individually set forth.

DESCRIPTION

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

FIGURE 1 is a schematic diagram of a gold recovery plant,

FIGURE 2 is a side elevation view of an embodiment of the gold recovery plant,

FIGURE 3 is a partially cutaway perspective view of an extractor of the gold recovery plant,

FIGURE 4 is a bottom plan view of a vacuum head of the gold recovery plant,

FIGURE 5 is a cross sectional view of the vacuum head at section AA of figure 4,

FIGURE 6 is a side elevation view showing the vacuum head in use,

FIGURE 7 is a partially cutaway perspective view of a screening separator of the gold recovery plant,

FIGURE 8 is a top plan view of the separator,

FIGURE 9 is a cross sectional side view of the separator at section BB of figure 8,

FIGURE 10 is a side elevation view of two pairs of vanes of the separator,

FIGURE 11 is a side elevation view showing flow over a fabric surface in the extractor,

FIGURE 12 is a plan view photograph of the surface of an example of a suitable fabric, and FIGURE 13 is a side elevation view photograph of the example of the fabric shown in figure 12.

With reference to Figure 1, a gold recovery plant (10) is shown in a schematic diagram, the plant having a vacuum head (11), a screening separator (13), a gold recovery apparatus (15), a first pump (17), a fine tailings separator (19), and a second pump (21). These items are connected in series by a piping system (23). In addition, the plant (10) includes a motor (25) or motors which can be used to drive the two pumps (17) and (21).

The first pump (17) is used to draw a slurry through the vacuum head (11) and through the screening separator (13) and through the gold recovery apparatus (15) and to pump the slurry to the fine tailings separator (19) at a pressure oiabout 15 pounds per square inch. The second pump (21) is used to boost the pressure of the water that drawn from the fine tailings separator (19) to a pressure of about 100 pounds per square inch for use by the vacuum head (11). The vacuum head (11) and its use is explained in greater detail with reference to figures 4 to 6 below, however at this stage it is worth mentioning that the vacuum head (11) uses the pressurised water supply to agitate the ore that is being mined to create the slurry that is processed by the plant (10). Optionally, some of this pressurised water can be directed via a recirculation pipe (26) to re-enter the circuit by being directed straight into the vacuum head (11). Preferably the slurry is made up of approximately six parts water to one part solids, by volume.

The screening separator (13) is explained in further detail with reference to figures 7 to 10 below. The screening separator (13) is used to separate out the larger stones and other larger fragments that may not pass through the gold recovery apparatus (15) because of their size.

The gold recovery apparatus (15) is explained in greater detail with reference to figures 3 and 11 below. Its use is to separate small nuggets, gold dust and flakes from the slurry that has passed through screen of the screening separator (13).

The fine tailings separator (19) is used to separate out the fine tailings from the slurry after the slurry has passed through the gold recovery apparatus (15), allowing the greater part of the water from the slurry to be re-used in the water jets of the vacuum head (11). In addition, the plant can include a pressure relief valve (26) and an air separator (27).

The pressure relief valve (26) can be situated between the screening separator (13) and the first pump (17) and can allow water into the piping system (23) if the vacuum within the system (23) becomes too great. For example, if the vacuum head (11) or the screening separator (13) become blocked the pressure relief valve (26) can open to allow water to continue to flow to the first pump (17). In addition the drop in vacuum at the vacuum head (11) or the screening separator (13) can allow a blockage to clear, for example debris about the vacuum head (11) could be allowed to drop away.

The air separator (27) can be helpful if placed just upstream of the second pump (21) as it can be used to get rid of any air that may jtend to get into the system, particularly though the fine tailings separator (19).

With reference to Figure 2, the gold recovery plant (10) is shown in a side view as it can be used in a gold recovery operation. The plant (10) is shown supported by a pontoon raft or barge (29) which is floating on a river, lake or pond (31) in a mining area. The plant (10) can be used to process the ore (33) on one side of the pond (31) and to deposit the tailings (35) on the other side, and in this way the pond and the plant (10) progressively move across the mining area to extract the gold present in the ore.

A number of the components ^"of the plant (10), for example the screening separator (13), the pressure relief valve (26) and the gold recovery apparatus (15) can be placed underwater. This can eliminate the need for absolutely water tight seals at joints, etc.

