US3731975A

US3731975A - Apparatus and process for undersea mining of mineral bearing sand and gravel

Info

Publication number: US3731975A
Application number: US00199986A
Authority: US
Inventors: L Lindelof
Original assignee: QVA CORP
Current assignee: QVA CORP
Priority date: 1971-11-18
Filing date: 1971-11-18
Publication date: 1973-05-08
Anticipated expiration: 1990-05-08

Abstract

A process and mobile apparatus for the undersea mining of sand and gravel deposits containing gold particles and associated heavy minerals such as platinum, magnetite, etc., includes an excavating device which continuously excavates the sand and gravel material. Conveyor means receive the excavated sand and gravel and conveys the material to a discharge point which is located a predetermined distance above and a predetermined distance upstream from a screen type collection device. The predetermined difference in elevation and the downstream spacing between the collection device and the discharge point is so related to the ambient ocean current adjacent the ocean floor that separation of the sand and gravel discharged from the discharge point takes place as a result of the action of gravity and the subsurface ambient current acting on the material. The gold and associated metal particles (platinum, magnetite, etc.) and sand and gravel particles which are slightly coarser than the gold particles will be moved downstream by the ambient ocean current as the material falls and will be received by the collection device, while the sand particles will be carried downstream beyond the collection device, and the more coarse materials will fall upstream with respect to the collection device.

Description

United States Patent 1 1 Lindelof [54] APPARATUS AND PROCESS F OR UNDERSEA MINING OF MINERAL BEARING SAND AND GRAVEL [75] Inventor: Leonard A. Lindelof, Minneapolis,

Minn.

[73] Assignee: QVA Corporation, Minneapolis,

Minn.

[22] Filed: Nov. 18, 1971 [2]] Appl. No.: 199,986

Primary ExaminerErnest R. Purser Att0rney-George F. Williamson et a1.

1 1 May 8,1973

[ 57] ABSTRACT A process and mobile apparatus for the undersea mining of sand and gravel deposits containing gold particles and associated heavy minerals such as platinum, magnetite, etc., includes an excavating device which continuously excavates the sand and gravel material. Conveyor means receive the excavated sand and gravel and conveys the material to a discharge point which is located a predetermined distance above and a predetermined distance upstream from a screen type collection device. The predetermined difference in elevation and the downstream spacing between the collection device and the discharge point is so related to the ambient ocean current adjacent the ocean floor that separation of the sand and gravel discharged from the discharge point takes place as a result of the action of gravity and the subsurface ambient current acting on the material. The gold and associated metal particles (platinum, magnetite, etc.) and sand and gravel particles which are slightly coarser than the gold particles will be moved downstream by the ambient ocean current as the material falls and will be received by the collection device, while the sand particles will be carried downstream beyond the collection device, and the more coarse materials will fall upstream with respect to the collection device.

5 Claims, 3 Drawing Figures PATENTEU MAY 8 1973 INVENTOR; Leonard A. Lindelof Wan APPARATUS AND PROCESS FOR UNDERSEA MINING OF MINERAL BEARING SAND AND GRAVEL SUMMARY OF THE INVENTION It is generally known that gold and associated heavy minerals are widely distributed in the sand and gravel sediments of submerged beaches and drowned river valleys of the continental shelf areas. Local concentrations of gold have been identified in surface sediments in the continental shelf off southern Oregon, and there is reason to believe that such concentrations exist off the shores of all five continents.

Although the presence of the gold particles throughout the sand and gravel sediments of the continental shelf areas is generally known, there are no known economic processes or methods of mining the sand and gravel deposits to economically remove the gold particles therefrom. Therefore, if it is assumed that gold is valued at 35 dollars an ounce, and it is further assumed that the recoverable concentration of gold particles in the sand and gravel deposits is approximately 25 cents per yard, then extremely large volumes of sand and gravel would have to be processed in order to justify mining these undersea deposits.

It is therefore a general object of this invention to provide apparatus and process for the undersea mining of sand and gravel deposits containing gold which may be economically accomplished even if, for example, the concentration of gold particles is no greater than 25 cents per yard (based on gold valued at 35 dollars an ounce). Generally speaking, the present process and apparatus contemplates concentrating or beneficiating the gold bearing sand and gravel deposits by using the action of gravity and the ambient subsurface ocean current to produce an initial separation of the gold particles from the sand and gravel deposits.

