Geothermal Exploration on the Island of Montserrat, Caribbean

GRC Transactions, Vol. 36, 2012 Geothermal Exploration on the Island of Montserrat, Caribbean Bastien Poux and Paul Brophy EGS, Inc., Santa Rosa, CA bpoux@envgeo.com Keywords Geothermal Exploration, Montserrat, Caribbean, Antilles, Soufriere Hills, geology, structure, geochemistry, geophysics, magnetotellurics ABSTRACT Montserrat is located in the Caribbean and, as with many of the islands of the Caribbean Lesser Antilles, is volcanic in origin. As a result, many of the islands have a potential for geothermal electrical power generation. EGS, Inc. (EGS) was contracted by the Government of Montserrat to conduct a scoping survey on geothermal activity on the island, and to develop a conceptual resource model based on existing and new exploration data. The exploration work completed by EGS included geologic, geophysical and geochemical surveys; lithologic correlation and structural interpretation constitute the geologic part of the work; the geophysical work included Magnetotelluric, Time-Domain Electromagnetic Induction techniques as well as a microseismicity study. Fluid geochemistry analyses consist of both a set of data from previous surveys and a new set of samples. All the data compiled led to a high probability for the occurrence of a geothermal system in the southwestern portion on the island. Priority areas for exploratory drilling were defined in a zone protected from volcanic hazard and corresponding to the intersection of faults and where a clay cap has been defined by the geophysical survey. 1. Introduction In 2009, EGS Inc (EGS) began a geothermal exploration program on the island of Montserrat in the Caribbean. The program was funded by the Government of Montserrat with the overall goal of assessing the economic feasibility of generating electrical power from the islands geothermal resources. Montserrat is a volcanic island, as are many of the islands in the Lesser Antilles arc, and has a potential for geothermal electrical power generation. (Figure 1) Geothermal exploration projects at various stages of development exist on many of the islands and an operating geothermal power plant with 15 MWe installed capacity is currently operating on Guadeloupe. A major constraint in completing geothermal exploration in Montserrat was the ongoing eruption of the Soufriere Hills volcano which began its current phase in 1995. This phase has included small-to-moderate ash eruptions, lava dome growth and pyroclastic flows that initially forced evacuation of the southern half of the island and then destroyed the capital city of Plymouth. The eruption has had an advese affect on both the island s economy and population and developing a new, environmentally sound source of low cost power is one of the island s major objectives for bringing back population and prosperity to the island. It will also have an important impact on reducing greenhouse gas emission since currently Montserrat burns fossil fuel for its electrical generation, However safety and potential volcanic hazard risks will play a significant role in planning and completing future development of the geothermal resources. The current load for the island is approximately 2MWe although additional load could encourage tourist, commercial development and the repatriation of local inhabitants. Large areas of southern Montserrat were inaccessible to geothermal exploration due to the risks associated with volcanic eruptions. However, and fortuitously the area around St. Georges Hill, Garibaldi Hill and Richmond has been relatively unaffected by ash flow and ash fall impacts. This also was an area of significant known pre eruption hot spring activity. For these reasons this area was considered the most practical place to test for a geothermal system from both a geologic, logistics and safety perspective (Figure 2). 2. Geologic Context 2.1 Regional Setting The island of Montserrat is in the northern section of the Lesser Antilles arc in the eastern Caribbean. It is a volcanic island that includes three major volcanic centers that range in age from Pleistocene to present day. 737

