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Fluid flow within the damage zone of the Boccheggiano extensional fault (Larderello–Travale geothermal field, central Italy): structures, alteration and implications for hydrothermal mineralization in extensional settings

Published online by Cambridge University Press:  22 December 2010

FEDERICO ROSSETTI ,
LUCA ALDEGA ,
FRANCESCA TECCE ,
FABRIZIO BALSAMO ,
ANDREA BILLI  and
MAURO BRILLI
FEDERICO ROSSETTI*
Affiliation:
Dipartimento di Scienze Geologiche, Università Roma Tre, 00146 Rome, Italy
LUCA ALDEGA
Affiliation:
Dipartimento di Scienze Geologiche, Università Roma Tre, 00146 Rome, Italy Dipartimento di Scienze della Terra, Sapienza Università di Roma, 00185 Rome, Italy
FRANCESCA TECCE
Affiliation:
Istituto di Geologia Ambientale e Geoingegneria, CNR, Rome, Italy
FABRIZIO BALSAMO
Affiliation:
Dipartimento di Scienze Geologiche, Università Roma Tre, 00146 Rome, Italy
ANDREA BILLI
Affiliation:
Istituto di Geologia Ambientale e Geoingegneria, CNR, Rome, Italy
MAURO BRILLI
Affiliation:
Istituto di Geologia Ambientale e Geoingegneria, CNR, Rome, Italy
*
†Author for correspondence: rossetti@uniroma3.it
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Abstract

The Neogene extensional province of southern Tuscany in central Italy provides an outstanding example of fossil and active structurally controlled fluid flow and epithermal ore mineralization associated with post-orogenic silicic magmatism. Characterization of the hydrodynamic regime leading to the genesis of the polysulphide deposit (known as Filone di Boccheggiano) hosted within the damage zone of the Boccheggiano Fault is a key target to assess modes of fossil hydrothermal fluid circulation in the region and, more generally, to provide inferences on fault-controlled hydrothermal fluid flow in extensional settings. We provide a detailed description of the fault zone architecture and alteration/mineralization associated with the Boccheggiano ore deposit and report the results of fluid inclusion and stable oxygen isotope studies. This investigation shows that the Boccheggiano ore consists of an adularia/illite-type epithermal deposit and that sulphide ore deposition was controlled by channelling of hydrothermal fluids of dominantly meteoric origin within the highly anisotropic permeability structure of the Boccheggiano Fault. The low permeability structure of the fault core compartmentalized the fluid outflow preventing substantial cross-fault flow, with focused fluid flow occurring at the hangingwall of the fault controlled by fracture permeability. Fluid inclusion characteristics indicate that ore minerals were deposited between 280° and 350°C in the upper levels of the brittle extending crust (lithostatic pressure in the order of 0.1 GPa). Abundant vapour-rich inclusions in ore-stage quartz are consistent with fluid immiscibility and boiling, and quartz ore vein textures suggest that mineralization in the Boccheggiano ore deposit occurred during cyclic fluid flow in a deformation regime regulated by transient and fluctuating fluid pressure conditions. Results from this study (i) predict a strongly anisotropic permeability structure of the fault damage zone during crustal extension, and (ii) indicate the rate of secondary (structural) permeability creation and maintenance by active deformation in the hangingwall of extensional faults as the major factor leading to effective hydraulic transmissivity in extensional terranes. These features intimately link ore-grade mineralization in extensional settings to telescoping of hydrothermal flow along the hangingwall block(s) of major extensional fault zones.

