Por: Brayan Vilcanqui, Fernando Guevara, Milene Escarcena y Rosa Cornejo, Escuela Profesional de Ingeniería Geológica, Universidad Nacional del Altiplano, y Raúl Montesinos, Colorado School of Mines.

Trabajo con Mención Especial en formato póster del II Concurso Internacional de Estudiantes SEG-SGA-IIMP.

Abstract

Ajaruni is an Ag-Pb-Zn intermediate sulfidation epithermal deposit located in southern Peru. The main mineralization is distributed in veins and hydrothermal breccias hosted by andesitic rocks. 

This study involved geological mapping, petromineragraphy, and geochemical and short-wave infrared (SWIR) analyses to characterize geological units, mineral paragenesis, and hydrothermal alteration patterns. 

The paragenesis is defined by four stages: I) low-temperature chlorite-carbonates and quartz, II) barite-hematite, III) pyrite-chalcopyrite, sphalerite-galena, argentite, and Ag sulfosalts, along with white micas, and IV) amethyst quartz and carbonates. 

The SWIR analysis on the white micas revealed Al-OH absorption peaks (2202-2220 nm), with a crystallinity index (CI) ranging from 0.28 to 4.7, which correlates with the mineralized zones. Multielement analyses showed Ag grades exceeding 100 ppm, Pb and Zn >1%, and anomalous Cu values (average 1000 ppm). Additionally, a phreatomagmatic breccia with a clast containing a quartz-pyrite veinlets (D-type veinlet) was identified.