In 2014, thyssenkrupp Industrial Solutions in Atlanta received an order to supply a POLYCOM® HPGR for the Soledad Mountain gold-silver project. The machine features studded rolls with dimensions of 1.7 m x 1.2 m and is equipped with two variable speed drives. The Soledad Mountain project, operated by Golden Queen Mining Company, is located outside the town of Mojave in Kern County in southern California, US. This application follows the successful operation of a similar installation at the Goldfields Ghana Tarkwa mine, supplied by thyssenkrupp in 2008.

The POLYCOM, which prepares feed for the heap-leach operation, is one of the highlights of the Soledad Mountain project. Comparative tests in the project phase indicated that the HPGR ensures the most favorable particle size distribution for a stable and successful heap-leach operation, allowing for increased minerals recovery, at a faster extraction rate. The metal recovery is enhanced, in part, by micro-cracks in the POLYCOM product, which occurs as a result of high-pressure inter-particle breakage, the inherent grinding mechanism in this machine.

Commissioning was successfully completed late in 2015. During the commissioning period thyssenkrupp trained the plant staff to operate and maintain the unit. As of the end of July 2016, the machine has treated more than 1.26 Mt of gold and silver bearing ore. Golden Queen Mining reports that POLYCOM HPGR exceeds their expectations and operates steadily at the design capacity and delivers consistent product fineness of 70-75% -6 mm, a key requirement for producing high quality agglomerates for optimised porosity and permeability in the leach pad.

thyssenkrupp Industrial Solutions states that it is the global minerals market leader for the High Pressure Grinding Rolls (HPGR) technology. “Since 1985, POLYCOM® HPGRs have been at the forefront of this transformational technology with successful installations and excellent operating results in various ore types and flowsheets positions.”