The North American and the Caribbean plates converge in an approximately ENE direction at a known rate of 2 cm/yr (Deng and Sykes, 1995; Dixon et al., 1998; DeMets et al., 2000). This Figure 1. Structural map of the Caribbean (modified after Feuillet et al, 2002). Figure 2. Structural and volcanic setting of Montserrat. motion is absorbed by the subduction of the Atlantic sea floor under the arc (Figure 1). The Lesser Antilles arc was initiated in the early Cretaceous, the oldest active intraoceanic island arc in the world. The main characteristics of the arc are: old subducted oceanic crust, a slow convergence rate, low volcanic production rate, low seismicity level, and a single back-arc spreading phase (Bouysse et al., 1989). The seismicity associated with slab subduction is ranging in depth from 50 to 200 km and dipping at that the clusters of seismicity fit a 50 dip of a typical Benioff zone (Bengoubou-Valerius et al., 2008) 2.2 Geologic Settings of Montserrat Montserrat is built on the south-central part of a submarine bank which is 200 m below sea level, and measures 15 km eastwest by 25 km north-south. The island was formed by successive andesitic eruptive centers ranging in age from the older Silver Hills (2,580 +/- 60 ka and 1,160 +/- 46 ka), Centre Hills (954 +/- 12 and 550 +/- 23 ka) (Harford et al., 2002) in the north to the currently active Soufrière and South Soufrière Hills in the southern half of the island (Figure 2). The summit area of the Soufrière consists primarily of a series of andesitic lava domes emplaced along an ESE-trending zone with block-and-ash flows and surge deposits associated with dome growth predominating on the flanks (Smith, 2007). Two prominent regional fault systems dominate the structural framework of Montserrat (Figure 2): The NNW-SSE striking Basse-Terre Montserrat fault (also known as the Montserrat - Marie Galante fault) is an important regional fault system extending from south of Montserrat to the west of Guadeloupe and deforms the southern sector of Montserrat. The Redonda fault system, named for a small island located a few miles west of Montserrat, strikes WNW but is less distinct than the Basse-Terre Montserrat system and has been mapped in cliff exposures on both east and west coast of Montserrat. 3. Geologic Survey 3.1. Main Elements Two major morphological features dominate the prospect area: Garibaldi Hill and St George s Hill. A review of aerial photography and satellite imagery suggest that a N-S fault separates the two distinctive blocks. Another fault, oriented NNE, cuts Richmond Hill and was also identified in the field in cliff outcrops nearby the Hot Water Pond. Field observations suggest that faulting affecting Garibaldi Hill forms a graben striking approximately N80 W. Exposed pyroclastic units in Richmond Hill are of similar lithology to those at Garibaldi Hill but with different orientation and dip suggesting that the two hills are separated by a N80 W striking extensional fault that dips NE and cuts the North edge of Richmond Hill. In St Georges Hill while exposures are poor, the bench and division of lithologies within the hill suggests that the separation is related to offset on a normal fault that drops the north side of the block down. The NW striking fault planes are consistent with the strike of the major Redonda fault system that passes through the island. 738

Rea (1974) interpreted Garibaldi Hill as a parasitic eruptive center related to Centre Hills and St George s Hill as a late-stage vent of Soufriere Hills that was the source of pyroclastic deposits in Richmond Hill. In contrast, Harford et al. (2002) concluded that instead of being parasitic centers, the volcanic rocks in the hills were distal outflow from one of the major volcanic massifs in the highlands and that the local sequence of volcaniclastic rocks were subsequently uplifted tectonically rather than erupted locally near their source. Based on the character of the eruptive units, there is no geologic evidence for a vent system centered on these hills. St Georges Hill consists mainly of andesitic block-and-ashflow deposits, pumice-and-ashflow deposits and epiclastic deposits. Garibaldi Hill and Richmond Hill are composed of similar pyroclastic and epiclastic sequences. Consequently, the predominant local lithofacies are more characteristics of modern flank environments or flank-slope deposits derived from a lava dome such as at the currently active Soufriere Hill Volcano, rather than deposits that would form around a small vent. 3.2. Hydrothermal Alteration Advanced argillic alteration with deposition of alunite, kaolinite, and other clay minerals affects the rocks cropping out in and nearby the four fumarolic fields. A hard sinter deposit covers the altered lavas throughout the Gages Upper Soufrière, whereas the past existence of a thermal spring in the Tar River Soufrière is testified by abundant blocks of amorphous silica. Several areas of older alteration have been identified in the northern portion of the island, and hydrothermally altered clasts are known to be present in some debris avalanche and block-and-ash pyroclastic flows of the Soufriere Hills. This alteration consists in the formation of clay minerals and phyllosilicates and is an evidence of the persistence of hydrothermal activity throughout the island s evolution (Geotermica Italiana, 1992). 