News ..Updated Adumbi Resource increases by 500,000 ounces
Loncor Gold pegs Adumbi at 28.18 Mt of 2.08 g/t Au ind.
2021-11-17 11:53 ET - News Release
Mr. Peter Cowley reports
LONCOR INCREASES TOTAL OPEN PIT MINERAL RESOURCES TO 3.66 MILLION OUNCES OF GOLD AT ADUMBI
Loncor Gold Inc. has increased and upgraded mineral resources at its Adumbi deposit in the Imbo Project (Loncor 84.68%) in the Democratic Republic of the Congo.
Compared to the inferred mineral resource of 3.15 million ounces of gold (41.316 million tonnes grading 2.37 g/t Au) outlined in April 2021 (see Company press release dated April 27, 2021), the additional drilling information and the increased gold price used, have contributed significantly to the increased mineral resources of the Adumbi deposit with improved confidence to 1.88 million ounces of gold in the indicated category and 1.78 million ounces of gold in the inferred category. 84.68% of these mineral resources are attributable to Loncor via its 84.68% interest in the Imbo Project.
Table I below summarises the Adumbi indicated and inferred mineral resources based on in-situ block cut-off grade at a 0.52 g/t Au for Oxide, 0.57 g/t Au for Transition and 0.63 g/t Au for Fresh material, and constrained within a US$1,600 per ounce optimized pit shell.
Commenting on today's mineral resource increase and upgrade at Adumbi, Loncor's President Peter Cowley said: "This increase in mineral resources within a US$1,600 pit shell to 3.66 million ounces of gold includes an indicated mineral resource of 1.88 million ounces of gold and was achieved by infill drilling the shallower part of the Adumbi deposit. Compared to the previous resource estimate in April 2021, the indicated and inferred tonnages, grades and ounces for this resource update, are expected and relate to drilling density and increasing gold grades with depth at Adumbi (see Company press release dated April 27, 2021-Table III). Gold mineralization is still open at depth below the pit shell where the favourable banded ironstone formation host ("BIF") is thickening and demonstrates potential for additional underground mineral resources. The mineral resources within the pit shell will be incorporated into the Preliminary Economic Assessment ("PEA") which the Company is undertaking to determine the economic viability of Adumbi and which is due for completion in December this year."
This mineral resource assessment was undertaken by the Company's independent geological consultants Minecon Resources and Services Limited ("Minecon"). The updated estimate for Adumbi was based on the additional drilling and a review of the Adumbi deposit including remodelling and grade estimation and considering the CIM requirement for mineral resources to have "reasonable prospects for economic extraction".
Drilling Results included in Mineral Resource Update
An additional fourteen core holes totaling 6,362.59 metres were drilled with the focus in areas within the pit shell where insufficient drilling had been undertaken to outline mineral resources. The upper part of the open pit shell was drilled at closer spacing in order to upgrade mineral resources from the inferred to indicated category.
Table III below summarises the significant intercepts of the additional drillholes that were included in this November 2021 mineral resource:
Core Logging & Geological Controls
Gold mineralization at Adumbi is found within a BIF (Banded Iron Formation) unit with a strike length of 850 metres and up to 130 metres in thickness. Four main zones of gold mineralization are present within the BIF and are located in:
- the upper part of the Upper BIF Sequence;
- the lower part of the Upper BIF Sequence separated by the Carbonaceous Marker, which is essentially unmineralized;
- within the Lower BIF Sequence.
There is a higher-grade zone of gold mineralization termed the Replaced Rock Zone ("RP Zone") associated with alteration and structural deformation that has destroyed the primary host BIF fabric. The RP Zone occurs in the lower part of the Upper BIF and in the Lower BIF, and transgresses the Carbonaceous Marker, located between the Upper and Lower BIF zones, both along strike and down dip.
Geological Modelling and Grade Estimation
The Adumbi 3-dimensional model was constructed by Minecon in collaboration with on site geologists using cross sectional and horizontal flysch plans of the geology and mineralization and was used to assist in the constraining of the 3-D geological model. The mineralization model was constrained within a wireframe at 0.5 g/t Au cut-off grade. Grade interpolation was undertaken using:
- 2 metre sample composites capped at 18 g/t Au to improve the reliability of the block grade estimates;
- Ordinary Kriging to interpolate grades into the block model;
- Relative densities of 2.45 for oxide, 2.82 for transitional and 3.05 for fresh rock were applied to the block model for tonnage estimation.
Pit Optimisation Parameters
To constrain the depth extent of the geological model and any mineral resources, an open pit for the Adumbi deposit was constructed based on the following pit optimisation parameters:
- A gold price of US$1,600 per ounce;
- Block size: 16 metres x 16 metres x 8 metre;
- A thirty-two metres minimum mining width and a maximum of four metres of internal waste was applied;
- Mining dilution of 100% of the tonnes at 95% of the grade;
- Ultimate slope angle of minus 45 degrees;
- Metallurgical recoveries of 91% for oxide, 88% for transitional and 90% for sulphide (based on diagnostic metallurgical testwork as part of PEA);
- Average mining cost of US$3.29/tonne mined;
- Average processing cost of US$17.81/tonne for oxides, US$18.92/tonne for transitional and US$22.13/tonne for sulphide;
- Average general and administration cost of US$4.20/tonne;
- Mineral resources were estimated at a block cut-off grade of 0.52 g/t Au for oxide, 0.57 g/t Au for transition materials and 0.63 g/t Au for fresh material constrained by a US$1,600 per ounce optimized pit shell;
- Transport of gold and refining costs equivalent to 4.5% of the gold price;
- No additional studies on depletion by artisanal activity was undertaken since the RPA study of 2014 and the same total amount of material was used by Minecon.
Tonnage/Grade Curve
Grade/tonnage curves for the Adumbi mineral resources at various gold cut-offs are summarised in Table IV and the graph below:
The Adumbi deposit is found within Loncor's Imbo Project, which contains two other deposits, Kitenge and Manzako. As a result of the increased mineral resources at Adumbi, the total inferred mineral resource of the Imbo Project is now 2.09 million ounces of gold (22.508 million tonnes grading 2.89 g/t Au) and is summarised in Table V below. 84.68% of this inferred mineral resource is attributable to Loncor via its 84.68% interest in the Imbo Project.
Combined with the Company's Makapela Project, which is situated approximately 50 kilometres northwest of the Imbo Project, total mineral resources at Loncor's properties in the Ngayu belt now stand at 2.497 million ounces of indicated mineral resources (30.390 million tonnes grading 2.56 g/t Au) and 2.639 million ounces of inferred mineral resources (25.731 million tonnes grading 3.19 g/t Au) as summarised in Table VI below:
Quality Control and Quality Assurance
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 by Company geologists and sent to the Company's on-site sample preparation facility. The core samples were then crushed down to 80% passing minus 2 mm and split with one half of the sample up to 1.5 kg pulverized down to 90% passing 75 microns. Approximately 150 grams of the pulverized sample was then sent to the SGS Laboratory in Mwanza, Tanzania (independent of the Company). Gold analyses were carried out on 50g aliquots by fire assay. In addition, check assays were also carried out by the screen fire assay method to verify high-grade sample assays obtained initially by fire assay. As part of the Company's QA/QC procedures, internationally recognized standards, blanks and duplicates were inserted into the sample batches prior to submitting to SGS Laboratory.
Qualified Person
Mr. Daniel Bansah, Chairman and Managing Director of Minecon, is the "qualified person" (as such term is defined in National Instrument 43-101) who is responsible for the mineral resource estimates and other technical information disclosed in this press release. Mr. Bansah has reviewed and approved the contents of this press release.