April 22, 2021

Mineral resources

Written by
Rate this item
(0 votes)

Overview – Resources continue to grow at Loncor’s flagship Adumbi Deposit

Total mineral resources at Loncor’s two main properties (Imbo and Makapela) in the Ngayu Greenstone Belt now stand at 4.016 million ounces of inferred mineral resources (46.2 million tonnes grading 2.70 g/t Au) plus 0.614 million ounces of indicated mineral resources (2.205 million tonnes grading 8.66 g/t Au ). One deposit, Adumbi, continues to be Loncor’s main focus with 3.15 million ounces of inferred resources now contained within the US$1500/oz pit shell. Drilling is ongoing at Adumbi to develop significant complimentary underground resources. The calculation of the underground resource should occur in Q3 3021.

The Imbo Project (84.68% of which is attributable to Loncor) contains 3.466 million ounces (43.0 million tonnes @ 2.51 g/t Au) of inferred mineral resources and the 100% owned Makapela Project has inferred mineral resources of 0.55 million ounces (3.22 million tonnes @ 5.30 g/t Au), plus 0.614 million ounces of indicated mineral resources (2.205 million tonnes grading 8.66 g/t Au ). Both projects are open at depth and along strike and good potential exists to further increase mineral resources by additional drilling.

On June 11 2021, a NI 43-101 technical report on the Imbo Project was filed on SEDAR and confirmed the inferred resource increase to 3.153 million ounces at Adumbi within the Imbo Project, having been prepared by Minecon Resources and Services Limited with an effective date of April 27 2021. A copy of the said report can be obtained from SEDAR at www.sedar.com.

Table 1: Summary of Loncor’s Gold Resources

Loncor controls 4.6 million ounces of resources.
Potential to grow further with Adumbi underground resources.

Loncor's indicated mineral resource - (Total & Attributable Ounces)
Deposit +
Attributable %
Gold Grade
(g/t Au)
Contained Gold
(000 oz)
Attributable Gold
(000 oz)
Makapela - 100% 2.21 8.66 614 614
Total Indicated 2.21 8.66 614 614
Loncor's inferred mineral resource - (Total & Attributable Ounces)
Deposit +
Attributable %
Gold Grade
(g/t Au)
Contained Gold
(000 oz)
Attributable Gold
(000 oz)
Adumbi - 84.68% 41.316 2.37 3,153 2,670
Kitenge - 84.68% 0.91 6.60 191 162
Manzako - 84.68% 0.77 5.00 122 103
Total Imbo Project 42.996 2.51 3,466 2,935
Makapela - 100% 3.22 5.30 550 550
Total Inferred 41.216 2.70 4,016 3,485

* Used US$1500/oz gold price for pit optimization and appropriate cost and cut-off assumptions

As part of an ongoing drill program discussed in the Adumbi Project section, on April 27 2021 Loncor announced a 44% increase in the Adumbi Open Pit resource (based on US$1500/oz pit shell outline). The grade and scale of the potential open pit deposit offers encouragement regarding the potential economic results of an ongoing Preliminary Economic Assessment that should be completed in Q3 2021. Additionally, further drilling should delineate underground resources at Adumbi during a similar time frame.

Figure 1: Location of Imbo Project Area (including Adumbi) and Makapela within the Ngayu Greenstone Belt

Location of Imbo Project Area in Ngayu Belt [map]

Imbo Project Resources - Includes Adumbi, Kitenge and Manzako deposits

On April 27 2021, Loncor announced an increase in open pit mineral resources of 44% to 3.15 million ounces of gold at its Adumbi Deposit. View detailed news release here

Figure 2: Imbo Project Simplified Geology

Imbo Project Simplified Geology [map]

In summary for the Imbo Project, the inferred mineral resource for the Adumbi, Manzako and Kitenge deposits now totals 3,466 million ounces of gold (43.00 million tonnes grading 2.51 g/t Au) and is summarised in Table 2 below.

84.68% of this inferred mineral resource is attributable to Loncor via its 84.68% interest in the Imbo Project.

Table 2: Inferred Mineral Resource for the Imbo Project (with an effective date of April 27 2021)

DepositTonnage (Tonnes)Grade (g/t Au)Contained gold ounces
Adumbi 41,316,000 2.37 3,153,000
Kitenge 910,000 6.60 191,000
Manzako 770,000 5.00 122,000
Total 42,996,000 2.51 3,466,000

Compared to the inferred mineral resource of 2.19 million ounces of gold (28.97 million tonnes grading 2.35 g/t Au) outlined in April 2020 (see Company press release dated April 17 2020), further drilling increased the Adumbi inferred mineral resource by 44% to 3.15 million ounces of gold (41.316 million tonnes grading 2.37 g/t Au), constrained within a US$1,500 open pit shell.

