Determining the origin of deep halloysite-kaolinite alteration, Cerro la Mina prospect, southern Mexico

The Cerro la Mina prospect, southern Mexico, contains Au-Cu-Mo mineralisation with porphyry-high sulfidation affinities. Prospect geology consists of a breccia pipe that cross-cuts the volcaniclastic stratigraphy. A late kaolin alteration occurring in a breccia pipe is the most obvious alteration turning the rock to a massive light grey-white. This alteration is comprised of an upper quartz + dickite rich zone and a lower halloysite + kaolinite rich zone extending to at least 800 metres below the surface. Mineralization in the quartz-dickite zone consists of pyrite + enargite + galena + sphalerite + barite. In the halloysite-kaolinite zone mineralisation consists of marcasite + pyrite ± sphalerite ± galena ± barite. Halloysite is a kaolinite group mineral traditionally regarded as supergene, however at Cerro la Mina its deep extent and association with sulfides suggest a hypogene origin. The origin of the halloysite was further studied using TerraSpec ASD, XRD, and SEM imaging. With an increased understanding of this deep kaolin alteration the exploration window is widened for the discovery of valuable deposits in the epithermalporphyry environment.