Geological Field Trips

Società Geologica Italiana

2015 Vol. 7 (1.2) ISPRA Istituto Superiore per la Protezione e la Ricerca Ambientale

SERVIZIO GEOLOGICO D’ITALIA Organo Cartografico dello Stato (legge N°68 del 2-2-1960) Dipartimento Difesa del Suolo

ISSN: 2038-4947

Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of Southern Tuscany Goldschmidt Conference - Florence, 2013

DOI: 10.3301/GFT.2015.02 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea M. Benvenuti - C. Boschi - A. Dini - G. Ruggieri - A. Arias GFT - Geological Field Trips geological fieldtrips2015-7(1.2) Periodico semestrale del Servizio Geologico d'Italia - ISPRA e della Società Geologica Italiana Geol.F.Trips, Vol.7 No.1.2 (2015), 91 pp., 67 figs. (DOI 10.3301/GFT.2015.02)

Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of Southern Tuscany Goldschmidt Conference, 2013

Marco Benvenuti1, Chiara Boschi2, Andrea Dini2, Giovanni Ruggieri3, Alessia Arias4 1 Dipartimento di Scienze della Terra, University of Florence, Via G. La Pira, 4, 50121 Florence, Italy 2 Istituto di Geoscienze e Georisorse, CNR, Via Moruzzi 1, 56124 Pise, Italy 3 Istituto di Geoscienze e Georisorse, CNR, Via G. La Pira 4, 50121 Florence, Italy 4 Enel Green Power SpA, Via Andrea Pisano 120, 56122 Pise, Italy

Corresponding Author e-mail address: [email protected] [email protected] [email protected] [email protected]

Responsible Director Claudio Campobasso (ISPRA-Roma) Editorial Board Editor in Chief Gloria Ciarapica (SGI-Perugia) M. Balini, G. Barrocu, C. Bartolini, 2 D. Bernoulli, F. Calamita, B. Capaccioni, Editorial Responsible W. Cavazza, F.L. Chiocci, Maria Letizia Pampaloni (ISPRA-Roma) R. Compagnoni, D. Cosentino, S. Critelli, G.V. Dal Piaz, C. D'Ambrogi, Technical Editor publishing group Mauro Roma (ISPRA-Roma) P. Di Stefano, C. Doglioni, E. Erba, R. Fantoni, P. Gianolla, L. Guerrieri, Editorial Manager M. Mellini, S. Milli, M. Pantaloni, Maria Luisa Vatovec (ISPRA-Roma) V. Pascucci, L. Passeri, A. Peccerillo, Convention Responsible L. Pomar, P. Ronchi, B.C. Schreiber, Anna Rosa Scalise (ISPRA-Roma) L. Simone, I. Spalla, L.H. Tanner, Alessandro Zuccari (SGI-Roma) C. Venturini, G. Zuffa. ISSN: 2038-4947 [online]

http://www.isprambiente.gov.it/it/pubblicazioni/periodici-tecnici/geological-field-trips

The Geological Survey of Italy, the Società Geologica Italiana and the Editorial group are not responsible for the ideas, opinions and contents of the guides published; the Authors of each paper are responsible for the ideas, opinions and contents published. Il Servizio Geologico d’Italia, la Società Geologica Italiana e il Gruppo editoriale non sono responsabili delle opinioni espresse e delle affermazioni pubblicate nella guida; l’Autore/i è/sono il/i solo/i responsabile/i. DOI: 10.3301/GFT.2015.02 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea M. Benvenuti - C. Boschi - A. Dini - G. Ruggieri - A. Arias geological fieldtrips2015-7(1.2)

INDEX

Information 6. Carbon dioxide sequestration by mineral carbonation in serpentinite rocks of Southern Tuscany ...... 41 Riassunto ...... 5 6.1 Geological framework ...... 41 Abstract ...... 5 6.2 The Malentrata deposit ...... 44 Program ...... 6 6.2.1 The serpentinite and the hydrated Mg-carbonates .....45 Safety, Hospital , Emergency Contact Numbers, 6.3 The Montecastelli carbonated area ...... 47 Accomodation, Visit ...... 8 6.3.1 The serpentinite and the hydrated Mg-carbonates ...49

Excursion notes Itinerary

st 1. Introduction ...... 9 1 Day - The geothermal field of Larderello and the 3 2. Geological setting of Southern Tuscany ...... 9 Malentrata mine 2.1 Geological background ...... 9 Stops 1.1-1.3: The Temperino Cu-Pb-Zn-Ag skarn deposit, 2.2 Neogene-Quaternary magmatism ...... 12 Campiglia Marittima ...... 51 2.3 Ore geology: state of the art ...... 13 STOP 1.1: The Temperino adit, from Etruscan to 3. Campiglia Marittima ...... 15 modern exploitation ...... 52 3.1 Geological framework ...... 15 STOP 1.2: Earle shaft and Gran Cava stope, the Cu-Pb-Zn-Ag 3.2 Ore geology and mineralogy ...... 17 skarn deposit ...... 55 4. Populonia in the framework of “Etruria Mineraria” ...... 22 STOP 1.3: Rocca San Silvestro, a time travel in a 5. The Larderello-Travale geothermal field ...... 25 medieval mining village ...... 57 5.1 Geothermal development in Tuscany ...... 26

5.2 Geological framework of the Larderello-Travale area ...28 Stops 1.4-1.6: The archaeological Park of Populonia-Baratti ..58 index 5.3 Reservoirs and present-day geothermal fluids ...... 32 STOP 1.4: Short visit to the Acropolis of Populonia ...... 59 5.4 Past hydrothermal activity ...... 33 STOP 1.5: The beach slag deposit at Baratti (Populonia) ...... 60 5.5 The K-horizon ...... 35 STOP 1.6: The Etruscan “Chariots Tomb” 5.6 Geothermal production process at Larderello-Travale ..38 (S. Cerbone necropolis, Populonia) ...... 64

Stops 2.1-2.4: The geothermal field of Larderello ...... 65 STOP 2.1: The Geothermal museum of Larderello ...... 65 STOP 2.2: The geothermal demonstrative well ...... 66 STOP 2.3: The geothermal equipment at the “Nuova San Martino” geothermal power plant ...... 67 STOP 2.4: Natural gas vents at Monterotondo Marittimo ...... 70

Stops 2.5-2.9: The Malentrata mine. Natural analogues of CO2 mineral sequestration (I) ...... 73 STOP 2.5: Malentrata mine, the Mio-Pliocene sedimentary cover ...... 75 STOP 2.6: Malentrata mine, the sedimentary envelope of the ophiolites ...... 75 STOP 2.7: Malentrata mine, the serpentinite protolith ...... 76 STOP 2.8: Malentrata mine, the serpentinite-argillite 4 contact ...... 77 STOP 2.9: Malentrata mine: Carbonated serpentinites and carbonate-silica veins ...... 78

3rd Day - The Montecastelli copper mine. Natural analogues of CO2 mineral sequestration (II)

STOP 3.1: The Montecastelli copper mine, ongoing carbonation in the underground works ...... 81 STOP 3.2: The Montecastelli copper mine, ongoing

carbonation in mining dumps ...... 83 index STOP 3.3: The Pavone river, hydromagnesite-aragonite vein network and water spring ...... 84

References ...... 86

DOI: 10.3301/GFT.2015.02 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea M. Benvenuti - C. Boschi - A. Dini - G. Ruggieri - A. Arias

Riassunto geological fieldtrips2015-7(1.2)

Questa escursione geologica di tre giorni permette di conoscere i differenti aspetti dell’attività idrotermale della Toscana meridionale, prodotta da una diffusa anomalia termica e da magmatismo che ha interessato la regione in uno stadio post-collisionale dell’orogenesi appenninica (dal tardo Miocene al Pleistocene). L’attività idrotermale, passata ed attuale, della Toscana meridionale è di grande importanza sotto il punto di vista storico, economico e scientifico poiché ha prodotto numerosi giacimenti, alcuni dei quali sono stati coltivati dal tardo Calcolitico per i loro alti contenuti di metalli, ed è responsabile della carbonatazione delle rocce serpentinitiche che rappresentano un analogo naturale del sequestro mineralogico di anidride carbonica. L’attività idrotermale attuale fornisce il vapore caldo che è estratto nelle aree di Larderello-Travale e Monte Amiata, che rappresentano due delle più importanti aree geotermiche del mondo. L’escursione prevede una visita al campo geotermico di Larderello, ad alcune interessanti emergenze giacimentologiche metallifere (lo skarn a Cu-Pb-Zn-Ag del Temperino, Campiglia Marittima; miniera di Cu del Pavone, Montecastelli) ed a spettacolari esempi naturali di sequestro di biossido di carbonio (miniera di magnesite di Malentrata; depositi superficiali di carbonati idrati di magnesio nell’area di Montecastelli). A questi aspetti squisitamente scientifici si accompagnerà la visita ad emergenze storiche ed archeologiche di 5 grande rilevanza (la Rocca altomedievale di San Silvestro; la città medievale di Massa Marittima; le tombe etrusche nelle necropoli di Baratti a Populonia). Parole chiave: Toscana meridionale, attività idrotermale, Etruschi, giacimenti minerari, campo geotermico di Larderello, sequestro mineralogico di CO2 information Abstract

This three-day geological field trip is focused on different aspects of the Southern Tuscany hydrothermal district, produced by the wide thermal anomaly and magmatism which affected the region in the post- collisional stage of the Apennine orogeny (from Late Miocene to Pleistocene). Past and present hydrothermal activity of southern Tuscany is of great importance from many historical, economic and scientific points of view as it produced numerous ore deposits, some of which were exploited for their metal contents since the late Chalcolithic, and it was also responsible for carbonation of serpentinites, that is a good example of natural DOI: 10.3301/GFT.2015.02 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea M. Benvenuti - C. Boschi - A. Dini - G. Ruggieri - A. Arias carbon dioxide sequestration. Present-day hydrothermal activity supplies the hot steam exploited in the

Larderello-Travale and Mt. Amiata areas, one of the most important geothermal districts of the world. geological fieldtrips2015-7(1.2) The excursion includes a visit to the Larderello geothermal field, as well as to some relevant ore deposits (the Cu-Pb-Zn-Ag skarn deposit of Temperino, Campiglia Marittima; the Cu mine of Pavone, Montecastelli), and to spectacular natural examples of carbon dioxide sequestration (magnesite mine of Malentrata; surface deposits of hydrated Mg-carbonates at Montecastelli). These exquisitely scientific aspects will be accompanied by a visit to historical and archaeological emergencies of great importance (the medieval towns of Rocca S. Silvestro and Massa Marittima; the Etruscan necropolis of Baratti-Populonia).

Keywords: Southern Tuscany, hydrothermal activity, Etruscan, ore deposits, Larderello geothermal field, CO2 sequestration.

Program

The three-day field trip starts with the visit to one of the most important skarn localities of Tuscany, i.e., the classical Cu-Pb-Zn-Ag skarn deposit of Temperino mine (Campiglia Marittima: Stops 1.1-1.3), which has been exploited since pre-Etruscan times up to a few decades ago. In the nearby Archaeological Park of Baratti- 6 Populonia (Stops 1.4-1.6) we shall visit the Etruscan Acropolis, Necropolis and beach slag deposit, where abundant metallurgical wastes dating at the Etruscan to Roman periods have been discharged. The 1st day will conclude in Massa Marittima, one of the medieval jewels of Tuscany. The ancient city name (“Massa Metallorum”) clearly refers to the mining activity for silver and copper, which has been such a distinctive feature of the city’s economic and social history. nd

The 2 day starts with the visit (Stops 2.1-2.4) to the world-famous Larderello geothermal area. More than 100 information years have passed since July 4th, 1904, when at Larderello, five light bulbs were lighted thanks to the conversion into electricity of the steam power stored in the Earth. Italy is currently one of the main producers of geothermal electricity in the world with over 700 MW. Indeed, geothermal power covers one fourth of the Tuscan region’s energy needs. The field trip would comprise the visit to the Geothermal Museum at Larderello, the opening of the demonstrative geothermal well, a visit along the perimeter of "Nuova San Martino" power plant, where geothermal equipment are exposed, and finally a visit to the natural manifestations of Monterotondo Marittimo. The field trip continues with the visit (Stops 2.5-2.9) to the magnesite deposit of Malentrata (Southern

Carbon dioxide sequestration by mineral carbonation is a potentially attractive way to mitigate increasing geological fieldtrips2015-7(1.2) global warming on the basis of industrial imitation of natural weathering processes. In the Malentrata deposit several carbonate-silica veins are hosted by silicified, carbonated and argillified serpentinites, embedded in pelite-carbonate formations.

On the 3rd day of the field trip, the program provides the visit (Stops 3.1-3.3) to the deposits of hydrated Mg-carbonates in the Montecastelli area. At Montecastelli site, a plurichilometric body of serpentinite, embedded in shales, has been deeply eroded by the Pavone River providing good geological exposures. The central portion of the serpentinite body (near the river) hosts a small copper ore deposit that was intermittently exploited during the 19th century up to 1869. The 7 mining dump, as well as the main adit of the Road map mine, is characterized by an intense carbonation and Stops with crusts of hydrated Mg-carbonates coating of the the serpentinite clasts. On the other side of the field trip. Pavone River, wide and incoherent escarpments of serpentinites show scattered white spots where information the rock was superficially coated and veined by hydrated Mg-carbonates, near an alkaline spring water. The visits to the main tunnel of the mine, the mine dump and the escarpment of serpentinite permit to fully evaluate different extents of atmospheric CO2 uptake (sequestration) through ongoing carbonation.

DOI: 10.3301/GFT.2015.02 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea M. Benvenuti - C. Boschi - A. Dini - G. Ruggieri - A. Arias Safety Visit geological fieldtrips2015-7(1.2) Hat, hiking boots, sunglasses and sunscreen are For the visit to the Archaeological Mines Park of San strongly recommended. Depending on weather Silvestro: conditions, the path in the Montecastelli area could http://www.parchivaldicornia.it/... be slippery. For the visit to the Archaeological Park of Baratti and Hospital Populonia: http://www.parchivaldicornia.it/... Ospedale Sant’Andrea, Via Risorgimento 43 - 58024 Massa Marittima (Gr); Tel:+39 0566909111. For the visit to the Larderello Geothermal museum and the close areas: Emergency Contact Numbers http://www.museivaldicecina.it/...

Medical Emergencies 118; Fire Department 115; For the visit (only guided tours) to the Montecastelli State Police 113 area, please contact the owner of the mine: 8 https://sites.google.com/... Accomodation

A list of hotels located in the Northern area of Massa Marittima is available at the following website: http://www.altamaremmaturismo.it/en/ information In the Malentrata area, the farm resort very close to the outcrops is: http://www.villettadimonterufoli.it/english.asp

DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2)

