DAY-1.

 Sátoraljaujhely-Sárospatak area

STOP-1. Sátoraljaujhely, Bányi hill (Tatárka hill) 279m

Local geology

The eastern margin of the Tokai Mountains is built up the oldest rocks in the mountains, badenien rhyolitic tuffs: dominantly crystal tuff and subordinate lapilli tuff. These tuffs were probably ejected from eruption centers aligned along the Szamos major fault. Fragments in the tuff are euhedral sanidine, hexahedral quartz and pumice. These pyroclastics were intruded by dacite at 13 Ma that was accompanied by introduction of fluid circulation along volcano-tectonic structures. Upon fluid percolation massive-banded-brecciated quartz-pyrite-gold veins were formed encompassed by K-metasomatic zones. In these zones altered tuff attains over 8% K₂O due to adularia sericite enrichment. Sanydine phenocrists are altered to sericite whereas adularia appears as euhedral pseudorombohedral crystals in vein quartz. Mineral paragensis and fluid inclusion petrography refer to boiling of mineralizing fluids that led to the precipitation of gold. P-T condition of fluid inclusions indicated 500m erosion (Molnar, 1993).

The Bányi Hill is in the middle of the K-metasomatized zone between Fekete hill and Száva hill. The hummocky relief of hillsides and tops indicates shallow depth open pit mining activity typical of medieval ages in the Tokai Mnts. The name of a closeby village Rudabányácska (Ore mine) indicates also the presence of historical mining in this area. The alignment of muck piles and trenches follows the strike of veins.

Prismatic quartz appears in altered tuffs along veinlets and in leached pumice, now vugs. Adularia can be found along fracture surfaces as splendid 1-4 mm euhedral translucent white pseudorombohedral solitary grains or groupings often associated with euhedral rombodecaherdal limonite-goethite speudomorphs after pyrite of 1-5 mm size (Picture 1). This very typical appearance of hydrothermal K-feldspar supports an extremely important field tool for economic geologists indicative to boiling of the mineralizing fluids hence the target zone of Au enrichment of this type of deposit.

 
Picture 1.: Limonite pseudomorphs after pyrite and speudorombohdral adularia appear together on fracture surfaces. (width of view is 3 cm)

STOP-2. Sárospatak, Botkõ and Király Hill

 Local geology

 Steam-heated hydrothermal alteration occurs along the eastern boundary of the Tokaj Mtns. North of Sárospatak, and it covers a ca. 9 km² area. Intensely altered and mineralized zones at Király Hill and Megyer Hill form a semicircular range around a local basin opening to the south. The area has a long history of raw material exploitation. The hydrothermally altered rocks provided excellent building materials for the surrounding settlements. The intensely silicified pyroclastic rocks were used as millstones dating back to the 16th century. The kaolin deposits has been explored and exploited from the beginning of this century up to the 1960s.

 The basement of the Tokaj Mtns. around Sarospatak consists of Triassic carbonates that is covered by a Lower Badenian subaqueous rhyodacite tuff unit (Gyarmati and Pentelényi, 1973). During the Upper Badenian volcanism evolved to a rhyolitic composition, and the related tuff is characterised by diagenetic alteration (clinoptilolite, heulandite, cristobalite, chlorite, montmorillonite), and occurrence of redeposited tuff, tuffite and argillic beds. The Mollusca fauna of the subaqueous units confirms the Upper Badenian age (Hoffer, 1925; Frits, 1960; Csepreghy-Meznerics, 1966). However, some parts of the area east of the major north trending fault were uplifted during the Upper Badenian and there subaerial tuff units were deposited (Gyarmati and Pentelényi, 1973). K/Ar ages of these tuffs are between 14.6-12.9 Ma (Pécskay et at., 1986). At the end of Badenian and Early Sarmatian a marine transgression occurred and rhyolite tuff and tuffite accumulation and reworking as well as shallow-water clay and sand sedimentation took place in the southern foreland of Király Hilt and Megyer Hill.

Figure 4.: Geological map, cross section showing hydrothermal alteration zones in the mineralized zone north of Sárospatak. Complied from Gyarmati and Pentelényi (1969), Mátyás (1979), Ilkey-Perlaki (1989) and Molnár (1993).

