File:Chalcopyrite veinlet in sulfidic shale (Kupferschiefer Formation, Upper Permian; Rudna Copper Mine, Lubin, Poland) 3.jpg

English: Chalcopyrite veinlet in sulfidic shale from the Permian of Poland. (oblique cross-section view; ~10.8 centimeters across at its widest)

This is a sample from the famous Kupferschiefer of Poland. The name means "copper shale". It is a thin (less than 1 meter thick), black shale horizon in the Permian of many parts of northern Europe - for example, Germany, Poland, and parts of Britain. The horizon is estimated to be present at the surface or in the subsurface over an area of at least 20,000 square kilometers.

The dark color of the host rock (not visible here) is due to a high organic carbon content. The material bubbles slightly in acid - it is calcareous. Kupferschiefer samples are heavy for their size - they contain a relative abundance of finely disseminated sulfide minerals. Sometimes, sulfide veins, veinlets, and sulfide-rich laminations are present (the former is seen here). Reported minerals include chalcocite (Cu2S - copper sulfide), chalcopyrite (CuFeS2 - copper iron sulfide), bornite (Cu5FeS4 - copper iron sulfide), pyrite (FeS2 - iron sulfide), galena (PbS - lead sulfide), sphalerite (ZnS - zinc sulfide), tetrahedrite (Cu12Sb4S13 - copper antimony sulfide), and others. Minor amounts of precious metals, such as gold and platinum-group elements, are also known.

The copper content has made the Kupferschiefer a mining target in northern Europe since Medieval times. Surficial smelting of Kupferschiefer outcrops was done as far back as the Bronze Age.

The origin of the Kupferschiefer's mineralization has been explained by several hypotheses in the literature. Traditionally, this stratabound copper sulfide deposit was interpreted as having formed by metal sulfide precipitation on an ancient Permian seafloor in stagnant water with reducing conditions.

Subsequent investigations have demonstrated that metal-rich fluids have gone through the Kupferschiefer, plus some overlying and underlying rocks, and precipitated various sulfide minerals. Two pulses of sulfide mineralization have been identified: at around 149 Ma (Late Jurassic) and 53 Ma (Eocene). Suggested causative events for the mineralization are the breakup of Pangaea during the Mesozoic and the closure of the Tethys Sea during the early Tertiary (see Borg et al., 2012).

The sulfide veinlet facing the viewer is composed of chalcopyrite, a copper-bearing variety of "fool's gold". Chalcopyrite is copper iron sulfide, CuFeS2. It has a metallic luster, a deep yellowish-brassy color, a dark gray streak, a hardness of about 3.5 to 4, and no cleavage. Many specimens develop a multicolored iridescent tarnish.

Stratigraphy: Kupferschiefer Formation, lower Zechstein Series, Upper Permian

Locality: Rudna Copper Mine, north of the town of Lubin, southwestern Poland

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Mostly synthesized from: Guilbert & Park (1986) - The Geology of Ore Deposits. 985 pp.

Borg et al. (2012) - An overview of the European Kupferschiefer Deposits. Society of Economic Geologists Special Publication 16: 455-486.

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See info. at: translate.google.com/translate?hl=en&sl=de&u=http...

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Photo gallery of chalcopyrite:

www.mindat.org/gallery.php?min=955