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The San Juan mine is located
in the mining district of San Juan de Chorunga of the
Nazca-Ocoña metallogenic gold belt in the southern part
of Peru. Metamorphic, igneous, volcanic and sedimentary
rocks are exposed in this area, ranging from
Precambrian to recent in age.
The stratigraphic column is composed
of metamorphic rocks (Precambrian) and sedimentary and
volcanogenic sedimentary rocks of Mid-Tertiary age. The
Precambrian is represented by metamorphic rocks that are
the basement of the stratigraphic sequence. These have
been upthrust in a horst block and uncovered by the
erosive action of the Ocona River. The upper portion is
represented by volcanic and volcanic-sedimentary rocks
of Mid-Tertiary to Quaternary age. The
veins at the San Juan mine are mesothermal veins which
fill open structures within the granodiorite host and
often are found in the same structure with andesitic
dikes. The gold mineralization is associated with the
presence of quartz and pyrite which fills fractures
ranging in width from 4 meters to microfractures. These
veins have been extensively exploited with mining going
back at least to Incan times and government records
indicating a total of 1.2 million ounces of gold
production to date.
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