TECTONIC SETTING, DEEP FAULTS AND MERCURY MINERALIZATION AT ALMADEN, SPAIN, AND NIKITOVKA, UKRAINE - AFFINITIES AND CONTRASTS

West of the Tornquist-Teisseyre Zone, between the Black Sea and the Ba ltic Sea, mercury and antimony deposits show a spatial relationship wi th late-orogenic extensional processes. This applies to the Alpine and Variscan orogenies and may also apply to the Cadomian orogeny. The Si lurian Almaden deposits and other mercury deposits in early to mid-Pal aeozoic host complexes in western and central Europe occur in a number of micro-continents that are thought to have been derived from the co ntinent of Gondwana, although relationships between the micro-continen ts have been largely obliterated by the Variscan and Alpine orogenic e vents. In the Almaden region aeromagnetic anomalies indicate the prese nce of deep faults, which, it is suggested, represent remnants of the pre-Variscan Cadomian tectonic framework. At Almaden the close associa tion between the mercury mineralization and alkaline basaltic volcanis m suggests that these faults may tap the upper mantle. East of the Tor nquist-Teisseyre Zone mercury is confined to the Pripyat-Dnieper-Donet s (PDD) rift and is generally accompanied by antimony and also, locall y, by base metals. Together with gold, these metals appear to express a spatially zoned association. Although the degree of surface outcrop is much less than in the Almaden region, the deeper crustal structure is better known from geophysical investigations. The PDD rift is locat ed in the Sarmatian block. Together with the Fennoscandian and Volgo-U ralian blocks it forms the crystalline Precambrian basement of the Eas t European Platform. In contradistinction to the other two blocks, the Sarmatian block appears to resemble the continents of the present sou thern hemisphere. Again, this would suggest a link between the mineral ization and the old Gondwanan continent. The present PDD rift was init iated in the mid-Devonian, although a Proterozoic precursor is debated . The rift is part of an orthogonal framework, apparently syntectonic, of northwesterly and northeasterly trending sets of grabens in the Ea st European Platform that rotate into each other rather than intersect . Some of the grabens are demonstrably underlain by early Proterozoic mobile zones that surround Archaean cratons. In the PDD rift the princ ipal phase of mid-Devonian to Carboniferous subsidence was followed by a phase of Permo-Triassic uplift, which, in the Donets segment (which contains the Nikitovka district), developed into a tectonic inversion . During the late Palaeozoic rifting major listric faults affected the Moho and probably reached into the mantle. In the Donets Basin these faults are interpreted to have been reactivated as thrusts in a dextra l deformation regime. Volcanic and plutonic rocks of mafic alkaline an d calc-alkaline affinity are abundant and it is generally assumed that there is a relationship between volcanism and mineralization. However , it is not clear which volcanic phase was principally responsible for the mercury-antimony mineralization, although a mantle source is gene rally accepted. Processes of remobilization should not be excluded, ho wever, in view of the complex evolution of the rift. The tectonic fram ework of the rift has provided ample pathways between the upper mantle and the crust during the various stages of its history. Isotopic dati ng of suitable minerals associated with the deposits should be given h igh priority. In view of the instability of the continental lithospher e in the early to middle Palaeozoic west of the Tornquist-Teisseyre Zo ne and its stability during the middle to late Palaeozoic in the Sarma tian Craton east of the zone, together with the emplacement of the Moh o at higher levels that is common to both settings, it is suggested th at major disturbances in the mantle provided the driving force for the concentration of mercury and antimony and probably also of other heav y metals.