Patent Description:
Narrow vein deposits are challenging to mine. Narrow veins are generally considered to have a thickness of <NUM> meters or less between the hanging wall and the foot wall. In some deposits, there are veins of valuable ores such as gold where they are not only narrow but also steeply dipping. These deposits become stranded because there is no effective way of mining them. Neither open pit methods nor underground cut and fill methods are economically viable for mining a steeply dipping ore vein and such methods, in fact, often would result in a net loss. The environmental impacts of these approaches are also unattractive.

That being said, just within the province of Newfoundland, Canada, there are an estimated <NUM> million ounces of gold resources that occur within these narrow steeply dipping ore veins.

Prior art document <CIT> discloses the preamble of claim <NUM>.

In accordance with a broad aspect of the present invention, there is provided a method for mining narrow vein deposit of ore, the narrow vein deposit having a hanging wall and a foot wall, the method comprising: drilling a pilot hole into the narrow vein deposit along a path substantially centrally between the hanging wall and the foot wall to a depth within the vein, following the pilot hole with a larger diameter drilling assembly to fragment the ore around the pilot hole into drill cuttings; circulating the drill cuttings with a fluid flow up to a wellhead; and collecting the drill cuttings for processing to recover the ore therefrom.

In accordance with another broad aspect of the present invention, there is provided a mining system for mining a narrow vein deposit of ore, the system comprising: a drilling rig; a pilot hole drilling assembly including a drill head for drilling a pilot hole in the ore, a downhole survey tool for locating a hanging wall and a foot wall of the narrow vein deposit relative to the pilot hole and a directional assembly for directing the drill head along a path between the hanging wall and the foot wall; a hole opener assembly including an end configured to follow the pilot hole and a hole opener drill configured to drill a borehole with a larger diameter than the pilot hole to fragment the ore into drill cuttings; a fluid circulation subsystem to move a fluid through the well to circulate the drill cuttings from the borehole to a well head.

It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of example. As will be realized, the invention is capable for other and different embodiments and several details of its design and implementation are capable of modification in various other respects, all captured by the present claims. Accordingly, the detailed description and examples are to be regarded as illustrative in nature and not as restrictive.

For a better appreciation of the invention, Figures are appended as follows:.

The detailed description and examples set forth below are intended as a description of various embodiments of the present invention and are not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

Narrow vein deposits typically have thicknesses of less than <NUM> meters (usually about <NUM> - <NUM> meters) between their hanging and foot walls. Narrow veins can be steeply sloped, such as dipping from <NUM> - <NUM>°, or most often <NUM> - <NUM>° relative to horizontal. They can be accessed from an access location, such as on or near surface or in an underground location such as in a mine shaft.

This method for mining includes: drilling a pilot hole from the access location down into the narrow vein deposit and along a path substantially centrally between the hanging wall and the foot wall to a depth within the vein; following the pilot hole with a larger diameter drilling assembly to fragment the ore into drill cuttings; circulating the drill cuttings with drilling fluid circulation up to the access location; and collecting the drill cuttings for processing to recover the ore therefrom.

From a sustainable mining perspective, the method offers one or more advantages over conventional methods such as:.

With reference to <FIG>, the new mining method is intended to mine stranded, narrow and possibly steeply dipping ore veins that are too small or isolated to be mined economically using conventional methods. An example of such a vein v is shown in <FIG>. Such an ore vein v has a strike length, such as typically of <NUM>-<NUM> metres, and a thickness T of less than <NUM> meters, for example typically about <NUM> - <NUM> meters, between its hanging wall <NUM> and foot wall <NUM>. The thickness T can vary along the depth and the strike length of the vein.

Narrow vein deposit v can be steeply sloped, such as dipping at an angle of from <NUM> - <NUM>°, or most often <NUM> - <NUM>° relative to horizontal. The vein can have a dipping angle that varies along its depth, for example being at an angle α1 near the upper end, which changes to α2 at a greater depth.

The vein can be accessed from an access location above the vein, such as on or near surface s. While an access location on surface is preferred, this mining method could also be conducted from an exposed vein deposit in a mine shaft that intersects the vein.

The mining method is a two-stage method that can be summarized as mining-by-drilling.

