Abstract
The Atacocha District is located in the eastern Cordillera of Central Peru, 20 km north of Cerro de Pasco. Pb-Zn ores of three mines (Machcdn, Atacocha, and Milpo) have been investigated. On the basis of geometrical criteria four types of ore can be distinguished: (1) strata-bound ore lenses in carbonate rocks (Pucara); (2) discordant bodies (veins or veinlets) of sphalerite/galena/pyrite; (3) irregular bodies in the contact zone of Tertiary intrusions/sedimentary rocks; (4) disseminations of sphalerite, galena, and pyrite in the sandstone of the Goyllarisquizga Group. Formerly, these four types of ore were often considered to be of epigenetic origin and to be related to the Tertiary intrusions. However, some authors discuss a syngenetic origin for the strata-bound ores. Pb isotope analyses carried out on samples of galena from all the four types of ore indicate a common source for the lead. Taking geometric as well as isotopic data into account the Pb of types (2), (3), and (4) originate from type (1) by remobilization processes.
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