The multistage (4 stages) mineralization has a high proportion of Mn-rich gangue minerals (johansenite and Mn-garnets in exoskarn; alabandite, bustamite, rhodonite, friedelite in veins and replacements; supergene Mn oxides in outcrop). The predominantly calcitic and Mn-carbonate + silicate gangue contains sphalerite, galena, tetrahedrite and a number of Ag-sulfosalts forming “bonanza” shoots (average grade 489 g/t Ag) in the 4th (latest) phase (pyrargyrite, proustite, freibergite, native silver, ucchuchaquite). “Bonanza-Ag” shoots in Mn-rich low- to intermediate sulfidation extensional vein and carbonate replacement system driven by heat from Neogene subvolcanic intrusions.
The presence of silver was known, and mined on a small scale, since the Spanish Vice-Regal period in Peru. In 1960 Buenaventura initiated modern exploration, opened up underground mines, and in 1975 erected the benefication plant.
In late 2000s “Chacua” was the fourth largest silver producer in the world.
Production from 1975 to 2008 was 218 Moz Ag,
2009 reserves were 3,065,275 t @ 1.06% Pb, 2% Zn, 10% Mn, 498 g/t Ag (in the silver zone).
Total endowment 8,984 t Ag.
The deposit is currently exploited by a cluster of several operating underground mines in recently deglaciated alpine country, with a central mill and benefication plant (August 2012).
(Source: Peter Laznicka, August 2012)