Copper slate

from Wikipedia, the free encyclopedia
Ground copper slate handpiece from the Mansfeld district with an "ore ruler" made of presumably chalcopyrite (copper pebbles)
Expansion of the Zechstein Basin approx. 255 million years ago (outlined in red) compared to the current geography of Central Europe

The copper shale is in Central Europe, especially in the underground rock layer widespread Upper Permian age, by calcareous, organic matter and finely divided pyrite dark colored, finely stratified marine shales is marked. Copper shale owes its name to the fact that it is locally highly enriched with sulphidic copper , zinc and lead ore minerals and, bound to these, a large number of other metals (including silver ).

Despite its name, the rock of copper slate is not slate in the petrographic sense, since its “foliation” was not created by the pressure of mountain formation , such as. B. that of the Thuringian roof slate. Instead, the schisty cleavage of the material is simply due to the original stratification and the compaction of the clay sediment due to the pressure of the younger sediment layers.

stratigraphy

The copper shale was deposited about 258 million years ago during the Wuchiaping stage of the Upper Permian ( Lopingian ), the last section of the ancient earth ( Paleozoic ). After a long mainland time, it marks the beginning of a period of marine cover in what is now Central Europe. This period is geologically documented in the form of the Zechstein series. The copper slate is officially the lowest and oldest deposit of the Werra formation , which in turn is the lowest and oldest formation of the Zechstein. It is one of the most distinctive geological guiding horizons in Germany and Europe.

Spread and facies

Zechstein transgression in the south edge region of the Zechsteinbeckens: carbonates (Mutterflöz, Zechstein limestone), dark colored and here strongly C org -containing including Kupferschiefer (weathered brownish), store discordant on steeply inclined graywackes and shales of the lower carbon (opencast mine Kamsdorf at room field, Thuringia ).

The sea in which the sediments of the Zechstein series were deposited is known as the Zechstein Sea . The basin in which this sea spread is called the Zechstein basin . It stretched from eastern Scotland and north-east England via the Netherlands and Denmark, Germany and Poland to Lithuania. The sea ingress, the so-called Zechstein Transgression , occurred from the north through a rift valley that sank between Norway and northeast Greenland (at the time immediately adjacent because the North Atlantic was only formed more than 150 million years later). Copper slate and its stratigraphic equivalents (e.g. the English Marl Slate ) are distributed over almost the entire Zechstein basin. You are either on the Variscides - molasses the Upper Carboniferous and Lower and Mittelperms ( Permian ) or directly onto the folded rocks of the Variscan mountain hull. In the latter case, one speaks of the Zechstein discordance .

The deposits of the Zechstein, and with them those of the copper slate, are not formed in the same way in the entire basin. A basin facies (also known as normal facies , represents a basin area with relatively high sea depth), a marginal facies (medium sea depth) and a threshold facies (relatively shallow sea depth or no sea cover) are distinguished.

In the basin facies , which in terms of area takes up the largest proportion of the Zechstein basin , the copper slate is typically a finely layered (laminated) black clay stone with carbonate proportions of 10–40%, an organic carbon (C org ) content of 0.5–13% and formed with thicknesses between a few centimeters and a few decimeters. The fine stratification represents an alternating layering of dark, C org -rich layers and lighter layers rich in carbonate. The depth of the sea in which the basin facies of the copper shale was deposited was probably more than 200 meters.

In the peripheral facies , the copper shale reaches greater thicknesses and carbonate contents (e.g. 2 meters or 70% in the Lower Rhine Basin). The carbonate-rich light layers of the lamination can in sections be thicker than the C org -rich dark layers, which gives the rock a generally lighter appearance. In addition, up to a few centimeters thick, light gray, clay-silty sediments can be switched on, which are interpreted as distal tempestites (storm deposits). Due to its lighter appearance and the higher carbonate content, the copper slate of the peripheral facies is also informally referred to as "copper marl" .

The threshold facies are limited to those basin regions that did not experience Rotliegend deposits before the Zechstein Sea collapsed. There, due to the alternation of steeply positioned, differently weathering and erosion-resistant rock layers, a z. Partly strong paleo-relief with small-scale thresholds and hollows. The thicknesses of the copper slate fluctuate accordingly there: it is relatively high in the hollows, and it decreases towards the small sleepers. In some cases, the copper slate even wedges out completely on the small sill edges. It is not uncommon for the copper slate in the threshold facies to feature coarse-grained sediments that are centimeter-thick ( iridescent limestones , sandstones, conglomerates), which go back to landslides or represent proximal tempestites.

