Overview
Stage | Production |
Mine Type | Open Pit / Underground |
Commodities |
|
Mining Method |
- Truck & Shovel / Loader
- Longhole open stoping
- Paste backfill
|
Processing |
- Gravity separation
- Agitated tank (VAT) leaching
- Carbon in pulp (CIP)
- Carbon adsorption-desorption-recovery (ADR)
- Elution
- Solvent Extraction & Electrowinning
|
Mine Life | 9 years (as of Jan 1, 2019) |
Source:
p. 370, 421
Gold Fields Limited indirectly owns 100% interest in the St Ives mine through it's wholly owned subsidiary St Ives Gold Mining Company (Pty) Ltd.
Deposit Type
- Vein / narrow vein
- Mesothermal
- Paleoplacer
Summary:
St Ives lies within the Kambalda domain, a subset of the Norseman-Wiluna Belt. The Kambalda domain is bound by the north-northwest trending Boulder-Lefroy fault (BLF) and Zuleika shear. The region has undergone four compressional events predated by early extension, and has been metamorphosed to upper greenschist or lower amphibolite facies.
The main structural feature of the St Ives area is the gently south-plunging Kambalda anticline, which extends 35km from the south end of the Kambalda dome to the Junction mine. The majority of known gold deposits are proximal to the trace of the anticlinal axis. A major second order structure known as the Playa shear splays off the BLF shear zone and can be traced through the St Ives field for a distance in excess of 10km.
There are several styles of gold mineralisation at St Ives. Individual deposits may contain more than one of these styles:
• Lode mineralisation: Archaean lode mineralisation typically consisting of 0.5m to 20m wide mesothermal vein complexes that may also have hydraulic breccias and/or mylonites. Mineralisation is typically discontinuous with short range predictability
• Supergene mineralisation: Broad zones of flat-lying gold mineralisation in weathered Archaean and overlying tertiary sediments
• Palaeoplacer mineralisation: Placer deposits hosted by palaeochannels in the unconsolidated tertiary sediments that overlie the Archaean basement.
Mining Methods
- Truck & Shovel / Loader
- Longhole open stoping
- Paste backfill
Summary:
St Ives currently operates three underground mines and one open pit. The underground is accessed via a decline. Mining contractors deploy long-hole stoping and paste/rock fill. Current underground mines are relatively shallow and are configured to mitigate geotechnical seismic risk through mine design, scheduling and defined ground support regimes.
Open pits are mined using conventional drill and blast with truck and shovel. Surface mining operations are carried out using contract mining.
Ore from both open pit and underground operations is transported with road trains from individual
mining operations to the central St Ives processing RoM pad.
Crusher / Mill Type | Model | Size | Power | Quantity |
SAG mill
|
|
|
|
|
Ball mill
|
|
|
|
|
Summary:
St Ives operates a 4.7Mtpa processing plant that consists of primary crushing, SAG/Ball milling, gravity and CIP circuits.
Processing
- Gravity separation
- Agitated tank (VAT) leaching
- Carbon in pulp (CIP)
- Carbon adsorption-desorption-recovery (ADR)
- Elution
- Solvent Extraction & Electrowinning
Source:
Summary:
The Lefroy Mill was commissioned in December 2004 and achieved design capacity within seven months. It treats medium- to high-grade ore through a 4.8 Mtpa variablespeed dual-direction 13.5 MW sag mill with wrap-around motor. Oversize from the mill (scats) is in closed circuit with a 140-tonne-per-hour pebble crusher. A gravity circuit recovers the gravity-recoverable gold from the milling circuit and the concentrate is treated separately through to bullion form. The mill cyclone overflow product flows to a five-stage leach circuit consisting of mechanical agitators, reagent addition and oxygen sparging.
Leached slurry passes through the six-stage carousel pump cell adsorption plant and subsequent five-tonne-capacity acid wash, elution and electrowinning circuits which produce calcine ready for smelting. Bullion is shipped to the refinery. Tailings are alternately deposited on two paddock-type tailings facilities which are constructed upstream.
