Mining

The current mining target is two large, geologically identified, Main Reef ore shoots within the Central and West CMR JORC Reserves. The ore body is accessed from the existing box cut at Slot 8 using a 5 m wide by 5.3 m high decline developed in the footwall of the Main Reef at a downward gradient of 1:7.  The decline had progressed approximately 810 linear metres and was about 110 vertical metres below surface at the end of March 2010.  The decline has been developed in a south-westerly direction to establish the Central stoping blocks.  A second decline servicing the West ore shoot will be established via a connecting decline from the Central decline.

A highly mechanised underground mining method is being used to extract the Main Reef. The reef is being accessed via 4 m wide by 4.8 m high cross-cuts developed from the decline to intersect the Main Reef at about 11.5 m vertical intervals.  The reef drives are being developed east and west of the cross-cut to the limits of the ore shoot leaving a 15 m long stope panel between each reef drive.

Reef development

The reef drives are being excavated to the full height of the Main Reef Leader hangingwall, and are being supported with a combination of rock bolts, cable anchors and mesh as recommended by local geotechnical consultants, Middindi.

The reef drives are being developed using a two-boom development jumbo, which drills blast holes and installs the ground support.  The reef drive drill pattern is designed to break the waste into much larger fragments than the reef.  This improves scalping and screening efficiency in the beneficiation process.  A 10 t capacity load-haul-dump loader (LHD) is used to muck the blasted ore to stockpiles in the cross cut and decline.

Pillars have historically been left in the mined out Main Reef Leader, either as local or regional stability pillars, or in areas of poor ground conditions (especially close to faulting).  It will be necessary to mine through these pillars and develop through the areas of poor ground where the Main Reef Leader hangingwall has collapsed. There is insufficient information to add such pillars into the Ore Reserves, but they obviously represent incremental ounces of gold to the project.

Stoping

Sampling of the reef drives will identify the payable zones on each level. The mine will be divided into a series of stoping “panels”. Each stope panel will comprise four reef drives and associated stope slots on either side of the access cross cut (or half levels).  Each level will comprise a series of 12 m wide by about 15 m long stope slots, separated by 3 m wide backfill ribs.

Geotechnical CAF pillars

Each stope panel must be supported with backfilled cement pillars prior to stoping.  To avoid sterilising the Main Reef below each backfill rib, a series of 3 m wide by 15 m long trenches is blasted every 12 m along the reef drive.  A barricade of poles and welded mesh is then constructed at the bottom of the trench to contain the backfill.

A standard cement aggregate truck then delivers cement slurry to the cross-cut to be mixed with current development waste using the development LHD.  The LHD  tips the Cemented Aggregate Fill (CAF) backfill mix into the top of the backfill slot.  Larger waste is be used to create a solid barricade at the bottom of the stope.  Once this backfill at the bottom of the slot has set and formed a plug, smaller waste and aggregate is used in the backfill to achieve a tight contact to the hangingwall.

A twin-boom mechanised drill is used to drill up to 15 m long blast holes in the waste parting and the Main Reef.  The parting section is blasted first and separately as larger fragments and tipped into the old voids.  The Main Reef is then blasted, loaded by the LHD and tipped into stockpiles at the cross-cut. The base case for the Mine Plan in the updated Snowden Competent Person’s Report considers only the economic value in the Main Reef itself. No value is accorded (primarily because there is insufficient data to meet the statistical rigour necessary for inclusion in JORC Reserves) to the parting between the targeted Main Reef and the Main Reef Leader void, or to Main Reef Leader pillars, or to the undoubted sweepings and vampings from the historical mining lying on top of the parting.

In areas where there are sufficient sweepings and vampings, or where a Main Reef Leader pillar has been mined, the parting will be hauled to surface and washed to recover the valuable fines and the reject waste parting will be sold for construction aggregate. Where there are economic grades in the parting, it will be hauled to surface and processed through the low-grade process route.

In areas where geological sampling suggests it is appropriate, the Main Reef and the parting (with the residual sweepings and vampings) will be mined as a single package. These alternatives represent potentially significant, but unquantifiable upside to the base case in the CPR.

Ventilation

The mine is being ventilated using the declines as main intake airways.  The proposed mining and ventilation system of CMR is a low resistance, low-pressure system. The South Reef, which was extensively stoped in the past, will act as the exhaust system. This results in very low fan power requirements.  Secondary ventilation using fans and ventilation ducting is used to ventilate blind development headings.

Second egress and escape ways will be constructed between each level, close to the cross-cut and again at the extremities of the reef drives.  Underground refuge bays, equipped with emergency air, communications, food and water, are in existence as currently required and will be located at strategic positions throughout the mine. All intersections within the Main Reef Leader will be closed once mining of the level has ceased. This can normally be done by sealing off the cross-cuts.

Utilities

Underground power will be reticulated from surface to a series of transformers underground.  The mine is largely dry, with limited water inflow.  Service water is required for drilling, dust suppression and cooling hydraulic motors.  Clean water is piped into the mine and once used is directed to sumps and pumped from the mine using a staged pumping system.

MINING SEQUENCE

  • Development Reef Drives on upper & lower levels using New fragmentation & burncut to reduce impact on the Hangingwall
  • Mine out CAF slot (3m x3m) between levels every 12m spacing within designated pay channels
  • Install Timber poles and reusable Jacks  at base of CAF slot to form bulkhead
  • Install CAF pillars – allow 7-14 days to cure
  • Drill production longholes 15m updip from level to level
  • Blast out Main Reef between CAF pillars from the centre of the stope working towards the CAF pillars
  • Haul ore to surface for processing

Main Reef Package

Development Extraction Process

Install Ground Support

Reef Development Fully Supported

Extract Middling For CAF Slot


Extract Main Reef For CAF Slot

CAF Slot

Install Bulkhead

Pour CAF Pillar

CAF Pillars Ready to Stope

Section Through Main Reef between CAF Pillars

Extract Middling Between CAF Pillars

Extract Main Reef Between CAF Pillars

CAF Slot Extraction & CAF Pillar Installation

Main Reef Stope Extraction between CAF Pillars