Per. Mineral. (2003), 72, SPECIAL ISSUE: Miocene to Recent... , 41-52 http://go.to/permin

An InternationalJournal of =; PERIODICO di MINERALOGIA MINERALOGY, CRYSTALLOGRAPHY, GEOCHEMISTRY, established in 1930 ORE DEPOSITS, PETROLOGY, VOLCANOLOGY

and applied topics on Environment, Arclweometrv and Cultural Heritage

CHAPTER 2

Ore deposits, industrial minerals and geothermal resources

ANDREA DINI*

CNR, Istituto di Geoscienze e Georisorse, Via Moruzzi, 1, 56124, Pisa,

2. 1 HISTORICAL PERSPECTIVE grew to become the great economic resource of Populonia, drawing increasingly on the rich Together with Sardinia, is the main mineral deposits of the Island of Elba often mining region of Italy, where almost three mentioned in ancient texts (Diodorus Siculus, millennia of exploitation yielded significant apocryphal writings of Aristotle). productions of iron, pyrite, base metals, silver, After the fall of the Roman Empire, the ore antimony, mercury, gold as well as industrial deposits of Elba Island and «Colline minerals and super-heated steam (Fig. 1 ). In Metallifere» ( area) fell in addition to its economic relevance, the Tuscan total oblivion for centuries. It was only in metallogenic province remains of primary Middle Age (XI-XIV century) and Renaissance scientific importance due to the occurrence of time (XVI-XVIII century) that mining activity diverse hydrothermal deposits associated with flourished again in Tuscany, particularly in the volcano-sedimentary, intrusive, metamorphic Ag-Cu (-Fe) district of «Massa Metallorum» and geothermal environments of pre- Alpine (now Massa Marittima in Southern Tuscany), and Alpine ages (Lattanzi et al., 1994 and but also in the Fe district of Elba Island. During reference therein). the XIX century, exploration and exploitation There are few indirect archaeological of ore deposits in Tuscany took advantage by evidences indicating that exploitation of iron the production of the first geological maps and ores from Elba, Cu-Pb-Ag ores from genetic studies of mineralogists and geologists Temperino and Massa Marittima, and tin ores from Italian and European Universities. After from Monte Valerio was possibly the Unification of Italy all mines became a accomplished since the VIII-VII century B.C state property and were granted in concession until the Roman period. However, the to different mining companies, up to 1990's, archeometallurgical products and rare furnaces found along the coasts of the Elba Island and when the last pyrite mine in southern Tuscany (Cam piano) shut down. Tuscany (e.g. Populonia) indicate that · extensive reduction of iron and copper minerals Today, the mining industry in Tuscany is was accomplished in the Roman period (Ill facing the typical problems of most European century B.C.). Especially the iron industry regions, and extraction is currently limited to ornamental stones, building materials and a few industrial minerals such as raw ceramic

* E-mail: [email protected] material. 42 A. DIN!

