Switzerland

Dictionary / Encyclopedia Article

Reference

Switzerland

JAFFE, Felice

JAFFE, Felice. Switzerland. In: Dunning, F.W. & Evans, A.M. Mineral deposits of Europe.

Vol. 3: Central Europe . London : The Institution of Mining and Metallurgy, 1986. p. 41-54

Available at:

http://archive-ouverte.unige.ch/unige:152766

Disclaimer: layout of this document may differ from the published version.

1 / 1

Switzerland

Switzerland is an industrial country with few signifi- cant mineral resources, but it should be stressed that the drastic change from an agricultural and pastoral economy would not have been possible without the existence of many small and diversified mineral deposits. The small size and the low grade of these deposits led to their closure in the first half of this century. Thus, mining activities have come to a virtual standstill-in particular, in the field of metallic ores. A reminder of ancient mining activity exists in the many names of mines, mills, smelters and forges in different parts of Switzerland. 1

Swiss mineral deposits have been studied in detail by generations of geologists-in particular, by university students for their doctoral dissertations. The available literature contains a great wealth of detailed and interesting mineralogical, petrological and geological data, but references to economic geology and to ore controls, grades and reserves are not always adequate.

This is probably due, in part, to the absence of a specialized governmental agency, such as a geological survey. To some extent the Swiss Geotechnical Commission• has replaced such a survey, and its contribution to the understanding of domestic mineral deposits should be emphasized.^{57 •74•}78 The Commis- sion has sponsored and financed more than a hundred different raw materials investigations, but the results have been published solely under the authors' personal responsibility, since the lack of financial means and adequate staff has precluded guidance and supervision in the field.

A recent and comprehensive description of Swiss mineral deposits is not available, except for iron ores.83 The last publication on this subject dates from the period before the second world war.⁵⁰ The metallo- genic map of France extends into parts of western Switzerland, but without explanatory notes.1 2

Summaries of wider regional interest mainly en- compass Switzerland's neighbouring countries-in particular, the Italian Alps.70•111 Hence, this review is based principally on many different publications and on the excellent geotechnical map of the country.79-82 To improve the clarity of presentation only the main mineral deposits are described. Although many small

•Swiss Geotechnical Commission, Sonneggstrasse 5, 8006 Zurich, Switzerland; sale of publications: Kummerly und .Frey, Hallerstrasse 6, 3012 Bern, Switzerland.

41

and abandoned workings are present in Switzerland, their inclusion would not represent a significant contribution to the understanding of the basic facts and problems of a metallogenic and economic nature.*

Geological and metallogenic provinces Despite the fact that Switzerland is a small country, its geographical position within the Alpine arc ac- counts for its highly diversified geological struc- ture.16· 19·42· 91·92· 110 The country can be sub- divided into five major geological provinces, which will be described from north to south (Fig. 1 ). A good correlation can be established between the geological nature of these provinces and the corresponding mineral deposits. The subdivision into well-defined metallogenic provinces is, however, somewhat hazard- ous, as deposits of the same kind are rather rare.

Jura

The Jura is a low mountain range approximately 240 km long on Swiss territory. It is composed of Mesozoic rocks-mainly limestones, dolomitic lime- stones, dolomites and Triassic evaporites. It is charac- terized by a succession of broad faulted anticlines and synclines, arranged in the so-called Jurassian or Appalachian structural style.

Iron26, 2s . 29, 83

Delemont, Jura⁹ (9)t During the Eocene terrestrial conditions with a hot and humid climate prevailed in the Jura region and numerous residual pisolitic limonite accumulations were formed by the erosion and redeposition of older, ferruginous sedimentary hori- zons-mainly those which were formed in the Dogger period. Residual iron deposits, siderolitique in French and Bohnerz ('bean ore') in German, are irregular in shape and size, ranging from small pod-like fillings of karstic cavities to extended but irregular layers several metres and even up to 30-40 m thick. These deposits were folded with the underlying rocks, generally of

• The geology of the neighbouring Principality of Lichtenstein, which occupies 160 km² between the eastern border of Switzerland and Austria, is well known. ^{1 7} No ore deposits are reported from this country.

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Fig. 1 Main mineral deposits of Switzerland (see also Table 1)

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Table l Main mineral deposits of Switzerland*

No. on

Fig. l Locality 2 l

3 4 6 5 8 7 10 9 ll 12 13 14 16 15 17 18 20 19 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52

Allondon Leysin Bex Bex Chamoson Granges Leissigen Napf Delemont Schweizerhalle Laufelfingen Kienberg Herznach Felsenau Ennetmoos Erzegg Miirtschenalp Miirtschenalp Gonzen Calanda Totalp S-charl Scortaseo Poschiavo Silberberg Bleiberg Barenbuhl Oberhalbstein Val Ferrera Alp Ursera Alp Taspin Astano Palagnedra Alp Nadels Trun Puntaiglas Bristenstock Pizzo Corandoni Trachsellauenen Goppenstein Baltschiedertal Naters Gondo Kaltenberg Grimentz St. Luc Praz Jean Iserables Mont Chemin Les Trappistes Le Chatelard Salanfe

• See also Fig. 1.

Canton Gen eve Vaud Vaud Vaud Wallis Wallis Bern Luzern Jura Basel Land Basel Land Solothurn Aargau Aargau Unterwald Bern Glarus Glarus St-Gall Grisons Grisons Grisons Grisons Grisons Grisons Grisons Grisons Grisons Grisons Grisons Grisons Tessin Tessin Grisons Grisons Grisons Uri Tessin Bern Wallis Wallis Wallis Wallis Wallis Wallis Wallis Wallis Wallis Wallis Wallis Wallis Wallis

Commodity Gold Copper Salt Gypsum Iron Gypsum Gypsum Gold Iron Salt Gypsum Gypsum Iron Gypsum Gypsum Iron Uranium Copper Iron Gold Nickel Lead-zinc Nephrite Nickel Lead-zinc Lead-zinc Lead-zinc Manganese Iron Copper Lead-zinc Gold Nickel Lead-zinc Uranium Copper Lead-zinc Phosphate Lead-zinc Lead-zinc Molybdenum Uranium Gold

