Indonesia-focused gold explorer Sihayo Gold has unveiled some compelling drill hits, including a standout strike of 11.1m going 7.49 g/t, inside a larger 31.5m hit at 4.29 g/t from 259m in North Sumatra.
The results form part of a seven-hole, 2216m diamond drilling campaign designed to test below and south of the company’s planned Sihayo open-pit mine where the company says the operation’s deeper-lying mineralisation remains open.
Other notable intercepts include 10.0 m at 7.90 g/t gold from 262m, 11.8 m grading 6.98 g/t from 98.0m and 11.1 m running 3.77 g/t from a depth just shy of 170m.
The company has already defined a 21.4 million tonne resource at its namesake deposit grading 2 g/t gold for 1.4 million ounces.
Notably, the asset takes in three distinct zones of mineralisation, oxide material at the top, fresh gold at the base and a layer of transitional material sandwiched between the two.
The company recently launched a new round of metallurgical test work on the operation’s transitional and fresh material and following an uplift in recoveries, says the ore can now be efficiently processed.
The work indicates the introduction of a caustic pre-leaching solution could push total recoveries at the project to more than 80 per cent up from about 71 per cent.
Sihayo says its new processing play will boost cash flow and extend the project's mineable areas.
The company plans on constructing an ore treatment plant at the project and says the ground’s oxide and transitional material make up about 62.5 per cent of the facility’s estimated feed. The 37.5 per cent balance is anticipated to be derived from Sihayo’s oxide material.
Sihayo’s fresh and transition ore is comprised of pyrite crystals mixed with gold-infused arsenian pyrite that under typical cyanide leaching fosters recoveries of about 20 per cent.
The company says its recent metallurgical program breaks down the arsenian pyrite rims and releases the gold for subsequent processing, fuelling over 80 per cent recoveries.
The new treatment process involves a 12-hour pre-leach with an acidic formulation known as “caustic” followed by a standard 24 hour cycle of cyanide leaching.
Recent work suggests the process could deliver an average oxide gold grade of about 1.57 grams per tonne with an 83.4 per cent recovery rate.
Treating the transition material is projected to return a grade of about 2.3 g/t gold with a recovery of between 80-85 per cent. Whilst using the pre-leach program to beneficiate the Sihayo’s oxide material is estimated to deliver a grade of 2.22 g/t gold with an 80-85 per cent recovery rate.
The results collectively pull together for an average grade of 2 g/t with an 80-85 per cent recovery.
Following the metallurgical program and recent success with the drill bit over deeper-lying parcels of mineralisation the company has ambitions of transforming the project into an underground mining operation and is evaluating the trade-off between open-pit and underground mining.
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By Matt Birney
