High-grade stratiform manto hosted by sandy tuff of the lower Pliocene Boleo Formation, with which it is in part syngenetic. Ore deposition occurred in a shallow marine basin. Mineralized fractures and hydrothermal alteration observed in the vicinity of the proposed source area suggest that the ore solutions originated from hot springs. Two types of alteration are related to mineralization: (1) destruction of mafic silicate minerals in volcanic rocks, and (2) argillization of glassy groundmass material.--Modified journal abstract.

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