Nickel-cobalt Copper Lead-zinc Lead-zinc Uranium Iron Fluorspar Uranium Gold

Geological province Molasse Calcareous Alps Calcareous Alps Calcareous Alps Calcareous Alps Calcareous Alps Calcareous Alps Molasse Jura Jura Jura Jura Jura Jura

Calcareous Alps Calcareous Alps Calcareous Alps Calcareous Alps Calcareous Alps Calcareous Alps Penninic Alps Austroalpine Alps Penninic Alps Penninic Alps Penninic Alps Penninic Alps Penninic Alps Penninic Alps Penninic Alps Penninic Alps Penninic Alps Southern Alps Penninic Alps Gotthard Gotthard Gotthard Gotthard Aar Aar Aar Aar Aar

Penninic Alps Penninic Alps Penninic Alps Penninic Alps Penninic Alps Penninic Alps Mt Blanc Mt Blanc Aiguilles Rouges Aiguilles Rouges

References 73 65 7, 105 81 21, 102 81 80 9 90 45 79 30,32 80 79 79 22, 102 4 4 25 5, 6, 15 72 27, 53 24 75 27 27 37, 114 27 40, 101 27 27 39,55 76, 106 56 35 35 52 104 87 49, 109 61,89, 100 58 41, 43 38 44 96 18 48 46 60, ll2 59 54, 85, 103

Cretaceous age, and covered by horizontal or subhori-

zontal Oligocene and Miocene molasse sediments. Residual iron ore has the average chemical compo- sition(%) 44·5 Fe, 0·3 Mn, 11·0 Si02, O·l Al203 , 0·1 CaO, 0·06 MgO, 0·03 P and 0· 1 S. Probable reserves are in the order of 2 SOO OOO tonne.

Small surface workings have been exploited since antiquity in many parts of the Jura. Underground mines were active in the nineteenth and the beginning of the twentieth centuries, the Delemont mining district being the largest and the most important.

Herznach-Fricktal,, Aargau30•32•51 •83 (13) Sedimen- tary Middle Jurassic (or Brown Jura) iron ores are well known throughout Central Europe. They exist in

44

Switzerland in the Jura mountain range as well as in the Calcareous Alps and are of Callovian (Upper Dogger) age. The ore horizon has a varying thickness of 2 ·0-7 · 5 m. The bulk of the iron ( 80 % ) is contained in ferruginous ooliths, and the cement is of a marly nature. The ooliths/cement ratio is generally 1: 1.

The average chemical composition (%)is 30 Fe, 0·3 Mn, 15 Si02' 6·5 Al₂0_3, 15 CaO, 1MgO,0·3 P and 0·2 S. Underground reserves with an iron content of 28%

and greater are of approximately 30 OOO OOO tonne.

Molasse basin

The Tertiary sedimentary basin, which consists mainly of sandstones, shales and conglomerates, was formed by the erosion of Alpine rocks and their subsequent sedimentation under marine, lacustrine and fluvio-terrestrial conditions during and mainly after the main phase of the Alpine orogeny.

Placer gold

Allondon, Geneva ^{7 3 (} 1) Small and uneconomic gold placers have been described in the Allondon river gravels near Geneva. The presence of gold in this region is due to the concentration of very small gold particles contained in moraine material composed of gold-bearing Alpine rocks.

Napf, Luzern57 •90 (8) In the Napf region a gold- bearing conglomerate of Miocene age was formed by erosion of Alpine formations situated to the southwest.

Small secondary gold-bearing placers exist in the gravels of the streams and rivers that intersect the conglomeratic formations. These placers have an average gold content of 0·45 g/tonne.

Past production for the Canton Luzern has been estimated from historical records at 31 ·4 kg gold ( 1523-1800). Larger quantities were produced in the nearby cantons of Aargau and Bern. Figures on reserves in river gravels are not available, but they are believed to be small and uneconomic.

Calcareous Alps

Autochthonous rocks of Upper Palaeozoic and pre- dominantly Mesozoic age were strongly deformed during the Alpine orogeny and emplaced in their present form of classic overthrusts (Helvetic, Ultra- Helvetic and Prealpes nappes). Sediments encoun- tered in the Helvetic overthrusts have a certain similarity to those which exist in the Jura.

Copper*

Prealpes⁶⁵ (2) Interesting copper mineralization of 'red bed' type was recently discovered in a pelagic series of Palaeocene age (couches rouges) in the Prealpes Medianes nappe in the Prealpes Romandes (Switzer-

• Pure copper ore deposits are not common in Switzerland. More frequently, copper-bearing minerals are associated with galena and sphalerite: hence, they are mentioned in conjunction with the lead- zinc deposits.

F. C. Jaffb land) and the Chablais (France). The copper minerals are sparsely disseminated in marls and can be followed along the same stratigraphic horizon for more than 60 km along the strike. In Fig. 1 only the copper showings near Leysin in the canton of Vaud are indicated. The most frequent mineral assemblage comprises bornite, chalcocite, covellite, chalcopyrite and barite. A less frequent association is formed of native copper, cuprite and barite. Minute malachite specks are often visible on weathered surfaces. The genesis of this mineralization is comparable with that of the White Pine, Michigan, copper deposit. The copper mineralization appears to be of no economic significance, but further detailed investigations are warranted.

Murtschenalp, Glarus4 (18) Here concordant small mineralized lenses are confined to so-called 'red bed type' Permian breccias, sandstones and dolomite of the Helvetic Glarner nappe. This sequence is also known locally under the name 'sernifite' for the coarser varieties. Bornite and chalcopyrite are the main copper-bearing minerals, often accompanied by tetra- hedrite and small amounts of other sulphides. In one of the 18 showings pitchblende has been noted in association with copper-bearing minerals. The genesis of this deposit is somewhat controversial. Grade and reserve figures are not available.

Gold

Calanda, Gnsons5•6 • 15 (20) The Taminser crystalline series, composed of slightly metamorphosed spilites, keratophyres and their associated volcaniclastics, be- longs to the Permian root zone of the Helvetic nappes.