4. Geophysics Geophysical surveys were completed with the Institute of Earth Science and Engineering (IESE) from the University of Auckland, New Zealand. IESE used the combined results obtained from resistivity and microearthquake seismic techniques to assist in the evaluation the geothermal potential of the project area. The main objective of this study was to identify the spatial extent of the important subsurface structures which control fluid flow. For this purpose, a magnetotelluric (MT) coupled with time domain electromagnetics (TDEM) survey were completed, and available microseismic data analyzed and interpreted.the results of a recent tomography survey were also integrated. time varying electrical and magnetic (EM) fields. The electrical fields are measured by two sets of orthogonal non-polarizing electrodes and the magnetic field is measured by induction coils. In this study, MT measurements were acquired at frequencies of 320-0.001hertz (Hz). IESE acquired MT data at 28 sites. The most serious restriction on data acquisition was the inability to access some sites, especially those in the north and east of St George s Hill adjacent to the volcano. 4.1.2 Time Domain Electromagnetic Survey The main purpose of the TDEM survey is to remove the static shift from the MT data interpretation caused by shallow polarization of the electromagnetic field due to local resistivity contrasts. TDEM data were acquired at 22 sites, corresponding to the location of 22 of the MT sites. 4.1.3 Results IESE constructed 2-D resistivity profiles along two lines to evaluate resistivity variations with depth (Figure 3). MT data were corrected for static shifts using the TDEM data. The approximately E-W cross-section (Figure 3a.) extends from the coast at Foxes Bay through St. George s Hill and the Soufrière Hills volcano to White s Yard. This cross-section clearly shows the low resistivity clay cap extending beneath Gages Mtn. The slight doming in this cap seen below St. George s Hill could indicate that this is an area of intense alteration due to steam a) b) 4.1 Electromagnetics Numerous published case histories from geothermal fields worldwide suggest that MT combined with TDEM, can be one of the most effective geophysical techniques to target geothermal wells and assess resource capacity. 4.1.1 Magnetotelluric Survey In the MT method, the resistivities of the rocks are determined from the measurements of orthogonal components of the natural Figure 3. 2-D inversion profiles, a) 2-D profile A, b) 2-D profile B (profile locations shown on Figure 4). 739

condensate from a hot up flow along the NW and NE trending fault zones. Also, a large high resistivity body can be seen below beneath the Gage s mountain at greater depth, this may signify a solidified pluton (old magma chamber). It is also possible that this body is still hot and therefore hosting high temperature geothermal fluids. The relatively low resistivity zone below 4000 mbsl under Garibaldi Hill and St Georges Hill could be a possible semi-molten material body heating up the fluids circulating in the area. The low resistivity body beneathwhite s Yard and the Soufriere Hill Volcano at depths from -3000 to -6000 m is likely to be the andesitic magma feeding the current eruption of the Soufrière Hills Volcano. The second 2-D resistivity cross section (Figure 3b.), oriented SW-NE also confirms the low resistivity clay cap in its north extension on Garibaldi Hill and to the southeastern part of Centre Hill. Also an important high resistivity body is located beneath the Centre Hill, this body is interpreted has a solidified intrusive body, probably responsible for the formation of the Centre Hill volcano. Resistivity maps were constructed to evaluate the spatial distribution of resistivity at different depths (Figure 4). The resistivity map at 1000 mbsl shows a linear low resistivity anomaly in the interest area. The low resistivity anomaly can be attributed to hydrothermal alteration along fluid filled fractures and coincides with the interpreted fault zones. The most significant feature shown in the resistivity map at 4000 mbsl is a low resistivity anomaly that occurs to the southeast of Montserrat associated with the volcano. This deep low resistivity anomaly may be associated with the magma chamber beneath the volcano. The uncertainty of using resistivity to image the geothermal system depends on the reliability of the resistivity imaging and also on how well all the data types are integrated to give a good conceptual model. Resistivity contrasts can be due to numerous geological formations that are not necessarily due to geothermal fluids. 