East Africa Metals Inc. is pleased to announce an updated independent mineral resource estimate for the Adyabo Project in Ethiopia.
The recent 40 x 40 metre spaced infill drill program strategically targeted on the core areas of Inferred Resource gold mineralization at Da Tambuk and Mato Bula (Figure 1). A total of 4,029 metres of diamond drilling in 31 holes was completed during the infill campaign.
Key highlights of the updated Resource include;
- The conversion of 446,000 gold equivalent ounces to the Indicated Resource classification.
- The gold grade for the Indicated portion of the resource has increased to 3.92 grams per tonne gold, compared with the initial overall Inferred Resource grade of 2.26 grams per tonne gold, an increase of 73%.
- In complement to this increased grade, over 95% of the Indicated equivalent gold ounces are recoverable via the near surface Pit Constrained model.
- For the Indicated Resource, Pit Constrained gold and gold equivalent grades are 3.94 grams per tonne, and 4.30 grams per tonne respectively.
The mineral resources reported herein have been estimated using criteria consistent with the Canadian Institute of Mining and Metallurgy ("CIM") Definition Standards (2014) and in conformity with the CIM "Estimation of Mineral Resources and Mineral Reserves Best Practice" (2003) guidelines. The disclosure of this Mineral Resource is compliant with National Instrument 43-101 Standards of Disclosure for Mineral Projects ("NI 43-101").
Adyabo Project Mineral Resource Estimate David Thomas, P. Geo. (Effective Date: May 31, 2016)
Footnotes to mineral resource statement:
Fladgate Exploration Consulting Corporation ("Fladgate") reviewed East Africa's quality assurance and quality control programs on the mineral resources data. Fladgate concludes that the collar, survey, assay, and lithology data are adequate to support mineral resources estimation.
Domains were modelled in 3D to separate mineralised rock types from surrounding waste rock. The domains were modelled based on copper and gold grades.
Raw drill hole assays were composited to 2 metre lengths broken at domain boundaries.
Capping of high grades was considered necessary and was completed for each domain on assays prior to compositing.
Block grades for gold and silver were estimated from the composites using a combination of ordinary kriging and inverse distance weighted (power of three) interpolation method into 5 metre (along strike) x 2 metre (across strike) x 5 metre (vertical) blocks coded by domain.
Dry bulk density varied by deposit area. The dry bulk densities are based on 559 specific gravity measurements at Da Tambuk, 1,755 specific gravity measurements at Mato Bula and 231 specific gravity measurements at Mato Bula North.
Blocks were classified as Indicated and Inferred in accordance with CIM Definition Standards 2014.
Indicated resources are classified on the basis of blocks falling within a drill hole spacing of 40 metres x 40 metres. The results of comparison with the previous mineral resource model, a drill hole spacing study and conditional simulation of gold grades were used to support the classification of Indicated mineral resources.
Inferred resources are classified on the basis of blocks falling within the mineralised domain wireframes (i.e. reasonable assumption of grade/geological continuity) with a maximum distance of 100 metres to the closest composite.
The mineral resource estimate is constrained within an optimised pit with a maximum slope angle of 50 degrees. Metal prices of $1,400/oz, $3.20/lb and $20.0/oz were used for gold, copper and silver respectively. Metallurgical recoveries of 97% for gold, 72% for copper and 50% for silver were applied at Da Tambuk. Metallurgical recoveries of 88.5% for gold, 87.5% for copper and 50% for silver were applied at Mato Bula and Mato Bula North.
A pit constrained $/t cut-off was estimated based on a total process and G&A operating cost of $23.9/t of ore mined. An additional mining cost of $40/t was used to estimate a $/t cut-off of $63.9/t for reporting underground mineral resources.
The contained gold, copper and silver figures shown are in situ. No assurance can be given that the estimated quantities will be produced. All figures have been rounded to reflect accuracy and to comply with securities regulatory requirements. Summations within the tables may not agree due to rounding.
Mineral Resources which are not Mineral Reserves do not have demonstrated economic viability. The estimate of mineral resources may be materially affected by environmental, permitting, legal, title, taxation, sociopolitical, marketing, or other relevant issues.
