Minsur SA is a Peruvian mining company, part of the Breca Group that owns and runs one of the largest underground tin mining operations in the world. Located in San Rafael in the Andes at an altitude between 4500 – 5200 m above sea level, the mine contributed approximately 6% of the total world production of tin in 2015. Roughly 1 million t of ore with an average grade of 2.13% was mined and processed, resulting in 20 kt of tin in concentrate.

The same year, Minsur initiated a number of activities to ensure the future value of its asset, addressing challenges that included declining head grades through depletion of rich parts of the deposit and operating costs.

The ore sorting project

Among these activities was the ore sorting project, started in 2015 in collaboration with Tomra Sorting Mining, with the objective of rejecting low grade material in coarse particle size. By separating sub-economic material before entering the more cost-intensive wet processing, the project addressed the bottleneck at the wet section and aim to improve productivity by increasing the feed grade. An added benefit expected from the project was the longer life of the mine.

Three main factors indicated that sensor-based particle sorting for waste rejection would be effective at the San Rafael mine. First, the high absorption of transmitting X-Rays of tin contained in Cassiterite; second, the structures of Cassiterite which are large enough to be detected by X-Ray Transmission (XRT) technology due to the way its mineralisation occurs; and finally, the significant degree of liberation of sub-economic waste on the particle level that may be subject to sensor-based particle sorting.

In order to assess the feasibility of the project, Tomra conducted metallurgical tests on geological samples from San Rafael, followed by performance test work. The tests showed the deposit of the mine to be especially suited for XRT technology due to the presence of 70 – 80% of uneconomic particles that could be rejected over a wide size range, from 6 – 70 mm.

The project was approved and in view of the economic potential it was fast tracked and completed in 14 months. Tomra and its partner in Peru, which supplied and installed the XRT sorting system, worked closely with Minsur throughout the 6 month ramp up period.

The project delivers positive results

The ore sorting project with the XRT system has delivered financial benefits from the beginning, with Minsur realising payback on its total capital expenditure in 4 months. In 2017, it contributed around 36% of Minsur’s total production with roughly 6000 t of tin.

The project’s impact on the San Rafael operation has contributed in several ways to a reduction in the mine’s capital and operating costs:

• • Added value: the plant converts uneconomic waste material into economic ore, as material below the cut-off for the main plant can be treated with lower operating costs and converted into reserves.
  • Increased capacity in the main plant, from 2950 tpd before implementation to 3200 tpd as a result of the crushing operation.
  • Improvement in the overall recovery in the main plant, from 90.5% – 92.5%. Sensor-based ore sorting rejects particles with very fine mineralised Cassiterite that is too small for detection by the XRT system, resulting in higher grade and size of mineralisation.
  • Extended life of mine: around 24% of the feed to the sensor-based ore sorting plant is contributed by low-grade ore from underground, which in the past would have been excluded for being below cut-off. This increase in reserves can extend the life of the mine.
  • Elimination of liabilities through the treatment and proper disposal of 100% of the stockpile.
  • Decreased tailings disposal, as the sensor-based ore sorting system reduces the amount of waste by increasing the grade in the feed to the plant.

The project has demonstrated the potential of XRT technology and, as a result, Tomra plans to include XRT sensor-based ore sorting as a possible process route in all future projects.

Fonte: Global Mining Review