Australia’s first stand-alone silver mine for many years, Twin Hills, is a greenfield discovery by Macmin Silver and is estimated to have measured, indicated and inferred reserves of 55Moz of silver equivalent.
The mine, which will be open pit, will supply a heap leach recovery circuit where run of mine ore is crushed in a mobile plant to minus 5mm. It will then be agglomerated with cement, then subjected to a cyanide heap leach process with electrowinning to produce a silver powder containing 98.5% silver.
Macmin has ordered an EMEW powder metal electrowinning plant from Electrometals Technologies that should produce high purity silver metal powder, precipitated from the leach solutions.
With three modules, each 60 cells, the plant is expected to produce to the initial production, expected to be 2.5Moz annually, compared with the nominal plant capacity of 3.5Moz.
Production cost is believed to be about $5.80/oz.
Current silver prices are roughly $10/oz so Macmin is nominating a revenue stream of about $40m in the first three years.
The Twin Hills mine site is on former farming freehold land acquired by the company and is part of a 300km2 area of exploration licences in the Texas district.
The pit is expected to be mined to 100m total depth, although the mineralisation continues beneath the optimum pit design and is open to the east.
Macmin is proposing a 45-member mining team and will benefit from the town of Texas, with a population of about 1000, being only 7km from the mine site.
The forecast for the plant is 94% recovery with a relatively high silver recovery obtained by the heap leach process in a matter of weeks, although the ores will remain on the pad for leaching for a longer time.
Even the low grade waste and under-mine-grade material will be subjected to a long term leaching program.
A 30t leaching trial is already underway on the site to prove up the silver recovery plan.
Macmin executive chair Bob McNeil said Twin Hills has a likely nine-year mine life although the company has designated about 12 more prospects in the surrounding region that have a high potassium signature obtained from radiometric surveys.
As the deposits rarely outcrop or have gossans, potassium is regarded as the signature element.
Macmin also holds the original Silver Spur deposit at Texas, which between 1898-1920 was an important silver producer. It also has the nearby Tuliambi prospect that has returned promising intersections.