Somituri Project – Metallurgy
Large samples were collected from 8 active artisanal sites and gold recoveries by the BLEG (Bulk Leach Extractable Gold) in a cyanide solution were determined. Gold recoveries were generally of the order of 93% to 99%.
As of 2012, metallurgical test work associated with the Imbo Licence has been has been primarily confined to the Adumbi Resource. Additional test work will be undertaken to further develop our understanding of the processing and environmental issues associated with the various mineralised and non-mineralised lithological domains associated with the Adumbi Resource, as well on the other key targets associated with the Imbo Licence.
Importantly, test work will also be expanded to incorporate the requirements of other technical disciplines, namely; geotechnical, geochemistry, geohydrology and environmental.
Preliminary metallurgical test work carried out to date indicates that:
- high gold recoveries (in excess of 90%) may be expected from the oxide horizon, when employing a gravity circuit in combination with a conventional cyanide leach circuit;
- with the exception of one of the three composite cores within the sulphide horizon, gold recoveries in excess of 90% were also observed utilising the aforementioned processing methodology; and
- Bond Ball Mill Work (BBMWI) Indices are low for a Banded Iron Formation (BIF), circa 12 kWh/t and less. This has favourable implications for the overall project power requirements and in the selection of the comminution circuit.
It is important to note that:
- recoveries as reported herein are to the gravity concentrate and to cyanide solution; and
- all test work to date is of a preliminary nature and the optimum processing route(s) and process parameters, as a function of the Life of Mine (LoM) plan are still to be defined.
Quarter core from seven diamond drill holes spatially distributed over the drilled strike length and depth extent of the Adumbi Prospect were submitted to Wardell Armstrong International (“WAI”) in the United Kingdom in 2011 for preliminary metallurgical test work. Four samples were selected from oxide and five samples were selected from sulphide mineralization. In addition, the samples represented the various lithological host rocks for the mineralization.
With the exception of the comminution test work, the mineralised zones from each core were composited into six discrete samples and processed separately to determine the overall metallurgical parameters for each core. All test work was undertaken by Wardell Armstrong International (WAI) in the United Kingdom.
The location of the samples selected are represented pictorially in the Figure below, with additional detail on naming nomenclature, sample depth, mass and grade (Au, Ag and S) presented in the Geochemistry Section
The head analysis for the composite samples are given in the table Following.
|KGL and Wardell Armstrong test work samples and head analysis|
|KGL Exploration||Wardell Armstrong|
|Composite||DD Hole||Depth (m)||KGL Exploration||Avg. Head Assays|
In a separate report, WAI also reviewed the elements present in the sulphide feed and the oxides tails, using a 50 element ICP analysis and other analytical methods where appropriate. The purpose was to identify elements which were potentially enriched in the deposit and that could be problematic from a processing and environmental management perspective. Key findings are summarised in the table following (gold excluded):
|Average enrichment factor relative to elements in the Earth’s crust (six cores)||Elements|
|2 to 10 x||Cr, Fe, Re|
|10 to 100 x||Ag, Bi, C, Mo, Pb, Sb, Se, Te|
|100 to 1000 x||S|
From the analysis received and a subsequent analysis undertaken by ourselves, namely; comparing the results obtained with typical concentrations of elements in the Earth’s crust and that of other gold projects (not listed here), it was concluded that for the composites tested:
- the samples are enriched in antimony (sb), circa 16 (S2) to 173 (S1) times. Thus, subject to confirmatory test work, some aurostibite (AuSb2) may be present;
- the samples are enriched in silver, but not at levels that would influence the design of a plant;
- sulphur levels in the mineralised zone are high and appropriate technical solutions will be applied to manage environmental issues;
- arsenic levels are high, in the oxide and in particular the sulphide horizons and thus like sulphur, appropriate technical solutions will be applied to manage plant and mining wastes;
- base metal levels are low with only lead (pb) reported to be elevated, circa between 0.6 to 45 times; and
- tellurium (Te) is moderately elevated, circa 21 to 25 times. Thus, subject to confirmatory testwork, gold tellurides may be present.
