Abstract:
A seafloor auxiliary mining tool for use in a seafloor mining system. The seafloor auxiliary mining tool has a seafloor locomotion system enabling traversal of the seafloor. Umbilical connections receive power and control signals from a surface source. A boom mounted auxiliary cutting tool is configured to cut extremities of a seafloor deposit. Cuttings produced by the auxiliary cutting tool are sized by sizing means, to ensure such cuttings are no greater than a desired size.

Description:
TECHNICAL FIELD The present invention relates generally to underwater mining, and in particular relates to a tool for carrying out seafloor mining in cooperation with other seafloor tools. 
     BACKGROUND OF THE INVENTION 
       [0001]    Seabed excavation is often performed by dredging, for example to retrieve valuable alluvial placer deposits or to keep waterways navigable. Suction dredging involves positioning a gathering end of a pipe or tube close to the seabed material to be excavated, and using a surface pump to generate a negative differential pressure to suck water and nearby mobile seafloor sediment up the pipe. Cutter suction dredging further provides a cutter head at or near the suction inlet to release compacted soils, gravels or even hard rock, to be sucked up the tube, Large cutter suction dredges can apply tens of thousands of kilowatts of cutting power. Other seabed dredging techniques include auger suction, jet lift, air lift and bucket dredging. 
         [0002]    Most dredging equipment typically operates only to depths of tens of metres, with even very large dredges having maximum dredging depths of little more than one hundred metres. Dredging is thus usually limited to relatively shallow water. 
         [0003]    Subsea boreholes such as oil wells can operate in deeper water of up to several thousand metres depth. However, subsea borehole mining technology does not enable seafloor mining. 
         [0004]    Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior an base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 
         [0005]    Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
       SUMMARY OF THE INVENTION 
       [0006]    According to a first broad aspect the present invention provides a seafloor auxiliary mining tool for use in a seafloor mining system, the seafloor auxiliary mining tool comprising:
       a seafloor locomotion system enabling traversal of the seafloor; umbilical connections for receiving power and control signals from a surface source;   a boom mounted auxiliary cutting tool for cutting extremities of a seafloor deposit; and   means for sizing cuttings produced by the auxiliary cutting tool to ensure such cuttings are no greater than a desired size.       
 
         [0010]    According to a second aspect the present invention provides a method for seafloor auxiliary mining in a seafloor mining system, the method comprising:
       a seafloor auxiliary mining tool traversing the seafloor using a seafloor locomotion system;   the tool receiving power and control signals from a surface source via umbilical connections;   a boom mounted auxiliary cutting tool cutting extremities of a seafloor deposit; and   a sizing means of the tool sizing cuttings produced by the auxiliary cutting tool to ensure such cuttings are no greater than a desired size.       
 
         [0015]    The means for sizing cuttings may comprise at least one pair of cutting heads which form the auxiliary cutting tool, the cutting heads being configured to preferentially draw cuttings between the pair of cutting heads, and the pair of cutting heads being spaced apart by a distance corresponding to the desired cutting size. In such embodiments, cuttings larger than the desired cutting size which are drawn between the pair of cutting heads will be further cut and/or crushed to be less than the desired cutting size. The spacing between the or each pair of cutting heads can be fixed at a predetermined spacing, for example depending on the ore being mined and the size of particles needing to be extracted. Alternatively, the spacing between the or each pair of cutting heads may in some embodiments be adjustable during mining operations. Alternatively, the means for sizing cuttings may comprise a sizing grill proximal to the auxiliary cutting tool, for example positioned above the cutting head between the head and the boom, and/or aft of the cutting head. Alternatively, the means for sizing cuttings may comprise other suitable sizing devices whether fixed or adjustable. The pair of cutting heads are preferably counter-rotating so as to draw cuttings between the cutting heads to effect sizing of the cuttings. 
         [0016]    By providing the auxiliary mining tool with an auxiliary cutting tool, and leaving bulk mining for a separate seafloor tool, the present invention provides for a relatively agile seafloor cutting tool which has enhanced mobility enabling operation in seafloor regions of complex topography and which can flexibly perform an array of cutting tasks. The auxiliary cutting tool can thus be used in preparation for bulk mining to cut down peripheries of complex seafloor formations in order to present relatively flat and horizontal benches suitable for a separate bulk mining tool. The present invention thus provides an auxiliary tool operable to function in cooperation with other seafloor mining tools to effect retrieval of the seafloor material, even when presented with a complex seafloor topography, while able to function alone when presented with complex seafloor topography. At some sites the agility of the auxiliary mining tool may be such that other tools may not be required to effect retrieval of the seafloor material. 
