Krusne Hory ( Erzgebirge ) - Cinovec / Zinnwald, Krupka, Krasno
Sn W U Ag
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The tin and tungsten deposits of the Krusné Hory (Erzgebirge) metallogenic province are distributed over an area of 8000 sq. km in northern Bohemia (Czech Republic) and Saxony (eastern Germany) in central Europe.
The deposits of this region have produced over 300 000 tonnes of Sn, 300 000 tonnes of Pb, 130 000 tonnes of U, 900 000 tonnes of barite, 270 000 tonnes of WO3, 25 000 tonnes of Cu, 1 000 tonnes of Ag and 500 000 tonnes of As2O3.
See also the Bohemian Massif record which describes the setting and origin of the broader massif that includes the Erzgebirge / Krusné hory, and concentrates on its uranium mineralisation.
Mining in the region dates back to at least the 13th century. It was an important source of metals up to and during the second world war and of uranium in addition following that same war. However, after the unification of Germany, the low grades mined rendered most of the deposits un-economic.
The region is located on the north-western margin of the Bohemian Massif in the Saxothuringian zone of the European Variscides and is related to a partially concealed Late Palaeozoic multiphase granitic batholith intruding an amphibolite facies Neoproterozoic to Carboniferous age metamorphic complex.
The Neoproterozoic basement is composed of migmatitic gneisses and mica schists with abundant interlayers of metamorphosed marls, dolomites, calc-silicates, quartzites, leptynites, ultrabasic and granulitic rocks which were migmatised and granitised during the Variscan orogeny. The overlying Lower Palaeozoic comprises marine clastics (mainly pelitic) and granitic rocks, which are transgressively overlain by Lower Devonian clastics. Middle Devonian clastics and carbonates with interbedded sub-marine spilite-keratophyre volcanics are followed by the Carboniferous Culm facies. The Palaeozoic succession of the Bohemian Massif formed in a basin between the Mid-European plate and the Teplá-Barrandian microplate which opened as a rift in the older Precambrian continental crust. Following the post-Variscan consolidation, the Bohemian Massif formed an emergent continental mass surrounded by Mesozoic and Cenozoic sedimentary cover.
Magmatic rocks within the massif are related to the Archaean to Paleoproterozoic, the Late Neoproterozoic to Lower Palaeozoic Cadomian/Baikalian (700 to 500 Ma), the Lower Palaeozoic Caledonian (500 to 390 Ma) and the Late Palaeozoic Variscan (350 to 300 Ma) orogenies. The bulk of the acid plutonic rocks, particularly the extensive granitic batholiths are partly of Caledonian age, but are predominantly Variscan in the 300 to 270 Ma range.
The granitoid batholiths of the Erzgebirge district outcrop over areas of tens to hundreds of sq. km. Many are composite bodies built up of a succession of temporally, texturally and chemically distinct sub-intrusions.
The distribution of the phases of the Variscan granitoids show that development moved from the core to the margins of the periphery with time, with the youngest penetrating to shallow depths in the Carboniferous and Permian. The 'tin granites' tend to be the late, most acidic members of the evolution of Variscan granites which were intruded at high plutonic to sub-volcanic levels of 5.5 to 0.5 km below the surface. The granite plutons of the Erzgebirge are also characterised by related breccia pipes and sub-volcanic intrusives.
These granites have been divided (Seltmann & Stemprok 1995, Seltmann & Breiter, 1993) into the:
i). Older Granites of 320 to 310 Ma age which are generally characterised by Au, W-Mo and Pb-Zn mineralisation; and
ii). Younger Granites of 305 to 290 Ma age which are accompanied by quartz-cassiterite type Sn-W, F and Li mineralisation. Greisenisation within this group usually takes place in several phases, manifested by the development of silica, zinnwaldite, sericitisation and topaz, suggesting the existence of two greisenisation stages, namely -
a). L1 type from 305 to 300 Ma, which host Sn-W pervasive greisen deposits with predominantly rare alkali element associations, characterised by Cs-Rb-Li-Sn-W-Be, in highly specialised granite stocks, developed at upper metasomatic levels, commonly with associated Li micas of the zinnwaldite type;
b). L2 type from 300 to 290 Ma, Sn-W-muscovite joint/fracture controlled greisen deposits with no rare alkali accumulations, which are restricted to the apical sub-intrusions and a Sn-W-Cu-Pb association, developed at lower metasomatic levels commonly with associated phengite type muscovite.
Wolframite-quartz type greisen tungsten deposits (without Sn-Li-F) are restricted to the biotite granites, mostly in the western part of the district, where they are spatially separated from the cassiterite wall rocks greisens.
