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  • Precious metals explorer Tesoro Resources (TSO) has achieved almost 99 per cent gold recovery in metallurgical testwork at the El Zorro project in Chile
  • The company says initial results are largely positive, with samples so far indicating the gold is recoverable through traditional methods
  • Future testwork will examine recoveries at coarser grain sizes to determine the optimal cost-to-recovery ratio
  • Further complex analysis will be undertaken and incorporated into future plans for plant design in scoping and feasibility studies
  • Tesoro Resources is up 5.1 per cent today, with shares trading for 8.3 cents each

Precious metals explorer Tesoro Resources (TSO) has achieved almost 99 per cent gold recovery in metallurgical testwork at the El Zorro project in Chile.

The company says initial results are largely positive, with samples so far indicating the gold is free-milling with strong cyanide leaching characteristics, and could be processed by conventional gravity and carbon-in-leach methods.

A series of tests were completed by ALS Laboratories using 50 kilograms of material from the Ternera deposit to optimise process yields. Results were reviewed and interpreted by Mintrex.

Best test

While the Ternera rock is classified as “very hard” with a Bond Ball Mill work index (BWi) of 20.4-kilowatt-hours per tonne, this is still comparable to a number of other operating mines around the world.

The upside is that it appears the rock can be treated at coarser grind sizes without substantially diminishing recovery rates.

This bodes well for potential milling and energy costs, and future testwork will involve coarser samples again to find the optimal cost-to-recovery ratio.

X-ray diffraction (XRD) and head assay results indicate gold grades of 2.39 grams per tonne and low levels of base metals.

There are only minor traces of deleterious elements and reagent consumers, which means the Ternera ore is favourable for leaching and adsorption.

Gravity recovery testwork was also completed, with indications up to 76 per cent of gold is reporting to the gravity circuit at the finest grind size. When coupled with leaching results, it appears the Ternera gold should be recoverable through a relatively economically viable process.

Next steps

Mintrex has advised further testwork to be undertaken, including further gravity, leaching and grinding work on different high and low-grade ore types.

The results of this complex analysis will be incorporated into future plans for plant design in scoping and feasibility studies.

It’s expected this phase will begin in the back half of 2020.

Tesoro Managing Director Zeff Reeves says the results are promising for the El Zorro mine planning.

“The high gravity and cyanide leach recoveries achieved in this work support the potential for processing of material from Ternera using conventional gravity and CIL processes at a relatively coarse grind size,” he said.

“This work will enable the development of a detailed metallurgical testwork program to fully define the project flowsheet and continue to progress the project toward development,” Zeff continued.

If the high-grade recoveries are sustainable at coarser grain sizes, Tesoro could have a relatively low-cost, high-yield resource on its hands.

Stay tuned for the next episode of El Zorro.

Tesoro Resources is up 5.1 per cent today, with shares trading for 8.3 cents each as at 3:30 pm AEST.

TSO by the numbers
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