Metallurgical Test Work Results
Kilo Goldmines (Kilo) submitted core from seven diamond drill holes to Wardell Armstrong International (WAI) in the United Kingdom, in April of 2011, for purpose of conducting preliminary/scouting metallurgical test work. The results as outlined herein pertain to WAI report MM584, dated August 2011.
The test work programme was designed to determine:
- amenability of the oxide samples to heap leaching at three crush sizes, namely: 20 mm, 15 mm and 12.5 mm;
- the recovery of gold by milling down to a P80 of 75 µm, followed by a conventional cyanide leach;
- the recovery of gold by milling down to a P80 of 75 µm in combination with a two stage gravity separation stage (500 µm and 100 µm), followed by a conventional cyanide leach of the combined gravity tails; and
- the Bond Ball Mill Work Index (BBMWI) of the samples tested.
The results from the conventional milling and leach circuit and the alternate circuit, comprising a gravity concentration stage are summarised in the Table following. Additional information on the results of the heap leach and comminution test work are discussed below.
In the gravity and leach test work undertaken, it is important to note that:
- the overall gold recoveries given are not actual gold recovery to a final product, but rather the recovery of gold to the gravity concentrate and the recovery of gold to cyanide solution. Additional gold losses may be expected when recovering gold from the gravity concentrate and gold from solution, albeit subject to validation, these losses are expected to be small;
- no pre-oxidation stages were employed, nor was oxygen or hydrogen peroxide used in the leach;
- dissolved O2 levels were not measured, nor was the oxygen uptake determined; and
- lead nitrate was not used as an additive.
|Wardell Armstrong Metallurgical Results (Gravity and CIL only), MM584, 2012|
|Gravity followed by conventional CIL||Conventional Leach|
(500 µm + 100 µm)
|Gravity tails leach||
P80 = 75 µm, pH =10.6,
Free NaCN (1g/t)
|NaCN||Free NaCN||Lime||Rec. Au||
Test work findings are summarised below:
- in order to simulate a heap leach, coarse bottle roll tests were undertaken on all oxide samples at a crushed product size of 20 mm, 15 mm and 12.5 mm. In all cases, recoveries in excess of 72% and up to a maximum of 88% were obtained. At this stage, there is no evidence to suggest that reducing crush size, increased gold recovery;
- preliminary test work indicates that the overall Bond Ball Mill Work Indices (BBMWI) for the oxide and sulphide horizon is of the order of 10.5 kWh/t and 11.8 kWh/t respectively. These results are significantly lower than what was expected of a Banded Iron Formation (BIF), having both positive implications for equipment selection and the overall project’s power requirements. Notwithstanding these results, additional test work is required to define comminution parameters by lithological domain and in accordance with the relative proportions of each domain reporting to the plant as a function of the Life of Mine (LoM) Plan.
- for the oxide zone and possibly the transition zone, recoveries in excess of 90% may be attainable though a combination of gravity and a direct cyanide leaching of the gravity tails. For the Adumbi deposit this possibly represents 0.88 Moz of Au, or 47% of the resource as currently defined; or in production terms; possibly the first 4 to 6 years of production;
- with the exception of S1, in excess of 30% of the gold contained in the RoM material is recoverable by gravity. S1 had no, to limited gravity recoverable gold. It is noteworthy that where gravity is applicable, the gravity mass pulls were very low; and
- with the exception of S1, recovery of gold from the sulphide zone is as good as, if not better than for the oxide horizons. Futrher testwork is required to determine the cause of the poor gold recoveries observed from S1.
In moving forward, additional work will be undertaken by lithological/mineralogical domain to determine gold deportment by mineral, by size and gold lock up in solid solution. This will entail a combination of: diagnostic leach test work; QEMSCAN work and petrographics.