         [0017]    The seafloor auxiliary mining tool is capable of traversing uneven ground and slopes, such capability being affected by the seafloor locomotion system. The seafloor locomotion system may comprise any suitable locomotion elements, for example wheels, continuous tracks, legs, or the like. The locomotion system preferably enables the auxiliary mining tool to traverse seafloor terrain sloped up to about 10 degrees, more preferably up to about 20 degrees and even more preferably up to about 25 degrees. 
         [0018]    The auxiliary mining tool in preferred embodiments is operable to work a seafloor site to prepare a bench for bulk mining. The auxiliary mining tool in preferred embodiments is further operable to work remnant edges left by a bulk miner. The boom for mounting the auxiliary cutting tool preferably comprises an hydraulically operated articulated arm. In one form, the boom may be mounted on an upper carriage assembly capable of slewing relative to the auxiliary mining tool centre line. 
         [0019]    In some embodiments of the invention, the seafloor auxiliary mining tool may comprise a detachable winch cable attachment point, allowing the tool to be winched between the seafloor and the surface, and to detach from the winch cable and self-propel once on the seabed. 
         [0020]    Further, the present invention provides a seafloor auxiliary mining tool adaptable in some embodiments to deployment at significant water depths. For example some embodiments may be operable at depths greater than about 400 m, more preferably greater than 11000 m and more preferably greater than 11500 m depth. Nevertheless it is to be appreciated that the auxiliary mining tool of the present invention may also present a useful seafloor mining option in water as shallow as about 100 m or other relatively shallow submerged applications. Accordingly it is to be appreciated that references to the seafloor or seabed are not intended to exclude application of the present invention to mining or excavation of lake floors, estuary floors, fjord floors, sound floors, bay floors, harbour floors or the like, whether in salt, brackish, or fresh water, and such applications are included within the scope of the present specification. 
         [0021]    In embodiments of he invention deployed to seafloor sites of complex topography, the seafloor auxiliary mining tool is preferably employed to initiate site excavation. For example the seafloor auxiliary mining tool may prepare a landing area for other seafloor tools, and may excavate extremities of the site in order to prepare a first bench ready for bulk mining. 
         [0022]    A preferred embodiment of the invention further includes a suction delivery line having an inlet adjacent to the auxiliary cutting tool and an outlet spaced from the auxiliary mining tool. In preferred embodiments of the invention, the auxiliary mining tool comprises a slurry pump system and a slurry inlet proximal to the cutting head(s), configured to capture cuttings in the form of a slurry. The slurry may be pumped a short distance from the seafloor auxiliary mining tool, for example simply to one side of the path taken or to be taken by the tool. Alternatively, the slurry may be pumped to a seafloor stockpile location some distance away from the seafloor auxiliary mining tool via a suitable transfer pipe. The slurry inlet, or suction inlet, may be positioned just all of the cutting head. In embodiments comprising two or more cutting heads, the or each suction inlet may be positioned between cutting heads. 
         [0023]    In preferred embodiments, a collection shroud partially surrounds the cutting head(s) to optimise containment and collection of cuttings by the slurry pump system. The seafloor auxiliary mining tool preferably comprises a blade to help keep cuttings ahead of the vehicle, and also preferably configured to shroud the cutting tool by maintaining cuttings near the cutting head and assist reworking of oversized cuttings. The blade is preferably arcuately shaped so as to effect substantially equal shrouding at differing slew positions of the cutting tool. The blade preferably assists a suction inlet of the tool in clearing cuttings produced by the cutting heads. The blade is also preferably configured to clear the path ahead of the auxiliary mining tool by acting as a push blade as the machine traverses forwards. 
         [0024]    The seafloor auxiliary mining tool may be an untethered remotely operated vehicle (ROV) or may be a tethered vehicle operated by umbilicals connecting to the surface. 
         [0025]    The seafloor auxiliary mining tool preferably clears its own cuttings to the spaced outlet at a dump site to enable the seafloor auxiliary mining tool to progress through a formation as it works. For example the auxiliary mining tool may pump its cuttings in slurry form to a position lateral to the tool&#39;s path of travel. 
