Por: Aldo Bendezú Juárez, Maskhay Consultores y Cesar Cabellos Roncal, West Mountain Company.

Abstract

Exploration for lithocaps is vectorized by identifying their mineralogical, geophysical and geochemical features plus key elements of regional-scale structures related genetically to them.

Lithocaps from the Miocene metallogenic belt, in the southwestern Ayacucho region, are mined by Au+/-Ag and they display mineral occurrences or high metal anomalies. In this region is recognized a main family of structures oriented ESE-WNW.

A group of these structures outline a narrow corridor (<10 km) with ~180 km length. Inside the corridor, structures are arranged in right-stepping en echelon segments, which have few tens of kilometers length. These segments “link” extensive lithocaps (<30 km2) hosting advanced argillic alteration bodies and marginal pollymetalic veins. The advanced argillic alteration bodies are characterized by displaying silica, alunite natroalunite, dickite, pyrophyllite, and APS group minerals.

The bodies have a strong structural control, systematic orientations and they are analog among them. Angular relationship (20°-40°) between orientation of the main family of structures and main maximum stress indicates that structures were oriented optimally favorable for a sinistral faulting. Orientations of advanced argillic alteration bodies are consistent with this movement.

Those characteristics, as well as spatial and angular relationships suggest structures ESE-WNW controlled the formation of lithocaps into local areas of transpression under a strike-slip regime.