Overview
The Tulawaka gold mine is located in northwest Tanzania. It is a 70/30 joint venture between Barrick and Northern Mining Exploration Ltd.
The mine consists of a completed open pit mine with an underground access ramp located at the bottom of the pit, waste rock dumps, an ore stockpile area and crushing plant, a processing plant, as well as water, waste disposal and ancillary facilities.
Total production in 2009 was approximately 94,000 ounces of gold at an overall recovery rate of 94.1 per cent.
Reserves of the open pit will be depleted soon. The feasibility of mining the East Zone ore body below the pit as an underground operation is being studied.
As at 31 December 2009, a total of 546 individuals were employed, consisting of 395 ABG Group employees and 151 contracted personnel.
Location
The Tulawaka gold mine is located in northwest Tanzania in Biharamulo District of Kagera Region and borders the Bukombe District of the Shinyanga Region, southwest of Lake Victoria near the northwest border with Rwanda. The deposit is located within the Biharamulo Forest Reserve. Annual average temperature ranges between 25° and 40°C. Average annual rainfall is in the region of 860mm.
Geology
The property is located in the western Rwamagaza greenstone belt with mineralization related to a regional northwesterly striking “Ushirombo” shear zone.
The Tulawaka mine comprises two orebodies, the East Zone and the West Zone. The East Zone is the main gold deposit. Geological modeling of the orebody determined the presence of six distinct mineralised domains. Gold largely occurs in a free state in fine sericitic parts within quartz veins or is finely disseminated between the quartz grains. The West Zone is still being explored.
The property consists of 7 contiguous prospecting licenses covering an area of 31,700 hectares within the Biharamulo District of Kagera Region and the Kahama District of Shinyanga Region in Tanzania. (Jan/05)
Gold mineralization of the East Zone has been traced over a strike length of 1,000 m, a depth of 100 m, and is open at depth. The shear zone contains at least 3 plunging ore shoots within the 1 km strike length. The high-grade mineralization in this zone is associated with quartz-tourmaline veins and minor sulphides. High-grade gold mineralization is associated with quartz-tourmaline veins within a 30 - 80 m wide shear structure.
Drilling results as well as air-photo structural interpretation indicate that the East Zone is intersected by NE faults. Block faulted segments of the main vein have an average strike length of 300 m with an apparent displacement of up to 90 m. The combination of the high grades and the simple geometry of the mineralized zone delineated at shallow depths highlight the East Zone as a potential development candidate.
The West Zone mineralization has been traced over a strike length of 750 m and is open in all directions. The mineralization in the West Zone is associated with disseminated sulphides with occasional quartz stringers and narrow quartz veins and is generally lower grade than in the East zone. Mineralization occurs within a sheared felsic intrusive.
Mining & Operations
Current operating capacity of the mill operations is approximately 1,320 tonnes per day. Total production in 2009 was approximately 94,000 ounces of gold at an overall recovery rate of 94.1 per cent.
The East Zone deposit is being mined in an open pit by the contractor, Caspian Ltd., which is a Tanzanian company.
The feasibility of mining the East Zone ore body below the pit as an underground operation is being studied.
Well-weathered ore and waste are mined and transported using Komatsu excavators, loaders, dozers and haul trucks. Benches are 5.0 m tall. The ultimate pit will cover 50 hectares and reach 135 m below surface, with a 42° wall slope. The average total amount of material excavated is 21,000 tonnes/day, at a waste/ore strip ratio of 18.3:1.
Processing
The plant runs 24 hours a day. The milling rate is 1,480 tonnes per day. Throughput has been above budget since operation commenced (up to 75tph vs 46tph).
The ore processing system includes run-of-mine stockpiling, primary crushing, single stage semi-autogenous-grinding (SAG), gravity recovery followed by intensive leaching and carbon-in-leach (CIL) gold extraction.
Run-of-mine ore is stockpiled and fed to a primary jaw crusher from Metso. The crushed ore is ground in a single-stage SAG mill from FFE with liners supplied by Metso. Free gold (50-70% of the output) is recovered using Knelson concentrators, a Gekko intensive leach reactor and electrowinning. The rest of the gold is recovered by conventional carbon-in-leach technology.
Cyclone overflow (at 110 microns) passes to a seven-stage leach plant. Reagent consumption is moderate at 0.60-1.0 kg/t NaCN. Conventional caustic solution stripping of carbon is followed by electrowinning. Lightnin supplied the agitators, Warman supplied the pumps, and ITT Goulds the process pumps.
The East Zone ore is free milling with coarse gold, and recoveries of up to 98% were obtained in testing by combined gravity and cyanidation, with medium reagent consumption.
Total gold recovery has been above budget since operation commenced (96.0% vs 94.9%). Mill availability has been above budget since start up (>95% vs 90%). Reagent consumption rates to date have been 40% below budget for cyanide and 60% below budget for metabisulphite. Costs have been in line with feasibility, with the exception of diesel costs.
A cyanide detoxification process is being used to reduce the cyanide concentrations in the tailings slurry. Tailings thickener is included to recycle water to the processing plant prior to discharging tailings slurry to the tailings storage facility.