In this figure, the vacuum head (11) is shown situated within a "boil hole" (37) in which the ore is stirred up into a slurry.

In this figure the apparatus is shown with a nugget trap (39) fitted to the outlet from the screening separator (13) to catch any nuggets that may be separated out of the slurry by the screening separator (13).

With reference to Figures 3, 11, 12 and 13, the gold recovery apparatus (15), or at least a single cell of an apparatus (15), is shown in greater detail. In figure 3 the apparatus (15) is shown partially cut-way to allow the inside of the apparatus (15) to be illustrated, and in figure 11 a small section of the apparatus (15) is shown in cross section.

The apparatus (15) has a duct (43), flow path or conduit through which a slurry can flow. In this example, each end of the apparatus (15) includes fittings (45) which enable it to be connected to a piping system.

The inventor has found that an enclosed duct (43) having a rectangular cross section with a substantially constant width and depth is suitable. A width (47) of about eighty to a hundred and twenty millimetres, and a depth (49) of about five to fifteen millimetres has been found to work. well. Such a cross section can help to promote a non-turbulent or laminar flow which, is relatively shallow. The depth (49) is ideally between about five and fifteen millimetres and is preferably between six and twelve millimetres. A duct (43) length of about 1.5 to 2.5 metres is suitable.

The apparatus (15) is ideally used with the length of the duct (43) aligned substantially horizontally. At least a portion of the lower part of the interior of the duct (43) has a non- smooth surface and it is this non-smooth surface that can be used to extract gold from a slurry. The lower part of the interior of the duct is generally flat, albeit having a non- smooth surface.

Ideally, in use the flow of ^"a slurry though the apparatus (15) is substantially non-turbulent or laminar, and only the flow adjacent to the non-smooth surface is non-laminar. The relatively slender cross section of the duct (43), and a controlled flow rate through the duct (43), such that the average velocity of the slurry is about 0.6 metres per second, allows this substantially non-turbulent or laminar flow to be achieved. The ratio of the width (47) to the depth (49) is ideally greater than about eight to one, or at least greater than six to one.

Figure 11 shows this substantially laminar flow, and the flow velocity arrows (53) show a typical flow velocity profile within a duct or conduit. The flow velocity is indicated by arrow length. The flow velocity is typically fastest away from the internal surfaces of the duct (43) and slowest adjacent to the internal surfaces. However, in addition to this typical flow velocity profile, because the apparatus (15) includes a non-smooth surface (51) on the floor of the duct, the flow velocity adjacent to the floor is further reduced and is caused to become non-laminar, or slightly turbulent, because of the non-smooth surface (51). The inventor has found that the ribs of a ribbed fabric, are suitable for creating this low level of turbulence. However, it is envisaged that other textured surfaces, or undulating surfaces, particularly surfaces including ribs, would also be suitable.

It is this slowing down, and small scale local turbulence, adjacent to the non-smooth surface that helps the apparatus (15) to separate gold particles from the slurry and to allow them to be retained by the apparatus (15). Initial trials have shown that, gold particles which are typically the heaviest particles in the slurry are allowed to migrate to the lower regions of the flow as it passes through the duct (43) because the flow is substantially laminar. Then the gold particles drop into any recesses, valleys or pockets in the non- smooth surface, and because the flow velocity adjacent to the non-smooth surface is relatively low, the flow of the slurry does not tend to wash the gold out.

The inventor has found that by adjusting the flow rate through the duct (43) it is possible to find the ideal flow rate that is slow enough to allow the non-smooth surface to retain the gold particles, but which is fast enough to allow the flow to keep any particles that have a lower density than gold moving along the duct and out the exit end of the duct (43). For example, the inventor has found that black sand which has a density that is not as high as that of gold, but which is high enough to cause problems in some gold recovery devices, can be separated relatively efficiently from gold in this apparatus (.15).

Preferably the plant (10) is adapted to supply slurry through the duct (43) at an average flow velocity in the range of 0.2 to 1.0 metres per second, and more preferably in the range of 0.4 to 0.8 metres per second.