9 excursion notes M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 1 - Schematic geological map of Boschi et al., 2013). Boschi et al., Tuscany, showing the tectonic units of Tuscany, the Northern Apennines (modified after DOI: 10.3301/GFT.2015.02 1. Introduction introduction to the main A general topics of the field trip is described more in the following pages. For details please refer to the papers cited in the text and reference list. All the scheduled stops are described in detail at the end of the guide. 2. Geological setting of Southern Tuscany 2.1 Geological background is structurally Southern Tuscany located in the inner part of Northern Apennines (Fig. 1). Its setting is a consequence structural processes: the of two contrasting first is related to the convergence and collision (from Late Cretaceous to Early Miocene) of the Adria geological field trips 2015 - 7(1.2) excursion notes 10 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 2 - Schematic stratigraphic columns of the Tuscan Fig. 2 - Schematic stratigraphic and Umbria-Marche units (from Finetti et al., 2001). and Umbria-Marche units (from Finetti et al., Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea The Ligurian units, composed of remnants The Subligurian units made up of arenaceous and The metamorphic Tuscan unit, belonging to the external Tuscan domain, consisting of greenschist-facies unit, belonging to the external Tuscan The metamorphic Tuscan The Tuscan nappe that includes sedimentary rocks, The Tuscan DOI: 10.3301/GFT.2015.02 microplate and the European plate, represented by 1971; Elter, Sardinia-Corsica Massif (Boccaletti et al., 1975; Molli, 2008); the second is related to extensional since the Early-Middle tectonics, which developed 1994; 1990; Carmignani et al., et al., Miocene (Jolivet 2000). The Adria/European collision Brunet et al., determined the stacking of tectonic units that were domains of the inner from the palaeogeographic derived Northern Apennines (Fig. 2). These are, from the top: (a) Jurassic-Cretaceous oceanic crust and its Jurassic- Jurassic-Cretaceous Cretaceous sedimentary cover. (b) calcareous turbidites of Late Cretaceous-Oligocene age. Ligurian and Subligurian units were thrust eastwards domain during the Late Oligocene-Early the Tuscan over Miocene. (c) carbonates and Fm.) to Jurassic-Cretaceous (Anidriti di Burano evaporites from Upper Triassic ranging group and Macigno Fm.). During the Early Cretaceous-Lower Miocene marine clastic deposits (Scaglia Toscana evaporite in duplex structures, detached along the Upper Triassic nappe, already involved Miocene, the Tuscan domain and the inner the external Tuscan to thrust over level part of the Umbria-Marche domain. (d) sedimentary succession, similar to that one metamorphic rocks deriving from a Triassic-Oligocene geological field trips 2015 - 7(1.2) excursion notes 11 ” Nuclei toscani M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea The Umbria-Marche domain consists of continental-margin deposits (Triassic to Late Miocene); this domain The Umbria-Marche domain consists of continental-margin deposits (Triassic DOI: 10.3301/GFT.2015.02 Auct.) surrounded by the Ligurian units (Brogi et al., 2005). Tuscan succession is characterized by Oligocene- succession is characterized 2005). Tuscan Auct.) surrounded by the Ligurian units (Brogi et al., and evaporites conditions. The Upper Triassic low-metamorphic under very Early Miocene thrusts, developed After group) acted as the main detachment horizons. marls (Scaglia Toscana the Cretaceous-Oligocene clayey succession and segmentation of the Tuscan the emplacement of tectonic units, extension produced lateral normal faults. The tectonism that occurred in the Burdigalian- group through low-angle of the basal Verrucano Messinian time span created tectonic depressions, where continental to marine Middle-Late Miocene sediments such as the Late within this framework, levels were deposited (Brogi & Liotta, 2008). The deeper structural by the Ligurian were directly overlain phyllites, group and the palaeozoic the Verrucano evaporites, Triassic normal faults that dissected the high-angle by NW-SE characterized was units. A second extensional event previous compressional and extensional structures. Marine sediments were deposited during Early-Middle zones. transfer Pliocene in these tectonic depressions. The main depressions are dissected by SW-NE between 22-24 km and 30-40 km, respectively The present crustal and lithospheric thicknesses, ranging view of the (Locardi & Nicolich, 1988), are a clear evidence of this extensional process. An alternative 1999; Bonini et of the Northern Apennines suggests a basically continuous (Bonini et al., evolution structural from the Cretaceous 2001) or pulsing (Bonini & Sani, 2002) collisional process, active 2001; Finetti et al., al., to Pliocene-Pleistocene times (Finetti, 2006). characterizing the inner Tuscan domain. The substratum of the Tuscan domain was involved in the collisional involved domain was of the Tuscan domain. The substratum the inner Tuscan characterizing metamorphic basement stage determining isoclinal folds and duplex structures. It is composed of a Palaeozoic group; quartzites and (Verrucano cover and its Triassic phyllites). (e) from the belt developed of the Northern Apennines, where a fold-and-thrust represents the external zone 2002). et al., Middle Miocene (Brozzetti rocks event, During this contractional show a NE direction of tectonic transport. Kinematic indicators invariably succession, thus determining the the external Tuscan group overthrust belonging to the Verrucano metamorphic conditions in which deformation occurred (Liotta, 2002). succession is exposed in Larderello and Monte Amiata areas as isolated outcrops (“ Tuscan geological field trips 2015 - 7(1.2) excursion notes 12 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Amiata, Monti Cimini and Capraia from 14 Ma to 0.2 Island. Ages range Ma, and show a tendency to decrease from west to east (Serri et magmatic 1993). The Tuscan al., complex and is very province includes crustal anatectic acid and granites, rhyolites peraluminous of mafic to and a wide range intermediate magmas. These vary among high-potassium calcalkaline, shoshonitic, potassic alkaline and lamproitic rocks. Mixing ultrapotassic affected both mafic appears to have and acid rocks; the latter bear xenocrysts, (mafic enclaves, textural etc.) and geochemical evidence of mingling and mixing with various calcalkaline types of mantle-derived to potassic melts. Fig. 3 - Location map for intrusive and volcanic rocks of the and volcanic Fig. 3 - Location map for intrusive Tuscan Magmatic Province (modified after Dini et al., 2005). (modified after Dini et al., Magmatic Province Tuscan Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 2.2 Neogene-Quaternary magmatism centres scattered through and extrusive consists of a series intrusive magmatic province The Tuscan area, The acid centres of the Tolfa-Cerveteri-Manziana Archipelago. and the Tuscan southern Tuscany of an overview Fig. 3 gives province. included within the Tuscan are also traditionally northwest of Rome, magmatism. Magmatic rocks consist of of the Tuscan locations, ages and main compositional characteristics edifices of Monte flows and domes, of the large volcanic necks, lava plutons, stocks, laccoliths, sills, dykes, geological field trips 2015 - 7(1.2) excursion notes 13 , 2 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 4 - Distribution of main ore types Southern Tuscany. in the Larderello geothermal area. 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 with local peaks up to 1000 mW/m 2.3 Ore geology: state of the art has been one of the about 30 centuries, Tuscany For most important mining regions of Italy and has of resources, including pyrite, produced a large variety iron, base metals, geothermal steam and several and rocks (Lattanzi et al. 1994, industrial minerals the mining industry in references therein). Today, (feldspars, is limited to industrial minerals Tuscany halite), ornamental stones, and building materials. The includes (Fig. 4): the Fe metallogenic province Tuscan deposits of Elba Island, the pyrite (± barite ± Fe oxide and Apuane Alps, deposits of Southern Tuscany oxides) the base- and precious-metals deposits of “Colline the Hg Metallifere” district (Southern Tuscany), deposits of the Monte Amiata area, and Sb belt (Cipriani & Tanelli, of the Capalbio-Monti Romani 1983). The newest addition to the 1983; Tanelli, in is the discovery of Tuscany metallogenic framework the mid ‘80s of “Carlin-type” epithermal gold Most of the Au prospects, limited mineralization. economic importance, are closely related to Sb deposits (Lattanzi, 1999). The thermal anomaly related to this prolonged magmatic activity drove intense deep convective fluid intense deep convective The thermal anomaly related to this prolonged magmatic activity drove mined in the past. The and ore deposits, some of which were extensively circulation that formed mineralization Larderello–Travale (i.e., geothermal systems of southern Tuscany anomaly is now responsible for the active 2005, and 1994; Lattanzi, 1999; Dini et al., 1983; Lattanzi et al., and Mt Amiata geothermal fields) (Tanelli, 120 mW/m by high heat flow that averages is characterized southern Tuscany references therein). Presently, geological field trips 2015 - 7(1.2) excursion notes 14 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 5 - Location of Tuscan skarn deposits (after Fig. 5 - Location of Tuscan Tanelli, 1977). Tanelli, DOI: 10.3301/GFT.2015.02 A number of different skarn deposits occur in the southwestern portion of the Tuscan metallogenic province (Fig. metallogenic province A number of different skarn deposits occur in the southwestern portion Tuscan Sassi Neri and Ortano at Elba Island; Niccioleta in 5): they include calcic iron skarns (Capo Calamita, Ginevro, mine in the Campiglia M.ma district; (-copper) skarns (Temperino the Colline Metallifere district) and lead-zinc authors (for details see been studied by several near Massa Marittima). These deposits have Serrabottini skarn deposits formed by (1977), the Tuscan 2004, and reference therein). According to Tanelli et al., Benvenuti carbonate rocks of the replacement of Triassic unit by metasomatic processes triggered Tuscan of the the emplacement at shallow crustal levels Province. Neogene magmatic rocks of the Tuscan be in contact with magmatic rocks Skarn bodies may distances mine), or at various at Temperino (e.g., from them (Niccioleta, Ortano). The presence of to skarn bodies magmatic rocks in close proximity does not necessarily imply a genetic link: at Ginevro, appear to predate skarn for instance, aplitic dikes skarn formation. Source(s) of elements for Tuscan Corsini et al. deposits are still poorly constrained. (1980) maintain that isotopic composition of sulfur skarn deposit is compatible with from the Temperino sulfides/sulfates a local, non-magmatic source (i.e., country rocks). On the other from Permo-Triassic hand, the uniform lead isotope composition of pyrite and galena from the Campiglia Marittima reflect contribution of lead Niccioleta deposits may (and other metals?) from Neogene-Quaternary 1994). magmatic rocks (Lattanzi et al., geological field trips 2015 - 7(1.2) excursion notes 15 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 6 - Geological sketch map of the Campigliese Fig. 6 - Geological sketch deposits (modified after Da Mommio et al., 2010). deposits (modified after Da Mommio et al., area showing the distribution of magmatic rocks and ore DOI: 10.3301/GFT.2015.02 3. Campiglia Marittima 3.1 Geological framework (for del Temperino The ore-deposits of Valle 2004 and et al., details see Benvenuti references therein) are located 2 km north of (Fig. 6). Campiglia Marittima village (Livorno) unit sequence formations of the Tuscan Several crop out in this area, which can be described as trending wedge-shaped horst (“Campiglia a N-S and NW-SE ridge”) bordered by high angle N-S trending faults on the western and eastern 2000, and (Acocella et al., margins, respectively references therein). The Campiglia ridge is formations, which belong to made up of several from Liassic massive unit, ranging the Tuscan limestone (Calcare Massiccio) to Oligocene unit turbiditic sandstone (Macigno). The Tuscan by the formations are tectonically overthrust allochthonous “Ligurian” and “Subligurians” units, consisting of calcareous, marly and shaly to Eocene age. The turbidites of Upper Jurassic latter sequences are then unconformably by Quaternary sediments, consisting of overlain geological field trips 2015 - 7(1.2) excursion notes 16 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias O contents. All the fertile skarn bodies exploited in Campiglia 2 and Na 3 O 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 7 - Road cut showing an acidic porphyry dyke hosted by marble. DOI: 10.3301/GFT.2015.02 alluvium, fluvial and beach deposits. Magmatic activity strongly affected the Campiglia Marittima area in Late bodies were emplaced, mostly with kinds of both plutonic and volcanic Miocene-Lower Pliocene time. Several exposed in the Campiglia acid to intermediate composition. The earliest emplaced magmatic body, an overall dated at 5.7 Ma. Most chemical data for the Botro ai Marmi di Botro ai Marmi”, Marittima area, is the “granito compositions. granodioritic field; some rocks encountered in drill holes have stock plot in the syenogranite by a N-S is marked The contact with the host rocks (mainly represented by Calcare Massiccio Formation) 5 km long, 1.5 wide and 300 m thick. The dominant trending thermo-metamorphic aureole, approximately by temperatures calcite-tremolite-diopside skarn assemblage suggests emplacement conditions characterized ≤500°C and pressures ≤1 kb. intruded the eastern part of Campiglia area. Three dikes of porphyry swarms Between 5 and 4 Ma, several and potassic (also called “green porphyry”), monzonitic can be distinguished: quartz-monzonite, types of dikes The “green porphyry” porphyry”). (“yellow alkaline porphyries also known as “augitic (“porfido verde”), represents a diopside-bearing mafic differentiate, with intermediate silica contents, high Mg#, porphyry”, low Al and relatively Ni and Cr, Marittima district are closely related to the “green porphyry”. The “yellow porphyry” (Fig. 7) and the quartz- porphyry” The “yellow Marittima district are closely related to the “green porphyry”. similar to the “Botro ai Marmi” intrusion), and display very are acidic in composition (i.e., porphyry monzonitic geological field trips 2015 - 7(1.2) excursion notes 17 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias where they have been mined, even if on been mined, even where they have 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 a small scale, from the surface at 250 m down to 50 m elevation. According to Corsini et al. (1980), the skarn a small scale, from the surface at 250 m down to 50 elevation. elongated masses, which consists of two west-northwest-east-southeast del Temperino complex of Valle (Figs. 8 and 9). appear to be strictly associated with the green porphyry a strong potassic alteration. The extensive degree of alteration of the Campiglia porphyry dikes makes it makes dikes of the Campiglia porphyry degree of alteration The extensive a strong potassic alteration. anddifficult to establish whether the quartz-monzonite products from the are both evolved porphyries “yellow” the north of Botro ai Marmi intrusion, San or represent independent magmas. To “green porphyry” Vincenzo were erupted at about 4.4 Ma. They probably resulted from mixing between a crustal rhyolites melt of possible “anatectic” melt and minor but significant amounts of subcrustal, mafic-intermediate According to Acocella et al. (2000) acalcalkaline affinity. strike-slip releasing bend formed during right-lateral the emplacement of Botro ai Marmi faulting on the western margin of Campiglia ridge favoured lineaments and probably controlled the the strike-slip intrusion. Pliocene extensional tectonics reactivated rhyolites. as well extrusion of the San Vincenzo emplacement of the Campiglia dikes 3.2 Ore geology and mineralogy 1980), skarn deposits (Corsini et al., (±Fe,Ag,Sn) The Campiglia Marittima area has long been known for Cu-Pb-Zn Mineraria” Generale In the “Relazione been exploited since pre-Etruscan times up to a few decades ago. which have in the district were estimated to be delle Miniere (1975), the reserves published by the Direzione Generale of about 700,000 0.8-1% Cu, and 20-70 g/t Ag (with inferred reserves order of 250,000 tons at 4% Zn, 2% Pb, 1983). These deposits lie 1-2 km E and NE of the Botro ai Marmi stock, in strict tons: data from Cipriani & Tanelli, of the only minor skarn occurs in the immediate proximity dikes; spatial association with (4-5 Ma?) porphyry and rocks are also mined in the district. The skarn-sulfide intrusion (Fig. 6). A number of industrial minerals dei Lanzi deposits of Campiglia Marittima can be subdivided between those outcropping in the area Valle orebodies from del Piombo) and the Cu (Pb-Zn) Cava mostly with galena>sphalerite: e.g., (predominant Pb-Zn, from contact are completely enclosed in white marbles, derived (Fig. 6). Both skarn complexes del Temperino Valle the skarn metamorphism of the liassic Calcare Massiccio by Botro ai Marmi and/or related intrusions. However, stock, but instead to the more extensive, ores of the Campiglia area are not related to Botro ai Marmi granite dikes. and green porphyry though not outcropping, parent intrusion of the network yellow deposits occur in an area of about 0.4 km del Temperino The Valle geological field trips 2015 - 7(1.2) excursion notes 18 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 9 - A small dyke of mafic porphyry crosscutting the skarn at of mafic porphyry Fig. 9 - A small dyke Temperino mine. Temperino Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 8 - Interpretive section of Temperino skarn section of Temperino Fig. 8 - Interpretive deposit (modified after Corsini et al, 1980). DOI: 10.3301/GFT.2015.02 The latter seems to be completely embedded in the orebodies, and is crossed by small bearing the calcite- veinlets mineralized and k-feldspar epidote-quartz, k-mica (up to 9.5 wt % MnO), hedenbergite- association. The skarn complex consists of manganoan ilvaite rhodonite, fluorite and ferroactinolite. of andradite, quartz, calcite, epidote, and traces johannsenite pyroxene, San End member johannsenite of the solid solution hedenbergite-johannsenite series occurs near Rocca (Fig. 10). Silvestro include Most common ore minerals porphyry. Epidote is particularly abundant in association with the yellow arsenopyrite, bismuthinite, chalcopyrite, pyrrhotite, sphalerite, galena, pyrite, magnetite, hematite (traces), are only present in the upper levels 1977). Supergene minerals mackinawite and galenobismuthinite (Tanelli, of the mines and in small gossans. geological field trips 2015 - 7(1.2) excursion notes 19 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias According to Corsini et al. (1980), three zones of According to Corsini et al. (1980), three zones magnetite, ilvaite with prevailing mineralization, and hedenbergite, occur between the green and the metamorphosed liassic limestone porphyry occurs only in the (Fig. 8). The magnetite zone of the skarn-sulfide deposit; it deepest levels aggregate of coarse consists of a 1m thick, massive crystals of magnetite with quartz and subhedral of pyrite, pyrrhotite and chalcopyrite. traces Fig. 11 - Pyrite, chalcopyrite and pyrrhotite ore in hedenbergite- ilvaite skarn; Temperino mine. skarn; Temperino ilvaite Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 10 - Textural and mineralogical variations of variations and mineralogical Fig. 10 - Textural the Temperino skarn. the Temperino DOI: 10.3301/GFT.2015.02 The ilvaite zone occurs directly at the contact zone The ilvaite the typical ore with the green porphyry: assemblage consists of chalcopyrite and pyrrhotite, with minor magnetite, pyrite and Fe- rich sphalerite (Fig. 11). Beautiful crystals of associated been found in pockets, have ilvaite with quartz (Fig. 12). Magnetite occurs here only as pseudomorphs after lamellar generally hematite. geological field trips 2015 - 7(1.2) excursion notes 20 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Pyrrhotite seems to be one of the earliest phases, and is replaced by the other mineral sulfides, as well by magnetite. Sphalerite is and has quite late in the sulfide paragenesis from 17.2 to 21.3 an iron content ranging mole % FeS. both is characterized The hedenbergite zone and concentric radiating by well-developed, with long fibers aggregates of clinopyroxene (Fig. 10), and by marbles corroded enclosed within the skarn bodies, showing that the were growing toward the skarn minerals limestone side of the complex. An increase in has been the Mn content of clinopyroxene recorded, from manganoan hedenbergite (2.6 to wt % MnO) in the core of skarn body, quite pure johannsenite (27.6 wt % MnO) at the contact with marbles. The ore assemblage consists of chalcopyrite, pyrite, iron-poor sphalerite and finally of galena, with only minor lamellar magnetite and hematite are quartz, remnants. Gangue minerals and andradite. calcite, epidote, minor ilvaite del deposition at Valle The ore mineral 1980) appears to (Corsini et al., Temperino been a multi-stage process, which can be have divided into three main stages. The first corresponds to the deposition of iron oxides, Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 12 - Ilvaite: cluster of prismatic Fig. 12 - Ilvaite: crystals up to 5 cm (photo by R. Appiani, collection). A. Lorenzelli DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) excursion notes 21 S = 5 to 12 34 (δ centuries, although there is th M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias ‰) and/or sulfide -20 th S = 12 to 14.6 34 (δ Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 evidence of older (Etruscan?) mining activity. According to Bertolani (1958), skarn sulfide mineralization evidence of older (Etruscan?) mining activity. The Campo alle Buche deposit has mineralization. occurs at some depth below the calcite-iron oxyhydroxide it can be considered the product of late- been regarded as a gossan-type ore by early authors; alternatively, responsible of fluids still related to the Pliocene magmatism which was hydrothermal stage, low-temperature 1977). (Ag,Sn) skarn bodies of the Campiglia Marittima district (Tanelli, the emplacement of Cu-Pb-Zn mainly magnetite. Temporary changes of physicochemical parameters allowed hematite to form at first in the parameters changes of physicochemical mainly magnetite. Temporary and to be quickly reduced again magnetite before the second stage took place. In outer zones, of pyrite (II). formed, then pyrrhotite, and a second generation (I) was stage, a first pyrite generation and hedenbergite took place. The third stage brought the During this second stage, crystallization of ilvaite the first to precipitate, followed by sphalerite and finally sulfides. Chalcopyrite was deposition of Cu-Pb-Zn hedenbergite, chalcopyrite and pyrrhotite. The replacement of ilvaite galena. The banded rocks contain ilvaite, absolute age As mentioned