In this regard, the sand and gravel deposits containing the gold particles is continuously excavated by an undersea mobile excavating device and the excavated material is moved to a predetermined height by suitable conveyor means. The excavated sand and gravel deposits is continuously discharged at a predetermined height directly into the ambient ocean current. A collection device, preferably a reciprocating screen type, is positioned below and downstream from the discharge point. The difference in elevation and the downstream spacing between the discharge point of the sand and gravel and the reciprocating screen collection device is so related to the magnitude of the ambient current as to cause the gold particles and the coarser sand and fine gravel under the influence of gravity and the ambient current to fall downstream upon the reciprocating screen receptacle. Although the gold particles are of comparable weight to the coarser sand and fine gravel particles, the gold particles are smaller and the reciprocating screen will produce a further separation.

The fine sand particles will be moved downstream beyond the reciprocating screen receptacle under the influence of the ambient current and the action of gravity while the heavier larger particles will fall upstream upon the ocean floor with respect to the collection device. Thus the use of the ambient current as a means of initially separating gold particles from sand and gravel deposits makes possible the economic mining of these deposits. These and other objects and advantages of this invention will more fully appear from.

the following description made in connection with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS FIG. I is a diagrammatic perspective view of the apparatus used in carrying out the novel process;

FIG. 2 is a diagrammatic elevational view of the apparatus showing a patterned separation of the gold bearing sand and gravel under the influence of gravity and the subsurface ambient current; and

FIG. 3 is a plan view of the reciprocating screen used in conjunction with the collection device.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings and more specifically to FIG. I, it will be seen that one embodiment of the novel underwater mining apparatus, designated generally by the reference numeral 10, is there shown. This apparatus is adapted to be controlled by a large ocean going surface craft 1 1, preferably an ocean going barge which is also capable of receiving the refined or beneficiated gold bearing deposits. In this regard, the underwater mining apparatus, in the embodiment shown, is adapted to be remotely controlled from the surface craft and a conduit 12 interconnects the surface craft II with the underwater mining apparatus. The conduit not only provides a passage for the refined gold bearing sand and gravel deposits, but also has associated therewith suitable electrical control cables to permit remote control of the undersea mining apparatus.

The mining apparatus I0 is adapted for continuous mining of the sand and gravel deposits which constitute the ocean floor and which contain gold particles. In the embodiment shown, apparatus 10 includes a selfpropelled crawler type bucket wheel excavator which in general construction may resemble the commercially available bucket wheel excavators. This excavator includes a revolvable bucket wheel 14 having a plurality of buckets or scoops which are circumferentially arranged so that as the bucket wheel is revolved, the sand and gravel deposits will be excavated and will be directed to an endless conveyor 18. The revolvable bucket wheel is mounted at the outer end of an elongate boom 15 which is shiftably connected at its inner end to the body I6 of the excavator. The body 16 is mounted for traversing movement along the sea floor by suitable surface engaging crawler assemblies I7.

The endless conveyor I8 conveys the sand and gravel deposits excavated by the revolvable bucket wheel 14 to a suitable guide type hopper device 19 positioned. adjacent the discharge end of the endless conveyor 18. The sand and gravel material are then conveyed to an elevator type conveyor 20 to a predetermined height where the material is discharged. Thus the elevator type conveyor 20 has one end portion thereof which receives the sand and gravel material from the endless conveyor Wand has a discharge end or discharge point 21 from which the sand and gravel material is discharged. The elevator conveyor is vertically adjustable so that the vertical spacing between the point of discharge of the conveyor and a collector device 22 may be variously adjusted.

