Overview
Stage | Restarting |
Mine Type | Open Pit |
Commodities |
|
Mining Method |
|
Processing |
- Calcining
- Gravity separation
- Carbon re-activation kiln
- Smelting
- Intensive Cyanidation Reactor (ICR)
- Centrifugal concentrator
- Agitated tank (VAT) leaching
- Carbon in leach (CIL)
- Elution
- Carbon adsorption-desorption-recovery (ADR)
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
|
Mine Life | 4 years (as of Jan 1, 2019) |
The Bronzewing Operations are in a care and maintenance phase. Bronzewing and Orelia open pits are currently undergoing development.
Northern Star will have the option to refurbish or divest Bronzewing’s processing plant which is currently under care and maintenance.
Northern Star intends to focus on exploration and resource definition drilling in the Bronzewing area, with $157 million growth capital committed over the next two years at Yandal to increase processing capacity and commence operations at Bronzewing’s Orelia and Julius deposits. |
Latest News | Macmahon untroubled by labour market July 20, 2021 |
Source:
p. 95
Summary:
Julius
The Julius Gold Deposit is located midway between the multi-million ounce Jundee and Bronzewing gold camps. Julius is situated underneath a minimum of eight metres of transported cover and located on the margin of a strongly sheared shallow north-west dipping granite greenstone contact. The deposit is deeply weathered up to 60 - 70 metres and comprises three zones of mineralisation.
These zones are an upper pisolitic laterite mineralised zone, sitting on top of a well-developed supergene gold zone, grading down into primary mineralisation characterised by strong shearing, sericite alteration, silicification, minor quartz veining and minor enrichment in sulphides, principally pyrite.
Extensive reverse circulation (RC), aircore (AC) and diamond drilling has defined the current extents of the deposit. Drill spacing ranges from 40 metres x 40 metres on the peripheries of the deposit, to 10 metres x 10 metres in the centre of the deposit.
Orelia
The existing Orelia open pit has been mined to a vertical depth of approximately 100 metres below natural surface. It was last mined and processed through the Bronzewing treatment plant in April 2013.
The main host rocks of mineralisation at Orelia are deformed and altered tholeiitic basalts, concordant dolerite units and felsic to intermediate sedimentary rocks. Cross-cutting felsic to intermediate porphyry dykes intrude the stratigraphy along pre-existing structures. Gold mineralisation typically occurs as southerly plunging oreshoots at the intersection between steeply-dipping transgressive faults and favourable lithological units, along fold hinges and on lithological contacts.
The deposit has several shallow trending high grade gold shoots with dimensions of approximately 50 m in vertical extent and 25 m in width, and down plunge extent in excess of 400 m. Confidence in the geological interpretation is good with the latest infill drilling allowing a detailed interpretation of the distribution of the Orelia gold mineralisation.
Summary:
Three different competencies of rock will be mined; oxidised, transitional or weakly oxidised, and fresh rock types.
Ore mined from the Julius and Orelia mines will be transported and processed at the existing Bronzewing plant following refurbishment of the plant and associated infrastructure. Julius pit will be mined in a single stage and the Orelia pit will be mined in two stages (1A and 1B). The Stage 1A pit will deepen the floor of the existing pit to target higher grade, lower strip ratio ore. The Stage 1B pit will include a cutback to the west and north walls as well as deepening below the Stage 1A floor.
MINING
All the currently defined Mineral Resource Estimates at the Yandal Gold Project are within an open pit mining environment and are a lode style of mineralisation requiring a degree of mining selectivity. The material to be excavated will be predominantly free dig from surface with blasting required deeper in the oxidation profile and into the fresh ore zones. Given these conditions, conventional open pit mining techniques using drill and blast with material movement by hydraulic excavator and trucks will be employed.
The project scale and selectivity would suit 120 t – 200 t class excavators in a backhoe configuration matched to 95 t class mine haul trucks and applicable ancillary equipment. To suit this sized equipment a bench height of 5m has been adopted. The benches will be excavated on 2 x 2.5 m high flitches, for blasted material this will be 2 x 3 m high flitches when swell is accounted for.
Ramp design parameters.
Orelia:
- 22 m wide dual lane ramps at a maximum gradient of 1 in 9 for ramps designed above the bottom 60 vertical metres of the pit base;
- 12.5 m wide single lane ramps at a maximum gradient of 1 in 8 for the last 60 vertical metres at the base of the pit;
- Minimum mining widths of 20 m.
Orelia Mine Design
Waste rock dumps have been designed to the east and west of the open pit. Dump design parameters are the same as used for the Julius waste dumps: 15 m high batters with 18° slopes separated by 10 m wide berms. The waste rock dumps for Orelia are extensions to existing dumps. The east dump adds two additional lifts to the existing dump giving a final elevation of 560 mRL (approximately 45 m above the existing topography). The western dump consists of three 15 m lifts from the existing topography to also give a final elevation of 560 mRL.
