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The Schneeberg ore deposit lies within the crystalline basement of the Oetztal-Stubai Alps. The metalliferous layers are in a very special position, in the upper part of the Variscan and pre-Variscan basement, embedded between the white Dolomit of the White Rocks of Schneeberg and Maiern and a multi-coloured series of garnet-bearing micaschists, marble and amphibolite of the Schneeberg Complex.
The ore-bodies are not only found at Schneeberg itself, but also in a relatively thin seam which starts approximately at St. Martin am Schneeberg, runs north-east across the Lazzacher Tal, and approaches the Pflerschtal. The sediments of the White Rocks of Schneeberg and Maiern, like the white band of the Gürtelwand, are Middle Triassic sedimentary rocks (Wettersteindolomit). They were thus formed at the same time as the corresponding rocks of the Dolomites: about 230 million years (MA) ago. These limestone deposits were laid down by plants and animals in a shallow sea and, in fact, if you look carefully, you can sometimes see fossil remains. Conglomeratic gneisses at the base of the Dolomites correspond to the Val Gardena layers (sandstone and conglomerates), deposited 290-245 MA ago in the Permian. During the Alpine orogenesis, these sediments were subjected to such pressures and temperatures that they were completely metamorphosed and today only specialists are able to distinguish them from the schistose rocks of the crystalline basement.
The rocks of the Schneeberg Complex, which flank the southern border of the ore-bodies, are clearly different from those of the crystalline basement. The multi-coloured marginal belt of the Schneeberg Complex consists of a series of yellowish and grey marbles, dark-green amphibolite, brownish-black amphibolitic schists, very hard yellowish-white quartzite, and silvery micaschists with well-formed garnets, sometimes several centimetres across. In the field, this series is easily identified, but it may also be found inside the Karl gallery, about 830 m from the entrance on the Passeier side.
Southwards, this clearcut association of rocks, between 10 and 100 m wide, passes to grey, highly schistose, garnet-bearing micaschists - not for nothing called the monotonous series of the central Schneeberg Complex.
While we know the age of the sedimentary rocks very well, little is known about the chronology of the Schneeberg complex, since several orogenetic phases have completely metamorphosed the rocks and obliterated all indications. Certainly, it is much older than the Permo-Triassic sediments.
The crystalline basement of the Oetztal-Stubai Alps consists here of a monotonous series of micachists and paragneiss, with numerous intercalations of orthogneiss and amphibolite. These intercalations include acidic and basic magmatic rocks which, together with the clayey-sandy sedimentary deposits, which make up the original materials of the micaschists and paragneiss, and were metamorphosed and incorporated together within the Oetztal-Stubai crystalline complex. The age of these rocks is not known, but the original sedimentary rocks may be older than 500 MA.
Two orogenetic phases intensely metamorphosed the rocks: the Hercynian orogenesis, which took place 300-360 MA ago, and the Alpine orogenesis, 80-100 MA old. This is an incredibly long period of time, during which a mountain chain first rose and was then demolished; in its place, seas and oceans appeared; and then a new mountain chain came into being - the Alps, which are still slowly rising.
The complex present-day geometry of this area, the contemporary occurrence in a small space of young marine sediments (the White Rocks of Schneeberg) and the original rocks of the crystalline basement and the Schneeberg Complex, have seen entire oceans change over the course of millions of years. It is thus very difficult to interpret the origin of the rocks and of the minerals to be found at Schneeberg.
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geological framework
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