Emergence

The typical copper slate of the basin facies was created by the sinking of clay particles into a sediment and the subsequent solidification of the sediment. Its characteristic black color is due to the relatively high proportion of C org and finely divided pyrite (pebbles, FeS 2 ). The proportion of C org and pyrite is high because it was deposited below the so-called redox thermocline, i.e. H. the sea water was stratified, with an oxygen-rich layer near the sea surface and an oxygen-free ( anoxic , euxinic ) layer underneath, and the redox thermocline formed the interface between the two bodies of water. In the anoxic deep water, organic material that reached the sea floor together with the clay particles was decomposed by anaerobic microorganisms by means of desulfurization ( reduction of sulfate to hydrogen sulfide , H 2 S). On the one hand, this retained a lot of C org , and on the other hand, the deep water was enriched with H 2 S, which led to the precipitation of pyrite. The incomplete conversion of the organic matter in and on the seabed during the deposition time of the copper slate is an important reason for the good preservation of the macrofossils it contains (most of the C org in the copper slate, however, comes from dead algae). The reducing milieu is also responsible for the discoloration of Rotliegend sediments, which are directly beneath the copper slate ( "gray areas" ).

The stratification of the sea water or the formation of an oxygen-free zone in free water is directly related to the Zechstein transgression. The deposition of copper shale occurs during the period in which the sea level in the Zechstein basin rose the fastest ( maximum flooding ). A rapidly rising sea level means rapid landward penetration of the sea and thus the rapid flooding of extensive areas of the mainland with nutrient-rich soils. In this way, large amounts of nutrients found their way into the sea water in a short time, which led to an explosive multiplication of algae. After the algae died and sank to the sea floor, the oxygen present there was used up relatively quickly due to the decomposition of the organic material by aerobic microorganisms. The redox thermocline, which normally lies in the sediment, rose into the body of water and anoxic or euxinic conditions arose in the deep water, which in the long term ensured a further enrichment of organic matter. In addition, the entry of sediment particles into a sea is generally low during a transgression. This, too, favored the accumulation of C org and pyrite on the seabed and thus the formation of a black clay stone at the base of the Zechstein sequence. Only with the slowing down of the transgression and a corresponding reduction in the nutrient input could the deep water be enriched with oxygen again and the black tone sedimentation, the duration of which is estimated at 20,000 to 60,000 years, ended.

The carbonate mother seam (also called Grenzdolomite, Grenzkalk or Productus limestone), which underlies the copper shale in some places in the threshold facies, was probably deposited at the same time as the copper shale but above the redox thermocline. Since the redox thermocline also rose with the sea level, areas of the sea floor that previously lay above the thermocline were flooded by Euxinian deep water and black clay was deposited on the mother seam (→  Walther Facies rule ).

Mineralization and origin of the metals

Ground copper slate handpiece from the Mansfeld district with an “ore ruler” made from Bornite (colored copper gravel). Thickness of the ore ruler: approx. 1 mm.

The predominant part of the copper slate deposits is comparable in terms of metal content to other black clay stones. Higher, at least historically mineable, metal contents occur only locally, which are epigenetic, i.e. H. by subsequent enrichment, and not already during the deposit. Copper ore minerals give their name to copper shale, but they do not always make up the main part of the mineralization. The ores can be finely distributed in the rock ("ore food") or as thin strips (so-called "ore rulers") or bean-shaped inclusions (so-called "hieken").

There are two types of minable mineralization:

