The company said the motor control centre (MCC) electrical connections at its flagship project were done, and the plant had been energised. Commissioning started once the MCC work wrapped up.
Additionally, the commissioning of the spirals and shaking table buildings "on water", a crucial element prior to feeding ore, is in process.
W officials said ore would be introduced into the circuit and first concentrate production from the new concentrator plant will come in September.
"The commencement of commissioning of the new concentrator plant is a long-awaited event and is a major step forward," chairman Michael Masterman said, adding that the commissioning will ensure a streamlined start-up of the mine's ramping up of production.
"The crusher and jig and mill plants are operations ready, and we have maintained the low-cost nature of this impressive world-class project by ensuring each phase is delivered to the highest standards as we prepare for first concentrate production."
The fully funded La Parrilla open-pit operation, 310km south-west of Madrid, was 100% acquired by W Resources in 2013. The operation has an expected mine life exceeding 11 years.