It is also desirable to properly orient the sand and gravel material discharged from the conveyor 20 so that this material will be directed in its downward descent from a discharge point which is disposed in a vertical plane arranged substantially normal to the direction of the subsurface ambient ocean current. To this end, a substantially flat inclined deflector device 24 is provided and is positioned slightly below and adjacent the discharge end 21 of the conveyor 20 to receive the sand and gravel material discharged therefrom. The deflector device 24 is inclined downwardly in the direction of the subsurface ambient current and may be provided with an upstanding flange 25 afflxed to the peripheral edges thereof. Suitable direction control vanes 26 may be affixed to the upper surface of the deflector device and these vanes may be preferably arranged so that they diverge towards the discharge edge 24a thereof. It will be noted that the discharge edge 24a of the deflector device is substantially Straight and disposed in a vertical plane arranged substantially normal to the subsurface ambient ocean current. Since the discharge edge or point 24a of the deflector device 24 is disposed in a vertical plane arranged substantially normal to the ambient current, the

downstream spacing between the discharge point 24a and the collection device may be more accurately determined. It is pointed out that the deflector device 24 is also vertically adjustable with the conveyor 20 so that the vertical spacing between the discharge point 24a and the collector device may be readily adjusted.

The collection device 22 is provided with a sectional reciprocating screen 23 at its upper surface which is operable to produce further separation of the gold particles from the sand and gravel particles. The sectional screen as shown includes a plurality of sections arranged side by side including screen section 23a, screen section 23b, and screen section 23c. It will be noted that the mesh size of screen section 23a is larger than the mesh size of screen section 23b, and that the mesh size of screen section 23b is larger than the mesh size of screen section 23c. it is apparent that additional screen sections could also be provided. The sectional reciprocating screen 23 reciprocates in the direction of the arrows so that the coarser material which will not pass through the screen section will be progressively conveyed along and discharged from the screen section. For example, the gold particles will pass through the openings in the screen section 23a while the gravel and coarser sand will be conveyed longitudinally along the screen section 23a and will be discharged therefrom.

These screen sections are so arranged that the smaller screen size is located further downstream from the larger screen size. Suitable arrows indicate the direction of the subsurface current. Thus the heavier and larger particles will fall upon the larger mesh screen section.

It will be noted that the conduit 12 is interconnected to the collector device 22, and, although not shown, a suitable pump will be provided for pumping water entrained beneficiated gold bearing sand and gravel upwardly to the surface craft 11. it is also pointed out that in some instances, further refinement below the surface of the water of the beneflciated gold bearing sand and gravel may be accomplished with additional known mechanical separating means. However, for the purposes of this invention, the beneficiated gold bearing sand and gravel deposits are illustrated as being pumped to the surface craft after it has been collected in the collector device 22.

One of the natural characteristics of the ocean is the essential condition which permits economic operation of the present process and apparatus. This characteristic of the ocean is ambient subsurface current and it is necessary to determine the direction of the current, as well as the magnitude of the current for optimum results with respect to the present process and apparatus.

Generally speaking, the sand and gravel deposits constituting the ocean floor may be mined in any direction but it is essential that the excavated gold bearing sand and gravel deposits be discharged so that the material is influenced by the ambient current as material falls by action of gravity towards the collection device. It will be seen that the collection device is positioned at a substantially lower level than the discharge point of the conveyor 20 and is also positioned substantially downstream from the discharge point. The vertical spacing and downstream spacing between the discharge point and the collection device will vary according to the magnitude of the ambient current. It has been found that the subsurface ambient current adjacent the ocean floor varies within the range of A knot to approximately 4 knots. Although the vertical spacing between the discharge point 24a of the deflector and the collection device will vary over a relatively large range, experimental evidence indicates that a desirable workable range for this vertical spacing is approximately 10 to 40 feet. It is also pointed out that the discharge point 24a would be spaced vertically above the ocean floor F a distance of 25 to 100 feet.

It has been found that the gold particles which are disseminated throughout the sand and gravel deposits of the Pacific continental shelf area, especially off the North American coast vary in size from particles which are of a size that will pass through a 10 mesh screen, but not a 20 mesh screen (plus 20) and those that are of a size that will pass through a 100 mesh screen (minus 100). It is thought that probably the greatest amount of recoverable gold and associated mineral particles occur within the range of sizes between minus 40 and plus 100 and smaller. The weight of these individual particles has been generally calculated to be approximately 1.0072 grams for the minus 10, plus 20 particles, 0.003 grams for the minus 20, plus 40 particles, and 0.0005 grams for the minus 40, plus 100 particles.