These veins occur in the shales of the Lower Dogger, overlying the Taminser crystalline basement. Native gold is found in calcite veins in association with pyrite and arsenopyrite. Faint traces of scheelite and fluorite have been reported from areas adjacent to the abandoned gold mines. The mineralization is consid- ered to be of late Alpine age. Grade and reserves are unknown, but are considered to be small.

Iron

Chamoson, Wallis21 ,iz.³o.s³ (5) The sedimentary oo- litic iron deposit near Charnoson lies in the Callovian (Upper Dogger) of the Helvetic Moreles nappe. The main oolitic layer horizon has a thickness of approxi- mately l m. Such a small iron deposit merits mention because it is the type locality of the mineral chamosite, (Fe+^2, Mg, Fe+_{3 ) 5}Al(Si₃Al)010(0H,O)g ²⁸-an iron chlorite well known in many parts of the world. Total reserves of iron ore (at 30% Fe) are approximately

1 OOO OOO tonne.

Erzegg, Bern22 •30•83• 1°2 ( 16) This deposit of sedi- mentary oolitic iron ore is similar to that of Chamoson.

Total reserves (with a content of 30% Fe) are estimated at approximately 1 200 000-2 OOO OOO tonne.

Manganese

Gonzen, St-Gal/2^5•83 (19) A manganiferous iron ore horizon, l ·5-3 m thick, occurs between underlying Se- quanian (Upper Jurassic) limestones locally called 'Unterer Quintenkalk' and overlying Kimmeridgian limestones ('Plattenkalk'). All these formations belong to the Malm (Upper Jurassic) of the Helvetic nappes.

A lower ore layer is entirely composed of hematite, with over it an upper layer also of hematite but with local concentrations of manganese ore in the form of elongated lenses. The transition from hematite to manganese ore takes place through a mixed zone of iron-manganese carbonate ore, which is followed by pure rhodochrosite and a core of small hausmannite lenses ( 1-20 m long and I m thick). The transition is very abrupt and the zones in which iron and manganese occur together never exceed 10 cm in thickness. The presence of an iron- and manganese- rich horizon in a calcareous sedimentary sequence is somewhat surprising. It is believed that the coexisting iron and manganese minerals may have been derived from the nearby Lower Penninic ophiolites and that their formation could be the result of precipitation from exhalative-sedimentary solutions.

Figures of average grade are not available, the Fe and Mn contents varying greatly within the deposit, which was not mined selectively. They are of the order of 34

%

%

Uranium•

Murtschenalp, Glan.4S4 ( 17) More than 50 concordant mineralized lenses are present in the so-called 'red bed type' Permian breccias, sandstones and dolomite of the Helvetic Glarner nappe to which they are confined.

Small concordant copper-bearing lenses are also known in the same region in the same geological environment. Pitchblende is associated with them only in one showing. The uranium-bearing radioactive zones are generally small. They occupy a surface area of 2-100 m² each.

The main uranium-bearing mineral is pitchblende, accompanied by small amounts of different sulphides.

The presence of pitchblende in gel-like structures, melnikovite-pyrite and bravoite is of interest since these minerals form at low temperatures. The genesis

• Uranium-bearing minerals as accessory constituents of pegmatites have been repeatedly reported,^{67 • 11} but the systematic search for uranium deposits was initiated oo1y in 1956 with funds provided by the Federal Government and to a lesser extent by Swiss and foreign private industry. The first radioactive anomalies were located io 1957, in the Fionnay-Ncndaz runnel (Valais) during the c-0ursc of the survey of the tunnels driven to harness the water of the Grande Dixence hydroelectric power scheme." Above this tunne.I an interesting ore zone was subsequently discovered in the !~rabies region. Radioactive anomalies were also dhcovered in other tunnels and surface channels, but proje.ctions to the surface could not be located or arc merely of secondary iotcrest. ^{23• 77} This in.itial stage of general uran.ium exploration, with a particular accent on the Alpine part of the country, has been completed and a general report with decaiJcd location maps is in preparation.

of these deposits is somewhat controversial. Grade and reserve figures are not available.

Hercynian massifs

The Mt Blanc-Aiguilles Rouges Massif in western Switzerland and the Aar-Gotthard Massif in the central and eastern part of the country consist of granite and granitoid rocks. These intrusive cores are surrounded by a suite of schists formed during the Hercynian and to some extent probably during the Caledonian orogenies. The granitic cores and their metamorphic envelopes were deformed again to some extent during the Alpine orogeny, in which they acted mainly as the stable 'basement' mass of the Alps, against and over which the rocks of the Alpine 'geosyncline' were thrust, generally from the south- east to the northwest.

Copper

Puntaiglas, Grisons^{35 •113} (36) Four km northwest of Trun a small orebody is present in the metamorphic formations of the Hercynian Gotthard Massif. It contains chalcopyrite in association with magnetite and pyrite.

Gold

Salanfe, Wallis54•85•103 (52) This deposit is in the metamorphic border zone of the Aiguilles Rouges Hercynian Massif. The bedrock consists of gneisses, micaschists and granite with intercalated marmorized limestones, partly transformed into skarns. The min- eralization consists of concordant, irregular, massive lenses and disseminations of arsenopyrite, lollingite and pyrite. Gold is rarely visible under the microscope, but it is always associated with arsenic-bearing minerals. The presence of scheelite associated with gold has been reported recently. Reserves amount to 10 OOO tonne at 35 g/tonne gold.

Iron

Mont Chemin, Wal/is4^{6 •83} (49) Several small magne- tite lenses occur approximately 4 km southeast of the town of Martigny. The host rock is a tightly folded sequence of sericitic gneisses and micaschists with intercalated marble lenses that belong to the metamor- phic envelope of the Hercynian Mont Blanc Massif.

The main ore mineral is slightly martitized magnetite associated with pyrite (rare) and safflorite (very rare).

Hornblende, biotite, garnet and stilpnomelane are the main gangue minerals. The metamorphic nature of the ore and the host rock bas completely obliterated all primary features, but it is assumed that the formation of the ore is probably related to Hercynian or pre- Hercynian granitic intrusions.