In a trial duct which included a glass top, the inventor observed that with an average flow velocity of between 0.6 and 0.8 metres per second, the small nuggets of gold would drop to the floor of the duct near the entrance, and the lighter flakes and dust would slightly further along the duct. The lighter particles in the slurry would tend to remain in the faster flowing sections of the flow and pass through the duct at about 0.6 metres per second, and the other heavier minerals or particles, for example black sand, would tend to migrate toward the lower regions of the flow, adjacent to or touching the floor, and would pass through the duct at about 0.1 to 0.2 metres per second. While the non-smooth surface (51) could be created in a number of ways the inventor has found that some fabrics are particularly effective, particularly ribbed and/or lightly piled fabrics. One such example is a ribbed rayon/nylon fabric. Preferably the non-smooth surface is the upper surface of a fabric connected to, or forming, at least a part of the lower part of the interior of the duct (43). The ribs should be aligned at an angle to the flow direction and preferably at right angles or perpendicular to it.

A ribbed and piled fabric is shown in cross section schematically in figure 11, and in the photographs of figures 12 and 13. The fabric shown in the photographs is a ribbed rayon nylon material and testing has been shown this fabric to be particularly suitable for the purpose of recovering fine gold.. The ruler shown in the photographs is graduated in half millimetres increments allowing suitable^" dimensions of the ribs can be scaled from the drawings. The ribs are shown schematically in figure 11 to highlight some of the key dimensions that are discussed herein.

The small valleys, troughs or channels between the ribs can allow localised eddies (55) to be formed which slows down the average flow velocity through the duct (43) adjacent to the ribs, and allows the gold particles to be held by the fabric or between the ribs. Similarly, the pile of the fabric can help to hold onto the fine gold flakes or particles and to prevent them being washed out of the duct (43).

If the rib height and pitch and/or the pile length is/are too large then the ribs or the pile tend to hold on to minerals such as black sand. However, if the rib height and pitch and/or the pile length is/are small enough the black sand tends to roll over the fabric instead of becoming trapped within it. The inventor has found that the apparatus (15) works well when the height of the ribs (57) of the fabric are only about 0.03 to 2.0 millimetres high or more preferably between 0.2 to 1.0 millimetres, and the ribs have a pitch (59) in the range 1.0 to 3.0 millimetres, or preferably about 2 millimetres. By comparison the duct height

(63) is ideally about five to fifteen millimetres as noted earlier.

Preferably the crest of each rib is curved having an average radius of curvature in the range of 0.7 to 1.4 millimetres. And preferably the valley between adjacent ribs is curved having a radius of curvature in the range of 0.1 to 0.6 millimetres. As noted above, it can be advantageous if the fabric has a light or fine or microscopic pile, or is a lightly brushed fabric. Preferably the average length of the pile, or the pile height (61), of the fabric is in the range of 0.1 to 0.5 millimetres, or at least in the range of 0.05 to 1.0 millimetres. The fabric shown in the photograph of figure 13 can be seen to have a very fine pile, or to be a lightly brushed fabric. The diameter of the fibres used in the fabric shown has been measured and is in the range of eight to twenty five micrometres, or is about fifteen micrometres.

The inventor has observed that the fine or microscopic pile is able to catch gold flakes that may otherwise pass through the duct (43). The gold flakes are relatively light and have a relatively large surface area. This means that the flow of slurry tend to have a larger effect on them. However, the flakes tend to" have jagged or rough edges and the pile is sometimes able to snag these edges and prevent the flakes from being carried away by the flow.

While a number of fabrics can work well to separate gold particles from a slurry, ribbed rayon/nylon fabric has been found to be particularly effective because it not, only works well at extracting the gold from the slurry, but the extracted gold can be removed from the fabric with relative ease by simply inverting the fabric, and shaking or vibrating it if necessary. The gold will then fall onto the smoother surfaces of the duct (43) and can be tipped out of the duct or be washed out with water.

Trials have shown that this apparatus (15) and method is capable of removing even fine gold dust from an ore, providing an opportunity to. increase the yield from a given quantity of ore. ^• - •

The inventor tried a number of materials and fabrics, including carpet, plastic grass, coconut matting, kevlar corduroy, foamed rubber, polar fleece, etc. While many of these worked to some extent, some would tend to clog, particularly with black sand, and it was difficult to extract the gold from some of them. The clogging is a significant problem because as soon as the fabric clogs, the lower surface of the duct (43) essentially becomes smooth and then even the gold is lost through the apparatus (15). It appears that the pile and/or ribs on some of these fabrics is too large, meaning that they tend to catch too much of the black sand from the slurry which causes the clogging. It is also a significant benefit if the gold can be recovered from the fabric easily as this can reduce the processing time significantly.

