DILL, H.G. (1994): Facies variation and mineralization in Central Europe from the late Paleozoic through the Cenozoic.- Economic Geology, 89: 42-61.

 

A b s t r a c t  After the Variscan orogeny, from the Upper Carboniferous to the Quaternary syn(dia)genetic and epigenetic mineralization occurred in the Mid-European Basin. The U (e.g. Müllenbach, St. Hippolyte, Freital, Stockheim), base metal (e.g. Freihung, Nova Ruda, "Bleiglanzbank"), Sr-F-Ba (e.g. Süntel, Deister Hills), Fe-Mn (e.g. Salzgitter, Auerbach, Lindener Mark, "Minette" ore in Lorraine and Luxembourg) and Au-Sn placer deposits (e.g. Fichtelgebirge)  are stratabound within clastic, volcaniclastic and calcareous rocks. Some vein-type and vein-like mineralization of post-­Variscan age is found in the uplifted basement blocks, and is spatially rela­ted to the late Variscan and late Alpine unconformities (e.g. Sauerland).

 

Post-Variscan mineralization may be subdivided into 7 types with respect to the deposited environment of their host rocks: (1) saprolite/peneplain (Cu, Pb, Zn, F, Ba, Fe, Mn) (2) alluvial fan (Fe, Sn, Au, U, Pb, Zn, F, Ba), (3) braided streams/bed load fluvial systems (Pb, Zn, U, F, Ba), (4) mean­dering to anastomosing streams/mixed load fluvial systems (U, Pb, Cu), (5) high energy shore zone of lake margins or coastal regions (Fe, Pb, Cu, U), (6) low energy lake centres or near-shore marine deposits (lagoons) (Fe, Pb, Zn, Cu, U), (7) mixed terrigenous calcareous shelf deposits (F, Sr, Zn, Pb).

 

There were various sources of metals for the stratabound mineralization. During the Late Paleozoic and Lower Triassic the metals were supplied from volcanites and volcaniclastic rocks of calc-alkaline affiliation (volcanic arc (?)). The Cu-Pb-Zn mining districts in the "Kupferschiefer" are located above or close to a suture zone that delineates a former active plate mar­gin with endogenous Cu-Mo porphyry deposits (e.g. Miedziana Gora, Zawierce). To follow down the stratigraphic column in the footwall of the "Kupferschiefer" the elements increase in the rever­se order, as they were enriched in the "Kupferschiefer". From the Lower Triassic to the Upper Jurassic metamorphic and granitic rocks in the Variscan basement highs became exposed to chemical weather­ing and acted as metal source. The denudation of the Variscan basement is mirrored by the element spectrum of the Triassic stra­tabound deposits, commencing with Pb/Zn deposits, e.g., Upper Silesia (gneisses) and leading to U depo­sits, e.g., Burgsandstein (granites). From the Lower Cretaceous onwards some of the metals in the mineralization were derived from the basement. Most of the mineralization, however, origi­nated from intra­basinal/in­tr­a-Mesozoic redeposition (e.g. ironstones).

 

Five "metallogenetic sequences" may be delineated, four of which start with mineralization in the fluvial environment and terminate with precipita­tion of Sr and F in a mixed clastic-carbonate shelf environment (sabkha). Metal­logenetic sequences reflect marine transgression and regression, which may be correlated with different rifting and spreading stages in the Atlantic ocean.

 

Two major unconformities, one caused by the late Variscan uplift, the other by Subhercynian and Laramide movements may be traced across the basin­. Supe­rgene (e.g. U/ Rudolphstein, Mn-Fe/ Hunsrueck-type) and hypogene (e.g. Pb-Zn) mineralization (e.g. Maubach-Mechernich) are directly related to these first-order geohydraulic planes. Minor uncon­formi­ties and erosional surfaces also influenced the de­velopment of host environments of stratabound ore deposits and the ter­mination of "metallo­genetic sequences". Low-relief erosional surfaces favoured restric­ted water circulation and resulted in the formation of trans­gressive black shales (e.g. Kupferschiefer). The develop­ment of a sabkha and its related mineral deposits also requires the presence of a low topography as well as an arid climate and resultant strong evapotrans­piration. Karstification, essential to the Mid-European MVT deposits, commenced more or less contem­poraneously with the evolution of tidal flats on these erosional surfaces in the supratidal zone and persisted until the hydrology was changed by a new transgression. Vein-type mineraliza­tion related to these unconformities was at least in part supplied by sulfur and strontium from sabkha-derived evaporites, as suggested by Sr and S-isotope analyses.

 

It is difficult to define the time of formation of the post-Variscan ore mine­ralization, except for syngenetic Fe-Mn, U ores (Tertiary) as well as Fe-(Cretaceous) and Sn-placers (Quaternary). The bulk of stratabound ore mineralization in the Mid-European Basin formed by diagenetic and epigene­tic processes. The few age data and some evidence from basin subsidence suggest that there were two inter­vals of diagenetic and/or epigenetic ore mineralization. The period from Lower Triassic to Upper Dogger correlates with the early rifting in the central parts of the Atlantic ocean. Another set of data which derived from U-F deposits in the upper Cretaceous and MVT deposits attests to a thermal and fluid influx from deep-seated rifts (Rhine Graben, Ohre Rift) during Late Tertiary.