According to Chilean newspaper Estrategia and wire service Reuters, the US$2 million upgrade and growth plan will increase the mill's capacity to 230,000 tonnes daily from 190,000t/d and give it an additional 21 years of mine life.
KGHM, the sources reported, will be keeping its overall production rate of 55,000t of copper cathodes.
Estrategia said the mine 60km south-west of Calama will comply with authorities on its tailings as well.
Commissioned in July 2014, Sierra Gorda produced 101,700t of copper in 2017. KGHM acquired its 45% interest in the project in 2012; the balance of ownership includes Japanese Sumitomo Metal Mining and Sumitomo Corporation.