AVZ Minerals Ltd (ASX:AVZ) has started pit floor drilling at Manono Lithium and Tin Project in the Democratic Republic of Congo with the aim of upgrading inferred resources to the indicated category.
The company will drill 10 new geological resource holes for 1,700 metres of diamond drilling at the Roche Dure pit in the next four weeks.
AVZ is also updating the mine plan, conducting geotechnical and hydrogeological investigations, as well as optimising the tailings storage facility (TSF).
Potential upgrade
Previous drilling at the pit defined more than 400 million tonnes of potential ore at an average grade of 1.65% lithium but the material immediately below the then water-filled open pit could not be accessed physically and, therefore, remained at an inferred resource category.
This means the pit floor rock could not be considered as mineable ore in the existing mine plan.
It is expected that some of the pegmatite may be upgraded to an indicated resource/probable reserve status by drilling this previously inaccessible area.
The updated geological resource is not expected to increase overall resource tonnes but the current combined indicated and measured resource tonnage is expected to increase.
Assay results are expected in November pending the drilling being completed by the end of October.
Updating the mine plan
Once the ‘wedge’ material directly under the pit floor is drilled and assay results returned, it is expected that some of this previously classified waste rock may then report as mineable ore.
This new data will allow the existing mine design to be re-run and optimised with the main advantage being that two years of potential pre-stripping will be avoided and the payback period for financing will be positively impacted pro-rata.
The re-run of the mine design, following the upgrade of the geological resource estimate towards the end of the year, will also allow for plant design optimisation studies to also be completed and incorporated into the new modelling.
A new ore reserves estimate and financial model will be generated based on the revised mine design, which is expected to be published towards the end of December 2020.
Test pits (green) and drill holes (pink) superimposed on the plant design.
Plant site geotechnical program
The company is planning a plant site geotechnical investigation program and the siting of 38 new test pits and nine geotechnical boreholes under significant weight-bearing locations.
PQ sized diamond core from the nine holes will be sent to a specialist geotechnical laboratory in Johannesburg for an array of specialist load-bearing strength tests and the data will allow for detailed planning of the future earthworks program for construction of the new plant site.
Tailings storage facility
AVZ has made the technical decision to optimise the storage of future mine tailings by placing them inside the waste rock dump to the west of the Roche Dure open pit.
The advantages of this Integrated Waste Landform (IWL) design include minimising land disturbance by storing the tailings inside a rock barrier, increased stability of the overall TSF, substantial savings on dam wall construction and ease of future rehabilitation.
Additionally, five locations within the IWL footprint have been selected for geotechnical drilling to be conducted, to examine the underlying soil and rock properties of the proposed site as part of the overall plant site geotechnical investigation.
Hydrogeological model field program
A specific hydrogeological investigation of Roche Dure is being undertaken following a regional appraisal of the hydrology of the site.
Water table monitoring piezometers will be installed around the perimeter of the pit to determine and model the various parameters of the free-standing water table, including potential recharge of the water table and how it may be affected by the deepening of the open pit.
This data may be used in the mine planning optimisation and the final hydrogeological model will then be included in the Manono Environmental and Social Impact Assessment report which will accompany the application for the Manono mining permit.
The company anticipates the field component of the phase two work program will be completed within the next two months.