The majority of the mineralised intrusions were controlled by NW-SE trending fault zones, as were the mineralised structures. Two major environments contain high level mineralisation, namely:
i). subvolcanic intrusions of highly evolved tin granites with Sn-W-Mo, commonly associated with breccia pipes, occurring as greisen and skarn type mineralisation which are limited to a narrow contact zone in the apical sections of the batholith and generally have accompanying Cu - the location of skarn mineralisation being controlled by the availability of suitable carbonate wall rocks, and
ii). deep shear and fracture zones, largely oriented NW-SE, which are related to zones of cataclastic or mylonite brecciation, with U and /or F and are accompanied by Fe sulphides.
Zonation with depth along the Erzgebirge district are illustrated by the following:
- Sub-volcanic levels at depths of around 500 m below the palaeo-surface at the Altenberg tin field in the Eastern Erzgebirge;
- Tin-tungsten mineralisation at the Ehrenfriedersdorf tin (-tungsten) field in the Central Erzgebirge at palaeo-depths estimated at ~2000 m;
- Fluorite (-tin-polymetallic) mineralisation at the Schönbrunn field in the Western Erzgebirge characterised by an intrusive level of around 4000 m below the palaeo-surface.
Uranium mineralisation is less closely related to granitic contacts and has a stronger association with lineaments/fracture zones, being largely confined to the West Erzgebirge/Krusné Hory pluton and the Jáchymov-Gera lineament where most of the significant deposits are located. The most important deposits are within the envelope to the granite, rather than the intrusive itself. In the Czeck part of the massif, there is a zonation from uranium associated with graphite in the surrounding sedimentary hosts, pitchblende in chloritic altered granite and carbonate (dolomite, calcite) veins in the envelope to the granite.
Significant poly-metallic Pb-Zn-Ag mineralisation is predominantly concentrated in the 40 sq. km Freiberg-Brand and 20 sq. km Halsbrücke-Grobschirma districts, although deposits with lower sphalerite and galena contents occur within the western Krusné Hory pluton.
Fluorite-barite deposits are exploited in the Eastern and Central Erzgebirge/Krusné Hory where they either occur with Pb-Zn-Ag or are developed separately. Associations include i). fluorite-quartz and fluorite; ii). hematite-barite; and iii). fluorite-barite with galena.
A zoning is suggested by Seltmann & Stemprok (1995), comprising an i). east-west band of tin deposits across the centre of the province; ii). a zone of tungsten deposits assymetrically developed to the north-west; iii). uranium mineralisation on the eastern margin of the western pluton of the Erzgebirge/Krusné Hory batholith; iv). Fe skarns in the Central Erzgebirge; v). a Mo zone and an important Pb-Zn-Ag zone in the Eastern Erzgebirge.
Cínovec (Zinnwald) Sn-W-Li deposit - which is 11 km NNW of the town of Teplice in Bohemia, northern Czeck Republic.
This deposit straddles the Czeck-German border. Reserves on the Czeck side, at Cínovec, included 55 Mt @ 0.2% Sn, 0.045% W as cassiterite, wolframite and scheelite, from which 40 000 t of tin were extracted. In additon there were 550 Mt @ 0.18% Rb, 0.26% Li and 0.01% Cs delineated.
The country rock in the region comprises Proterozoic metamorphic complex muscovite-biotite orthogneisses and paragneisses and Lower Palaeozoic phyllite and epiamphibolites to the east and partly migmatised muscovite-biotite paragneiss to the west. These are overlain and cut by the Teplice Rhyolite, composed of extrusive and partially intrusive rhyolites, dacites and ignimbrites and their tuffs with arkosic and Mid-Carboniferous coal interbeds. A thick north-south trending dyke of syenogranite porphyry up to 2 km wide intrudes along or near the contact between the eastern gneisses and the Teplice Rhyolite, while smaller dykes and masses are found elsewhere within the Teplice Ryolite and basement rocks.
The ore deposit is contained within a cupola of the 330 to 295 Ma Cínovec-Zinnwald granite which intrudes the Teplice Rhyolite and is exposed as an oval shaped, north-south elongated 1.3 x 0.3 km outcrop. The western contact is steep, while to the east and south-east it dips at 10 to 30°. The exposed pluton is composed of lithium (zinnwaldite) albite granite (with no plagioclase), representing the upper skin, underlain at a depth of >730 m by medium grained porphyritic granite. In the cupola there are two textural varieties, an earlier porphyritic and later medium grained seriate granite enclosing relics of the porphyritic phase. These lithium granites contain 0.11% Lispan class="chemno">2span class="normalh">O, 4.62% Kspan class="chemno">2span class="normalh">O. They contain cassiterite, fluorite, topaz and tantalite as the main accessory minerals, as well as bastnaesite, uranpyrochlore and synchisite. The underlying granite averages 0.05% Lispan class="chemno">2span class="normalh">O, 5.34% Kspan class="chemno">2span class="normalh">O, with accessory zircon, tantalite, monazite, xenotime and rutile.
