Step 1. Mine design

The Mt. Charlotte orebodies were outlined using pneumatic and hydraulic diamond drill rigs from both the surface and underground, from the drill results a basic ore body shape was defined as a 10 x 10 block model. Using the block model the mine geologist in conjunction with the mine planning engineer plan and design the required underground development drives.

Factors considered during the planning are:

• Grade
• Total tonnes
• Economics
• Seismicity

If after all factors are considered the orebody is economically viable then plans are issued and development can commence.

Step 2. Development

The current Mt. Charlotte monthly development target is 275m, this as achieved using:

• 1 x Atlas Copco Jumbo(2 boom electric/hydraulic)
• 1 x 980C Rockbolter (custom made on site)
• 1 x R1700 Elphinstone loader.
• Cat IT28 tool carrier

The mine surveyor surveys all new development, laser points are installed to give direction of advance and grade up/down.

Decline development is taken at 6m wide by 5.5m high while the millholes are 4.5m x 4.5m and advanced at a rate of 3.5m per firing.

Scratch back
Prior to the Jumbo boring, the development end is scratched back by the R1700 loader. This entails removing all loose material from the face back to a distance of 4m and down to solid to expose any lumps or misfires. The loader operator then exposes all the lifter butts inspects and clears them of any explosive then marks them with a paint ring to show their location.

Mark up
Once the scratch back is completed the mark up is carried out. A laser is inserted into the laser hole which projects a light point onto the development face, and a paint mark is then placed at this point. Using the laser point mark and development plans supplied by the planning engineer, the face is now marked up to the desired height, width and grade, and all remaining butts are inspected and marked in preparation for the arrival of the Jumbo.

Boring
On arrival at the development end the Jumbo is plugged in and powered up, water hoses run out and turned on, (water is run through the drill steel to prevent dust during drilling) the jumbo is now ready to commence boring. The Jumbo operator using twin booms bores out the heading, 60 – 70 holes for a 4.5 x 4.5 drive, taking 3 – 4 hours. On completion the Jumbo is packed up and moved to the next heading to be bored.

Charge up
Charge up is a 2 man operation using an IT28 Loader fitted with a charge platform and pneumatic ANFO loader. Dry holes are charged with Nonel detonators with powergel primers, and ANFO, wet holes are charged with Powergel and perimeter holes charged with SF – 5. NFO is blow loaded into holes then all Nonel detonators are connected to a trunk line of instantaneous detonating cord, which is initiated by 2 electric detonators from a safe distance. Prior to firing the development charge up person will inspect all areas that may be affected by the blast and instruct personnel to move to a safe area.

Re-entry after firing
Once all fumes have cleared from the blast area, a re-entry is conducted by the development charge up person. This involves disconnecting the bell wire from the main firing line and twitching the ends of the firing line together to prevent the build up of static electricity, the bell wire is rolled up and disposed of. The ventilation bag is re-established or repaired as required.

Watering down the muck pile
Prior to bogging the muck pile must be watered down to prevent dust. This is done manually using a 1 inch water hose, dirt is washed down until muck pile is wet. Washing down commences from the end of the ventilation bag which should be no further than 20m from the face and includes the walls, backs and any butts.

Bogging
The muck pile will be inspected by either the Geologist or the Supervisor, to determine if it is ore or waste. If it's ore it will be bogged (Elpinstone R1700) either to a stockpile or directly to trucks (Atlas Copco MT 5000) for transportation to the surface, if waste it will be trucked to the nearest internal waste pass and used to fill previously mined voids.

Ground support (Bolting)
Due to the possibility of injury from rock fall, all work areas must be bolted and in line with industry standard mesh is also installed to prevent scats from falling. The two main types of bolts used at Mt. Charlotte are the Gewi bolt and the Split Set.

Bolting is done with an onsite custom built rockbolter mounted onto a 980C loader chassis Fig.2. The operator works from a basket mounted to a Hiab boom and uses a pneumatic drill boom to bore a 28mm hole to a depth of 2300mm. In this hole is placed a chemical resin sausage followed by the Gewi bolt, the bolt is then pneumatically spun for approximately 15 seconds to mix the resin, and the machine is then stopped for 5 seconds to allow the resin to set. The operator lifts a 3.0m x 2.4m sheet of mesh into place using the boom of the bolter, once correctly aligned a butterfly and pressure plate are placed onto the bolt along with a nut and using the spinner the nut is fully tensioned. This cycle will continue until the roof is bolted up to the face. Bolts are installed at 1.5m spacings but may vary according to the ground conditions.

Prior to the Jumbo boring the face both walls of the heading must be secured with split sets. The operator will use 1 boom to bore two rows of 43mm x 3.5m holes at a 1.5m dice five pattern, and with the other boom install the Split Sets. Split Sets are hammered into the smaller diameter holes with the Jumbo percussion.