Orelia will be mined in two stages (Stages 1A and 1B). The initial pit stage (Stage 1A), deepens the existing pit floor. This will provide just over a year’s mill feed and provides a low risk start to mining at the Orelia deposit as no additional stripping is required. The Stage 1A pit is 516m north to south, 255 m east to west and deepens the current pit floor from 410 mRL to 315 mRL.
The second pit stage (Stage 1B) has been designed on the pit shell providing the greatest discounted cash flow and pushes back the existing pit’s western and northern wall to deepen the pit from 315 mRL to 240 mRL.
Ramp design parameters.
Julius:
- 12.5 m wide single lane ramps at a maximum gradient of 1 in 9 was used for the pit design;
- Minimum mining width of 20 m.
Julius Mine Design
The Julius pit will be mined in a single stage. The final pit for Julius is 550 metres long by approximately 200 metres wide. It has a depth 62.5 metres at its deepest point.
The waste rock dump has been placed directly to the south of the pit, mineralisation does not continue along strike to the south. The dump has been designed with a single 15 m high lift with final batter angles of 18°.
Both Julius and Orelia were scheduled in the same scheduling run, with optimal blend of oxide to fresh ore being utilised during periods when oxide ores are available.
Mining commences with a PC2000 excavator mining at Julius and a R9150B excavator mining at Orelia Stage1A. At the completion of the 495mRL in Julius the excavators are swapped between the pits.
Mining of Julius is then completed utilising the smaller R9150B excavator. Julius has a mine life of seven months, whereby on completion the mining fleet and associated infrastructure will be demobilised to the Orelia mining area and two mining fleets will commence mining at Orelia from month 8. Whilst two excavators are mining at Orelia, the larger excavator has been scheduled to mine the waste in the cutback of Stage1B and the R9150B will mine the ore in Stage 1A. On completion of the 420mRL in Stage 1B the PC2000 will be demobilised from site and only one mining fleet will remain to complete the Orelia Stage 1B pit. This has been scheduled to occur during month 19 of the LOM.
The mine plan has been developed so that the PC2000 has minimal amounts of ore mining in Orelia. Ore production will utilise the smaller R9150B excavator to minimise ore loss and dilution issues.
Flow Sheet:
Crusher / Mill Type | Model | Size | Power | Quantity |
Jaw crusher
|
|
|
|
1
|
Cone crusher
|
|
|
|
2
|
Pebble crusher
|
|
|
|
1
|
Ball mill
|
|
|
|
1
|
Summary:
The Bronzewing treatment plant has a two-stage crushing circuit, followed by ball mill with installed pebble crusher.
Processing
- Calcining
- Gravity separation
- Carbon re-activation kiln
- Smelting
- Intensive Cyanidation Reactor (ICR)
- Centrifugal concentrator
- Agitated tank (VAT) leaching
- Carbon in leach (CIL)
- Elution
- Carbon adsorption-desorption-recovery (ADR)
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
Flow Sheet:
Summary:
The previously producing Bronzewing project includes a processing mill which is under care and maintenance.
The comminution circuit includes gravity gold extraction, followed by CIL and carbon elution circuits.
Recoveries & Grades:
Commodity | Parameter | Avg. LOM |
Gold
|
Recovery Rate, %
| 92.1 |
Gold
|
Head Grade, g/t
| 1.86 |
Projected Production:
Commodity | Units | Avg. Annual | LOM |
Gold
|
oz
| 95,000 | 379 |
All production numbers are expressed as metal in doré.
Operational Metrics:
Metrics | |
Stripping / waste ratio
| 4.63 * |
Waste tonnes, LOM
| 31,820 kt * |
Ore tonnes mined, LOM
| 6,867 kt * |
Total tonnes mined, LOM
| 38,687 kt * |
Tonnes processed, LOM
| 6,867 kt * |
Annual processing capacity
| 2 Mt * |
* According to 2019 study.
Reserves at March 31, 2021:
Category | Tonnage | Commodity | Grade | Contained Metal |
Proven
|
3,600 kt
|
Gold
|
2 g/t
|
234 koz
|
Probable
|
11,891 kt
|
Gold
|
1.5 g/t
|
557 koz
|
Proven & Probable
|
15,491 kt
|
Gold
|
1.6 g/t
|
791 koz
|
Measured
|
2,800 kt
|
Gold
|
2.6 g/t
|
237 koz
|
Indicated
|
17,116 kt
|
Gold
|
1.9 g/t
|
1,045 koz
|
Inferred
|
5,310 kt
|
Gold
|
1.5 g/t
|
263 koz
|
Total Resource
|
25,226 kt
|
Gold
|
1.9 g/t
|
1,545 koz
|
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