(foto di: Enrico Vettorazzo)
Access: short itinerary around the former mining center of Val Imperina
The copper valley
Val Imperina, known above all for its important mining past, is a lateral valley of torrent Cordevole, situated along the very evident structural discontinuity (Valsugana overthrust) where the very ancient rocks of the metamorphic basement (phyllites) come into contact with the stratified dolomitic rocks of Dolomia Principale (see the geological cross section). The transversal profile of the valley highlights a marked asymmetry (asymmetric valley), caused by the lithological diversity of the two slopes: the right slope, more steep (sometimes rocky) is sculpted in the compact/tough formation of Dolomia Principale, the left slope (gentler) is shaped into the soft and degradable rocks of the metamorphic basement (phyllites). However, Val Imperina is known above all for its mines that have been working, despite their ups and downs, for over five centuries (from 1400 to 1962). In the district of Val Imperina, a considerable deposit of sulfurs (above all cupriferous pyrite) was cultivated for a long time. Cupriferous pyrite (iron and copper sulfides), thanks to a complex metallurgical process (roasting, leaching, and several fusions; see notes) was used to obtain a good-quality malleable metallic copper, appreciated above all for its high resistance to alteration (for instance, it was used between the 17th and 18th century by the Serenissima Republic of Venice in cannon building, ship coating, and minting). At the end of the 19th century, after the fall of the world copper price (as a consequence of the discovery of huge deposits in Latin America), the production of Val Imperina became soon “way above market value”. With the Montecatini management (1910-1962), the activity was reconverted and pyrite was used to produce sulfuric acid (used in the chemical industry for the production of fertilizers).
Rocks, environments, and other features
Rocks: Phyllites of the metamorphic basement; along the shores of torrent Imperina, rests of the mining and metallurgical working
Environment / Landscape
Abandoned mining landscape (recent recovery measures carried out within a project of cultural enhancement of the industrial archaeology sites)
Notes
Copper metallurgy in Val Imperina
The metallurgical processes used in the mining district of Val Imperina to obtain metallic copper from cupriferous pyrite were mainly two: intermediate processes to obtain enriched minerals (roasting and leaching); repeated fusions to obtain metallic copper.
Roasting. Slow roasting (lasting some months) of the mineral in piles (called “roste”) under big roofs (called “teazzi”). During the process, the liquid fraction of sulfur was collected and sold for the production of gun powder. However, great quantities of sulfur were released as toxic fumes of sulfur dioxide (air pollution: acid rain). At the end of the roasting process, the roasted mineral fragments were formed by copper enriched compact nuclei (that were sent to the smelting furnaces) wrapped up in a friable and earthy crust that, after being separated, underwent a leaching process (an extraction process exploiting the different solubility of the degradation products of roasting).
Repeated fusions. The enriched mineral was sent to the smelting furnaces, where it underwent a cycle of fusions (called “fondite”):
- a) “raw” fusion
- b) “black copper” fusion
- c) “refining” fusion
- d) eventual final refining fusion.
At the end of the metallurgical process, good-quality metallic copper was obtained, appreciated above all for its considerable resistance to chemical alteration (a quality mainly depending on the presence of small quantities of tin).