The contact between the lithium-albite granite and the Teplice Rhyolite is marked by irregular developments of a pegmatite-like (Stockscheider) rim. The deposit is composed of:
- Irregular metasomatic greisen and greisenised granite zones from several tens to 100 to 200 m thick following, and located near or at the upper contact of the cupola. It is variably composed of quartz and zinnwaldite with or without topaz, with irregular admixtures of sericite, fluorite and adularia-potash feldspar. Some are intensely hematised.
- Thin, flat greisen zones enclosing quartz veins up to 2 m thick with irregular wall-rock greisenisation within the broader greisen zone described in the previous point. Both the greisen and veins parallel the intrusive contact of the cupola, dipping shallowly to the north, south and east. The ore minerals are cassiterite, wolframite and scheelite. In the greisens, disseminated cassiterite predominates, while in the veins wolframite is roughly equal to, or more abundant than cassiterite.
The Krupka tin deposit is located approximately 5 km south-east of the Cínovec deposit in Bohemia, the Czeck Republic, and is possibly the oldest know tin occurrence in Bohemia. Placers were worked during the bronze age while primary ore was mined from the 13th century, reaching a peak in the 16th century. Wolframite was exploited from the Lukas Vein in World War I, and molybdenum from Knotl during World War II. The district geology is basically as described above for the Cínovec district. The acid volcanism of the Teplice Rhyolite was related to the development of a resurgent 25x45 km caldera (that included the Cínovec district also) and the intrusion of granite porphyry dykes around the margin of the caldera. This was followed by the intrusion of two granite types along NW-SE trending faults crossing the central section of the caldera, namely i). older biotite granite, comprising a multiphase intrusive of pinkish, porphyritic biotite granites with varied textures; and ii). younger albite-zinnwaldite granite which is directly related to all of the Sn-W, Rb-Li and Mo mineralisation of the field, and forms a 10 km, NW-SE trending ridge. It is strongly vertically zoned, with an outer skin of pegmatites (stockschieders) of quartz, orthoclase and Li-Fe micas. The upper most cupolas and stocks protruding from the main batholith consist of medium grained, white, non-porphyritic, quartz, albite, perthitic K feldspar, zinnwaldite granite, with accessory topaz, fluorite, cassiterite, tantalite, with rare bastnaesite, uran-pyrochlore and REE fluorides. These zinnwaldite granites are characterised by high Zr, Y, Nb, Th and HREE and low P. They are underlain by medium grained, porphyritic granite.
In the Krupka district, the albite-zinnwaldite granite occurs in two prominent, intensely mineralised cupolas, i). the Preiselberg cupola, which lies at the contact between the Teplice Rhyolite and the gneiss complex and is a conical body 265 m across at its widest and 180 m high, terminated in the upper sections by greisen caps with cassiterite, wolframite and sulphides; ii). the Knotl cupola which forms a WNW-ESE trending ridge which defines a steep-sided stock which splits into many apophyses. Greisenisation is weaker, but the pegmatite and marginal quartz veining is better developed than in the Preiselberg cupola. The stock is continuous with a tabular breccia which outcrops and is composed of gneiss cm to metre scale clasts in a matrix of fine grained granite, which has been silicified and greisenised. The quartz rim in places is a 4 to 5 m thick rim composed of giant zonal crystals, separated by mica coatings.
Both cupolas comprise a root zone of of medium grained albite-zinnwaldite granite, which passes upwards into sericite, kaolinite, hematite, feldspar altered granites and then to greisens with upper pegmatite rims and marginal quartz veins (often with Mo). Tin mineralisation occurs lenses, nests, disseminations and thin veinlets on both steep and flat fractures/joints.
There is a vertical zoning of greisens in the Preiselberg cupola, with very fine grained quartz and quartz-topaz with cassiterite, arsenopyrite and copper sulphides in the upper levels, while at deeper levels coarser quartz-mica greisens have an average of 0.3% Sn+W and flat quartz-zinnwaldite veins with greisen rims. Deeper still quartz-mica greisen alternates with sericitised granite is virtually barren.
