An International Journal of CHAPTER 5 Campiglia Marittima and Gavorrano Intrusive Magmatism 5.1 HISTORICAL PERSPECTIVE from Etru
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Per. Mineral. (2003), 72, SPECIAL ISSUE: Miocene to Recent... , 127-132 http://go.to/permin An InternationalJournal of : �· PERIODICO di MINERALOGIA MINERALOGY, CRYSTALLOGRAPHY, GEOCHEMISTRY, established in 1930 ORE DEPOSITS, PETROLOGY, VOLCANOLOGY and applied topics on Environmelll, Archaeometry and Cultural Heritage CHAPTER 5 Campiglia Marittima and Gavorrano intrusive magmatism SERGIO ROCCHI1*, ANDREA DINI2, FRANCESCO MAZZARINI1 and G!AMPIERO POLI3 1 Dipartimento di Scienze della Terra, Universita diPisa, Via S. Maria, 53,Pisa, 56126, Italy 2 CNR, Istituto di Geoscienze e Georisorse, Via Moruzzi, 1, 56124, Pisa, Italy 3 Department of Earth Sciences, University ofPerugia, Piazza Universita, 06100, Perugia, Italy 5.1 HISTORICAL PERSPECTIVE Indeed, the settlement was built with the aim of keeping the workers and all the phases of From Etruscan times to the recent past, man production under control. Within the village has bored into the rocks of the Campiglia walls of Rocca San Silvestro, a whole area has Marittima area to extract ore minerals. Here, been identified which was set up for the deposits of ore minerals hundreds of metres metallurgical processing of the local minerals of thick blanket two porphyritic dykes. The ores copper, lead and silver. Traces of smelting are mainly mixed sulfides ( argentiferous galena, activity detected here include waste from metal chalcopyrite, sphalerite) and cassiterite. At the working, blocks of the fire-proof stone used in surface the deposits are composed of limonite, the construction of kilns, baked clay, mineral the so-called «cappellaccio». The occurrence of fragments, and the remains of constructions mineral resources influenced the location and used for smelting. Outside the walls of Rocca development of settlements from Etruscan times San Silvestro, the reduction furnace and the onwards. In 1984, an archaeological research forge of an iron smelting and smithing complex program started at Rocca San Silvestro, close to have been discovered. Here, the production of Campiglia Marittima, with excavation of the iron was driven by great internal demand linked site. These studies unveiled a medieval village to the mining and production activities of the set up for ore exploitation and metal production. village rather than to any commercial The fifteen mine workings linked with the exploitation of iron as such. Rocca were mostly vertical shafts a few to tens After being abandoned for over 200 years, of metres deep. In Medieval times, copper and mining activities were significant over two silver were used together with gold as the main centuries. Exploration studies were undertaken components of coins, thus they were considered at the beginning of the nineteenth century, precious metals, and the revenues and political leading to mining concessions to French then importance deriving from the control of their English companies during the second half of production was considerable. Rocca San the century. The first scientific description of Silvestro is a demonstration of the importance ore deposits from French, German and Italian of the management of mineral resources and of engineers and geologists date back to these the control of the whole metal production cycle. times. At the end of the 1950s, exploitation started again by Italian companies, and Corresponding author, E-mail: [email protected] operated until 1976 when the mine was forced 128 S. RocCHI, A. DINI, F. MAZZARINI and G. Pou to close, and the area has since then been The nappe pile resulted from eastward-directed exploited principally for opencast limestone thrusts associated with the convergence and quarrying. Following the studies by the collision between the European margin and the archaeological research team, the San Silvestro Adria microplate in late Oligocene time. Since Archaeological Mines Park was sketched out in late Tortonian time, the internal zone 1989. The aim was to give value to, and make a underwent post-collisional extension related to museum out of, a whole historic landscape the opening of the northern Tyrrhenian Sea. In arising from centuries of mining activity. Also southern Tuscany, crustal extension was linked included in the Park are the buildings, to the igneous activity of the Tuscan Magmatic Province. infrastructures, tunnels, washing plants, roasting and reduction furnaces set up from the beginning of the nineteenth century to 1976. 5.3 THE INTRUSIVE UNITS 5.3.1 Botro ai Marmipluton 5.2 GEOLOGIC SETTING In the area of Campiglia Marittima, intrusive rocks crop out over a limited area at Botro ai The geological framework of the area (Fig. Marmi, and are found in boreholes at M. 1) consists of several stacked tectonic units Spinosa and M. Valerio, 3 km south of the producing a stratigraphy starting at the bottom outcrop (Fig. 2). Samples from the pluton with Tuscan Basement, successively overlain display a monzogranite or alkali feldspar by the Tuscan nappe and the Ligurian nappe. granite composition (Fig. 3; Caiozzi et al., SIENA ...