Summary and conclusions: a model for the epithermal mineralizationof the Tokaj Mtns.

The majority of volcanic and hydrothermal features exposed in the Tokaj Mtns. were formed 10-12 million years ago and have undergone minor erosion. The paleosurface of some hydrothermal systems is still preserved. The location of alteration zones is controlled by faults and appears spatially related to shallow andesitic intrusions emplaced in circular, caldera-like volcanic structures (Telkibãnya, Regëc, Mad) or rhyolitic volcanic centers (Mad, Sãrospatak).

 The generalized pattern of mineralization and alteration is shown in Figure 22, and is based on field observations as well as mineralogical, geochemical and fluid inclusion data from the Tokaj Mtns. Similar zonation is also well known in other low-sulfidation (adularia-sericite) type epithermal deposits (Buchanan, 1981; Berger and Eimon; Hayba et al., 1985; Silberman and Berger, 1985; Sillitoe, 1993) and geothermal fields (Henley and Ellis, 1983; Hedenquist, 1990).

 Hottest mineralization temperatures range from 1700C to 2700C in the deep zones. The presence of adularia, quartz pseudomorphs after bladed calcite, and fluid inclusion petrography prove that the fluid was boiling in places. The metasomatic-replacement and later fracture-filling by adularia resulted in elevated potassium content of altered rocks.The two-stage appearance of K-feldspar probably reflects the variation of gas-content (C02, H2S) of fluids during boiling resulting in fluctuating pH conditions. The adularia-sericite alteration zones are surrounded by propylitic alteration, which probably reflect hydrothermal recrystallization of the volcanic host rocks (Telkibánya, Regëc, Mad).

 The alunite-kaolinite alteration zones above adularia bearing alteration levels (Telkibanya, Sárospatak, Mad) can be related to gas loss and boiling. The steam-heated acid-sulfate waters formed primarily in tuffaceous units (Mad, Sarospatak, Regec, Telkibánya). Silica transported by the descending steam-heated fluids together with the silica content of the upflowing hydrothermal fluid precipitated in flat mushroom-like bodies along the paleowater table (Sárospatak, Mad). The occurrence of steam-heated alteration zones below the flat-lying silica bodies reflects the subsidence of the paleowater table due to tectonism and erosion during the hydrothermal activity.

 Hydrothermal brecciation of the massive silica bodies also occurs (Sarospatak). The hydrothermal brecciation at depth resulted accumulation of hydrothermal eruption breccias on the paleosurface (Regec). The fluids outflowing at those places where the groundwater table cut the paleosurface may still have had a significant amount of dissolved silica. Due to cooling, this silica precipitated around the hot-spring centers cementing hydrothermal explosion breccias and forming layered siliceous depists (Regéc). The still silica rich fluids fed local lacustrine basins where their silica content was deposited as silica mud in the periods of less terrigenous accumulation in the lacustrine/swamp environment (Mad).

 The adularia-sericite alteration envelope of quartz veins, stockwork and hydrothermal breccias, platy calcite occurrences correspond to gold and silver mineralization and enrichments of Zn, Cu and Pb at depth (Telkibanya). The overlying steam-heated alteration zone with kaolinite-alunite may overprint earlier and deeper alteration and mineralization due to change in the level of the paleowater table. Sb, As, Hg forms the most characteristic anomalous element association at shallow levels.

 The model for the Tokaj Mtns. highlights the characteristics of shallow level alteration-mineralization associated with low sulfidation epithermal environments in which the steam-heated alteration zones with intense argillitisation were preserved. These features are promising signs for exploration of blind epithermal precious metal mineralization in the region.