  • “Red rot” : This is characterized by an average metal content of around 3%. It occurs only in the edge areas of the former Rotliegend basin and shows a zoning which, simplified, comprises three successive socializations. In the core, the actual red rot, an oxidation zone depleted in metals with hematite, various iron oxide hydrates and gypsum / anhydrite. Beyond the oxidation front there is a copper association with chalcosine (copper luster), digenite (α-copper luster), covelline (copper indigo) and bornite (colored copper gravel) as typical mineral associations. This is followed by a lead-zinc association with galena (galena) and sphalerite (zinc blende). As a rule, the mineralization also extends into the rock units immediately below and above the uppermost Rotliegend (so-called sand ore ) and the Werra carbonate. The formation of these sulphidic mineralizations is generally seen in connection with the mobilization of metals in the underlying Rotliegend sediments and volcanics or the Variscan basement by ascending, oxidizing salt solutions. If the solutions enriched with metals in the form of metal-chloride complexes reached the chemically reducing copper shale level, the metal ions combined with the sulphide sulfur in the sediment and precipitated as ore minerals. In the areas where the oxidizing solutions penetrated the copper shale level, the pyrite, which was finely distributed in the sediment, was transformed into hematite, iron oxide hydrates and gypsum, i.e. H. to the actual red rot, oxidized. The temperature of the solutions involved in the formation of the red rot deposits is estimated at around 120 ° C. Temporally, this mineralization probably falls into the Triassic . The mineralization of the red rot type is characteristic of the deposits in copper shale and the like. a. the Lausitz and Lower Silesia . In Lower Silesia the copper content of the ore reaches up to 15%.
  • "Back" : These are hydrothermal passages that are linked to disturbances. Their emergence goes back to the tectonics in connection with the long-range effects of the formation of the Alps and falls into the late Cretaceous and the Tertiary . A distinction is made between cobalt - nickel - arsenic - barium association (so-called cobalt backs ) with predominantly skutterudite , in the Mansfeld district more nickel - linse , as well as safflorite and millerite as typical ore minerals and a copper-silver-arsenic association with tennantite , enargite , lollingite and arsenopyrite as typical ore minerals. The average metal content is around 0.7%.

In addition to the above-mentioned metals and semi-metals copper, lead, zinc, cobalt, nickel, arsenic and barium containing ores of Kupferschiefer partially considerable amounts of other metals in the crystal lattice of the ore minerals diadoch are installed, d. This means that their atoms take up a small part of the position of the similarly sized atoms normally located there, without this affecting the properties of the corresponding mineral. These are vanadium , molybdenum , uranium , silver , antimony , bismuth , selenium , as well as cadmium , thallium , gold and platinum metals . In Lower Silesia the silver content of the ores is up to 80 g / t. The gold content of the sand ore is still 2 g / t.

use

Building material

Bus station on Klosterplatz in Eisleben (2010) with cobblestones made of copper slate slag

Poorly mineralized copper shale, which was not suitable for smelting, was previously only used for makeshift or temporary structures (e.g. walls) or as road gravel. Because of its rather poor cleavage properties and its low resistance to weathering, it is not suitable for roof coverings or facade cladding. On the other hand , the blue-gray, glassy paving stones cast from the slag from copper slate smelting are known and widely used as an excellent building material . They shape the streetscape in the Mansfeld region, but can be found all over Europe and in the 20th century were a not insignificant economic factor of Mansfeld AG and the former Mansfeld combine. In addition to the paving stones, so-called winding slag (about 40 × 40 × 60 cm) was produced and used for building buildings. Due to the apparently relatively high level of radioactive radiation from the slags, they were no longer allowed to be used to build living spaces from the 1970s onwards.

The Zechstein limestone (Werra carbonate) on top of the copper slate was often used in the past for building houses. Today it is fetched from the mining dumps or mined in quarries and processed into gravel for road construction.

Ores

Traces of copper slate mining in the Mansfeld region : the dump of the Ernst-Thälmann shaft near Siersleben .
Copper slate mining in the Mansfeld district in the 1950s

For a long time the ore deposits of copper slate were economically more important, some of which were already being exploited from the Middle Ages on the edges of the low mountain ranges, where copper slate spreads out and could easily be mined. With the development of industrial mining it became possible to follow the copper slate into ever greater depths, until it was finally penetrated in places over 1000 meters depth.

The most important copper slate districts were located

Copper shale is currently only mined in Lower Silesia (Poland). With an estimated 680 billion tons of raw ore with an average copper content of 2%, it is one of the largest copper deposits in the world.

The mining of copper slate for metal extraction has been discontinued in Germany since 1990 because it was no longer economical. In fact, he was no longer makes economic sense since about the 1930s, but was out of self-sufficiency aspirations out state- subsidized operated. Compared to other copper ore deposits, the ores have a relatively high copper content (2–3%, in the Richelsdorf district only approx. 1–1.5%), but it is due to underground mining and the relatively small thickness of the deposits (rare more than 1 meter) relatively costly to dismantle.

In the wake of rising world market prices, KSL Kupferschiefer Lausitz GmbH was founded in 2007 as a subsidiary of the international mining company Minera , which sank the first exploratory well near Spremberg in 2009 and thus raised hopes that copper slate mining could revive in Germany. The thickness of the mineralization of the so-called Spremberg-Graustein-Loop deposit is up to 8 meters and the copper reserves are estimated at around 1.5 million tons. By spring 2019, however, the project to build a mine east of Spremberg did not get beyond the phase of the spatial planning procedure . KSL is apparently moving the project forward at a speed just enough not to lose the search permit. Currently (as of spring 2019), the company is announcing the planned start of funding for 2030. The Polish company KGHM , which had carried out explorations in the Weißwasser area , officially ended its involvement in Lusatia in May 2016 due to unfulfilled expectations.