Table 3 below summarises the Adumbi inferred mineral resource based on in-situ block cut-off at a 0.68 g/t Au for Oxide and Transition materials and 0.72 g/t Au for Fresh material, and constrained within a US$1,500 per ounce optimized pit shell.

Table 3: Adumbi Deposit Inferred Mineral Resource by Material Type (effective date: April 27, 2021)

Material TypeTonnage (Tonnes)Grade (g/t Au)Contained gold ounces
Oxide 4,623,000 2.24 333,000
Transition 3,674,000 2.53 299,000
Fresh 33,019,000 2.38 2,521,000
Total 41,316,000 2.37 3,153,000

Note: Numbers may not add up due to rounding.

Commenting on the inferred mineral resource increase at Adumbi, Loncor’s President Peter Cowley said: “This major increase in mineral resources within a US$1,500 pit shell to 3.15 million ounces of gold is an important milestone in demonstrating the potential economic viability of the Adumbi deposit. Sensitivities show this mineral resource within the pit shell is robust and not markedly sensitive to changes in the gold price. Gold mineralization is open at depth below the pit shell where drilling is continuing with the objective of outlining underground resources. Drilling at Adumbi also demonstrates that grade is increasing at depth, which bodes well for a significant underground resource to be outlined. Going forward, once drilling has been completed in Q2 2021, we will embark on a Preliminary Economic Assessment (PEA) to determine the potential economic viability of Adumbi.”

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, grade and considering the CIM requirement for mineral resources to have “reasonable prospects for economic extraction”.

Additional Drill results included in the April 2021 Mineral Resource Update

An additional six core holes totalling 2,557.25 metres were drilled with the initial focus in areas within the pit shell where insufficient drilling had been undertaken to outline mineral resources. Later drilling has and is being undertaken at depth below the open pit shell to outline potential underground mineral resources.

The following table summarises drill results incorporated into the April 27 2021 mineral resource:

Borehole NumberFrom (m)To (m)Intersected Width (m)Grade (g/t) Au
LADD001 202.58 223.35 20.77 1.72
LADD001 231.27 237.17 5.90 1.89
LADD001 251.27 258.60 7.33 5.80
LADD001 295.25 298.70 3.45 2.10
LADD001 301.62 321.95 20.33 2.47
LADD001 Incl. 317.11 321.95 4.80 5.40
LADD003 224.55 235.00 10.45 3.88
LADD003 253.50 286.80 33.30 3.25
LADD003 Incl. 253.50 259.20 5.70 7.00
LADD003 Incl. 277.73 286.80 9.07 5.11
LADD004 429.00 457.00 28.00 3.26
LADD004 Incl. 432.00 436.90 4.90 6.96
LADD004 Incl. 450.62 454.15 3.53 8.30
LADD004 473.80 478.40 4.60 2.07
LADD004 505.85 526.15 20.30 2.83
LADD004 Incl. 506.85 513.40 6.55 4.64
LADD004 Incl. 523.85 526.15 2.30 7.25
LADD006 299.37 302.25 2.88 2.64
LADD006 308.00 309.00 1.00 21.20
LADD006 322.10 337.30 15.20 1.67
LADD006 353.35 357.85 4.50 3.25
LADD007 99.95 107.80 7.85 1.45
LADD007 540.62 596.05 55.43 2.76
LADD007 Incl. 583.60 596.05 12.45 8.11
LADD007 607.90 611.27 3.37 4.61
LADD008 235.05 278.15 43.1 1.68
LADD008 291.8 298.9 7.1 1.34
LADD008 305.15 305.93 0.78 21.8
LADD008 323.8 338.78 14.98 3.62
LADD008 Incl. 335.75 338.78 3.09 13.28
  1. It is estimated that the true widths of the mineralized sections for core holes LADD001, LADD003, LADD004, LADD006, LADD007 and LADD008 are, respectively, 82%, 80%, 81%, 95%, 89% and 62% of the intercepted widths in the above table.
  2. Deep core hole LADD009 results, which included 32.15 metres grading 6.17 g/t Au and 15.36 metres grading 3.73 g/t Au, are not included in current mineral resource update due to timing.
  3. Core holes LADD002 and LADD005 were discontinued before intersecting mineralized zone.