The average grade is 25-30% Fe. Proven reserves do not exceed 7000 tonne, but the presence of additional reserves in the lower levels of the deposit should not be completely ruled out.

46

Lead-zinc

Alp Nadels, Grisons³⁵ (34) Small and narrow galena- sphalerite veins occur in a gangue of quartz and carbonates 4 km south of Trun.

Bristenstock, Uri⁵² (37) Small sulphide lenses occur in the metamorphic envelope of the eastern Aar Massif. The main ore minerals are arsenopyrite, galena, sphalerite and chalcopyrite in a quartz- sericite-chlorite gangue. They have been compared with the classic Freiberg 'kiesige Bleiformationen'.

Geochemical orientation surveys with the applica- tion of different field methods were carried out in the vicinity of known orebodies. Satisfactory results were obtained by biogeochemical sampling of grasses ( Calamagrostis vil/osa (Chaix), Calamagrostis arundin- acea L., Astrantia minor L., Juncus trifidus L. and Astrantia minor L. ).

Trachsellauenen, Bern⁸⁷ (39) Several veins, weakly mineralized with galena and sphalerite in a barite gangue, occur in the pre-Triassic migmatitic base- ment of the western Hercynian Aar Massif. The veins, which are believed to be Hercynian or Alpine in age, have been affected by Alpine metamorphism.

A detailed geochemical survey in this region was successful inasmuch as anomalies in stream sediments and soils can be correlated quite satisfactorily with the known veins. In several instances their extension under the Quaternary cover in a very mountainous area could be located.

Goppenstein, Wal/£sa.49 • 109 ( 40) This deposit is in the pre-Hercynian metamorphic envelope of the Aar Massif. Granite porphyries, biotite-gneisses and am- phibolites are the prevailing rocks of the region. The ore zone is a concordant 'vein' in this metamorphic environment. It can be followed over a total length of 6 km with an average width of 0·50--2 m. The main ore minerals are sphalerite, galena, pyrite, pyrrhotite accompanied by smaller amounts of arsenopyrite, tetrahedrite and chalcopyrite. Quartz, calcite, barite and fluorite form the gangue. The deposit was mined intermittently until the end of the second world war.

Grades and remaining reserves are unknown.

Molybdenum

Baltschiedertal, W allis^{61 •89 (} 41) Molybdenite-bearing granite occurs north ofVisp in the Bietschhorn region.

This granite is a border facies of the Aar granite, the intrusive core of the Hercynian Aar Massif. Ten mineralized quartz veins have been reported in thin shear zones on a rather steep cliff composed of a granite body approximately 300 m long. The lower part of the vein system probably continues under a thick scree cover.

The entire mineralized zone-not just the single veins-has to be considered for the calculation of average grade and reserves and for possible mining operations. The deposit is at a high elevation (2700- 3000 m) in difficult terrain and partly hidden under a

F.

c.

heavy scree cover. Lichen growth on the rocks makes it difficult to observe the molybdenite in the field. It has been reported recently that molybdenite is associated with scheelite. Results of recent prospecting and drilling activities undertaken by a private mining company are not available.

Other occurrences ( Wa/lis)¹⁰⁰ Other small molybden- ite showings have been described from several local- ities in the western Aar granite.

Uranium

Trun, Grisons^{56 •113} (35) Radioactive anomalies are present l ·5 km south of Trun in mica-schists and gneisses of the Tavetscher Zwischenmassif, a small elongated body composed of metamorphic rocks, between the Hercynian Aar Massif to the north and the Hercynian Gotthard Massif to the south.

Uraninite is associated with pyrite, magnetite and hematite as well as small amounts of polymetallic sulphides (Co, Ni, Cu, Pb, Mo) and native gold.

Quartz, sericite and chlorite are the main gangue minerals. A hydrothermal genesis of Hercynian age with a subsequent Alpine remobilization has been

proposed.

Naters, Wa/lis⁵⁸ (42) A narrow zone with weak and apparently irregular uranium mineralization occurs in the southern metamorphic (gneissic) envelope of the Hercynian Aar Massif in the region of Brig. This zone is concordant with the gneisses in which it is situated.

Pitchblende occurs frequently as minute accessory granules (1-10 µm in diameter) in mica-rich gneisses and schists, augen gneisses, and on shear planes in intercalated granite-aplite layers. If coarser pitch- blende occurs in the same rocks, it is associated with pyrite, galena or molybdenite. The presence of pyrite is evidenced by a faintly gossanous zone on the road- cut near Naters. The mineralization is considered as pre-Alpine (Permian, Hercynian or older). A surface rock sample of approximately 5 tonne yielded an average uranium content of 0·26-0·3 kg U/tonne.

Le Chatelard and Les Marecottes, Wal/is⁵⁹ (51) Many radioactive anomalies exist in the Vallorcine biotite- granite, an elongate and thin body (15 km x 0·5-1·5 km) that stretches northeastwards from the French border to the Rhone Valley near Mieville. This granite is part of the Hercynian Aiguilles Rouges Massif. The mineralized zones are generally confined to shear zones, mylonites and fissures within the granite, but extensions into neighbouring rocks have also been observed. Pitchblende occurs in quartz or calcite gangue without accompanying ore minerals and, less frequently, with minor amounts of sphalerite and galena. It can be assumed that the uranium ore is of a Hercynian age but underwent a considerable remobili- zation during the Alpine orogeny.

Heavy vegetation and scree cover in rugged moun- tain terrain are hindering factors in a detailed exploration of this promising area, in which field work

is still in progress. Selected hand specimens yield grades of 0·2-20 kg U/tonne.

Penninic, Austroalpine and southern Alps This unit, in which the highest mountains of Switzer- land are found, consists of a complicated sequence of sedimentary, volcanic and mainly metamorphic rocks of Precambrian ( ?), Palaeozoic and Mesozoic age.

Their deformation, which occurred during the Alpine orogeny, gave rise to large and complicated over- thrusts, such as the St. Bernard-Monte Rosa nappe and the Dent Blanche nappe in the western and central part of the country and the numerous Penninic and Austroalpine nappes in the eastern part. Towar.ds the south these overthrusts are separated from the meta- morphic southern Alps by what is termed a 'root-zone' in classic Alpine terminology. A new interpretation of this root-zone in the light of plate tectonic concepts is currently emerging, but the original position of the nappes of the whole region before they were thrust into their present position remains conjectural.

