Sunstone Metals Ltd (ASX:STM) has delivered wide intersections of up to 1 g/t gold equivalent, paving the way for a maiden mineral resource estimate (MRE) at Brama-Alba discovery within the Bramaderos Gold-Copper Project in Southern Ecuador.
Standout assays include:
- 401.2 metres at 0.58 g/t gold equivalent (0.41 g/t gold and 0.1% copper) from 31.5 metres, including 50 metres at 1.01 g/t gold equivalent (0.83 g/t gold, 0.10% copper) from 102 metres;
- 66 metres at 0.62 gold equivalent (0.45 g/t gold and 0.09% copper) from 254 metres; and
- 72.7 metres at 0.68 g/t gold equivalent (0.55 g/t gold and 0.07% copper) from surface.
Notably, these results provide more firm evidence that the Brama-Alba discovery is large by global standards and contains grades in line with many well-known porphyry projects.
Also, the company has received positive initial metallurgical test-work results, indicating recoveries above 86% for copper and 88% for gold achieved when targeting a saleable concentrate grade of above 20% copper.
Drilling is ongoing with three rigs underpinning expected strong news flow over the remainder of 2022 and targeting a maiden MRE at Brama-Alba in the December quarter
“Very good gold-copper grades”
Sunstone managing director Malcolm Norris said: “We continue to increase the size of the Brama-Alba discovery with wide intersections with very good gold-copper grades from the surface.
"We are also very pleased with the early metallurgical test-work results
“These results further strengthen the outlook for the initial mineral resource estimate this year.
“The gold-equivalent data allows for comparisons to more readily be made with other global porphyry systems where results are often reported as gold equivalent or copper-equivalent.
“Drilling is continuing with two rigs at Brama-Alba and one at Limon.
"The Brama-Alba drilling is filling in any gaps leading to the resource estimate and extending the scale of the system to the southeast and laterally.
“At the Alba end of the system, we are drilling holes that are discovering new areas of mineralisation and we will continue to expand this zone to the west of hole BMDD007.
“At the eastern end of Brama, the deposit is plunging towards a significant magnetic body, which has not yet been drilled.
“This gives us reason to be optimistic of further mineralisation in this area.”
Metallurgical test-work
Early-stage metallurgical test-work completed on a range of mineralisation styles from the Brama-Alba gold-copper porphyry deposit was undertaken by Base Metallurgical Laboratories in Kamloops, British Columbia.
Sighter metallurgical test-work completed on the breccia and diorite lithologies, of the Alba and Brama deposits, yielded encouraging results.
The results indicate that recoveries in excess of 86% for copper and 88% for gold can be achieved with a combined flotation and leach circuit when targeting a saleable concentrate grade of above 20% copper.
Further testing, including alternative reagent and grind size regimes, will focus on improving recovery responses in a flotation-only circuit configuration to determine whether that configuration is feasible.
Additional optimisation testing of the current flotation-leach selection, to further improve recoveries, will also be conducted.
“Outstanding location”
The adjacent Melonal and Playas targets are emerging as highly promising prospects with strong potential to grow the size of Bramaderos. These two targets will be drilled in 2022.
Norris adds: “It is also important to appreciate the outstanding location of Bramaderos, which is a key component to its value.
“The project is located immediately adjacent to the Pan American highway and within a reasonable distance of available hydroelectric power, supporting the economics of potential development opportunities.
“The project is also supported by nearby commercial airports and significant cities (Loja) and the project has strong community support.
“Ecuador sources 88% of its power from hydroelectricity and is ideally placed to participate in the global demand for clean energy sourced metals.”