The relationship between the open fractures and mineralized fractures in Oligocene sandstones of Leghorn coast (Tuscany, Italy) – the hydrogeological relapses

Abstract. The Oligocene-Miocene turbidite sandstones of fore-deep in the Northern Apennines form a very great aquifer that originally, before the reduction by Plio-Pleistocene erosion, is extended over an area of 60 000 sq/km (minimum) to 1.5 km–4.5 km tickness.

The spatial relationships between the open fractures and mineralized fracture (veins) in the outcrops of foredeep's sandstones (Macigno) along the Tuscany coast, between Leghorn and Piombino (Northern Apennines), are analyzed and discussed.

Also is discussed a conceptual model that allows a virtual surface of separation between an upper zone in open fractures and a fracture in the lower zone mineralization. The position of this surface than the topography surface, depends on the difference between the velocity of erosion and the velocity development of open fractures by reduction of the lithostatic load, during the exhumation of the system.

The lack of the open fractured zone, below this surface suggests that the deep water circulation into the Macigno sandstones along the coast area, depends exclusively on the connection between the major faults and the primary discontinuity (stratification).

Based on the results of fracturing analysis of the coastal Macigno the authors aim to extend the research to internal areas, and in particular to the ridge of the Northern Apennines, where the foredeep's sandstones are well developed and continued.