Keywords

fluid flowhydrothermal mineralizationalterationfracture permeabilityextensional faultingLarderello geothermal fieldItaly
Type
Original Article
Information
Geological Magazine , Volume 148 , Issue 4 , July 2011 , pp. 558 - 579
Copyright
Copyright © Cambridge University Press 2010

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References

Arisi Rota, F. & Vighi, L. 1971. Le mineralizzazioni a pirite e a solfuri misti. Rendiconti Società Italiana di Mineralogia & Petrografia. 27, 370–422.Google Scholar
Asprey, L. B. 1976. The preparation of very pure fluorine gas. Journal Fluorine Chemistry 7, 359–361.CrossRefGoogle Scholar
Bakker, R. J. 2003. Package FLUIDS 1. Computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties. Chemical Geology 194, 3–23.CrossRefGoogle Scholar
Batini, F., Brogi, A., Lazzarotto, A., Liotta, D. & Pandeli, E. 2003. Geological features of Larderello-Travale and Mt. Amiata geothermal areas (southern Tuscany, Italy). Episodes 26, 239–44.CrossRefGoogle Scholar
Bellani, S., Brogi, A., Lazzarotto, A., Liotta, D. & Ranalli, G. 2004. Heat flow, deep temperatures and extensional structures in the Larderello geothermal field (Italy). Constraints on geothermal fluid flow. Journal Volcanology Geothermal Research 132, 15–29.CrossRefGoogle Scholar
Bertani, R. 2005. World geothermal power generation in the period 2001–2005. Geothermics 34, 65–690.CrossRefGoogle Scholar
Bertini, G., Casini, G., Gianelli, G. & Pandeli, E. 2006. Geological structure of the Larderello geothermal field. Terra Nova 18, 163–9.CrossRefGoogle Scholar
Billi, A., Valle, A., Brilli, M., Faccenna, C. & Funiciello, R. 2007. Fracture-controlled fluid circulation and dissolutional weathering in sinkhole-prone carbonate rocks from central Italy. Journal of Structural Geology 29, 385–95.CrossRefGoogle Scholar
Bodnar, R. J. 1995. Fluid inclusion evidence for a magmatic source for metals in porphyry copper deposits. In Magmas, Fluids and Ore Deposits (ed. Thompson, J. F. H.), pp. 139–52. Mineralogical Association of Canada, Short Course no. 23.Google Scholar
Bodnar, R. J. & Vityk, M. O. 1994. Interpretation of microthermometric data for H2O–NaCl fluid inclusions. In Fluid Inclusions in Minerals; Methods and Applications (eds De Vivo, B. & Frezzotti, M. L.), pp. 117–30. Short Course of the IMA Working Group, Blacksburg, Virginia.Google Scholar
Boiron, M. C., Cathelineau, M., Ruggieri, G., Jeanningros, A., Gianelli, G. & Banks, D. A. 2007. Active contact metamorphism and CO2–CH4 fluid production in the Larderello geothermal field (Italy) at depths between 2.3 and 4 km. Chemical Geology 237, 303–28.CrossRefGoogle Scholar
Bons, P. D. 2000. The formation of veins and their microstructures. In Stress, Strain and Structure, a Volume in Honour of W.D. Means (eds Jessell, M. W. & Urai, J. L.). Journal of the Virtual Explorer 2.Google Scholar
Boyce, A. J., Fulignati, P. & Sbrana, A. 2003. Deep hydrothermal circulation in a granite intrusion beneath Larderello geothermal area (Italy): constraints from mineralogy, fluid inclusions and stable isotopes. Journal of Volcanology and Geothermal Research 126, 243–62.CrossRefGoogle Scholar
Brogi, A., Lazzarotto, A., Liotta, D. & Ranalli, G. 2003. Extensional shear zones as imaged by reflection seismic lines; the Larderello geothermal field (central Italy). Tectonophysics, 363, 127–39.CrossRefGoogle Scholar
Caine, J. S., Evans, J. P., Forster, & C. B. 1996. Fault zone architecture and permeability structure. Geology 24, 1025–8.2.3.CO;2>CrossRefGoogle Scholar