 Hydrothermal mineralization

 The hydrothermal alteration of this area occurs in two, north-south zones parallel to the major fault to the west (Fig. 4). The epithermal alteration consists of two major types:

1. siliceous horizons underain by alunite and kaolinite alteration zones (Botkõ, as well as Király Hill, Megyer Hill and Cinegés)

2. deeper adularia-sericite alteration (Király Hill)

 Strongly silicified rock bodies cap the top of Király Hill, Megyer Hill, Cinegés and Botkõ Hill (Figs. 4 and 5). The concentration of silica in these rocks is> 95 wt⁰/o and the original texture of tuff is totally destroyed; only quartz phenocrysts are observeable (Gyannati and Pentelényi,. 1973; Mátyás, 1979). The siliceous material is mostly quartz at Megyer Hill, Király Hill and Botkõ; however, it is predominantly brecciation at Király Hill and Botkö. The angular to subround breccia clasts range from 0.1 and 10 cm. The matrix of breccia as well as the groundmass of the silicified rock consists of microcrystalline quartz and barite laths. These minerals also occur as several centimeter long euhedral crystals in the open spaces. Cinnabar is present as dust-like encrustations in the vugs or dendritic dissemination in the silicified rock. Rare pyrite, and abundant hematite are also associated with these minerals (Kulcsár and Barta, 1969; Molnár, 1993).

 
Figure 5. Sections with zonation of hydrothermal alteration and fluid inclusion data from mineralized zone of Sárospatak. Complied from Gyarmati and Pentelényi (1969), Mátyás (1979), Ilkey-Perlaki (1989) and Molnár (1993).

 The strongly silicified rocks are characterised by geochemical anomalies of Sb (up to 370 ppm), Hg (up to 41 700 ppm), As (up to 210 ppm), Tl (up to 18 ppm), as well as Ba and Sr (Kulcsár and Barta, 1969; (Gyarmati and Penteldnyi, 1973; Szakáll, 1991).

 The silicified rocks are surrounded (Cinegés) and underlain (Botkö, Cinegés and Király Hill) by kaolinite-alunite-hematite alteration (Fig. 5). Alunite is fie-grained (l0-5O0~mm) and replaces groundmass and pumice fragments and fills fractures. The amount of alunite and the degree of silicification decreases away and downward from the silicified-brecciated zones. Parallel with this the dominant Si0₂ mineral changes from quartz to opal and cristobalite. Illite and montmorillonite dominated alteration zones (with subordinate amount of kaolinite) are also present beneath the kaolinite-alunite zones at Király Hill. There, an adularia bearing zone also occurs at lower elevations. In this deep zone inclusions of fresh pseudorhombohedral adularia crystals (10-100 mm) occur in mosaic textured hydrothermal quartz of the altered groundmass and quartz veinlets. Sanidine phenocrysts and the groundmass of the tuff are altered to illite and kaolinite (Kulcsár and Barta, 1969; Molnár, 1993). At Botkõ, illite alteration forms irregular zones within the kaolinite-alunite bearing zones and the deep adularia-bearing zone is not known (Mátyas et al; 1971; Ilkey-Perlaky, 1989). Quartz from quartz-adularia veinlets as well as barite and quartz from the hydrothermal breccia at Király Hill host liquid-rich and vapor-rich fluid inclusions indicating boiling trapping conditions.

Picture 2. Brecciated massive silica with hematite crackfilling, Botkõ.

Picture 3. Brecciated massive silica cemented by quartz and cinnabar (width of view is 3 cm)

Most common homogenization temperatures for liquid-rich inclusions range from 200 to 260⁰C in the adularia bearing zones and from 140 to 210⁰C from the breccia (Fig. 14). Salinities for these inclusions range from 0.7 to 4.2 NaCl equiv.wt% (Molnár, 1998; 1993). Fluid inclusion homogenization temperature data correspond to a minimum depth of 150 m below the paleowater table for the upper, silicified-brecciated unit, and a minimum depth of 270 m below the paleowater table for the adularia bearing alteration of Király Hill (Fig. 14). The location of samples from different levels along the same boiling curve suggests that the deeper adularia alteration and the shallow silicification formed under the same hydrostatic pressure gradient.

Homogenization temperatures of secondary fluid inclusions in quartz phenocrysts from the strongly silicified and brecciated Lower Sarmatian redeposited tuff at Botkö range from 120 to 230⁰C, and salinities are between 0.4 and 2.5 NaCl equiv. wt⁰/o (Molnár, 1988; Fig. 14). However, salinities for inclusions with the most common homogenization temperatures at around 130-1 50⁰C are below I NaCl equiv. wt⁰/o. This temperature range is very similar to those for steam-heated, C0₂-rich marginal fluids of geothermal fields (Hedenquist et at., 1992), but it is higher than typical temperatures for acidic steam heated waters.