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 (see Figures 3 and 4 in Press Release dated April 27 2021): Geologic Plan and Geologic Cross Section of the Adumbi Deposit). 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, and
  • 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 (see Figure 5 in Press Release dated April 27 2021). 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$1,500 per ounce.
  • Block size: 8 metres x 8 metres x 8 metres.
  • A two-metre 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 95% for oxide and transitional material and 90% for fresh rock (no additional metallurgical studies have been undertaken since the April 2020 resource).
  • Average mining cost of US$3.29/tonne mined.
  • Average processing cost of US$22.02/tonne processed.
  • Average general and administration cost of US$4.20/tonne.
  • Mineral resources were estimated at a block cut-off grade of 0.68 g/t Au for oxide and transition materials and 0.72 g/t Au for fresh material constrained by a Whittle pit.
  • 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.

Additional resource potential at Imbo and recommendations for further work

There is significant additional resource potential within the Imbo project with a number of the deposits outlined in Figure 2:

  • At the Adumbi deposit, the drilling of additional holes under the proposed pit outline has the potential to create significant underground mineral resources. After this proposed drilling program has been completed, additional drilling may be undertaken (subject to securing the necessary financing), while a Preliminary Economic Assessment is initiated to include additional mineral resource determinations, metallurgical test work, open pit and potential underground studies, metallurgical plant processing, infrastructural, environmental and economic studies.
  • At the Kitenge and Manzako deposits (see below), additional drilling may also be undertaken (subject to securing the necessary financing) to further define and increase the inferred mineral resources at these deposits.
  • Ongoing exploration including gridding, soil sampling, trenching and channel sampling is planned to be undertaken at the Imbo East prospect, 10 kilometres southeast of Adumbi along the same mineralized trend as Adumbi in order to generate potential drill targets.

Makapela Project Resources

The Makapela deposit (which is 100%-owned by Loncor) has an indicated mineral resource of 614,200 ounces of gold (2.20 million tonnes grading 8.66 g/t Au) and an inferred mineral resource of 549,600 ounces of gold (3.22 million tonnes grading 5.30 g/t Au). The resource, initially announced in 2012 and updated in 2013, extends to a maximum depth of 500 metres over a mineralized zone of 2.2 kilometres. The zone includes significant artisanal pits that include Sele Sele, North, Main and Bamako pits. The geology of the area is characterised by a series of sub-vertical sheared BIF and quartz veins in mafic rock with the principal reefs varying between 1 and 6 metres in width, and based on historic drilling containing gold intersections up to 64 g/t Au in grade.

Figure 3: Location of significant drill intercepts and main areas of artisanal activity at Makapela

Location of significant drill intercepts Makapela [map]

In April 2013, the Company announced increases and upgrades of mineral resources at the Makapela prospect compared to the maiden mineral resources in May 2012. The updated mineral resources incorporated an additional 13 core holes from the initial, inferred-only maiden resource.

Tables 3 and 4 below summarise the current indicated and inferred mineral resources at Makapela using various cut-off grades including a base case economic cut-off grade of 2.75 g/t Au that used a US$1,500/ounce gold price and appropriate cost parameter assumptions and metallurgical recoveries.

Core drilling began at Makapela in October 2010 and focused on a quartz vein system within a sequence of basalts, thin units of banded iron formation and dolerite sills. A total of 71 core holes totalling 21,635 metres (including deflections) were used to estimate these indicated and inferred mineral resources at Makapela. Drilling was focused on three main veins: Reef 1, Reef 2, and Sele Sele that occur over a total strike length of 2.2 kilometres. Core drilling was undertaken on an approximate grid pattern of 80 by 80 metres down to a vertical depth of 240 metres and then on a 160 by 80 metre grid pattern down to a maximum depth of 480 metres.

Table 3: Makapela Indicated Mineral Resources (with an effective date of April 9 2013)

Cut-off Grade (g/t Au)Average Grade (g/t Au)Tonnes (Mt)Gold Content (Ounces)
1.00 7.45 2.683 643,000
2.00 8.14 2.407 629,700
  2.75* 8.66 2.205 614,200
3.00 8.87 2.130 607,200
4.00 9.97 1.764 565,500

Minimum mining true thickness of 1.5 metres. *Cut-off grade estimated using a US$1,500/ounce gold price with appropriate cost parameter assumptions for mining and other economic factors.

