Geology of the Rhyolite-Perlite Extrusions Along Ósva Valley, Telkibánya
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GEOLOGY OF THE RHYOLITE-PERLITE EXTRUSIONS ALONG ÓSVA VALLEY, TELKIBÁNYA János Szepesi Department of Mineralogy and Geology, University of Debrecen szepesij@delfin. unideb. hu Abstract: Comparative analysis of subareal dome and lava flow activity could have been carried out in the Telkibánya acid palaeo-volcanic field. The composite (Cser Hill) or monogenetic (Ó-Gönc, Ork Hills) character and the relative erosion scale of the forms were determined on the basis of facies successions. The survey verified an acid palaeo-flow structure in the surroundings of Kőgát Hill. This flow was dissected by both horizontal (vent, flow region) and vertical sections (facies zones) on the basis of outlining textural domains and structural elements. Due to regional concen- trations of perlite raw material research, comparative facies geochemistry description could have been carried out. Oxidation processes caused sharp element ratio changes in the outer brecciated- vesiculated and in the inner devitrificational zones. In the case of perlite facies the progression of hydration and ion exchange processes was accompanied by the decrease of volume weight, leaching of Na.20 and Si02 and increasing ratio of K20 and A1203. Keywords: lava dome, flow, rhyolite, perlite, hydration, leaching 1. INTRODUCTION AND HISTORICAL REVIEW The acid lavas of the Eperjes-Tokaj (Slanské-Zemplínske) Mountains are em- placed in unique diversity amongst the members of the Inner Carpathian volcanic chain. The ore bearing neutral and acid volcanism of Telkibánya is especially has been a classic area in the Carpathian Basin for more than two centuries to attract Hungarian and foreign researchers (Fichtel, 1791, Townson, 1797, Esmark, 1798, Zipser, 1817). The mountain ranges framed by the Ósva Valley and its tributary valleys gave a unique study area for petrographers who revealed the igneous bod- ies eroded at variable scales with a diversity of horizontal and vertical lava facies. Most of the observations concentrated only on the Kánya Hill gold-silver mining area, while only sporadic references have considered the acid lavas. The 2nd half of the 19Lh century was the revolutionary period of igneous petrography. One of its most important stages was the one when Richthofen (1861) defined the rock category rhyolite on the basis of mineralogical and chemical studies. Telkibánya and its surroundings was an important area in his synthetic research 171 János Szepesi where he distinguished the basic rhyolite (fluidal, lithoidal) and perlite (obsidian like, spherulitic) types. The formation of perlite with the contemporary "neptun- ist" approach was explained by lava flowing into water. Szabó J, a mining geologist was the first Hungarian researcher of rhyolites. He also carried out observations in relation to obsidians in Telkibánya and separated perlite from obsidian in its origin (Szabó, 1867). The first monographic description of the area was made by LifFa A. who summarized results of more than 20 years of research (Liffa 1953a, b). He correctly recognized that "the perlite rushed to the surface as a facies of rhyolite lava" but this very important finding has not been taken into account in subsequent researches. The last representative of the cycle, Hermann M. (1952) addressed petrographic and geochemical characterization of the rhyolites. The rhyolite subtypes of her meticulous microscopic thin-section studies, reflected the diversity of devitrification. However, their field identification and determina- tion was an almost impossible task. Geological mapping and raw material research in the Tokaj Mountains was started in the 1960s, its results required the development of a new volcanological model. The system dissected and clearly separated the major categories of lava - foam lava - pyroclast flow (Pantó, 1964 and I. Perlaki, 1972a) on the basis of volatile contents, however, the close genetic relationship between them was not considered. Detailed ideas of the area were published in the geological explana- tion and maps of Gönc and Nyíri of the scale 1:25000 (I. Perlaki, 1966, 1978). However, this scale was still unsuitable for depicting the diversity of acid lava facies (often in m scale) only the tendency and ratio of perlites and rhyolites were shown. In the surroundings of Telkibánya (especially in the vicinity of Kőgát) large amount of perlite was identified and a two-cycle raw material research was per- formed to determine the exploration stocks (I. Perlaki, 1972b, Gyarmati, 1981). Although the principles of perlite raw material distribution were interpreted on the basis of Russian model tests (Volarovich, 1944), the exploration of the rela- tionship between facies belts and erosion structures