Native gold special page
This group of mines is well known in Italy as "Brusson mines" or "Ayas valley abandoned mines" . The mines are famous, at least in Italy since they are one of the few places in the alpine area where was possible to find some samples of native gold, in dendrites, arborescent or in small XX. For a long time no more findings were made, but in the last years some new work made for collection pouposes made possible some new very interesting findings . The gold samples from this locality are very attractive both for the geological rarity of native gold in the alpine mountains and for the cristallisations, very attractive from the aesthetic point of view.
In this page you can find a description and some curiosities about the locality.
The old mines of Brusson are very close to Brusson city, along the Ayas valley. The mines are in two groups of galleries, exploiting some quartz veins outcropping in the two parts of the valley of the Evancon river. The most important group of veis is in the north western area, very close to Brusson. This goup of veins outcrop in the almost vertical wall south of the city. The veins are very visible from the road in the valley ( SS n. 506 ) as white veins north dipping. They are organized in two distinct groups of filonian rocks, the northern one ( Fenillaz) being the most important and exploited, with at least 7 galleries open in it. The material external to the mine is very limited and almost all the minerals can be found only in the galleries. Another group of galleries ( Challant Saint Anselme ) is reachable following the road from Brusson to Orbeillaz-Arbaz-Punta Zuccore. Very close to Arbaz there is an old track that in about 20 minutes of walk arrives to the several old galleries open in this goup of veins.
From the geological point of view the mine is located on a classic filonian mineralisation. The gold is in relatively small quartz veins ( with a thickness from few centimeters to 1 meter or something more) crossing both the Rosa mountain gneiss and some scists, called "pietre verdi".
These mines are very old and have been exploited in different times but with minor and sporadic works in the centuries. Sometimes we have notifications of some important finding, like the finding of a geode with a sample of native gold of more than 1 kilogram in 1740 !!!! The mines have been exploited with some economic interest at the end of the ninetenth century. After that period they have been abandoned and some new work was done in the period 1930-1940. All the different attemps of exploitation weren't anyway very important due to the relative scarcity of the veins in terms of gold content.
The mine, the minerals and the research campaign
The mine is not so much complex and extended. The most important and rich galleries, the northern ones close to Brusson city, are relatively short galleries that follow the quartz veins how much is possible, since they are dipping at high angle. In recent times a group of old miners and collectors initiated an excavation campaign that gave some interesting results...
The most common mineral is the Quartz, still present in interesting groups of XX also of 10-20 cm white or trasparent.. Famous from this locality are the Japan geminatons ( 90° gemination ).
In the veins some sulphurs are very common, like the pyrite, in nodules or small XX, less frequent are pirrotine and calcopyrite.
The very interesting and most famous mineral of the mines is the gold, native gold, in fom of laminae, dendrites, small nodules or cristals, with a cristalisation composed by octaedrons, cubes and rhombododecaedrons combined.
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