2.2 METALLOGENY past century, earlier scientists considered the Late-Alpine intrusions as the sources of heat The metallogeny of Tuscany is rather and metals (e.g. Lotti, 1929). More recently, complex, and several aspects still await a new epigenetic models have been proposed definite answer. (Marinelli, 1983; Dechomets, 1985), according According to Lattanzi et al. (1994), three main to which the intrusions acted as heat sources metallogenic epochs seem to be relatively well and promoted the circulation of hydrothermal established in Tuscany: (i) a Lower-Middle fluids, although the source(s) of the fluids Palaeozoic stage, leading to the formation of themselves and dissolved metals should be protores/preconcentrations of metals (e.g. the looked for elsewhere. Thus Marinelli (1983) Ag-Pb- Zn Bottino deposit and the Hg Levigliani suggested that Fe could derive from deposit in the Apuane Alps) strictly related to the metasomatic reactions taking place at the Ordovician calcalkaline magmatism; (ii) an peripheral portions of the intrusive bodies: Upper Palaeozoic -Triassic Fe (and Ba) event, chloride-rich metamorphic and/or connate possibly related to a pre-Tethyan aborted rift, that waters would have been enriched in Fe through is documented in various areas, such as Elba reaction with magmatic biotite. On the other Island, Southern Tuscany and Apuane Alps; (iii) hand, Dechomets ( 1985) proposes that an Alpine event, well documented both in hydrothermal fluids of dominant marine origin Apuane Alps and in Southern Tuscany (e.g. the scavenged Fe from host rocks. The authors epithermal Hg-Sb-Au deposits, the Cu-Pb-Zn favouring the second genetic model sulfide ore bodies), characterized by («syngenetic/hydrothermal-metamorphic») hydrothermal systems triggered by both regional acknowledge the importance of the Alpine metamorphism and magmatism. tectono-magmatic event in reworking the iron One of the most debated themes is the origin ores, but believe that, at least as protores, they of iron-bearing deposits occurring in Tuscany were formed in sedimentary and/or (barite-iron oxide-pyrite deposits of Apuane hydrothermal sedimentary environments of Alps, pyrite deposits of Southern Tuscany and Triassic and/or Palaeozoic age (Deschamps et the iron ores of Elba Island). Total production al., 1983; Tanelli and Lattanzi, 1983; Zuffardi, from the three districts may be estimated in the 1990). According to these authors, the Late­ order of 150 million tons ore: the Apuane Alpine extensional tectonics, metamorphism, deposits yielded about 0.5 million tons of magmatism and related hydrothermalism pyrite + Fe oxides, whereas more than 80 would be responsible for the more or less million tons of high-grade mineral concentrate remobilisation and metamorphism of the metal were obtained by exploitation of several pyrite preconcentrations. deposits in Southern Tuscany (Niccioleta, Gavorrano, , etc.), and not less 2.3 THE FE DEPOSITS OF ELBA ISLAND than 60 million tons Fe ore have been extracted from Elba deposits from ancient times up to As shown in figure 1 and 2, the Fe deposits nowadays. A number of hypotheses have been of Elba Island are restricted to a relatively put forward in the last two centuries in order to narrow belt extending NS along the eastern explain the genesis of Tuscan Fe deposits. coast of the Island (see Tanelli et al., 2001 and They can be grouped in two basic genetic reference therein). The ore bodies, even at the models (Tanelli and Lattanzi, 1986): (i) scale of individual deposit, occur in variable «plutonistic epigenetic», and (ii) settings, from stratiform to pod-like or vein­ «syngenetic/hydrothermal-metamorphic». type, although the first appears to be dominant According to the first model, ore genesis is a (Zuffardi, 1990). Stratiform Fe bodies, either or direct consequence of the intrusion of the Late­ not associated with veins and/or irregular Alpine granitic plutons. In the first half of the masses, are «strata-bound», at least in the wider Ore deposits, industria/minerals and geothermal resources 43

S A Larderello field \ IEN B � \ ..- \ __ ). -- �- ...... - • 4.;. -t* \ "Cu-Pb-Zn-(Ag)

: _. _. I -- "'\ '0 \ zone" ..- 1 � r:ilfnpigltg_ _. .tJ '- 11 Ca'mbia o \ -- l 1 D .,!_,1 1 � , 4 Niq:ioleta• , • 1 v-- \ _. Botro I ,... _....�- 1 �--1 \ "Hg 1 ai Marmi / zone" I _. _. \ • / li -- Q \ ,{, L/":J\:: . - • ·-- --·-.". 1 1 \ �v� � � / ih Marina -- \-+_. / .A.1 : 1 Gavorrano 1 I "7\� ·' '*�� i}t t _. 1 l )( / ' 1 ( //�Monte _1 /\' i:f * A1Terranera --1- / \ Amiata • 1 / -�-···/ Elba I ( I \ / / f'1e Id .c4po Calamita � , N 1\ / / I\ *A / � / X \ "Fe oxide , r"N 1 / , zone" / *' \ **' \ * *' "Sb - Au \ zone" J11rm!ecn:r/rJ "pyrite zone"

0 30km

LEGENDA

Intrusive rocks of Tuscan Magmatic Province 0 Cu-Pb-Zn-(Ag) ore

Volcanic rocks of Tuscan Magmatic Province * Sb-Au ore

A Fe-oxides ore * Hg ore

• Pyrite ore � Raw ceramic material

Fig. I -Major deposits and mineral belts of Southern Tuscany (modified after Tanelli and Lattanzi, 1983). meaning of the word. In fact they are Hematite (± pyrite, limonite) ores from Rio predominantly hosted by Palaeozoic-Triassic Albano up to Rio Marina mining area are formations belonging to Tuscan Domain neither directly associated with intrusive bodies (Complex I, II and Ill; see Part Ill, Chap. 1). (plutons, dykes) nor with skarn bodies of 44 A. DIN!

