This technical report presents an updated Mineral Resource and Mineral Reserve estimate for the Twangiza Gold Mine as of December 31, 2014, including the first inclusion of non-oxide material in the reserve.
Report context
This NI 43-101 technical report was prepared for Twangiza Mining SA, a subsidiary of Banro Corporation, with an effective date of July 29, 2015. The report presents a compilation of information prepared by Twangiza Mining and includes findings from a reconciliation study completed as part of the review process and Mineral Reserve estimate. The Twangiza project is located in the South Kivu Province of the Democratic Republic of the Congo, approximately 45 kilometres south-southwest of Bukavu, the provincial capital. The property consists of six exploitation permits totalling 1,156 square kilometres, wholly-owned by Twangiza Mining. These permits expire in 2016 and are subject to renewal for consecutive 15-year periods. The Twangiza project poured its first gold in October 2011.
Processing route
The technical report describes both the historic plant configuration that was operated and the proposed design modifications that were being implemented or planned. The plant began as a refurbished facility designed primarily to process oxide material at 1.3 million tonnes per annum (Mtpa). Since commissioning, the plant was improved and expanded to 1.7 Mtpa and was shown to be able to process harder non-oxide material.
Proposed design throughput and modifications
The report documents the planned expansion and upgrade of the original processing plant to allow processing of non-oxide material at an annual throughput of 1.7 Mtpa. This upgrade and capacity increase enabled the addition of approximately 12.8 million tonnes of non-oxide ore to the Mineral Reserve. The process plant design modifications included upgrades to the front end, crushing and screening, the secondary plant feed point, upgrade of feed weightometers, milling, carbon-in-leach (CIL), acid wash, elution and regeneration, electrowinning and smelting, tailings systems, and water supply systems.
Historical operating data
The report notes that the process plant had not worked at design capacity historically, mainly due to a shortage of funding. The plant had been refurbished and SRK Consulting (UK) Limited considered it would be capable of operating at 1.7 Mtpa to fulfil the mine plan, as long as reagents, consumables and spares were adequately funded and supplied in good time. In recent years, some non-oxide material had been increasingly blended into the plant feed, averaging 20% in the second half of 2014.
Metallurgical testwork results
The report reviews metallurgical testwork from scoping study, pre-feasibility study, and feasibility study phases. Testwork included mineralogy, comminution results of composite and variability samples, gold recovery testwork, gravity and intensive cyanidation testwork (oxides only), variability leach testwork (oxides only), cyanide detoxification (oxides only), transition and fresh (main and north) optimisation recovery testwork, settling and viscosity testing, gravity recovery for main and north transition and fresh samples, and cyanide destruction testwork. Comminution circuit parameters to process 1.7 Mtpa were investigated by Orway Mineral Consultants.
The non-oxide material was noted to have very variable metallurgical recoveries. The report states that detailed lithological and weathering models ensure accurate estimation of recoverable gold grade within the deposit and that a cut-off grade is applied on this basis.
Process plant description
The general process plant described in the report includes mobile crushing and screening, a Run-of-Mine (ROM) pad storage area primary feed point, in-plant crushing and scrubbing, a secondary feed point, milling and classification, gravity and intensive cyanidation, trash removal, leach and adsorption circuit, carbon safety and detoxification, tailings dam storage and return, acid wash, elution, electrowinning, regeneration, and a gold room.
Consumables identified in the report include mill balls, cyanide, caustic, lime, sodium metabisulphite, copper sulphate, plant diesel, carbon, hydrochloric acid, air services, and water services.
Tailings management
Metago Environmental Engineers, who designed the current tailings management facility (TMF), evaluated accelerated wall raising costs on the existing TMF and were designing and costing an additional TMF to supplement the existing designed tailings capacity. The existing facility was not considered cost effective. The report notes that the increased Mineral Reserve requires increased tailings storage capacity.
Key reported parameters
| Parameter | Value | Unit | Basis |
|---|---|---|---|
| Original plant design throughput | 1.3 | Mtpa | Design (initial) |
| Expanded plant design throughput | 1.7 | Mtpa | Design (proposed) |
| Non-oxide material in feed (second half 2014) | 20 | % | Historical operating data |
| Mineral Reserve (Proven + Probable) | 22.38 | Mt | Estimate (December 31, 2014) |
| Mineral Reserve grade (Proven + Probable) | 2.28 | g/t Au | Estimate (December 31, 2014) |
| Mineral Reserve gold content (Proven + Probable) | 1.64 | Moz | Estimate (December 31, 2014) |
| Life of Mine gold production | 1,246 | koz | Forecast |
| Production period | 14 | years | Forecast |
| Annual gold production (first 5 years) | 109 | koz | Forecast |
| Total capital costs | 104 | USD/oz | Forecast |
| All-in costs | 888 | USD/oz | Forecast |
| Post-tax net present value (5% discount, USD1,200/oz gold) | 285 | USD million | Forecast |
| Net cash flow after tax and capex | 395 | USD million | Forecast |
| Mining operating cost | 5.96 | USD/t processed | Forecast |
| Processing operating cost | 20 | USD/t processed | Forecast |
| G&A operating cost | 12.9 | USD/t processed | Forecast |
| Total operating cost | 39 | USD/t processed | Forecast |
| Total operating cost | 62 | USD million/annum | Forecast |
| Total operating cost | 699 | USD/oz poured | Forecast |
Project website: https://www.draglobal.com/projects/twangiza/
Technical qualifications
The report is a compilation of information prepared by Twangiza Mining and presents findings from a reconciliation study completed as part of the review process and Mineral Reserve estimate. The Mineral Resource and Reserve figures are estimates and no assurances can be given that forecast levels of gold will be produced. The estimates are expressions of judgment based on knowledge, mining experience, analysis of drilling results and industry practices, and valid estimates made at a given time may significantly change when new information becomes available.
Mineral Resources that are not Mineral Reserves do not have demonstrated economic viability. There is no certainty that Mineral Resources can be upgraded to Mineral Reserves through continued exploration. Due to the uncertainty attached to Inferred Mineral Resources, it cannot be assumed that all or any part of an Inferred Mineral Resource will be upgraded to an Indicated or Measured Mineral Resource as a result of continued exploration.
The operating cost estimates were based on a zero-based cost analysis following review of 2014 historical costs and implementation of several cost saving measures. The cost savings are based on plans which are at an early stage of implementation and require confirmation in practice. Regarding lower power costs anticipated from a hydroelectric scheme, these savings will only be realised after the hydroelectric facility has been built, and investors and contractors had yet to be identified at the time of reporting.
Capital costs for the tailings management facility were based on designs and costs from studies completed some years ago, and the report notes that these designs, costs and construction schedules need to be updated to address the specific requirements of the current mine plan.
The non-oxide material has very variable metallurgical recoveries. The various ore types appeared in different proportions in the mining schedule on an annual basis and the report recommends further smoothing of the mining schedule.
The report contains forward-looking statements that address activities, events or developments which are believed, expected or anticipated will or may occur in the future, including statements regarding estimates and assumptions in respect of net present values and future cash flows, Mineral Resource and Mineral Reserve estimates, future gold production, costs, mine life, gold recoveries, potential Mineral Resources and Reserves, and development and exploration plans and objectives.
Source: NI 43-101 Technical Report, Mineral Resource and Reserve Update, December 31, 2014, Twangiza Gold Mine, Democratic Republic of the Congo, effective July 29, 2015.
