Mali Lithium has completed a new mineral resource estimate at its 100% owned Goulamina Lithium project in Mali, West Africa.
The new measured, indicated and inferred mineral resource estimate is 108.51 million tonnes at 1.45% Li₂O for 1.57 million tonnes contained Li₂O. Measured and Indicated Resources are 64.6 million tonnes at 1.49% Li₂Ofor 0.964 million tonnes of contained Li₂O.
The June 2018 Indicated and Inferred Mineral Resource estimate announced in the Pre-Feasibility Study (PFS) was 103.2 million tonnes at 1.34% Li2O for 1.39 million tonnes Li2O and included 43.7 million tonnes at 1.48% Li₂O of Indicated Mineral Resource.
“It is promising to see both the size and quality of the Goulamina Resources improve. This will provide the basis for an uplift in ore reserves. We will endeavour to complete the Ore Reserve and the Definitive Feasibility Study as soon as possible, now that COVID-19 delays are behind us,” commented Dr Alistair Cowden, Mali Lithium managing director.
The new resource represents a 48% uplift in measured and indicated resources. The Measured and Indicated Resources are the basis of a new ore reserve estimate being undertaken for the Goulamina Definitive Feasibility Study (DFS). A material improvement to PFS ore reserves and mine life is expected. The DFS will be completed in two months.
Resource Definition Drilling
A total of 445 RC and diamond drill holes for 52 012 metres have been drilled for resource and metallurgical, geotechnical, exploration and water exploration purposes at the Goulamina Lithium deposit to date.
During the 2019-2020 dry season, Mali Lithium drilled 36 RC drill holes for 6 842 metres for resource purposes into the Goulamina deposit. The drilling targeted areas where the previous pit optimisation was limited by the extent of the 2018 resource estimate in the Sangar l and Sangar ll domains, as well as infill drilling in the Danaya resource area.
The drilling program has successfully extended the Sangar l and Sangar ll spodumene pegmatites at depth and has extended the resources of those domains down dip. The interpreted domains in the north east part of the Goulamina deposit are organised into sub parallel mineralised lodes that dip 65 – 75 degrees towards the east northeast. Minor splays and linking structures are in evidence, though these are not generally modelled due to their sporadic and narrow nature.
At Danaya, infill drilling on three sections (12 RC drill holes), and interpretation of down hole acoustic imaging data that was received during the year, has resulted in a re-interpretation of the geology and orientation of pegmatites in that area. Consequently, the modelled resources in the area have been significantly modified. The resources published herein for Danaya have been tightly constrained and are considered conservative, particularly in areas of sparse drilling.
Weathered pegmatite material in all domains is excluded from all the Mineral Resource Estimates. Detailed metallurgical test-work on the generally low-grade weathered material has not been completed, but experience at other spodumene pegmatite operations point to poor product recoveries from the oxide zone which renders the oxidised pegmatites not economically treatable.
Resources in the Main, West l, and Sangar l domains that are supported by dense information have been upgraded to Measured Mineral Resources. The upgrade is based on the resolution of various issues highlighted in previous resource estimates. These included:
- Apparent high iron grades;
- Anomalies in QAQC sampling; and
- Dealing with wet samples while drilling
Iron is a contaminant to the beneficiation process. The dominant cause of high iron results in previous assaying has been identified as the use of steel pulverising equipment to prepare samples for assay. The very hard spodumene material was causing accelerated wear to the equipment. This resulted in elevated iron grades. In this campaign, tungsten carbide bowls are used and result in lower iron contamination.
QAQC reference standards used in previous drilling campaigns were determined to be inappropriately selected for the sample digestion method used (sodium peroxide fusion). The certificates for these QAQC samples do not quote a reference grade for sodium peroxide fusion (this was due to the provider not having completed sufficient test work to establish a statistically meaningful expected value), and analysis of the QAQC results appeared to show a positive sample bias. The uncertified reference standards are useful in showing that the variation from the sample mean does not in general exceed 3 standard deviations and that there was no apparent assay drift in the 2017/2018 drilling campaign. In this campaign reference standards have been supplied by a different supplier and they are fit for purpose.
Additional compressor and booster capacity has been used in the 2019/2020 drilling campaign to assist with keeping samples dry. In some places where drilling intersects aquifers, lower lithium grades are most likely caused by chemical dissolution or degradation of the spodumene.
There remains significant potential to further increase resources at Goulamina in the Danaya, and at depth in the Sangar zones.
The areas of highest potential for additional Indicated Mineral Resources are North and south of the Indicated mineral resources identified in the Danaya domain. A program of drilling to infill current drilling is expected to provide sufficient data to report a large increase in Indicated Resources. Timing of any further drilling is dependent on the results of the DFS.