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An Overview of the European Kupferschiefer Deposits *

By
Borg Gregor
Borg Gregor
1
Economic Geology and Petrology Research Unit, Institute for Geosciences and Geography, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, D-06120 Halle, Germany
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Adam PiestrzyŃski
Adam PiestrzyŃski
2
Economic Geology Centre, AGH-University of Science and Technology, Cracow, Poland
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Gerhard H. Bachmann
Gerhard H. Bachmann
1
Economic Geology and Petrology Research Unit, Institute for Geosciences and Geography, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, D-06120 Halle, Germany
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Wilhelm Püttmann
Wilhelm Püttmann
3
Institute of Atmospheric and Environmental Sciences, Goethe University, Frankfurt (Main), Germany
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Sabine Walther
Sabine Walther
1
Economic Geology and Petrology Research Unit, Institute for Geosciences and Geography, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, D-06120 Halle, Germany
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Marco Fiedler
Marco Fiedler
1
Economic Geology and Petrology Research Unit, Institute for Geosciences and Geography, Martin-Luther-University Halle-Wittenberg, Von-Seckendorff-Platz 3, D-06120 Halle, Germany
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Published:
January 01, 2012

Abstract

The Kupferschiefer of northern central Europe is not only one of the largest sediment-hosted accumulations of copper ores worldwide (largest 1% of deposits with >60 Mt contained Cu) but has also one of the longest continuously documented mining histories, starting from at least 1,199 A.D. in the Mansfeld district of Germany. Kupferschiefer ores are currently mined in Poland from several large underground mines with active near-mine exploration and possible downdip extensions at a planning stage. Kupferschiefer mines in the Mansfeld and Sangerhausen districts of Germany had been largely exhausted by 1990 but a new exploration campaign is currently targeting a major deep Kupferschiefer resource near Germany's eastern border with Poland.

The Cu-rich part of the Kupferschiefer mineralization is dominated by chalcocite, chalcopyrite, and bornite and is hosted by several rock types including footwall sandstone and conglomerate, black shale, carbonate rocks in the immediate hanging wall, and anhydrite even higher in the hanging wall. Orebodies can range in thickness from 0.3 m, contained largely within the black shale of the Kupferschiefer sensu stricto, up to more than 50 m, where sublevel stoping, backfilling, and pillar mining reflect the pervasive mineralization. The ore zone can occur at various stratigraphic levels from (1) as low as some 35 m below the Kupferschiefer sensu strict, to (2) within and immediately adjacent to the black shale unit, to (3) several tens of meters above the base of the Zechstein limestone. Economic mineralization also occurs locally where no black shale has been deposited at all, for example, above Weissliegend sand dunes at the basin margin of the Kupferschiefer Sea that were never covered by the black euxinic mud. Ore textures include disseminated ores, disseminated replacement of dia-genetic and framboidal pyrite, crosscutting and bedding parallel veinlets, impregnation and replacement ore of carbonate and anhydrite cements, replacement of fossil shells, and even replacement of detrital feldspar and feldspar in lithic clasts.

All copper deposits share a marked metal and ore mineral zonation pattern adjacent to a major secondary redox front, the so-called Rote Fäule. This three-dimensionally, roughly hemispherically zoned mineralization system is transgressive and locally even steeply crosscutting to stratigraphy. It grades from an Fe3+ zone (hematite), through a locally developed precious metal (Au, Pt, Pd) zone, an always redox-proximal Cu zone (chalcocite, bornite, chalcopyrite), a locally overlapping Pb and Zn zone, into a distal Fe2+ zone of preore, commonly framboidal or early diagenetic pyrite. The oxidized part of the zoned orebodies commonly originates from permeable zones such as fault structures or sand dunes, which might have acted as valves through the relatively impermeable Kupferschiefer.

In general, the Kupferschiefer mining districts occur exclusively within an arcuate belt that is situated above basement rocks of magmatic arc origin, the Mid-European Crystalline High, typically at the intersections with major NW-SE– and NNE-SSW–trending fault structures. Local and regional studies have shown that regional metal distribution, orebody geometry, and metal grades are largely structurally controlled, although divergent opinions were originally expressed as to the timing of metal introduction via these conduits. An absolute age of ca. 255 Ma is generally accepted as the sedimentation age for the “Kupferschiefer” black shale. However, recent paleomagnetic age dating of mineralization at Sangerhausen has revealed late epigenetic mineralization ages of 149 and/or 53 Ma. The results argue for a new metallogenic model, which involves two major epigenetic pulses of metal introduction to the Kupferschiefer ores as impregnations, replacements, and subsequent veins and breccias.

A holistic understanding of the Central European Basin, which hosts the Kupferschiefer ores in its lower part of the stratigraphy, from the basin's origin in the Late Carboniferous to the Tertiary, and particularly the various related extensional and compressive tectonic events helps to put the individual stages of Kupferschiefer mineralization into a European plate tectonic perspective. The time span from Late Jurassic to Mid-Cretaceous was a period of major crustal rearrangement with the break-up of Pangea and the potential for the remobilization of major pulses of metalliferous brines. Both the main quantity of the Kupferschiefer ores and the giant Mississippi Valley-type (MVT) Pb-Zn ores of Upper Silesia appear to have formed at this stage. The younger, Tertiary, mineralizing event is also noted in both base metal provinces and was probably, again, related to crustal movement that involved metalliferous fluid flow. Additionally, this period was accompanied by magmatic pulses in the wider area of the Kupferschiefer metalliferous belt. Locally, late vein-type Co-Ni-rich mineralization, upgrading preexisting impregnation and replacement ores, gives evidence for this latest hydrothermal event, for example, in the German mining districts of Spessart/Rhön and Richelsdorf.

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Contents

Special Publications of the Society of Economic Geologists

Geology and Genesis of Major Copper Deposits and Districts of the World: A Tribute to Richard H. Sillitoe

Jeffrey W. Hedenquist
Jeffrey W. Hedenquist
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Michael Harris
Michael Harris
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Francisco Camus
Francisco Camus
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Society of Economic Geologists
Volume
16
ISBN electronic:
9781629490410
Publication date:
January 01, 2012

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