Cameli, G. M., Dini, I. & Liotta, D. 1993. Upper crustal structure of the Larderello geothermal field as a feature of post-collisional extensional tectonics, Southern Tuscany, Italy. Tectonophysics 224, 413–23.CrossRefGoogle Scholar
Cartwright, I. & Buick, I. S. 1999. The flow of surface-derived fluids through Alice Springs age middle-crustal ductile shear zones, Reynolds Range, central Australia. Journal of Metamorphic Geology 17, 397–414.CrossRefGoogle Scholar
Cathelineau, M., Marignac, C., Boiron, M. C., Gianelli, G. & Puxeddu, M. 1994. Evidence of Li-rich brines and early magmatic water–rock interaction in a geothermal field: the fluid inclusion data from the Larderello field. Geochimica Cosmochimica Acta 58, 1083–99.CrossRefGoogle Scholar
Cavarretta, G., Gianelli, G., & Puxeddu, M. 1982. Formation of authigenic minerals and their use as indicators of the physicochemical parameters of the fluid in the Larderello-Travale geothermal field. Economic Geology 77, 1071–84.CrossRefGoogle Scholar
Clayton, R. N., O'Neil, J. R. & Mayeda, T. K. 1972. Oxygen isotope exchange between quartz and water. Journal of Geophysical Research 77, 3057–67.CrossRefGoogle Scholar
Coelho, J. 2006. GEOISO – A Windows™ program to calculate and plot mass balances and volume changes occurring in a wide variety of geologic processes. Computers and Geosciences 32, 1523–8.CrossRefGoogle Scholar
Corsini, F., Morelli, F. & Tanelli, G. 1991. A polymetallic sulfide (Cu–Pb–Zn) assemblage from the Boccheggiano-Campiano (Tuscany) pyrite deposit: application of the stannite–sphalerite geothermometer. Neues Jahrbuch für Mineralogie, Monatshefte 11, 523–8.Google Scholar
Cortecci, G., Lattanzi, P. & Tanelli, G. 1985. C- and O-isotope and fluid inclusion studies of carbonates from pyrite and polymetallic ore deposits and associated country rocks (southern Tuscany, Italy). Chemical Geology 58, 121–8CrossRefGoogle Scholar
Costantini, A., Elter, F. M., Pandeli, E., Pascucci, V. & Sandrelli, F. 2002. Geologia dell'area di Boccheggiano e Serrabottini (Colline Metallifere, Toscana Meridionale) (with English abstract). Bollettino della Società Geologica Italiana 121, 35–50.Google Scholar
Cox, S. F. 1995. Faulting processes at high fluid pressures: an example of fault valve behavior from the Wattle Gully Fault, Victoria, Australia. Journal of Geophysical Research 100, 12841–59, doi:10.1029/95JB00915.CrossRefGoogle Scholar
Cox, S. F., Knackstedt, M. A. & Braun, J. 2001. Principles of structural control on permeability and fluid flow in hydrothermal systems. Review in Economic Geology 14, 1–24.Google Scholar
Curewitz, D. & Karson, J. A. 1997. Structural settings of hydrothermal outflow: fracture permeability maintained by fault propagation and interaction. Journal of Volcanology and Geothermal Research 79, 149–68.CrossRefGoogle Scholar
Davis, G. H. & Reynolds, S. J. 1996. Structural Geology of Rocks and Regions. New York: Wiley.Google Scholar
De Paola, N., Faulkner, D. R. & Collettini, C. 2009. Brittle versus ductile deformation as the main control on the transport properties of low-porosity anhydrite rocks. Journal of Geophysical Research 114, B06211, doi:10.1029/2008JB005967.CrossRefGoogle Scholar
Dini, A. 2003. Ore deposits, industrial minerals and geothermal resources. Periodico di Mineralogia 72, 41–52.Google Scholar
Dini, A., Gianelli, G., Puxeddu, M. & Ruggieri, G. 2005. Origin and evolution of Pliocene–Pleistocene granites from the Larderello geothermal field (Tuscan Magmatic Province, Italy). Lithos 81, 1–31.CrossRefGoogle Scholar
Dini, A., Innocenti, F., Rocchi, S., Tonarini, S. & Westerman, D.S. 2002. The magmatic evolution of the late Miocene laccolith–pluton–dyke granitic complex of Elba Island, Italy. Geological Magazine 139, 257–79.CrossRefGoogle Scholar