Many fundamental and classic studies on Alpine metamorphism have been carried out in this part of the Alps as well as in the Hercynian massifs and the Calcareous Alps. Several interesting reviews on this subject and maps of metamorphic facies are available in the recent literature.3.33,^{6 6.68}

In detail, the polyphase metamorphism prevalent in these geological provinces is rather complicated.

After a more or less well-preserved pre-Alpine metamorphism the first Alpine phase of Upper Cretaceous age was characterized by low-tempera- ture-high-pressure conditions that gave rise to a limited development of blue-schist and eclogite facies rocks. Subsequently, the main phase, of Eocene- Oligocene age, produced rocks of typical Barrovian greenschist-amphibolite facies grade (gneisses, am- phibolites, calcareous and pelitic schists, locally called schistes lustres or Bundner Schiefer).

The chemical, mineralogical and structural trans- formations that most ore deposits underwent during Alpine and even earlier phases of metamorphism did not attract the attention of many geologists until recently.⁶⁹ There is little doubt that the careful evaluation of the impact of metamorphism on Alpine ore deposits will yield results of great interest for the establishment of modern and more accurate genetic models.

The Casanna schists, which form the crystalline core of the large St. Bernard nappe in Wallis, deserve particular mention, as several generally concordant polymetallic veins occur in them. Originally they were a sedimentary sequence with intercalated acid and basic lavas as well as primary and reworked tuffs. In their present epimetamorphic state they consist of amphibole-chlorite-sericite schists and gneisses, grad- ing into biotite gneisses, massive ophiolites in the greenschist facies, which are locally called 'prasinites',

quartz porphyries and thin graphitic layers. The Casanna schists are sheared and tightly folded. A Permo-Carboniferous age is generally put forward although the presence of older rocks cannot be ruled out completely.11 •88

Most of the polymetallic, strata-bound and meta- morphic ore deposits in the Casanna schists are part of the same metallogenic province. In the past they were thought to be of hydrothermal origin, owing to Swiss geologists' almost exclusive exposure to classic magmatic theories, but they may represent the result of a primary syngenetic deposition in a volcano- sedimentary environment with subsequent reconcen- tration during the Alpine orogeny. If this new working hypothesis is confirmed, they could well be compared with similar deposits in other metamorphic belts.

Although such a debate may seem of purely academic nature, it might have a significant bearing on future exploration programmes.

Copper

Alp Ursera, Grisons² 7 ( 30) Near the village of Andeer a small copper deposit occurs between gneisses and Triassic quartzites of the metamorphic core of the Penninic Suretta nappe. The principal minerals of the narrow ore zone are silver-bearing tetrahedrite, chal- copyrite and pyrite with accessory bornite and galena in a barite gangue.

Grimentz, Wallis4⁴ (45) Cu-Bi-Ag mineralization occurs northeast of the village of Grimentz in the Upper Anniviers valley. It is in sericite-chlorite schists that belong to the Casanna schists of the Penninic St.

Bernard nappe. The Casanna schists have been described in this region as a laminated and strongly folded sequence of sericite-chlorite schists and gneisses, with interbedded amphibolites and musco- vite-tourmaline-bearing pegmatitic rocks. Mineral- ized veins, generally concordant with the bedrock, occur mainly in sericite-chlorite schists. In the richest zone, in which the abandoned Baicolliou mine is situated, the average thickness of the ore does not exceed 10-15 cm, but extends for 350 m along the strike and 100 m downdip. The principal ore minerals are chalcopyrite, tetrahedrite, pyrite and bismuthinite.

They are embedded in a gangue composed of ankerite, quartz, barite and albite. The average ore grade has been assayed as l ·54

%

%

The Val d 'Annivier.s ores have been considered to be of typical hydrothermal origin, but their concordant position in a metamorphic sequence of volcano- sedimentary origin and their constant relationship to the same host rock along the strike raise genetic questions that warrant a modern structural and metallogenic appraisal of the whole district.

Gold

Astano, Tessin^39•55 (32) The Astanoregion, in the so- called 'Seengebirge', one of the main units of the

48

Southern Alps, is composed of rocks of sedimentary and volcanic origin with clear evidence of a polyphase metamorphism and a complicated history of major successive structural deformations. Tightly folded meso- to kata-metamorphic K-feldspar, two-mica and plagioclase gneisses were formed in the Astana region (Malcantone). Narrow barren and mineralized veins occur in this region. The veins have a well-defined zonal distribution.

In the veins of the central or Miglieglia zone, occupying a surface area of approximately 4 km^2, arsenopyrite, galena, sphalerite and chalcopyrite are the most abundant ore minerals. In addition, this zone is characterized by the presence of such antimony- bearing minerals as native antimony and antimonite, as well as of antimony sulphides in variable quantities ( tetrahedrite, jamesonite, gudmundite, bournonite, miargyrite, pyrargyrite, etc.). Native gold is frequent, at times in discrete macroscopic grains 1-2 mm in diameter. These grains cannot be seen with a hand lens on weathered or broken hand specimens, but they are clearly visible as soon as a specimen is sawn. Although grades of 226 g/tonne Au and 13·750 g/tonne Ag have been indicated, practically no mining activity has been reported from this area owing to the limited extension of the veins, at least on or near the surface. Quartz and ankerite are the most important gangue minerals.

Typical wallrock alteration consists of chloritization, sericitization and ankeritization.

The outer or Astana zone surrounds the central zone. It is completely devoid of antimony-bearing minerals. The typical mineral association of its veins consists of pyrite, arsenopyrite, sphalerite and galena.

Pyrrhotite, chalcopyrite and marcasite occur in minor amounts. Gold occurs principally when the four main sulphides are present, and is less abundant when only galena and sphalerite or arsenopyrite and pyrite are predominant. Native gold occurs in the form of inclusions in pyrite and arsenopyrite and also as discrete grains between other sulphide grains. The inclusions have a diameter of 5-15 µm, whereas the discrete grains tend to be somewhat larger (5 µm x 20 µm). Finally, gold also occurs in solid solution in arsenopyri te.