In the first stage (<FIG> and <FIG>), if necessary, the site is prepared such as by removing any overburden ob to access the vein's upper end. Thereafter, a pilot hole <NUM> is drilled from the access location down into the depth of the vein v between the hanging wall <NUM> and the foot wall <NUM> using drilling assembly including a pilot bit <NUM> on a drill string <NUM>. Directional drilling tools <NUM> and methods and downhole survey tools <NUM> and methods may be used to maintain the pilot hole within the vein along its depth and to map the vein. Non-destructive survey methods may be used to determine vein trajectory and the distance from the pilot hole to the hanging wall and foot wall. As such, pilot bit <NUM> can drill down while remaining substantially centered between the hanging wall and the foot wall without side tracking beyond the margins of the ore deposit into the over and under lying waste rock. At the same time, the vein can be characterized such as including its dip angles and thickness.

The non-destructive survey may including near bore imaging technologies. The survey and imaging may be conducted at least at regular intervals. Thus, from time to time while drilling the pilot hole, a downhole survey may be undertaken. In one embodiment, an imaging and survey tool such as a wireline survey and/or geophysical tool, measures the borehole trajectory and the location and geometry of the vein near the borehole and about the bit. The pilot hole trajectory is then changed, as needed, to follow the dip and stay within the vein, for example, substantially midway between the hanging wall and foot wall contacts.

The survey tools may be carried on the drilling assembly or they may be run into the pilot hole from time to time. In one embodiment, drilling is stopped occasionally and the survey tools <NUM> are run in to assess the vein and position of the pilot hole. This may include pulling string <NUM> and bit <NUM> and running in with the survey tool or pulling only a portion of the drilling assembly such as all or a portion of pilot bit <NUM> such that the survey tool <NUM> can be run through the string, such as on wireline, and operated in the pilot hole. When the hole <NUM> is drilled to survey depth, a portion of the pilot bit, such as wireline core or bit plug 10a, is removed to open a passage through string <NUM> at its distal end, the string is pulled up a short distance from bottom hole 6a and at least a portion of survey tool <NUM> is extended out into the pilot hole to measure well trajectory and distances, including for example, vein imaging (<FIG>). Thereafter, the tools <NUM> can be removed, the pilot bit restored and the course steered, if necessary, to stay along the deposit dip and halfway between the hanging wall and the foot wall. In this way, the pilot hole is drilled within the vein to total depth.

When the pilot hole is drilled to a desired total depth, the pilot hole drilling assembly and string can be pulled out of the hole. The hole can be left open, which is uncased.

In the second stage, shown in <FIG>, hole opening drilling, possibly with underreaming, is used to mine the vein by following the pilot hole. The method includes moving a hole opening assembly <NUM> along, and centered on, pilot hole <NUM>. The hole opening assembly includes a string <NUM> carrying a hole opening bit <NUM> that has a leading end <NUM> configured to follow the pilot hole. Because the pilot hole <NUM> has been drilled within the vein v and possibly substantially centered between the hanging wall <NUM> and foot wall <NUM>, the hole opening bit drills out an enlarged borehole <NUM> with diameter D centered on the pilot hole. Based on the survey information regarding vein thickness obtained during pilot hole drilling, the hole opening can be extended out to the limits of the vein and the vein is thereby mined out to about its full thickness without drilling up much waste rock w. A hole opening bit drilling diameter can be selected according to the survey/imaging information mapped previously while drilling the pilot hole. The second stage mining proceeds while allowing the hole opener drill string to flex to follow the trajectory of the pilot hole. This second stage can include one or more drilling passes and optionally with underreaming to open the hole to a greater diameter along selected lengths. The diameter of the drilled hole may be <NUM>-<NUM> and this can be done in a limited number of passes, such as one, by selection of a drilling assembly with a <NUM>-<NUM> diameter.

The ore is retrieved as drill cuttings that are circulated with circulation fluid flows up to the well head. The drill cuttings can be from the pilot hole, which are circulated up with fluid, arrows F. However, due to the relative sizes of the holes, the ore drill cuttings will be for the most part from hole opening. Circulation may be in the forward or reverse directions. The forward direction being down the string and up the annulus between the string and the borehole wall, while reverse circulation is down the annulus and up the string. In hole opening, circulation, arrows R, may be in the reverse, using reverse circulation drilling methods. The hydraulic pressure of the circulation fluids supports the borehole wall such that no casing or additional hole supports or liners are required. However, if serious instability is found to occur in a vein, the hanging wall can be presupported by installation of cables and bolts before hole opening. The borehole does not require dewatering, as the fluid circulation and lifting of cuttings can occur even in the presence of geological water.

