Summary of geothermal setting in Geo-Caraïbes target islands Dr Simon R Young Consultant to OAS Presentation made at the Guadeloupe workshop, 27 April 2004
St Lucia - overview Only one broad target area - Soufrière valley, or Qualibou Depression Surface manifestations include hot springs and fumaroles and diverse warm springs Now identify major volcanic collapse and debris avalanche scar filled with more recent deposits (pyroclastics and lava domes) as main feature Area is topographically complex. Sulphur Springs subject of significant investment for improvement of eco-tourist facilities
Soufrière town and Qualibou Depression from the North
Sulphur Springs
3-D rendition of swath bathymetry showing major debris avalanche deposit offshore of Soufrière. From Deplus et al (2001)
St Lucia - exploration history 50s & 60s - General interest and some research 70s - UK-funded project - geology, geophys. & geochem. and drilling of 7 holes to ~700m depth Early 80s - Exploration projects by RGI (US), Aquater (Italy) and LANL (US) Late 80s - Two deep holes (~2km) drilled with UN money; SL1 at Belfond (hot, no perm.), SL2 at Sul. Spr. (hot, acid steam with high non-condensables) Early 90s - GENZL review project Early 00s - MIT run new SP and re-interpret UK res. lines with state-of-the-art inversion techniques
British well #3 at Sulphur Springs
Contrasting views of the geology of the Qualibou Depression; at left from Tomblin (1964) and at right from Wohletz et al (1986)
Deep well SL-2
MIT re-interpretation of British resistivity line #9 (from Morgan et al. (2004)
St Lucia - resource character Much exploration has proven a resource, but reveals challenging chemistry (acid) and permeability issues Sul. Spr. area has been main focus, but environmental and acidity problems would be expensive to overcome New geophysics supports previous interest in Belfond area not too far from SL1 Lack of deep geophysics makes detailed evaluation tough but data is consistent with a resource of many 10s of MW Main challenge is overcoming complex geology to find permeability and better resource chemistry
MIT Selfpotential map for Qualibou. From Vichabian et al. (2004)
Summary of recommended sites or areas for drilling from the various studies undertaken on St Lucia
Dominica - overview Most volcanically active island in eastern Caribbean Four main target areas defined - Boiling Lake, Wotten Waven, Soufrière and Galion, all in south of island Surface manifestations are numerous in all of these target areas, and are especially diverse in WW Geology is complex: Galion is on side of most recent (~500yr) lava dome; Soufrière valley is a collapse scar with surface emanations around the scarp faults WW is associated with?recent phreatic activity and close to Micotrin, source of major Roseau Tuff eruption; and Boiling Lake is global-scale thermal feature
Map of Dominica showing the volcanoes and surface thermal emanations
Morne Patates volcano from Upper Sulphur Springs
Boiling Lake
Dominica - exploration history Some UK work in 70s as part of regional studies Main BRGM (French) studies in early 80s included geophysics, geochem. and some geology Recent geological studies by Alan Smith (UPRM), SRU (as part of hazards study after 98-99 eqs) and French IPGP group - none geothermal-specific SRU has collected useful earthquake data from recent volcano-seismic crises Consensus is that both WW and Soufrière have potential - but exploration to date suggests WW is better initial target
Summary of BRGM gravity and resistivity data for Wotten Waven prospect
Backscatter image detailing one of the debris avalanche deposits off Dominica. From Deplus et al (2001)
Summary of 1998-99 earthquake epicentres and 1974 swarm (orange). Data from Seismic Research Unit.
Dominica - resource character Existing data for WW is very encouraging, but need more geophysics and geology to produce a comprehensive geothermal reservoir model Indications suggest a substantial heat source (possibly shared with Boiling Lake) and fault-related permeability around River Blanc area. Geophysics suggests good general reservoir characteristics Previous resource estimates of many 10s to several 100s MW are not yet substantiated but are consistent with our existing knowledge WW is favourable terrain for exploitation
Map of the Wotten Waven prospect
Boiling pool at Wotten Waven
St Kitts-Nevis overview Both islands have potentially active volcanoes, though Nevis considered less dormant Mt Liamuiga in northern St Kitts probably has long-lived magma source (=heat) region beneath, but surface geothermal manifestations are limited to the crater, Brimstone Hill area and wells around Basseterre (+/- offshore vents) Nevis Peak dominates Nevis and certainly has a magma storage region 5-10km beneath at 700-800ºC Geothermal emanations are diverse, main ones at Farms/Bath Estate & Cades Bay/Estate, other indicators in well water from Belmont area and Saddle Hill. Main surface emanations show structural control
Basseterre, St Kitts from offshore to the south
Farms Estate solfatara on Nevis, with Nevis Peak behind
St Kitts-Nevis exploration Relatively little work done on either island. Surface emanations and associated geology are mapped and sampled but no geophysics On basis of surface indicators and with some comparative information from the region, Farms/Bath Estate on Nevis is best prospect Charlestown fault is major, active structure controlling the emanations. Seismic swarms indicate active hydrothermal field and geochemistry is consistent with reservoir temps of 200-250ºC (taking M rat as a model)
Redevelopment of The Baths with Charlestown Fault scarp behind
St Kitts-Nevis resource character Main challenge is to collect sufficient information (mainly through geophysics) to adequately define the resource Excellent knowledge of the hydrothermal and volcanic system of neighbouring Montserrat will be of great benefit to modelling Nevis Resource estimates of several 10s of MW are consistent with current knowledge Farms Estate area adjacent to the soufrière is an ideal location for exploitation if subsurface resources are located there - flat, industrial and close to current generating facilities
Comparison of surface thermal features and structure on Montserrat (red/orange) and Nevis (blue)
Farms Estate thermal features and industrial area