4.2. Microseismicity Study The catalogue of microearthquakes (MEQ) was replotted and showed that most MEQ occur along the interpreted NW and NE trending fault zones with the majority of earthquakes found at depths ranging from 3 to 5km (Figure 5). The deepest earthquakes are found to the northeast and southwest of the volcano. Another cluster of earthquakes is found around the St. George s Hill Area also associated with fault zones and their intersections. The data acquired from the SEA-CALIPSO (Shalev et al., 2010) experiment were used to construct a velocity tomography map (Figure 5) showing distinct low velocity zones (shown in red) and high velocity zones (shown in blue). The SEA-CALIPSO experiment utilised artificial seismic sources generated by a ship-borne airgun and a large array of land and sea deployed seismometers to determine variations in the velocity of seismic waves through the subsurface of Montserrat. Variations in seismic wave velocities can occur due to changes in material type (e.g. altered or unaltered material) or bulk properties (e.g. degree of melting). The Centre Hills area is associated with a velocity and resistivity high. This may mean that the Centre Hills area has massive low permeability body that could be a cooling old magma body. 5. Geochemistry Prior to the onset eruptive activity in 1995, well known fumaroles of Tar River, Gages and Galways soufrieres were Figure 4. MT-TDEM survey resistivity maps, a) resistivity at 1000 mbsl, b) resistivity at 4000 mbsl. (The blue and red lines respectively indicates the location of 2-D profiles A and B). Figure 5. Microearthquake and tomography surveys results. 740

still accessible on the summit slopes of the active Soufriere Hills volcano. Galway s soufriere was the largest fumarolic field comprising several hundred steaming vents (98 C) (Figure 2), mud pots and boiling pools in a 16 hectare (ha) area on the southern flank of the volcano. The Upper and Lower Gages fumaroles field covered approximately 4 ha within a larger intensely altered area on the western volcano slope. The Tar River Soufriere comprised approximately 10 fumarolic vents on the northeastern volcano slope. The fumaroles were buried or destroyed by a sequence of explosive ash eruptions that eventually buried the town of Plymouth on the western coast of the island. The thermal spring feeding the Hot Water Pond, located 1km NW of Plymouth represented the most prominent evidence of an active hydrothermal activity on the island. The Plymouth hot springs consisted of several seepages and pools at approximately 200 m from the coast. Total discharge is close to 5 kg/s, and maximum outlet temperature approaches 90 C. In addition to the above description there are other areas of hydrothermal manifestations that have been reported. Younger (2006) reported the observation of steam plumes rising from the oceanic shallows along the Plymouth shoreline. A hotel spa, called the Montserrat Springs was built on the beach below Richmond Hill, where a bathing pool was fed with hot water obtained from a borehole, now buried under ash. Verbal descriptions of steaming ground in the area, and hot ground on Richmond Hill during foundation construction were also reported All these surface manifestations strongly suggest that a longestablished geothermal system was present in the southern portion of the island before the last volcanic crisis. The presence of thermal springs fed by deep Na-Cl waters coming from a geothermal system (reservoir temperature: 245-250 C) mixed with shallow steam heated waters, and the four fumaroles field, support this conclusion (Principe, 2008). 5.1 Sampling Background 5.1.1 Hot Springs and Fumaroles Most modern geochemistry work on Montserrat (Chiodini and others, 1996; Hammouya and others, 1998; Boudon and others, 1998; Young and others, 1998) has been applied to understanding and monitoring precursors of eruptive events over the past decade. The fumaroles that were the basis of early monitoring efforts are destroyed but the chemistry of their gases provide evidence of continuing magmatic input and strong magmatic heat sources for a viable geothermal system on Montserrat. 