Geothermal resources in Martinique (Lesser Antilles): new insight of geochemical isotopic tools.
Résumé
Geothermal exploration of Martinique Island started in 1967 but was interrupted successively at 3 times. Additional geothermal exploration program was conducted by BRGM, in 2001-2003 and recently in areas known for their geothermal interest: Mount Pelée volcano and Diamant. A complementary exploration is now proceed with new sites of interest such as "Pitons du Carbet" massif after recent dating (Germa et al., 2011). A conceptual model of reservoir was established for Mount Pelée volcano and on the Piton du Carbet massif, but the extension of these greenfield remains unknown. We propose new approach through geochemistry by the integration to the prospection of chemical compositions of river waters adding to hot springs and well waters. Rivers catchment in Lesser Antilles and their hydrothermal impact have been studied in order to quantify and identify the magmatic contribution into the river (Rad et al., 2011). Chemical analyses and new isotopic tools such as Lithium isotopes 7Li/6Li (expressed as δ7Li) are measured in river waters. Among these multi chemical parameters, isotopic in particular (H, Li, C, O, Sr...) the Li isotopic signature appear to be conservative and allows to identify new target with high temperature water-rock interactions or in case of high fractionation, reflecting low temperature water-rock interactions, to avoid an extended zone. These new technique was applied to the Mount Pelée and confirm the pre-existent model established in previous exploration campaign. For Pitons du Carbet massif all the river catchment of the massif have been sampled, first results show a potential western extension of the reservoir, confirm by an important gas leak of hydrothermal origin. For tropical volcanic environment with sharp relief, dense vegetation, and high precipitation, chemical and isotopic analyses, particularly lithium isotopes, in river waters, allow to identify zone of interest. To conclude, river catchment studies dedicate to geothermal exploration, especially in a context of difficult topography, seems to be a fast method and good indicator of hydrothermal manifestations at large scale before focusing on detail zones.