Fossils

Coelurosauravus jaekeli (live reconstruction), a gliding reptile that u. a. was found in the copper slate of Germany and the Marl Slate of England.
Fossil fish from the copper shale, probably all specimens of the by far most common species Palaeoniscum freilebeni . The white spots are probably plaster of paris from the oxidation of pyrite.
Palaeoniscum freilebeni from the Marl Slate , the British equivalent of copper slate, in the British Museum of Natural History in London.

Copper schist is known among paleontologists and collectors for its excellently preserved fossils . Many of the finds were made on the mine dumps.

All marine animals handed down in the black clay stone lived relatively close to the sea surface in oxygen-rich water and only sank to the sea floor after they died. Remains of fish (both bony fish and cartilaginous fish ) are very common , with around 90% of all specimens belonging to just one species, the "Eislebener Schieferfisch" or "Kupferschieferherring" Palaeoniscum freilebeni . The term “copper shale herring ” is more likely to be seen in connection with the size of the fish, because Palaeoniscum belongs to the so-called cartilage organoids and is therefore more closely related to sturgeon than to herrings. Invertebrates also lived in the Zechstein Sea at the time the copper slate was deposited. They are mainly found in the carbonate tempestite layers of the marginal and threshold facies, i. that is, they were brought there by storms from oxygen-rich shallow waters. Echinoderms , bog animals , cephalopods , snails , mussels and arm pods can be found there . A special form of conservation for invertebrates in copper slate is that of the stomach contents of fish. Remnants of the flaps of the armfoot Horridonia horrida (formerly: Productus horridus , the eponymous fossil of Productus lime) and remnants of the moss animal colony Acanthocladia anceps were found as stomach contents of the holocephalier Janassa bituminosa in the Richelsdorf copper slate and the remains of decipod crustaceans in the Lower Rhine region were found as the stomach of the same decipod shrimp .

In addition to marine animals, there are also remains of land creatures, especially reptiles and land plants, in the copper slate and in the English Marl Slate. They were probably washed into the sea by rivers. The Upper Permian reptile fauna of Central Europe is represented by the early diapsids Protorosaurus speneri and Coelurosauravus jaekeli . The latter is the oldest known vertebrate that was able to move from tree to tree by gliding, as it was u. a. today's giant gliders , flying squirrels or kites do. Parasaurus geinitzi , the first Pareiasaur ever to be scientifically described, is so far only known from the copper slate, not from the Marl Slate. The traditional flora consists of giant horsetail , cordaites , early coniferous plants , early ginkgo plants and seed ferns . Plants are also passed down in the form of stomach contents in some specimens of Protorosaurus and Parasaurus .

Remarks

  1. ↑ Paul (2006) publishes the Maximum Flooding published by Strohmenger et al. (1996, see individual evidence) had been postulated for the copper shale, in the deeper part of the Werra carbonate, which, however, is based on the different understanding of the term maximum flooding . Paul (2006) uses it in terms of the time of the highest sea level , Strohmenger et al. (1996) in the correct sequence stratigraphic sense of the period of the fastest rise in sea level .
  2. ↑ According to Litholex ( Geismar formation ), the Geismar copper laces correspond stratigraphically to the base clay ( stink slate ) of the Staßfurt formation and not to copper slate.