5.2 Recent Sampling Accessible springs, water supply wells and monitoring wells in central Montserrat were sampled by EGS and ThermoChem in the summer of 2009 and analyzed for major and trace elements. At least five sample sites were replicates or approximately the same locations as fluid samples collected by Chiodini and others (1996) in 1991 prior to the Soufriere Hills volcano eruption. One of the goals of the geothermal program was to confirm that the 1996 sampling by Chiodini (which was completed in the early part of the 1990 s but published after eruption had commenced) was still representive of the shallow hydrogeology and geochemical characteristics had not changed as a result of the eruption. Gas sampling, completed during the early 1990s, could not be replicated because the fumaroles fields of Galway s Soufriere, Gage s Soufriere and Tar River Soufriere around the summit of Soufriere Hills were obliterated by successive eruptive events. A considerable effort was made to locate additional lowland springs, water supply wells and monitoring wells to establish whether any lowland waters might be related to geothermal outflow but few if any of the samples have any indication that they might have a geothermal component. A sample location map is presented in Figure 6. 5.1.2 Water Wells Keith Consulting drilled in 1967-68 supply wells on Montserrat Island, some within the primary prospect area identified in this study and encountered hot water and sometimes steam at relatively shallow (<100m) depth. Apparently samples were not collected from these wells during earlier geochemical studies and documenting the geochemistry of these wells was a significant part of the recent sampling in this study. Figure 6. Geochemical sampling map. 741

5.3 Analytical Results The analytical results from the sampling of Montserrat springs indicate that good quality representative samples were collected, ion balance differences range from 1 to 7 %.In general, low temperature bicarbonate and higher temperature chloride springs occur in the lowlands near the western coast while high temperature sulfate rich springs were related to fumaroles at higher elevations that were sampled prior to the current volcanic unrest while the springs still existed. a) b) 5.4 Major and Trace Element Geochemistry Samples plotting within or near the Mature Waters portion of the ternary diagram (Figure 7) were designated by Giggenbach (1991) as most representative of equilibrium in a potential geothermal system and are the most relevant samples to assessing the geothermal potential. Therefore, high temperature samples 1 and 2 (the two chloride springs north of Plymouth) sampled by Chiodini et al. (1996) and MHP-1 and STG-55 of the 2009 EGS/TCI survey are the only liquid samples that need be considered. Comparative analyses (Table 1) illustrate that the chloride springs of Montserrat are reworked seawater. Discounting an evaporite origin, the relationship between seawater and the hot chloride spring chemistry requires several processes to evolve the hot springs from seawater: Probable sulfate deposition to remove Mg and SO4. Re-equilibration at higher temperatures and with silica-rich mineralogies to change the Na/K ratio and elevate the SiO2 and B content. Boudon and others (1998) document silica polymorphs as the predominant hydrothermal alteration product in most of the Montserrat rocks. Possible dilution with a steam-heated water to produce the lower ph and elevated HCO3 and B contents. Dolomitization as seawater passes through carbonates to account for the large addition of Ca to the hot springs. Note that sample STG-55 taken from a water well is more likely to have been diluted with shallow meteoric waters. Analyses of replicate samples collected from springs sampled before the 1996 eruptions show little evidence of any impact from the destructive volcanic events that affected the island. Spring outflow temperatures are relatively unchanged between the two sampling events. Major element chemistry remained within a fairly narrow range for both sample suites and trace elements such as boron that might be linked to increased geothermal input varied little between sampling events. Figure 7. Giggenbach diagrams for selected samples, a) Ternary Cl-HCO 3 - SO 4 plot, b) Ternary Na-K-Mg plot. Table 1. Selected water sample analyses results. Series ID Sample T ( C) ph Na K Ca Mg SiO2 B Cl SO4 HCO3 EGS/TCI MHP-1 59 5.57 7233 1001 1944 247 259 22 16340 222 161 EGS/TCI STG-55 38 7.33 396 35 52 24 91 0 553 100 292 Chiodini 1 90 6.60 7880 1030 2510 302 315 23 18220 161 128 Chiodini 2 48 6.00 6200 458 2070 454 232 19 15000 174 195 Seawater Seawater 10 6.80 10500 390 410 1350 6 5 19000 2700 142 5.5 Light Stable Isotopes Light stable isotopes of oxygen ( 18 O) and hydrogen (deuterium or