Produzione mineraria, bonifica territoriale e recupero ambientale in un'area pedemontana

Abstract

The paper reports preliminary geo-engineering investigations carried out as a part of a feasibility project of land restoration at a quarry area near Saltrio (province of Varese, northern Italy). Mesozoic carbonatic series of Norie ("Dolomia Principale", dolomitic limestone) and Lias times ("Calcare Selcifero", flint limestone) characterize the area. At present, an open pit quarry of flint limestone Is being exploited for high quality road metal, with consequent modification of the mountain side landscape. Quarrying is carried out from top to the bottom with recovery of mining dumps. A first stage of land restoration has been carried out in the northern part of the quarry area with re-planting of vegetation. In the past, the lower carbonatic layer - a bioclastic calcarenite - was exploited underground for the production of an ornamental stone known as "Saltrio stone". The exploitation rooms of the underground quarry have been abandoned, forming a series of underground voids which are a hazard for the stability of the whole area and greatly limit the development of the present open-pit quarry activity. In order to evaluate the conditions of the pillars of the old underground exploitation rooms a study using geophysical methods and geotechnical lab tests has been carried out. A realistic project of land restoration should consider the remodelling of the original slope in order to attain three main objectives: i) creation of a landscape well inserted in the surrounding countryside; ii) reclamation of the residual old mining spaces; and iii) an economically accebtable continuation of current quarry activities. The project has to forecast a gradual excavation of the layer of useful flint limestone, with the stripping stage carried out at the same time of the infilling of underground rooms. This can be done by blasting the rock layer at the roof of the old exploitation rooms, leaving the material in place up to a predefined hight In order to obtain suitable sized "Saltrio" calcarenite blocks to be used in restoration works of historical buildings, the project considers the possibility of a new small underground quarry in an adjacent area. Exploitation rooms of this small underground quarry have to be of such a size as to guarantee stability in time, and should be run using modern stone-cutting technology. It has been evaluated that an underground quarry using the room-and-pillar method may economically exploit the deposit for another 20 years.