When the drill cuttings arrive at surface, they are then separated from the circulation fluids and ore is recovered from the drill cuttings.

Once the hole <NUM> is completely mined, the drilling assembly <NUM> is pulled out of the borehole. Thereafter, the borehole can be filled (<FIG>), for example with backfill. The backfill can be include waste mill tailings and optionally a carrier or binder such as cement. Thus, the method may include filling the hole or pumping the tailings and a binder into the hole. This provides an environmental benefit as the tailings need not be stored on surface and the geology is stabilized. In addition, the backfill, when consolidated by a binder, permits a mining-by-drilling operation to be conducted directly alongside the filled borehole.

Mining of the vein continues by moving along the strike length of the vein and mining further boreholes including drilling a pilot hole 6a followed by hole opening 26a at a plurality of locations. In one method, time is permitted to allow the backfill <NUM> to set before mining an adjacent borehole so that new holes can be mined directly up to, and possibly partially overlapping with, cured backfill in completed holes <NUM> to ensure maximum ore recovery. One method that permits continued mining while the backfill in the first borehole sets, includes mining and filling a first borehole <NUM> (termed a primary) and then mining and filling another primary borehole 6a, 26a spaced apart from the first (<FIG>), so that opened borehole 26a so that an undrilled portion of the vein remains between the holes <NUM>, 26a and borehole 26a is out of communication, does not contact or overlap, with the first borehole <NUM>. Further pilot holes 6b, 6c can be planned to mine a remaining section of the vein. For example, after time is permitted for the backfill in holes <NUM>, 26a to set, a secondary borehole 6b can be drilled and opened alongside the first primary, to mine the undrilled portion of the vein between the two primary holes <NUM>, 26a. <FIG> shows the first two primaries <NUM>, 26a backfilled and between them, an intervening secondary pilot hole 6b drilled and ready to be opened. Further proposed or drilled pilot holes 6c, 6d will mine a remaining section of the vein. Hole opening can be scheduled for a plurality of primary pilot holes before starting on secondary pilot holes between the oldest primary pilot holes. Alternatively, the mining schedule may alternate primary pilot holes and secondary pilot holes. Pilot hole drilling can be independent of hole opening or the entire pilot hole and hole opening can be completed before moving to a next location along the vein. Because the pilot holes can be precisely placed, the vein can be mined efficiently by hole opening to the vein thickness, controlling any overlap between mined holes or out into the waste rock, and backfilling completed holes.

The method may require site preparation before the first stage. For example, the surface may be cleared to expose the vein or the drilling operation may drill down through surface materials to access the vein.

This method can selectively open the hole substantially only within the vein and minimizes or at least provides control over how much waste rock is drilled up. Thus, the drill cuttings to be processed for ore recovery can have little contamination from waste rock from the hanging and foot walls or backfill from adjacent mined, backfilled holes. This is beneficial for the drill cuttings to be processed for ore recovery.

Each enlarged borehole drilled can span substantially the thickness of the vein, such as <NUM>-<NUM> meters, and can be drilled to a considerable depth, such as <NUM> or more along the vein, which in a dipping vein may be about <NUM> deep. For a hole drilled into an ore-containing vein of specific gravity <NUM> tonnes/m<NUM>, with a <NUM> meter diameter and a length of <NUM>, that hole therefore may produce roughly <NUM> tonnes of ore.

A mining system for mining a narrow vein deposit of ore may include: a drilling rig; a pilot hole drilling assembly including a drill head for drilling a pilot hole in the ore, a downhole tool for locating a hanging wall and a foot wall of the narrow vein deposit relative to the drill head and a directional assembly for directing the drill head along a path between the hanging wall and the foot wall; a hole opener assembly including an end configured to follow the pilot hole and a hole opener drill configured to drill a borehole with a larger diameter than the pilot hole to fragment the ore into drill cuttings; and a circulation subsystem to circulate the drill cuttings from the borehole to a wellhead for collection and processing to recover the ore.

