Fabio letto, Matteo Federico* LA MINIERA DI SALGEMMA E LE RISORSE DI VALLE NETO (CALABRIA). Utilità private e danni ambientali THE SALT MINE ANO RESOURCES OFTHE NETOVALLEV (CALABRIA, ITALV). Private Utilities and Environmental Damage Sommario Le condizioni di rischio territoriale derivanti dall'attività di estrazione mineraria di salgemma, nei pressi dell'abitato di Belve­ dere Spinello (Kr), vengono qui presentate e discusse. A tal proposito sono state eseguite analisi geochimiche, su campioni d'acqua di falda e superficiali, che hanno rilevato un diffuso e consistente inquinamento delle risorse idriche naturali e per un'estensione di gran lunga superiore a quella di concessione mineraria. Condizione di crisi territoriale ulteriore, è rappre­ sentata dagli elevati e diffusi tassi di subsidenza su tutto il bacino minerario. Questi, negli ultimi 20 anni di attività estrattiva, J hanno portato alla formazione di 5 camini di collasso, talvolta con fuoriuscita, fino a massimi di 1 * 1 (J6 m , di salamoia satura. llfenomeno, a ogni evidenza di terreno, è tutt'ora in atto. Viene così evidenziata come un 'utilità essenzialmente privata (la miniera) possa compromettere la sicurezza e l'economia di base di una comunità antropica residente. Parole chiave: Valle Neto, Tettonica del sale, Inquinamento, Subsidenza. Summary The potential hazard conditions to the land caused by salt mining near the town of Belvedere Spinello (Province of Crotone, Calabria) are presented and discussed. Geochemical analyses were carried out on aquifer and surface water samples. These showed that there is widespread and substantial pollution of the natural water resources and this contamination regards an a­ rea well beyond the immediate mining district. A further hazard in terms of land management is represented by the high rates of subsidence throughout the mining area. These movements, in the last 20 years of mining activity, have brought about the for­ mation of 5 collapse vents, sometimes with an outflow of up to i * 1 (J6 m·l of saturated brine. This phenomenon, on the basis of .field evidence, is still very much in progresso it is very elear, therefore, how an essentially private utility (the mine) can damage the safety and basic economy of a neighbou­ ring community. Key words: Neto Valley, Salt Tectonics, Pollution, Subsidence. 1. INTRODUCTION The salt mine of Belvedere Spinello, in the valley of the River area or to new more or less neighbouring areas. Another effect Neto (Calabria, Southern Italy ), exploits the salt banks inter­ of the 1984 events on the mining activity was that of the gra­ bedded in the evaporitic sedimentary succession of the Crotone duai substitution of the "multiple wells" system of working neogenic basino The method of working is the dissolution with a system of "single wells". This has made it easier to mo­ (Frash system) of productive banks at depths of between 250 nitor some of the dissolution cavities in new production areas. and 300m. Mining activity started in 1969, and until 1984 a However, besides the brine f100ding of 1984, the most evident "multiple wells" system was used. This involved the pressuri­ negative effects of the mining activity, from a land manage­ sed injection of hot water into the beds and the pumping of bri­ ment and environmental point of view, from 1983 (at about 14 ne from one or more neighbouring wells, among which links years from the start of mining) to today, are: were created by means of water fracturing and dissolution of Widespread subsidence; the mineraI. The only control of the effects induced by the mi­ Large collapse vents at the surface of the mine roof, re­ ning was the periodical measurement of surface subsidence of specti vely in 1983, 1984, 1986, 1992, 1993; the working area. After the disastrous events of 1984, with a Spontaneous outflow of brine at the soil and in points of up sudden collapse of the mine roof and expulsion into the soil of to a hundred metres or so outside the perimeter of the area more than 1 * 106 m3 of brine (Ietto, 1988), the various delibe­ of mining concession. rations of both public and private authorities brought about a progressive abandonment of the most intensively mined area Furthermore, as already foreseen and feared during the events ("old mine "). Minerai working was shifted to the edges of this of 1984 (letto, 1988), another less evident but far more dama- *Fabio letto, Dipart. Sciellze della Terra - UNICA L -87036 Arcavacata di ReI/de, (CS)- 0984493663- [email protected]; Matteo Federico, Dip. Scienze della Terra - UNICAL-87036 A rcavacata di Rende, (CS)- I1Ifederico @ullical.it. 55 ging effect of the mining activity has been, and stili is, that of ci ng different sedimentary thicknesses depending on the time. the subterranean outflow of industriai brine into the large and In this regard, greatly summarising the specific li terature, we adjoining water-bearing stratum of the River Neto. This is sug­ can say there is essential agreement on: gested by the results of a hydrogeological and geochemical