The average descent time of gold particles in water, as well as other particles, can also be determined and this information must be known in order to properly interrelate the discharge point of the conveyor 20 with respect to the collection device 22. Gold particles of a minus 10, plus 20 size have an average descent time of approximately 3.52 seconds in a 35 inch vertical column of water. Similarly, gold particles of a minus seconds in the same column of water. Gravel, on the other hand, of a plus size has an average descent time of approximately 4.13 seconds while the average descent time for sand depends upon the size of the sand particles. In this regard, sand ofa minus 10, plus size has an average descent time of approximately 6.20 seconds, a minus 20, plus 40 size sand particles has an average descent time of approximately 11.20 seconds, and sand particles of a minus 40, plus 100 size has an average descent time of approximately 23.20 seconds.'

The sand and gravel descent times were also based on a vertical column of water approximately 35 inches in height.

It has also been determined that the particular configuration of the gold particles affects the descent characteristics of the particle in water. In this regard, the heavier, bulky particles without being influenced by any ambient current will fall directly down without any spinning motion, while the flatter shaped particles while descending straight down at a slightly lower rate tend to spin rapidly about a vertical axis. In every instance the gold particles descend faster than sand or gravel particles of the same approximate size. In a given screen section, smaller bulky shaped (fast descent) particles will be collected along with the larger particles for which the screen is sized.

It has been determined that the coarser sand and fine gravel of the ocean floor deposits will have the same general rate of descent as the rate of descent of the gold particles found in these deposits. Thus, when the discharge point of the elevator conveyor is arranged in its predetermined relation with respect to the collector device, the gold particles within the range of minus 10,

plus 20 to minus 100 (the size of particles normally exprogressively smaller. With this arrangement, the

heavier but smaller gold particles will fall through the openings in the screen section 23a while the plus 10 gravel particles will be conveyed as tailings from the section. The progressively smaller screen sizes will permit the same separation with respect to those sand, gravel and gold particles carried further downstream by the ambient current and the action of gravity.

When the direction of the ambient ocean current as well as the magnitude thereof is determined, the verti cal spacing between the discharge point for the ex cavated sand and gravel deposits and the collection device may be determined and the downstream spacing between the discharge point and the collection device may also be determined. It will be seen that the heavier larger particles will obviously be less influenced by the ambient current and will fall upstream with respect to the collection device. The gold particles and coarser sand and fine gravel will be influenced by the subsurface ambient current and will be moved downstreamfrom the point of discharge and fall upon the collection device 22. The ambient current will cause the lighter weight particles to be carried downstream beyond the collection device. Thus, since the current is continuously present, it will be seen that it is merely necessary to adjust the vertical spacing and the downstream spacing between the discharge point and the collection device, depending upon the magnitude of the current.

Test experience indicates that the present process permits a high percentage recovery of the gold particles in the sand and gravel deposits. It is thought that the percentage of gold recovery from the sand and gravel deposits should exceed 92 percent and is thought to be as high as 95 percent recovery. it has also been found that that portion or cut of the sand and gravel deposits that would be directed to the collection device by the action of gravity and the ambient subsurface current is approximately 25 percent of the entire material constituting a yard of material excavated. Therefore, assuming that the quantity of gold particles in each yard of sand and gravel deposits is approximately $0.25 per yard, then based on the test evidence of expected recovery (that is, a 90 percent of the gold available in a yard of material) then approximately $0.225 worth of gold would be recovered along with 0.250 yards of sand and gravel. The ore would be beneficiated to 22.5 cents/0.250 yards 90 cents/yard. This calculated beneficiated value, 90 cents/yard, results solely from the gravity-current separation and would therefore be the calculated value of the ore falling upon the screen.

As pointed out above, the present beneficiation (by ambient current separation) of the gold bearing sand and gravel deposits has been based on a recovery of 90 percent of gold bearing particles from each yard of the deposit process. Because of the classifying effect of the ambient current the material landing on the screen can be beneficiated by an additional 90 percent by the screening action. Therefore, if each yard of sand and gravel deposit contains gold particles having a value of 25 cents (based on a 35 dollar per ounce value of gold) then it is thought that using the present process, each yard of the beneficiated material would have a value of $9.00 (90 I01 yard). It is also pointed out that preliminary sampling would be run to show the particle size classification of not only gold, but the sand and gravel deposits. As soon as this information is made known, the economics of the gold separation with respect to any given sand and gravel deposit could be readily estimated. 1