Geological setting of the Eastern part of the Island of Elba. modified from PERRIN ( 1974): - Yll: intrusive Eastern Elba Quartz monzonite. - Lower Tuscan Units: T0 = basement of the Ca- lamita Unit; T1 =carbonatic cover of the Calamita Unit; T2 = Ortano Unit; T3 =Unit of"Schists and Crystalline Limestones"; T4 = Rio Marina Unit. - Upper Tuscan Units: T5a and T5b = Limestone Units. Ligurian Units: S = interlayered serpentine; L1 - Ophiolites; L2 = Helminthoides bearing !lysch. - Iron Deposit: I a Ginevro; I b = Stagnone; I c = Sassi Neri; 2 = Calamita; 3a = Terra Nera; 3b = Ortano; 4 = Valle Giove; 5a Bacino: 5b = Vigneria; 6a = Zuccoletto; 6b = Rialbano; 6c = Monte Calendozio; 7a = Valle di Catone: 7b = Rossetto; 7c = Le Conche, 7d = Fornacelle.

Fig. 2-Geological setting and location of Fe ore deposits of Elba Island (modified after Deschamps et al., 1983).

presumable magmatic affiliation. However, Rio Marina is especially famous worldwide for mineralogical, textural and fluid inclusion its beautiful crystals of hematite (variety analyses of hematite+adularia assemblage from «oligisto» = glaze iron) and pyrite. Hematite Valle Giove stopes at Rio Marina) (Deschamps may show either a typical lamellar-micaceous et al., 1983) would indicate that it formed habitus, or rhombohedral, complex, crystals through reaction of relatively hot (T= 310 oc) often covered by iridescent films of iron saline fluids with pyrite-biotite-quartz-bearing hydroxides; euhedral pyrite pyritohedra, rocks. In addition, isotopic dating of the octahedral and cubes are frequently associated hematite+adularia assemblages from the same with micaceous hematite and also embedded in stope by Lippolt et al. ( 1995) point to ages of soft chlorite aggregates. 6.4 ± 0.4 to 5.3 ± 0.1 Ma (U+ Th vs. He ages of Moving southwards from Rio Marina hematite and K/Ar age of associated adularia), towards the Calamita Peninsula, the association i.e., very close to those estimated for the Porto of iron ores with skarn bodies and/or aplitic Azzurro pluton (5.9 Ma; Maineri et al., 2003). dykes becomes more and more distinctive. Ore deposits, industrial minerals and geothermal resources 45

Actually, skarn bodies were encountered in the the presence of two distinct type of skarn: a Rio Marina mining area as well, although at garnet (andradite)-rich skarn, quantitatively the depth (drillings in the Vigneria stapes). most abundant, and an ilvaite-hedenbergite Immediately south of Rio Marina village, just a skarn. few metres after the old tower, decametric The exploited ores were spatially associated skarn bodies with hedenbergite, ilvaite, with both types of skarns, and consisted of epidote, quartz, magnetite, pyrite, and lenses and massive bodies of magnetite (± pyrrhotite extend along the coast, replacing hematite, goethite) and trace amounts of base calcschists. Beautiful specimens showing metal sulfides. However, magnetite was not the ilvaite prismatic crystals, green and primary Fe mineral to form: the presence of amethystine quartz and fibrous-prismatic magnetite with lamellar habitus and the hedenbergite have been collected here in the presence of relic lamellar structures in euhedral past. Moving southwards, other skarn bodies magnetite are evidences of pseudomorphic are encountered, often in association with Fe replacement after earlier hematite. Of some ores of variable size and economic relevance: interest is the presence at Ginevro and Sassi at Ortano and Terranera pyrite, ematite, Neri of a relatively uncommon skarn mineral pyrrhotite and magnetite are associated with like ferropargasite, associated with grossular­ pyroxene-ilvaite-epidote skarn bodies. In this almandine garnet, and only minor amounts of area, aplitic-pegmatitic dykes linked to the hedenbergite, ilvaite, and epidote. Porto Azzurro pluton frequently intersect (or As discussed more extensively elsewhere (cf. are in close proximity to) Fe ores and skarn Tanelli and Lattanzi, 1986), none of the genetic bodies. The Terranera deposit provided some models so far proposed for iron deposits of of the most elegant and brilliant pyritohedra eastern Elba Island is completely satisfactory. crystals of pyrite ever found in the island. The Descriptive models for the individual deposits association between ores, skarn and aplitic are largely incomplete, so that inferred genetic dykes is particularly evident in the Calamita models are obviously qualitative and poorly Peninsula, where several skarn-bearing iron constrained. Anyway, taking into account the deposits (Capo Calamita, Ginevro, Sassi Neri, previously reported textural, geological and Stagnone) are hosted by Complex I. The Capo geochronologic data, Tanelli et al. (200 1) Calamita deposit (Fig. 3) is characterized by suggest that the stage of iron concentration

Nuova zona 0 100 200 m.

