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Project Topic
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NewOres is a project devoted to the: i) development of new models of ore deposition relevant for the W-Sn (Nb-Ta-Li) mineralisations, and intend to propose of new exploration guides for this type of mineralization, by building a fully comprehensive model for the behaviour of metals during crustal magmatic events, and ii) by understanding the behaviour of these metals at the hydrothermal stage, thanks in particular to by refinement of the in-situ analysis of trace elements especially Nb and Ta in oxides (SnO2, FeWO4) and in fluid trapped as fluid inclusions, and by building a new thermodynamic database for Nb and Ta species. iii) Finally, a major goal is the development of new flow sheets for the processing of low grade and fine-grained ores and tailings, in particular from a major W mine (Panasqueira) from already mined deposits thanks to new intensive flotation devices, the combination with centrifugal gravity separation, and search to develop a new energy saving mineral processing.
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Project Results
(after finalisation)
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A new vision of the W-Sn, Nb-Ta concentration processes for better industrial choices in exploration, exploitation and ore processing: NewOreS is a project devoted to the development of new models of ore deposition relevant to the W-Sn (Nb-Ta-Li) mineralisations, and intends to propose new exploration guides for this type of mineralization, by building i) a fully comprehensive model for the behaviour of metals duringcrustalmagmatic events, 7
Project NewOres
Development of New models for the genesis of Rare Metal (W, Nb, Ta, Li) Ore deposits from the European Variscan Belt and valorization of low grade and fine grained ore and mine tailings
and ii) by understanding the behaviour of these metals at the hydrothermal stage, and the factors controlling metal deposition thanks to a more precise reconstruction of the pressure-temperature evolution. One of the major targets was Panasqueira which represents the largest W deposit in Europe linked to a series of granite intrusions. One of the main goal was the development of exploratory mapping of particular mineral chemistry features aiming at the assessment of possible compositional zonings that may provide clues about the superposition of ore-forming processes (eventually controlled by distinct sources and structures). The results gathered show that: (1) the western and eastern sectors of the mine display contrasting features recognised at different scales and impacting both the metallogenic model for the Panasqueira system and the ongoing short range exploration surveys. On the basis of the relative abundance of various mineral phases (namely, coarse-
grained muscovite, topaz, tourmaline, cassiterite and wolframite), the influence of at least two distinct metal sources may be inferred, both recording a similar geochemical evolution: the early stages of mineral infillings in the western sectors suggest the prevalence of B F(±P)-rich fluids, while in the eastern sectors the fluids involved in these initial stages would have been more enriched in F(±P±B). Accordingly, cassiterite (along with topaz) is much more abundant in the western sectors of the mine, as the exploitation works carried out in the last years have also shown. A third different source of fluids and metals, possibly centred at Vale de Ermida (to the NW), can be glimpsed if differences in the relative abundance of Bi, As, Sb (and Ag) mineral phases are considered. Ore genesis: from field studies and in situ metal analysis in minerals to conceptual and numerical modelling. From province to magmatic body and fault scale, methodology consisted in coupling: i) field studies with systematic analyses of ore mineralogy and relative chronology, as well as trace elements in ore minerals, ii) paleofluid studies with precise reconstruction of pressure-temperature-fluid composition evolution, iv) dating of the main fluid events, fluid flow reconstruction based on mineral textures, followed by mass and heat transfer modelling. The targets are various parts of the Hercynian chain, especially i) NW Massif Central (France) with representative examples of rare-metal enriched granite bodies, and pegmatites mineralized in Sn-W-Li-Nb-Ta deposits (Puy-les-Vignes and St Sylvestre pegmatites) and ii) Iberia (Portugal) with the Argemela granite, and the Panasqueira deposit (Portugal). A mineralogical and numerical modelling approach to interpret the geometry and constrain the fluid circulations (directions, velocity) in the deposit has been applied to Panasqueira. At Argemela, the structural and geophysical constraints have shown that the intrusion is a pipe-like body. The mechanisms of the magmatic-hydrothermal transition have been characterized and illustrate as a rare example of deposition of Mn-rich wolframite deposited from magmatic fluids. A new ore deposit model is set up for Panasqueira deposit. Contrary to most recent interpretations, the deposit appears to be a focus of fluid flow and large convection cells implying metamorphic fluids and little evidence of true magmatic fluids probably mixed and/or buffered quickly by the host rocks. The overall system is linked to a major and deep zone of partial melting and successive magmatic pulses are necessary to explain the huge complexity and duration of the W-Sn (Nb-Ta) ores, in association with exhumation of the belt and subsequent changes in fluid pressure , and the amounts of other brought metals (Cu, Zn). Same conclusions concern French Massif Central. Ore processing and mine tailings: The processing of low grade and fine-grained ores has been attempted for the recovery of copper from tailings from already mined deposits, in particular from Panasqueira, but appears rather difficult due to the ore oxidation after storing in waste piles. Thus, the processing of low grade and fine-grained ores and tailings from Panasqueira wastes has been attempted for the copper by flotation, but Cu exploitation from mine tailings remains difficult. Besides successive upgrading of eluvial Sn ores have been obtained successfully on the Bejanca ores.
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