it is thought that the present apparatus should be capable of processing approximately 10,000 yards of ore (mineral bearing sand and gravel deposits) per hour. An example of the equipment having the capability to accomplish this operation would, for example, typically require a revolvable bucket wheel ll l having a diameter of 50 feet and-mounted on an elongate boom 15, having a length dimension of approximately feet. The boom 15 would be swingably mounted on the body 16 so that its arc of swinging movement would permit the excavation of a trench approximately (142) feet wide. The forward velocity of the apparatus would be approximately (6.35) inches per minute. The endless conveyor 18 and the conveyor 20 would typically be approximately (20) feet wide and each would carry excavated material thereon having a depth dimension of approximately (22.5) inches at a velocity of approximately (2) feet per second. The distributor or deflector 24 will be of a size to distribute the material over a length corresponding to the length (preferably 60 feet) of the sectional screen of the collection device. Again, the discharge point 24a under normal conditions would preferably be spaced from about (25) feet to (100) feet above the surrounding ocean floor.

It will be seen that the downstream spacing of the leading edge of the sectional screen 23 would be dependent on the velocity of the ambient subsurface current and on the characteristics of the ore. Assuming the subsurface ambient current to be approximately 1 knot (1.69 feet per second), the collection device and leading edge of the sectional screen could be typically located approximately feet below and approximately 25 feet to 80 feet downstream with respect to the discharge point 24a of the distributor. The width dimension of the sectional screen assembly 23 would be approximately (40) feet and the width dimension would be oriented in the direction of the ambient current. The sectional screen assembly would also preferably be approximately (60) feet long and would reciprocate in a direction disposed substantially normal to the direction of the ambient subsurface current.

As pointed out above, the material excavated with this apparatus would be approximately 10,000 yards of material per hour and approximately (2,500) yards per hour of this material would land on the reciprocating screen. Approximately (250) yards per hour of this material would pass through the screen and approximately (2,250) yards per hour of the material would pass over the end of the screen as tailings. It is pointed out that the reciprocating screen of a size and having the general features described hereinabove would be capable of this capacity under normal operating conditions. If material is conveyed along the screen at a velocity of (2) feet per second, the average depth of material on the sectional screen 23 would be approximately (2) inches. It will be appreciated that the capacities and sizes of the components of the above described apparatus are merely illustrative of the apparatus that would be employed to process approximately l0,000 yards of ore per hour.

It will be further appreciated from the aforementioned description that the primary energy which is used to accomplish the separation of gold and associated metals from the sand and gravel deposits is the subsurface ambient ocean current. The quantum of energy provided by the ambient ocean current is very substantial. This quantity of energy can be more readily envisioned if it is contemplated that ambient current has a velocity of approximately 1 knot and the material to be beneficiated is dropped from a height of approxi mately l5) feet and is discharged from a distributor so that the material will fall on a screen having a length of approximately (60) feet. By way of contrast, if the same amount of water were supplied in a land based operation and was pumped against only a 10 foot head without allowing for any losses whatsoever, then well over (1,000) horsepower would be required. However, in actual practice, it is thought that approximately I horsepower per hour yard per of ore would be required to provide the necessary washing, separation and classifying action obtained by discharging the ore into the ocean current.

From the foregoing description, it will be seen that l have provided novel process and apparatus for economically mining the sand and gravel deposits that constitute the ocean floor. It will be seen that the present process contemplates the use of the ambient ocean current along with the action of gravity to provide a means of beneficiating the gold bearing sand and gravel deposits. Thus in carrying out the process on an economical basis, it is merely necessary to sample the deposits to be processed to determine the textural characteristics of the deposit and then to determine the magnitude and direction of the ambient current to properly orient the discharge point with respect to the collection point. The present process and apparatus is capable of extremely high volume operation and thus renders possible the economic recovery of gold particles from sand and gravel where the amount of gold in each yard of deposit is extremely small. Thus it will be seen that l have provided anovel process and apparatus of a type never before contemplated for the economic undersea mining of gold bearing sand and gravel deposits.

