Australian gold producer Tribune Resources Limited ('Tribune' or the Company, ASX: TBR) is pleased to announce the results of the maiden Mineral Resource Estimate (MRE) for the Adiembra gold deposit at the Japa Project in Ghana.
The MRE was undertaken by Mining Plus Pty Ltd following a 34,115 metre drilling campaign during the first half of 2020 that complemented more than 42,000m of previous drilling completed by the Company at Adiembra since acquiring the project in 2005.
Commenting on the outcome of the Resource estimate, Tribune Managing Director Mr Anton Billis said: 'A maiden gold resource in excess of 21 million tonnes at 2.7 grams per tonne is outstanding and reinforces our confidence that the Japa Project could be a major long-life gold production centre in Ghana.
'We are already well advanced in planning the next drilling campaign aimed at expanding and upgrading the Adiembra Resource, with drilling expected to commence in the next few months'
Results from the drilling to date has outlined a large 1400m by 700m mineral system constituting two principal lodes - Adiembra West and Adiembra Central. The Adiembra mineralisation remains open along strike and at depth due to limited drill coverage, and it is evident that there is significant opportunity to extend the mineralisation at Adiembra and potentially build on the Resource. Further drilling is planned aiming to upgrade the Resource classification to Measured and Indicated, assess lateral extensions to the system, test specific areas beneath the current $3000 per ounce pit shell used for the Resource estimation and evaluate a relatively untested area immediately southeast of the Central Lode.
Overview
The Japa Project is located in the Western Region of Ghana, approximately 110 km South West of Kumasi and 50 km North of Tarkwa, centred in the village of Gyapa in the Wassa Amenfi East District. Mining Lease PL2/310 covers a 26.2 square kilometre area over part of the Akropong Belt, an offshoot of the highly endowed Ashanti Belt, within the Birimian Supergroup that hosts many of the most significant, multi-million-ounce Ashanti type orogenic lode-gold deposits of West Africa.
Tribune Resources (Ghana) Limited acquired its interest in the Japa Project in 2005. Initial work by Tribune expanded on surface geochemical sampling conducted by previous explorers which was followed by drill testing of identified gold anomalies. Successive phases of drilling, amounting to over 98,000 metres completed to date, has defined extensive gold mineralisation within numerous prospects across the Mining Lease. Two deposits, Adiembra and Japa-Dadieso Trend, have been the principal focus areas of this work over the period of tenure and these deposits form the base from which Tribune is planning to grow and develop the Japa Project.
Adiembra Gold Mineralisation
Gold mineralisation at Adiembra is hosted by narrow quartz and quartz-pyrite veins which crosscut a sequence of metamorphosed shale (phyllite), siltstone and sandstone in a regular orientation almost normal to the eastnortheast trend of the rock package. The mineralised sequence has undergone variable degrees of shearing together with sericite and chlorite alteration.
Adiembra is a very broad mineralised system currently defined over 1400 metres long, up to 700 metres wide and to a maximum depth of 270 metres below surface. Within this large system, mineralisation is concentrated in two distinct lodes, Adiembra West and Adiembra Central. Adiembra West has a strike length of over 1250 metres and ranges from 40 to 80 metres in width whilst Adiembra Central has a strike length of over 1400 metres and ranges from 60 to 180 metres in width. Both lodes are open along strike and at depth, where limited drilling has been conducted, and drill testing of these potential extensions is a priority for the Company
Exploration Data
Drilling and Sampling
Reverse Circulation Percussion (RC) and Diamond Core (DD) drilling methods were employed to evaluate the Adiembra deposit. Drilling was conducted in three main phases: 2007-2008, 2011-2018 and 2020, with 563 holes totalling 76,320 metres constituting the drill data used for the MRE. RC drilling was conducted by both Contractor and Tribune owned equipment with all DD being performed by Contractors. RC drilling utilised face sampling hammers with bit sizes of 133 or 140 millimetres diameter. Samples were collected in predominantly single metre or three metre composite intervals either directly from the rig cyclone or utilising an adjustable cone splitter mounted beneath the cyclone.
RC sample recovery was estimated visually. Monitoring of sample quality and quantity was undertaken by geologists and technicians attending the rigs during drilling operations. RC sample recovery and maintenance of hole integrity were maximised through the use of auxiliary and booster air compressors to manage sample circulation and control ground water inflow. Diamond core was of HQ or NQ2 size drilled using conventional wireline core recovery techniques. HQ core was collected by triple tube method with 1.5 metre barrel and NQ2 core was collected with three metre standard barrel. DD holes were drilled directly from the land surface or from pre-collar holes drilled by the RC method. Diamond core recovery was measured by comparison of core length retrieved with drill run length.
NQ2 size diamond core was oriented using Reflex ACT II or ACT III electronic orientation tools. HQ core was not able to be definitively orientated. All core was marked with depth labels, orientation lines and cut lines prior to the capture of photographic records, cutting and sampling. Drill hole collars were located using GPS or Differential GPS. Hole trajectories were measured using Reflex EZGyro or EZ-Trac down hole survey tools.
Sub-sampling
RC samples were riffle split where necessary to obtain appropriate sample weight of nominally three kilograms for analytical purposes. Samples deemed too wet to adequately pass through the riffle splitter were subsampled by either tube-spear or grab methods. These sub-sampling methods were also used to obtain field duplicate samples for quality assurance and quality control (QAQC) purposes. Diamond core was predominantly sampled over intervals of between 0.3 metres and 1.2 metres length using an electric core saw or, where necessary due to extreme weathering or friability of the recovered material, using a trowel or chisel. In most instances, half core was submitted for analysis and half core retained in the core trays for reference. Quarter core sampling was used to obtain duplicate samples for QAQC purposes. Core cutting and sampling was performed by Tribune personnel and Contractors.