Dipple, G. M. & Ferry, J. M. 1992. Metasomatism and fluid flow in ductile fault zones. Contributions to Mineralogy and Petrology 112, 149–64.CrossRefGoogle Scholar
Einaudi, M. T., Hedenquist, J. W. & Inan, E. 2003. Sulfidation state of fluids in active and extinct hydrothermal systems: transitions from porphyry to epithermal environments. In Volcanic, Geothermal, and Ore-Forming Fluids: Rulers and Witnesses of Processes Within the Earth (eds Simmonds, S. F. & Graham, I.), pp. 285–314. Society of Economic Geologists, Special Publication no. 10.Google Scholar
Fournier, R. O. & Potter, R. W. 1982. An equation correlating the solubility of quartz in water from 25° to 900°C at pressures up to 10,000 bars. Geochimica Cosmochimica Acta 46, 1969–73.CrossRefGoogle Scholar
Franceschini, F. 1998. Evidence of an extensive Pliocene-Quaternary contact metamorphism in Southern Tuscany. Memorie della Società Geologica Italiana 52, 479–92.Google Scholar
Francus, P. 1998. An image-analysis technique to measure grain-size variation in thin sections of soft clastic sediments. Sedimentary Geology 121, 289–98.CrossRefGoogle Scholar
Friedman, I. & O'neil, J. R. 1977. Compilation of stable isotope fractionation factors of geochemical interest. In Data of Geochemistry, 6th edition (ed. Fleischer, M.). US Geological Survey Professional Paper 440-KK.Google Scholar
Gianelli, G., Manzella, A. & Puxeddu, M. 1997 Crustal models of the geothermal areas of southern Tuscany (Italy). Tectonophysics 281, 221–39.CrossRefGoogle Scholar
Giggenbach, W. F. 1992. Magma degassing and mineral deposition in hydrothermal systems along convergent plate boundaries. Economic Geology 97, 1927–44.Google Scholar
Grant, J. A. 1986. The isocon diagram a simple solution to Gresen's equation for metasomatic alteration. Economic Geology 81, 1976–82.CrossRefGoogle Scholar
Haar, L., Gallagher, J. S. & Kell, G. S. 1984. NBS/NRC Steam Tables.Google Scholar
Hanson, R. B. 1995. The hydrodynamics of contact metamorphism. Geological Society of America, Bulletin 107, 595–611.2.3.CO;2>CrossRefGoogle Scholar
Hedenquist, J. W. & Lowenstern, J. B. 1994. The role of magmas in the formation of hydrothermal ore deposits. Nature 370, 519–27.CrossRefGoogle Scholar
Heinrich, C. A. 2005. The physical and chemical evolution of low-salinity magmatic fluids at the porphyry to epithermal transition: a thermodynamic study. Mineralium Deposita 39, 864–89.CrossRefGoogle Scholar
Henley, R. W. 1985. The geothermal framework of epithermal deposits. Reviews in Economic Geology 2, 1–24.Google Scholar
Jagodzinski, H. 1949. Eindimensionale Fehlordnung in Kristallen Und ihr einfluss auf die röntgen interferenren. Acta Crystallographica 2, 201–7.CrossRefGoogle Scholar
Jefferies, S. P., Holdsworth, R. E., Wibberley, C. A. J., Shimamoto, T., Spiers, C. J., Niemeijer, A. R. & Lloyd, G. E. 2006. The nature and importance of phyllonite development in crustal-scale fault cores: an example from the median tectonic line, Japan. Journal of Structural Geology 28, 220–35.CrossRefGoogle Scholar
Jolivet, L., Faccenna, C., Goffé, B., Mattei, M., Rossetti, F., Brunet, C., Storti, F., Cadet, J. P., Funiciello, R., D'Agostino, N. & Parra, T. 1998. Midcrustal shear zones in post-orogenic extension: example from the Northern Tyrrhenian Sea (Italy). Journal of Geophysical Research 103, 12123–60.CrossRefGoogle Scholar
Knight, C. L. & Bodnar, R. J. 1989. Synthetic fluid inclusions: IX. Critical PVTX properties of NaCl-H2O solutions. Geochimica Cosmochimica Acta 53, 3–8.CrossRefGoogle Scholar
Lattanzi, P. 1999. Epithermal precious metal deposits of Italy-an overview. Mineralium Deposita 34, 630–8.CrossRefGoogle Scholar
