Overview
Stage | Production |
Mine Type | Underground |
Commodities |
|
Mining Method |
- Sub-level caving
- Longhole open stoping
- Transverse open stoping
- Longitudinal stoping
|
Processing |
- Bacterial leaching
- Gravity separation
- Calcining
- Flotation
- Concentrate leach
- Inline Leach Reactor (ILR)
- Counter current decantation (CCD)
- Carbon in leach (CIL)
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
|
Mine Life | 20 years (as of Jan 1, 2017) |
Obuasi had been on care and maintenance since 2016, until the start of its redevelopment in 2019, following the receipt of the requisite approvals from the Government of Ghana. The first face blast took place in February 2019 with first gold being poured in December 2019. |
Latest News | Ausdrill-Barminco JV continues contract success in Africa October 29, 2018 |
Source:
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The five-year mining contract was awarded to a joint venture Underground Mining Alliance Limited (UMA) formed by Ghana’s Rocksure International (Rocksure) (30%) and Australia’s African Underground Mining Services (AUMS) (70%), which will also help facilitate the transfer of underground mining expertise to Accra-based Rocksure. The contract will employ and train around 550 Ghanaians.
Summary:
Gold mineralisation is associated with, and occurs within, graphite-chlorite-sericite fault zones. These shear zones are commonly associated with pervasive silica, carbonate and sulphide hydrothermal alteration and occur in tightly-folded Lower Birimian schists, phyllites meta-greywackes, and tuffs, along the eastern limb of the Kumasi anticlinorium.
Two main ore types are mined, namely quartz vein and sulphide ore. The quartz vein type consists mainly of quartz with free gold in association with lesser amounts of various metal sulphides containing iron, zinc, lead and copper. This ore type is generally nonrefractory. Sulphide ore is characterised by the inclusion of gold in the crystal structure of arsenopyrite minerals. Higher gold grades tend to be associated with finer grain arsenopyrite crystals. Sulphide ore is generally refractory.
The mine is located within the Obuasi concession area in south-western Ghana along the north easterly-striking Ashanti volcanic belt. The deposit is one of the most significant Proterozoic gold belts discovered to date. The Ashanti belt predominantly comprises sedimentary and mafic volcanic rocks, and is the most prominent of the five Birimian Supergroup gold belts found in Ghana. The belt is a 300km wrench fault system that propagated from Dixcove in the south-west to beyond Konongo in the north-east.
The Birimian was deformed, metamorphosed and intruded by syn- and post-tectonic granitoids during the Eburnean tectonothermal event around two billion years ago. Folding trends are dominantly north-northeast to north-east. Elongate syn-Birimian basins developed between the ridges of the Birimian system and these were filled with the Tarkwaian molasse sediments made up primarily of conglomerates, quartzose and arkosic sandstones and minor shale units. Major faulting has taken place along the same trends.
Mining Methods
- Sub-level caving
- Longhole open stoping
- Transverse open stoping
- Longitudinal stoping
Summary:
Mine designs are done to delineate development layouts and production stopes by taking into consideration economic cut-off grade and geotechnical design parameters for each mining block, mining level and section. The underground development system extends to a depth of 1,500m from surface. Mining levels lie between 15m and 20m intervals with major levels between 30m-60m intervals. Underground production was by open- stope mining (both longitudinal and transverse), and sub-level caving method; with future designed production by longhole open stope mining methods with paste fill.
Processing
- Bacterial leaching
- Gravity separation
- Calcining
- Flotation
- Concentrate leach
- Inline Leach Reactor (ILR)
- Counter current decantation (CCD)
- Carbon in leach (CIL)
- Solvent Extraction & Electrowinning
- Cyanide (reagent)
Source:
Summary:
The processing facilities currently consist of a Sulphide Treatment Plant (STP) and an Alternate Ore Treatment (AOT) Plant which treats low grade oxide material and tailings. The operation has two Tailings Storage facilities (TSF’s), one of which is no longer receiving tailings material and the other is due for closure by the end of 2015. A new TSF is currently under design and is planned to come into operation to take over from the one currently receiving STP tailings.
The Sulphide Treatment Plant (STP) has a design capacity of 274 tons per hour (tph) of refractory transitional and primary sulphide sulphur ores yielding 30tph of sulphide sulphur concentrate for processing in its BIOX® facility. The treatment process flow includes primary crushing, semi-autogenous/ ball milling, flash flotation and conventional flotation, bio-oxidation and carbon in leach (CIL) gold recovery. Gravity Recoverable Gold (GRG) is recovered at the Mill and BIOX® Circuits via Knelson concentrato ........

Recoveries & Grades:
Commodity | Parameter | 2016 | 2015 | 2014 |
Gold
|
Head Grade, g/t
| 4.4 | 1.47 | 4.67 |
Production:
Commodity | Units | 2016 | 2015 | 2014 |
Gold
|
koz
| 3 | 53 | 243 |
Operational Metrics:
Metrics | 2016 | 2015 | 2014 |
Annual processing capacity
| 2.4 Mt | 2.4 Mt | |
Tonnes processed
| | 1 Mt | 2.2 Mt |
Reserves at December 31, 2019:
Category | Tonnage | Commodity | Grade | Contained Metal |
Proven & Probable
|
24.26 Mt
|
Gold
|
9.13 g/t
|
7.12 M oz
|
Total Resource
|
130.74 Mt
|
Gold
|
7.39 g/t
|
31.04 M oz
|
Commodity Production Costs:
| Commodity | Units | 2016 | 2015 | 2014 |
Total cash costs
|
Gold
|
USD
|
167 / oz
|
966 / oz
|
1,086 / oz
|
All-in sustaining costs (sold)
|
Gold
|
USD
|
440 / oz
|
1,185 / oz
|
1,374 / oz
|
Financials:
| Units | 2019 | 2016 | 2015 | 2014 |
Capital expenditures
|
M USD
| ......  | ......  |
23
|
82
|
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