The main gangue mineral is quartz, but the presence of tourmaline is worthy of mention. Sericiti- zation, ankeritization and silicification are the typical wallrock alteration types in this zone. Past production figures of Costa mine are not available. It is thought that remaining reserves are of the order of 10 OOO tonne at an average grade of 20 g/tonne gold.

A further interesting and somewhat puzzling fea- ture of the Astana region is the presence of two rather well-delimited areas in which ore boulders of un- known origin occur in Quaternary formations over a surface of approximately 0·8 km² and 2·5 km^{2 •} Two distinct boulder types have been defined : the first consists of pyrite, magnetite, arsenopyrite, marcasite,

F.

c.

chalcopyrite and sphalerite with minor amounts of galena and molybdenite in an ankerite-quartz gangue;

in the second only pyrite, sphalerite, galena and some cassiterite are present in a quanz gangue. It would certainly be interesting to establish the origin of these boulders, but the almost sub-tropical density of vegetation renders direct exploration methods diffi- cult. Hence, modern geochemistry and geophysics have to be applied.

Gondo, W allis4^{1.43 (} 43) This deposit is the only known occurrence on Swiss territory of the Italian Monte Rosa metallogenic gold province. More than 20 small gold- and silver-bearing veins cross the two- mica gneiss of the Lower Penninic Antigorio nappe.

The thickness of the quartz veins varies greatly, but at times reaches 30 cm. Pyrite is irregularly distributed in the quartz veins and appears to be the main gold- bearing mineral. Small native gold inclusions, excep- tionally up to 0· 1 mm in diameter, can occasionally be observed in pyrite crystals. Galena, probably silver- bearing, chalcocite and covellite have also been observed. A rare interesting silver mineral is schapba- chite (mixed crystals of matildite (AgBiS2 ) and galena in widely varying proportions).⁸⁴

The average grade of the veins is not well known, but has been tentatively estimated at 5·7 g/tonne from mining records that date from the end of the last century. The gold content of hand-picked specimens can vary between 1 and 84 g/tonne, and the silver content is between 20 and 520 g/tonne. A more accurate re-evaluation of the Gonda gold deposit, though certainly desirable, is made arduous by its location at an elevation of 1000--2000 m in a relatively inaccessible mountainous region.

Iron

Val Ferrera, Grisons^{40•82•83•101} (29) Small iron-man- ganese ore deposits occur in folded epimetamorphic Jurassic quartzites, dolomites and marbles of the Penninic Suretta and Schams nappes. These small orebodies, older than the Alpine movements, are concordant with the folded sediments. The main ore minerals are hematite and braunite in a quartz- sericite--calcite gangue. The iron ore is finely stratified, whereas the manganese ore is concentrated in small lenses and nodules. The ore deposits are considered to be of marine-sedimentary origin, syngenetic with the Triassic sediments. The average grade is not available and reserves are very small. In the same region small veins and lenses of siderite and hematite have also been described in Triassic rocks. They are considered to be genetically related to the nearby iron-manganese ores.

Lead-zinc

S-charl, Grisons^{27 •53} (22) South of the village of Scuol narrow concordant veins occur in dolomites of Anisian, Ladinian and Carnian (Triassic) age that belong to the Austroalpine Campo nappe. They consist

of galena and sphalerite, with accessory jamesonite, tetrahedrite and pyrite in a ftuorite-baryte-quartz gangue.

Silberberg, Bleiberg and BiirenbUhl, Grisons²⁷ (25- 27) Three small strata-bound deposits occur near Filisur in the Anisian and Ladinian (' Arlberg Dolo- mit') dolomites of the Penninic Sivretta nappe. The thickness of the mineralized zone is l ·5 m, but the main ore zone is only 0·70--0·80 m thick. The typical mineral association consists of sphalerite (and/or galena) with minor amounts of jamesonite and pyrite.

The name of Silberberg is somewhat misleading, no significant silver production ever having been reponed.

Alp Taspin, Grisons²⁷ (31) Near the village of Zillis small and narrow mineralized veins occur in gneiss of the Penninic Margna nappe. The thickness of the veins is 0·20--0·30 m (exceptionally, l m). Galena is accom- panied by accessory pyrite, tetrahedrite, sphalerite, chalcopyrite and bornite in a quartz-barite gangue.

St. Luc-Bella Tola, W allis⁹⁶ ( 46) In the lower Anniviers valley there are numerous small concordant veins in the Casanna schists of the Penninic St.

Bernard nappe. The usual mineral association com- prises galena, sphalerite, tetrahedrite, chalcopyrite and in some instances also bornite. The gangue is composed of quartz, less frequently of quartz and ankerite, and occasionally of baryte.

PrazJean, Wallis¹⁸ (47) Thebedrockofthemineral- ized zone is composed of sericite schists and gneisses of the Casanna schists of the Penninic St. Bernard nappe.

The thickness of the mineralized zone, which is generally concordant with the bedrock, is approxi- mately 20-35 cm. The most common mineral assem- blage is a mixture of galena and sphalerite with some tetrahedrite, jamesonite, pyrite, pyrrhotite and chal- copyrite in a quartz-ankerite gangue. Tourmaline inclusions have been noted in the quartz and sphalerite grains.

The silver content of the galena is very high. Some samples have yielded l ·5-2·0 kg/tonne silver in the lead and in one instance even 4 kg. Reserves are unknown, but are thought to be small.

Manganese

Oberhalbstein, Grisons37·1 14 ( 28) Manganese ore de- posits are associated in the region south of Bivio with the ophiolites of the Penninic Plana nappe. The manganese-bearing zones are confined to folded red radiolarian cherts. Braunite is the prevailing ore mineral. It may partially or completely replace the quartz test of radiolarian micro-organisms in the cherts. Late fissures contain small amounts of the fol- lowing secondary manganese minerals, which have been discovered and determined for the first time in this region: tinzenite31 ((Ca, Mn, Fe)Al₂BSi40 15(0H)), sursassite31 (Mn₅Al4Si50 21.3H20( ?)) and parsetten- site31 (Mn₅ +2Si₆0 13(0H)s( ^?)).

