In the Upper Surselva region, along the Rein Anterior, the space between the Aar Massif to the North and the Gottard Massif to the South is occupied essentially by the intermediate Tavetsch unit. From its start below Trun in the East and to above Sedan to the West, this formation extends over a length exceeding 30 kilometers. Its width varies between 1 and 3
kilometers.
 
In the Alpine range, the Tavetsch unit is somewhat peculiar for two reasons:
 
1. Geologically the unit does not quite "fit in" exactly in the Alpine building. Theoretically a fairly well developed Mesozoic sedimentary synclinal basin should have its place between the mainly granitic Hercynian units of the Aar and the Gottard. While the sedimentary basin is still present, its size is severely reduced and "replaced " by the polymetamorphic and strongly sheared Tavetsch unit, which for this reason was called the intermediate or "Tavetsch Zwsischengebirge" (thereafter for simplification: Tavetsch). The presence and the origin of the Tavetsch unit is not quite understood as yet and can give origin to several diverging geotectonic interpretations.
 
Lithology:
 
Predominant sericite - muscovite schists, generally considered to be metamorphic acid tuffs.
Muscovite bearing gneiss.
Amphibolites and diorites in small lenses.
Serpentinites and talcschists lenses.
 
2.  Three different types of gold occur in the Tavetsch unit.
 
A.  Alluvial gold



In the Medel Rein, just South of Disentis/Muster and near the Touring Club camping, a gold placer has been known for many years. It is attracting an increasing number of amateur gold panners from near and far, and is by now the most popular in Switzerland. One nugget of 125 grams and several nuggets of 10 grams have been reported.
The presence of nuggets remains unexplained until now.  The problem of their origin has not been addressed as yet.



In l987, the Canadian company Narex carried out a preliminary regional gold panning program, mostly in the southern affluents of the Rein Anteriur, between Trun and the Oberalp pass, which all cross Tavetsch unit formations. Encouraging results have been recorded. 


B.  The Sumvitg Valley bonanza
 


In the year 2000 Mr. René Reichmut, an independent prospector from  Muotatal, discovered a quartz vein with 1 - 1.4 kilograms of  gold "somewhere" in the Sumvitg valley.
This discovery is the most important one in the Alps in recent times.
 
The exact location of such a major bonanza is and of course remains unknown and mysterious. As times goes by, new legends about the discovery are being circulated, and at one time at least suspicions of a "fake" may well have been raised.
The Chur Nature Museum for instance requested the curator of the mineralogical collection in the Museum of Bern to certify the origin and the authenticity of the specimen (Synthetic alluvial gold nuggets can be produced and sold at times as authentic ones. In the specimen under a glass window at the Museum of Chur, small shining faces of cubic gold crystals can be noticed, which may  be interpreted as a positive proof of authenticity).
15 quartz pieces with gold were discovered and sold for a supposed amount of Swiss francs 500,000, or almost US$ 400,000.
The cleaning and the sale of the specimens was entrusted to Mr. Bruno Higgins, from the Rockart Gallery in Arosa, the cleaning has been performed mainly in California. The largest piece is exposed in the Nature Museum in Chur. Other pieces went to the Universities Museums of Basel, Bern and Lausanne, and other buyers.
The specimen in the Chur Museum was "cleaned" with hydrofluoric acid, a rather unusual procedure in public mineralogical collections.
As the bonanza is situated in MinAlp's concession, it is planned to acquire more detailed and reliable information on the discovery and its location, in order to integrate its geological setting in future exploration endeavours. The essential question to be addressed is to grasp the origin and the metallogenetic significance of a sizable native gold discovery in the Tavetsch unit.

 
C.  Gold associated with sulfides



Gold is practically always associated with sulfides horizons present in many localities within the sericite schists prevailing in the Tavetsch unit, from Trun to Sedrun.  This type of gold, which is practically never visible, occurs for instance in the type locality on the road in the Lukmanier Schlucht (gorge) of the Medel Rein.
 
Ore mineralogy:
Pyrite, pirrotite, arsenopirite, tetraedrite (?).
minor amounts of chalcopyrite and sphalerite, gold.
Turmaline, a complex aluminium boro silicate, occurs exclusively in association with the ore minerals.
 
Generally sulfide concentrations can be recognized easily in the field by the presence of a fine reddish gossanous coating over the whitish sericite schists.



The attention of the reader is drawn to the observation that in the David Bell mine in Hemlo, Ontario, Canada, gold is also associated with sericite schists and sulfides.
 
Exploration history
 
In 1983 gold was (re)discovered on the Lukmanier pass road near Disentis by Karl Naert, a Canadian exploration geologist and David Knopf, a Swiss consulting geologist. Along the road several outcrops of gossanous and gold bearing sulfides imbedded mainly in sericite schists can be easily seen.
The locality in the Lukmanier gorge (Luklmanierschlucht) has been described as the "discovery point".
 
In the years 1986 and l987, exploration work was carried out by Narex and Mitcham, two associated Canadian companies, concentrating in the region in and around the Lukmanier Schlucht. (cf Mining Magazine). It has yielded promising preliminary results, but came to an abrupt end when Karl Naert, Narex's driving force, perished in a plane accident during a field trip in Argentina in 1994.