A compressive Messinian phase (Ortolani, 1978; Di Noce­ survey presented here. ra et a/ii,1974); A compressive middle-Pliocenic ph ase (Ortolani, 1978, 1985); 2. GEOLOGICAL CONTEXT OF THE DEPOSIT A tensive plio-Pleistocenic phase (Ortolani, 1978; Tortori­ ci, 1981 ). The rock salt in the Neto Valley was already being mined at the begi nning of the 20" century (subterranean or open mining Of these stages, the compressive phases, which according to on portions outcropping at the surface - e.g. near the town of some Authors occurred throughout the Pleistocene (Tortorici, Verzino). It is found in various lenticular intercalated beds in 198 1), are those most interesting in terms of their influence on the Messinian interval of the sedimentary succession extending the deformations in the body of the soft neogenic sediments. In from the Tortonian to the Pleistocene and is transgressive on fact, in the corresponding sedimentary series, the late-Mioce­ the Sila crystalline complexes of the Calabrian Are (S ignorini, nic saline beds are the mechanically most sensitive and least 1942; M igl iorini, 1952; Selli, 1957, 1962; Ogniben, 1955, competent features as regards the dissipation of forces. Thrust 1973; Roda, 1965, 1965b). surfaces, reverse faults or various folding movements can The sedimentation, in the alpine tectogenetic band of the Are, strongly deform the beds with a plastic behaviour, like those of is located in an area of foredeep (DI Nocera et a/ii, 1974, 1975; the rock salt, according to various ki nematic processes, depen­ Ortolani, 1978), which could be in a piggy-back position as ding on surface loads, bed thicknesses, the presence of fl ui ds suggested by the repeated olistostromes of scaly clays interca­ and so ono For the effects of compressive tectonics on th e salt lated at the base of the succession, as indicated by Ogniben beds, some probable deformational styles can therefore be ( 1955). schematised as in the following Figures: The prevalent lithology of the neogenic series is mai nly silico- clastic, with facies variable from silty clays to conglomera­ tes, depending on the diversi­ fied tectonic and palaeogeo­ graphical conditions. Focussing the analysis on the aim of the research, the same series fro m bottom to top can be subdivided into: Basai transgressive complex (Tortonian), represented by: conglomerates, sandstones and marly clays; whic h x groups together different Jo:' K xXX' )(' xY.xx x- Jr x ~ formations variously distin­ guished by several Authors Figure 1 - A) crystalline basement; B) Tortonian transgressi ve series; C) rock salt; D) (Selli, 1957; Roda, 1965; 0- Messinian sediments; E) post-Messinian sediments; F) Plio-Quaternary and continental gniben, 1973); sediments. Evaporitic/Messinian com- plex, subdivided by Roda (1965, 1965b) , into: Lower evapori tic com­ -_ r:.­ plex (mean thickness 25m); • , .: ~ ", • • '" J M" ..... • • .. , . E: Detritic-saline complex; , . Upper evaporitic com­ ,J •• 4 pie x (mean thickness 150m); Summit plio-Pleistocenic complex made up of: con­ glomerates, sandstones (of­ ten molasse), clayey marls and silty clays, divided into various formations by Roda ( 1965). The tectonic activity of the se­ diments is quite complex becau­ se it occurred with repeated Figure 2 - A) crystaffine basement; B) Tortonian transgressive series; C) rock salt; D) phases of both compression and Messinian sediments; E) post-Messin ian sediments; F) Plio-Quaternary and continental tension, consequently influen- sediments. 56 In one or the other ex ampie, the overlapping of saline masses are al so referred to by the Official Appraiser's Report (1994), along flow surfaces is, therefore, highly credible, to the point produced by the Court of Crotone after the flood of 1984, re­ where the large domed thickenings, detected by the mining fen'ed to herein. surveys, can be clearly justified without resorting to over-ela­ Today, therefore, it can be affirmed that the Belvedere Spinello borate reconstructions. mine, with the mining dissolution system, exploits the salt beds On the basis of a rereading of the surveys in Roda (1965) and at the summit of one or more diapiric masses under plastic following new analyses, after the catastrophic mining events of flow towards the surface. The flow of the salt masses entails, 1984, Ietto (1985) hypothesised that the thickenings of the salt in turn, that the tensive tectonics of the mining area, which to­ bed of Belvedere Spinello were due to compressive tectonics, day can be seen at the surface, are for the most part due to ri­ suggesting that "salt tectonics " were in act, that is phenomena sing geological bodies. It is therefore likely that many of the of diapiric salt domingo These concepts were openly rejected in high angle faults with limited displacemenl, which are delecla­ the 1980s by experts and non-experts of the sector, as shown ble at the land surface, originate at the summit or in the depres­ by the extensive documentation relative to the confrontation sions of the saline masses (Levorsen, 1954).