In these figures just a single cell is shown. In practice a gold recovery apparatus (15) would typically comprise a number of these cells arranged in parallel to allow a greater rate at which the ore is mined. -

Preferably the gold is recovered from the non-smooth surface (51) by inverting the non- smooth surface (51) to allow the gold to drop out, and/or by washing it out.

With reference to Figures 4, 5 and 6, the vacuum head (11) is shown and described in

- greater detail. The vacuum head (11) comprises a first set of nozzles (67) which can be connected to a high pressure water supply via a hose fitting (69). In this example the hose fitting (69) is connected to a manifold (71) onto which each of the first nozzles (67) are mounted.

The vacuum head (11) also comprises a- second nozzle (73) which tan be connected to a vacuum source via a second fitting (75). In this example the second nozzle (73) is in the form of a relatively large cylinder which has a number of large holes (74) in it. The holes (74) should be smaller than the diameter of the second fitting (75) to avoid internal blockages.

In use a high pressure supply of water can be supplied to the first nozzles (67) to erode the

-- surface of a deposit of ore. ^~ This will create a slurry,- or a mixture of ore and water, which can be sucked up through the second nozzle (73). Figure 6 shows the vacuum head (11) in use within a boil hole (37), the arrows showing the eroding action of the high pressure jets and the slurry that is created being drawn into the entrance holes (74) of the second nozzle

(73).

Since the second nozzle (73) is relatively large and it has a number of entrance holes (74) it can continue to operate even if some of the holes (74) become blocked. And also, since the second nozzle (73) has a number of entrance holes (74), the flow velocity through each one is relatively low and therefore larger rocks or debris will not tend to be drawn right up to the holes (74) and will not tend to become caught in the holes (74). With reference to Figures 7 to 10, the screening separator (13) is shown and described in greater detail. The screening separator (13) has a main body in the form of a cylindrical chamber (81) with a conical lower chamber (83). The separator (13) also has an internal liner or screen (85) which has a cylindrical upper portion and a conical lower portion.

The internal liner or screen (85) separates the cylindrical chamber (81) into an inner chamber and an outer chamber. The internal liner or screen (85) can be made from a number of materials, for example a steel wire mesh having a suitable sized mesh. The size of the -mesh is determined at least in part by the dimensions of the gold recovery apparatus (15) as any particles that pass through the mesh must also be able to pass freely through the gold recovery apparatus (15). Screen material having a six millimetre mesh size has been found to work well. ■ ^" -

In addition, the separator (13) has two sets of paddles, an upper paddle set (87), and a lower paddle set (89). These paddle sets are not shown in figures 7 and 9 for clarity.

An inlet passage (91) is aligned to promote a swirling action as slurry is introduced into the inner chamber of the cylindrical chamber (81). The inlet passage (91) passes through the wall of the cylindrical chamber (81) and through the internal screen (85) so that slurry can be discharged into the inner chamber. The inlet passage (91) is aligned substantially tangentially to the circular shape of the upper part of the internal screen (85) so that any liquid that comes into the inner chamber will tend to promote a swirling action within the cylindrical chamber (81). _-. . . .

Preferably the slurry is introduced into the inner chamber at a flow rate of approximately five to ten metres per second to promote a strong swirling action. As the slurry rotates within the separator the water and the finer ore particles can migrate through the internal screen to the outer chamber and then fall towards a floor (92) of the cylindrical chamber (81) and then pass out a fine tailings outlet passage (93).

Any oversize tailings that cannot pass through the screen tend to fall down to collect in the conical lower chamber (83). They initially rest on a valve (95) which is biased to a closed position, and when the weight of the oversize tailings is sufficient they can open the valve (95) and exit the separator (13) via an oversize tailing exit passage (97). It has been found that the conical lower chamber (83) should be made of a cone with an included angle of about 60 degrees, this gives a suitable compromise between storage capacity and steepness of the sides of the cone to ensure that the tailings will flow out. If the separator is situated on the suction side of a pump, then suction within the separator (13) can be used to help close the valve (95) again when the oversize tailings have exited. In this way the operation of the separator (13) can be largely automatic. The oversize tailings can be washed or pumped away using a high pressure water jet which is aligned to flush the tailings away through a suitable pipe or duct.