D) suggest the involvement of arc-magmatic type waters in springs and fumaroles. The ratio of helium isotopes 3 He/ 4 He in gases relative to the ratio in air (Ra) are often the most direct evidence of magmatic input. Background crustal fluids generally have 3 He/ 4 He ratios less than 0.1 Ra while eruptive centers like mid-ocean ridges have 3 He/ 4 He ranging from 7-9 Ra, mid-ocean hot spots like Hawaii 16.5 Ra, siliceous continental eruptive centers like Yellowstone caldera 8.2-30 Ra and volcanic arcs like Montserrat 6-8 Ra. The measured 3 He/ 4 He ratios on gases from Montserrat fumaroles range from 8.3 Ra at Galway s Soufriere to 5.9 Ra at Gages Lower Soufriere (Chiodini and others, 1996) and water samples from the Plymouth hot springs yield results of 5 Ra (Hammouya and others, 1998). The isotopic results are strong indicators of the long-term magmatic heat source for the potential geothermal system on Montserrat. 742

5.6 Geothermometers The best temperature estimate using silica geothermometry for a potential liquid dominated geothermal system on Montserrat is between 180 and 198 C using the chalcedony estimates but could be as high as 260 C using estimates from Na/K geothermometry. Chalcedony is considered the most reasonable silica-based geothermometer temperature of a potential Montserrat geothermal reservoir. Table 2. Geothermometer temperature estimates for selected water samples (in degrees Celcius). Series ID Sample Chalcedony Conductive Quartz Quartz Max Conductive Steam Loss 6. Geothermal Conceptual Model Na-K-Ca Assessment has focused on the areas where geothermal manifestations exist or were known to exist prior to the onset of the current eruptive phase in 1995 and where reasonable access is available. 6.1 Heat Source The presence of a heat source to drive a geothermal system is not in doubt. Research has indicated that the shallow magmatic system associated with the post-1995 eruptive phase of the Soufriere Hills volcano is generally confined to the area directly beneath the present dome occupying English Crater. Whether a larger active magma chamber occurs only under the dome conduit, or also in the shallow crust on the flanks of the volcanic edifice, is not known nor is a more limited magmatic system suggested in any of the literature. 6.2 Structure / Permeability One of the primary requirements for a geothermal system to be developable is the presence of permeability (or porosity) within the reservoir rocks. EGS has identified a number of potential fracture targets in the area from various data sources, including remote sensing data, aerial photography and surface geologic mapping. Na-K-Ca Mg Corr Na/K (Giggenbach) K/Mg (Giggenbach) EGS/TCI MHP-1 180 199 183 229 132 260 153 EGS/TCI STG-55 105 132 129 180 40 223 87 Chiodini 1 198 215 195 225 131 255 151 Chiodini 2 171 191 177 187 73 209 118 The geothermal potential in this area is probably controlled by NW and SE trending fault zones. However, it is not clear which structure is more permeable. 6.4 Geochemistry The analytical results from the sampling effort confirm the earlier analyses of Chiodini and others (1996) that identified the high chloride springs north of Plymouth on the island s west coast as potential outflow from an active geothermal system on Montserrat. The high chloride hot springs near Plymouth on the western seacoast appear to represent a connection to a young partially-equilibrated geothermal system with benign chemistry. A geothermal brine on Montserrat is likely to be the result of convecting seawater through hot silicic rocks, precipitating sulfates (MgSO4) and dissolving or exchanging Mg with carbonates. The stable isotope model of mixing with andesitic waters is the single best evidence of a mature geothermal system at depth The best temperature estimate using silica geothermometry for a potential liquid dominated geothermal system on Montserrat is between 180 and 200 C. 6.5 Recommendations for Drilling The proposed drilling targets are projected in a fractured fault zone at the boundary of the deep high and low resistivity contrasts (Figure 8). The exploratory well should be designed to test the presence of the geothermal system below the inferred clay cap. This will require drilling to a depth of at least 1000-2000 m in order to get beneath the clay cap. The primary drilling area is outlined in Figure 8. Two potential targets in this area would be the two fault intersections. 6.3 Geophysics The interpreted results of combined geophysical studies suggest the possibility that a viable geothermal resource exists in the area of interest at depths between 800 and 1200 m based on the interpreted depth of a low resistivity clay cap confining the potential system. Lateral flow is largely controlled by the volcanic stratigraphy, in particular at the contacts between different eruptive units, but fluids ascend vertically through interconnected fracture channels that are most abundant within fault zones. Figure 8. Summary map showing priority drilling areas. 743

