The Warka IG-1 borehole is located 50km south of Warsaw, near Warka village (Fig. 1). The borehole was drilled in 1972 by the Polish Geological Institute (Polish Geological Survey) during the geological study of central Poland. Preliminary research on the Zechstein cupriferous series was made in 90's. In the borehole the Kupferschiefer was reached at 2428 m depth, and the thickness of the shale was 30 cm wich is the average thickness of the Kupferschiefer in the Poland.
Sulfide minerals occur as finely disseminated grains (up to 2 mm in size) and in the form of thin (up to 3 mm) streaks of sulphides. The sulfide mineralization is dominated by marcasite and pyrite occurring mainly as aggregates of framboids and as single idiomorphic grains (Fig. 2). Pyrite with marcasite encrusts fragments of microfauna, mainly crushed clam shells, ostracod and foraminifera (Agathammina) (Fig. 2). Marcasite is a major component of the sulfide streaks, arranged parallel to the shale lamination. In addition, sphalerite, and galena crystals occur as large, irregular particles (commonly to 300 micrometers in diameter). Mutual intergrowths of these minerals and replacements of carbonate material and quartz and feldspar grains, by galena and sphalerite can be observed. In addition, sphalerite and galena cement brecciated and fractured grains of marcasite and pyrite (Fig. 2).
EDS (Energy Dispersive Spectrometry) and EPMA (Electron Probe Micro-Analyzer) analyses showed (Fig. 3) that the light carbonate laminae are composed predominantly of dolomite with a high content of iron and manganese (Fig. 4). Carbonates occasionally contain high values of lead and zinc (wt% Zn up to 1,5% and wt% Pb up to 0,8%). Due to the high content of dolomite, rocks can be classified as dolomitic-clay shale. There are no significant impurities in the iron and lead sulphides. It is notable that sphalerite has a high average content of cadmium 2,25 wt% (ranging up to 8 wt%) and averages about 0.8 wt% iron (up to 2 wt%). Small (up to 1 micrometers) cadmium sulfide inclusions occur within sphalerite crystals (mainly in the marginal zones of sphalerite grains).
The irregular lamination of the shale, the large thickness of carbonate laminae, the strongly disturbed structure of the laminae, and the presence of numerous skeletal grains indicate sedimentation on a shallow shelf (Oszczepalski 1989)(Fig. 5). Abundant admixture of fine-grained terrigenous material (quartz, feldspar, and accessory minerals typical of mafic rocks) derived from adjacent East European Craton. Sphalerite and galena replacing carbonates, quartz and feldspar, as well as crack fillings cracks in iron sulphides, should be interpreted as secondary mineralization postdating iron sulfides and superimposed on early-diagenetic pyrite-marcasite composites. The enrichment of dolomite with iron, manganese, lead and zinc can be attributed to the influence of infiltrating metal-bearing fluids during subsequent stages of progressive diagenesis. The strong predominance of iron sulphides over galena and sphalerite and the lack of copper sulfides indicate a significant distance from the feeder areas for the Lower Zechstein copper mineralization.
References:
Oszczepalski S., Rydzewski A., 1997 - Atlas metalogeniczny cechsztyńskiej serii miedzionośnej w Polsce. Państwowy Instytut Geologiczny - Wydawnictwo Kartograficzne Polskiej Agencji Ekologicznej SA. Warszawa
Oszczepalski S., 1989 - Kupferschiefer in southwestern Poland: sedimentary environments, metal zoning, and ore controls. Geol. Assoc. Canada Spec. Paper 36: 571-600.
Figure 2. Kupferschiefer mineralization. A - BSE (backscattered electrons) replacements of quartz by galena, B - BSE (backscattered electrons) galena cement brecciated and fractured grains of pyrite, C - (reflected light) pyrite encrusts fragments of microfauna, D - (reflected light) aggregates of framboids and single grains of marcasite.
Figure 3. The EPMA analysis, columns 1#,2#,3#,4#,5# - number of analysis, rows - elements analysed
Figure 4. The EDS dolomite analysis with high contain of Fe.
Figure 5. Kupferschiefer, organic-rich dolomitic-clay shale. Shallow shelf. - Warka IG-1 borehole. 1 - reflected light, crossed nicole, 2 - reflected light, one nicole.