Recoveries & Grades:
Commodity | Parameter | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 |
Gold
|
Recovery Rate, %
| ......  | ......  | ......  | ......  | ......  | ......  |
Gold
|
Head Grade, g/t
| 2.76 | 2.88 | 2.96 | 3 | 3.2 | 2.6 |
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Production:
Commodity | Units | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 |
Gold
|
koz
| ...... ^ | ......  | ......  | 364 | 363 | 372 |
All production numbers are expressed as metal in doré.
^ Guidance / Forecast.
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Operational Metrics:
Metrics | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 |
Total tonnes mined
| ......  | ......  | ......  | 43,973 kt | 24,418 kt | 19,517 kt |
Ore tonnes mined
| ......  | ......  | ......  | 4,300 kt | 3,033 kt | 3,705 kt |
Waste
| ......  | ......  | ......  | 39,674 kt | 21,385 kt | 15,813 kt |
Stripping / waste ratio
| ......  | ......  | ......  | 10.7 | 11.5 | 9.29 |
Plant annual capacity
| ......  | ......  | ......  | 4.7 Mt | 4.7 Mt | |
Tonnes processed
| ......  | ......  | ......  | 4,046 kt | 3,867 kt | 4,553 kt |
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Reserves at December 31, 2019:
Category | OreType | Tonnage | Commodity | Grade | Contained Metal |
Proven
|
Stockpiles
|
4,240 kt
|
Gold
|
1.1 g/t
|
149 koz
|
Proven
|
In-Situ (OP)
|
170 kt
|
Gold
|
1.53 g/t
|
8 koz
|
Proven
|
In-Situ (UG)
|
553 kt
|
Gold
|
4.61 g/t
|
82 koz
|
Proven
|
Total
|
4,963 kt
|
Gold
|
1.5 g/t
|
240 koz
|
Probable
|
In-Situ (OP)
|
7,329 kt
|
Gold
|
2 g/t
|
476 koz
|
Probable
|
In-Situ (UG)
|
8,502 kt
|
Gold
|
5.73 g/t
|
1,567 koz
|
Probable
|
Total
|
15,894 kt
|
Gold
|
4 g/t
|
2,043 koz
|
Proven & Probable
|
Stockpiles
|
4,240 kt
|
Gold
|
1.1 g/t
|
149 koz
|
Proven & Probable
|
In-Situ (OP)
|
7,562 kt
|
Gold
|
1.99 g/t
|
484 koz
|
Proven & Probable
|
In-Situ (UG)
|
9,056 kt
|
Gold
|
5.66 g/t
|
1,649 koz
|
Proven & Probable
|
Total
|
20,858 kt
|
Gold
|
3.4 g/t
|
2,283 koz
|
Measured
|
Stockpiles
|
4,240 kt
|
Gold
|
1.1 g/t
|
149 koz
|
Measured
|
In-Situ (OP)
|
597 kt
|
Gold
|
2.56 g/t
|
49 koz
|
Measured
|
In-Situ (UG)
|
977 kt
|
Gold
|
4.81 g/t
|
151 koz
|
Measured
|
Total
|
5,814 kt
|
Gold
|
1.84 g/t
|
350 koz
|
Indicated
|
In-Situ (OP)
|
9,104 kt
|
Gold
|
2.94 g/t
|
860 koz
|
Indicated
|
In-Situ (UG)
|
11,854 kt
|
Gold
|
5.89 g/t
|
2,264 koz
|
Indicated
|
Total
|
20,958 kt
|
Gold
|
4.61 g/t
|
3,106 koz
|
Inferred
|
In-Situ (OP)
|
2,707 kt
|
Gold
|
2.61 g/t
|
277 koz
|
Inferred
|
In-Situ (UG)
|
4,989 kt
|
Gold
|
4.49 g/t
|
721 koz
|
Inferred
|
Total
|
7,696 kt
|
Gold
|
3.83 g/t
|
947 koz
|
Total Resource
|
Stockpiles
|
4,240 kt
|
Gold
|
1.1 g/t
|
149 koz
|
Total Resource
|
In-Situ (OP)
|
12,408 kt
|
Gold
|
2.85 g/t
|
1,135 koz
|
Total Resource
|
In-Situ (UG)
|
17,820 kt
|
Gold
|
5.44 g/t
|
3,118 koz
|
Total Resource
|
Total
|
34,468 kt
|
Gold
|
3.97 g/t
|
4,403 koz
|
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Aerial view:
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