Genesis of the exotic chrysocolla — “copper pitch/wad” — atacamite/brochantite ore at the Exótica (Mina Sur) deposit, Chuquicamata, Chile

Abstract Detailed mineralogical and textural studies, combined with sequential X-ray diffraction geochemical modeling, helped to solve the “copper pitch/wad” enigma in Exótica deposit located downstream of Chuquicamata porphyry copper deposit. Copper pitch wad are essentially chrysocolla co-precipitated Mn oxides, mainly birnessite, as well pseudo-amorphous oxide/oxyhydroxides. Linking mineralogical, geochemical, evidences geological, tectonic, climatic evolution Chuquicamata–Calama area, a four-step genetic model for is presented: (A) formation mature supergene enrichment profile at (~ 30–25 Ma ~ 15 Ma) during an erosion-dominated regime (?900 m erosion) which was accompanied by acidic (pH ?2–4) Cu-Mn-Si-dominated rock drainage (ARD) fluid flow southwards through valley towards Calama Basin, resulting strongly kaolinized chrysocolla/copper wad-impregnated bedrock deposit; (B) deposition Fortuna gravels (starting ?19 intercepted ARD, triggering main chrysocolla, pitch/wad mineralization syn-sedimentary chiefly surficial altered gravels; (C) tectonic freezing onset hyper-aridity (?15–11 exposed enriched chalcocite blanket oxidation, 2–4) Cu-Si-dominated solutions less Mn. These percolated slightly more reducing groundwater path mineralized relatively unaltered pure chrysocolla; (D) ingression confined chloride-rich upper oxidation zone Chuquicamata, most likely between 6 3 Ma, responsible atacamite/brochantite 5.5–7) northern central part