A summary of the volcanic stratigraphy and the geochronology of magmatism and hydrothermal activity in the Yanacocha Gold District, northern Peru


The Yanacocha Mining District in northern Perú contains the largest and most
productive group of high-sulfidation epithermal gold deposits in the world. Districtscale
geologic mapping coupled with detailed radiometric 40Ar/39Ar geochronology,
geochemistry and petrography, serve as the basis to establish the volcanic history of
the area and analyze the temporal and spatial evolution of volcanism, hydrothermal
alteration, and gold-silver-copper mineralization. Late Cenozoic magmatic activity
in the ~1000 km2 study area that includes Yanacocha spanned from 19.5 to 8.4 Ma
and produced a calc-alkaline rock suite that evolved from andesite to rhyolite. Eight
volcanic sequences are distinguished based on mineralogy, composition, and age.
Rocks older than 15 Ma erupted from pre-Yanacocha volcanic centers outside the
district. Volcanic rocks of the Yanacocha Volcanic Field in the district erupted over
an interval of 6.1 m.y. from 14.5 to 8.4 Ma contemporaneous with magmatichydrothermal
quartz-alunite that is directly associated with the deposition of gold
ore. Alunite ages define several discrete pulses of hydrothermal activity that spanned
5.4 m.y. from 13.6 to 8.2 Ma.
Magmatism and hydrothermal activity progressed from southwest to northeast
through time across the district. Five periods of volcanic activity and seven pulses of
hydrothermal activity have been interpreted from the volcanic stratigraphy and age
data. Volcanism alternated between effusive and explosive stages, whereas magma
compositions evolved temporally from andesite to rhyolite. Effusive eruptions began
at 14.5 Ma with pyroxene-hornblende andesite lavas in the west and ended with
explosive dacite volcanism in the east (San Jose ignimbrite). Magmatism then shifted
to oxidized dacite to rhyolite compositions forming domes and isolated intrusions of
porphyry plugs, and ended in the final explosive eruption of the Negritos rhyolite ignimbrite
at 8.4 Ma. Hydrothermal activity began in the west at 13.6 Ma (Cerro Negro
Oeste) and migrated east to Quilish, Carachugo and Maqui Maqui, and finally
became centered at Cerro Yanacocha until ~8.2 Ma. The 40Ar/39Ar dates demonstrate
that both magmatic and hydrothermal activity were longer and more persistent than
previously hypothesized for Yanacocha.

SKU: 2005-51 Category:

Additional information


Primary Author

Anthony Longo




Deposit Type

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Mining District

Geologic Era

Exploration Method

Geochronological Method