Humic-sourced organic matter from the Upper Silesian ZnPb deposits (Poland)

Abstract

Black, amorphous organic matter from the Upper Silesian ZnPb sulphide deposits (northwest of Krakòw), hosted in the dolomitized Middle Triassic limestones, is a humic substance of unknown origin. In the Pomorzany Mine this organic matter occurs in the interfragmental voids of mineralized, hydrothermal karst collapse breccias and as discontinuous layers and concordant laminae in the mineralized internal sediments that fill the pockets in the dissolutional surface beneath collapse breccias. Samples of organic matter were studied with reflected light (RLM) and scanning electron (SEM) microscopes, and were also subjected to chemical analyses, Rock-Eval pyrolysis and gas chromatography. The results obtained indicate that the organic matter has a humic, allochthonous nature and was subjected to migration under oxidizing conditions. Petrologically, the organic matter consists of eugelinite, with a reflectance ( R r) of <0.3%. It is proposed that the organic matter is dopplerite (calcium humate). It precipitated from humic acids, migrating downwards in aqueous solutions and loaded with Ca cations released from the surrounding carbonates by ascending, hydrothermal solutions. The probable source of humic acids was highly oxidized, plant-derived organic matter. The coalified remnants of flora are abundant in various Upper Triassic stratigraphic members overlying the ore deposits. Geological observations indicate that the organic matter and the sulphide ores were both deposited within the karst collapse structures at the same time and are genetically related. It is suggested that the organic matter and humic acids played a critical role in the precipitation of sulphide ore minerals as reductants of partly oxidized, sulphur- and metal-bearing, hydrothermal, ascending solutions.