         [0026]    The seafloor auxiliary mining tool&#39;s weight is preferably selected in order to apply the forces required for the auxiliary mining tasks. In order to further stabilise the auxiliary mining tool, movable anchoring spuds may be provided. 
         [0027]    The bench may comprise an ore bench of valuable ore to be retrieved, or may comprise a bench of hard rock, or other seafloor material to be removed for other purposes. The ore may comprise seafloor massive sulphides. 
         [0028]    In an alternative embodiment of the system, the auxiliary miner is configured with slurry transfer pipes which are arranged to deliver cuttings from the tool in a slurry form to a stockpile site distal from the cutting location of the tool. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    An example of the invention will now be described with reference to the accompanying drawings, in which: 
           [0030]      FIG. 1  is a simplified overview of a subsea system incorporating an auxiliary mining tool in accordance with a preferred embodiment of the present invention; 
           [0031]      FIG. 2  is a side view of an auxiliary mining tool in accordance with one embodiment of the present invention; 
           [0032]      FIG. 3  illustrates the cutting and suction process of the auxiliary mining tool of  FIG. 2 ; 
           [0033]      FIG. 4  depicts the overall auxiliary mining tool system; 
           [0034]      FIG. 5  is a perspective view of the boom-mounted cutting head of the auxiliary mining tool; and 
           [0035]      FIG. 6  is a cross sectional view of the boom-mounted cutting head of the auxiliary mining tool in operation. 
           [0036]      FIG. 7   a  depicts the auxiliary mining tool performing site preparation; 
           [0037]      FIG. 7   b  depicts the auxiliary mining tool trimming remnant edges of an ore bench; 
           [0038]      FIG. 8  depicts a further embodiment of the auxiliary mining tool with a moveable anchoring/stabilising spud system; 
           [0039]      FIGS. 9   a - 9   d  illustrate an auxiliary cutter in accordance with another embodiment of the invention; and  FIGS. 10   a  and  10   b  illustrate an auxiliary cutter in accordance with a further embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]      FIG. 1  is a simplified overview of a subsea system  100 , which incorporates an auxiliary mining tool (AUX)  116  in accordance with an embodiment of the present invention. A derrick  102  and dewatering plant  104  are mounted upon an oceangoing production support vessel (PSV)  106 . The PSV  106  has ore transfer facilities to load retrieved ore onto barge  108 . The present embodiment provides a tool  116  operable to about 2500 m depth, however alternative embodiments may be designed for operation to about 3000 m depth or greater. During production operations, seafloor mining took (SMTs) will be used to excavate ore from the seabed  110 . The SMTs comprise a seafloor bulk miner  112 , a seafloor gathering machine (GM)  114  and a seafloor auxiliary mining machine  116  and a stockpiling system  124 . The bulk miner (BM)  112  and gatherer  114  may be of any suitable form. In this embodiment ore mined by the auxiliary mining machine  116  and hulk mining machine  112  is gathered and pumped by each respective machine in the form of a slurry to a stockpile system  124 , for example through stockpile transfer pipe  126  (shown interrupted in  FIG. 1  for clarity). 
         [0041]    The stockpiled ore is gathered and pumped, in the form of slurry, through a riser transfer pipe (RTP)  120  to a subsea lift pump  118 , which then lifts the slurry via a rigid riser  122  (shown interrupted in  FIG. 1 , and may he up to about 2500 m long in this embodiment). The slurry travels to the surface support vessel  106  where it is dewatered by plant  104 . The waste water is returned under pressure back to the seafloor to provide charge pressure for the subsea lift pump  118 . The dewatered ore is offloaded onto transport barge  108  to be transported to a stockpile facility before being transported to a processing site. 
         [0042]    The seafloor auxiliary mining tool  116  of this embodiment is provided for cutting and if/as required pumping material away from a work face location. The seafloor auxiliary mining tool  116  is a remote operated vehicle, capable of operating to a water depth of about 2500 m, and is operated from on board the PSV  106 . Operation of the seafloor auxiliary mining tool  116  is controlled subject to ore grade, over-all production rate and operational and maintenance constraints. Excavated particle size is controlled by the auxiliary mining tool  116  cutter type, cutter rotation speed, speed of advancement of the cutter heads, depth of cut, cutter pick spacing and angle and cutter head spacing. 
         [0043]    Bulk mining and gathering can then be carried out by any suitable means. 