above, overlap. indicates that these two minerals by hedenbergite and vice versa measurements and the geological reconstruction of Campiglia area indicate a Pliocene age for indicates that the maximum stratigraphy skarn-sulfide complex. Regional del Temperino formation of the Valle about 1500 to 2000 meters. the Calcare Massiccio during Pliocene was thickness of the sediments over del and S-isotope data, Corsini et al. (1980) estimated that sulfide deposition at Valle Based on mineralogy from about occurred during decreasing temperatures Temperino 400 °C to 250 °C. They also suggest that been sulfate have sources of sulfur for these deposits may ‰) associated with the Paleozoic/Mesozoic basement formations (namely, the “Filladi di Boccheggiano” and/or basement formations (namely, ‰) associated with the Paleozoic/Mesozoic consisting of A different type of mineralization, both of them containing evaporites. “Calcare Cavernoso”), (mainly goethite, hematite, siderite ± marcasite, chlorite) and sparry calcite crystals, iron minerals layered with apparently karstic features, occurs in the old mining locality of Campo alle Buche. This deposit has been exploited by both underground and open pit mine workings in the 19 geological field trips 2015 - 7(1.2) excursion notes 22 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias century. Even in Even century. th Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 13 – Sketch map of “Etruria Mineraria” with map of “Etruria Mineraria” Fig. 13 – Sketch (modified after Sestini, 1981). location of the main ore deposits, part which by the Romans exploited by the Etruscans and, later, DOI: 10.3301/GFT.2015.02 more recent times some mineral resources, more recent times some mineral such as the Elba iron ores, were successfully 1983; Mascaro et exploited (Cipriani & Tanelli, 2012). et al., 1991; Benvenuti al., The western portion of ancient Etruria lying to the north and Monti della between Volterra to the south is known in Tolfa as “Etruria Mineraria” archaeological literature because of the abundance ore resources Fig. 13). The tin, etc., (incl. iron, copper, role in a key played Etruscan town of Populonia of metals (especially, the production and trade 4. Populonia in the framework of “Etruria Mineraria” long been have resources of Tuscany Mineral exploited, at least since Chalcolithic times, and of important in the development were very civilizations; in medieval Etruscan and Roman important derived times, numerous city-states from mining exploitation and metal revenues production. The same applies, on a larger under the scale, after the unification of Tuscany in the 16 Medici government geological field trips 2015 - 7(1.2) excursion notes 23 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Millennium BC. Populonia was an important was Millennium BC. Populonia st century AD (Corretti & Benvenuti, 2001). Such a century AD (Corretti & Benvenuti, st Fig. 14 - Sketch map of the Populonia-Baratti area with location of map of the Populonia-Baratti Fig. 14 - Sketch sites mentioned in the text (modified after Benvenuti et al., 2000). et al., sites mentioned in the text (modified after Benvenuti ), 3 century BC up to the 1 th Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 iron production centre from the 6 prominent role was mainly due to its strategic location, midway between the large iron deposits of eastern location, midway mainly due to its strategic prominent role was ores of the Campiglia Marittima area. The huge heaps Elba Island and the polymetallic Cu-Pb-Zn-Fe-Ag-Sn of 40,000 m slags (probably in excess but not exclusively, iron) in the Mediterranean area during the 1 iron) in the Mediterranean but not exclusively, discharged along the foreshore of Gulf could document a total iron production Baratti, of some thousands tonnes iron bloom (up to 1988). half a million tonnes according to Voss, a detailed research In the last twenty years, (Fig. 14) area at Populonia in the Baratti program with the aim of has been undertaken, establishing the types and extent of metallurgical activities, as well the of smelted ores in the 1st provenance Millennium BC. The main results so far obtained et been published elsewhere (Benvenuti have 2000, 2002, 2003a, b; Cartocci et al., al., with 2009a, 2009b, et al., 2007; Chiarantini references), and will be briefly summarized area and fieldwork in the Baratti here. Recent textural, mineralogical, detailed stratigraphic, and chemical analyses of the metallurgical some gave still partly preserved wastes interesting results which can be briefly as it follows: summarized • carried out since 2002 in the so- excavations called “beach slag deposit” (Fig. 14) - probably located some 100 m ahead from the shoreline geological field trips 2015 - 7(1.2) excursion notes 24 century nd centuries BC th –8 th century and the 2 th M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias century BC or earlier), particularly in the rd Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 (Cartocci et al., 2007), followed by predominant iron production between the 7 (Cartocci et al., BC in agreement with archaeological and historical documents; • are hindered by output estimates and direct dating of primary iron production at Populonia characterization, Although intense reworking of slag deposits during the past century for re-use in siderurgic plants at Piombino. attempt to reconstruct of smelting furnaces can be found among metallurgical debris, any abundant fragments 2003b) and preliminary et al., their technological design is based upon assumptions (Benvenuti archaeometallurgical experiments; • for iron working, made with local sandstone blocks and bricks lined smithing/reheating hearths employed Cerbone deposit; they can be mostly dated to the V-II been found in upper portion of the S. have with clay, century BC; • production (dating to the 3 there is also evidence of local bronze in Etruscan times - indicate an earlier copper metallurgy, radiocarbon dated to the 9 radiocarbon in Etruscan times - indicate an earlier copper metallurgy, “Campo VI” site, adjacent to the ancient defensive walls of Etruscan Popluna (Populonia; Fig. 13); (Populonia; of Etruscan Popluna walls “Campo VI” site, adjacent to the ancient defensive • tin+tungsten anomalous content of iron slags) and Pb-isotope analyses element geochemistry (e.g., trace 2013), et al., mainly from eastern hematite-rich ores Elba Island (Benvenuti both indicate that iron was ore the nearby Cu–Pb–Zn–Fe–Sn source area for smelted copper (and tin?) was whereas the most likely del skarn sulphide deposits of Valle district of Campiglia Marittima (Fig. 14), and particularly the Cu-Zn,Pb,Ag 2009b). et al., Lanzi (Chiarantini Temperino–Valle geological field trips 2015 - 7(1.2) excursion notes 25 . 2 Fig. 15 - Temperature distribution in Fig. 15 - Temperature from Cappetti et al. (2005). M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias the Larderello–Travale geothermal field. the Larderello–Travale (1) Outcrops of permeable formations; at (2) geothermal wells; (3) temperature (4) the top of shallow reservoir; Modified at 3000m b.s.l. temperature The present installed capacity is with 22 units in 594.5 MW, and 200 MW with 8 Larderello, field. in Travale units in operation some 50°C of superheating (Barelli 1995, 2000) (Fig. 15). At et al., 3000 m depth, the 300°C isotherm contour includes both areas, with a total extension of about 400 km Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 5. The Larderello-Travale geothermal field with a reservoir is one of the few superheated steam geothermal systems in world, i.e., Larderello-Travale This peculiarity is the consequence of a natural gradient. pressure that is much lower than the hydrostatic fields, to the current steam phase. Larderello and Travale of the system from initial water-phase evolution extended turned out to belong the same geothermal system when drilling was initially considered separate, and pressure distribution shows that the whole system is steam dominated with to 3-4 km depth. Temperature geological field trips 2015 - 7(1.2) excursion notes 26 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Cerchiaio”, at Monterotondo Marittimo. Fig. 16 - Plaque in memory of U. F. Hoefer acid in the water of pond called “Lagone that in 1777 discovered the presence of boric century BC). However, the earliest scientific and economic appraisal of the earliest scientific and economic appraisal century BC). However, rd Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 the “lagoni” area is due to Uberto Francesco Hoefer, director of the grand duchy’s pharmacies, who, in 1777, pharmacies, who, duchy’s director of the grand Hoefer, the “lagoni” area is due to Uberto Francesco of “Lagone Cerchiaio” Monterotondo Marittimo the occurrence of boric acid within water demonstrated from geothermal resources began in Italy 1995). Commercial power generation (Fig. 16; Burgassi et al., 5.1 Geothermal development in Tuscany first exploited for industrial purposes, and it is still one of Italy is the country where geothermal energy was geothermal manifestations as “lagoni” (small pools or Natural the leading producers of geothermal energy. to bubble up) and “soffioni” (jets of steam, which can be with gas cause the water where steam mixed craters di Cecina, Sasso Val Montecerboli, Castelnuovo localities (Larderello, violent) originally occurred in several and Massa etc.) lying between Pomarance Travale, Lagoni Rossi, Monterotondo Marittimo, Serrazzano, Pisano, atmospheres. The first evidence of an reached 100-200°C, with pressures of several Marittima. Temperatures of a large public bathing use of geothermal phenomena came from the discovery intentional and organized complex in the Sasso Pisano area (3 geological field trips 2015 - 7(1.2) excursion notes 27 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 17 - Wells opening for flow measurement in Larderello (1916), from Larderello historical archive. DOI: 10.3301/GFT.2015.02 1913 with a 250 KW unit. A significant increase in the production of water-steam boric mixtures was obtained boric mixtures was 1913 with a 250 KW unit. A significant increase in the production of water-steam at stayed generation from wells drilled to increasing depths, up 250-300 m, in early 1900 (Fig. 17). Power interrupted only in 1944 by and continuously, until 1938, but since then it has risen rapidly modest levels from II (UGI, 2007). The Italian experience of electricity generation War occurring during World events unit endogenous fluids remained the sole example in world until 1958, when first power generation (New installed in Wairakei was more than 1900 GWh of electric energy was In the same year Zealand). 2000). produced in the Larderello area, with an installed capacity of 300 MW (Cappetti et al., geological field trips 2015 - 7(1.2) excursion notes 28 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias 5.2 Geological framework of the Larderello-Travale area geothermal The Larderello-Travale area, shown in Fig. 19, is characterized basins by late-to post-orogenic according to or semi-grabens (grabens 1993; Martini & Sagri, Bossio et al., basins according to 1993; thrust-top 2001) filled with Bonini et al., Neogene, continental to marine by ridges sediments and separated where the Apenninic tectonic pile of nappe and Ligurian nappes (i.e. Tuscan and Sub-Ligurian units) crops out 2001, and 1994; Vai, (Bertini et al., Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 18 - Gross electricity in generation Italy from 1914 to 2012. DOI: 10.3301/GFT.2015.02 The positive results of deep exploration and reinjection programs, which began in the late 1970s, have made which began in the late 1970s, have and reinjection programs, results of deep exploration The positive (involving it possible to reassess the field potential of geothermal areas and plan both development (replacement of old units with new ones, programs additional wells and power plants) renewal impact). by higher efficiency and lower environmental characterized of 3436 GWh (Cappetti 625.7 MW with an energy generation In 1995 the total installed capacity in Italy was with an installed capacity 2000, and reference therein). In comparison, at present, Enel Green Power, et al., di 33 geothermal power plants in Val in Italy of 874.5 MW (running capacity 722 MW), currently operates 8700 users of district heating, 25 hectares heated with over Cecina and Monte Amiata (Tuscany), greenhouses, and an electrical production of about 5.2 TWh in 2012 (Fig. 18). In 2012, the geothermal 2% of total production, ≈7% ENEL and the renewable production in Italy was region consumption. ≈26% of the Tuscan production. The geothermal production covers geological field trips 2015 - 7(1.2) excursion notes 29 crystalline Bs) Quaternary deposits; Q) M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias terrigenous formations of Tuscan units (Upper terrigenous formations of Tuscan Ft) neo-autochthonous terrigenous deposits (Lower Pliocene – Upper neo-autochthonous P) vulcanites; mainly carbonate formations of Tuscan units (Upper Triassic-Malm); mainly carbonate formations of Tuscan V) St) basement (Upper Carboniferous). Modified from Arias et al. (2010). Ligurian and sub-Ligurian complex (Jurassic-Eocene); Ligurian and sub-Ligurian complex (Jurassic-Eocene); Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fl) Plio-Quaternary travertines; Plio-Quaternary travertines; tr) Cretaceous – Lower Miocene); Miocene); Fig. 19 - Schematic geology of the Larderello-Travale area. Geologic legend from top to bottom: Fig. 19 - Schematic geology of the Larderello-Travale DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) excursion notes 30 sensu stricto : the Ligurian units M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias sensu lato (Jurassic-Eocene) composed by ophiolites and a pelagic (Jurassic-Eocene) and the Sub-Ligurian unit (Eocene–Oligocene) sedimentary cover, limestones and shales; (Late Triassic), nappe): evaporitic unit (Tuscan (3) The Tuscan Cretaceous), and pelagic–turbiditic carbonate (Late Triassic–Early (Cretaceous-Early Miocene) successions; quartzite and phyllite (4) A tectonic wedge complex: Triassic and the Late Triassic phyllite group), Palaeozoic (Verrucano nappe; of the Tuscan evaporites and quartzite, phyllite complex: Paleozoic (5) The phyllite-quartzite lenses, dolomites and basic metavolcanites of anhydritic layers affected by the Alpine greenschist metamorphism, which overprints a previous Hercynian blastesis; rocks (garnet-bearing (6) The micaschist complex: Paleozoic affected by micaschists and quartzites with amphibolite zones) Alpine and Hercynian deformations; polymetamorphic gneiss and (7) The gneiss complex: pre-Alpine with intercalations of amphibolites and orthogneiss. paragneiss did not affect the gneiss complex (Elter & The Alpine orogeny 1990). Pandeli, The two deepest units were found only in deep drillings. Deep and felsic boreholes encountered also numerous acidic intrusive references therein). The main tectono-stratigraphic units found in the references therein). The main tectono-stratigraphic deep geothermal drillings are shown in Fig. 20. Larderello-Travale They are from top to bottom: (1) Neogene and Quaternary deposits: Late Miocene to Pliocene Quaternary continental to marine sediments, filling up the extensional tectonic depressions, which, in the geothermal areas, the pre-Neogene substratum; unconformably overlie (2) The Ligurian complex Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 20 - Structural-stratigraphic and Fig. 20 - Structural-stratigraphic Modified from Bertini et al. (2006). hydrogeologic sketch of the geothermal area. sketch hydrogeologic DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) excursion notes 31 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 21 - Heat flow density map of the from Baldi et al. (1995). Larderello-Travale geothermal field. Modified Larderello-Travale 1995; Fig. 21). This framework and the 1995; Fig. 21). This framework modeling suggest the geophysical and still active existence of a long-lived magmatic system in the Larderello- geothermal area (GianelliTravale et al., 1998). The buried 1997; Mongelli et al., isotopic ages have solidified granites from 3.8 to 1.3 Ma (Villa et al., ranging 2005, and references 2006; Dini et al., therein), and, owing to the limited effects that erosion and tectonic during such a exhumation played short time, their present relatively depth (top of intrusions around 3–4 km and geologic below the ground level), setting, probably do not largely differ from those at the time of emplacement. Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea and geothermal gradients greater than 100°C/km with maximum values of 300°C/km (Baldi et al., greater than 100°C/km with maximum values and geothermal gradients 2 DOI: 10.3301/GFT.2015.02 dykes at different depths (from about 2000 to more than 4600 m below the ground level) whose emplacement at different depths (from about 2000 to more than 4600 m below the ground level) dykes 1990; 2002; Elter & Pandeli, rise to contact aureoles in the metamorphic host rocks (Gianelli & Ruggieri, gave 1982). et al., processes (Cavarretta 2002 and references therein) related hydrothermal Musumeci et al., magmas This magmatism is related to asthenosphere upwelling and underplating/intrusion of mantle-derived crust since Miocene time. The thermal anomaly which produced the wide thermal anomaly in Tuscan ones formed by mixing/mingling between triggered the formation of crustal magmas and hybrid magmas (Dini et al. 2005). This thermal anomaly is still extremely high in the crustal- and mantle-derived from 120 to more than 1000 ranging geothermal area and produces heat flow with values Larderello-Travale mW/m geological field trips 2015 - 7(1.2) excursion notes 32 , 4 , CH 2 magmatic O = 0±2‰ (all 18 δ subduction-related O (up to 95%) with CO 2 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias D = 40±2‰ and δ A ‘‘large O = -7‰, resulting from limited water-rock interactions due interactions O = -7‰, resulting from limited water-rock 18 δ deep-seated magma body. deep-seated magma body. D = 40±2‰ and δ O (before re-injection) indicate meteoric water as the main source of the vapor (Craig, as the main source of vapor O (before re-injection) indicate meteoric water 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea as major components, with the noble gases present in ppm only (Scandiffio et al., 1995). Stable as major components, with the noble gases present in ppm only (Scandiffio et al., O value towards more positive values. The latter end-member is a secondary steam derived from the The latter end-member is a secondary steam derived values. more positive towards O value 2 18 δ S and N 2 DOI: 10.3301/GFT.2015.02 boiling of fresh waters, having having boiling of fresh waters, isotope ratios are relative to VSMOW), resulting from extensive water-rock interactions, which shifted the original interactions, water-rock to VSMOW), resulting from extensive are relative isotope ratios meteoric H 1963; Ferrara et al., 1965). A simple mixing between two end-members could explain the isotopic composition et al., 1963; Ferrara 1995). 1995; Scandiffio et al., et al., of the steam produced in field (Panichi of typical values The former end-member is a primary deep steam having 5.3 Reservoirs and present-day geothermal fluids The cap rocks of the geothermal field are usually represented by flysch formations Ligurian complex geothermal 2010). Two et al., and, where present, by Neogene formations (Batini et al. 2003; Romagnoli is hosted at 500-1500 1) a shallow steam-dominated reservoir occur below the impermeable cover: reservoirs of tectonic levels nappe units and in the evaporitic carbonate formations of the Tuscan m depth in the Mesozoic of about 220- temperatures present-day by medium-high permeability, wedges complex, and is characterized in vapor- 250°C and a pressure of about 20 bar at 1000 m depth; 2) deep superheated steam reservoir, static equilibrium with the shallow one, is hosted in metamorphic basement and thermometamorphic between 300- ranging by a high anisotropic permeability distribution, temperatures rocks, and is characterized pressure of 70 bar at 3000 m depth. 350°C and a reservoir both in size variability, The high fracture a secondary permeability due to fractures. have Both the reservoirs case greater than 5 mD (Bertani that are in any of permeability values determines a wide range and density, low (1- rocks is homogeneous and very & Cappetti, 1995). Otherwise, the primary porosity of all reservoir system is usually homogenously distributed in the shallow carbonate- 1978). The fracture 5%) (Cataldi et al., in the rocks highs. On the other hand, fracturing formations, with higher densities in structural anhydrite The of permeability. showing a wide range of the metamorphic basement is inhomogeneous and localized chemical composition of the geothermal fluids at Larderello is dominated by H isotope data on H to a short residence time in the reservoir. An alternative explanation of the steam’s origin has been proposed by explanation of the steam’s An alternative to a short residence time in the reservoir. and magmatic the mixing of two end-members, meteoric waters, & Bolognesi (1994), who hypothesize D’Amore the crystallization of a fluids produced by geological field trips 2015 - 7(1.2) excursion notes 33 He- 4 /Ar ratios, indicating /Ar ratios, 2 /He and N 2 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias He ratios (expressed as R/Ra, where R (expressed as R/Ra, He ratios 4 He/ 3 excess. Moreover, a mantle component in the Moreover, excess. 2 He data and high N 4 He-enriched fluid, derived from the mantle, and a He-enriched fluid, derived He/ 3 3 is the measured ratio and Ra is the typical value for air), is the typical value and Ra is the measured ratio 2003, of 2.7–3.2 (Magro et al., reaching maximum values range R/Ra and references therein). Thus, the observed interpreted to be (0.5-3.2) of the geothermal fluids was mainly the result of different mixing proportions between a geothermal fluids at Larderello is suggested by the high relatively enriched fluid originating in the crust and most likely rocks. A good stored in the geothermal reservoir correlation exists between the depth to seismic K- areal (see description below) and the R/Ra horizon distribution (Fig. 22). The culmination of the reflector at a depth of about 3000–3500 m matches the highest R/Ra identify an area where well; this may contour lines very uplift of fluids mantle origin allows therapid existence in a typical crustal melting values high R/Ra of relatively 2003). (Magro et al., environment a large N Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 22 - Correlation between depth of the top K Magro et al. (2003). horizon (meters below the surface level) and R/Ra areal and R/Ra (meters below the surface level) horizon distribution in the Larderello geothermal area. Full dots: geothermal wells; full triangles: fumaroles; modified after DOI: 10.3301/GFT.2015.02 5.4 Past hydrothermal activity of the evolution field arises from the natural of the Larderello-Travale The steam-dominated characteristic context allowed the geothermal system to pass from an initial water system. In fact, the thermal and structural phase (shown in fluid inclusions) to the current steam condition. The depressurization of reservoir by the first drilling data happened prior to the industrial exploitation of geothermal resource, as verified 1975). The liquid phase is presently confined to a few local structures that facilitate in the area (Celati et al., 1995). (Barelli et al., into the reservoir the seepage of meteoric waters contribution’’ in the Larderello geothermal gases has been suggested by these authors on basis of stable in the fluids, as well existing isotope variations geological field trips 2015 - 7(1.2) excursion notes 34 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 23 - conditions P–T present during different stages in the geothermal system of Larderello obtained from fluid inclusion studies. Modified from Gianelli and Ruggieri (2002). Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 The oldest hydrothermal circulation in the deeper levels of field is likely related to the emplacement of of field is likely circulation in the deeper levels The oldest hydrothermal (with isotopic ages of 1.3-3.8 Ma) and the related thermal metamorphism. Thermally granitoids crystallization of by post-tectonic characterized micaschist and gneiss are generally metamorphosed phyllite, and pyrite, graphite plagioclase, muscovite, quartz, biotite, andalusite, cordierite and tourmaline; moreover also occur in garnet, corundum and sanidine may less frequently wollanstonite, spessartine and grossular-rich 2005). et al., 2002; Pandeli amounts (Gianelli & Ruggieri, variable rocks, contact-metamorphic of granite, alteration Subsequent fluid circulation caused hydrothermal and also of the sedimentary rocks tectonic metamorphic rocks not affected by contact-metamorphism been recognized have alteration main types of late hydrothermal nappe. Two wedge complex and of the Tuscan 1994): et al., 1982; Pandeli et al., (Cavarretta • of epidote, by veins characterized alteration, propylitic-type titanite, actinolite, chlorite, quartz, calcite, K-feldspar, proportions; albite and pyrite in variable anhydrite, • chlorite and quartz in different with K-mica, sericitic-type, and calcite filling veins proportions. In addition hydrothermal 1997). also occurs in sedimentary rocks (Gianelli et al., voids geothermal activity in the Larderello-Travale The long-lived types of fluids fields is reflected by the occurrence of several as fluid inclusions within igneous quartz, contact- trapped The different types minerals. metamorphic and hydrothermal of inclusion fluids within the magmatic and contact- metamorphic assemblages are the result of a complex during evolving sequence of fluid trapping 1994; conditions (Cathelineau et al., pressure–temperature 2007, and references therein) (Fig. 23). Li-Na- Boiron et al., rich saline fluids and compositionally complex brines and aqueous-carbonic fluids from granites), (exsolved rocks during contact (produced by heating of Paleozoic geological field trips 2015 - 7(1.2) excursion notes 35 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea , are thought to be of prevalently meteoric origin, while liquids with variable salinities and containing meteoric origin, while liquids with variable , are thought to be of prevalently 2 DOI: 10.3301/GFT.2015.02 dissolved Ca and Mg, in addition to Na, are believed to be derived from the interaction of (meteoric?) water from the interaction to be derived Ca and Mg, in addition to Na, are believed dissolved nappe and/or to represent connate waters sequences occurring in the Tuscan with evaporite-carbonate during geothermal activity and/or to be the result of fluid boiling and mixing processes (Gianelli et mobilized 1999). et al., 1997; Ruggieri al., 5.5 The K-horizon 2005) highlighted the presence of an 1997; Brogi et al., 1983; Gianelli et al., seismic data (Batini et al., Reflection crystalline basement, intense and continuous reflector exhibiting local “bright spot” features inside the Palaeozoic and 8–10 km in the Travale between 3–4 km in the western zone Its depth varies the so-called K-horizon. is associated with the 400°C isotherm and considered 2006). The K-horizon geothermal area (Bertini et al., et (Romagnoli base of the reservoir in the reached during deep drilling, except never was 2010). The K-horizon al., fluids, and its nature is still a subject of of pressurized well, which blew out on reaching this zone SANPOMPEO_2 the only phenomenon that is able to account regardless of the interpretation K-horizon, debate. However, filled locally by fluids (Marini & and micro-fractures for this seismic “bright spots” is the presence of micro-cracks at the shear zone has been interpreted also as the upper boundary of an active 2005). The K-horizon Manzella, 2003). In this interpretation the lateral 1999; Brogi et al., (Liotta & Ranalli, top of the brittle-ductile transition where Pliocene-Present is interrupted by intersections with brittle shear zones continuity of the K-horizon normal that the loss of seismic reflectivity in correspondence to faults coalesce (Fig. 24). It has been hypothesized is connected to fluid migration and the top of brittle-ductile transition intersections between the shear zones 2003). (Brogi et al., along the shear zone to shallower levels from the K-horizon metamorphism) circulated during early hydrothermal activity linked to the intrusion of granites (Cathelineau to the intrusion of granites activity linked metamorphism) circulated during early hydrothermal usually at 1994). These fluids probably circulated at depth >2500 m below the ground level, et al., or at pressures 90–130 MPa of 425–690°C and under lithostatic pressures approximately temperatures (only the aqueous-carbonic fluids) during system decompression (Fig. 23). A more below lithostatic values and also as late in secondary minerals stage is also recorded in fluid inclusions trapped recent hydrothermal temperature by trapping quartz. This stage is characterized inclusions in magmatic and contact-metamorphic 1999, et al., salinities (Ruggieri pressures (Fig. 23), and fluids with variable usually of 150-400°C, hydrostatic aqueous liquids, sometimes containing small amounts of low-salinity and references therein). The relatively CO geological field trips 2015 - 7(1.2) excursion notes 36 – Paleozoic micaschist – Paleozoic 1 – Late Triassic evaporites; Monticiano evaporites; – Late Triassic M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias 1 – phyllite – quartzitic group; MRU – phyllite 2 – Early Miocene Rhetic sequence; TN 2 – Mesozoic – Paleozoic group; MRU – Paleozoic – Mesozoic 3 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 24 - Geological section of the Larderello area obtained integrating borehole stratigraphies, field data, and reflection borehole stratigraphies, Fig. 24 - Geological section of the Larderello area obtained integrating group; G: gneiss complex. Modified from Brogi et al. (2003). seismics interpretation. The K-horizon is interpreted as the upper boundary of an active shear zone (see text). Locations of shear zone is interpreted as the upper boundary of an active seismics interpretation. The K-horizon P – Pliocene sediments; M Miocene L: Ligurian and outcropping normal faults are shown by black arrows. Key: nappe (TN): TN Sub-Ligurian complex; Tuscan – Roccastrada unit (MRU): MRU – Roccastrada DOI: 10.3301/GFT.2015.02 On the other hand, Bertini et al. (2006) suggest that the K-horizon occurs at the top of a Quaternary granite On the other hand, Bertini et al. (2006) suggest that K-horizon and related contact metamorphic rocks which are permeated by carapace and corresponds to the granite which can be represent in micro-cracks are likely supercritical fluid (Fig. 25). The fluids in the K-horizon process in rocks, a plastic or reactivation This micro-crack by episodes of fluid overpressuring. activated semi-plastic condition, is vital for the life of entire geothermal system because it enhances cyclic to the 2–3.5 km depth zone low-permeability and very high-temperature from a very heat transfer advective where most of the geothermal wells are actually drilled. with seismic features similar to the (H-horizon) another seismic horizon Bertini et al. (2006) also characterized at depths of 2–4 km, corresponding to the contact metamorphic rocks. the latter, but occurring above K-horizon geological field trips 2015 - 7(1.2) excursion notes 37 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias transition and by the very high volumetric thermal expansion at the high volumetric and by the very transition α–β Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 25 - Geological cross-sections of the Larderello area; H and K seismic horizons, isotherms and the radiometric ages of isotherms and the radiometric Fig. 25 - Geological cross-sections of the Larderello area; H and K seismic horizons, “granites” and thermo-metamorphic rocks are also shown. From Bertini et al. (2006) modified. “granites” DOI: 10.3301/GFT.2015.02 The H-horizon is interpreted as a fossil K-horizon, corresponding to the top of older granite intrusions. The corresponding to the top of older granite is interpreted as a fossil K-horizon, The H-horizon supercritical and related to the magma, during an early magmatic was horizon fluid hosted in this fractured were filled subsequently with fluids of stage of the system, as suggested by fluid inclusion data. The fractures 2006). Another explanation for the steam (Bertini et al., meteoric origin, and are now filled by super-heated (2005), who suggest that the proposed by Marini & Manzella was presence of pore-fluids in the K-horizon in quartz in quartz. Micro-cracking of micro-cracks is related to the development permeability in the K-horizon by the is favored pressure–temperature conditions around the depth of K-horizon. pressure–temperature geological field trips 2015 - 7(1.2) excursion notes 38 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 5.6 Geothermal production process at Larderello-Travale project begins with the identification of a geothermal resource that develops A geothermal development through the following steps: • of geothermal manifestations (hot springs, fumaroles, geysers, steam jets, investigation Surface exploration: an give Drilling shallow boreholes (50 to 200 m) may surveys. etc.), geological, geochemical and geophysical area indicate the most favorable The results of surface exploration gradient. indication of the local temperature phase. deep exploration to focus the more expensive • commercial diameter (up drilling of slim-holes (up to 1000 m deep) and/or wells having Deep exploration: to some km deep). The confirmation of the presence geothermal resource during deep exploration phase. will lead to the development • phase: drilling of wells for production and reinjection purposes, surface gathering system Development geo-thermoelectric power plant construction. an impact on our land. In the case of Larderello- A geothermal plant contains different elements that have at arrives reservoir from the vapor-dominated geothermal system, the superheated steam extracted Travale the nearest power plant through a steam gathering system (Fig. 26). The total fluid composition, at wellhead, is about 300°C while, when in the reservoir is usually 90-98% steam and 2-10% gas. The temperature of 200-240°C depending on the inlet pressure. is in the range at the power plant, its temperature it arrives 267 for production, 51 reinjection, and the remaining 173 ENEL drilled a total of 491 wells in Tuscany, other uses such as field monitoring and gas production. The steam pipe system (213 km long) is made up of with a sheet of aluminum painted steel pipes (150-800 mm diameter) insulated with rock wool and covered of the power plant, steam feeds turbine for conversion At with colors according to the vegetation. the turbine is returned to liquid state The exhaust steam leaving thermal energy into mechanical energy. geological field trips 2015 - 7(1.2) excursion notes 39 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 26 - Elements of a geothermal project. Photos from ENEL (2009). Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 in a condenser, while the non-condensable gas contained in steam is dispersed to atmosphere after an in a condenser, produced by the power plant cooling towers must be injected at depth appropriate treatment. The water new or to give cycle through appropriate drilled wells (reinjection wells) in order either to close the natural connected to the pipe system is 317 km long. The generator, fuel to the geothermal field. The ENEL water geological field trips 2015 - 7(1.2) excursion notes 40 abatement system (ENEL, 2009). M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias ® Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 27 - Simplified scheme of a standard geothermal power plant equipped with AMIS DOI: 10.3301/GFT.2015.02 turbine axis, transforms the mechanical energy into electrical energy that is subsequently transmitted to the the mechanical energy into electrical that is subsequently transmitted turbine axis, transforms to 132 kV and feeds it into the national grid. the voltage raises (Fig. 27). The transformer step-up transformer Control Center”where located in Larderello, All of the ENEL power plants are remotely controlled by a “Remote In addition, alarm messages are sent in order to alert the appropriate staff. and any parameters the operating personal computer connected to the ENEL network remote supervision from any have ENEL personnel also may access to all the power plant data, their processing and diagnostics, etc. (ENEL, 2009). which gives geological field trips 2015 - 7(1.2) excursion notes 41 siderite, 3 calcite, FeCO 3 safely over geological times safely over 2 -bearing phases to form. 2 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias dolomite, CaCO 2 ) 3 wollastonite) to geologically and thermodynamically 3 and solid reactants require transport to a surface and solid reactants require transport 2 -bearing meteoric/hydrothermal fluids where prolonged regional -bearing meteoric/hydrothermal 2 magnesite, MgCa(CO 3 serpentine, CaSiO 4 (OH) 5 O 2 Si 3 mineral sequestration (where CO sequestration mineral dawsonite). This technology attempts to mimic natural low-temperature alteration (carbonation) alteration low-temperature dawsonite). This technology attempts to mimic natural Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea 2 forsterite, Mg 4 ex situ )(OH) SiO 3 2 geological storage and consists of an induced exothermic alteration of metal-rich non-carbonate minerals alteration and consists of an induced exothermic geological storage 2 DOI: 10.3301/GFT.2015.02 stable mineral carbonates (i.e., MgCO carbonates (i.e., stable mineral Magnesite deposits, hosted in extensively altered ultramafic rocks, are common throughout the world and occur altered ultramafic Magnesite deposits, hosted in extensively or stockwork bodies of cryptocrystalline magnesite, with minor amounts talc, quartz and dolomite as veins are usually interpreted as 2009, and references therein). Metric to kilometric magnesite veins (Boschi et al., with CO interacted rocks that have ultramafic of widespread silicate rocks (i.e., peridotite, serpentinite, basalt) that trap CO peridotite, serpentinite, basalt) that trap of widespread silicate rocks (i.e., (Seifritz, 1990; Goff & Lackner, 1998; Lackner, 2003). Since Seifritz (1990) proposed the idea of an induced 1998; Lackner, (Seifritz, 1990; Goff & Lackner, industrial 6. Carbon dioxide sequestration by mineral carbonation in serpentinite rocks of Southern Tuscany 6.1 Geological framework to is a potential alternative silicate minerals through carbonation of natural sequestration mineral Carbon dioxide CO tectonics have been active, and have produced continuous networks of shallow crustal fractures. produced continuous networks of shallow crustal fractures. and have been active, tectonics have been first noted in having in Tuscany, recent discovery Serpentinite-hosted magnesite deposits represent a relatively exploited between 1914 & Orlandi, 1972). They were actively 1900 (Marinelli, 1955; Sartori, 1967; Grassellini-Troysi bricks in the iron industry production of magnesite (0.3 Mt) used for refractory and 1945, leading to a considerable NaAl(CO sequestration site), many carbonation approaches were proposed and several gas–solid and aqueous–solid carbonation approaches were proposed and several site), many sequestration and economic reactions. Most of in order to design more effective been investigated carbonation processes have shown that induced carbonation does not go to completion because the experimental studies on serpentine have inhibiting the of the serpentine act as a diffusion barrier, precipitated carbonates or remaining silica-rich layers of serpentine 2009, and references therein). In addition, the slow rate of the process (see Boschi et al., evolution dissolution and decrease of porosity during the reaction lower efficiency reactions. The study low- analogues of the induced rocks and associated magnesite deposits, natural carbonated ultramafic temperature studies and provide and demonstration can complement laboratory sequestration, mineral carbon dioxide the boundary conditions and mechanisms for CO opportunities to constrain (i.e., Mg (i.e., geological field trips 2015 - 7(1.2) excursion notes 42 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias , a 2 mineralogical 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 28 - Two polished slabs of Malentrata ore displaying polished slabs of Malentrata Fig. 28 - Two al., 2009). al., the brecciated-crustiform texture, and variations in color. the brecciated-crustiform texture, and variations magnesite, Dol: dolomite, Fe-rich (Mgs: magnesite, Fe–Mgs: serp: silicified serpentinite; from Boschi et Chalc: chalcedony, DOI: 10.3301/GFT.2015.02 spontaneous carbonation of buried serpentinites and could be an ideal place to test in situ CO (Boschi et al., 2009, 2010). Several deposits are known 2009, 2010). Several (Boschi et al., from almost all the serpentinite outcrops in Tuscany Colline Metallifere, Elba Island). The (Monti Livornesi, large, magnesite deposits are considerably inland Tuscan up to 15 m thick and being represented by tens of veins a vertical that were exploited over 800 m on strike extent of at least 100 m. All the ore bodies show similar sub- a general Fig. 28) and have (e.g., mineralogy coherent with the attitude trending NNW–SSE, vertical faults in the region. main extensional, high-angle The deposits lie at the northern periphery of active geothermal field where granite Larderello–Travale intrusions were cored at depths of about 3300–4800 m 26B, 2A and 7, VC11 Radicondoli in the Monteverdi 2005; Fig. 29). The 29 and 30 wells (Dini et al., presence of the Larderello geothermal field entails that heated at anomalous the buried rocks are naturally in this area, at a deep less than 1000 m temperatures; is of about 150°C the temperature below ground level, 2008,(see Boschi et al., for details). This peculiar geological situation enhances, in the presence of CO geological field trips 2015 - 7(1.2) excursion notes 43 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias , 2 is important. A new 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 29 - Geological map of Southern Boschi et al., 2009). Boschi et al., Tuscany (Italy) showing the distribution of Tuscany magnesite, and other ore deposits with geothermal respect to the Larderello–Travale field. The occurrence of magmatic rocks at the surface and at depth (red triangles highlight geothermal wells that intersected at depth of Pliocene–Quaternary granites about 2500–5000 m) is also reported. Red the temperature dashed contour lines display distribution at depth of 3000 m below sea Super heated steam production level. are indicated by dashed orange reservoirs areas. Black areas indicate main towns (from DOI: 10.3301/GFT.2015.02 sequestration of unaltered buried sequestration serpentinites. Boschi et al. (2008) showed serpentinites can that outcropping Tuscan store up to 100 gigatons of CO equivalent to 40-220 years of total Italian to 40-220 years equivalent 580 Mt/yr for emissions (approximately assuming that only 2010). Even the year 10% of the ophiolite bodies can be into magnesite, the amount transformed of sequestered CO detailed study (Trumpy et al., 2010) et al., detailed study (Trumpy the most suitable areas in Tuscany reveal potentials for and their CO2 storage CCS mineral applying in-situ and ex-situ technology. geological field trips 2015 - 7(1.2) excursion notes 44 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias U dating of dolomite from Malentrata indicates an age of less than 200,000 years for indicates an age of less than 200,000 years U dating of dolomite from Malentrata 234 Th/ Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea 230 DOI: 10.3301/GFT.2015.02 6.2 The Malentrata deposit area are represented by a complex stacking sequence, made up several The ligurides in the Malentrata (cherts, limestones and shales), turbiditic tectonic units that include ophiolites, sedimentary cover sediments. The main ophiolitic bodies, dominated by serpentinites with minor gabbros and basalts, form an a stack formed by ENE trending discontinuous alignment (Fig. 29). The Ligurian units lie tectonically above metamorphic units nappe and the Palaeozoic–Triassic units). The Tuscan units of continental affinity (Tuscan magnesite deposit to the south of study area (Fig. 29), while below Malentrata crop out extensively as indicated by some geothermal they are buried at a depth of about 1300–1500 m below sea level, 1998). 