Overview
Stage | Pre-Feasibility |
Mine Type | Underground |
Commodities |
|
Mining Method |
- Cut & Fill
- Longhole open stoping
|
Processing |
- Gravity separation
- ACACIA reactor
- Centrifugal concentrator
- Carbon re-activation kiln
- Smelting
- Agitated tank (VAT) leaching
- Concentrate leach
- Carbon in leach (CIL)
- AARL elution
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
|
A pre- feasibility level study has been completed which has identified a technically achievable and economically viable mine plan.
Tower Hill is located approximately 2 km north of the Leonora Processing Facility. Intermittent mining has occurred in the vicinity of Tower Hill since 1898. Early mining was from a small open cut and underground mine to 66 metres depth.
Larger scale open pit mining began in 1984 by Forrest Gold Pty Ltd, a subsidiary of CRA Limited. The mine was subsequently taken over by Austwhim Resources NL, then Dominion Mining Ltd and finally Plutonic Resources Ltd. Mining operations ceased in 2003 with total historical production of around 220,000 ounces. |
Source:
p. 14
The Tower Hill project is 100% owned by St Barbara Limited.
Summary:
Gold mineralisation at Tower Hill is hosted within a moderately (35 - 50°) east-dipping quartz vein package adjacent to the contact of granite and strongly foliated ultramafic rocks. Quartz-gold vein lodes strike north to north-northwest with strike lengths of up to 600 m and widths from less than a metre to a vein package with a horizontal width of up to 50 m.
The mineralised domain was defined by quartz veining, the granite contact and structural controls as well as gold grade.
Quartz-gold vein lodes strike north to north-northwest and dip moderately (30-50o) east with strike lengths of up to 600 m and widths from less than 1m to a vein package with a horizontal width of up to 50m. Mineralisation has been defined over a 1.1km strike length and has been tested to a maximum depth of approximately 525m below surface.
Mining Methods
- Cut & Fill
- Longhole open stoping
Summary:
The anticipated mining method is open stoping and cut and fill mining.
The Tower Hill Ore Reserve has been estimated by generating detailed mining shapes for all development and stoping shapes. Modifying factors for dilution and mining recovery have been completed post-geological interrogation to generate the final diluted and recovered ore reserve.
A pre-feasibility level of study has been completed for the Tower Hill mine. St Barbara successfully operated the King of the Hills mine using the mining methods planned for Tower Hill. The planned mining methods align with external geotechnical recommendations for the regional geology.
Stope size, development placement and ground support strategies have been designed in line with recommendations from external evaluations. Grade control drilling will be completed in advance of production with Grade control drilling plans generated as part of the final Definitive Mining Study.
The model used to estimate the Ore Reserve is consistent with that produced for the Mineral Resource declared for the Tower Hill deposit. This model is internally known as twh_feb2011.mdl.
Mining dilution has been applied at 5% at a grade of 1.3g/t Au for the Long Hole stoping areas and 6% at a grade of 0g/t Au for the cut and fill stoping areas. This is consistent with the dilution factors applied for the similar King of the Hills mine.
A mining recovery of 95% has been applied to all stopes. This recovery has been applied to allow for any ore loss that may occur during stoping extraction. This is consistent with the recovery factors achieved for the similar King of the Hills mine.
For the longhole stoping production, a global minimum mining width of 3.5m is used. While the ore body width generally exceeds the minimum mining width, where the ore body is narrower, stoping outlines are designed to honour the minimum width and include planned dilution. The cut and fill areas are mined to a minimum height of 5m, though split firing of the production face is used to prevent dilution of the ore zone.
The vast majority of the life-of-mine plan is classified as a Probable Ore Reserve. Inferred Mineral Resources are included in the life-of-mine plan to allow for well-informed strategic planning. They are not included in the Ore Reserve estimate.
The infrastructure requirements of the stoping methods used have been accounted for in the life-of- mine evaluation on which the project costings are based.
Tower Hill is located approximately 2 km north of the Leonora Processing Facility. Intermittent mining has occurred in the vicinity of Tower Hill since 1898. Early mining was from a small open cut and underground mine to 66 metres depth. The existing Mineral Resources and Ore Reserves for Tower Hill will remain in place while work continues on the best extraction and processing options for this mineralisation.
Flow Sheet:
All Tower hill ore will be trucked to the Gwalia processing plant. The processing plant is located at St Barbara’s Leonora Operations and consists of a three stage crushing circuit and single stage milling circuit.
Processing
- Gravity separation
- ACACIA reactor
- Centrifugal concentrator
- Carbon re-activation kiln
- Smelting
- Agitated tank (VAT) leaching
- Concentrate leach
- Carbon in leach (CIL)
- AARL elution
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
Flow Sheet:
Summary:
All Tower Hill ore will be trucked to the Gwalia processing plant. The processing plant is located at St Barbara’s Leonora Operations and consists of a three stage crushing circuit, single stage milling circuit and hybrid CIL circuit with one designated leach tank and 7 adsorption tanks. Gold is recovered from activated carbon into concentrated solution via a split AARL type elution circuit. Electrowinning and smelting are conducted in an adjacent secure gold room. The tailings from the process are thickened and pumped to a paddock type tailings storage facility with multi-spigot distribution.
The technology associated with processing of Tower Hill ore is currently in operation and is based on industry standard practices.
Target Recovery Performance is 95%.
Reserves at June 30, 2021:
Ore Reserves Cut-off Grades: 2.8 g/t Au.
Mineral Resources Cut-off Grades: 2.5 g/t Au.
Category | Tonnage | Commodity | Grade | Contained Metal |
Probable
|
2,572 kt
|
Gold
|
3.7 g/t
|
306 koz
|
Indicated
|
4,604 kt
|
Gold
|
3.9 g/t
|
574 koz
|
Inferred
|
489 kt
|
Gold
|
3.3 g/t
|
51 koz
|
Total Resource
|
5,093 kt
|
Gold
|
3.8 g/t
|
625 koz
|
Mine Management:
Job Title | Name | Profile | Ref. Date |
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Oct 7, 2021
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