JOHANNESBURG (miningweekly.com) – Gold developer Dalradian Resources is considering investing in technology to separate high-grade gold from waste at the Curraghinalt project, in Northern Ireland, using ore sorting technology.

The company recently had a bulk sample of 5 t of mineralised material grading 9.52 g/t tested by Outotec, in Germany, and was presented with “very good results”, Dalradian COO Eric Tremblay reported on Monday.

Testing showed that X-ray and laser technology, plus additional screening prior to processing, could reduce the waste material that would be sent to the mill in an operating mine by 35.8%. The grade increased by 54.6% to 14.72 g/t with a gold recovery of 99.3%.

Using only X-ray technology with rougher stage material, waste removal of 50.5% with a gold recovery of 97.8% was achieved. When the laser scavenger step was added, which is used to recover additional mineralised material from the X-ray waste material, total gold recovery increased to 99.3% at the expense of a decrease in total waste removal to 35.8%.

Applying the results of the testing to the Curraghinalt deposit mineral reserve estimate would potentially eliminate about 1.87-million tonnes of waste material prior to processing. Using the base case feasibility cost estimate of $27.8/t for milling, this could result in savings of $52-million, against a revenue loss of about $12.6-million, owing to recovery being reduced by 0.7%.

Dalradian said that further cost savings could be achieved by replacing the cut-and-fill mining previously adopted for dilution control with mechanised long hole mining. 

Using ore sorting also had the potential to decrease the cutoff grade, which would result in more mineable ounces and increase the throughput of the mine.

It is anticipated that ore sorting will be a good fit at Curraghinalt because of the large contrast in density and colour between the high-grade quartz-sulphide veins and the surrounding country rock.

Tremblay said that Dalradian planned to further investigate the use of ore sorting by visiting operations using the technology prior to designing its own ore-sorting infrastructure for inclusion in an updated feasibility study.

Using a gold recovery rate of 94.3%, a December 2016 feasibility study calculated that a mine at Curraghinalt will produce 1.36-million ounces of gold and 380 000 oz of silver over an initial ten-and-a-half years. The operation will produce gold at a rate of 130 000 oz/y in the first ten years, with an average cash cost of $556/oz and an all-in sustaining cash cost of $674/oz.

The study is based on proven and probable reserves of 1.44-million ounces of gold and 660 000 oz of silver, held in 5.24-million tonnes grading 8.54 g/t gold and 3.9 g/t silver. Measured and indicated resources stand at 2.1-million ounces gold contained in 5.61-million tonnes grading 11.61 g/t gold.

The net present value, at a 5% discount rate, is $301-million and the internal rate of return is 24.4%, at an assumed gold price of $1 250/oz.