remained unclear. The structure and erosion transport processes of Cserenkő (stream of the Ósva Valley) catchment was examined by Kozák (1979). Study of opal varieties along Kurtabérci-creek also focused the attention of rhyolite varieties and clarified the genetic relationships (Kozák, 1979, Gyarmati et al, 1986) between them. The processing of domestic mineral deposits summarized the geological knowledge of acid lavas and the associated opals (Kozák, 1994, Takács, 1994, Papp, 1994). Last year Szepesi and Kozák (2008) published a new volcanological - petrogenetic 172 Geology of the rhyolite-perlite extrusions... overview of the area. Based on our new volcanological findings the acid extru- sions dismembered also their horizontal and vertical extent. 2. GEOLOGICAL SETTING The eroded palaeovolcanic rhyolite-perlite field is situated southeast from Telkibánya (Fig. 1). Starting with the characteristic Cser Hill rising above the vil- lage mounted toward the Ó-Gönc along the Ósva Valley. The products of acid volcanism are covered in a much larger area and can be followed on the surface (Fig. 1) towards east and southeast to Pálháza and Háromhuta. Formation of the stratovolcanic complex of the Tokaj Mountains started at the onset of the Badenian stage in a 100 km long NNE-SSW striking volcanic- tectonic depression. Amongst the internal members of the Carpathian Volcanic Chain it has a well defined bimodality with the unique appearance of rhyolitic and andesitic rocks approximately in the same ratio. The centre-labial ordered volcanic centres conformed to the meso-tectonic structure of the wider region and to the major fractures of the basement. Volcanism, in accordance with the general trends of basin development started in a submarine environment. Due to the increasing volume of volcanic material, the mainland relief gradually became dominant. In addition to andesitic-dacitic centres (Regéc - Baskó, Vágáshuta - Fekete Hill), contemporary operation of acidic volcanic centres generated pyrocalstic flows and plinian eruptions (Telkibánya - Pálháza, Erdőbénye - Erdőhorváti, Abaújszántó - Szerencs - Bodrogkeresztúr). The formation of thick tuff horizons (Sátoraljaújhely, Szerencs, Vizsoly Rhyolite Tuff Formation) with the reduction of explosion energy was followed by variable intensity of dome and flow activity, subareal (submarine) extrusive or shallow with subareal or intrusive emplace- ment. The Sarmatian cycle was the most voluminous eruption series during the evolution of the mountains ("upper rhyolite tuff" in Szerencs Rhyolite Tuff Forma- tion: Kozák and Püspöki, 1999,2004; Gyalog and Buday, 2004). The intensity peak and greatest territorial extent was reached at the Northern Rhyolite District (Fig 1.), extending from Gönc to Pálháza, in Szádeczky's words (1887) creating "Hun- gary's biggest rhyolite mass". The acid palaeovolcanic districts were dismembered into smaller units on the basis of palaeo-settings of the volcanism and the significant differences in the rate and territorial division of the explosive-extrusive products (Szepesi, 2004). Thus, the present study area is the part of the Gönc-Telkibánya district between the 173 János Szepesi Fig. la Geological map of the study area (Based on the 1:25000 scaled geological maps of Gönc and Nyíri and those of Telkibánya-Kőgát scaled 1:1000, and 1:5000 (I. Perlaki, 1967,1972b, 1978) and that of the Tokaj Mts. (Gyarmati, 1981) perlite predictions. Legend: Bedrocks (Sarmatian): 1. Andesite (Baskó Andesite Formation) 2 Acidpyroclasts (reworked, ash fall tuffs and ignimbrites, 3 Clay (Szerencs Rhyolite Tuff Formation, Kéked, Füzérkomlós Members), Acid lavas (Sarmatian-Pannonian, Szerencs Rhyolite Tuff Formation, Kishuta Rhyolite and Pálháza Perlite Members): 4 Rhyolite (grey fluidal and red) 5 Perlite (obsidian- like, grey perlite). 6 Spherulitic perlite 7 Perlite breccia 8 Pumiceous perlite Fig. lb Simplified geological map of the Northern Tokaj Mountains (modified from the structural-volcanotectonic sketch of the Tokaj Mts, Gyarmati, 1972 ), colouring based on 1:100 000 geological maps of the Tokaj Mountains (Pentelényi, 2005a, b). 174 Geology of the rhyolite-perlite extrusions... Gönc Nagy Creek and the Sényő Valley, and characterized by the dominance of acid lavas over tuff varieties (Fig 1). Perlites and rhyolite varieties cover about 20% of catchment area of the Cserenkő Creek. Their bedrocks were ash fall and flow tuffs of Sarmatian stage and its often reworked tuffitic varieties, which often mixed with siliciclastic sedi- ments. (Szerencs Rhyolite Tuff Formation, Kéked Member). The development of the tuff succession caused volcano-tectonic subsidence, therefore the reworked tuff beds revealed in the cellar row of Telkibánya (Templom Hill) fell into varying depths in E-SE direction. While borehole Tb-3 drilled down to 451 meters