UNIVERSITÀ DEGLI STUDI DI URBINO CARLO BO Dipartimento di Scienze Pure ed Applicate (DiSPeA) Corso di Dottorato di Ricerca in Scienze di Base e Applicazioni Curriculum Scienze della Terra - XXXI ciclo Titolo della tesi: SURFACE EXPLORATION AND PETROLOGICAL APPLICATIONS IN HIGH ENTHALPY GEOTHERMAL AREAS: A MULTIDISCIPLINARY APPROACH FOR THE CERRO PABELLÓN PROJECT (NORTHERN CHILE) ESPLORAZIONE DI SUPERFICIE ED APPLICAZIONI PETROLOGICHE IN AREE GEOTERMICHE AD ALTA ENTALPIA: UN APPROCCIO MULTIDISCIPLINARE NELL'AMBITO DEL PROGETTO CERRO PABELLÓN (CILE SETTENTRIONALE) Settore Scientifico Disciplinare SSD: GEO/08 Candidato Marco Taussi Relatore: Co-relatore: Prof. Alberto Renzulli Prof. Diego Morata Anno Accademico: 2017-2018 INDEX CHAPTER 1 - MOTIVATIONS, GENERAL INTRODUCTION AND SUMMARY OF THE THESIS .................. 4 Motivations ......................................................................................................................................... 5 1.1. Geothermal energy: current World situation ........................................................................... 6 1.2. Geothermal exploration in Chile ............................................................................................... 9 1.3. Chilean main geothermal systems ......................................................................................... 10 1.4. Cerro Pabellón geothermal project ........................................................................................ 11 1.5. Summary and structure of the thesis ..................................................................................... 13 1.5.1. Chapter 2 ............................................................................................................... 14 1.5.2. Chapter 3 ............................................................................................................... 15 1.5.3. Chapter 4 ............................................................................................................... 16 1.5.4. Chapter 5 ............................................................................................................... 16 CHAPTER 2 - PETROLOGICAL EVOLUTION OF THE APACHETA-AGUILUCHO VOLCANIC COMPLEX AND CONSTRAINTS FOR THE MAIN HEAT SOURCE............................................................................. 18 2.1. Introduction ............................................................................................................................... 19 2.2. Geological background............................................................................................................ 22 2.2.1 Apacheta-Aguilucho Volcanic Complex and dacitic domes ............................................ 22 2.2.2 Altiplano-Puna Magma Body ..................................................................................... 23 2.3. Sampling and analytical methods .......................................................................................... 23 2.4. Results ....................................................................................................................................... 24 2.4.1 Petrography and mineral assemblages ....................................................................... 24 2.4.1.1 Apacheta-Aguilucho Volcanic Complex lavas ........................................................... 24 2.4.1.2 Domes ................................................................................................................. 25 2.4.1.3 Micro-vesiculated enclaves ..................................................................................... 27 2.4.2 Data on major-trace element and Sr-Nd-Pb isotopes .................................................... 28 2.5. Discussion ................................................................................................................................ 39 2.5.1 The origin of the enclaves ......................................................................................... 39 2.5.2 Depth of interaction between andesitic and dacitic magmas .......................................... 40 2.5.3 Petrological model for evolution of lavas and domes of the Apacheta-Aguilucho Volcanic Complex area .................................................................................................................. 42 2.5.4 The youngest dacitic domes in the framework of the Altiplano-Puna Volcanic Complex .... 46 2.6. Summary and conclusions ...................................................................................................... 46 CHAPTER 3 - CLAY MINERALS ASSOCIATIONS FROM THE ACTIVE HYDROTHERMAL SYSTEM ........ 49 3.1. Introduction ............................................................................................................................... 50 3.2. Geological setting .................................................................................................................... 52 3.3. Sampling and analytical methods .......................................................................................... 54 3.4. Results ....................................................................................................................................... 59 3.4.1 Subsoil hydrothermal system ..................................................................................... 59 2 3.4.2 Clay-rich fumarolic field samples ................................................................................ 62 3.5. Discussion ................................................................................................................................ 65 3.5.1 Clay mineral associations in the boreholes and related temperatures of formation ........... 65 3.5.2 Superficial hydrothermal alteration ............................................................................. 67 3.7. Final remarks ............................................................................................................................ 70 CHAPTER 4 - SEALING CAPACITY OF CLAY-CAP UNITS OF THE GEOTHERMAL RESERVOIR ........... 71 4.1. Introduction ............................................................................................................................... 72 4.2. Geological background............................................................................................................ 73 4.3. Fluid geochemistry at AAVC ................................................................................................... 74 4.4. Material and methods............................................................................................................... 76 4.4.1. Soil CO2 fluxes measurements at the Cerro Pabellón area ........................................... 76 4.4.2 Soil temperatures measurements at the AAVC fumarolic field ....................................... 76 4.4.3 Soil CO2 fluxes and temperature data processing ........................................................ 77 4.5. Results ....................................................................................................................................... 78 4.5.1 Soil CO2 flux and soil temperatures ............................................................................ 78 4.5.2 Soil temperatures at the AAVC fumarolic field ............................................................. 80 4.6. Discussion ................................................................................................................................ 82 4.7. Concluding remarks ................................................................................................................. 88 CHAPTER 5 - OVERALL FINAL REMARKS AND FURTHER WORKS ................................................ 90 5.1. Overall final remarks ................................................................................................................ 91 5.2. Further works ............................................................................................................................ 95 REFERENCES ......................................................................................................................... 97 APPENDIXES ........................................................................................................................ 114 3 CHAPTER 1 MOTIVATIONS, GENERAL INTRODUCTION AND SUMMARY OF THE THESIS 4 Motivations The present thesis was carried out in the frameworks of a collaboration with Enel Green Power and of a Memorandum of Understanding between the Department of Pure and Applied Sciences (DiSPeA) of the University of Urbino and the Faculty of Physical and Mathematical Sciences of the Universidad de Chile (Santiago). The Cerro Pabellón geothermal system, located in Northern Chile, which is the main object of this work, is classified as a blind (or hidden) geothermal field. In fact, the only hydrothermal manifestations are represented by two fumaroles located on the top of the Apacheta volcano, set to the west and about 600 m higher than the Cerro Pabellón geothermal area. The aim of this PhD research project was to deepen the knowledge concerning the heat source and the evolution of the related magmatic plumbing system, define the clay-cap units and constrain its role and importance in the circulation of fluids toward the surface, producing an update conceptual model. A multidisciplinary approach was involved and focused on three complementary scientific studies: • A petrological, geochemical and isotopic study on the Apacheta-Aguilucho Volcanic