Programa de conferencias
Structural Controls on Alteration Stages at the Chuquicamata Copper-Molybdenum Deposit, Northern Chile
Jorge SkarmetaGeólogo Estructural @Skarmeta Geological Services SpA
Jorge Skarmeta is a geologist from the Universidad de Chile with a PhD, MSc and DIC from the University of London. He has developed a varied career with dedication to structural, regional and detailed mapping in the Patagonian and Central Andes of Chile, the Southern Andes of Peru, the Cantabrian Mountains, the Pyrenees, the Rocky Mountains, the Basin and Range of northern Mexico and the cratonic shields of Brazil. He has participated and led the development of 3-D structural models of large porphyry copper deposits in northern and central Chile, in the development of GIS and probabilistic systems for the selection of exploration targets and studies and exploration in fractured hydrocarbon deposits. . He has given invited talks in England, Australia, China, Peru, Argentina, Ecuador and Mexico, and numerous courses to companies and universities, related to issues of structural geology, structural control of mineralization, interrelationships between fluids and mineralization and structural models of deposits. . He is currently a consultant on these issues.
Resumen
All existing bench and tunnel vein and fault structural data with identified mineral infill, acquired in Chuquicamata, were georeferenced, digitized, and, according to their mineralogy, assigned to one or more of the major alteration events developed between 35 and 31 Ma. The spatial distribution of the hydrothermal events plotted within the major fault framework indicates these had either a permeable or an impermeable behavior through time. Based on vein orientation a stress analysis was carried out for all alteration events. The analysis indicates that the local principal horizontal stress trajectories are nonlinear and non-coaxial through the alteration events, differing from the previous and following stages, and in the majority of cases do not coincide with the extant east-northeast orientation of the inferred tectonic far-field stress orientation. The differences between the local stress trajectories, away from the far-field stress orientation throughout the evolution of the system, are considered to be related to the dynamic variations experienced by the stress components, such as thermal-magmatic and elastic overburden-related stresses developed during uplift and erosion. The calculated differential stress was contractional during the early alteration stages, decreasing to an isotropic state at the contraction-extension stress reversal that hosted the main hydrothermal mineralization and becomes extensional at the shallow late-hydrothermal stage. The continuous local stress fluctuations led to bulk stress readjustments and cyclical stress-fluid interactions for local fault reactivation, damage zone modification, brecciation, permeability creation/destruction, and fluid focusing, as well as the discharge of hydrothermal fluids throughout the evolution of the system.