50 liv. mare

--50

"Terre" ferrifere [8 Calcare cavernosa Silicati di skarn Verrucano s.l. D {scisti quarzoso- micacei) Carpi minerari

Fig. 3 -Simplified geological section of Capo Calamita Fe-skarn deposit (modified after Tanelli, 1977). 46 A. DIN! could have preceded (at least in part) the subvolcanic products constitute a sub-vertical emplacement of the Porto Azzurro pluton and dyke swarm, trending NNW-SSE, that crosscut related aplites, as well as the formation of skarn the thermometamorphic structures of marbles bodies. In this scenario, fluids triggered from induced by the emplacement of Botro ai Marmi Porto Azzurro intrusion modified and pluton. «Porfido Giallo» is monzogranitic in remobilised mineralogy and structures of pre­ composition whereas the «Porfido Verde» has Alpine (Palaeozoic-Triassic) Fe ore a more mafic composition, but a correct preconcentrations. classification is precluded due to the strong alteration. Several skarn masses occur completely embedded in white marbles as well 2.4 THE Cu-PB-ZN SKARN DEPOSITS OF as at the contact between marble and porphyry V ALLE DEL TEMPERINO-V ALLE DEI LANZI dykes. The subvertical, elongated, geometry (CAMPIGLIA MARITTIMA) (pipe-like) of the three main masses is known owing to the detailed informations derived The skarn-sulfide deposits of Campiglia from underground works, that followed such M.ma area have been mined, on a rather small structures from 400 m (at surface) to 50 m scale, for chalcopyrite, and minor sphalerite a.s.l.. The «Porfido Verde» is commonly and galena. These deposits have been regarded completely embedded in the orebodies and is as a classic example (Fig. 4) of a replacement penetrated by small calcite-epidote-K-feldspar­ skarn deposit formed by hydrothermal fluids quartz veins. «Porfido Giallo» (sometimes related to the emplacement of porphyry dykes deeply epidotized) is occasionally associated along fractures of limestones (see Corsini et al., with and/or embedded in the orebodies, always 1980, and reference therein). In the mine, two in the vicinity of a «Porfido Verde» dyke. kinds of porphyry, «Porfido Giallo» and The skarn complex is almost entirely formed «Porfido Verde», have been observed. Such a by manganoan ilvaite, and hedenbergite with

0 so lOOm

+100 r.±::Etl Porfido giallo � Porfido verde - Magnetite zone c::::Jllvaite zones IZZi! Hede n berqite zones -·-Approximate skarn·sulfide SW(A) bodies/marble boundary (B)NE

Fig. 4-Schematic cross section of the Valle del Temperino deposit (modified after Corsini et al., 1980). Ore deposits, industria/minerals and geothermal resources 47