The quantity and grade of reported inferred resources in this estimation are conceptual in nature and there has been insufficient exploration to define these inferred resources as an indicated or measured mineral resource and it is uncertain if further exploration will result in upgrading them to an indicated or measured mineral resource category.
Andrew Lee Smith, President and CEO, stated, "Moving 446,000 equivalent ounces of gold into an Indicated Resource category with just over 4,000 metres of drilling demonstrates both the predictable and consistent nature of the mineralization targeted, and the corporate focus on results-oriented project advancement. We look forward to further adding value and building on the potential at Adyabo, and also the Harvest Project in Ethiopia."
East Africa will continue to advance both its Harvest and Adyabo resource projects in Northern Ethiopia.
Identified resources at Adyabo will continue to be upgraded through further delineation and engineering work. Additional surface targets remain to be tested on the Mato Bula trend, and the development of targets to depth remains a key consideration. At Harvest, engineering and metallurgical testing is ongoing for the Terakimti Oxide deposit, and additional review is being conducted on the Supergene copper sulfide mineralization below the oxide.
Additional details on the Mineral Resource update
Adyabo Project Indicated Mineral Resource Estimate, David Thomas, P. Geo.
(Effective Date: May 31, 2016)
Adyabo Project Inferred Mineral Resource Estimate, David Thomas, P. Geo.
(Effective Date: May 31, 2016)
The initial Adyabo Resource was completed in 2015 and for comparative purposes is outlined below:
Initial Adyabo Project Inferred Mineral Resource Estimate, David Thomas, P. Geo. (Effective Date: April 27, 2015)
43-101 Technical Report Filed June 17, 2015
East Africa requested that Fladgate update the Adyabo initial mineral resource estimate utilizing the additional infill diamond drilling and trench information collected during the fall of 2015 and winter of 2016. This drilling was concentrated on the core areas of mineralization at the Mato Bula and Da Tambuk mineralized zones.
Fladgate undertook quality assurance and quality control studies on the mineral resource data for the Adyabo Project, including the comparison of 76.5% of original assays from this latest program, to original assay certificates. There are a total of 84 core diamond drill holes for 15,295.8 metres, and 2,808 trench metres within the database used to support mineral resource estimation. The drill database was provided by East Africa as a MS Access® database and in MS Excel® files. The database cut-off date for Mineral Resource estimate purposes was April 13, 2016.
Fladgate imported the collar, survey, lithology, alteration, and assay data into MineSight®, a commercial mining software program. Topographic contour lines were based on a surface supplied by East Africa with contour lines spaced 2 metres apart. The topography is based upon GeoEye images collected at a resolution of 50centimetres.
Fladgate checked and compared that the drill hole collars matched the topographic surface and found only minor differences of < 1 metre in elevation between the surveyed drill hole collars and the topography. No corrections were made to the drill hole collar elevations. All data used the local grid coordinate system.
The gold-copper mineralization on the Da Tambuk, Mato Bula North, and Mato Bula areas on the Adyabo Project are hosted by intensely deformed and altered sericite-altered schists and mafic meta-volcanic rocks which form prominent northeast trending ridges. At Mato Bula, the mineralization is in contact with meta-sedimentary rocks.
At Da Tambuk, mineralization occurs in two sub-parallel zones with a strike length of 650 metres in a northeast-southwest direction, a vertical extent of 200 metres and horizontal widths up to 50 metres. Mineralization is enriched in gold relative to copper with a Au:Cu ratio (Au g/t to Cu %) of 24.7 to 1.
At Mato Bula, mineralization occurs in three sub-parallel zones with a strike length of 850 metres in a northeast-southwest direction, a vertical extent of up to 450 metres and a horizontal width of up to 80 metres. The southern part of Mato Bula has a higher copper content relative to gold. The overall Au:Cu ratio is 8.1 to 1.
