Złoże rud miedziowo-polimetalicznych monokliny przedsudeckiej i jego związki z osadami cechsztynu

Abstract

COPPER-POLYMETALLIC ORE DEPOSIT IN THE FORE-SUDETIC MONOCLINE AND ITS RELATION TO ZECHSTEIN SEDIMENTS Summary The studies carried out in mining works and on core material from exploratory drillings made it possible to compile geological characteristics and reconstruct conditions of sedimentation of Lower Zechstein strata and structure and origin of copper-polymetallic ore deposit in the Fore-Sudetic Monocline. Close genetic and spatial relations of the ore mineralization and distribution of Lower Zechstein euxenites (in which the deposit occurs), are evidenced. The studied area has been situated in a zone of sublittoral and neritic facies in southern, nearshore part of epicontinental Zechstein sea. The sea level was here subjected to seasonal oscillations due to vertical epeirogenic movements of basin floor, successive inflows of waters from the Boreal ocean, and evaporation proceeding under conditions of a break in connections (locked basin). Lithology of sediments cyclically deposited on basin floor was primarily determined by changes in depth, water salinity, redox values, etc. Sedimentation of euxenites - Zechstein black shales and clay dolomites, representing products of reducing (Eh < 0) and alkaline (pH > 7.8) environment - started directly after transgression. The strata were originating in wide depressions in sea floor (so-called sedimentary traps), situated in direct neighborhood of old structural thresholds. Sedimentation of the shales was accompanied by precipitation of sulfides of copper and other metals from seawater strongly enriched in metal ions by metal-bearing thermal solutions /coming to the basin along deep fractures of the lithosphere -faults of the Middle Odra zone. Without supply of metals from that source it appears impossible to explain mechanisms of ore-forming processes, responsible for supply of enormous amounts of metals (of the order of some tens millions t) to that relatively small deposit area (several hundred sq. km) in a very short time (about a dozen thousands years) of sedimentation of the shales. Metal sulfides supplied to euxenites by deposit-forming precipitation processes in reducing environment (stage of sedimentogenesis) were subsequently, at the stage of dia- and katagenesis, mobilized and displaced by deposit processes within the parent and adjoining rocks, e.g. sandstones. Pore solutions were taking part in these processes, and changes in redox conditions in Lower Zechstein and Weissliegendes rocks were here of marked importance. In result of these deposit-forming and deposit processes there originated forms of sedimentary mineralization (pelite of Cu culfides, often forming streaks consistent with lamination of shales), and dia- and katagenetic ones (diagenetic streaks, concentrations, veinlets, etc.). That is why this sedimentary-diagenetic deposit is characterized by a complex, multistage genesis. The deposit is characterized by stratified, single-layer structure typical of platform area, and variability in thickness, concentration of metals, lithological composition (shales, sandstones, and dolomites), and type of copper-polymetallic mineralization (Pb, Zn, Ag, Ni, Co, Mo, V, Re, Ga, Au, and others). Post-mineralizational fault tectonics may explain cutting of the previously formed deposit into blocks. Any evidence for direct relations of the deposit and volcanic and magmatic phenomena and tectonics is still missing, besides the above mentioned indirect relation, reflected by the inferred rise of metal-bearing thermal solutions to the marine basin along fractures of the Middle Odra zone. The above presented characteristic features make possible differentiation of this copper deposit as a separate type of stratified copper ore deposits - the copper-polymetallic deposit from the Fore-Sudetic Monocline. The interpretation of the gathered data should not be treated as final and it should be improved or, eventually, modified on the basis of results of further, indispensable studies.