Stanisław Speczik

The possible role of organic matter in transport and accumulation of metals exemplified at the Permian Kupferschiefer formation

Abstract The Permian Kupferschiefer in the Central European Zechstein Basin has been deposited under anoxic sedimentary conditions. The shale contains on average about 5% of organic matter which is classified as kerogen Type II. In areas where an ore-grade mineralization of the Kupferschiefer is not observed (i.e. NW Germany), the organic matter follows solely a temperature-induced transformation process. Copper and silver enrichment in the Kupferschiefer is associated with the occurrence of Rote Faule. At those places where Rote Faule came in contact with or very close to the Kupferschiefer, secondary alteration reactions are detectable in the solvent-extracted organic matter as well as in the kerogen. This effect is pronounced in the Kupferschiefer of the Konrad mine investigated in the present study. The analysis of solvent extracts has been carried out using methods such as gas chromatography coupled to mass spectrometry (GC/MS). For the investigation of the kerogen pyrolysis experiments (“Rock-Eval”) have been undertaken. In a closely sampled Kupferschiefer profile from the Konrad mine (SW Poland), significant depletion of the organic matter and the hydrogen content of the organic matter is found in the bottom part of the section approaching the Rote Faule horizon. The precipitation of copper from ascending oxidizing solutions occurred primarily in the inner part of the Kupferschiefer section, where sufficient hydrogen for abiotic thermochemical sulphide production was still available. Thus, the organic matter acted as a reducing barrier mediating the metal accumulation from upwards migrating metal-bearing brines (ascending brine theory). The determination of the maturity parameters indicates, that the organic matter was mature when oxidation occurred.

The Kupferschiefer mineralization of Central Europe: New aspects and major areas of future research

Abstract A proposal is given for the composite, multi-stage and multi-source origin of the Kupferschiefer mineralization in Central Europe. The major factors controlling the occurrence of ore-grade mineralization were the availability of thermal energy related to Lower Permian rifting, and the fault-controlled evolution of Variscan depressions and paleohighs along the border of the Saxothuringian and the Rhenohercynian Belts. The processes leading to the formation of ore-grade mineralization inside the Kupferschiefer horizon of Central Europe were probably everywhere generally the same, with observed differences being related to the material of the source rocks, timing of base metal leaching, preconcentration and emplacement, and the local geological development. The organic material of the Kupferschiefer was a major agent for production of both biogenic and thermocatalytic sulphide sulphur. A critical review of available data makes it possible to list major interesting areas of future research. They include the problem of source rocks for the base metals of the Kupferschiefer (particularly for Pb and Zn occurrences), the relative roles of biogenic and thermocatalytic sulphide sulphur in base metal precipitation, the mechanism and the timing of base metal preconcentration, the time of base metal emplacement, and the precise role of the Lower Permian and mid-Triassic riftings.

A stable isotope and organic geochemical study of the relationship between the Anthracosia shale and Kupferschiefer mineralization (SE Poland)

Abstract There are at least two mineralized horizons that occur in association with the Rotliegendes, red-bed sediments of Central Europe. The first is the well-known Kupferschiefer at the top of the Rotliegendes, the second is the Upper Anthracosia shale of the North Sudetic Depression — in the middle part of the red-bed section. In the present study, Upper Anthracosia shale has been investigated by use of various geochemical methods and results have been compared with those obtained from previous studies of the Kupferschiefer. Both mineralized horozins show the same organic geochemical phenomena and isotope variations interpreted as a result of post-depositional migration of mineralizing fluids, originating from red-bed sediments. Both organic-rich horizons acted as reducing traps for migrating metals. Therefore, the processes that led to the base-metal emplacement in the ore-grade areas of the Kupferschiefer are shown to have an universal character, also with regards to the Upper Anthracosia shale. The patchy occurrence of Cu mineralization in the Anthracosia shale horizons is related to the fault-controlled movement of mineralized fluids. The Cu-dominated composition of mineralization is explained by the simplicity of the base-metal source, preferentially Rotliegendes formation waters of mostly meteoric origin. New data on the isotopic compositions of C in organic materials and of C and O in carbonates, combined with an organic geochemical study of a non-mineralized section through the Lower Anthracosia shale, provide information on the sedimentary environment and conditions during diagenesis. The changes during sedimentation of the Lower Anthracosia shale are related to subsidence (the thickness of water column), sedimentation rate, redox potential and paleoclimatic conditions. In the center of the profile from the Lower Anthracosia shale the amounts of calcite and organic carbon concomitantly increase, which can be explained by the development of anoxic bottom waters. Due to enhanced subsidence of the basin the water column might have temporarily increased, resulting in increased biomass production and better preservation of organic material. In the lower and the upper parts of the profile the biomass production was significantly lower due to increased rate of sedimentation and probably decreasing water column.

Distribution and characteristics of a Middle Ordovician oolitic ironstone in northeastern Kansas based on petrographic and petrophysical properties: a Laurasian ironstone case study

Abstract The margins of Gondwana are generally considered to be the major sites of oolitic ironstone production during the Ordovician, and appear to be linked with global eustatic sea-level rise. Occurrences of oolitic ironstones within the North American craton are less well documented, but provide important supplementary data. The low latitude of Laurasia contrasted with Gondwana allows useful comparisons of climatic and temporal patterns of Ordovician ironstone formation. Middle Ordovician ironstones occur in siliciclastic sequences in the American mid-continent and appear to become progressively younger as the epicontinental sea advanced from the southwest across a predominantly carbonate terrain. In northeastern Kansas, the regional distribution pattern of primary, syndiagenetic goethite iron oolites within the St. Peter Sandstone indicate deposition peripheral to a north-northeast-trending chain of islands underlain by predominantly granitic rocks, located along an ancestral Nemaha uplift. Detailed compositional mapping in the subsurface was made possible by the distinctive petrophysical properties of the goethite zone and the extensive regional control of wireline-logged exploration wells. Petrographic data from ironstone core- and drill-cuttings both validate log analysis and give insights on possible modes of genesis. We propose that eustatic changes in sea level were the primary factor governing the formation and observed distribution patterns of the oolite bed(s). The relationship of the observed occurrence patterns to major rift-related faults of the Central North American Rift system suggests that synsedimentary tectonism also influenced this process. The most likely source of iron appears to be by derivation from intensive, humid weathering of granite exposed extensively on the ancestral Nemaha uplift archipelago.

Fluid inclusion study of epigenetic veinlets from the Carboniferous rocks of the Fore-Sudetic Monocline (southwest Poland)

Abstract Thermobarogeochemical investigations have been conducted on abundant veinlets that cut Carboniferous rocks of the Fore-Sudetic Monocline. Temperatures of the veinlet formation have been found to be relatively high, ranging mainly from 150° to 300°C. The results suggest that the paleogeothermal field of the Fore-Sudetic Monocline was generally uplifted. The actually observed positive geothermal anomaly of southwestern Poland overlaps the paleogeothermal one and is caused by a deep thermal disturbance on the contact of lithosphere and the upper mantle. This disturbance, of Variscan age, still produces remnant heat.