Source-Transport-Trap Models for Base and Precious Metals in Basins

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Many economic resources such as energy (petroleum & uranium) and metals (lead, zinc, copper & gold) are products of basin-scale fluid flow systems operating over long periods of time and at distinct stages of basin evolution. The potential for sedimentary basins to host economic resources is a function of the environment in which they formed, how they were deformed and how and when fluids migrated and interacted with the rocks over time. Most mineralized basins normally host only one major type of economic deposit, however, the Vazante basin in central Brazil is one of the rare examples that hosts a variety of lead and zinc deposit types and minor gold occurrences. Although it is generally recognized that processes related to sedimentation, diagenesis, deformation, fluid-rock interaction and exhumation are relevant in the formation and preservation of the various types of lead and zinc deposits, there are still important open questions about the processes responsible for the formation of economic concentrations of these metals. This is due in part to the fact that most of the previous research on basins focused only on one major aspect of the entire ore-forming process: either the metal sources, or the fluid composition or fluid flow dynamics, or the depositional mechanisms. My research program will address the unresolved issues by applying a holistic and innovative approach to investigate all aspects of the source, transport and deposition of the metals. In the next five years, my research team will focus on establishing (a) the mechanisms by which zinc and lead are liberated from possible source rocks where they occur in low concentrations; (b) how and when they are transported by hot fluids and (c) what causes the metals to precipitate in economic ore deposits. The Vazante Basin hosts an unusual type of silicate zinc deposit, as well as the typical lead-zinc sulphide deposits formed by hot fluids interacting with sedimentary rocks in the basin. Therefore, it is an ideal setting in which to investigate the mechanisms responsible for the formation of these distinct types of deposits and develop exploration models to be used in similar settings (e.g., Mackenzie Basin in Canada). We would like to test the hypothesis that the source of metals and the nature of the fluids for both types of base metal deposits are similar, but the depositional processes are different, producing the major differences in the mineralogy and composition of the mineralized areas. To attain these objectives, we will integrate robust field and laboratory work, including the state-of-the art techniques, in collaboration with experts from the various fields of geoscience, geochemistry and geophysics. The expected impacts of this research are: (1) Identification of the critical factors that control the formation of large lead and zinc deposits in sedimentary basins, and the establishment of conceptual genetic models and exploration strategies. These findings will lead to the identification of basins that are more likely to host world-class base metal deposits, particularly large silicate zinc deposits which are still rare and poorly understood; (2) Elaboration of innovative approaches integrating various disciplines, and developing new techniques to understand the processes of metal liberation from source rocks, and their transport and deposition (possibly also applicable to environmental studies); (3) Finally, it will allow for the training of highly qualified professionals (1 M.Sc and 3 Ph.D students and undergraduate students) who will learn to acquire and integrate data from various subdisciplines and to develop new methodologies and analytical techniques in a highly collaborative environment, preparing them to work in academia, government and industry.