- ...-',•_ \ \ r--1 \ \ \ 0 30 km \ Rotcastf\ada I \ ....- / ai Marmi I \ Monte ...... ..,... Q / ...... \J� I 1\r--��� ...... , ...... \ .)... \ ....- ....- 1 Gavorrano \ ;((Jm�a�a1 1 / ( GROSSETO \ / \ I / \ / Elba �� • \ / / I \ \ \ Y / \ y I / Intrusive rocks of Tuscan Magmatic Province Volcanic rocks of Tuscan Magmatic Province Fig. I -Location of intrusive and effusive rocks of the Campiglia area. Campiglia Marittima and Gavorrano intrusive magmatism 129 S. 5 0I 6 4 7 3 I 8 2 I 9 0 I L c___ _ --�· �-----J Km Fig. 2 Schematic geological map of the area north of Campiglia Marittima. I) Limestones (Lias); 2) Limestones (Lower Lias); 3) Marls and chert (Dogger-Oligocene); 4) Flysch (Oligocene); 5) Ophiolites s.l.; 6) Pliocenic volcanics; 7) Botro ai Marmi pluton; 8) porphyry dykes; 9) faults. Modified after Barberi et al. (1967b ). 1998; Poli et al., 1989). The mineralogical replaced by K-feldspar. Mafic phases are assemblage consists essentially of subhedral almost lacking, with primary biotite replaced orthoclase and anhedral quartz. Plagioclase by chlorite and/or muscovite (Lattanzi et al., occurs rarely as small euhedral crystals, often 2001; Poli et al., 1989). Botro ai Marmi rocks 130 S. RoccHI, A. DIN!, F. MAZZARINI and G. Pou 1111 Bolro al Marml Tuscan Nappe (Fig. 2). The dykes crop out 0 Gauorrano- main fades discontinuously over a length of 7 km, with 0 Gauorrano- le uco fades thicknesses ranging from a few cm to several 40 � Caslel dl Pie lra tens of metres. Samples are invariably quite . altered, but three different types of porphyry dykes can be recognised (Barberi et al., 0 30 1967b). Type-1 are cordierite-bearing acidic dykes. Primary phenocrysts are: sericitised andesinic plagioclase, abundant strongly embayed quartz, scattered euhedral potassic feldspar, pseudomorphs after euhedral cordierite, and biotite deeply transformed to chlorite, muscovite, iron hydroxides and Ti rich products. The groundmass shows a felsitic microgranophyric texture with quartz ANOR feldspathic phases. Type-2 are Na-poor, K-rich Fig. 3 - Normative Q' vs. ANOR classification diagram acidic dykes. Primary phenocrysts are: (Streckeisen and Le Maitre, 1979) for Gavorrano and Botro embayed quartz, potassic feldspar as both ai Marmi intrusions, and Type-3 porphyries. Data from euhedral crystals and anhedral patches, and Caiozzi et al. (1998), Peccerillo et al. (1987), and pseudomorphs after euhedral cordierite and unpublished data from Innocenti. For comparison, v�riation fields for the Caste! di Pietra subsurface intrusiOn are biotite. The groundmass has variable grain size. shown (data from Franceschini et al., 2000). These dykes represents Type-1 dykes that suffered K-metasomatism with secondary replacement of plagioclase by K-feldspar. plot in the leucocratic facies field of intrusives Type-3 are pyroxene-bearing dykes of from TMP (Fig. 4). intermediate composition. Primary phenocrysts Secondary phases have been generated in are: rare sanidine up to 5 cm, oscillatory-zoned large part by autometasomatism involving late plagioclase, strongly embayed quartz, diopsidic stage hydrothermal fluids, with minor pyroxene almost completely replaced by a contributions from interaction with COTrich chlorite-epidote assemblage, and biotite fluids and carbonate country rocks (Barberi et transformed to chlorite + sphene. The al., 1967b; Poli et al., 1989). The role of groundmass shows a felsitic texture with hydrothermal chlorine brines exsolved from the plagioclase, sanidine and pyroxene. The age of magmas during the late stage of crystallisation dyke emplacement is constrained by the 4.3 Ma is also considered essential as a carrier of K-Ar age for a Type-2 metasomatised porphyry metals (Fe, Cu, Sn, Zn, As) for the nearby ore dyke (Serri et al., 2001, and references therein). deposits (Caiozzi et al., 1998). The A close spatial link exists between these dykes emplacement age of the pluton is poorly and the extensive skarn and Cu-Pb-Zn ore constrained at ea. 5 Ma (Serri et al., 2001, and mineralisation of the Campiglia area. references therein). The apical part of the Compositions of two samples of Type-3 are intrusion is quarried as a raw ceramic material reported in Figure 3, however strong alteration (Lattanzi et al., 2001). impedes a deeper geochemical study. 5.3.2 Porphyry dykes 5.3.3 Gavorrano intrusion In the area of Campiglia Marittima, about 1- 2 km ENE of the Botro ai Marmi pluton, Data from mining activity, along with field several N to NW trending porphyry dykes work, indicate that the Gavorrano intrusion is a crosscut the early Jurassic reef limestone of the laccolith emplaced at the base of the Tuscan Campiglia Marittima and Gavorrano intrusive magmatism 131 1.4 lntrusives 1.2 Enclaves Normal Facies 1.0 Leucocratic Facies 0.8 Castel di Pietra ON I- Monte Spinosa 0.6 Botro ai Marmi 0.4 Gavorrano main facies Gavorrano leuco facies 0.2 0.0 ��--���--��--��--��--._�--��--�_.--�_J 54 56 58 60 62 64 66 68 70 72 74 76 Si02 Fig. 4 - Si02 vs Ti02 diagram for Botro ai Marmi and Gavorrano intrusions. Data from Poli (1992); Festoso (1989); Pinarelli et al.