quartz, calcite, epidote, johannsenite and traces quartz crystals (max. 50 cm) and ilvai�e of andradite, rhodonite and thaumasite. Ore crystals (max. I 0 cm) were saved for public minerals include chalcopyrite, pynhotite, pyrite, and private collections. sphalerite, galena, magnetite and traces of bismuthinite, arsenopyrite, etc .. In particular, 2.5 PYRITE ORES AND Cu-PB-ZN-(AG) SULFIDE Cu-Fe ores are prevalent at Valle del Temperino, ORES OF SOUTHERN TUSCANY while Pb-Zn ores dominate at Valle dei Lanzi. Skarn bodies are zoned with an Ilvaite zone One of the major mining resources of (substituted by a magnetite zone at the deepest Tuscany (fig. I) was pyrite which was exploited levels) at the contact with the «Porfido Verde», to produce H2S04 and Fe-oxide pellets; the heat followed by a distal hedenbergite zone that can given off during the oxidation process was also change to a johannsenite zone at the external exploited, yielding about 300 kWh energy per contact with marbles. The highest chalcopyrite­ ton of treated pyrite. Mining for pyrite started at pyrrhotite concentrations occur in the ilvaite the end of the past century and stopped in the zone, whereas Pb-Zn sulfides tend to be 1990's, when the last pyrite mine in southern concentrated in the external pyroxen-bearing Tuscany (Campiano) shut down; in this period zones. Nevertheless, the observation of rhythmic about 100 million tons of high-grade mineral deposition of ilvaite, hedenbergite, chalc�pyr�te concentrate have been obtained and processed. and Pb-Zn sulfides, and replacement of 1lva1te According to their geologic settings, pyrite ores by hedenbergite indicate that fluctuations of can be subdivided into three main groups physicochemical parameters, with time and (Tanelli and Lattanzi, 1983): space, caused some overlapping of these 1) Lens-shaped (Fig. 5), near comformable relationships. massive pyrite bodies, in association with During the exploitation, many large cavities sulphate-carbonate lenses and skarn within (up to several cubic metres) were encountered phyllites (Paleo zoic- Triassic?) belonging to the in the skarn mass, and spectacular groups of metamorphic basement (Niccioleta-I, Campiano-

s F.so Val d'Aspra F.so del Corvo F.so Stregaio N 500

300

100

I. m.

liguridi s.l. Anidrite e dolomite

Calcare massiccio - Pirite

j'?v".1 I Ca!care cavernosa Silicati di skarn

Verrucano s.l. 0 100 200 300 m. (scisti quarzoso-muscovitici) I

Fig. 5 - Simplified geological section of Niccioleta pyrite deposit (modified after Tanelli, 1977). 48 A. DIN!

I, Serrabottini-I). Apart from Campiano-I, Cu­ 2.6 THE SB-AU AND HG EPITHERMAL Pb-Zn grade in these deposits is uneconomic. DEPOSITS OF SOUTHERN TUSCANY 2) Lens-shaped bodies (fig. 5), partly discordant, associated with Upper-Triassic The most relevant addition in recent years to calcareous dolomitic formations ( «Calcare the metallogeny of Southern Tuscany is Cavernoso») at their bottom contact with represented by the discovery in the mid'80s of phyllitic formations (Paleozoic-Triassic?) of «Carlin-t ype» (s .1.), carbonate hosted, the metamorphic basement (Boccheggiano-I, epithermal Au prospects (Tanelli et al., 1991). Niccioleta-II, Serrabottini-II, Gavorrano-I, The Au prospects occur along a belt extending Argentario). Higher Cu-Pb-Zn grade than from Montagnola Senese to Monti Romani, group 1) but uneconomic. which was previously known for the presence 3) Ore bodies (veins and masses) associated of Sb and Hg deposits (fig. 1 ). Sb-Au and Hg with Mio-Pliocenic, high-angle, extensional deposits show a strict association with faults (Montoccoli, Ritorto), sometimes at the structural highs where the «Calcare tectonic contact with Pliocenic intrusions (e.g. Cavernoso» of the Tuscan Nappe is directly Gavorrano-II, Giglio Island). These overlain by the flyschoid, impermeable, mineralizations are of much smaller importance Liguride Nappe (Fig. 6). for extraction of pyrite, but in some cases they These deposits are associated with prominent show economic Cu-Pb-Zn-(Ag) concentrations hypogene and supergene alteration, and with (Boccheggiano-II, Campiano-II, Fenice recent or present-day thermal manifestations Capanne, Montieri-). (travertines, hot springs, etc.). The deposits are Many aspects of origin and evolution of localized in the peripheral parts of the these ores are still to be elucidated. However, Larderello and Monte Amiata geothermal Tanelli and Lattanzi ( 1983) considered the fields, and their emplacement is ascribed to group 1) and 2) hydrothermal-sedimentary in convective circulation of meteoric fluids origin (Palaeozoic-Triassic), possibly related to triggered by recent (Pliocene-Quaternary) a pre-Tethyan aborted rift. Hydrothermal magmatic activity in the area. activity during Mio-Pliocenic magmatic events Sb-Au mineralization consists of jasperoid produced metamorphism, recrystallization and and vuggy silica masses which replace remobilisation of these ore bodies. Ore bodies carbonatic rocks (mostly Triassic «Calcare of group 3 ), clearly emplaced in connection Cavrnoso») at the contact with the overlying with Mio-Pliocenic tectonic and magmatic argillaceous formations (Liguride Nappe). Ore activity, and probably partially derived metals minerals are stibnite, pyrite, native gold, base and sulphur from remobilisation of the former metal sulfides, orpiment, realgar included in mineralizations [group 1) and 2)]. chalcedony, coarse quartz, calcite, fluorite, Niccioleta and Boccheggiano mines provided barite, gypsum, alunite, clay minerals and some of the finest groups of pyrite, cubic, kaolinite. In these deposits cinnabar is seldom crystals ever found in the world. Boccheggiano found as thin earthy varnishes lining late and Gavorrano mines also provided fractures in ore. Beautiful specimens of stibnite pyritohedral and complex cube-pyritohedral in groups of well terminated, prismatic, crystals. The latter are frequently deeply striated, crystals (up to 20 cm) have been found striated and are locally named «pirite triglifa». in cavities of vuggy silica or embedded in Niccioleta mine also provided metre-long spatic calcite veins. Secondary, whitishyellow­ gypsum crystals and good crystals of many red, Sb oxides and sulphates frequently encrust other sulfides. Finally, Campiano mine the stibnite crystal faces. produced incredible specimens of anhydrite in Tuscany has long been a major mercury large lozange-shaped crystals (up to 30 cm) and producer through the exploitation of the in radiating groups of acicular crystals. worldclass epithermal deposits of Monte Ore deposits, industrial minerals and geothermal resources 49

