Composition and fabric of the Kupferschiefer, Sangerhausen Basin, Germany and a comparison to the Kupferschiefer in the Lubin mining district, Poland.

摘要

The Kupferschiefer, or "copper shale," is a thin carbonaceous marly shale deposited during the Late Permian within the Zechstein Basin of central Europe. A classic example of a sediment hosted stratiform copper deposit, the Kupferschiefer is mineralized with Cu and other metals of economic interest such as Pb, Zn, and Ag. The unit is overlain by the Zechstein Limestone and underlain by the Weissliegend sandstone; it is most well known in Germany and Poland. Overall, the Kupferschiefer in the Sangerhausen Basin in Germany has been less studied than its counterpart in the Lubin mining district in Poland. Some previous studies compare the Kupferschiefer from the Lubin mining district, and more rarely the Sangerhausen Basin, to other stratiform copper deposits, but few compare data from both locations.;This study analyzes, compares, and contrasts geochemical, mineralogical, and petrologic data from five Sangerhausen Basin locations and four locations in the Lubin and Rudna mines of the Lubin mining district. A total of 101 samples were examined: 61 Sangerhausen samples (41 from above the Kupferschiefer-Weissliegend contact, and 20 from below the contact) and 41 Lubin mining district samples (28 from above the Kupferschiefer-Weissliegend contact, and 13 from below the contact). Of these, 62 (36 Sangerhausen and 26 Lubin mining district) were geochemically analyzed, and 65 samples were observed in thin section (35 Sangerhausen, 30 Lubin mining district).;The Sangerhausen Basin Kupferschiefer exhibits textural, geochemical, and mineralization characteristics broadly similar to those of the Lubin mining district Kupferschiefer, with a few distinct differences. Sulfide mineralization, in the form of disseminated spherules, blebs, aggregates, framboids, and bedding-parallel and -perpendicular veins, is observed in both locations on macro- and microscopic scales. The most abundant sulfide in mineralized samples from both locations is chalcocite, followed by chalcopyrite. Sulfide mineralization is commonly associated with the presence of quartz and carbonate veins in Lubin mining district samples, while mineralization is rarely associated with these veins in Sangerhausen Basin samples. Fluorescence from hydrocarbons is observed in association with sulfide mineralization in some samples, and is generally more common in samples from the Sangerhausen Basin than in those from the Lubin mining district. Both locations show similar geochemical trends with stratigraphic depth, as the units transition from Weissliegend to Kupferschiefer to Zechstein Limestone. The Sangerhausen Basin Kupferschiefer exhibits P 2O5 enrichment (averaging 0.26 wt.%) compared to Lubin mining district Kupferschiefer and average shale P2O5 values (averaging 0.13 wt.% and 0.16 wt.%, respectively). Copper concentrations are greater in samples from the Lubin mining district (∼14 wt.% max, most samples above ∼1 to 2 wt.%) compared to Sangerhausen samples (∼10 wt.% max, most samples below 0.5 wt.%). The lower ∼25 cm of the Kupferschiefer is enriched in ore metals (Cu, Ag, Pb, Zn, and U) in both locations, and in the Sangerhausen Basin, in middle rare earth elements (REEs) as well. This suggests that the reactions resulting from interaction between fluids migrating from the underlying Weissliegend and overlying Zechstein evaporates mostly occurred in the lower 20 cm of the Kupferschiefer. Assuming that the REEs were carried in the mineralizing fluids, the differences in REE patterns from Sangerhausen samples taken 7 and 8 cm above the basal contact of the Kupferschiefer suggest that even within a single basin the reactions resulting from fluid interaction did not occur at the same stratigraphic level at all locations.;The strata-form nature of the deposit suggests large scale bedding-parallel fluid flow. On a smaller scale, the orientation of sulfide, quartz, and carbonate veins and of elongated sulfide macro-blebs suggests that the local, small-scale flow direction is preferentially bedding-parallel as well, especially in the lower 20 to 30 cm of the Kupferschiefer where the matrix is primarily composed of alternating lenses of carbon- and clay-rich pods, and carbonate-rich pods. However, the presence of bedding-perpendicular sulfide blebs and carbonate and quartz veins illustrate that flow was not exclusively bedding-parallel. The Lubin mining district probably experienced at least two pulses of fluid flow, as illustrated by the presence of veins that exhibit alternating carbonate and sulfide precipitation; similar characteristics were not observed in the Sangerhausen Basin samples. The presence of both yellow and blue fluorescence of bitumen in Sangerhausen samples, however, suggests that there were at least two pulses of hydrocarbon migration. The generally well-sorted Lubin mining district Weissliegend was more permeable than the poorly-sorted Sangerhausen Basin Weissliegend.