Liotta, D., Ruggieri, G., Brogi, A., Fulignati, P., Dini, A. & Nardini, I. 2009. Migration of geothermal fluids in extensional terrains: the ore deposits of the Boccheggiano-Montieri area (southern Tuscany, Italy). International Journal of Earth Sciences 99, 623–44.CrossRefGoogle Scholar
Martarelli, L., Ferrini, V. & Masi, U. 1995. Trace-element evidence for the genesis of the pyrite vein deposit of Campiano (southern Tuscany, Italy). Periodico di Mineralogia 64, 349–66.Google Scholar
Masotti, A. & Favilli, G. 1987. Il giacimento di Campiano. L'Industria Mineraria 4, 27–38.Google Scholar
Mongelli, F., Pialli, G. & Zito, G. 1998. Tectonic subsidence, heat flow and uplift in Tuscany: a new geodynamic and geothermal approach. Memorie della Società geologica Italiana 52, 275–82.Google Scholar
Moore, D. E., Hickman, S., Lockner, D. A. & Dobson, P.F. 2001. Hydrothermal minerals and microstructures in the Silangkitang geothermal field along the Great Sumatran fault zone, Sumatra, Indonesia. Geological Society of America, Bulletin 113, 1179–92.2.0.CO;2>CrossRefGoogle Scholar
Moore, D. M. & Reynolds, R. C. Jr. 1997. X-Ray Diffraction and the Identification and Analysis of Clay Minerals. Oxford: Oxford University Press, 378 pp.Google Scholar
Neuzil, C. E. 1995. Abnormal pressures as hydrodynamic phenomena. American Journal of Science 295, 742–86.CrossRefGoogle Scholar
Okamoto, A. & Tsuchiya, N. 2009. Velocity of vertical fluid ascent within vein-forming fractures. Geology 37, 563–6.CrossRefGoogle Scholar
Oliver, N. H. S. 1996. Review and classification of structural controls on fluid flow during regional metamorphism. Journal of Metamorphic Geology 14, 477–92.CrossRefGoogle Scholar
Oliver, N. H. S. & Bons, P. D. 2001. Mechanisms of fluid flow and fluid–rock interaction in fossil metamorphic hydrothermal systems inferred from vein-wallrock patterns, geometry and microstructure. Geofluids 1, 137–62.CrossRefGoogle Scholar
Oliver, N. H. S., Rubenach, M. J., Fu, B., Baker, T., Blenkinsop, T., Cleverley, J. S., Marshall, L. J. & Ridd, P. J. 2006. Granite-related overpressure and volatile release in the mid crust: fluidized breccias from the Cloncurry District, Australia. Geofluids 6, 346–58.CrossRefGoogle Scholar
Reyes, A. 1990. Petrology of Philippine geothermal systems and the application of alteration mineralogy to their assessment. Journal of Volcanology and Geothermal Geology 43, 279–309.CrossRefGoogle Scholar
Rimstidt, J. D. 1997. Quartz solubility at low temperatures. Geochimica Cosmochimica Acta 61, 2553–8.CrossRefGoogle Scholar
Robert, F., Boullier, A. M. & Firdaous, K. 1995, Gold-quartz veins in metamorphic terranes and their bearing on the role of fluids in faulting. Journal of Geophysical Research 100, 12861–79.CrossRefGoogle Scholar
Roedder, E. 1984. Fluid Inclusions. Mineralogical Society of America, Reviews in Mineralogy 12.Google Scholar
Rossetti, F., Balsamo, F., Villa, I. M., Bouybaouenne, M., Faccenna, C. & Funiciello, R. 2008. Pliocene-Pleistocene high-T/low-P metamorphism during multiple granitic intrusions in the southern branch of the Larderello geothermal field (Southern Tuscany, Italy). Journal of the Geological Society, London 165, 247–62.CrossRefGoogle Scholar
Rowland, J. V. & Sibson, R. H. 2004. Structural controls on hydrothermal flow in a segmented rift system, Taupo Volcanic zone, New Zealand. Geofluids 4, 259–83.CrossRefGoogle Scholar
Ruggieri, G., Cathelineau, M., Boiron, M. C. & Marignac, C. 1999. Boiling and fluid mixing in the chlorite zone of the Larderello geothermal system. Chemical Geology 154, 237–56.CrossRefGoogle Scholar
