Earth Sciences Institute of Orléans
ISTO, UMR 7327,
Univ Orléans, SNRS, BRGM, OSUC, F-45071 Orléans, France
Metallogeny and geo-energies
Metallogeny is a discipline at the interface between geology and economics of mineral raw materials. The notion of deposit depends as much on geological concepts as well as economic factors. From the point of view of academic research, the objective is to describe the mineralized objects, their geological environments, and to understand, at all levels, the geological environments and, at all scales, the key processes of metal concentration formation. The approach is based on the proposal of conceptual models justified by observation, experimentation and modeling.
Axis 1 : Preconcentrations and orthomagmatic deposits: from fusion to deposit
The partitioning of metals between liquid and crystalline phases defines the enrichment processes capable of producing fertile magmas during crustal or mantle melting. Using the experimental approach we also study the processes (e.g. immiscibility, fractional crystallization, outgassing, assimilation of the enclosing rocks) at the origin of (i) the formation of orthomagmatic deposits during the emplacement of magma in the crust, and (ii) the production of magmatic fluids feeding hydrothermal systems feeding high temperature hydrothermal systems. Our research group employs the experimental approach to determine how metal partition coefficients vary as a function of magmatic conditions (e.g., temperature, pressure, redox conditions), and magma composition (including dissolved volatiles and fluid phase, dissolved volatiles and the fluid phase). The sample tested to identify fertile magma sources is done in coordination between field geologists and experimenters, the former proposing the samples to be tested by the latter.
Axis 2 : Hydrothermal mineralization: analysis of metasomatic flows
The characterization of the physico-chemical processes involved in the formation of mineralized hydrothermal systems aims to improve our knowledge of metallogenic systems. The main stages of genesis are identified and simplified according to the complexity of the natural environment and synthesized in a qualitative and/or quantitative conceptual model.
The team proposes to describe the hydrothermal processes which form the mineralized objects by developing approaches taking into account hydrodynamics, deformation and reactivity. Deformation and reactivity produce feedbacks that significantly increase or decrease flows. The results are exploited in numerical models of reactive transport evaluating instantaneous flux quantities and mass balances to test the different feedbacks between alteration, deformation and chemical fluxes. A concrete application of these developments is the construction of deterministic models in support of mineral exploration.
Axis 3 : Regional metallogeny and favorability
The grouping of deposit types in space and time, in relation to the regional geological history, defines metallogenic districts and crises. The evaluation of the influence of geodynamic scale phenomena requires changes in scale. In this part, the emphasis is put on the research of the thermodynamic, kinetic, physical, geodynamic, …, of first order controlling the localization of mineralizations in time and space. The results will be used as a basis to model and propose favorability maps combining the statistical approach (spatial analysis) with the deterministic approach (based on genetic models).
