Knelson Concentrators, a corporate partnership dba Knelson

Gravity Concentration Gravity Concentration at Ashanti Goldfields BIOX Plant at Ashanti Goldfields BIOX Plant Obuasi Mine; Ghana, W. AfricaObuasi Mine; Ghana, W. Africa

CONTENTSCONTENTS

1. Introduction1. Introduction - Knelson Concentrator - Overview - Knelson Concentrator - Overview - Obuasi STP-Biox Plant Flowsheet - Obuasi STP-Biox Plant Flowsheet

2. Testwork2. Testwork - Results from lab scale testing - Results from lab scale testing

3. Construction and Installation3. Construction and Installation - Materials of Construction - Materials of Construction

4. Circuit Metallurgy4. Circuit Metallurgy - Operating parameters of the circuit - Operating parameters of the circuit - Impact of the Knelson Concentrator - Impact of the Knelson Concentrator

5. Summary5. Summary

ASHANTI - OBUASI OPERATIONSASHANTI - OBUASI OPERATIONS

Pompora Treatment Plant (PTP) 1.8 Float, Roast,CILSulphide Treatment Plant (STP) 2.9 Float, Biox, CILOxide Treament Plant (OTP) 2.9 CILTailings Treatment Plant (TTP) 1.9 CIPHeap Leach 1.1 Agglomerated

PLANT CAPACITY(Mtpa) PROCESS

Grind

Re-grind

Flotation

BIOX CCD

CIL

Flot. Tail

Conc.

On-site Lab Test WorkOn-site Lab Test Work

1. Three Streams Tested1. Three Streams Tested

a) CCD Thickener #5 U/Fa) CCD Thickener #5 U/F

b) Biox-CIL Tailings b) Biox-CIL Tailings

c) Final Tailings (from flotation) c) Final Tailings (from flotation)

2. Considerations2. Considerations - severe corrosion of the lab test machine- severe corrosion of the lab test machine - corrosive nature of the Biox process (pH 1.3 - - corrosive nature of the Biox process (pH 1.3 - 1.8)1.8)

- free gold- free gold- easily visible- easily visible

Objective: To determine the presence of free gold in the STP Biox circuit.Objective: To determine the presence of free gold in the STP Biox circuit.

- fine free gold- fine free gold- visible under the microscope- visible under the microscope

- flat gold flakes - easily visible - flat gold flakes - easily visible - flat shape attributed to grinding- flat shape attributed to grinding

1. Photomicrographs and visual observations indicated the1. Photomicrographs and visual observations indicated the presence of free gold in all of the streams tested. presence of free gold in all of the streams tested.

2. Free gold passed through the CIL circuit without complete leaching.2. Free gold passed through the CIL circuit without complete leaching.

3. Internal work by Ashanti indicated that free gold is liberated in the3. Internal work by Ashanti indicated that free gold is liberated in the Biox Process. Biox Process.

4. +90% of the liberated gold particles are <20 micron.4. +90% of the liberated gold particles are <20 micron.

5. Any installation of a Knelson Concentrator in the Biox/CCD5. Any installation of a Knelson Concentrator in the Biox/CCD circuit would have to address the corrosive nature of this circuit would have to address the corrosive nature of this slurry (pH 1.3 - 1.8). slurry (pH 1.3 - 1.8).

Lab Test Work SummaryLab Test Work Summary

CIL

No. 5Thickener

No. 6Thickener

Cyclone

ThickenerFeed Box

KnelsonConcentrator

ConcentrateHopper

Table

ModificationsModifications toto the Knelson the Knelson ConcentratorConcentrator

Materials of Construction EvaluatedMaterials of Construction Evaluated a) Hastelloy C-276 a) Hastelloy C-276 b) Incolloy 825 b) Incolloy 825 c) Stainless Steel 904L c) Stainless Steel 904L d) Stainless Steel 304L d) Stainless Steel 304L

- Ashanti indicated that 304L had performed very well for other - Ashanti indicated that 304L had performed very well for other equpiment located in that part of the plant. equpiment located in that part of the plant.

- The other alloys would have at least doubled the cost of - The other alloys would have at least doubled the cost of manufacture compared to the standard unit. manufacture compared to the standard unit.

Materials of ConstructionMaterials of Construction

General Assembly Stainless Steel (304L)General Assembly Stainless Steel (304L) - Tail. Launder Linatex Rubber Lined - Tail. Launder Linatex Rubber Lined - Motor Cover - Motor Cover - General Assembly - General Assembly - Upper & Lower Frame Assemblies - Upper & Lower Frame Assemblies - Conc. Launders - Conc. Launders

Electroless Nickel Plated Electroless Nickel Plated - Upper & Lower Bearing Exteriors- Upper & Lower Bearing Exteriors - Drive Sheave/Bushing - Drive Sheave/Bushing

Knelson Concentrator Hourly TonnageKnelson Concentrator Hourly Tonnage 33 - 40 tonnes33 - 40 tonnes

Pulp Density of Knelson FeedPulp Density of Knelson Feed 25 - 27% (w/w)25 - 27% (w/w)

Temperature of Knelson FeedTemperature of Knelson Feed 3030ooCC

Slurry pHSlurry pH 2 - 32 - 3

Size distribution of Knelson FeedSize distribution of Knelson Feed 90% passing 90% passing 4545 microns microns

Concentrating Cycle TimeConcentrating Cycle Time 3 hours/cycle3 hours/cycle

Knelson Fluidization Flow (USgpm)Knelson Fluidization Flow (USgpm) 130 gpm130 gpm

Operating ParametersOperating Parameters

Plant Au Recovery Prior to KC InstallationPlant Au Recovery Prior to KC Installation 87%87%

Plant Au Recovery After KC InstallationPlant Au Recovery After KC Installation 90 - 92%90 - 92%

Percentage of Total Gold Recovered by KCPercentage of Total Gold Recovered by KC 4 - 5%4 - 5%

CIL Tails Grade Prior to KC InstallationCIL Tails Grade Prior to KC Installation 2 - 3 g-Au/t2 - 3 g-Au/t

CIL Tails Grade After KC Installation CIL Tails Grade After KC Installation 1 - 1.5 g-Au/t1 - 1.5 g-Au/t

Process ImprovementsProcess Improvements

Knelson Concentrator Installation at Knelson Concentrator Installation at AGC Obausi Mine; Ghana, W. Africa AGC Obausi Mine; Ghana, W. Africa

SUMMARY & CONCLUSIONSSUMMARY & CONCLUSIONS

1. Lab testing identified free gold present in the CCD circuit, CIL tails1. Lab testing identified free gold present in the CCD circuit, CIL tails and final tails. and final tails.

2. Free gold passed through the CIL circuit without complete leaching.2. Free gold passed through the CIL circuit without complete leaching.

3. Decision to install a Knelson Concentrator in the CCD circuit after 3. Decision to install a Knelson Concentrator in the CCD circuit after the Biox process.the Biox process.

4. The materials of construction were modified to 304L stainless steel4. The materials of construction were modified to 304L stainless steel to withstand the severely corrosive nature of the slurry. to withstand the severely corrosive nature of the slurry.

5. Installation was extremely successful with significant improvents to 5. Installation was extremely successful with significant improvents to gold recovery. gold recovery.