Dossena Mines

MILLION

years ago

The Earth consisted of a single continent called Pangaea, covering about one third of the globe’s surface, surrounded by a single vast ocean called Panthalassa.

MILLION

years ago

A rift occurred in the eastern part of Pangaea, within which a new ocean, called Tethys, formed.

MILLION

years ago

The American continent broke away from Pangaea, moving westwards; the African continent began to push northwards, giving rise to the Apula lithospheric plate (Italy) and the Mediterranean Sea. To the east, the Tethys Closure took place due to the northward shift of the Indian Plate, which detached from the Australian continent and raised the Himalayan mountain range; Antarctica and Australia moved southwards.

MILLION

years ago

Within the Mediterranean, as a result of volcanic explosions and continuous telluric shifts, Sardinia and Corsica broke off to the west; the Apennines rose due to the shift (still ongoing) of the peninsula to the east. Following the opening of the Strait of Gibraltar, the Mediterranean Sea dried up, resulting in the deposition of saline (gypsum, anhydrite, rock salt) and organic (shells, crustaceans, corals) sediments.

MILLION

years ago

The sediments were shifted northwards by the continuous thrust of the African plate, giving the Alps their current shape; their orography, together with that of Europe and the Mediterranean, will be defined following the last ice age, which began about 100,000 years ago and was completed with the melting of the ice between 40,000 and 15,000 years ago.

An example of a fault visible within several tunnels. Research excavation was often initiated along the faults, precisely because of the lesser difficulty encountered in breaking up the rock and the greater structural stability offered by solid rock walls.

Metamorphic rock, formed as a result of frequent telluric shifts:

• Sedimentary: marble, limestone, dolomite, chalk, sandstone, bauxite
• Magmatic: basalt, granite, diorite.

The rocks in this area date back 230 million years. At that time, the present-day area looked like today’s tropical islands; in fact, these rocks were deposited in the carbonate platform marine environment (corals, shells, mollusc shells, crustaceans, all visible when observing the rocks under a microscope), forming the mineral by diagenesis. These rocks (limestones) are very porous and within them we find voids or air pockets that, over millennia, fill with various minerals; these voids were formed by the passage of water with a high calcium, magnesium and iron content, forming the mineral by the effect of sublimation.

Sublimation: Within closed cavities, excavated by the passage of water, the sediments left behind are altered and transformed by the high temperatures developed by constant tectonic pressure, passing from the solid state to the gaseous state without passing from the liquid state. The gases generated crystallise to form the mineral.

Diagenesis: In geology, diagenesis is any chemical/physical change undergone by a sediment after its deposition, between other rock layers or other sediments, during its solidification; the mineral is formed if the sediment has not already begun the lithification process (transformed into rock) or undergone alteration by the external environment (erosion).

Oxidation and Corrosion: from the moment rocks and minerals come into contact with the atmosphere they undergo deterioration caused by elements in the air.