Democratic Republic of Congo – An annual review of mineral resources and mineral reserves at the Canadian gold mining company Banro Corporation’s four wholly-owned projects, namely Twangiza, Namoya, Lugushwa and Kamituga, on the Twangiza-Namoya gold belt in the Democratic Republic of the Congo, has resulted in a substantial increase in mineral reserves with the conversion of transition and fresh mineral resources into mineral reserves at Twangiza.
- The Twangiza proven and probable reserves increased 59% to 1.64 Moz of gold (22.38Mt grading at 2.28g/t gold) with the inclusion of non-oxide materials in the reserve pit shell which have been proven economically treatable with the existing plant. This expands the Twangiza mine life utilizing the existing plant to 14 years.
- At Namoya, the proven and probable mineral reserves have decreased 5% to 1.27 Moz (20.53Mt grading at 1.92g/t gold), primarily due to mining depletion.
- Banro’s overall mineral reserves have grown by 23% to 2.91 Moz (42.91Mt grading at 2.11g/t gold) at US$1,200/oz gold price.
- Banro’s total measured and indicated resources for all its properties is 7.73 Moz (154.91Mt grading at 1.55g/t gold), and 5.26 Moz (97.78Mt grading at 1.67g/t gold) in inferred resources
”The reserve growth at Twangiza has been achieved through the proven ability of the current plant to economically process non-oxide materials existing within the reserve pit shell. This achievement will extend the mine life of the current installed operations to 14 years, and provide a foundation for future optimization and the possible future expansion of the existing Twangiza operations,” Banro CEO and president John Clarke commented.
During 2014, the company scaled down its exploration activities at its Twangiza, Namoya, Lugushwa and Kamituga projects and focused its geological expertise on supporting the production growth at Twangiza, development at the Namoya Mine and identification of near mine high grade targets.
In order to consolidate Banro’s position on the various exploration sites, some limited exploration activities are planned for 2015 using small teams focused on generating new oxide targets in Lugushwa and Kamituga.
At Namoya, exploration drilling activities will be focused on near mine resource upgrade and resource generation activities. The primary objective is to upgrade inferred resources within the Namoya Summit-Filon B reserve pit into a higher confidence resource for conversion into mineral reserves. Another objective is to define additional near mine oxide resources within 5 km of the Run-of-Mine pad.
At Twangiza, delineation drilling will be focused on near mine oxide resources generation on the Twangiza East and West mineralisation.
Banro’s measured and indicated mineral resource has decreased 7.37% to 7.73 Moz (154.91Mt grading at 1.55g/t Au) compared with 8.35 Moz representing 161.10Mt grading at 1.61g/t gold as at December 31, 2013, and inferred mineral resources have decreased by 1.14% to 5.26 Moz (97.78Mt grading at 1.67g/t gold) compared with 5.32 Moz representing 98.32Mt grading at 1.68g/t Au as at December 31, 2013.
The reduction in the mineral resource is mainly attributed to mining depletion. The mineral resource estimates discussed consist of in situ mineral resources at a 0.4 g/t gold (Namoya, Lugushwa and Twangiza) cut-off constrained within a US$1 600/oz optimised pit shell.
The underground mineral resources at Kamituga are those situated below the Mobale open pit, estimated using historical underground information at a cut-off grade of 1.5 g/t gold. The mineral resource estimates for Kamituga were prepared by SRK Consulting (UK) using historical data. These estimates have not been updated. Banro has since 2011 carried out extensive exploration including some amount of drilling to verify the historical results at Kamituga. Further work planned, especially drilling work to update the Kamituga resource, was deferred as the focus shifted to mine development at Namoya and the process plant expansion at the Twangiza mine.
Below are the key assumptions, parameters and methods used to estimate the Twangiza, Lugushwa and Namoya mineral resources:
- Wireframing was restricted to borehole intersections above a 0.3 to 5g/t gold cut-off grade for Lugushwa and 0.4g/t gold for Namoya, Twangiza East and West;
- Gold grades have been determined using Ordinary Kriging interpolation into a 3-Dimensional block model constrained by mineralisation wireframes;
- The mineralization models were constrained within the wireframe with primary block dimensions of 20 m N-S (along strike), 20 m E-W (across strike) and 10 m in the vertical direction;
- Estimation used dynamic anisotropy;
- Datamine Studio 3TM was the modelling package; and
- At all times, the relationship between geology, mining and economic factors was taken into account.
Drill cores for assaying were taken at a maximum of one metre intervals and were cut with a diamond saw with one-half of the core placed in sealed bags and sent to the company’s sample preparation facility in Bukavu, DRC.
The core samples were then crushed down to minus 2 mm, and split with half of the sample pulverized down to 90% passing 75 microns. Approximately 150g of the pulverized sample was then shipped to the SGS Laboratory (which is independent of the company) in Mwanza, Tanzania where the samples were analysed for gold by fire assay using a 50g charge. As part of the company’s QA/QC procedures, internationally recognized standards, duplicates and blanks were inserted into the sample batches.
Drill core samples were respectively taken from Lugushwa, Namoya, Twangiza East and West to determine relative density measurements for the various deposits and the oxide, transitional and fresh rock components.
The proven and probable mineral reserve of Twangiza has increased by 59% to 1.64 Moz (22.38Mt @ 2.28g/t Au) from 1.03 Moz (13.69Mt @ 2.34g/t Au) (December 31, 2013). This 59% increase is comprised of net mining depletion, discount on bulk density, artisanal mining voids and an increase in reserves as a result of the proven ability to process by blending the portions of the non-oxide ore within the reserve pit using the upgraded Twangiza plant.
A reconciliation exercise carried out under the supervision of SRK recommended a revision of the bulk densities of the top 15m material in the Twangiza Main and North pits, from an average of 2.05 t/m3 to 1.80 t/m3 and 1.89 t/m3, respectively. Due to the extensive degree of weathering and artisanal mining, a further 19.5% discount was applied to the overall bulk densities of the measured component of the Twangiza Main pit. These modifications were not captured in the Feasibility Studies published in July 2009.
The proven and probable mineral reserve estimate at Namoya is 1.27 Moz (20.53Mt grading 1.92g/t gold).
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