hot travertml springs r E 0 0 hot springs r-

copertura tmpermeabtle EL]rocce carbonattche __ -=- basamento ftllad1co s 1 (formaztont flyschioidl cz.::=:zJ (calcare cavernosa) , l argtlhttche. arenacee e marnose: Ltgundi s.l.)

Fig. 6 - Schematic geological section of a Sb-Au deposits in Southern Tuscany (modified after Tanelli et al. 199 1 ); (A) Quartz, calcedony, calcite± Sb and Fe oxides and hydroxides, alunite, clay minerals, gypsum, barite, sulfides, sufates, Cl oxides, Sb sulfur oxides, gold; (B) quartz, calcedony ± clinozoisite, calcite, sericite, stibine, pyrite, marcasite, galena, sfalerite, tetraedrite, arsenopirite, cinabro, gold.

Amiata area. In the 1970's the Monte Amiata pyrite, marcasite, and minor realgar, orpiment, mines were gradually closed because mercury stibnite, metacinnabar, native mercury, with was progressively replaced in many industrial calcite, gypsum and celestite as gangue processes. Monte Amiata Hg deposits are minerals. Sometimes the surfaces of open spatially related to the Sb-Au ones, but fractures in sandstones are covered by esthetic cinnabar and stibnite do not occur in equal spherical and botryoidal aggregates of cinnabar amounts in the same deposits and appear to named «fragole» («strawberries»). exclude each other (Klemm and N eumann, 1984). In few Hg deposits, stibnite sporadically 2.7 THE RAW CERAMIC MATERIAL occurs as scattered and isolated aggregates of DEPOSITS OF SOUTHERN TUSCANY needles. Hg ores occur as cinnabar veinlets and impregnations (replacing carbonatic cement Among industrial minerals of Tuscany, raw and matrix of host rocks), in limestones, materials for the ceramic industry are calcarenites and sandstones (Liguride Nappe). especially important (ea. 600,000 t/yr, about Impregnations of cinnabar have been also one third of total Italian production). The main found in Pliocene sands, and rare micro­ activity was localized in four deposits crystals were observed in vacuoles of Monte (Marciana and La Crocetta in Elba Island, Amiata lava flow. Cinnabar is associated with Botro ai Marmi near Campiglia M.ma and 50 A. DIN!