2000; Barbier et al., wells (Bertini et al., exploratory hosted by silicified, carbonated and carbonate–silica veins magnesite deposit consists of several The Malentrata argillified serpentinites of the Ligurian units (Fig. 30a, b). Serpentinite silicification and carbonate–silica veining Castiglioni is common in the Monterufoli district, but it reaches highest intensity Malentrata–Poggio area. The ophiolite host constitutes disrupted decametric to pluri-kilometric masses embedded in a complex arenites and calcarenites; sequence of sedimentary formations (shales, calcilutites, siliciclastic–carbonatic Serpentinite-hosted veins occur in the sedimentary envelope. never 2000). Carbonate–silica veins Bertini et al., show sharp terminations against magnesite the sedimentary formations, as already reported for other Tuscan deposits (Marinelli, 1955). The Ligurian units in the Monterufoli area are limited to west by NNW–SSE deposit, Neogene La Sterza basin. This basin suddenly changes orientation 2 km south of the Malentrata basin (Fig. 29). trending, Neogene Serrazzano–Cornia segment connected to the N–S an eastward developing The tectonic structures at the scale of deposit reflect previously described pattern with faults and and anti-Apenninic showing a bimodal distribution of their orientation: Apenninic (NNW–SSE) fractures show a quite regular attitude with dominance of the carbonate–silica veins However, and E–W). (NE–SW 2009). They are (Fig. 30; see also Fig. 2 in Boschi et al., strikes and NW–SE and minor NNE–SSW NNW–SSE dipping to the west. immersion to the east and only few veins (dip 50–90°) with a general mostly sub-vertical sudden changes in thickness (from a few cm up to 4 m) and length meters display The veins up extent of a vertical to 200 m), and they were explored/exploited by underground open pit works over about 100 m. geological field trips 2015 - 7(1.2) excursion notes 45 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 30 - a, b) Representative examples of carbonate–silica veins hosted by silicified, carbonated and argillified examples of carbonate–silica veins Fig. 30 - a, b) Representative serpentinites at Malentrata. DOI: 10.3301/GFT.2015.02 the veining event (Bertini et al., 1996). During such a short time span, erosion can have removed only a few removed 1996). During such a short time span, erosion can have (Bertini et al., event the veining shallow crustal levels. formed at very tens of meters and suggests that the veins 6.2.1 The silicified serpentinite host and the main carbonate–silica veins into brownish friable rocks containing opal, montmorillonite, Fe-rich Serpentinite host rocks were transformed The silicified–carbonated serpentinites experienced several magnesite and minor iron sulfides oxides. of small veins infilling. They are crosscut by a network of very stages of brecciation and carbonate vein to the main showing an attitude sub parallel of dolomite veins, magnesite and by a subsequent generation spacing (Fig. 31). In some brecciated portions, opal occurs as dispersed and a variable carbonate–silica veins, geological field trips 2015 - 7(1.2) excursion notes 46 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias fragments cemented by a magnesite fragments matrix. In other portions, magnesite embedded in appears as fragments precipitated opal suggesting a non- systematic sequence of precipitation. the early stage of magnesite Overall, indicates that carbonate veining associated with the precipitation was silicification of the rock and repeated resulting in a brecciation events, texture. complex brecciated-veined are Main carbonate–silica veins infill by an early massive characterized of cryptocrystalline creamy-white magnesite (Fig. 28) containing angular (millimetric to decimetric in fragments of the silicified serpentinite. size) Cryptocrystalline magnesite shows a showing polygonal texture with grains small nuclei surrounded by Fe- Fe-rich poor larger rims. Most of the massive are brecciated and show a veins “cement supported” brecciated of the early structure with fragments magnesite infill and host rocks cemented by banded Fe-rich magnesite, green and pale-brown quartz and opal. dolomite, chalcedony, from millimetric to vary Fragments Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 31 - SEM images in backscattered electron mode showing the typical from Boschi et al., 2009). from Boschi et al., texture of the altered serpentinite host rock: a) example bastite replaced by b) Detail shows lepispheres of opal-CT; montmorillonite and opal-CT. and amounts of water) micrometric intergrowth of opal-CT (with variable crosscutting altered serpentinite magnesite veinlets magnesite; c) Fe-zoned cemented by magnesite and late dolomite (modified host; d) opal fragments DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) excursion notes 47 loss (boiling) 2 century, and was century, th and depleted in MgO (see Boschi 2 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias -rich and silica-rich hydrothermal fluids; 2) in situ silica precipitation -rich and silica-rich hydrothermal 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 et al., 2009, particularly their Fig. 10). These data suggest that silicification of the Malentrata serpentinites was 2009, particularly their Fig. 10). These data suggest that silicification of the Malentrata et al., system. Most likely, accompanied by external input of silica, and mobilization magnesium to the vein and were focused in fluids escaped from their original reaction zones pH Mg-bearing hydrothermal moderate/low where they experienced pressure loss and precipitated carbonates. About 70% of the original the fractures, into incorporated while the remaining 30% was to the main veins, leached and mobilized magnesium content was of magnesite, resulting from The calculated volume the host rock as carbonate disseminations and veinlets. proportion volumetric of serpentinite, is consistent with the observed magnesium mobilization of a unit volume and altered serpentinites in the field. between main carbonate veins of the fractured we identified the following processes: 1) dissolution at low temperature In summary, serpentinites by slightly acidic CO centimetric (up to 15 cm). The fragments of the host rock display irregular shape, while cryptocrystalline of the host rock display centimetric (up to 15 cm). The fragments Whole-rock been observed. have angular fragments are mostly rounded although many magnesite fragments chemical analyses of the altered serpentinites show that they are enriched in SiO resulting in a brecciated texture, and local magnesite precipitation; 4) migration of fluids into a network resulting in a brecciated texture, and local magnesite precipitation; 4) migration 5) boiling of the escaped fluids and beginning pathways; and consequent focusing along main structural fractures precipitation of magnesite and lateof the massive 2008, 2009, 2010). The two-step- dolomite (Boschi et al., reaction proposed here – from the congruent dissolution of serpentinite and precipitation carbonates away –host-rocks into the rock. allowing for a more efficient fluid infiltration led to an increase of the initial porosity, 6.3 The Montecastelli carbonated area kilometers across at the Montecastelli site, embedded in shales, has been deeply A body of serpentinite several portion of the serpentinite body good geological exposures. The central and provides River eroded by the Pavone intermittently exploited during the 19 hosts a small copper ore deposit that was (near the river) penecontemporaneous with serpentine dissolution; 3) hydraulic fracturing and subsequent CO fracturing with serpentine dissolution; 3) hydraulic penecontemporaneous definitively closed in 1869. Bornite, chalcopyrite, chalcocite and pyrite veinlets and nodules, in a chlorite-serpentine- closed in 1869. Bornite, chalcopyrite, chalcocite and pyrite veinlets definitively crosscutting the serpentinites. The ore narrow deformation zones soapy gangue, characterize brucite-amphibole not high period was during the exploration and most of the material extracted low grades bodies contain very of the mine, forming a dumped directly in front of the entrances for industrial processing and it was enough grade geological field trips 2015 - 7(1.2) excursion notes 48 the (c) (d) and the distal (b) represents a (a) (e) Fig. 32 - Pictures of: from Boschi et al., 2013. from Boschi et al., M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias are close up views of (a), showing clasts of serpentinite encrusted by whitish carbonates; of the particular of the carbonated wall serpentinite escarpment (d). Modified part of the mine tailing and; serpentinite escarpment; small mining dump. Further small mining dump. activities inside the mine exploration Intense than 60 years. are younger carbonation produced a crust of Mg-carbonates coating the hydrated serpentinite clasts of the mining of dump and the serpentinite walls 2013). the mine adits (Boschi et al., On the western side of Pavone a large escarpment of River, incoherent serpentinites shows scattered, narrow spots, some meters wide, of whitish carbonated serpentinites that were shielded from (Fig. 32). alkaline spring waters These altered areas are by an intense characterized Mg- precipitation of hydrated along the carbonates and aragonite and at the rock surface. fractures Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) excursion notes 49 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 In the serpentinites escarpment (Figs. 32d, e), a network of fractures crosscut the rocks, showing large In the serpentinites escarpment (Figs. 32d, e), a network of fractures the oriented, clearly post-dating are randomly Mg-carbonates. Fractures partially filled by hydrated cavities at the Montecastelli mine (Figs. 32a, c) are composed of a bottom Tailings early oceanic serpentine veining. distributed up to 4m thick, of serpentinite clasts (up 60 cm in diameter) that are randomly incoherent layer, from 10 cm to 1 m in thickness, consists ranging between clasts. An intermediate layer, with frequent voids whitish carbonate-rich materials embedding altered clasts of serpentinites and copper fine-grained of very a 15-40 cm of type c soil is alternating with minor quantities serpentinite clasts the top, sulfide-rich ore. At and tree and grained disappears, and very-fine roots. On the distal part of tailings, bottom layer part prevail. alternating with a greenish serpentinite- and clay-rich incoherent carbonate-rich layers in intercepted a gently dipping fracture In the mine, an inclined rising adit, approaching Cu-rich orebody, along the roof and produces a film of water flow from the fractures serpentinite. Continuous water massive Aragonite hanging wall. dripping from the fractured of the adit as well water the walls Mg- and hydrated carbonates continuously form on the wet surfaces of adit. 6.3.1 The serpentinite and the hydrated Mg-carbonates indicate their original texture. OM and SEM-EDS observations The Montecastelli serpentinites mostly preserve that the mesh texture of serpentine after olivine, surrounded by magnetite-enriched rims and relicts Fe- fine-grained Very of primary spinel (Mg-chromite), typical oceanic serpentinites, are easily recognized. either associated with serpentine at SEM-EDS observations brucites are frequently observed poor and Fe-rich A later network of light green chrysotile veins, cutting the earlier minerals. in the mesh texture, or as veins represent crosscut the outcrops. These veins centimeters, pervasively thickness up to several with variable of weakness where later meteoric fluids could be concentrated. preferential zones growing on the along these fractures, Mg-carbonate precipitate is often observed the hydrated Actually, is accompanied by carbonate precipitation as a laminar/rounded surfaces. Carbonate veining external vein whitish crust on the external surface of rocks and/or as spherules up to 1 cm in diameter with radiating the laminar crust or directly on top of rock (Fig. 33). In addition to these types, a needles above with them. to be intermixed fibrous whitish material has been observed geological field trips 2015 - 7(1.2) excursion notes 50 O), 2 ·4(H 16 )(OH) 3 (CO 2 Al 6 O) and minor amounts of 2 ·4(H M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias 13 uptake. 2 Fig. 33 - Examples of hydrated Mg- Fig. 33 - Examples of hydrated on the external surfaces of rock. )(OH) 3 carbonates on serpentinites of the Mantecastelli area. The sample shows the two main type of precipitation: laminar whitish crust and spherules Ca= 0.02 mEq/l). These data suggest with interacted rainwater that infiltrated the host serpentinite rock, increasing pH and Mg content, without buffering its isotope composition. The three areas show evidence of a rapid Mg-carbonates as precipitation of hydrated and between rainwater result of interaction serpentinites with ongoing atmospheric CO O), manasseite, Mg 2 +(CO 3 Fe ·3(H 6 3 O), brugnatellite, Mg 2 ·4(H 16 )(OH) 3 +2(CO 3 Fe Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea 6 DOI: 10.3301/GFT.2015.02 aragonite (Boschi et al., 2013; Bedini et al., 2013). No silica has been detected or observed in the field. 2013). No silica has been detected or observed 2013; Bedini et al., (Boschi et al., aragonite fluids (sampled close to the serpentine escarpment) show high pH (~8.2) and Mg Ca Spring water (pH = 5.7; Mg= 0.04 and compared to the local rainwater (57 and 6.1 mEq/l, respectively), concentrations XRD analyses of selected samples revealed that the hydrated Mg-carbonate minerals are mostly hydromagnesite, Mg-carbonate minerals that the hydrated XRD analyses of selected samples revealed amount of nesquehonite, MgCO with minor and variable pyroaurite, Mg geological field trips 2015 - 7(1.2) itinerary 51 century. th M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias century BC. Narrow shafts and inclined tunnels th century BC. -6 st th Day st 1 century for a systematic exploitation of the Cu-Pb-Ag ores. From 1841 several century for a systematic exploitation of the Cu-Pb-Ag From ores (Temperino mine, Campiglia M.ma) to From ores (Temperino th metals (Baratti-Populonia archaeometallurgical site) metals (Baratti-Populonia century, the Grandukes of Tuscany undertook new exploration and small-scale production for undertook new exploration of Tuscany the Grandukes century, Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea th – The Etruscan “Chariots Tomb” (S. Cerbone necropolis, Populonia) (S. – The Etruscan “Chariots Tomb” – The Temperino adit, from Etruscan to modern exploitation – The Temperino skarn deposit stope, the Cu-Pb-Zn-Ag Cava – Earle shaft and Gran mining village in a medieval a time travel San Silvestro, – Rocca – Short visit to the Acropolis of Populonia – (Populonia) The beach slag deposit at Baratti DOI: 10.3301/GFT.2015.02 mining companies began to explore the deeper part of ore deposits by excavation of crosscut adits and shafts. mining companies began to explore the deeper part of ore deposits by excavation silver but we must wait the 19 but we must wait silver were excavated directly on the Cu-rich orebodies at the surface, and driven to significant depth (around 100 m) directly on the Cu-rich orebodies at surface, and driven were excavated in the (oil lamps, vases) of Etruscan ceramics fragments several below the surface. Archaeologists discovered exploitation led to the formation of quite large rooms at depth that were underground works. The intensive abandoned in the 1 when the mine was by water invaded STOP 1.1 STOP 1.2 STOP 1.3 STOP 1.4 STOP 1.5 STOP 1.6 Stops 1.1-1.3: The Temperino Cu-Pb-Zn-Ag skarn deposit, Campiglia Marittima mine during the 9 Mining activity started at the Temperino During the 16 After almost one millennium, between the 900 and 1300, mining activities flourished again. Chalcopyrite- activity was (up to 2 kg per ton) and medieval are particularly rich in silver galena-rich ores at Temperino demand for coinage at the Pisa mint. The powerful family Della Gherardesca triggered by the increasing silver to control the whole process: from ore San Silvestro) established a settlement in the mine area (Rocca underground works similar in shape miners excavated exploitation to metal production (mainly Ag). Medieval deposits in other areas and the political decline of richer Pb-Ag to the Etruscan ones. The discovery and size abandonment of the area at beginning 14 of Pisa contributed to the rapid geological field trips 2015 - 7(1.2) itinerary 52 (15 cm). openings crystals on exploitation from Etruscan chrysocolla crusts Fig. 34 – Gypsum M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 Modern underground works intercepted many old stopes, Modern underground works intercepted many and exposing beautiful rooms with walls off water draining by blue-green crusts of chrysocolla, malachite covered and azurite lined by large crystals of gypsum and copper (Fig. 34). Exploration dendrites of native small-scale exploitation intermittently continued until the but all the companies had severe War, Second World and the mineral availability problems with water processes. Between 1950 and 1976 a small separation the mine and introduced flotation, ran mining company resource in karstic a significant water and discovered marbles at the bottom of main Earle shaft. Total production during the last management consisted of 40000 t of galena/sphalerite and 30000 chalcopyrite In 1983, mining with about 24 tons of silver. concentrates permits expired and since 1996 the whole area of mine has been part of the San Silvestro Temperino Archaeomining Park. STOP 1.1: The Temperino adit, from Etruscan to modern exploitation of San at the Archaeological Mines Park After arrival could start the (guided) visit of (Website), you Silvestro adit mine from the so-called “Temperino” the Temperino is located in an old mining (Fig. 35); the entrance dug around the mid- adit was building. The Temperino 1800s to explore the southern end of skarn deposit and the deepest part of ore bodies reached by miners. The first part of the Etruscans and medieval geological field trips 2015 - 7(1.2) itinerary 53 th and th century because it th M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias century) exploitation activities. Most of th was one of the main access paths for miners was of the mine (see to the lower levels inclined shaft on the right descending to 2 and 3). level 20 underground path is a typical meandering 19 century drift crosscutting marble host rocks. After about 70 m we enter the skarn orebody of dark-green layers that exhibits rhythmic with hedenbergite and black ilvaite and masses of disseminations, veinlets chalcopyrite, pyrite, pyrrhotite, galena and sphalerite. this point the morphology of underground At works suddenly change from a narrow adit to an irregular “rooms and pillars” excavation of old opening that resulted from the overlap and modern (19 (Etruscan, medieval?) the narrow Etruscan excavation openings are the narrow Etruscan excavation partially or totally occupied by mining infill (poorly sorted clasts of both barren and ore- rich skarn) cemented by chrysocolla, malachite, azurite, gypsum and native assemblage A similar mineral copper. in the upper part encrusts the exposed walls openings (not visible of the old excavation along the tourist path; Fig. 36). The large opening was “rooms and pillars” excavation mainly dug during the 20 of the stops. showing the location Fig. 35 – Sketch map of the Temperino mine Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) itinerary 54 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias . The surfaces of geodes are lined by prismatic 3 up to several m up to several 3 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 36 – Upper part of an old excavation opening showing encrustation of chrysocolla and gypsum. Fig. 36 – Upper part of an old excavation DOI: 10.3301/GFT.2015.02 crystals of quartz (up to 40 cm in length) and more rarely by fine crystals of ilvaite (1-8 cm), pyrite and, more by fine crystals of ilvaite crystals of quartz (up to 40 cm in length) and more rarely of acidic dyke trending subvertical are crosscut by a NW-SE garnet. Marble, skarn, and mafic porphyry rarely, The walls and roof of the main opening provide a very good 3D picture of textures/mineralogy of skarn orebody good 3D picture of textures/mineralogy a very and roof of the main opening provide The walls the typical entirely hosted by skarn, display of mafic porphyry, masses. Masses and dykes and mafic porphyry olivine texture with phenocrysts of plagioclase, pyroxene, greenish-grey colour and a prominent porphyritic of sanidine (centimetric megacrysts) and quartz. Several and biotite associated with resorbed xenocrysts or irregular spheroidal (geodes) are found in the skarn. Most of geodes show pipe-like residual voids hedenbergite-ilvate layered geometries but, sometimes, they mimic the cuspate geometry of rhythmically from few cm skarn. Their dimensions range geological field trips 2015 - 7(1.2) itinerary 55 Earle shaft, Fig. 37 – The Temperino mine. M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 porphyry. The acidic porphyry (originally syenogranitic in composition) (originally syenogranitic The acidic porphyry porphyry. is made by small phenocrysts of quartz, groundmass. When hosted by marble, the acidic fine-grained plagioclase and biotite set in a very K-feldspar, sericite potassic alteration; maintains its original magmatic texture (in spite of the pervasive porphyry and adularia), while portions hosted by skarn are totally replaced a propylitic assemblage (epidote ± calcite epidosite. fine-grained quartz) resulting in a beautiful olive-green, drift, wider than the we enter a long, straight the northern end of main “rooms and pillars” excavation At along this drift you dug in the 1960s as a minor haulage drift of mine. Walking previous one: it was and spectacular drapes openings, beautiful outcrops of skarn and ore minerals, encounter other old excavation surface of the tunnel. It is an ongoing process triggered by meteoric the lateral of blue chrysocolla covering path followed a downward leached copper and silica from the Cu-rich skarn above, that, after having water is frequently water until it dripped off at the top of tunnel. Dripping Cu-saturated fractures along tiny are still soft. (depending on the season) and blue crusts drapes observed through the marble host until exit of tunnel. walk the skarn body and you leave After a few metres you quickly reaching the next stop. uphill through the Ortaccio Valley, Now we walk STOP 1.2: Earle shaft and Gran Cava stope, the Cu-Pb-Zn-Ag skarn deposit can you uphill along the Ortaccio Valley Walking slope of the hill the south-western observe mantled by large mining dumps (Fig. 35). They represent the residue of old and modern narrow inclined In fact, several excavations. shafts pierce the hill connecting surface to opening seen previously in the the excavation reach the adit. In a few minutes you Temperino the main shaft Earle shaft (212 m elevation): and for hoisting of drainage for ventilation, personnel and materials (Fig. 37). The original hoist house, cage and steel wire headframe, geological field trips 2015 - 7(1.2) itinerary 56 th M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias made difficult by widespread coatings. oxidation From the Earle shaft, moving north-east along the Ortaccio at the station of arrive you Valley, for tourists. The the mine train follows the path of tourist railway the Ortaccio adit (the so-called a 20 “diretta Lanzi-Temperino”), century tunnel connecting the to the Lanzi Valley Ortaccio Valley where the ore (to the north-west) were treated in the minerals flotation plants. The Ortaccio adit dug in marbles but, after a was Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea century) called the “Coquand shaft” from the name of French mining engineer that reopened mine th Fig. 38 – 3D view of the Coquand Section (modified after Da Mommio et al., 2010). Fig. 38 – 3D view of the Coquand Section (modified after Da Mommio et al., DOI: 10.3301/GFT.2015.02 ropes are still in good condition and the last descent was performed in 1998. It was originally (second half of performed in 1998. It was ropes are still in good condition and the last descent was 19 after many centuries of neglect. The main skarn orebody passes to the west shaft.after many Here, there is a small This known as the “Coquand Section”. that was quarry exposing a complete section of skarn and porphyries were described geological section represents the first locality in world where skarn textures and mineralogy and mapped cleared of vegetation the “Coquand Section” was 1868; Burt, 1982). Recently, Rath, in detail (vom layered and rhythmically ilvaite, in great detail (Fig. 38). Different skarn types (hedenbergite, massive is are well exposed but the observation acidic porphyry and epidotized mafic porphyry hedenbergite-ilvaite), few hundred