Quartz veins with molybdenite represent the earliest mineralisation and were emplaced between the albite-zinnwaldite granite intrusion and the main stage of greisenisation. Quartz-cassiterite veins were introduced as an older, gently dipping set and a younger, steeper group. The Lukas vein is an example of a flat vein. It averages 25 cm in thickness, with a 10 cm greisen selvage, and dips at 25 to 30° SW with an average grade of 2.2% Sn. In the higher levels it comprises quartz with cassiterite (as bands up to several cm thick), wolframite, Cu and Bi sulphides, apatite, scheelite and fluorite. Down dip the cassiterite and sulphides decline while Li-mica and feldspars are enriched. The steep ore veins are generally located above the albite-zinnwaldite granite, particularly in the gneisses, while in the rhyolite and granites they bifurcate and wedge out rapidly. They comprise quartz with cassiterite, wolframite and sulphides, including arsenopyrite, chalcopyrite, sphalerite, galena, pyrite and bismuthinite, and have greisen selvages. They are generally perpendicular to the granite contact and have an erratic grade distribution.
The Krasno, Horní Slavkov and related tin deposits are located 10 to 20 km south-west of the town of Karlovy Vary and around 100 km south-west of the Cínovec deposit in Bohemia, the Czeck Republic. Placer tin was exploited in the district from at least the 12th century or earlier over intervals of 10 to 12 km, while hard rock mining began after 1355. The peak of mining was in the 16th century with 32 000 tonnes of tin metal having been produced between 1500 and 1620. Mining largely ceased during the 19th century, but was resumed in 1955 with an annual output of around 0.3 Mt at a grade of 0.15 to 0.25% Sn, 0.045% W from both underground and limited open pit operations. All mining ceased in 1991.
The geology of the district comprises a series of Proterozoic metamorphic rocks folded into a complex arch, intruded by Variscan post-orogenic granitoids of the Saxo-Thuringian zone. The granitoids are divided into an i). Older intrusive complex; ii). Younger intrusive complex which have been altered by fluid components; iii). transitional (or intermediate) granites.
Sn-W-Li mineralisation is associated with the Younger intrusive complex, particularly the Li-F rich members, while U and Ag-Bi-Co-Ni-As ores are related to late stage processes. The Li-F rich members occur as two small multiphase bodies at Krudum to the north and Lesný-Lysina to the south. The Krudum body covers an area of 50 sq. km with a core of porphyritic biotite granite surrounded by a marginal shell of two mica granite and Li-mica albite granite occurring as a NE-SW trending laccolith on the southern margin of the larger mass, separating it from the gneisses of the country rock. A NW-SE trending fault zone downthrew the eastern part of the mass by 300 to 400 m to preserve the upper parts of three cupolas, while the equivalent apical zones of those to the west were eroded.
Two of the three NE-SW aligned cupolas, the Hub and Schnöd stocks, are truncated, ellipsoidal cones, surrounded by gneiss. One of the earliest products of granitic magma was an albite-topaz microgranite cementing brecciated gneiss and as dykes found in the roof of the main granitic body. The outer margin of the granite is occupied by Li-F rich marginal pegmatite (Stockscheider) which contain coarse K feldspar, Li biotite and quartz crystals in the form of lenticular bodies on the flat dipping upper contacts of the underlying albite granite. The albite granite is leucocratic and mica poor and forms a hood to the main intrusive. The upper, apical protrusion of the intrusive, namely the stocks were greisenised over vertical intervals of 150 to 200 m with gradational downward contacts with poorly altered granites. The leucocratic albite granite is underlain by a feldspathite layer which is tens of cms to tens of metres in thickness and then by the main Li-mica fluorite granite of the Younger igneous complex.
Tin-tungsten mineralisation is closely associated with the Li-F granites and occurs as: i). Quartz veins rooted in the greisen zones of the cupolas and passing into the surrounding gneisses. These were historically worked over vertical intervals of 50 to 100 m over thicknesses of up to 50 cm and contained cassiterite, wolframite and minor Cu sulphides; and ii). Mineralised stocks, representing the great bulk of the ore exploited. The uppermost parts of the stocks are composed of leucocratic quartz-topaz greisen containing Sn-W-As-Cu (with a Sn:W ratio of 5:1), passing downwards into darker quartz-mica-topaz greisens with accessory cassiterite.
This record is largely summarised from Seltmann & Stemprok (1995), and Seltmann & Breiter, (1993).
The most recent source geological information used to prepare this summary was dated: 1995.
This description is a summary from published sources, the chief of which are listed below.
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Dolnicek Z, Rene M, Prochaska W and Kovar M, 2012 - Fluid evolution of the Hub Stock, Horní Slavkov–Krásno Sn–W ore district, Bohemian Massif, Czech Republic: in Mineralium Deposita v.47 pp. 821-833|
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