         [0044]    While the auxiliary mining tool  116  may be utilised in any suitable mining process, in the embodiment shown in  FIG. 1  the ore recovery sequence is as follows. First, any unconsolidated sediment is removed using the gathering machine (GM), and deposited in a pre defined area that may or may not form part of the mine. Then, obstructions are cut down using the AUX  116  of this embodiment, to prepare a level landing area for the BM  112  and GM  114 , This site preparation by the auxiliary mining machine  116  is illustrated in  FIG. 7   a.    
         [0045]    Next, ore left by the auxiliary mining tool  116  is gathered with the GM  114 . Benches are cut using the BM  112  then cut and sized ore is gathered using GM  114 , this being repeated until remnant edges are about 4 metres high. Then, the remnant edges are trimmed using the AUX  116  of this embodiment, as shown in  FIG. 7   b.    
         [0046]    Thus, the AUX  116  initiates seafloor mining operations and prepares an adequate landing area for other seafloor tools, and if required for other seafloor devices such as a stockpiling device. The AUX  116  is also used to remove edge sections of ore benches which cannot be accessed or efficiently mined by a bulk miner. 
         [0047]      FIG. 2  is a side view of auxiliary mining tool  116  in accordance with this embodiment of the present invention.  FIG. 2  illustrates the size of the AUX  116  of this embodiment, giving insight into its functionality. The AUX  116  pumps ore utilising a slurry dredge pump system  202 , to a seafloor stock pile area., which is then gathered at a later date by suitable seafloor gathering machine (GM)  114 . Continuous tracks  204  provide for seafloor locomotion of the tool  116 , even over complex seafloor topography. Winch cable attachment point  206  permits detachable attachment of the tool  116  to a winch cable to permit winching of the tool  116  between the surface and the seafloor. Cutting head  210  is mounted on boom  208 , permitting use of cutting head  210  in a versatile range of positions, heights, and angles. 
         [0048]      FIG. 3  illustrates the cutting and suction process of the auxiliary mining tool  116 . As can be seen, the AUX  116  is a vehicle with tracks  204  and a cutter suction boom assembly  208 , which is articulated and capable of boom stewing of about +/−40 degrees laterally of the machine centre tine and is capable of rising above and below the machine. As seen in  FIG. 5 , cutting head  210  comprises two pairs of counter rotating cutter heads  212  which are electrically or hydraulically driven via umbilical power supply to cut ore and deliver cuttings to an inlet in the form of a centrally located suction head  214  located in between the counter-rotating cutter heads  212 . Suction head  214  can be in various shapes and sizes to suit the size and type of material being cut and extracted. Shown in  FIG. 2 , a bucket/blade  216  is also provided to assist with material clearing and add to the effectiveness of the cutters  212 . Bucket/blade  216  also acts as a shroud for the cutters to aid in the suction removal of the cuttings. A shroud  218  in  FIG. 2  is also provided to assist in the effectiveness of the suction head  214  in  FIG. 5  and size the cuttings and control the size of the cuttings. 
         [0049]    Tool  116  may further comprise a water jet system (not shown) for high pressure water injection to the cutter head  210 , and a slurry/ore suction/delivery line  202 , using a suction dredge pump system, to pump cut material and transport it to a subsea stock pile zone via a stockpile hose  126  of  FIG. 1  and connector system, and stockpile system  124 . In another embodiment, an upper carriage assembly  220  in  FIG. 2  provides the capability of stewing the auxiliary mining vehicle&#39;s cutting heads, In another embodiment a further assembly (hydraulic cylinder  222 ) on the cutter heads allows the spacing of the cutter heads to be adjusted during operation to improve cutting efficiency and cuttings extraction efficiency and size the cuttings and control the size of the cuttings. 
         [0050]    In this embodiment the tool  116  has a dry land weight of approx 200 to 250 tonnes, a cutting power to tool weight ratio suitable for this type of machine, and a number of primary functions, The tool  116  removes obstructions and high points and prepares a clear landing area for other tools to commence cutting operations, as shown in  FIG. 7   a . Tool  116  cuts and cleans areas of the bench that are inaccessible to a less agile bulk miner, as shown in  FIG. 7   b . The tool  116  can pump cut material to a seafloor stockpile area, and assist with levelling and grinding up seafloor chimneys. The boom action of the tool  116  enables cutting of bench heights of up to about 4 m, even on a slope, and enables the tool  116  to clear bench edges and/or footwall interfaces which are not readily accessible by less agile seafloor tools. 