The drilling rig, of course, directs drilling fluids, handles the drill pipe and drilling tools, applies weight on bit (WOB) and applies or at least reacts torque in the string. In this system, it is desirable that one rig can handle all of the drilling, both drilling the pilot hole and drilling the enlarged hole. It is desirable that the one rig can handle both the near surface operations and operations through to total depth, all of which are required to mine an entire borehole through the vein. As such, for example, the rig should be capable of handling the drilling equipment for both the pilot hole and for the second stage large diameter, hole. This means, for example, handling drill bits in diameter range of from <NUM> for the pilot hole to <NUM> meters for the hole opening operation. Considering that a typical gold ore has a host rock strength of about <NUM> - <NUM> MPa and the process includes a large variance in hole diameters, the drilling rig must be capable of applying <NUM> to 450kN WOB. The drilling rig may also be configured to drill in slant, in order to drill into dipped ore deposits. The rig may also need to operate with circulation in the forward as well as reverse directions, where cuttings flow up the inside of the drill string to surface.

Considering that the method may require the drilling of a number of spaced apart boreholes into the vein and the remote location of some vein deposits, the drill rig should be relatively mobile. The drilling rig may be moveable, for example, by crane, an attached skid or a transport undercarriage such as a trailer or attached tractor conveyance.

In one embodiment, a pile top drill rig may be useful. A pile top drill rig is operated on the top of a casing pipe and is typically used for construction such as placement of piles. A pile top rig includes a floor mounted on top of a casing pipe, table and clamps on the floor and in the casing pipe and a super structure above the floor including an arch-shaped mast with side structures and an upper section, a top drive with power swivel supported in the upper section of the mast and a pull down cylinder in each side structure. A suction pipe is in communication with the top drive. Such a rig is relatively small and capable of being transported to remote locations. While it is normally used for large diameter drilling, the rig in this embodiment is configured for handling equipment to drill holes ranging in size from <NUM> to <NUM> meters from the same rotary table. Additionally such a rig may be configured for drilling using direct (forward) or reverse circulation. The rig can function with both liquid and gaseous drilling fluids.

The pile top drill rig, however, may require some modifications to most effectively operate for this mining method. For example, since mining sometimes requires drilling early on into bedrock, it may be difficult to place the casing on which the rig is mounted. Thus, the system and method may be configured to carry out additional drilling steps at surface in order to achieve casing placement. In particular, a typical pile top drill rig requires a casing length of about <NUM> meters to generate enough pressure head to lift cuttings. In this embodiment, the bedrock may be very close to surface and, so, it is difficult or impossible to achieve the <NUM> meter depth. Thus, the system uses a shorter or variable length casing pipe possibly in combination with pressurized circulation to permit the pile top drive to operate without the <NUM> meter casing pipe. Modifications may also be necessary to accommodate the hole opening drill string fully below the rig floor before normal drilling operations can be commenced. Also, the rig table and/or top drive may require modification to handle the variously dimensioned pipes such as drill pipe and larger space pipe in one string. Alternatively or in addition, the rig may benefit from a rig to ground surface anchor system to enhance the rotary torque and thrust force capabilities.

<FIG> and <FIG> show two pile top drill rigs configured for drilling into a narrow vein. While both rigs are moveable due to their compact size, the rig of <FIG> is more readily mobile.

The mobile rig of <FIG> includes a pile top drill rig structure <NUM> mounted on a transport undercarriage <NUM>, for example on a track-type, also called a caterpillar-type or crawler, undercarriage. The transport undercarriage allows rig mobility between drilling sites and operational flexibility to drilling operations. The transport undercarriage has the capacity to run on uneven and unconsolidated surfaces. In this embodiment, a casing pipe <NUM> is supported on the undercarriage. The pile top drill rig is fixed to an upper end of the casing pipe through a casing attachment device. The mobile platform may further include an anchoring system <NUM> for securing the rig to the ground. The anchoring system may be specifically dimensioned to support the reaction forces during the drilling operation. In one embodiment, the rig is anchored to the ground by grouted rebar anchored firmly into the bedrock. The anchoring system is configured to resist the drilling reaction forces, while avoiding interference with the drilling operations.

The rig may include a base platform for storage of equipment, for example set over the undercarriage.

While not shown, the mobile rig may be configured for operations in slant, where the casing <NUM> and the rig's superstructure <NUM>, effectively the drilling axis defined between top drive 118a and the floor clamps 118b is inclined, such as by use of a hydraulic inclination system, for example in the undercarriage. The undercarriage, for example, may include an actuator to tilt the casing <NUM> and superstructure <NUM>. In one embodiment, there is an undercarriage system, for example based on hydraulic actuation, that drive the casing and superstructure to tilt forwardly or rearwardly relative to the direction of travel, which is parallel to the long axis of the tracks. These functions allow the rig to be inclined to drill a hole that matches the vein inclination angle at surface.