Piloni di Torniella near Roccastrada; fig. 1) All and/or fluids contributed by the Porto Azzurro these occurrence are associated with magmatic, pluton, which crops out in the La Crocetta area, acidic, rocks of the Tuscan Magmatic Province. is ruled out by field, geochemical and geochronological data (4 0Ar-39 Ar age of Porto

2.7.1 Marciana and La Crocetta (Elba Island) Azzurro = 5.9 Ma, i.e. significantly younger than the sericitization event). Fluid inclusion At Marciana (western Elba), exploitation was studies suggest that sericitization was focused on a lenticular, subvolcanic, body of associated with a low-temperature ( < 250 °C) porphyritic aplite (alkaly feldspar granite in hydrothermal system. Fluids were locally composition) belonging to the Capo Bianco boiling, of variable salinity (4-17 wt% NaCl Unit. The mined rock is composed of a very equiv.), and contained some C02 (XC02 = fine-grained aggregate of albite, K-feldspar, 0.027). Their ultimate source is not quartz and magmatic muscovite that maintain unequivocally constrained; meteoric and/or the original magmatic, porphyritic, texture. magmatic contributions may be possible. Low Only minor alteration effects are visible (scarce salinity ( = 2.6 wt% NaCl equiv.), low pyrite-calcite-sericite disseminations and temperature ( < 250°C) fluids are associated veinlets), hence the economic qualities of the with the late carbonate veining. They are rock (high alkali K20 = 4 wt%, Na20 = 4 wt%, considered to be of dominantly meteoric nature and very low Fe, Ca and S contents) are the because of their low salinity. In summary, result of primary magmatic processes. sericitization at La Crocetta is regarded as the The La Crocetta mine (Maineri et al., 2002) product of a detachment fault-related, low is located in central-eastern Elba, and temperature hydrothermal system, resulting represents the currently exploited portion of a from the structurally controlled focusing of mineralised area including the old mine of meteoric and possibly magmatic fluids. Hence, Buraccio to the north. Exploitation focuses on a potential targets for exploration for similar pervasively sericitized, porphyritic, aplite sill resources are represented by aplitic bodies belonging to the same intrusive unit exploited located in the hanging wall of Elba Centrale in Marciana (Capo Bianco Unit), which Fault. underwent significant potassium enrichment during sericitic alteration. The ore bodies are 2.7.2 Botro ai Marmi (Campiglia M.1na) located along the hanging wall of the Central Elba Fault, a low-angle extensional lineament The Botro ai Marmi feldspar deposit is of regional significance. A later carbonatization associated with the apical part of a shallow stage, apparently associated with highangle sienogranitic to granodioritic intrusion closely extensional tectonics, locally overprinted the associated with a porphyritic dyke swarm sericitized facies. It is expressed by carbonate ± (both acid and mafic products), and several pyrite ± quartz veins, with adverse effects on Cu-Pb-Zn skarn and Sn deposits. The economic ore quality. Sericitization was accompanied by value of the mined rocks lies in their high addition of potassium, and loss of Na (± Ca, K (K20 = 7.4 wt% ), low Ca-Fe-S contents. Fe). Rubidium was not enriched along with Mineralogically, this high K content potassium during sericitization, contrary to is expressed by the occurrence of two what would be expected for interaction with generations of K-feldspar; the first one late-magmatic fluids. New 40Ar-39Ar data from is magmatic, whereas the second is late­ eurites provide an isochron age of about 6.7 Ma magmatic/hydrothermal and replace for the sericitization, whereas the age of the plagioclase. Explanation for the high K content unaltered protolith is ea. 8.0-8.8 Ma. Field of this material include: 1) displacement evidence indicates the Central Elba Fault to be toward the K-feldspar apex of the melt the main channel for the hydrothermal fluids. composition because of assimilation of On the other hand, the involvement of heat carbonate country rocks (Poli et al., 1989), and Ore deposits, industria/minerals and geothermal resources 51