Ruggieri, G. & Gianelli, G. 1999. Multi-stage fluid circulation in a hydraulic fracture breccia of the Larderello geothermal field, Italy. Journal of Volcanology and Geothermal Research 90, 241–61.CrossRefGoogle Scholar
Sharp, Z. D. 1990. A laser-based microanalytical method for the in situ determination of oxygen isotope ratios of silicates and oxides. Geochimica Cosmochimica Acta 54, 1353–7.CrossRefGoogle Scholar
Sheldon, H. A. & Ord, A. 2005. Evolution of porosity, permeability and fluid pressure in dilatant faults post-failure: implications for fluid flow and mineralization. Geofluids 5, 272–88.CrossRefGoogle Scholar
Sibson, R. H. 1987. Earthquake rupturing as a mineralizing agent in hydrothermal systems. Geology 15, 701–4.2.0.CO;2>CrossRefGoogle Scholar
Sibson, R. H. 1992. Implications of fault valve behaviour from rupture nucleation and recurrence. Tectonophysics 211, 283–93.CrossRefGoogle Scholar
Sibson, R. H. 1996. Structural permeability of fluid-driven fault fracture meshes. Journal of Structural Geology 18, 1031–42.CrossRefGoogle Scholar
Sibson, R. H. 2000. Fluid involvement in normal faulting. Journal of Geodynamics 29, 469–99.CrossRefGoogle Scholar
Sibson, R. H. 2004. Controls on maximum fluid overpressure defining conditions for mesozonal mineralisation. Journal of Structural Geology 26, 1127–36.CrossRefGoogle Scholar
Simmons, S. F., White, N. C. & John, D. A. 2005. Geological characteristics of epithermal precious and base metal deposits. Economic Geology, 100thAnniversary Volume, pp. 485–522.Google Scholar
Sterner, S. M. & Bodnar, R. J. 1991. Synthetic fluid inclusions; X, Experimental determination of P-V-T-X properties in the CO2 -H2O system to 6 kb and 700°C. American Journal of Science 291, 1–54.CrossRefGoogle Scholar
Streit, J. E. & Cox, S. F. 1998. Fluid infiltration and volume change during mid-crustal mylonitization of Proterozoic granite, King Island, Tasmania. Journal of Metamorphic Geology 16, 179–212.Google Scholar
Tanelli, G. 1983. Mineralizzazioni metallifere e minerogenesi della Toscana (with English abstract). Memorie della Società Geologica Italiana 25, 91–109.Google Scholar
Titley, S. R. 1976. Evidence for a Mesozoic linear tectonic pattern in southeastern Arizona, Arizona. Geological Society Digest 10, 71–101.Google Scholar
Velde, B. 1985. Clay minerals, a physico-chemical explanation of their occurrence. Developments in Sedimentology 40, 427.Google Scholar
Villa, I. M., Ruggieri, G., Puxeddu, M. & Bertini, G. 2006. Geochronology and isotope transport systematics in a subsurface granite from the Larderello-Travale geothermal system (Italy). Journal of Geophysical Research 152, 20–50.Google Scholar
Walters, R. J., Elliott, J. R., D'Agostino, N., England, P. C., Hunstad, I., Jackson, J. A., Parsons, B., Phillips, R. J. & Roberts, G. 2009. The 2009 L'Aquila earthquake (central Italy): a source mechanism and implications for seismic hazard. Geophysical Research Letters 36, L17312, doi:10.1029/2009GL039337.CrossRefGoogle Scholar
White, N. C. & Hedenquist, J. W. 1995. Epithermal gold deposits: styles, characteristics and exploration. Society of Economic Geology Newsletter 23, 9–13.Google Scholar
Wilkinson, M., McCaffrey, K. J. W., Roberts, G., Cowie, P. A., Phillips, R. J., Michetti, A. M., Vittori, E., Guerrieri, L., Blumetti, A. M., Bubeck, A., Yates, A., & Sileo, G. 2010. Partitioned postseismic deformation associated with the 2009 Mw 6.3 L'Aquila earthquake surface rupture measured using a terrestrial laser scanner. Geophysical Research Letters 37, L10309, doi:10.1029/2010GL043099.CrossRefGoogle Scholar
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