The rig may further be equipped with a floor <NUM> and a levelling system for the floor, for example also through hydraulic actuators. Thus, permitting the floor to be maintained as level, for example substantially horizontal, even though the undercarriage, superstructure and/or casing are inclined. This facilitates operations for workmen on the floor.

The rig may further be equipped with a height adjustment assembly for the rig deck including height adjustable, such as telescopic, legs <NUM>, a telescoping casing pipe <NUM> and a system to drive height adjustment movement. This allows for height variation of the rig deck and casing pipe. Drilling operations proceed from the rig deck down through the casing pipe and then into the ground surface, such as the vein, to be mined. Initially casing pipe <NUM> is set on the ground surface. In particular, similar to the system of <FIG>, a lower flange of the casing pipe is installed on the ground surface with an o-ring type seal therebetween to seal the interface and provide fluid containment within the casing pipe. The lower flange may be configured to float on the casing pipe in order to be adjustable for the angle of the casing to be oriented to substantially match the dip angle, while the flange lower face is oriented parallel to the ground surface.

The telescopic configuration 114a in the casing pipe, for example, permits the casing length to be longer when the rig deck <NUM> needs to be higher, for example in the early stages of drilling, and then the casing can be shortened by telescopically collapsing one length of casing axially into a second larger diameter length of the casing. The casing may need to be higher during initial hole opening stages when the hole is more shallow in order to provide the required drilling pressure at bottom hole. As the hole depth increases, the telescopic casing and rig can be lowered to reduce the height of the rig. The telescopic configuration may include a telescoping interface between the two casing lengths and a pressure-holding sliding seal. A casing pipe with the flange may be on the bottom and a vertical displacement assembly, such as a hydraulic system, may be at the telescoping interface to permit adjustment of the casing flange (during installation) and when reducing the height of the casing pipe and rig.

In this mining operation, the casing pipe may be sealed against the surface of, or extend a short distance into, the vein, to permit a fluid seal between the casing and the hole. This permits the hole to be extended with open hole, non-lined, drilling.

<FIG> shows a pile top drill rig <NUM> fixed and installed on a pad <NUM>. While mounted in one position, the costs to dismount, move (as by use of a crane) and remount the rig on a new location along the vein may be an acceptable alternative considering the cost of the moveable undercarriage. The pad, made from concrete, may provide a solid, level base onto which the rig's casing pipe <NUM>' can be installed. The pad is poured over an access location for the vein v, for example on a cleared area of rock directly over the exposed vein. If desired, the pad in one operation can extend along a length of the vein greater than the space needed to install the rig so that there is space to move the rig down and drill a next borehole without having to construct another pad. A flange connection <NUM> may be employed between the casing pipe and the pad. A gasket <NUM> can be employed between the flange and the pad to improve drilling fluid retention in the above ground casing pipe. The bolts employed to secure the casing flange on the pad should be dimensioned to support the axial and torsional stress during the drilling operation. In one embodiment, the flanged pipe is anchored to the bedrock using grouted bolts/rebar that pass through the flange and penetrate the concrete slab and the underlying bedrock b.

The casing can be installed on a slant that corresponds to the vein's initial angle of inclination such that the drilling axis substantially follows the vein. The casing pipe's flange <NUM> therefore may be configured as angled, not orthogonal with respect the casing long axis. This flange helps to secure the casing pipe at an inclination, specifically the angle of the flange relative to the long axis of the casing pipe defines the angle at which the casing pipe will extend up from the pad and thereby the drilling axis relative to the vein. The rig floor <NUM> may be secured in a level, horizontal orientation while rig superstructure <NUM> above the floor, such as the pipe handling apparatus and top drive, may be on a slant and axially aligned with the long axis of the casing pipe.

The rig may also include support pillars <NUM> to support the rig floor in addition to the casing pipe. The support pillars are rigidly connected, as by bolting or welding, to the casing <NUM>' and superstructure <NUM>, to thereby act during the drilling operation to accommodate device weight, rotary torque and thrust due to rig pull up force.