What is claimed is: 1. A process for high volume undersea mining of gold bearing sand and gravel deposits, comprising excavating undersea sand and gravel deposits containing gold particles,

conveying the excavated gold bearing sand and gravel deposits to a discharge point located adjacent the ocean floor,

positioning a collection medium at a predetermined distance below the discharge point, and at a predetermined distance downstream from the discharge point with respect to the ambient subsurface current adjacent the ocean floor, discharging the excavated gold bearing sand and gravel material from the discharge point and allowing the material to fall by action of gravity, the predetermined downstream spacing and the predetermined vertical spacing between the collection medium and the discharge point being so related to the magnitude of the ambient ocean current adjacent the ocean floor so that the coarse sand and fine gravel, and the gold particles will move downwardly and downstream under the influence of gravity and the ocean ambient current and will be received by the collection medium, while the finer sand deposits will be carried downstream beyond the collecting medium, and the heavier particles will fall upstream from the collection medium.

2. The process as defined in claim 1 and screening the material received by the collection medium whereby the smaller gold particles will be separarated from the coarser sand and fine gravel particles.

3. The process as defined in claim 1 wherein said gold bearing sand and gravel deposits is continuously excavated and is continuously conveyed to the discharge point to be continuously discharged therefrom.

4. Apparatus for undersea mining of sand and gravel deposits containing gold particles comprising an excavating device adapted to be moved along the ocean floor for continuously excavating gold bearing sand and gravel deposits, the conveying device having a receiving portion for receiving excavated sand and gravel material, and having a discharge portion,

a collection device having an upper portion posigravel particles will be moved downwardly and tioned a predetermined distance be o Sai downstream under the influence of gravity and the discharge portion of the conveyor device, and being disposed a predetermined distance downstream from the discharge portion of the conveyor device with respect to the subsurface ambient ocean current, the predetermined from the collection device downstream spacing and the predetermined dif- 5 Th t d l 4 h ference in height between the collection device appafa i as 6 me P c w erem and the discharge portion of the conveyor being 10 collection device lncludes a reciprocating screen at its related to the magnitude of the ambient ocean curupper Porno and the gold particles and rent adjacent the ocean floor so that the gold par'tithe coarser sand and gram Pamcles cles and the accompanying coarse sand and fine ambient subsurface ocean current and received by the collection device, while the finer sand particles will be carried downstream beyond the collection device, and the heavier particles will fall upstream

Claims

1. A process for high volume undersea mining of gold bearing sand and gravel deposits, comprising excavating undersea sand and gravel deposits containing gold particles, conveying the excavated gold bearing sand and gravel deposits to a discharge point located adjacent the ocean floor, positioning a collection medium at a predetermined distance below the discharge point, and at a predetermined distance downstream from the discharge point with respect to the ambient subsurface current adjacent the ocean floor, discharging the excavated gold bearing sand and gravel material from the discharge point and allowing the material to fall by action of gravity, the predetermined downstream spacing and the predetermined vertical spacing between the collection medium and the discharge point being so related to the magnitude of the ambient ocean current adjacent the ocean floor so that the coarse sand and fine gravel, and The gold particles will move downwardly and downstream under the influence of gravity and the ocean ambient current and will be received by the collection medium, while the finer sand deposits will be carried downstream beyond the collecting medium, and the heavier particles will fall upstream from the collection medium.

4. Apparatus for undersea mining of sand and gravel deposits containing gold particles comprising an excavating device adapted to be moved along the ocean floor for continuously excavating gold bearing sand and gravel deposits, the conveying device having a receiving portion for receiving excavated sand and gravel material, and having a discharge portion, a collection device having an upper portion positioned a predetermined distance below said discharge portion of the conveyor device, and being disposed a predetermined distance downstream from the discharge portion of the conveyor device with respect to the subsurface ambient ocean current, the predetermined downstream spacing and the predetermined difference in height between the collection device and the discharge portion of the conveyor being related to the magnitude of the ambient ocean current adjacent the ocean floor so that the gold particles and the accompanying coarse sand and fine gravel particles will be moved downwardly and downstream under the influence of gravity and the ambient subsurface ocean current and received by the collection device, while the finer sand particles will be carried downstream beyond the collection device, and the heavier particles will fall upstream from the collection device.

5. The apparatus as defined in claim 4 wherein said collection device includes a reciprocating screen at its upper portion and upon which the gold particles and the coarser sand and grain particles fall.