Occurences of precious metals in the German Kupferschiefer
Sabine Walther
Abstract
The Kupferschiefer, a black shale horizon at the base of the Zechstein, Upper Permian, and its adjacent strata have been in the focus of scientific discourse since many years (e.g. Dette and Rentzsch 1964; Diedel 1986; Eisentraut 1939; Knitzschke 1965; Knitzschke 1961; Kulick et al. 1984; Rentzsch 1964; Rentzsch and Franzke 1997; Rentzsch et al. 1997; Rentzsch and Knitzschke 1968; Richter 1941; Wedepohl and Rentzsch 2006). Here the main attention is given to the copper mineralization in the Kupferschiefer sensu stricto. More recently also mineralization in the footwall sandstones and the hanging wall carbonates has come into focus of scientific research especially by polish workers (e.g. Blundell et al. 2003; Borg 1991; Jowett and Craig 1986; Kopp et al. 2008; Kucha 1990; Kucha and Pawlikowski 1986; Oszczepalski 1999; Piestrzynski 1997; Wodzicki and Piestrzynski 1994).
Several historical mining districts in Germany (Sangerhausen/ Mansfeld and the Richelsdorf district) as well as reported anomalies of copper (Spremberg/ Weisswasser and Spessart/Rhoen area) occur along the southern margin of the Kupferschiefer basin. Although these areas have been the subject of several investigations referring to the copper mineralisation only sparse work has been done on the content of precious metals (e.g. Hammer et al. 1988, Borg et al 2005). Thus the focus of this PhD-study is to show the distribution of gold and PGE within the Kupferschiefer and associated strata in the German Kupferschiefer mining districts.
An initial investigation on the content of Au and PGE in the German part of the Kupferschiefer has been carried out by Borg et al. (2005) where within two local occurrences elevated amounts of Au and PGE have been found. Here the elevated precious metal values occurred between the copper zone and the zone of secondary oxidation, the Rote Fäule (Borg et al. 2005).
Within the current study several drill cores from boreholes intersecting the Kupfeschiefer and its adjacent strata from the Sangerhausen and Richelsdorf mining district have been investigated on its content of Gold and PGE.
First results show that in the Sangerhausen as well as the Richelsdorf mining district drill core samples with elevated amounts of Gold could be found. The maximum gold value (e.g. borehole Ldo 6/62 in the Sangerhausen district with 1,2 ppm Au) occurs just below the highest copper content within the borehole and often in close association with the oxidized facies (Rote Fäule).
Therefore a spatial and most probably metallogenetic association of the copper and precious metal mineralisation as well as the late diagenetic to epigenetic oxidising event (Rote Fäule) can be identified in all investigated areas. The lateral distribution of precious-metal-bearing and barren areas within the copper mineralised districts is still under investigation but a structural and lithological (Basement) control appears likely.
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