The pilot hole drilling assembly acts in the first stage of the method to create a pilot-sized borehole through the vein. The pilot hole follows the dip of the vein and is drilled along a trajectory within the vein, for example, substantially centrally between the hanging wall and the foot wall. The pilot hole drilling assembly includes:
The drill head <NUM> for drilling a pilot hole in the ore - the drill head may be any drill bit and connections configured for advancing a drilling assembly through ore bodies such as gold deposits. In one embodiment, the drill head may be configured to drill by a combination of rotation and percussion. The drill head is also configured to handle the drilling fluid of interest such as in one example air, mud or combinations. In one embodiment, for example, a hydraulic turbo-type or a pneumatic rotary percussion drill head is employed. The pilot hole drill head may be configured to drill a hole of <NUM> to <NUM> or more likely <NUM> to <NUM>. The drill head <NUM> may be removable up through the string, while the string remains down hole (this alternative is not according to the claimed invention), or it may include a removable core barrel or bit plug 10a, to permit access to be opened from the string's distal end out into the borehole (this alternative is according to the claimed invention).

The downhole survey tool <NUM> for locating the hanging wall and the foot wall of the narrow vein deposit relative to the drill head is a non-destructive survey tool such as a downhole imaging tool. The survey tool is configured for near borehole imaging and may include, for example, a geophysical tool incorporated on the drill head or conveyed by string or on wireline and employing technologies such as one or more of ground penetrating radar, high frequency acoustic, ultrasonics, x-ray, magnetic resonance imaging (MRI), etc..

In one embodiment, a near borehole imaging tool is used during the pilot hole drilling stage. At various depth intervals while drilling the pilot hole, a survey is taken with the imaging tool. If the imaging tool is not incorporated into the pilot hole drilling assembly, surveying may include running into the hole with the downhole imaging and survey tool either by wireline and/or by attachment at the end of the drill string.

One possible downhole imaging and survey tool has two major components: i) The first component is a geophysical imaging system that provides a high resolution image of the near well bore region to identify the distance of the borehole from the hanging wall and foot wall vein contacts, information about the continuity of the vein in the lateral direction along the strike of the vein, and information about the continuity of the vein ahead of the bit; and ii) The second component is a directional information system including a combination of accelerometers, magnetometers and north-seeking gyros that provide the information about the inclination and azimuth of the borehole trajectory, and the tool face angle of the imaging tool.

The downhole imaging and survey tool information is used to determine if the bore hole trajectory is deviating from a path within the vein, for example a position about halfway between the hanging wall and foot wall vein contacts, if the trajectory is deviating from the dip of the vein, if the vein is changing thickness or direction, or some combination of these. If the bore hole is deviating from the required trajectory, then the near well bore information is used to plan a trajectory adjustment using downhole steering tools.

The geophysical imaging system for the survey tool may be ground penetrating radar. However, other embodiments using high resolution acoustics, ultrasonics, XRF, or magnetic resonance imaging (MRI) are also possible.

The pilot hole drilling assembly also includes the directional assembly <NUM> for directing the drill head along a path between the hanging wall and the foot wall. The directional assembly is configured to steer the drill string such that it can drill the pilot hole path within the vein, for example substantially centrally between the hanging wall and foot wall. The directional assembly may include wedges, whipstocks, bent subs, automated kickers or other directional tools. Care may be taken to ensure that the directional assembly works with the drill string, drill head and fluids being employed.

The pilot hole drilling assembly drill string may further include drill collars, stabilizers, centralizers, logging tools, etc..

While the rig can be operated both for the first and the second stage drilling, during the first stage, pilot hole drilling, the system may require a crossover 112a to connect American Petroleum Institute (API) drill pipe in the pile top drill rig. The crossover is an interface between the top drive of the pile top drill rig and API standard drill string. It allows direct circulation of the drilling fluid. The lower end of the crossover is an API pin connection. The crossover may include a connection between the fluid injection points of the top drive. In particular, if rotary percussion drilling tools are used to drill the pilot hole, compressed air, with or without foam, is used and is direct circulated down the string and up the annulus. The proposed crossover allows switching over from the direct compressed air circulation of pilot hole drilling to the air lift assisted reverse circulation of the hole opening drilling.

The hole opener assembly acts in the second stage of the method after a length of the pilot hole has been drilled to enlarge the hole diameter along the pilot hole. This, thereby, recovers more of the ore within the vein. There may be one or more passes of the hole opener to enlarge the hole to substantially the thickness of the vein. The process may include underreaming so that thicker regions the vein can be mined with the hole opener. With reference to <FIG> and 5A and 5B, one useful hole opener assembly includes:.

