Crusader Resources reports the following update on BFS metallurgical test work at its Borborema gold project. As part of the BFS the company is undertaking an ongoing technical and financial optimisation of the 2.0 Mt/y project. This optimisation work includes detailed metallurgical test work utilising samples originating from eight large diameter (PQ) diamond drill holes which have provided approximately 6 t of sample from 1,200 m of core. The holes are deemed representative of the larger orebody, both along strike and down dip, and reflect the various lithologies present at Borborema. Finalisation of the metallurgical test work and subsequent processing plant flowsheet design is a critical path item for the completion of the BFS for Borborema. Highlights
- Orway Mineral Consultants (OMC) is evaluating comminution flowsheet options. Evaluations suggest the Borborema ore is amenable to single stage SAG milling which will reduce upfront capital expenditure compared to the previous three stage crush / ball mill option
- Recommissioned test work on the Borborema resource has confirmed the validity of a simple crush‐grindcyanidation processing circuit to provide high gold extractions in excess of 90%
- As expected heap leach and flotation options have been further evaluated and have been shown not to be optimal
- Recent test work has identified 80% material tests passing 106μm as the optimum grind size when operating costs and revenue benefits are analysed
- Mineralogical evaluations are continuing to assess the gold deportment and mineralogical associations. Notably the role of mica present in the ore and gold liberation characterisation as a function of mica content and grinding energy input.
An opportunity has been identified in minimising the use of grinding media via optimisation of the grinding circuit. Work is ongoing, with OMC embarking on assessment of operating cost criteria for the comminution circuit options. Options under evaluation are:
- Single stage SAG (lowest capex option) recently shown suited to achieving the nominal 106 μm grind
- A SAG/ball mill flowsheet (SAB)
- A multiple stage crush/ball mill flowsheet, as previously proposed in the PFS
- A hybrid coarse fed ball mill/SAG which includes primary crushing, and open circuit secondary crushing feeding a high ball charge SAG mill.
Work completed indicates the optimal grind size of 80% material passing 106 μm and a leach residence time of 24 hours. The 106 μm grind size provides a positive impact on the project’s NPV over both finer and coarser grinds and residence time considerations. Final grind size selection is expected to be confirmed post the completion of the OMC operating cost criteria determinations.
Ongoing metallurgical testing is focusing on variability testing where some 40 composites along strike and down dip will be subjected to a matrix of gravity‐leaching test work encompassing variables of grind size, cyanidation conditions and Borborema BFS metallurgical testing residence time. Short range variability testing will also be undertaken to populate a geo‐metallurgical model to forecast process recovery. Bulk test work will generate the key design parameters needed to take the BFS forward by providing the basis for capital and operating cost estimation as well as revenue estimates. This data will also ultimately support detailed design of the facility as the project is taken forward to production.
Marcus Engelbrecht, CEO of Crusader said: “The metallurgical test work on the Borborema BFS is progressing well and is delivering some key positives with regard to optimising work‐streams. In particular the results from the OMC review regarding the SAG mill option, as well as the conclusions reached on grind size will have a real and positive impact on capital and operating costs and project economics.”
Borborema is in the Seridó area of the Borborema province in northeast Brazil. It is 100% owned by Crusader and consists of three mining leases covering a total area of 29 km² including freehold title over the main prospect area. Previously mined as a heap leach in the 1980s, Crusader has completed more than 95,000 m of drilling on an orebody which is tabular and mineable as an open pit. Free milling ore with expected gold recoveries of 93%, the project is favoured by its location which has a dry climate and excellent infrastructure (roads, power, water and nearby sophisticated population centres). The Company benefits from a favourable taxation regime, significant existing infrastructure and on‐site facilities and the critically important Environmental Licence (LP) which Crusader received in 2017.
