ALUNITE TYPES (K-KNa) IDENTIFIED THROUGH AISIRIS THEIR ABUNDANCE AND SPATIAL DISTRIBUTION IN THE TANTAHUATAY Au-Ag DEPOSIT CAJAMARCA-PERU

The epithermal deposit of Au-Ag located in the NW of Peru in a volcanic complex of pyroclastic flows and andesitic lavas presents halos of hydrothermal alteration. This summary focuses on advanced argillic alteration. Terraspec samples were taken throughout the lithocap of the deposit, and the AI aiSiris was used to define and quantify the types of alunite, resulting in the following abundant types: Alunite-K, Alunite-KNa, Alunite-NaK, Alunite-Na, and Alunite-Ca, with the first two determining the hydrothermal alteration and having some control over the economic mineralization in the deposit. They are also spatially distributed according to their stability and temperature, as Alunite-K is shallower than Alunite-KNa and the other types restricted to smaller lithological units.

In the transitional zone below the 3800m elevation there is an alunite-KNa assemblage with pyrophyllite, an assemblage that dominates another part of the deposit and in contact with the stockwork zone that also has implications for the mineralization of sulfides (Cu-arsenical) and Gold. The hydrothermal breccias present a silicification alteration but with alunite content, including Alunite-NaK and Na.

The Au-Ag deposit is variable in mineralization and is not restricted to being controlled by hydrothermal alteration, but also to lithological and structural control. Moreover, in the transition zone to the porphyritic system, the alteration is much more diverse and variable, identifying prograde zones of alteration.