Approximately 7000 tonne at an average grade of 30-36% Mn has been mined, reserves being estimated at some 13 OOO tonne.

Nickel in ultrabasic rocks

Poschiavo, Grisons;⁷⁵ (24) Totalp, Grisons;⁷² (21) and Palagnedra, Tessin34• 76• 106 (33) Pentlandite, awar- uite and heazlewoodite are normal accessory nickel- bearing minerals in Alpine ultrabasic intrusions. They have been reported from the Malenco serpentinites near Poschiavo, the Totalp serpentinites near Davos and the Pinero peridotites in the Centovalli region (Locarno). In the latter intrusion, which belongs to the Ivrea zone, layered chromite concentrations have also been observed. Although the nickel content of these ultrabasic intrusions appears to be normal (0·2- 0·3% Ni), higher than average nickel concentrations (up to 1-2% Ni) in the Finero peridotite near the village of Palagnedra are presently being investigated, but results are not available.

Nickel-cobalt

Kaltenberg, Wal/is³⁸ (44) A narrow mineralized and generally concordant zone is present in a chlorite- sericite schist sequence. One layer of hornblende- epidote schist has been observed in this sequence, which is part of the Casanna schists of the Penninic St.

Bernard nappe.

The mineral assemblage is composed of a great variety of Ni-Co minerals, and particularly of smaltite, chloanthite, saffiorite, rammelsbergite, arsenopyrite, cobaltite, niccolite, maucherite and some magnetite and bismuth. The gangue is essentially composed of carbonates (ankerite, siderite and dolomite) and quartz. A grade of l·0-1·8% Co, 1-2 % Ni and 0·1-2(/0

Bi is indicated. Reserves are unknown, but are considered to be small.

Uranium

lserables, W allis⁴⁸ ( 48) A discontinuous uraniferous zone more than 5 km long is present in the Casanna schists of the Penninic St. Bernard nappe. This zone stretches from the Iserables region to the Col des Mines near Verbier. The main host rock is a chlorite- sericite-albite paragneiss. The main ore mineral is pitchblende, which is generally associated with pyrite and minor amounts of chalcopyrite and tetrahedrite.

It has been suggested that the uraniferous minerals were deposited within elastic sediments of Permian age, and subsequently underwent a considerable remobilization during the Alpine orogeoy. Prelimi- nary sampling results indicate a rather low average uranium grade of 0·3 kg/tonne. In acid leaching tests the soluble rate of uranium is of 71-93% by weight.

Reserves are unknown, and further exploration work in this region is planned.

50

Non-metallics Fluorspar

Les Trappistes, W allis60• 1 1 2 ( 50)

Several fluorite veins .exist in the Sembrancher region, among which the Trappistes vein is the best known and possibly the most important. The veins are concordant in laminated two-mica gneisses and quartz porphyries that belong to the metamorphic envelope of the northern termination of the Mont Blanc Hercyn- ian granite massif.

The Trappistes vein is composed of calcite, whitish fluorite, quartz and lenses of country rock, some silver-bearing galena, sphalerite and small amounts of pyrite and chalcopyrite. The fluorite vein is 1250 m long, 800 m deep and 0·5-1 ·5 m wide. It is lenticular and often ramified. It is believed that the vein is of Permo-Carboniferous age. A rather conservative esti- mate of reserves of 44 OOO tonne at an average grade of 14 % CaF ₂ has been given.

The fluorite veins in the Tete des Econduits area, in the nearby Col des Planches region, are currently under investigation by a private mining company. The results of this investigation are not available, but renewed fluorspar mining activity in this region should not be completely ruled out.¹¹²

Gypsum

Bex, Vaud;⁸¹ (4) Granges, Wallis;⁸¹ (6) Leissigen, Bern;⁸⁰ (7) Lii.ufelfingen, Basel Land;¹⁹ (11) Kienberg, Solothurn;⁷⁹ (12) Felsenau, Aargau⁷⁹ (14) and Ennet- moos, Unterwald7⁹ (15)

Gypsum occurs in considerable quantities in the Triassic evaporites in the Jura and the Calcareous Alps. It is currently exploited in seven localities, mainly for the production of cement additives and plaster. The annual production of 350 OOO tonne covers the total needs of the country. Reserves are considerable.

Nephrite

Scortaseo, Grisons²⁴ (23)

The interesting nephrite-talc deposit of Scortaseo is near the village of Poschiavo. It occurs in a 'Schuppen- zone' assigned partly to the Upper Penninic Margna nappe and partly to the reduced continuation of the Schams nappes. The deposit occurs as two lenses, 100 m long, 3-5 m wide and at least 30 m deep. One lens is embedded in dolomitic marbles and the other is at the contact of these rocks and muscovite-chlorite gneisses. The actual nephrite rocks consist principally of very pale green nephrite masses in bundles and tufts that exhibit a finely felted texture. Especially charac- teristic are aggregations of nephrite in lens-shaped grains (1-10 mm in diameter) surrounded by talc margins and a calcite cement. This fine amphibole felt is an almost pure (Fe- and Al-free) grammatite nephrite.

F.

c.

The nephrite-talc lenses are believed to have been formed through the metasomatism of dolomitic mar- bles by the introduction of silicic acid solutions. These solutions are genetically related to the nearby Malenco serpentine.

The annual production of the small operating mine reached 1500 tonne of nephrite-bearing rock. The material was used for the manufacture of different types of 'Swiss jade' jewellery, and particularly of necklaces. Talc-rich material was shipped to nearby Italian paper factories. Production ceased because of the danger of rockfalls.

Phosphates

Pizzo Corandoni, T essi·n ^{104 (} 38)

Two apatite-biotite schist layers are present in two- mica and garnet-bearing gneisses of the metamorphic envelope of the Gotthard Hercynian Massif. The width of the apatite schists varies between 0·3 and 7·9 m, but a width of 1-3·5 m has been used for tonnage calculations.

