With the increase of stope height due to increasing mechanization in the years 60 to 90, more waste were produced for the same amount of ore (dilution) resulting in higher amounts of low grade ore reaching the plant. It was necessary to replace the pre-concentration done by manual selection (handpicking) and jigging, with a more efficient method and with greater capacity to deal with the greater volume of ore plus waste that reached the plant. In 1971 a Heavy Medium separation (HMS) was installed which carries out pre-concentration in a very effective way and with minimal losses. Due to improvement in the mine stopping method and greater need for fragmentation for the medium separation, a fines recovery circuit was installed in the 60's which was improved and expanded in the 80s.