7. Summary and Conclusion The primary conclusions reached during this geothermal assessment on the island of Montserrat indicates a high probability of a geothermal system existing in the southwestern portion of the island. Structural geology, geophysical surveys and geochemical sampling and analysis completed in the study area permitted establishment of a conceptual model of the geothermal resource beneath the southwestern part of Montserrat. The main elements controlling the resource appear to be the major faults acting as permeability pathways and controlling the fluid flow and a possible clay cap identified by the MT survey. The temperature of the resource, estimated to be between 180 and 200 C from the analysis of the fluid samples, using geothermometry is in the range of economic and technically suitable temperature for electricity generation. The drilling of a confirmation well will be the next step to move forward to the eventual development of the resource, and will give critical information about the overall capacity of the reservoir to sustain a power generation facility. The most practical surface site capable of development is between St Georges Hill and Garibaldi Hill, this area is accessible and safe in light of the present eruptive activity of the Soufriere Hills volcano. It is recommended to complete test drilling to demonstrate the presence of the system. Future production well should initially be vertical with possibility of sidetracking if necessary, to a recommended estimated depth of up to 2,000 m. References Bengoubou-Valerius, M., Bazin, S., Bertil, D., Beauducel, F., and Bosson, A., 2008. CDSA: A new Seismological Data Center for the French Lesser Antilles, in Seismological Research Letters, v. 79, n. 1, p. 90-102. Boudon, G., B.Villemant, JC.Komorowski, P.Ildefonse and M.P.Semet, 1998. The hydrothermal system at Soufriere Hills volcano, Montserrat (West Indies): Characterization and role in the on-going eruption. Geophysical Research Letters. Vol. 25, No. 19, pages 3693-3696, October 1, 1998. Bouysse, P., Westercamp, D., and Andreieff, P., The Lesser Antilles island arc, in Proceedings of the Ocean Drilling Program, Scientific Results, v.110, p. 29-44. Chiodini, G., Cioni, R., Frullani, A., Guidi, M., Marini, L., Prati, F. and Raco, B., 1996. Fluid geochemistry of Montserrat Island, West Indies, in Bulletin of Volcanology, v. 58, p. 380-392. Deng, J., and L. R. Sykes, 1995. Determination of Euler pole for contemporary relative motion of Caribbean and North American plates using slip vectors of interplate earthquakes, in Tectonics, v. 14, p. 39 53. EGS, Inc., 2010. Final Report, Geothermal Exploration in Montserrat, Caribbean. 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Pre-and syn-eruptive geochemistry of volcanic gases from Soufriere Hills of Montserrat, West Indies. Geophysical Research Letters, 25, 19, 3685-3688. Harford, C.L., Pringle, M.S., Sparks, R.S.J. and Young, 2002. The volcanic evolution of Montserrat using 40 Ar/ 39 Ar geochronology, in: DRUITT, T.H., & KOKELAAR, B.P. (eds) The Eruption of Soufriere Hills Volcano, Montserrat, from 1995 to 1999.Geological Society, London, Memoirs; v. 21, p. 93-113. Harford, C.L., 2000. The volcanic Evolution of Montserrat. PhD thesis, University of Bristol. Keith Consulting, 1968. Logs of Test Holes, p. 119. Principe, C., 2008. Geothermal potential in Montserrat, scoping survey report. Istituto di Geoscienze e Georisorse, CNG, Pisa, Italy, 24 p. Rea, W.J., 1974. The volcanic geology and petrology of Montserrat, West Indies, in Journal of the Geological Society, v. 130, p. 341-366. Shalev, E., Kenedi, C.L., Malin, P., Voight, V., Miller, V., Hidayat, D., Sparks, R.S.J., Minshull, T., Paulatto, M., Brown, L., Mattioli, G., 2010. Three-dimensional seismic velocity tomography of Montserrat from the SEA-CALIPSO offshore/onshore experiment. Geophysical Research Letters, Vol. 37, 6p. Younger, S.R., 2006. Preliminary assessment of the technical feasibility and likely costs of the development of geothermal power generation on the island of Montserrat, East Caribbean, Report to Montserrat Utilities Ltd. University of Newcastle and Institute for Research on Environment & Sustainability internal report, p. 37. 744