Quartz and other minerals in Alpine fissures67, ^71,98,99

For many centuries the Swiss Alps have been famous for the magnificent quartz crystals and various other minerals that can be admired in many private and public collections worldwide. In a broad sense Alpine fissures can be considered as ore deposits since the minerals extracted from them have, at times, proved to be of a certain commercial value. They continue to be actively traded, even though, as in the case of quartz, they are no longer used for the production of crystal glass or vases, as in the last century. Accurate production figures of crystal are not available, but, according to rather conservative estimates, they are of the order of value of several hundred thousand Swiss francs per year.

From a consideration of the above facts it becomes evident that the traditional interest in Alpine crystals has led to the special development of Swiss crystallog- raphy and mineralogy and this, in turn, has stimulated many young Swiss to devote themselves to the study and practice of earth sciences.

Apart from quartz, classic minerals in Alpine vugs are adularia, a transparent variety of orthoclase (the name originates from Pizzo Adula, Tessin), albite, hematite ('iron rose'), pink fluorite, titanite, epidote, actinolite, anatase, brookite, rutile and many others of interest.

Exploration for and exploitation of Alpine cavities are traditionally the privilege of prospectors who live in Alpine valleys, better known under their German name Strahlers. Tales and legends about the discovery and the secret location of famous · vugs are numerous and often romantic. Although 'Strahlers' continue to exercise their trade in line with ancestral methods,

often passed from father to son and remaining in the same families for centuries, less responsible groups, by the use of mechanized means, have recently changed exploitation methods dramatically. Reports of the utilization of helicopters, jackhammers and dynamite are unfortunately common. This somewhat ruthless search for crystals may rapidly deplete Alpine cavities if appropriate legislation in this field is not enacted and enforced rapidly.

Alpine quartz crystals have also been studied with positive results for their piezoelectric properties and applications, but low reserves of suitable raw materials preclude their use in the electronic industry.³⁶ It may be mentioned in this regard that the Swiss production and export of synthetic gemstones (rubies, sapphires, etc.) is well developed.

Salt

Rheinfelden, Aargau-Schweizerhalle, Basel Land⁴⁵ ( 10) This salt layer, which is part of a Triassic evaporite sequence, is intercalated in anhydrite of the so-called sulphate zone. It has been intersected by drilling to a depth of 150-400 m and varies in thickness from 29 to 59 m. The salt is exploited by solution mining in Rheinfelden. Annual production varies between 250 OOO and 300 OOO tonne. The brine is also used locally for curative purposes in the Rheinfelden spa.

Saltisalsoextractedbysolutionminingfromthesame layer near Zurzach, Aargau, 30 km east of Rheinfel- den. It is employed exclusively for industrial purposes, mainly for the production of soda, by the Schweizer- ische Soda Fabrik, a member of the Belgian Solvay group. Annual production is put at more than 100 OOO tonne. The production of the salt deposits immediate- ly south of the Rhine river (and that exploited near Bex, Wallis), meets Swiss domestic and industrial requirements.

Bex, Vaud7·¹⁰⁵ (3)

This salt is contained in an irregular brecciated layer ( breche salifere) within a Triassic evaporite sequence that consists mainly of anhydrites and gypsum. Owing to its strong tectonic deformation, the thickness of the entire sequence cannot be measured accurately, but it is est.imated to be of the order of 400-500 m.

Underground mining took place as early as the fourteenth century. At present salt is extracted by solution mining from underground workings through drill-holes. Annual production is of the order of 15 000-20 OOO tonne.

Conclusions and outlook

The purpose of this review is to emphasize the great variety of Swiss mineral deposits. Notwithstanding the wealth of available information, there is ample scope for further pure and applied research in this field.

Geochronological dating and detailed structural ana- lysis are required to solve the old controversy of Hercynian versus Alpine emplacement of many vein- type deposits. Ore microscopy studies should be complemented by microprobe trace mineral investiga- tions. Geochemical and geophysical exploration meth- ods, which have been tested in the past in some rare instances, should be applied more frequently and systematically.52 •54•62•63•87· 1°7 Detailed grade and tonnage figures are necessary, but in many instances they cannot be obtained without preliminary clearing and reopening of old workings.

Future investigations could be hindered by various adverse factors, such as the existence of a thick glacial and soil cover in many parts of the country, particular- ly below the timber line, rising concern for environ- ment and landscape protection in those parts of the country that rely heavily on the tourist industry and the traditional lack of domestic risk capital. These limiting factors are certainly compensated for by a renewed interest in scientific circles in a better understanding of metallogenic and economic prob- lems and by the growing concern in government and industry about the almost total reliance on imported mineral raw materials.

In this respect it may be worthwhile mentioning that from 1980 to 1984 the Swiss National Science Foundation sponsored for the first time a mineral exploration project. This project was carried out in the Hercynian and Penninic formations of the Canton of Wallis by the Universities of Fribourg, Geneva and Lausanne. Modern geochemical and geophysical ex- ploration methods applied to a mountainous alpine environment were utilized to establish an up-to-date metallogenetic model for the known ore deposits, and on a regional base, and to evaluate the potential of the area under study in regard to base metals, gold, scheelite, etc. A comprehensive final report on this project was submitted to the Swiss National Science Foundation in 1985.

Acknowledgement

The author wishes to thank Professor F. de Quervain, Past-President of the Swiss Geotechnical Commis- sion, for his critical reading of this manuscript and his pertinent comments on many Swiss ore deposits.

References

l Amsler A. Die alten Eisenindustrien des Fricktales, bei Erlinsbach und in benachbarten Gebieten des ostlichen Juras im Licht der Flurnamen. Beitr. Geol. Schweiz, geotech. Ser., kleinere Min. no. 6, 1937, 56 p.

2 Aubert D. and Badoux H. Carte geologique generale de la Suisse, 1: 200.000, feuille 1, Neuchii.tel (Berne: Kummerly &

Frey, 1956 ).

3 Ayrton S. N. and Ramsay J. G. Tectonic and metamor- phic events in the Alps. Schweiz. miner. petrogr. Mitt., 54, 1974, 609-39.