Project Description

Dossena Mines

Geological origins

250/200

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.

190

MILLION

years ago

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

83/60

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.

20/15

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.

7/5

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.

The several natural cavities present (there are vertical shafts measuring 70 to 200 metres in depth) were formed over the last 10,000 years, thanks to the erosive action of water and melting ice following the last ice age.

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.

UNTIL THE EARLY 1900s

Conformation of the Alps

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.

INTERESTING FACTS

How does a mineral come into being?

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.

  • Smithsonite (ZnCO3): calcite crystals containing zinc.

  • Calamine (Zn 3[(Oh)2Si2O7]H2O+ZnC): formed from silicates and zinc, rusty in appearance, found near calcite and fluorite. Zinc is obtained; it is used in metallurgy due to its high iron content.

  • Fluorite (CaF2): calcium fluoride, glassy appearance with white, pinkish-purple (zinc), yellow (calamine) colours. Used in steel furnaces to lower the melting temperature of metals, to create hydrofluoric acid, in optics for the production of special lenses.

  • Calcite (CaCO3): similar to quartz, intense white in colour.
    Aragonite, Vaterite: shapeless stalagmites, white in colour like calcite.
    These three minerals are the three forms in which calcium carbonate occurs in nature.

  • Barite (BaSO4): Mount Ortighera, various crystalline forms, similar to calcite, used in various areas for its white pigments.

  • Sphalerite, also known as Blenda (ZnFe S): similar to pyrite, used for its zinc content.

  • Galena (PbS): grey in colour, occurs in granular form or cubic crystals. Used for the extraction of lead.

  • Gypsum, Azurite, Pyrolusite, Cerussite, Malachite, Wulfenite, Chalcopyrite… in addition to the main minerals, whose deposits have been exploited, there are around 30 different types, often formed from different minerals combined together. Many of them appear the same in their geological state, but they can be subdivided by observing their crystalline structure.