Table 4: Makapela Inferred Mineral Resources (with an effective date of April 9 2013)

Cut-off Grade (g/t Au)Average Grade (g/t Au)Tonnes (Mt)Gold Content (Ounces)
1.00 3.49 6.944 779,800
2.00 4.29 4.900 675,900
  2.75* 5.30 3.223 549,600
3.00 5.69 2.781 508,700
4.00 7.26 1.640 382,600

Minimum mining true thickness of 1.5 metres. *Cut-off grade estimated using a US$1,500/ounce gold price with appropriate cost parameter assumptions for mining and other economic factors.

In terms of material type, approximately 9% of the total mineral resources are in oxides, 6% in transitional and 85% in fresh rock.

These mineral resource estimates were prepared by independent consultants Venmyn Deloitte ("Venmyn"). The geology and drilling information was analysed, interpreted and estimated by Andrew Clay of Venmyn, a "qualified person" as such term is defined in National Instrument 43-101. Mr. Clay visited the site to review data collection procedures, geological interpretations and modelling, and estimation using geostatistical techniques. Venmyn also reviewed the geological and grade continuity to supplement the review of data quality in order to confer mineral resource classification categories to reflect the variable sample coverage. Venmyn was satisfied that all drilling, sampling, database and geological modelling protocols comply with the standards prescribed by National Instrument 43-101.

The following key assumptions, parameters and methodologies were used to estimate the mineral resources:
  • Datamine Studio 3 software was the modelling package used for the determination of the mineral resources.
  • Gold grades were determined using ordinary kriging interpolation into a 3-dimensional block model constrained by mineralization wireframes developed from a 2g/t Au sample cut-off grade and a minimum horizontal width of 1.5 metres.
  • The mineralization models were constrained within the wireframe with primary block dimensions of 10 metres N-S (along strike), 5 metres E-W (cross strike direction) and 10 metres in the vertical direction.
  • Grade interpolation was effected separately for the individual mineralized zones and Datamine's dynamic anisotropy process was employed to control the orientation and axes of the search volumes.
  • The down dip extrapolations were restricted to three times the variogram range from the last drillhole used in the interpolation and the model was trimmed off at a maximum depth of 500 metres from the surface for reporting purposes.
  • Portions of the resource were re-classified from Inferred to Indicated based on increased geological confidence and grade continuity due to data quality and data density following infill drilling. Criteria for Indicated are sufficient samples within one variogram range to achieve valid local estimates, in respect of positive kriging efficiency.

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 SGS Laboratory (which is independent of the Company) in Mwanza, Tanzania. The core samples were then crushed down to minus 2 mm, and split with one half of the sample pulverized down to 90% passing 75 microns. Gold analyses were carried out on 50g aliquots by fire assay. In addition, checks assays were also carried out by the screen fire assay method to verify high-grade sample assays obtained by fire assay. Internationally recognized standards and blanks were inserted as part of the Company's internal QA/QC analytical procedures.

A total of 2,614 core samples were taken to determine relative density measurements for the various reefs and oxide, transitional and fresh rock components.

Qualified Person

Peter N. Cowley, who is President of Loncor and a "qualified person" as such term is defined in National Instrument 43-101, has reviewed and approved the technical information on this website relating to Loncor’s mineral properties.

Technical Reports

Additional information with respect to Loncor’s Imbo Project (including the Adumbi deposit) is contained in the technical report of Minecon Resources and Services Limited dated April 17 2020 and entitled "Independent National Instrument 43-101 Technical Report on the Imbo Project, Ituri Province, Democratic Republic of the Congo". A copy of the said report can be obtained from SEDAR at www.sedar.com and EDGAR at www.sec.gov. A further 43 101 Technical Report will be available on SEDAR from June 2021 relating to the April 2021 Resource Increase at Adumbi.

Additional information with respect to Loncor’s Makapela Project, and certain other properties of the Company in the Ngayu gold belt, is contained in the technical report of Venmyn Rand (Pty) Ltd dated May 29 2012 and entitled "Updated National Instrument 43-101 Independent Technical Report on the Ngayu Gold Project, Orientale Province, Democratic Republic of the Congo". A copy of the said report can be obtained from SEDAR at www.sedar.com and EDGAR at www.sec.gov.

Read 1231 times Last modified on June 14, 2021
More in this category: « North Kivu project IMBO project »

Leave a comment

Make sure you enter all the required information, indicated by an asterisk (*). HTML code is not allowed.