Plagioclase crystals show various degrees of sericitization
, but some display relict zoning and twinning (Fig.
Hydrothermal alteration of alkali-feldspar and plagioclase commonly results into the formation of quartz and white mica in the form muscovite or paragonite which are collectively termed sericite due to sericitization
(Que and Allen 1996).
A black mineral of the tourmaline group is one of the most common Llallagua species, because sericitization
of feldspars was followed by tourmalinization, and practically all of the original feldspar in the porphyry was replaced by fine-grained tourmaline.
continues into the orebody and K-silica alteration is sometimes developed in association with high grade ore.
Albitization and sericitization
of plagioclase led to the mobilization of Ca whereas elevated concentrations of K and Ba seem to be related to the newly formed hydrothermal K-feldspar.
Within the Central Zone, Main Stage veins are enclosed by broad envelopes of pervasive sericitization
with silicification immediately adjacent to the veins.
The dacite in the lower part of the stock is marked by strong propylitization, sericitization
and pyritization, whereas silicification dominates in the upper levels.
The dikes have undergone extensive hydrothermal alteration, typified by sericitization
, kaolinization and pyritization.