metres, it crosscuts a second main skarn orebody, parallel to the one we visited in Temperino parallel few hundred metres, it crosscuts a second main skarn orebody, of the Ortaccio adit (north near the entrance passes through the valley of acidic porphyry adit. A thick dyke sanidine phenocrysts and texture with centimeter-scale side). The magmatic rock shows a prominent porphyritic groundmass (the so-called fine-grained smaller quartz, plagioclase, and biotite phenocrysts set in a yellowish that we saw earlier: it represents the is quite different from the acidic porphyry This dyke porphyry”). “yellow acidic porphyry. and also the epidotized crosscutting skarn, mafic porphyry, last magmatic event geological field trips 2015 - 7(1.2) itinerary 57 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias building, and metallurgical techniques of a medieval is via a path The access to the Rocca community. uphill, for about 20 starting from Villa Lanzi, walking minutes, through old mining areas (from Etruscan to modern time). and economic organization, the eating habits, The visitor follows an itinerary designed to show the social The visitor follows an itinerary on its industry and the managerial skills of lords. Silvestro as a center whose birth, development and decline depended as a center whose birth, development Silvestro the living quarters, the church, and the castle, which reveal Rocca San Rocca the living quarters, church, and castle, which reveal organization of the settlement, with areas set up for metallurgical production, organization of the living quarters to be defined. It is precisely internal spatial site, has revealed the complex layout of the village and allowed functional the complex layout site, has revealed centuries AD in order to exploit the local deposits of copper and silver-rich lead ore (Fig. centuries AD in order to exploit the local deposits of copper and silver-rich th numerous European university departments. The excavation, involving two thirds of the involving departments. The excavation, numerous European university and 11 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea th Fig. 39 – The medieval village of Rocca San Silvestro DOI: 10.3301/GFT.2015.02 6). These metals were used for coin production principally in the Tuscan mints (“zecche toscane”) of Pisa and mints (“zecche 6). These metals were used for coin production principally in the Tuscan times close commercial relations with these cities during the period. In medieval Lucca; the village lords enjoyed in has been discovered (a millstone, or “palmentum”, a Palmento” known by the name of “Rocca this village was dedicated. the oil press below church) and owes its present name to saint whom church was were started in 1984 by the San Silvestro village of Rocca at the medieval The first archaeological excavations with of Siena, in collaboration of Archaeology and History Arts the University Department of Teaching The last outcrop to be visited is the “Gran Cava” stope (Great Quarry): a large, horizontal excavation opening excavation stope (Great Quarry): a large, horizontal Cava” The last outcrop to be visited is the “Gran by the Etruscans and then enlarged during subsequent exploitation (20x15x60 m), (possibly) excavated is on the opposite side Cava” of the “Gran renaissance and modern times. The entrance workings in medieval, skarn, mafic porphyry, from the Earle shaft. Beautiful outcrops of hedenbergite-ilvaite of the Ortaccio Valley Cava”. occur at the “Gran acidic porphyry and epidotized STOP 1.3: Rocca San Silvestro, a time travel in medieval mining village founded as a seigniorial enterprise village of miners and smiths (Fig. 39), was a medieval San Silvestro, Rocca between the 10 geological field trips 2015 - 7(1.2) itinerary 58 Fig. 40 – Sketch map of the Fig. 40 – Sketch Benvenuti et al., 2000). et al., Benvenuti “Populonia - Baratti Archaeological - Baratti “Populonia with location of stops. The Park” dotted circle encloses the “Industrial area” (modified after M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 Stops 1.4-1.6: The archaeological Park of Populonia-Baratti Thus we enter the “Populonia-Baratti the road to Populonia. and take Piombino, back towards move We Archaeological Park” museum which includes a significant part of the ancient a real open-air (Website), Cerbone a unique Etruscan settlement built directly on the sea. After parking car at S. “Pupluna”, (Fig. 40). parking area, we can get on the shuttle bus to reach ancient Acropolis of Populonia geological field trips 2015 - 7(1.2) itinerary 59 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias nd century BC th -9 th Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 41 – The Acropolis of Populonia: view of the paved Fig. 41 – The Acropolis of Populonia: (courtesy of the Società Parchi Val di Cornia SpA). Val (courtesy of the Società Parchi street connecting the Temples with “Le Logge” edifice street connecting the Temples DOI: 10.3301/GFT.2015.02 STOP 1.4: Short visit to the Acropolis of Populonia two hills at the top of The acropolis extended over del del Castello and Poggio the promontory: Poggio (Fig. 41). From the very Molino (o del Telegrafo) the spectacular can enjoy hilltop of the Acropolis you view of the promontory Piombino and Gulf with the island of Elba at some distance and Baratti, the Etruscan necropolises, calcarenite quarries, and the industrial ironworking quarters below along plain. the Baratti “Villaggio delle capanne” join the Villanovian You (“village of huts”), where in the 8 cent. BC built important temples, thermal spas, and sanctuaries right in the heart of city. important houses were built on the Acropolis, to of accommodate the most ancient aristocracies There remain faint and picturesque traces Populonia. of these houses on the summit acropolis, not far from the monumental structures of another one, which around the 2 the Roman Populonia, geological field trips 2015 - 7(1.2) itinerary 60 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 42 – The Baratti beach slag deposit (photo by M. Benvenuti, 2007). beach slag deposit (photo by M. Benvenuti, Fig. 42 – The Baratti DOI: 10.3301/GFT.2015.02 STOP 1.5: The beach slag deposit at Baratti (Populonia) at the beach to see the shuttle bus and arrive Cerbone necropolis, we leave After returning to the S. an erosional slag discharged over remains of the slag deposit, a poorly cemented heap Etruscan and Roman and fragments cakes (Fig. 42). The bottom portion of the deposit mostly consists large plano-convex terrace of copper sulfides) on alteration of copper slags, clearly identifiable by the greenish spots (due to exogenous century BC. dated to the IX-VIII been radiocarbon have their surfaces. Copper slags from these layers of 26 to 40 cm (Fig. 43a); some them are diameters in the range have 2007). Slag cakes (Cartocci et al., films of magnetite by tiny crystals of olivine separated made of small needle-like each layer multilayered, of most the copper slag is quite homogeneous: a groundmass 2009b). Mineralogy et al., (Chiarantini minor) amounts of (but always olivine, hedenbergite, magnetite and scarce glass includes variable fayalitic preliminary main types of copper slags sulphides and metallic phases (Fig. 43b). Two “matte”(Cu-Fe±Zn) et al. proportions of matte sulphides and metallic phases were distinguished by Benvenuti based on relative geological field trips 2015 - 7(1.2) itinerary 61 copper slag cake; (a) M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias fragments of copper slag. fragments (c) Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea reflected light microscope image of a matte-rich copper slag showing several matte (±copper) droplets in a matrix of reflected light microscope image of a matte-rich copper slag showing several Fig. 43 – Macroscopic and microscopic features of copper slag from the Baratti beach slag deposit: Fig. 43 – Macroscopic and microscopic features of copper slag from the Baratti fayalite, pyroxenes and subhedral magnetite crystals; and subhedral pyroxenes fayalite, (b) DOI: 10.3301/GFT.2015.02 (2000): (1) slags enriched in metallic copper (called “type-A” slags), and (2) matte-rich slags (“type-B” (2000): (1) slags enriched in metallic copper (called “type-A” although in a small group of samples the two types metal-bearing phases occur almost equal amounts. by the presence of a silicate groundmass with The first group of copper slags (“Cu-rich slags”) is characterized abundant magnetite and droplets (up to 400 μm in diameter) of metallic copper (Fig. 43c), sometimes chalcocite, and digenite (Fig. covellite, metallic bismuth, lead and copper sulphides like associated with rare and copper does not occur in the form of metallic magnetite is scarce in the “matte-rich slags”, 43c). However, copper but as matte droplets (50-150 μm in diameter) showing fine exsolution textures (Figs. 43a-b). These features could indicate a multi-stage copper smelting process, with type-B slag belonging to an earlier (matte slags. production) stage than type-A geological field trips 2015 - 7(1.2) itinerary 62 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias in composition, as well calcium 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 tungstates (Figs. 44c-d). These mineralogical and geochemical features are in agreement with a provenance These mineralogical tungstates (Figs. 44c-d). W–Sn- of smelted iron ore from the hematite-rich deposits nearby Elba Island, which show characteristic 2013). et al., rich geochemical signatures (Benvenuti beach deposit. They are made up of of smelting furnaces are also commonly present in the Baratti Fragments 2003b). et al., (Benvenuti clay local Macigno sandstone and baked carried out in the last decades upper portion of beach slag deposit Archaeological excavations (Fig. 45). unearthed a number of simple hearths made with local sandstone blocks and bricks lined clay 2009a), have et al., These structures, interpreted as smithing/reheating hearths for iron working (Chiarantini been dated to century 2007). These hearths closely resemble the III-II century BC (Cartocci et al., the V-II (1988) in the upper portion of slag beach deposit, although latter BC furnaces described by Voss slag occurs in the upper than a forge. Abundant plano-convex author described it as a smelting furnace rather (wüstite, magnetite) and and iron oxides part of the deposit (Fig. 44e). Most them are made up fayalite which are the dominant processescould be related genetically to slagging and metal oxidation occurring high amounts of iron particles and during the heating of metal for hot forging. The relatively in some samples (Fig. 44f), observed oxides/hydroxides, indicate that a significant loss of iron took place added to the during iron working, while the abundance of quartz relics could imply use siliceous fluxes during the fashioning of and/or to minimise iron oxidation surface of the metal during welding operations 2009a). et al., objects (Chiarantini The largest portion of the archaeometallurgical deposit consists iron slag produced by both primary ironworking (smithing, etc.). The iron bloomery slags (Fig. 44a) (bloomery) smelting and by post-reduction olivine (with up to 1.45% CaO) in an iron-rich interstitial glassy are mainly a silicate groundmass of fayalitic Wüstite, which in itself is normally a eutectic of anorthite and fayalite. matrix (up to about 25 wt.% FeO), quartz, hematite and scheelite, occur in variable magnetite, hercynite, and partially smelted, relic phases like crystals in tapped slags occur as small laths amounts, and are especially abundant in furnace slags. Fayalite show a associated with micrometric dendrites of wüstite (Fig. 44b), while in furnace slags both minerals show abundant relics of tapped and furnace slags, conglomerates Unlike significant increase in size. glassy groundmass. Iron slags almost invariably hematite and quartz a more silica-rich (and FeO-poor) contain contain droplets of metallic iron (Fig. 44b). Some slags are enriched in tin and tungsten may and FeSn FeSn approximating micrometric globules of iron-tin alloys, geological field trips 2015 - 7(1.2) itinerary 63 (b) ̈ ), fayalitic ̈ stite (wü Tapped slag; Tapped (a) M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias backscattered image of a furnace slag, showing a grain of relic scheelite (sch). backscattered image of a furnace slag, showing grain (d) Reflected light image of globular hammerscale from sample shown in (e). Reflected (f) Reflected light image of an iron slag showing lamellar Ca-W phases (probably scheelite) and light image of an iron slag showing lamellar Ca-W Reflected (“hardhead”); (c) 2 Cross-section of a plano- convex slag showing inclusion of charcoal and, on the lower surface, hammerscale Cross-section of a plano- convex Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea (e) Fig. 44 – Macroscopic and microscopic features of iron slag from the Baratti beach slag deposit. Fig. 44 – Macroscopic and microscopic features of iron slag from the Baratti and particles from ground level; and particles from ground level; reflected light image of a tapped iron smelting slag showing a droplet of metallic iron (Fe) associated with wu reflected light image of a tapped iron smelting slag showing droplet metallic (Fe) olivine (ol) and glass (gl); and FeSn droplets of FeSn Scale = 10μm; DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) itinerary 64 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 45 – “Furnace III” (V-III cent. BC). This Fig. 45 – “Furnace III” (V-III aerial view at Baratti: Fig. 46 – The Charriots Tumb (courtesy of the Società Parchi Val di Cornia SpA). Val (courtesy of the Società Parchi a horseshoe, quadrangular shape. a horseshoe, quadrangular furnace, interpreted as a smithing hearth, was partly furnace, interpreted as a smithing hearth, was It has an internal in a slag-rich layer. excavated are made of diameter of about 25 cm; furnace walls in bricks or tiles, arranged sandstone blocks and clay DOI: 10.3301/GFT.2015.02 STOP 1.6: The Etruscan “Chariots Tomb” (S. Cerbone necropolis, Populonia) surely worth visiting at least one of the It’s most famous Etruscan tombs located in the Cerbone necropolis: the “Chariots nearby S. a fine example of the so called “tombe Tomb”, made up of rectangular burial a tumulo”, with an earthen tumulus chambers covered (Fig. 46). This monumental type of burial (with a diameter of 28 metres) appeared at in the VII cent. BC. The Chariots Populonia is the largest burial edifice found at Tomb It owes its name to the presence of Populonia. wheels within the a chariot with four-spoked in discovered The tomb was burial chamber. 1914 by A. Minto. geological field trips 2015 - 7(1.2) itinerary 65 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Day nd 2 The geothermal field of Larderello and the Malentrata mine The geothermal field of Larderello and the Malentrata Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea – The geothermal demonstrative well – The geothermal demonstrative San Martino” geothermal power plant – The geothermal equipment at the “Nuova at Monterotondo Marittimo gas vents – Natural mine: The Mio-Pliocene sedimentary cover – Malentrata of the ophiolites mine: The sedimentary envelope – Malentrata mine: The serpentinite protolith – Malentrata contact mine: The serpentinite-argillite – Malentrata mine: Carbonated serpentinites and carbonate-silica veins – Malentrata – The Geothermal museum of Larderello Fig. 47 – Location of Larderello geothermal (Stop 2.1 and Stop 2.2). museum and of demonstrative geothermal well museum and of demonstrative DOI: 10.3301/GFT.2015.02 STOP 2.1 STOP 2.1: The Geothermal museum of Larderello Massa Marittima, follow the signs to Leaving Larderello. The first stop is dedicated to the Geothermal museum (Fig. 47). The museum is located in one of the first buildings, recently restored, that the de Larderel family built during the initial period of STOP 2.2 STOP 2.3 STOP 2.4 STOP 2.5 STOP 2.6 STOP 2.7 STOP 2.8 STOP 2.9 Stops 2.1-2.4: The geothermal field of Larderello geological field trips 2015 - 7(1.2) itinerary 66 Larderello. Geothermal Fig. 48 – The demonstrative well at demonstrative M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias centuries, to the present time with exploitation and exploration th and 18 th century). The museum, founded by the Larderello Joint Stock Company in the late century). The museum, founded by the Larderello Joint Stock Company th Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 industrial exploitation (18 STOP 2.2: The geothermal demonstrative well The geothermal well N120 is located about 700 m ESE from the Geothermal Museum (Fig. 47). This purposes. It was well is used for demonstration drilled in 1956 into the first geothermal reservoir and it is equipped with an electrically controlled Both the depth and capacity of this opening valve. This well, when it well are considered moderate. column of rise to an impressive is opened, gives steam at about 220°C (Fig. 48). The main well features are: • depth: 740 m Total • Casing: up to 600 m depth • Steam capacity: 20 t/h • 220°C Steam temperature: • Output pressure: 5 bar • Outflow speed: 400 m/s • sequence: formations belonging to Stratigraphic the Ligurid unit and tectonic wedge complex. 1950s, outlines the local history of geothermal energy (Website). It hosts finds and tools from Etruscan 1950s, outlines the local history of geothermal energy (Website). periods when the geothermal resources were mainly used for thermal baths, continuing through Roman production in the 17 period of borax for electricity production, and showing drilling methods (well-illustrated with models and original equipment) for electricity production, and showing drilling methods (well-illustrated as well certain aspects of using geothermal fluids to produce thermal and mechanical energy, different ways of theof the social development from the Larderello area are also exhibited. area. Samples with minerals geological field trips 2015 - 7(1.2) itinerary 67 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias of ENEL (Fig. 49). This Stop will visit examples in the different geothermal equipment involved geothermal production process. The equipment (comprising drilling technology of geothermal the wells, a sectioned turbine with an alternator, AMIS system, and examples of the use steam for multiple purposes) are exhibited educational San purposes along the perimeter of Nuova Martino geothermal power plant (Fig. 50). Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 50 - Nuova San Martino geothermal Fig. 50 - Nuova power plant (built 2005). Fig. 49 – Location of Stop 2.3 (Nuova San Fig. 49 – Location of Stop 2.3 (Nuova (Natural gas vents at Monterotondo Marittimo). gas vents (Natural Martino geothermal power plant) and Stop 2.4 DOI: 10.3301/GFT.2015.02 STOP 2.3: The geothermal equipment at the “Nuova San Martino” power plant route, and at pass the village along SS398 From Larderello follow the road signs to Monterotondo Marittimo, San Martino Centrale about 1.5 km from Monterotondo Marittimo turn on the left following sign for Nuova geological field trips 2015 - 7(1.2) itinerary 68 ® ® ® M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias (over 95% by weight of the NCG). (over 2 S and Hg. 2 S and 95% for Hg. The first commercial unit (Figs. 51 and 52) was installed in 2002 on a S and 95% for Hg. The first commercial unit (Figs. 51 52) was 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea system has been installed on new and existing geothermal power plants in a continuing program ® DOI: 10.3301/GFT.2015.02 that is still in progress. A recent study (Pertot et al., 2013) evaluated the air quality controlled by AMIS 2013) evaluated et al., that is still in progress. A recent study (Pertot The drilling equipment on display are part of the drilling technology utilized by ENEL for a geothermal drilling are part of the drilling technology utilized The drilling equipment on display The geothermal 4000 m deep. both well design and drilling of geothermal wells over project. ENEL develops depth, and the determines the well’s well design is a “bottom-up” process: the location of production zone determines the diameter at bottom hole. ENEL standards usually consist of 9” 5/8 expected flow rate production casings and an 8” ½ larger casing strings at profile continues by successively open hole. The well’s in order to isolate the well from as required by drilling or geological considerations shallower levels connects the well to steam the surface, a wellhead controlled by valves surrounding grounds (Fig. 53). At gathering system. and the HH300 automatic rig, specially designed present, ENEL has eight drilling rigs including MASS6000 At by the can be provided according to ENEL specifications. During the drilling process drill string movement motors suspended from the hook and connected to a short electric or hydraulic rotary table or by top-drive, up and down the derrick. The lower portion of section of pipe. In this case the rotary mechanism is free to travel 20 MW power plant in the Mt. Amiata area, where the steam characteristically had high mercury concentrations. 20 MW power plant in the Mt. Amiata area, where steam characteristically The AMIS AMIS is the acronym for “Abatement of Mercury and Hydrogen Sulfide” in the Italian language. The italian for “Abatement AMIS is the acronym 4.4% by by a high Non Condensable Gas (NCG) content, averaging geothermal power plants are characterized weight in the steam fed to turbines. NCG is composed mainly of CO by ENEL (Baldacci, 2001). The AMIS technology (Baldacci & Sabatelli, 1997), entirely designed and developed abatement system is placed before the gas enters cooling towers and treats NCGs with efficiencies near for H 100% removal contribution to the annual average system and indicated a significant reduction of the geothermal power plant’s of H atmospheric concentration Hydrogen sulfide is partitioned between the gas discharged to the atmosphere and the cooling water and it is Hydrogen sulfide is partitioned between the gas discharged to atmosphere and cooling water bad smell, it constituted a stripped from the latter stream in cooling towers. Since it has a characteristic Owing to the particular features of italian power plants (small point of view. problem from an environmental and unattended) of the geothermal fluids (high content NCG), abatement technologies available sizes costs. As a consequence, it became necessary to were not suitable and entailed excessive on the market of the AMIS through the invention achieved was abatement process. This objective an innovative develop geological field trips 2015 - 7(1.2) itinerary 69 plant ® of an AMIS Fig. 52 - Simplified process flow diagram (Sabatelli et al., 2009). (Sabatelli et al., M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias 6) 9) mercury 3) SOR2R scrubber; inlet gas; cooled gas output; 5) 8) 2) gas outlet from the blower. 