A Mid‐Triassic paleomagnetic age of the Kupferschiefer mineralization in Poland, based on a revised apparent polar wander path for Europe and Russia

Abstract

Extensive mineralization occurs in southwest Poland as zoned blankets of Cu‐Ag‐(Pb‐Zn) sulphides in the Kupferschiefer and Zechstein Limestone across the base of the Late Permian Zechstein restricted marine sequence, and in the Weissliegendes sandstone at the top of the Early Permian Rotliegendes continental volcanic and siliciclastic sequence. The Rote Fäule (RF) zone, an oxidized, hematitic equivalent of the normally pyritic basal Zechstein, directly underlies the copper ore and is part of the metal zoning. Although the origin has generally been considered to be syngenetic, geologic controls of the RF‐ore systems in Poland suggest a late diagenetic origin by converting metalliferous brines migrating through the Rotliegendes clastic redbeds up along basement highs, oxidizing the pyritic Kupferschiefer to form the RF, and precipitating base and precious metals on the reduced side of this oxidation‐reduction front. A paleomagnetic study of the ore zone in five mines in Poland, the RF zone in three mines, and of the barren pyritic basal Zechstein from outcrops and quarries in Poland, Germany, and England was undertaken to determine the absolute age of the mineralization. In the barren pyritic rocks and the copper sulphide ore, thermal demagnetization and vector subtraction revealed an unstable low‐temperature first‐remanence component (76.9°N, 12.2°E; A63 = 1.6°), parallel to the ambient field, and a second, higher temperature component (82.6°N, 145.9°E; A63 = 1.9°), which could be Miocene (10–20 Ma) or, less likely, Cretaceous (110 Ma) or Jurassic (180 Ma). This second component is erased at 350°–400°C and is thought to be carried by a product of weathering after Alpine age uplift and erosion. No primary magnetization could be isolated in the copper or pyritic zones. The RF hematite, however, contained a very stable third, reversed component (49.0°N, 157.2°E; A63 = 2.2°) which was revealed typically between 500° and 620°C, and is considered to represent a secondary chemical remanent magnetization acquired during the mineralizing process. In order to date the isolated magnetic components, Carboniferous to Neogene apparent polar wander (APW) paths for Europe and Russia were constructed using paleopole catalogs. Mean paleopoles every 10 Ma from 350 to 0 Ma, with A63 circles of confidence, were calculated as running averages using overlapping 20‐ and 30‐Ma time intervals. The RF pole, corresponding to the third remanence component, coincides extremely well with a Middle Triassic age of 240 Ma on the 20‐Ma APW path and a Late Triassic age of 230 Ma on the 30‐Ma APW path. Statistical analysis yields upper and lower age limits of 250 and 220 Ma. This Triassic paleomagnetic age supports the proposed late diagenetic origin of the Kupferschiefer ore deposits, and suggests that the RF‐ore systems were formed immediately after Triassic continental rifting associated with the opening of the Tethys ocean to the south—a likely source of the thermal anomaly necessary to initiate adequate convective velocities within the Rotliegen...

A multistage origin for Kupferschiefer mineralization

“…Jowett et al (1987a) were not able to measure primary magnetization in sulphide material but they did find that the Rote Fäule hematite had a chemical remnant magnetisation which they thought had been acquired during the mineralization process. Using the accepted European polar wandering curves, their results favoured an age of hematite formation (and thus Cu sulphide mineralization also) at ca.…”

“…One of the first determinations of the age of Kupferschiefer mineralization resulted from a palaeomagnetic study in mines in the North Sudetic trough of SW Poland (Jowett et al, 1987a). Jowett et al (1987a) were not able to measure primary magnetization in sulphide material but they did find that the Rote Fäule hematite had a chemical remnant magnetisation which they thought had been acquired during the mineralization process.…”

Controls on the distribution of rare earth elements in the Kupferschiefer series of SW Poland

“…As com monly ar gued, Rotliegend for ma tion wa ters were char ac ter ized by a rel a tively low pH, high Eh (in the sta bil ity field of he ma tite), con sid er able sa lin ity, high con cen tra tion of chloride ions, and el e vated tem per a tures in creas ing the abil ity of the fluid to trans port met als (e.g., Jowett et al, 1987;Wodzicki and Piestrzyñski, 1994;Oszczepalski, 1999;Speczik et al, 2003). Such flu ids can dis solve as lit tle as up to 4 ppb REE (Gieré, 1996;Jaireth et al, 2014), but chlo ride complexation and REE mo bil ity suf fi ciently in creases with in creas ing tem pera ture (Gam mons et al, 1996;Gieré, 1996;Migdisov et al, 2016).…”

“…Sub stan tial flows of met al lif er ous so lu tions pro ceeded within the Rotliegend ba sin to wards palaeohighs, spread ing upward and out ward, as ev i denced by ox i da tive footwall al ter ation in feeder ar eas (Rydzewski, 1978;Rydzewski, 1991, 1997;Oszczepalski, 1999). Fluid flows were triggered by con vec tion, com pac tion, brine recirculation, seis mic pump ing, ep i sodic re lease or a com bi na tion of the pro cesses (Kucha and Pawlikowski, 1986;Jowett et al, 1987;Oszczepalski, 1989Oszczepalski, , 1999Cathles et al, 1993;Wodzicki and Piestrzyñ ski, 1994;Blundell et al, 2003). The tem per a ture of miner al iz ing so lu tions did not ex ceed 150°C (Oszczepalski, 1999;Oszczepalski et al, 2002;Speczik et al, 2003).…”

“…This se ries is de vel oped as black or dark grey organic-rich and metal sul phide-con tain ing fa cies ("re duced zone"), and as red-stained or ganic mat ter-de pleted and iron oxide-bear ing rocks ("ox i dized zone" = "Rote Fäule"). The Rote Fäule is a zone of post-depositional ox i da tive al ter ation ex hib it ing he ma tite min er ali sa tion heavily over print ing sul phide min er als (Rydzewski, 1978;Jowett et al, 1987;Oszcze palski, 1989Oszcze palski, , 1994Oszcze palski, , 1999Oszczepalski and Rydzewski, 1991), and fea tures in dic a tive of ex ten sive de struc tion of or ganic mat ter, trans for mation of clay min er als, and sta ble iso tope vari a tions (Speczik and Püttmann, 1987;Püttmann et al, 1989;Bechtel et al, 1999Bechtel et al, , 2001aBechtel et al, , 2002Kucha and Przyby ³owicz, 1999;Speczik et al, 2003). The met als are dis tinctly zoned not only ver ti cally, but also lat er ally in belts pre dom i nated by copper, lead, zinc and py rite min er ali sa tion, which sur round suc cessively the Rote Fäule ar eas in di cat ing di rec tion of ore flu ids flow (Oszczepalski and Rydzewski, 1997;Oszczepalski et al, 2016).…”