Figure.2 980C Rockbolter

The heading is now ready to commence the development cycle again this cycle is repeated until the planned development is achieved. As development is advanced so to are the necessary services ie. Power, water, air, communications and pump lines.

Step 3. Drill and Blast – Production
Historically mining at Mt. Charlotte employed large primary open stopes, which were mass blasted via crown and rib pillars, but due to seismicity in some areas a change in mining methods was adopted.

Currently all mining is remnant mining (taking lower grade material by enlarging existing stopes) using a modified sub level caving technique – target of 100,000 tonnes per month.

Drilling
On completion of development drill ring designs are formulated using the Block Model and current level plans, these will include all survey requirements for all rows and drilling information for the driller.

Survey plans will be issued to the mine surveyor for the mark up of the required rows and laser lines for the correct alignment of the drill rig. Plans are then issued to the driller in preparation for drilling.

All production drilling is currently carried out using an Atlas Copco 1357s electric/hydraulic long hole rig. 76mm diameter holes are bored tilted 15 degrees forward of vertical and up to a depth of 34m. Holes are spaced at 2.5m intervals with a maximum burden of 2.25m.

To assist with grade control the mine geologist may request that some of the blast holes in every row be sampled. This is done by recovering and bagging the drill cuttings as they are flushed from the hole, the hole row, number and depth that the cuttings came from are recorded on the bag for ease of cross referencing.

Blasting

Prior to charging a pad of fine dirt, to within 2.5m of the back is placed beneath the rows to be charged this enables the holes to be easily reached by the charge up personnel.

Charge up is a 2 man operation Fig.3 using an IT28 Loader fitted with a charge platform and pneumatic NFO loader.

Figure.3 Charging up holes by stope charge crew

Before charging all rows to be fired are identified and all holes found, blown out and depthed to ensure the holes are clean and correct row is fired.

Holes are charged with Nonel dets/Stope primers/ANFO. If holes are wet then emulsion is used or holes are lined with a plastic sleeve and charged with ANFO, then all Nonel detonators are connected to a trunk line of instantaneous detonating cord which is initiated by 2 electric detonators from a safe distance.

All production blasts are electrically fired at the end of day shift once all personnel are above the blast area.

A normal uphole blast of 1 – 2 rings will yield 2 – 4000 tonnes.

After firing the blast a re-entry is conducted, normally no earlier than 2 hours after firing but this will depend on the area fired, and could be as long as 12 hours. During the re-entry the entire area is check scaled, dust suppression sprays installed and the shot inspected for any misfires.

Step 4. Production Bogging/Trucking

The current production fleet consists of:

• Trucks - 1 Cat 769C – 30t
• 2 Atlas Copco MT 5000's – 50t
• 3 Atlas Copco MT 5000's – 50t (leased)
• 1 Elphinston AD40 – 45t (leased)

Loaders - 2 Elphinstone R2900 LHD's (leased)

• 1 Elphinstone R1700 LHD (leased)
• 1 Cat 980G

Bogging
The fired millholes are bogged until waste rock comes through, depending on the grade of the fired rock and the grade of the fill material, up to 200% of the fired tonnes may be bogged. Alternatively as little as 25% of the fired rock may be bogged. Millholes are checked daily by the geologist and continually monitored by the loader operator and supervisor for any change in status.

The loaders will load either to trucks for transportation to the surface, or to a pass for future trucking to the surface.

Trucking
Trucks are loaded directly from the draw points, or from a pass and then transported to the surface crusher via the Sam Pearce decline Fig4, round trip times vary depending on the area being worked, the current longest round trip is 14.5km (70 minutes).

Figure.4 Mt 5000 exiting the Sam Pearce portal

Ventilation
Primary ventilation for the underground workings is from the:

• Charlotte Ore Body fan (COB) ~ 160m3/s via a 3.5m diameter rise from the 2100 level to the surface.
• Northern Ore Body fan (NOB) ~ 60m3/s via a 2.5m diameter rise from the 3200 level to the surface
• Southern Ore Body fan (SOB) ~ 90m3/s via a 2.44m diameter rise from the 3900 level to the surface

These 3 fans giving a combined flow of ~310m3/s.

Secondary ventilation
Any working area with no flow through ventilation mus be ventilated using secondary ventilation fans (110, 90 and 60 kw), these fans are located in a fresh air source and direct air through vent bag to the area required.

Community awareness

To help reduce the impact of underground mining on the local community the following initiatives have been introduced at Mt. Charlotte:

• Blast monitors installed to monitor blast vibration.
• Size of blasts (tonnes) reduced to reduce vibration.
• Timing of blasts, maximum length of charge in 1 hole designed to reduce vibration.
• Letter drops to nearby residents to inform them of any abnormal blast activity.
• Spray systems installed at underground vent regulators and surface fans to reduce fumes.
• Spray system on conveyor system to suppress dust.