Occurrence of K-feldspar-bearing hydrothermal breccias in the Bouillante geothermal field (Basse Terre – Guadeloupe)

Abstract

International audienceSurficial indicators of recent to present geothermal activity are present around Bouillante (Guadeloupe, French West Indies). Until lately, most mineralogical parageneses identified in this area were typical of low temperature alteration (< 100°C) with the occurrence of dioctahedral aluminous smectites accompanied by zeolites (heulandite-clinoptilolite) ± calcite ± silica ± kaolinite, as an evidence of the cap rock of the geothermal system. Recently, numerous boulders of highly silicified breccias containing high temperature minerals (> 200°C) have been identified in the Bouillante bay (Anse Marsolle). Their petrographic study revealed several hydrothermal parageneses typical of a multistage alteration process. Stage 1) An early potassic alteration facies typical of a high-temperature geothermal system characterized by K-feldspar/adularia + quartz + pyrite. K-feldspars have been shown to be present both in the clasts (replacement) and cement of these breccias. They are associated with quartz whose textural properties have revealed fracturing associated with boiling. Stage 2) An acid-sulphate advanced argillic alteration facies with the occurrence of jarosite, gypsum ± silica (≥ 150°C) as usually observed in the upper part of epithermal systems worldwide as marker of deeper boiling. Stage 3) An argillic alteration facies (illite/smectite mixed layers ± smectite ± calcite). With temperatures typically ranging from 100 to 200°C, this alteration facies is associated with near neutral fluids of mainly meteoric origin as known in the present geothermal reservoir (pH = 5.4). This alteration is the later one as evidenced by petrographic observations. These results highlight mineral assemblages and mineral textures characteristic of high temperature hydrothermal alteration in epithermal settings. The occurrence of these breccias involved the existence of eruptive events (magmatic/hydrothermal explosion) which ejected this material. Isotopic (oxygen, argon) and geochemical (trace elements) studies are now necessary to clarify the timing of these breccias and the nature and the connection of the original fluids with current geothermal fluid

Petrophysical properties of volcanic rocks and impacts of hydrothermal alteration in the Guadeloupe Archipelago (West Indies)

“…High gypsum and pyrite contents are observed in the most altered areas. All of these elements match with a high-temperature hydrothermal paragenesis developed in an epithermal context (Patrier et al, 2013). Verati et al (2016) also demonstrated that the development of this highly hydrothermalized area is controlled by the intersection of two major normal fault systems N090-N110 and N130-140 ( Fig.…”

Tectono-metamorphic evolution of shallow crustal levels within active volcanic arcs. Insights from the exhumed Basal Complex of Basse-Terre (Guadeloupe, French West Indies)

“…Several authors have focused their petrographic and geochemical studies on fresh volcanic rocks of the southern active volcanic part of the archipelago, and most of the studies have concentrated further south or near La Soufrière volcano or Bouillante geothermal field providing a revision of the ages of the volcanic formations and the lithological contours Dagain, 1981;Blanc, 1983;Boudon et al, 1989;Samper et al, 2007Samper et al, , 2009Patrier et al, 2013;Verati et al, 2014;Ricci et al, 2017). A recent study has shown the evolution of petrophysical properties from fresh to hydrothermalized volcanic rocks in the volcanic island of Guadeloupe archipelago (Navelot et al, 2018).…”

Timing of geothermal activity in an active island-arc volcanic setting: First 40 Ar/ 39 Ar dating from Bouillante geothermal field (Guadeloupe, French West Indies)

“…Breccias have been recognized at the surface in the northern Although this rock appears heterogeneous macroscopically (cement and numerous clasts of different colours), its mineralogy is rather homogeneous (Patrier et al 2013). (1) A high-temperature assemblage (adularia + quartz + pyrite); and (2) later parageneses consistent with advanced argillic alterations (mainly jarosite + smectite + illite + illite-smectite mixed layers).…”

“…part of Bouillante Bay (Patrier et al 2013). All of the breccias are located in a N1708-orientated alteration zone, bounded by the east-west-trending Bouillante Fault and a N508-trending fault.…”

“…These hydrothermal parageneses are affected by supergene alteration. Following the detailed mineralogical investigations of Patrier et al (2013), the development of adularia at the expense of plagioclases, as well as adularia in equilibrium with quartz in the cracks, results from a high-temperature (i.e. 250 -350 8C) hydrothermal event.…”