As noted above, the screening separator (13) also includes two sets of paddles. The first set of paddles (87) is situated within the inner chamber of the cylindrical chamber (81), and the second set of paddles (89) is situated within the lower regions of the outer chamber of the cylindrical chamber (81). Both sets are mounted such that they can rotate about a vertical axis that is substantially aligned with the principal axis of the cylindrical chamber (81).

The swirling action of the slurry with the separator (13) causes the sets of paddles (87) and (89) to rotate. In turn, the paddles act to stir any sediment that may tend to accumulate within the inner or outer chambers. The paddles therefore act to help prevent blockages within the separator (13) and help to move any sediment toward the outlet passage (93).

VARIATIONS

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

While the above example has been described with reference to the recovery of gold, it is envisaged that the same apparatus, plant and method can be configured to extract other relatively heavy minerals from ores in which the particular heavy mineral can be found.

Similarly, the plant, or components of it can also be used for general dredging operations and even for geological, archaeological or historical exploration. The screening separator (13) can also be used for screening gravel or similar materials where it is necessary to divide it by size.

DEFINITIONS

Throughout this specification the word "comprise" and variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.

ADVANTAGES

Thus it can be seen that at least the preferred form of the invention provides a gold recovery apparatus or plant or method which is capable of recovering gold in the form of nuggets right through to gold flakes and gold, flour or dust, from a slurry. For this reason, the apparatus and plant is able to efficiently process alluvial deposits that may ^"have previously been considered uneconomic. _{. .} . ; - _.

In addition the plant is capable of depositing the tailings from a mining operation in a desirable manner, for example the larger tailings can be deposited lower down with finer tailings deposited above, in preparation for the replacement of top soil and land reclamation.

Claims

1. A gold recovery apparatus having at least one flow path through which a slurry can be passed, and at least a portion of the lower part of the interior of the or each flow path having a non-smooth surface, the or each flow path being configured to promote a substantially non-turbulent or laminar flow in any slurry passing through it except adjacent to the non-smooth surface.

2. A gold recovery apparatus as claimed in claim 1, wherein the or each flow path is an enclosed flow path.

3. A gold recovery apparatus as claimed in any one of the preceding claims, wherein the non-smooth surface is adapted to produce localised non-laminar flow in any

^"flow of slurry adjacent to the non-smooth surface.

4. A gold recovery apparatus as claimed in any one of the preceding claims, wherein the non-smooth surface is a ribbed surface with the ribs aligned at an angle to the direction of flow of the slurry through the flow path.

5. A gold recovery apparatus as claimed in claims 6, wherein the ribs are aligned substantially perpendicular to the direction of flow of any slurry through the flow path.

6. A gold recovery apparatus as claimed in any one of claims 6 to 7, wherein the pitch of the ribs is in the range of one to three millimetres.

7. A gold recovery apparatus as claimed in any one of the preceding claims, wherein the non-smooth surface is the upper surface of a fabric connected to, or forming, at least a part of the lower part of the interior of the or each flow path.

8. A gold recovery apparatus as claimed in claim 10, wherein the fabric is a ribbed fabric.

9. A gold recovery apparatus as claimed in any one of claims 10 or 11, wherein the fabric is a brushed fabric or has a fine or microscopic pile.

10. A gold recovery apparatus as claimed in any one of the preceding claims, wherein the flow path is oriented such that slurry can flow through the flow path in a substantially horizontal direction.

11. A gold recovery plant incorporating at least one gold recovery apparatus substantially as specified herein.

12. In a third aspect, the invention may broadly be said to consist in a method of recovering gold from the ground or an ore, including the steps of;

mixing the ground or ore with water to produce a slurry,

^■■. producing a substantially non-turbulent or laminar flow in the slurry while passing the slurry over a non-smooth surface, the non-smooth surface being adapted to promote a non-linear flow in the slurry ^"adjacent to the non- smooth surface, and

recovering any gold that is retained by the non-smooth surface.