         [0051]    The auxiliary mining tool  116  is further operable to perform tidying cuts to clean up the mine site at the completion of mining, and can also cut an access ramp for other seafloor tools to high points of a mine, and/or cut a ramp up to a peak area thus generating its own access way to the peak itself. 
         [0052]    The tool  116  is manoeuvred on the seafloor by means of crawler tracks  204 . It is capable of handling rocky ground and rough terrain, and has an ability to both operate and manoeuvre on slopes. The tool  116  can also be lifted and landed to relocate around the site using its main winch wire  402 , from the support vessel. 
         [0053]    The AUX  116  is designed to cut and gather ore, pumping it to either a stockpile or to a side cast zone just behind or beside the vehicle. The AUX  116  is designed with a counter rotating cutter head  210  complete with central suction head  214  to cut ore efficiently and if/as required deliver it to a stockpile at a spaced location. 
         [0054]    The cutter/suction head  210  is mounted on an articulated boom  208  capable of slewing, lifting and lowering, and changing the angular position of the cutter suction head  210  in the vertical plane. The forward and aft spacing of the cutter heads can be changed by mechanism  222  to adjust and increase cutting and suction efficiency during operations and size the cuttings and control the size of the cuttings. 
         [0055]    The overall Auxiliary Mining Machine system is outlined in  FIG. 4 . The Production Support Vessel (PSV) hosts the control room from which the AUX  116  is operated, along with the winches for both the umbilical and the lift wire, and an A frame for deployment and recovery of the AUX  116 . The AUX is connected to the vessel by means of an umbilical cable  404 , and a main hoist wire  402 . 
         [0056]    The umbilical cable  404  provides electrical power to drive the motors and pumps required to drive the main components of the AUX  116 , such as track drive motors, hydraulic system drive motor(s), dredge system pump drive motor(s) and the cutter drive system. 
         [0057]    The umbilical  404  also provides control lines suitably in the form of multiplexed fibre optic communication links between the AUX  116  and the operational controls on the PSV  106 . 
         [0058]    The AUX  116  is lowered from the PSV  106  to the seafloor, via the main hoist wire  402 . When the AUX  116  is landed out on the seafloor, the hoist wire  402  can be disconnected and recovered either back to the PSV  106 , or to a safe height whereby it will not get tangled with the umbilical  404  during mining operations. 
         [0059]    The AUX  116  incorporates systems within the chassis to find, engage, secure and disconnect the stockpile hose connector (also incorporating a coupling, emergency disconnect system and swivel). If required, a stockpile hose may be stored within the AUX chassis on a stowage arrangement such as a wind-out reel. Once the AUX  116  is on the seafloor, a stockpile hose is connected (if required for stockpile mining operations) and the AUX  116  is then ready for cutting and stockpiling operations. 
         [0060]    When the AUX  116  is ready to be recovered to the PSV  106 , the hoist wire  402  is reconnected and the stockpile hose disconnected. The cutter boom  208  is slewed to the zero degree, fully extended and lifted position. Tool  116  can then be lifted from the seafloor, and recovered to the PSV  106 . 
         [0061]    As previously outlined, the AUX incorporates two different methods for ore placement, those being the vehicle rear or side-cast method, and the stockpile transfer method. As shown in  FIG. 3 , control of suitable valves allows slurry from suction head  214  to be selectively directed to either a stockpile hose connector system  302 , or a rear/side cast lay down outlet  304 . The rear or sidecast method is utilised in areas that are easily, and efficiently accessed by the gathering machine  114  (for subsequent clean up and recovery of the material). The stockpile method is utilised for restricted access areas so as to transfer the ore to a pre-defined stockpile location from which the GM  114  will recover the ore. Appropriate mine planning can define which ore placement method will be adopted for which location. 
         [0062]    A dual counter-rotating drum cutter  210  is used for the main cutting head which is outlined in general in  FIGS. 5 and 6 . The cutter  210  is mounted on a two function hydraulic boom  208  which is capable of lifting and lowering in the horizontal axis, and slewing around the vertical axis. The boom  208  provides a versatile mounting for the cutter assembly  210  and allows a large volume of rock to be cut without moving the vehicle itself. This versatility allows the arm  208  and cutter  210  to ‘target’, for example, steps or other discontinuities, such as isolated towers, as may be encountered in the mine. The rock cutter head  210  is of about 600 kW power, on an articulated arm  208 , which provides a versatile mounting for the cutter and allows large volumes of rock to be cut without moving the auxiliary miner itself. 
