Fresnillo is the largest primary silver mine in the world and operates an underground Pb-Zn-Ag mine and a concentrator of 8kt/d ore (2,640kt/a). According to Fresnillo, in 2014 the average silver ore grades have continued their natural and expected declines. To offset this, Fresnillo was initially evaluating the expansion of Fresnillo mill from 8kt/d ore to 10kt/d. This assumed the construction of a new 2kt/d concentrator at a capital cost of around US$170 million and was going to be located close to the San Carlos vein. However, this has been postponed until sufficient mine development is attained. In September 2015, Fresnillo instead announced their optimisation programme, at a cost of approximately US$30 million, in order to expand capacity to 9kt/d from 2017 onwards.