Mineralization at Mato Bula North is hosted in two zones, with dimensions of 200 metres in a north-south direction, a vertical extent of 170 metres and a horizontal width of up to 60 metres. Mineralization is enriched in copper relative to gold with a Au:Cu ratio of 0.6.
East Africa provided Fladgate with sectional interpretations of the mineralization based on copper and gold grades. Fladgate created wireframe models of the mineralized zones using East Africa's drill hole intercepts with Minesight's implicit modeller. Fladgate reviewed the wireframe models and found the wireframe boundaries correctly honour the drill hole intercepts and inspected drill holes displaying gold and copper grades. No significant zones of mineralization fall outside of the wireframes.
Fladgate composited the assays into 2 metre composites. The length weighted mean gold and copper grades of 2 metre length composites are very similar to those of the assays; therefore Fladgate is confident that the compositing process worked as intended.
Where the coefficient of variation (CV) values of the capped assays are greater than 2, further domaining of the copper and gold grades is warranted. As a result of the multiple gold composite populations and high CV in a number of zones, probability indicator models were created.
At Da Tambuk, the CV of the low grade composites is highly affected by the misclassification of two high grade composites. This composite misclassification was not adjusted. Overall the indicator coding is successful in separating low grade mineralization from higher grade mineralization.
At Mato Bula, minor adjustments were made to the classification of composites to avoid high grade composites coded to the lower-grade subdomain and vice-versa. Overall the indicator coding is successful in separating low grade mineralization from higher grade mineralization.
Fladgate estimated grades from the 2 metre composites into regular blocks with a size of 5 metres along strike x 2 metres across strike x 5 metres vertically. At Da Tambuk and Mato Bula, Fladgate used an ordinary kriging (OK) grade interpolation method in two passes using Minesight's dynamic unfolding (DU) module to account for significant changes in the orientation of the mineralization wireframe.
Global and Local bias checks were performed and reviewed, as were grade smoothing checks.
Density sampling was performed at site using unsealed immersion technique to measure the weight of each sample in air and in water. Fladgate assigned Specific Gravity values ranging from 2.83 to 2.85 to blocks within the mineralized zones. The SG values have been used directly as the dry bulk density to report the tonnage estimates of the mineral resource. The rock types intercepted in the drill holes are generally not porous, therefore the amount of porosity is not expected to cause a large difference between the SG and bulk density.
Block models were validated to ensure appropriate honoring of the input data through a number of methods including; 1) nearest-neighbour (NN) grade model review to validate the OK grade models, 2) visual inspection of block grade vs composited data in section and plan, 3) comparison of metal removed by capping, 4) bias checks on OK and NN estimates, and 5) grade smoothing checks. Fladgate classified blocks with a maximum distance of 100 metres to the closest composite to the Inferred category.
A review was conducted of the geological model, data quality, geological continuity and metallurgical characteristics for classification of mineral resources. The mineralized zone wireframes are supported by drilling with a spacing of between 40 metres and 80 metres. This drill spacing is sufficient to assume that the mineralization is continuous between drill holes. A 100 metres maximum distance to the closest composite permits a reasonable local estimate of grades (as demonstrated by model validation).
Fladgate conducted an analysis of confidence limits using quarterly panels of production for a 4,500 t/day pit constrained mine operation. The accuracy of grade estimates was then scaled to annual production. Accuracy of ±15% or better at a 90% confidence limit on annual production was used as the criteria to select a drill hole spacing to be used to classify Indicated mineral resources. The results show that a drill hole spacing of 40 metres (along the easting) x 40 metres (along the northing) is sufficient to classify Indicated mineral resources.
Fladgate completed an analysis of the classification categories using conditional simulation of grades for specific zones, and additionally conducted a comparison of the updated resource in the 40 metre x 40 metre spacing infill drill area.
Fladgate is of the opinion that the results support the classification of Indicated mineral resources to certain areas of the Adyabo resource. Fladgate classified blocks to the Indicated category using the following criteria:
- A maximum distance to the closest hole of 40 metres.
- A maximum average distance from two holes of 31 metres (approximately ½ the diagonal distance within a 40 metre x 40 metre grid with a 10% contingency).