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At the buried Atlántida deposit (Cu–Au–(Mo)) in the Atacama Desert of Chile, highly saline pockets of fine-grained material 10 cm–3 m in diameter were identified on the alluvial surface using remote sensing and detailed regolith mapping. The median salinity (NaCl dominant) of the saline pockets is 2.2% compared to background alluvial material with a median salinity of 0.01%. Their distribution along mapped fault structures and the highly saline nature of the material suggest they form as an expression of groundwater forced through fractures to the surface during seismic activity. A targeted geochemical survey, oriented parallel to the orientation of the structures (sample spacing 250 m along structural trend) specifically sampling saline pockets on relatively old surfaces, was performed over the deposit. Deionized water extraction of soluble salts and analysis by inductively coupled plasma mass spectrometry revealed strong correlations of increasing salinity and increasing concentrations of porphyry copper pathfinder elements. Elevated responses of Se, Mo, Re and Te normalized to a groundwater volume proxy are present directly over the Atlántida deposit. This suggests the rate of erosion and sedimentation is slow enough in the Atacama Desert to preserve surficial anomalies as saline pockets, formed by periodic seismically induced surface flooding of groundwater along faults extending to surface. Targeted sampling of saline pockets along structural trends using weak leach geochemistry in terrains dominated by transported cover can serve as a routine exploration method for the potential discovery of buried copper porphyries and other styles of mineralization in the Atacama Desert of Chile.

This paper describes saline pockets (10 cm–3 m in diameter) of fine-grained material distributed on alluvial surfaces. These saline pockets are localized along structural trends at the Atlántida buried porphyry-skarn Cu–Au–(Mo) deposit in the Atacama Region of Chile. The distribution and highly saline nature of the material suggest formation by the pooling and evaporation of groundwater forced through fractures to the surface during seismic activity. These saline pockets are a surface expression of the hydrological effects of seismic activity along faults. Saline pockets with similar distribution and characteristics were also identified at three additional alluvium-covered areas, all located in the Antofagasta Region of Chile. Identification and mapping of these saline pockets relies on the ability to identify the continuation of structures through overlying gravels. Regolith mapping using high-resolution drone imagery and digital elevation modelling identified geomorphic markers of faulting which aided mapping the distribution of saline pockets. Saline pockets provide a unique opportunity to sample the direct expression of transported groundwater reaching the surface from depth and provide a prime target medium for mineral exploration through transported gravels.