Guiding lines for the improvement of the triassic Metalliferous mining heritage in Lombardy

GUIDING LINES FOR THE IMPROVEMENT OF THE TRIASSIC METALLIFEROUS MINING HERITAGE IN LOMBARDY. A few tens of meters thick horizon of partly dolomitic limestones, with bituminous intercalations and quartziferous bodies, Ladinian-Carnian in age, is well known in geological literature and Lombard mining tradition as “Metalliferous”. It is stratigraphically confined between a thick sequence of carbonatic platform limestones at the footwall and a siliciclastic lagoon sequence at the hanging wall; it’s extension reaches about 80 km, striking W-E, from the Lecco Lake to the Sabbia valley. This horizon hosts several Zn-Pb-F-Ba ore bodies, extensively mined during the last millennium. Gorno is the most important mining field of the Seriana valley (BG), where about 10 Mt raw sphalerite, galena and calamine ores were extracted. There are a lot of minor mining sites as well, located where the peculiar type of metallogenic event (strata-bound ore deposits with lateral zoning) produced alternations of calamine ore deposits, or metal sulphides, or exclusively fluorite – or barite – like the Laghetto di Polzone and Cespedosio mines. Today these mining sites are abandoned. The orebodies have a inhomogeneous distribution inside the “Metalliferous”, and are irregular in shape (lenticular, columnar or stratiform), attitude (from sub-horizontal to sub-vertical) and size (elongation ranging from 100 m to more than 1 km, thickness from few m to more than 10 m). As a consequence, the mining exploitation techniques varied as well, and the companies that mined during the last 2 centuries made use of dissimilar techniques, depending on technology, planning, extension of the mining concession and investments. These mining activities placed, both at the surface and underground, represent a huge heritage of ore geology and industrial archaeology. Hundreds of km of galleries – from the valley floor to more than 2000 m in height – allow detailed mineralogical, lithological, stratigraphical and structural observations (i.e. imposing mining stopes), as a live, suggesting 3D representation. The remnants of the ore conveyance and processing plants – like cableways, decauvilles, dumps and washing plants – aren’t only decayed mining plants to reclaim, but in fact they have a much bigger value: they testify that the mining activities marked this area, moulding in the centuries a unmistakable “mining landscape”. Briefly the “Metalliferous”, winding and binding some valleys of the Lombard Alps, is like a thread of an ideal geological, industrial, historical and tourist route (some mining districts lie inside a Regional Park). These values combined as a whole, make the “Metalliferous” as a “unicum”, requiring comprehensive improvement, because it deserves the qualification of “The Orobic Pb and Zn Route”. During the planning stage it’s essential to contemplate different proposals for a wide consumer range (from school-children to universities). The appropriate tools could be a sort of “Supplemented Tourist Routes” (STR), planned for the peculiar technological, natural and social requirements of the different consumers. The STR will be able to create a revival both of underground experiences (the suggestion of the darkness and the ore mineral) and open air phenomena (geology, flora, fauna and landscape). The STR will allow cultural enrichment of visitors, through didactic reconstructions of historical, geological or technical aspects, or by guided mineral search and collection. At present time, there are some initiatives managed and supported both by the Lombardy Region and by communes, universities and authorities, in order to improve and to make safe some mining sites. Nevertheless, all these initiatives lack in the tragic dispersion and unavailability of the technical documents and records, and at the same times they favour more ludic or parochially-minded aspects. For this reason, a investment for the recovery of these documents is essential and still possible, thanks to the historical memory of technicians and researchers that worked in the old mines.