10) abatement system (patentee: ® Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea gas cooler; inlet water; inlet water; HR2RS reactor; 7) 1) 4) Fig. 51 - AMIS Photo from ENEL (2009). treated gas; removal; removal; gas inlet to the blower; ENEL SpA). DOI: 10.3301/GFT.2015.02 the drill-string consists mainly of bit, mud motor drill collar, (in directional drillings), stabilizers, drill-pipe and jarring devices. The heavy-weight force for the bottom hole assembly must provide a hostile mechanical bit to break the rock, survive the and provide and chemical environment, directional control of the well in case a target geological field trips 2015 - 7(1.2) itinerary 70 area. geothermal well in Larderello Fig. 53 – Typical profile of a deep Fig. 53 – Typical M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea plant Yes ® DOI: 10.3301/GFT.2015.02 displaced from the well vertical axis (Fig. 53). The most displaced from the well vertical common rock bit is composed of three cones with hard metal inserts free to rotate at the bottom of hole. is usually used for plus bentonite clay) Mud (water formations. Otherwise, the drilling through cover by high formations, usually characterized reservoir and total loss of circulation, are drilled with temperature as the circulating fluid. The main features of water San Martino power plant are: Nuova Type Cooling tower AMIS 6 units (mechanical drafts) Direct contact condenser STOP 2.4: Natural gas vents at Monterotondo Marittimo region has of the boraciferous environment The natural Steam is completely been modified by human activity. for energy production, and the hydrothermal utilized At manifestations are now present in limited areas only. natural and impressive present, of the many geothermal manifestations of the Larderello-Travale field found in the past, a few can be seen area between Sasso Pisano and Monterotondo Marittimo along a normal fault system that displaces the Tuscan nappe sequence. to the Monterotondo Marittimo village road Returning by recent crosses the neoautochtonous deposits, covered Installed Capacity 40 MW N ° groups 1 geological field trips 2015 - 7(1.2) itinerary 71 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias of the (1967). Fig. 54 - Lazzarotto the natural Modified from Monterotondo Marittimo area manifestations. Geological map with locations of Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 detritus in places, and also crosses modest outcrops of the flysch units. As it approaches village, road plunges into the largest outcrop of non-metamorphic (Fig. 54). of the zone unit that is characteristic Tuscan the road signs for “biancane” and go up to Follow thermal manifestations of hill to the extensive geological field trips 2015 - 7(1.2) itinerary 72 (b) general view; general (a) growth of tiny sulphur crystals growth of tiny detail on natural manifestations; detail on natural Fig. 55 – Monterotondo natural needles at the hydrothermal vents. needles at the hydrothermal manifestations: radiolarites; altered and fragmented (c) (d) thinness, shows a particularly These are deeply broad outcrop. altered by circulation of fluids channelled to hydrothermal the surface through a fracture network, mostly with a nearly attitude. Hydrothermal vertical circulation produced a complete “bleaching” (= whitening and hence the local name “biancane”) usually of the siliceous layers, and weight loss. variegated, Widespread beautiful sulphur crystal blooms are present at the (Fig. 55). vents hydrothermal M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 Monterotondo (Fig. 49), which are characterized by steam and gas emanations and intense alteration of the by steam and gas emanations intense alteration Monterotondo (Fig. 49), which are characterized are exposed in this zone: outcrops. The rocks that usually constitute the top of shallow geothermal reservoir limestone” (Lias) to “Macigno sandstone” (Upper Oligocene - Lower Miocene), is unit, from “massive the Tuscan thanks to a tectonic window of an exposed in the southern and eastern part of “Il Monte” hill (755 m elevation) (jasper) formation that, despite its radiolarites anticline structure. The fumaroles are located in the Middle Jurassic geological field trips 2015 - 7(1.2) itinerary 73 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias century AD for the production and mineral sequestration (I) th 2 . Production of magnesite in Tuscany displays three peaks that correspond to the “Great War” displays . Production of magnesite in Tuscany 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 This Stop also offers a panoramic view of the whole southwest sector Larderello area: looking south, on your This Stop also offers a panoramic Monterotondo is a direct steam power plant (10 MW installed capacity) built in 2002 place of right the Nuova since 1958). the old Monterotondo power plant (in operation Stops 2.5-2.9: The Malentrata mine. Natural analogues of CO (1915-18), the 1920s (expansion of Italian steel industry) and autarkic period fascism (1936-43). local scale using simple exploitation techniques and manual conducted at a very Magnesite production was of the Tuscan character a detractive opal) was sorting. The significant amount of silica (quartz, chalcedony, costs, caused the closure of mines. high transport magnesite ore that, when coupled with the relatively near the Canneto creek of the La Sterza River, magnesite deposit is exposed along a lateral The Malentrata carbonate–silica veins village and at the periphery of Larderello geothermal area. It consists several were dominated serpentinites of the Ligurian units. Some veins hosted by silicified, carbonated and argillized (during the main famous and used in Tuscany opal) and they were relatively by silica phases (chalcedony, since the 16 activity of the Opificio delle Pietre Dure; Firenze) Tuscany hosts several small hydrothermal deposits of magnesite, embedded in the serpentinites Ligurian small hydrothermal hosts several Tuscany Monti Livornesi Tuscany: ophiolitic units. Most of the magnesite ores are located in central-southern Monterufoli and San Dalmazio mines), (Castiglioncello and Campolecciano mines), Colline Pisane (Malentrata, d’Elsa (Querceto mine). Minor outcrops occur on Elba Island. and Val for the first time on Elba Island and has been locally exploited production of discovered Magnesite was debated the composition of mineralogists During the nineteenth century several since the Renaissance. ceramics dug in Elba Island, alternately attributing it to magnesite (named “giobertite”), sepiolite, mineral the white earthy or kaolin. The real industrial phase starts at the beginning of the 1900s with opening large open pits in and Colline and exploited in the Monti Livornesi of magnesite were discovered veins massive Elba Island. Later, II War d’Elsa (1917). Exploitation continued intermittently until the beginning of World Pisane (1915), and in Val production of bricks for the metallurgical industry). Total the national needs at time (refractory and covered estimation amounts to ca. 3 Mt, corresponding 1.5 Mt of naturally about 0.3 Mt while reserve magnesite was sequestered CO workmanship of semiprecious stone furnishings (Targioni Tozzetti, 1768-79). Tozzetti, workmanship of semiprecious stone furnishings (Targioni geological field trips 2015 - 7(1.2) itinerary 74 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias the stops. showing the location of Fig. 56 – Malentrata area Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 From a parking area near the La Sterza River you walk uphill (30-40’) following the path of old mining walk you From a parking area near the La Sterza River station of Casino di Terra that connected the abandoned La Villetta mine of lignite to railway railroad a nice geological section from the sedimentary envelope (ca. 10 km to the north; Fig. 56). This path displays to the ophiolite body that hosts magnesite deposit. geological field trips 2015 - 7(1.2) itinerary 75 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 57 – Pliocenic sands and conglomerates at the top Fig. 57 – Pliocenic sands and conglomerates of Neogene sedimentary cover of the ophiolitic suite. of Neogene sedimentary cover DOI: 10.3301/GFT.2015.02 STOP 2.5: Malentrata mine, the Mio-Pliocene sedimentary cover are scattered because Neogene extensional tectonics dismembered the Ophiolite outcrops in southern Tuscany since Late Miocene and mantled the ophiolitic units with sedimentary basins developed orogenic stack. Several on the after fording the La Sterza River, deposits. Along the first part of trail, alluvial and shallow-marine sub-horizontal flank of the hill one can observe (Pliocene) (Fig. of sands and conglomerates layers 57). This formation represents the upper part of sequence, while the Miocene sediments are buried in the deeper part of basin. Near bottom (Late Miocene) layers the sequence, some clay contain abundant lenses of lignite that were exploited by the La Villetta mine between 1850 and 1925. Some shafts and inclined drifts were dug down to 180 m below the surface, where a pluri- a total production kilometric net of tunnels provided of ca. 1.5 Mt lignite. The remains this activity of the main shaft are represented by the headframe loading station, now restored and and the rail into a touristic residence. transformed STOP 2.6: Malentrata mine, the sedimentary envelope of ophiolites the Neogene sediments and enter leave you Continuing along the path of old lignite mining train, been and tectonic sub-units have stratigraphic of the ophiolite bodies (Fig. 58). Several sedimentary envelope position and internal stacking. age, paleogeographic defined inside the Ligurian units on basis of relative from argillites to marls, with ranging compositions of the sedimentary units are similar, the overall However, geological field trips 2015 - 7(1.2) itinerary 76 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias excavated through the steep trench Fig. 59 – The serpentinites. limestone, calcilutite and sandstone layers. The net result is the almost complete wrapping of ophiolite lenses (from decametric to pluri- by quite impermeable kilometric in size) (Fig. 58). The significant argillitic envelopes is deformation of these sedimentary cover responsible for the sudden changes in bedding attitude as well the local folding. The on top of Ligurian units stay sedimentary cover serpentinite body but of a large, sub-horizontal the contact is not visible here due to detrital cover. Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 58 – Large boulder of serpentinite completely encased by argillites and marls of the sedimentary cover. DOI: 10.3301/GFT.2015.02 STOP 2.7: Malentrata mine, the serpentinite protolith After a few hundred metres the path enter steep through the excavated trench that was serpentinites and allowed the passage of (Fig. 59). Beautiful outcrops of mining train serpentinites are here exposed and show the geological field trips 2015 - 7(1.2) itinerary 77 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 60 – Contact between boudined serpentinites (below) and argillites (above). be easily observed in the mining dumps and be easily observed a take If you among road's gravel. for secondary road to the left and walk a could observe about 100 metres uphill you nice outcrop along the road cut exposing the contact between serpentinites and argillites/marls (Fig. 60). Here, serpentinites show strong deformation, boudinage and carbonation. The contact between argillites/marls and along also be observed serpentinites may the towards road, moving the main gravel mining site (Fig. 61). Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 typical structure with lenses of massive porphyroclastic serpentinite wrapped by an anastomosing network of serpentinite wrapped porphyroclastic typical structure with lenses of massive of serpentine. This outcrop represents the westernmost edge serpentinite body where fibrous veins limited. Within a few hundred metres from here, the carbonation effects carbonation effects were very mine. increase and reach their maximum at the Malentrata progressively STOP 2.8: Malentrata mine, the serpentinite-argillite contact (on the left) uphill path, and take the path of mining train leave Immediately after the trench, you a small may road that intersects the old mining dumps. Abundant magnesite-dolomite-silica blocks and fragments gravel geological field trips 2015 - 7(1.2) itinerary 78 On the (B) M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 61 – Contact between serpentinites and argillites/marls along the main gravel road. along the main gravel STOP 2.9: Malentrata mine: Carbonated serpentinites and carbonate-silica veins road for some 300-400 meters along the gravel walk We and we finally reach the lower part of excavations with small open pits and adits. Beautiful outcrops are exposed large blocks of carbonate-silica veins the road (Fig. 62). in the area above everywhere On the left an example of brecciated and carbonated serpentinite, infilled by dolomite veins; On the left an example of brecciated and carbonated serpentinite, infilled by dolomite veins; Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea (A) Fig. 62 – right, brecciated magnesite vein, partially cemented by dolomite and silica. right, brecciated magnesite vein, DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) itinerary 79 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 Textures and mineralogy of both veins and carbonated serpentinites can be examined either by comfortable of both veins and mineralogy Textures into of the open pits and adventuring on block surfaces in the dumps or by climbing steep walls observation infill of cryptocrystalline by an early massive are characterized the old adits. Main carbonate–silica veins of the carbonated- (millimetric to decimetric in size) magnesite containing angular fragments creamy-white acquire a nodular structure with magnesite nodules and magnesite veins massive silicified serpentinite. Locally, are brecciated and show a “cement veins cauliflower aggregates cemented by dolomite. Most of the massive of the early magnesite infill and host rocks with fragments supported” structure (cement up to 50% vol.) quartz and opal. Beautiful samples of magnesite magnesite, dolomite, chalcedony, cemented by banded Fe-rich dolomite can be easily collected. Sliced and polished, they clasts encrusted by banded, green and creamy-white in artistic compositions showing large variations amazing natural provide geometry and colours. Quartz, (geodes). into the residual voids and opal represent the last phases to crystallize chalcedony path and could turn back to the mining train and sampling you After a reasonable break for field observation old bridges, and finally reaching the twice over uphill (along gentle slopes), crossing the river continue to walk could follow the entire you Alternatively, could spend the night (Website). loading station where you old rail car. to reach your in the opposite way pathway geological field trips 2015 - 7(1.2) itinerary 80 2 Day rd 3 – The Montecastelli – The Montecastelli – The Pavone river: – The Pavone Natural analogues of CO Natural mineral sequestration (II) sequestration mineral Fig. 63 – Montecastelli area showing the location of stops. The Montecastelli copper mine. Stop 3.1 copper mine: ongoing carbonation in the underground works. Stop 3.2 copper mine: ongoing carbonation in mining dumps. Stop 3.3 vein hydromagnesite-aragonite spring. network and water M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias century, one of these copper deposits (Montecatini Val di one of these copper deposits (Montecatini Val century, th Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 Cecina) became famous due to the discovery of a large bonanza where more than 50000 tons copper were Cecina) became famous due to the discovery copper mine in Europe, and the huge the most productive the Montecatini mine was a few years For extracted. expectations among prospectors exploring the rest of ophiolite outcrops in profits stimulated exaggerated The ophiolitic sequence of the Ligurian units host several small copper deposits that were formed by oceanic The ophiolitic sequence of the Ligurian units host several time. The original ore deposits were dismembered and locally circulation during Jurassic hydrothermal portion of the processes that affected the Tuscan by the complex tectonic and hydrothermal mobilized Apennine chain. During the first half of 19 geological field trips 2015 - 7(1.2) itinerary 81 ) Isabella adit century but after 1941 th M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias copper mine, ongoing carbonation in the underground works sequestration process with respect to Malentrata (magnesite, dolomite and opal). process with respect to Malentrata sequestration 2 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 From the old medieval village of Montecastelli you walk downhill for about 30’ walk village of Montecastelli you From the old medieval road, and along a small gravel to contact the owner of copper mine and the mining site (Fig. 63). Remember River reach the Pavone trip (Website). before planning your is located inside one of these buildings. The owner the property recently restored part underground works and included a new lighting system. The adits are safe scenically lightened. An iron gate at the us along the visit. that will accompany of a small bat colony allows the survival entrance and late tectonic structures The adit is completely dug in serpentinites that are crosscut by serpentine veins and, during lined by breccias and soapy serpentine. This adit is connected inclined stopes to the upper levels the colder underground air column flows out from Isabella adit. After a few tens of metres the summer, and the roof of adit change when the colours of walls a first observation: inside the adit we can make by white the rock surfaces are covered from two different directions (Fig. 64). Looking inward, observed the typical dark colour of serpentinite is dominant. This phenomenon coatings and spots, while looking outward coatings, efflorescences and cauliflower aggregates over is caused by the preferential growth of hydromagnesite of the adit. The study these efflorescences is in progress but the entrance the surfaces exposed towards Tuscany. Private investors Private Tuscany. industrial plants and digging exploratory lost large sums of money building oversize example of this story: many ophiolites. The Montecastelli mine is a representative adits/shafts in Tuscan the hills, and ruins ofkilometers of adits and shafts penetrate large industrial buildings are strewn in the the production of a few tons bornite and woods. The net result of such a big effort (1841-1869) was activities were carried out at the beginning of 20 chalcopyrite. Minor exploration STOP 3.1: The Montecastelli of serpentine along the path The road cuts show good exposures of serpentinites crosscut by fibrous veins can you River, from Montecastelli to the abandoned copper mine. Arriving at mine site near Pavone of the main adit ( the ruins of mining plants scattered through woods. The entrance observe the area was completely abandoned. Since 1970 this area was frequented by mineral collectors looking for frequented by mineral completely abandoned. Since 1970 this area was the area was spherules) in the (fibrous-radiating (prismatic crystals) and hydromagnesite nice specimens of aragonite new scientific interest in the area of of serpentinites (Brizzi & Meli, 1989). This information sparked fractures and aragonite Mg-carbonates (mainly hydromagnesite) Montecastelli, because the presence of hydrated highlights a different CO geological field trips 2015 - 7(1.2) itinerary 82 th (Fig. 64). The 2 asymmetric distribution may of hydromagnesite be related to seasonal of airflow and variations pCO a Following century. narrow deviation on the left, we explore a more part of the adventurous Isabella adit reaches the main internal shaft that connects all of the underground works. of The concrete walls the shaft show several examples of writing left by the miners during the activity in 19 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 64 – The main adit of the Fig. 65 – Dripping and flow of water along the lateral walls along the lateral Fig. 65 – Dripping and flow of water directions (A and B). associated with spotted aggregates of hydromagnesite. Pavone mine. The colours of the Pavone and roof change when walls adit’s in two different opposite observed responsible for the continuous growth of an aragonite flowstone responsible for the continuous growth of an aragonite mine (optional part). This adit connected the Isabella to but it is now interrupted. However, the exploitation zone an interesting for a few tens of metres we observe walking dripping at the top of an inclined with significant water zone are walls dripping and flow along the lateral stope. Water responsible for the continuous growth of an aragonite flowstone associated with spotted aggregates of (Fig. 65). hydromagnesite Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) itinerary 83 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea Fig. 66 – Carbonated serpentinite clasts of the mine dump. DOI: 10.3301/GFT.2015.02 STOP 3.2: The Montecastelli copper mine, ongoing carbonation in mining dumps of the Isabella adit and follow a narrow creek connecting mining plants to uphill from the entrance walk You of the mine. The erosion along creek exposes an interesting section old mining dump the upper levels (Fig. 66). The dump is mainly made up of serpentinite clasts, with minor amounts Cu-ore A fragments. between the Mg-carbonates in voids of this site is the widespread precipitation hydrated prominent character clasts. White coatings, crusts, spherules, and cauliflower aggregates act as weak cement for the dump material. geological field trips 2015 - 7(1.2) itinerary 84 M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Fig. 67 – Carbonated serpentinites of the serpentinite escarpment. observed and sampled. Persons observed a closer view of interested in having the outcrop can carefully climb Hydromagnesite spherules and wall. crusts fill a network and of fractures, recently exposed surfaces of the by covered rock are also rapidly coatings. Aragonite hydromagnesite occurs either as fibrous radiating or aggregates with hydromagnesite infill made by large as an exclusive prismatic crystals (up to 10 cm). A spring is visible to the small water The spring right of this outcrop. (pH has an alkaline character water =8.5) and high Mg Ca as compared to the concentrations, (pH = 5.7; Mg= 0.04 local rainwater and Ca= 0.02mEq/l). of serpentinite crosscut by a widespread network of hydromagnesite and aragonite of serpentinite crosscut by a widespread network hydromagnesite 3 Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea DOI: 10.3301/GFT.2015.02 STOP 3.3: The Pavone river, hydromagnesite-aragonite vein network and water spring downhill for a few walk you After the simple ford of river, River. reach the Pavone From the mine you of serpentinites. Serpentinites at this site are hundred metres and reach the base of a large steep wall a whitish spot and rock falls sometimes happen. In the middle of large serpentinite wall, strongly fractured represented by a few m veins is quite evident (Fig. 67). Many blocks of this outcrop fell to the base of the wall and can be easily blocks of this outcrop fell to the base wall is quite evident (Fig. 67). Many veins Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea M. Benvenuti - C. Boschi - A. Dini - G. Ruggieri - A. Arias g e o l o g i c a l