2) late- to post-magmatic K-metasomatism. Development of ore-grade material is the result Recent studies (Lattanzi et al., 2001 and of a combination to various degrees of reference therein) seem to favour the second magmatic and hydrothermal processes. Primary mechanism, although the first one may have magmatic rocks are already characterized by contributed as well. Specifically, t1uids inferred comparatively high alkali, and low iron and to be in equilibrium with the second generation calcium, contents. Therefore, in some cases of K-feldspar show temperatures as high as 500 (notably Marciana) they may represent ores in oc, with salinities up to 38 wt % NaCl and 19 themselves. In other localities, the commercial wt % KCl. These features are typical of qualities of the currently mined rocks arise porphyry-related metalliferous deposits, also from hydrothermal alteration, resulting in characterized by potassic alteration; however, either K-enriched (Crocetta, Botro ai Marmi) or in the Botro ai Marmi system the potassic kaolinite (± alunite)-rich material ( di alteration is metalpoor: metalliferous Torniella). The nature of the fluids involved mineralization occurs in a later skarn to vein range from high-temperature, high salinity, stage, and is mostly localized away from the presumably magmatic, fluids (Botro ai Marmi), intrusion. to moderate temperature fluids of mixed magmatic and meteoric origin (La Crocetta), to 2. 7.3 Piloni di Torniella (Roccastrada) presumably steam-heated meteoric fluids (Piloni di Torniella). The Piloni di Torniella deposit results from hydrothermal alteration of Quaternary (2.4 Ma) peraluminous rhyolitic lavas and domes, 2.8 THE LARDERELLO AND MONTE anatectic in origin. Field evidences suggest that AMIATA GEOTHERMAL FIELDS the hydrothermal alteration was mainly controlled by high-angle fault systems. There are two important geothermal fields in Hydrothermal kaolinite + alunite replace Southern Tuscany (fig. 1 ): the Larderello field, magmatic feldspar and glass. However, have and the Monte Amiata field. Shallow intrusive been also described minor occurrences of bodies, belonging to the Tuscan Magmatic sedimentary (re-worked?) kaolinite in small Province, and hypothetical mafic injection lacustrine basins; in these occurrences, of better and/or uprising mantle dome, seems to be the economic quality, alunite is scarce or absent. In most plausible heat sources of these two comparison with other deposits of this study, geothermal areas, which were extensively the chemical composition of mined rocks is drilled and exploited by ENEL (Italian widely variable, and S contents are locally Electricity Board) during recent decades. high, because of the presence of alunite; in fact, The geothermal field of Larderello is a alunite was also mined in the past, but vapour-dominated system, one of the world's nowadays it severely detracts from the quality rare super-heated steam producing systems. of the ore. Even if there is no recent detailed The main reservoir of the Larderello field is research on the locality, the available found within a limestone formation (the information may suggest that this deposit «Calcare Cavernosa», Upper Triassic in age) represents an advanced argillic alteration belonging to the Tuscan Nappe. They rest on assemblage formed in a shallow environment top of a schistose quartzitic rocks of Paleozoic­ by meteoric t1uids interacting with hot gases. Triassic age which unconformably overly a metamorphic basement made up of phyllites, 2. 7.4 Conclusions micaschists and gneisses. The cap rocks of the The main deposits of ceramic raw material in reservoir are represented by an impermeable Tuscany are associated with acid magmatic flysch formation (the «Liguridi Nappe rocks of the Tuscan Magmatic Province. Complex») and by Neogene clay sediments. At 52 A. DIN!

Larderello the first industrial extraction of The geothermal area of Monte Amiata is boric acid started during the 18th century, while characterized by the presence of a Quaternary the possibility to generate electricity from volcanic structure having a trachydacitic-latitic geothermal steam was successfully proven for composition. This volcano is located on a wide the first time in the world in 1904. In the late structural high where Liguridi and Tuscan 1970s a deep exploration program through out Nappe crop out. The main geological the field significantly improved the knowledge difference with Larderello is the nature of the on temperature distribution at depth, and metamorphic substratum, which consists productive levels were discovered in the deep­ mainly of Palaeozoic graphite-bearing phyllites seated metamorphic basement. Peraluminous, and phyllitic quartzites, metasandstones, leucogranites and monzogranites with limestones and dolostones. Geothermal significant F and B content, and their research in the Mt. Amiata area started in the thermometamorphic aureoles, were found in 1950s and led to the discovery of several several deep wells (between 2.5 and 4.5 km shallow reservoirs (160-220°C). The top of depth). The occurrence of intensely fractured these reservoirs is located at a depth ranging zones inside the granites could represent a from 400 m to 1000 m in correspondence to target for the future reservoir exploration. positive structures of the carbonate-anhydrite Intensive exploitation caused a pressure drop formation of the Tuscan Nappe. Based on inside the reservoir with the consequent sharp experience gained from deep drilling in the decline in fluid production. To test the Larderello field, the research in the Monte feasibility of increasing steam production water Amiata area was resumed in 1978: two deep injection in the Larderello area started in 1979. exploratory wells were drilled to find From 1984, re-injection of waste water became additional fluid below the layers already under an important part of the exploitation strategy, exploitation. At depths ranging from 1300 m to and the process was monitored by determining to 3000 m, water-dominated productive the isotopic and chemical composition of horizons have been discovered, with fluids. temperatures of 300 to 360 °C.