         [0063]    The boom  208  operates in successive downward/sideward cuts to complete a full sump depth, full width cut of the mine face to an approximate sumping depth around 1 metre. The boom and cutter angle positions can then be adjusted to carry out a further 1 metre sumping depth cut before the vehicle is required to reposition forward. 
         [0064]    The excavated material can be drawn away from the work area, through the suction nozzle  214  detailed in  FIGS. 5 and 6 , by a high flow dredge pump system. The slurry flow circuit is shown in more detail in  FIG. 3 . A dilution system is used to reduce the chances of blockage and control the slurry density in the suction and delivery lines. A densitometer and flow meter is used to constantly monitor the concentration and velocity gradients through the slurry circuit. 
         [0065]    The AUX  114  of the further embodiment is a tracked vehicle. Whilst mining, a moveable anchoring system taking the form of stabilising spuds engage and penetrate the seafloor surface layer in order to provide more positive control of the miner, as shown in  FIGS. 7   a  and  7   b . As further shown in  FIG. 8 , each movable spud  802  of a vehicle anchoring/stabilising system is independently powered, allowing limited ability to level the vehicle on uneven ground. The spuds are designed to penetrate through any loose surface material to locate into good quality ground. For soft ground, larger area shoes can be fitted to the spuds. The spuds can also each be in the form of a blade. The blade then allows the functionality of a spud and also allows an ability to move material during forward or aft locomotion of the machine. 
         [0066]    A jet water system  306  is installed to provide clearance of the suction grizzly  214  in the event of blockage, and agitation of the material face to be cut if required. The jet system  306  can clean the cutter head  210  or tracks  204  in the event of clogging. The jet system may also assist with slurry line blockage prevention/clearance. 
         [0067]    The AUX  116  can move from one area of the seafloor to another in one of two ways. The AUX  116  is capable of tracking on seafloor topographies of less than about 10 degrees, at rates &gt;about 600 m/hour. Alternatively, the vehicle  116  can be hoisted off the seafloor using the main hoist wire  402 , and manoeuvred to the next site. 
         [0068]    When manoeuvring in the locality, the powerful track assemblies  204  provide for efficient repositioning of the vehicle  116  for maximum operational production capability. The AUX  116  thus provides more efficient cutting and stock-piling of excavated material. 
         [0069]      FIGS. 9   a - 9   d  illustrate an auxiliary cutter  900  in accordance with another embodiment of the invention, comprising a cutting tool support boom  902 , front swing-out stabilising legs  904  with vertical jacking, tracks  906  for site traversing, a rear sonar array  908 , electronic control pod indicated at  910 , a rear stabilising anchor/blade  912 , main cutting tools  914 , a crown cutter stockpile gathering system  916  mounted to the underside of boom  902 , two thrusters  918 , a lifting point and capture bowl  922  for 20 degree slope recovery, a stockpile hose interface  924  and a slurry transfer pump and motor  926 . 
         [0070]      FIG. 10  illustrates a further embodiment of the invention in which an auxiliary miner  1000  has a blade  1010  to push cuttings ahead of the chassis and minimise or avoid cuttings passing beneath the tool  1000 . Blade  1010  is semicircularly curved so that the aft cutting heads remain at a substantially constant distance from the blade when moved azimuthally, as shown in  FIG. 10   b . This arrangement effects improved efficiency of gathering by the suction inlet adjacent the cutting head, as visible in  FIG. 10   b , and also clears stray cuttings from the path of the tool. 
         [0071]    It is to be appreciated that particular terms used herein may he synonymous with other terms which equally describe the present invention and the scope of the present application is thus not to he limited to any one such synonym. For example, seafloor mining tools may also be referred to as subsea machines, a production support vessel may be referred to as a surface vessel and/or surface facilities, ore may be equally or alternatively referred to as rock, consolidated sediment, unconsolidated sediment, soil, seafloor material, and mining may comprise cutting, dredging or otherwise removing material. Moreover, particular values provided give an illustration of scale in the described embodiments but are not to be considered restrictive as to the scale or range of values which might be used in other embodiments to suit the environment of application. 
         [0072]    It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described, The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.