The circulation subsystem circulates drilling fluid through the well, for example, to lift the drill cuttings from the borehole to a wellhead for collection and processing for ore recovery.

The type of drilling fluid selected may depend on the type of drilling. For example, drilling fluids may be water-based, foamed or gaseous. It is possible that one type of fluid will be used for pilot hole drilling while another type of fluid is used for hole opening. In one embodiment, compressed air is employed for pilot hole drilling, possibly with foamed compressed air at greater depths. For hole opening, water may be used optionally with air lift assistance, as described above with respect to conduits <NUM>.

The circulation system may include pumps, conduits, valves and a device to change the drilling fluid circulation direction (reverse vs direct) at the drill rig. This device allows drilling fluid circulation direction to be changed and can work with various fluid types such as water, compressed air, and foam. The device may include a valve set and a mixer that can produce foam with selected characteristics. In one embodiment, the circulation direction is switched when reconfiguring from pilot hole drilling to hole opening drilling.

The drill cuttings both from pilot hole drilling and hole opening are valuable, as they contain ore. Thus, there are cutting collection systems that collect the cuttings in both stages. Thus, the system includes collection pathways operable both for direct and reverse circulation. There may be returns from the drill string or from the annulus depending on the direction of circulation. Thus, cuttings-containing returns may be conveyed through the top drive 118a and out through a discharge line 118c or out through ports <NUM> in the casing for annular communication.

As noted above, casing pipe <NUM>, which spans the distance between the rig deck <NUM> and the ground surface, accommodates therein drilling operations and equipment both for pilot hole and enlarged hole drilling. The casing pipe <NUM> therefore has an inner diameter large enough to permit passage therethrough of the hole opening assembly and therefore may be at least one meter and may be about <NUM> in diameter. There are a few considerations with operations through the casing pipe.

As noted above, in some situations, such as when drilling close to surface (i.e. when the bottom hole assembly is just starting to drill or is close to surface), there may be insufficient casing height and head volume to provide adequate drilling pressures. In such an embodiment, the hole pressure above the bit may be increased to provide a more suitable hydrostatic pressure.

For example, when drilling the pilot hole, the drill string is many times smaller diameter than the casing pipe <NUM>. As such, when drilling the pilot hole, a cutting collection device and adaptor for the smaller diameter drilling pipe <NUM> may be employed, which is configured to stabilize the smaller diameter string inside the larger diameter casing and to allow the drilling fluid and cuttings to flow out during the pilot hole drilling operation. As shown in <FIG> and <FIG>, that device includes a pipe housing <NUM> with a diameter larger than the outer diameter of drill string <NUM>, but much smaller than casing <NUM>. The pipe housing provides a fluid tight conduit through which string <NUM> can be run and operated. The pipe housing extends along the length of the casing <NUM> to span between the rig deck and clamps 118b and the ground surface, such as exposed vein v, into which the pilot hole is to be drilled. The pipe housing <NUM> creates an annular space between its inner wall <NUM>' and the drill string, to accommodate fluid circulation. Thus, during direct circulation, which is normally used with the pilot hole drilling assembly, the drilling fluid and cuttings can to flow out of the annulus and prevent cuttings from going down the pilot hole. In addition, the device includes i) a stuffing box <NUM> that isolates the hole from atmospheric pressure; ii) a centralizer <NUM> on the pipe housing that stabilizes and fixes the device inside the casing pipe <NUM>; iii) a port 61a through which the drilling fluid and the cuttings can exit the pipe housing; and iv) an elastomeric seal <NUM> installed between a bottom end of the pipe housing <NUM> and the ground surface. Elastomeric seal <NUM> avoids leakage of drilling fluid between the housing pipe <NUM> and the ground surface. In the pilot hole drilling operation, the device including pipe housing <NUM> is fixed substantially co-axially inside the casing pipe <NUM> through centralizer <NUM> and a return line is connected at port 61a. A drilling pipe string <NUM> can be run in through stuffing box <NUM> and worked inside housing <NUM>. A normal pilot hole drilling operation can be commenced from housing <NUM> into vein v. Below seal <NUM>, the pilot hole is drilled open hole. Direct fluid circulation can exit the hole through pipe housing <NUM> and be discharged through port 61a. The space between housing <NUM> and casing <NUM> remains open but is not in fluid communication with the inside of pipe housing <NUM>. When the pilot hole is complete, the device including pipe housing <NUM> and centralizer <NUM> is removed from the casing pipe <NUM>. This leaves the casing pipe open for drilling activities with the hole opener assembly <NUM>.

