Download the thesis as pdf (Dropbox link):                 Master thesis - Christian Lehmann

 
Left - Dolomitization (CL image). Middle - Upward migration of mineralizing fluids. Right - Dedolomitization.

Abstract of the thesis  "Cement stratigraphy of mineralized Zechstein carbonate rocks
                                   of the Cu-Ag deposit Spremberg-Graustein, Lusatia, Germany."

The Kupferschiefer-type sediment-hosted Cu-Ag deposit Spremberg-Graustein is located above the Mulkwitz anticline in the Niederlausitz (Eastern Germany). The deposit contains 1,5 Mt copper as well as notable amounts of silver, lead, zinc and other metals. In the present study two drill cores (CuSp131/09 and CuSp136/09) have been investigated to characterize carbonate-hosted Cu mineralization in the Hangend rocks. The aim of the study is to contribute to the characterization of the mineralization and constrain the genesis and timing of the mineralization processes. Therefore thin sections made from rock samples have been investigated using transmitted/reflected light microscopy, SEM, CL microscopy and EMPA.
Drill cores are very similar in their petrography. The Hangend consists of sparitic dolomitic limestone. Quartz, clay minerals and feldspar occur as minor constituents. The dolomite is cut by bedding-parallel stylolites and vertical fractures filled by calcite and anhydrite. Locally, dolomitic limestones appear brecciated. With CL microscopy a luminescent, Sr-rich and Fe/Mn-poor early diagenetic dolomite (DcmIa) and a non-luminescent Sr-poor, Fe/Mn-rich late burial dolomite (DcmIIa) can be distinguished. The DcmIa formed through near-surface diagenesis of the Ca1 limestone. Both dolomitization (left figure) and dedolomitization (right figure) processes have been observed in the thin sections. Calcite forms a bright luminescent and a dull luminescent subtype, which can be found in fractures associated with metal sulphides. Quartz, clay minerals, feldspar and solid organic matter are mainly accumulated within the stylolites. The DcmIIa originates from recrystallization processes during burial diagenesis and has only been found very scarcely.
Metal sulphides, mainly chalcopyrite and covellite, but also traces of sphalerite, galena, tennantite and pyrite, occur widespread and finely disseminated in the Ca1 carbonate rocks, and also reach the overlying anhydrite. Typical ore textures include disseminations, ore veinlets and replacement of carbonates and anhydrite. The sulphide mineralization postdates diagenetic dolomitization but predates late carbonate- and anhydrite-filled fracture and breccia infill.
Based on the observed paragenesis and different textural associations, syn-, dia- and epigenetic stages of mineralization can be distinguished. Pyrite precipitated syngenetic while the surrounding sediment was still plastic. During early diagenesis precipitated minor base metal contents. The vast majority of metals were deposited during late diagenesis. Textural observations suggest that mineralization took place after dolomitization, but before formation of epigenetic breccia and fractures. Arsenic sulphides were closely associated with Cu sulphides and precipitated simultaneously. The metals originate from an ascending brine, which in contact with a reducing environment precipitated at favorable trap sites like fractures, stylolites or by replacing carbonates. The Kupferschiefer and the stylolites slowed down the upward movement and sometimes caused swelling of the brines below them and accumulation of metal sulphides (middle image). Overall, the study provides a deeper understanding of the genesis of Kupferschiefer-type deposits and implications for their exploration.