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DOI: 10.3301/GFT.2015.02 geological field trips 2015 - 7(1.2) references 86 . : n . he he cent bution uthern , cultura lo–Travale n ores from of southern M. Benvenuti - C. Boschi A. Dini G. RuggieriM. Benvenuti - A. Arias Geothermal resources, ore deposits and carbon mineral sequestration in hydrothermal areas of southern Tuscany Sea -mineral sequestration environment. Abstract FIST2013. Abstract environment. sequestration -mineral 2 CO Tuscany. In: Proceedings of Geothermal Congress 1995, 18–31 May,Tuscany. Florence, Italy (E. Barbier et al. eds.), 693–696. CNR, Pisa. Geothermal Congress geothermal system. In: Proceedings World Japan, 965–970. Larderello–Travale 2000, Kyushu-Tohoku, 1275–1278. Geothermal Congress 1995, Florence, Italy, Proceedings World 25, 219–235. and geological data. Mem. Soc. Geol. Ital., geophysical Italy). Episodes, 26, 239–244. geothermal areas (southern Tuscany, Tuscany; the Campiglia Marittima case. Boll. Soc. Geol. Ital., 119, 517-528. the Campiglia Marittima case. Boll. Soc. Geol. Ital., Tuscany; Geothermal Congress 2010, Bali, geothermal system (Italy), for a regional numerical modelling. In: Proceedings World 11. Indonesia, p. 31-41. Proceedings of NEDO International Geothermal Symposium, Conservation. trip guide book - B18. Mem. Descr. Carta Geol. d’It., LXIII (Vol. 2), 24 pp. LXIII (Vol. Carta Geol. d’It., trip guide book - B18. Mem. Descr. from researches at Monte Valerio and Baratti-Populonia (southern Tuscany, Italy). In G. Mair & F. Lo Schiavo (eds) “Le Lo Schiavo Italy). In G. Mair & F. (southern Tuscany, and Baratti-Populonia from researches at Monte Valerio Congress, Liège, 2-8 septembre 2001, Colloquium 11.2. problème de l’étain à l’origine la métallurgie” XIV UISSP Archeopress, BAR, 1199, 55- 65. e scienza. In: G. Pratesi (ed.), Il Museo di Storia Naturale dell’Università di Firenze. Volume IV. Le collezioni mineralogiche IV. 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Proceeding of the 2 magnesite deposit (Tuscany, the Malentrata accelerated carbonation for environmental and materials engineering, 29 carbonation for environmental accelerated (Finlandia). pp. Dicembre 2010, Turku Novembre-1 139-146. ISBN 978-952-12-2505-5 (ISBN 978-952-12-2506-2 .pdf version) Italy). Proceeding of the 4 examples from Montecastelli serpentinites (Tuscany, DOI: 10.3301/GFT.2015.02 Benvenuti M., Pecchioni E., Chiarantini L., Chiaverini J., Mariani A. & Mascaro I. (2003b) - An investigation on iron smelting Mariani A. & Mascaro I. (2003b) - An investigation J., Chiaverini L., Chiarantini E., Pecchioni M., Benvenuti Benvenuti M., Mascaro I., Costagliola P., Tanelli G. & Romualdi A. (2000) – G. & Romualdi Tanelli smeltin Costagliola P., (Populonia): Iron, copper and tin at Baratti Mascaro I., M., Benvenuti Bertani R. & Cappetti G. (1995) - Numerical simulation of the Monteverdi zone (western border of the Larderello geothermal zone Bertani R. & Cappetti G. 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