It was noted above that steps may be taken to ensure adequate hydrostatic head when drilling near surface. This is particularly, noted during hole opening. As noted above, in some embodiments, the casing pipe <NUM> and rig can be elevated to achieve about a <NUM> casing column height above the bit face. With reference to <FIG>, sufficient drilling fluid pressure Pl in the upper annulus can be achieved by pressuring up the annulus above the hole opener bit <NUM>, possibly with forward circulation. For pressuring up the annulus, an apparatus can be employed that creates an annular seal between the hole opening drill string <NUM> and the inner surface of casing pipe <NUM>, so that the pressure can be increased therebelow. The upper pressuring apparatus is installed on string <NUM> and positioned in the casing <NUM>. The apparatus includes a flange <NUM> with an annular seal <NUM>, together forming a rotating seal assembly, which spans the annular area between the casing and the drill pipe. The flange can rotate with the drill string while the pressure seal is maintained through seal <NUM> being urged against the casing pipe wall. <FIG>, for example, shows bit <NUM> ready to spud an enlarged borehole through pad <NUM> and into the bedrock or vein as guide end <NUM> rides in pilot hole <NUM>. While the casing length as illustrated is not high enough to provide sufficient hydrostatic head for drilling operations, the pressure below flange <NUM> and seal <NUM> can be increased to that pressure Pl. The casing above flange <NUM> is open to atmosphere.

As drilling progresses, flange <NUM> moves down in casing pipe <NUM>. A port such as port <NUM> maintains fluid communication between the casing pipe and the annular area between string <NUM> and casing pipe <NUM> and is the port through which the annular pressure is maintained. The rotating seal assembly, therefore, must remain above that port. Thus, eventually the string <NUM> and flange are pulled out of the hole and further pipe joints are added to the string between flange <NUM> and bit <NUM>. When the hole opener reaches a depth where the fluid column is sufficient to support drilling operations, the rotating flange assembly may be pulled out of the hole and hole opening can proceed without pressuring up the upper annulus. The opened hole is mined without a casing liner and the seal <NUM> prevents leakage. At that point, if circulation was in the forward direction, circulation may be reversed to bring returns up through the string <NUM> inner diameter.

During hole opening, the drill cuttings are collected at the well head and processed for ore recovery. Regardless of whether they arise from pilot hole drilling or hole opening, return flows are a mixture of cuttings and the fluid used. The cuttings can be separated from the fluid by passive settling or active phase separation. Settling can be in a settling chamber or tank or in a pond. Active processing may be by cyclones or screens such as shale shakers. The rate of separation or the fragment size may guide choices.

The cuttings, once separated, are processed for ore recovery. Because the vein is fragmented through the mining by drilling process, the crushing and grinding requirements may be minimized and possibly eliminated.

Claim 1:
A mining system for mining a narrow vein deposit (v) of ore, the system comprising
a drilling rig (<NUM>);
a pilot hole drilling assembly including a drill head (<NUM>) for drilling a pilot hole (<NUM>) in the ore, a downhole survey tool (<NUM>) for locating a hanging wall (<NUM>) and a foot wall (<NUM>) of the narrow vein deposit (v) relative to the pilot hole (<NUM>) and a directional assembly (<NUM>) for directing the drill head (<NUM>) along a path between the hanging wall (<NUM>) and the foot wall (<NUM>); and
a hole opener assembly i (<NUM>) including an end (<NUM>) configured to follow the pilot hole (<NUM>) and a hole opener drill (<NUM>) configured to drill a borehole (<NUM>) with a larger diameter than the pilot hole (<NUM>) to fragment the ore into drill cuttings, characterised by
a fluid circulation subsystem to move a fluid through the well to circulate the drill cuttings from the borehole (<NUM>) to a well head,
and wherein
the drill head (<NUM>) for drilling a pilot hole (<NUM>) in the ore includes an opening (10a) and
the downhole survey tool (<NUM>) for locating a hanging wall (<NUM>) and a foot wall (<NUM>) of the narrow vein deposit (v) is configured for extension through the opening in the drill head (<NUM>).