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Subsurface geology and hydrothermal alteration of Cachaços-Lombadas sector, Ribeira Grande geothermal field, São Miguel island, Azores

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dc.contributor Jarðhitaskóli Háskóla Sameinuðu þjóðanna is
dc.contributor.author Franco, António is
dc.date.accessioned 2016-10-06T09:12:07Z
dc.date.available 2016-10-06T09:12:07Z
dc.date.issued 2016
dc.identifier.issn 1670-7427
dc.identifier.uri http://hdl.handle.net/10802/11656
dc.description Í: Geothermal training in Iceland 2015, bls. 113-160 is
dc.description.abstract The present report focuses on the high temperature geothermal area of CachaçosLombadas in the 245°C two-phase liquid dominated Ribeira Grande geothermal system in São Miguel Island. Subsurface geology and hydrothermal alteration are studied, using data from four of the eight existing wells. Emphasis is laid on the determination of the lithostratigraphy and identification of possible correlations between the geological units and the permeability encountered in the wells, including the analysis of tectonic structures inferred in the area. The present work reveals that pyroclastic rocks dominate the upper part of the subsurface geology, locally interrupted by trachyte lava flows and, at deeper levels, basalt lavas are the predominant lithological unit. Furthermore, the results show that north-northwestern trending structures probably play a very important role in the distribution of permeability in the Cachaços-Lombadas area. is
dc.description.abstract Temperature distribution in the area was also investigated and the results are consistent with the main conclusions from previous studies, showing a clear boundary of the geothermal system in the southern part of the area and suggesting that the location of the upflow zone of the geothermal system is likely to be in the east to northeastern parts of the Cachaços-Lombadas area. The alteration mineralogy allowed determining the alteration zoning pattern in the Cachaços-Lombadas area, identifying two zones of hydrothermal alteration, smectite zone and chlorite zone, beneath a shallow zone of relatively unaltered rocks. The hydrothermal alteration investigations were complemented with the study of fluid inclusions, allowing determination of the thermal history of the geothermal system. The results reveal that the geothermal system was hotter at some point in the past. However, since cooling has occurred, the system has been in equilibrium, with evidence of some fluctuations of the fluid levels within the geothermal reservoir. is
dc.format.extent 48 bls. is
dc.language.iso en
dc.publisher United Nations University is
dc.publisher Orkustofnun is
dc.relation.ispartofseries United Nations University., UNU Geothermal Training Programme, Iceland. Report ; 2015 : 10
dc.relation.uri http://os.is/gogn/unu-gtp-report/UNU-GTP-2015-10.pdf
dc.subject Jarðhiti is
dc.subject Ummyndun is
dc.subject Asoreyjar is
dc.title Subsurface geology and hydrothermal alteration of Cachaços-Lombadas sector, Ribeira Grande geothermal field, São Miguel island, Azores en
dc.title.alternative Geothermal training in Iceland en
dc.type Tímaritsgrein is
dc.identifier.gegnir 991007547649706886


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