Individual evidence

  1. ↑ M. Menning, B. Schröder, E. Plein, T. Simon, J. Lepper, H.‐G. Röhling, C. Heunisch, K. Stapf, H. Lützner, K.‐C. Käding, J. Paul, M. Horn, H. Hagdorn, G. Beutler, E. Nitsch: Resolutions of the German Stratigraphic Commission 1991–2010 on Permian and Triassic of Central Europe. Journal of the German Society for Geosciences, Vol. 162, 2011, No. 1, pp. 1–18, DOI: 10.1127 / 1860-1804 / 2011 / 0162-0001
  2. ↑ Josef Paul: Weißliegend, Grauliegend and the Zechstein conglomerate: the Rotliegend / Zechstein border. In: German Stratigraphic Commission (ed .; coordination and editing: H. Lützner and G. Kowalczyk for the sub-commission Perm-Trias): Stratigraphie von Deutschland X. Rotliegend. Part I: Innervariscan Basin. Series of publications by the German Society for Geosciences, Vol. 61, 2012, pp. 707–714
  3. ↑ Christian Strohmenger, Ellen Voigt, Johannes Zimdars: Sequence stratigraphy and cyclic development of Basal Zechstein carbonate-evaporite deposits with emphasis on Zechstein 2 off-platform carbonates (Upper Permian, Northeast Germany). Sedimentary Geology. Vol. 102, 1996, No. 1-2, pp. 33-54, DOI: 10.1016 / 0037-0738 (95) 00058-5
  4. ↑ Frank Becker, Thilo Bechstädt: Sequence stratigraphy of a carbonate-evaporite succession (Zechstein 1, Hessian Basin, Germany). Sedimentology. Vol. 53, 2006, No. 5, pp. 1083-1120, DOI: 10.1111 / j.1365-3091.2006.00803.x
  5. ↑ a b Jürgen Kopp, Andreas Simon, Michael Göthel: The Spremberg-Graustein copper deposit in southern Brandenburg. Brandenburg geoscientific contributions. Vol. 13, 2006, No. 1/2, pp. 117–132, online (PDF; 10 MB)
  6. ↑ Trace of Stones Der Spiegel, 50/1991, pp. 59–61
  7. ↑ a b KSL Kupferschiefer Lausitz GmbH Official website of the company
  8. ^ Christian Taubert: Lausitzer copper plans on ice. lr-online.de (Lausitzer Rundschau), May 5, 2018
  9. ↑ Christian Taubert: The dream of Lausitz copper remains. lr-online.de (Lausitzer Rundschau), September 8, 2016
  10. ↑ Günther Schaumberg: New evidence of bryozoa and brachiopods as food of the Permian holocephalic Janassa bituminosa (S CHLOTHEIM ). Philippia. Treatises and reports from the Natural History Museum in the Ottoneum in Kassel. Vol. 4, 1979, No. 1, pp. 3–11, online (PDF; 2.2 MB)
  11. ↑ Friedrich Bachmayer, Erich Malzahn: The first evidence of a decapod cancer in the Lower Rhine copper schist. Annals of the Natural History Museum in Vienna, Series A. Vol. 85, pp. 99–106, online (PDF; 1.7 MB)
  12. ↑ Annalisa Gottman-Quesada, P. Martin Sander: A redescription of the early archosauromorph Protorosaurus speneri Meyer, 1832, and its phylogenetic relationships. Palaeontographica, Section A (Paleozoology, Stratigraphy), Vol. 287, 2009, No. 4-6, pp. 123-220
  13. ^ Günther Schaumberg, David M. Unwin, Silvio Brandt: New information on the Late Permian gliding reptile Coelurosauravus. Paleontological Journal. Vol. 81, 2007, No. 2, pp. 160-173, DOI: 10.1007 / BF02988390
  14. ↑ Linda A. Tsuji, Johannes Müller: A re-evaluation of Parasaurus geinitzi , the first named pareiasaur (Amniota, Parareptilia). Canadian Journal of Earth Sciences, Vol. 45, 2008, No. 10, pp. 1111-1121, DOI: 10.1139 / E08-060
  15. ↑ Wolfgang Munk, Hans-Peter Sues: Gut contents of Parasaurus (Pareiasauria) and Protorosaurus (Archosauromorpha) from the Kupferschiefer (Upper Permian) of Hessen, Germany. Paleontological Journal. Vol. 67, 1993, No. 1/2, pp. 169-176, DOI: 10.1007 / BF02985876

literature

  • Josef Paul: The copper slate: lithology, stratigraphy, facies and metallogenesis of a black slate. Journal of the German Society for Geosciences. Vol. 157, 2006, No. 1, pp. 57–76 ( abstract , preview PDF with summary in German)
  • DJ Vaughan, M. Sweeney, G. Friedrich, R. Riedel, C. Haranczyk: The Kupferschiefer: An Overview with an Appraisal of the Different Types of Mineralization. Economic Geology. Vol. 84, 1989, No. 5, pp. 1003-1027, DOI: 10.2113 / gsecongeo.84.5.1003
  • Hartmut Haubold, Günther Schaumberg: The fossils of the copper slate: flora and fauna at the beginning of the Zechstein, an ore deposit and its paleontology. Neue Brehm Bücherei, No. 333, A. Ziemsen, Wittenberg 1985 (2nd unchanged edition: Westarp, Hohenwarsleben 2006, ISBN 978-3-8943-2388-2 )

Web links