Drill Sample Logging
Drill holes were logged for a range of geological features according to Tribune logging codes. Representative subsamples of RC samples were retained in chip trays for library reference. Definitively orientated diamond core was used for detailed structural measurements that were used for subsequent interpretation and modelling for the MRE. Core was photographed prior to cutting and sampling and remnant core was retained in core trays at Tribune's site base for future reference.
Sample Analysis
Drill samples were submitted to Intertek Minerals laboratory in Tarkwa, Ghana for analysis by fire assay and atomic absorption spectrometry (AAS). Sample preparation processes include sorting and validation, drying, crushing, pulverising and splitting. Fire assay was performed on a 50 gram pulverised subsample with AAS used for gold determination to a lower detection limit of 0.01 parts per million. All data was reported via digital file transfer. Submitted with the primary samples were commercially prepared Certified Reference Materials and duplicate samples for QAQC monitoring purposes. These standards and duplicates were included with each batch submitted to the laboratory at an average frequency of 12% of all samples submitted.
Database Management
All Adiembra exploration data is remotely stored in digital format by Maxgeo data management consultants. This remote and independent storage ensures data integrity and security are maintained.
Mineral Resource Estimation
The Adiembra Mineral Resource Estimate (MRE) was conducted by Mr Richard Hingston, Principal Geology Consultant of Mining Plus Pty Ltd, independent mineral industry consultants. The MRE was prepared in compliance with the guidelines of the 2012 Edition of the Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (The JORC Code).
Classification
As defined in The JORC Code, Mineral Resources are classified as follows:
Measured - Tonnage, densities, shape, physical characteristics, grade and mineral content can be estimated with a high level of confidence.
Indicated - Tonnage, densities, shape, physical characteristics, grade and mineral content can be estimated with a reasonable level of confidence.
Inferred - Tonnage, grade, and mineral content can be estimated with a reduced level of confidence.
Estimation parameters and methodology
Drill Hole Data Analysis
Only RC and Diamond Core drilling data has been used for the MRE. Mining Plus conducted a comprehensive audit of the Tribune drill hole database including back-to-source checks of collar, down hole survey, assay and bulk density data, analysis of assay QAQC data, evaluation of variances between drilling methods and drilling campaigns, and any potential sample contamination issues from the drilling, sampling and analysis processes. Mining Plus did not identify any significant issues with the data that would materially affect the overall validity and relative accuracy of the MRE.
Geological Interpretation and Wireframing
The MRE was constrained and domained by wireframes created from the drill data. Surface topography was created from a concatenation of drill collar surveys, physical survey traverses and UAV aerial survey data. Weathering surfaces were created using Leapfrog Geo from geological logging data at the bottom of complete oxidation and top of fresh rock to distinguish oxidised, transitional and fresh rock domains. Lode haloes for Adiembra West and Adiembra Central were manually created as gross lode boundaries to constrain the estimation. Within the lode haloes the mineralisation was modelled in Leapfrog Geo based on statistical analysis of the assay data and vein orientation data from drill core measurements to produce grade shell domains at 0.25g/t for Adiembra Central and 0.4g/t for Adiembra West. Further high grade domains were modelled for Central and West lodes, constrained by the respective low grade domains.
Mining Depletion
Areas of significant disturbance by artisanal miners have been identified by aerial and topographic surveys, wireframed and excised from the MRE.
The block model envelopes the interpretation wireframes and was rotated to accommodate the trend of the lodes and the contained mineralisation solids. A parent block size of 20m by 20m by 5m was selected based on nominal drill spacing of 40m, with sub-blocking down to 0.5m by 0.5m by 0.5m to accurately reflect the mineralisation wireframe volumes.
Grade interpolation into the block model was by Inverse Distance to the Power Zero (ID0) with up to four interpolation passes applied. This estimation method was selected due to the high nugget nature of the mineralisation and the poor grade correlation between drill holes as determined from the statistical analysis of the assay data. Grade estimation of sub-blocks has been completed at the parent block scale and so they reflect the parent block grade. High grade yield restrictions were applied to some estimation domains to limit the influence of individual high grade samples. Bulk density values were assigned to the block model based on the weathering code using 200 data points determined from core samples by the Archimedes Principle.
Model Validation
Gold grade estimates have been validated by statistical analysis and visual comparison of the composite assay data and block model grades for each mineralised domain, with the majority of the domains having model grades within 10% of the composite grades. Swathe plots were also generated and used to compare block model grades with the input data grades.
Classification
The Resource classification is based on a combination of factors including the drill hole data spacing, confidence in geological interpretation, continuity of mineralised veins, gold grade distribution and continuity, and a bulk mining scenario as an anticipated means of eventual economic extraction. Adiembra mineralisation that has been defined by drilling at or closer than 35m by 35m spacing and with a reasonable level of confidence in the grade and geological continuity has been classified in the Indicated Resource category. Mineralisation defined by drilling at or closer than 70m by 70m spacing with a suitable level of confidence in the grade and geological continuity has been classified in the Inferred Resource category. Mineralisation defined by drilling greater than 70m by 70m spacing or that which has been estimated by pass four of the interpolation process is unclassified.
The Mineral Resource as reported is constrained within an optimised open pit shell based on a bulk mining scenario with the following parameters: Bulk open pit mining method only
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