Újabb adatok a füzérradványi hévforrásos epitermális arany-ezüst ércesedésről

Abstract

The drilling program carried out during the period 2007–2009 supplied important new data on the geology, structural setting and precious metal mineralization of the northern part of Tokaj Mts. Corresponding to the earlier geological interpretations lacustrine sediments of nearly 100 m thickness were formed by the end of the Sarmatian rhyolite tuff deposition. As a result of the intrusion of a rhyolite subvolcanic body the lacustrine sediments were altered by a steam-heated system. It was followed by multiple brecciation events accompanied by hot-spring style, low sulphidation gold-silver mineralization.
Drilling in 2007 proved the existence of wide, low-grade gold mineralization zones related to the NNW oriented, silicified, brecciated structures, exposed on the Korom-tető ridge. Some borehole intercepts were also characterized by high-grade silver contents. Drilling in 2008 proved the existence of mineralized structures with high-grade gold and silver contents in drillhole FR–105 which is also located at the Korom-tető.
In 2009, drilling with an oriented core technique, it was proved, that the mineralization has a more complicated pattern to the one that can be observed on the surface. Three main orientations of the mineralized structures were observed: NNW, N and NE-striking ones. With respect to the high-grade mineralization intersected by the FR–105 drill hole, it could be related either to a NE-striking structure or to a more local ore shoot at the intersection of mineralized
structures of different orientation.
Based on the morphology of ore bodies, host rocks and mineralogy of the ore four types of mineralization were distinguished. In the upper part of the epithermal system crustiform, banded chalcedony-quartz veins (type 1) and a goldbearing halo hosted by the silicified lacustrine sediments, rhyolite tuff and tufits were observed(type 2) characterized by the following mineral assemblage: electrum, acanthite, naumannite, SbFe-oxid and pyrite. About 100–150 m deeper,
crystalline rocks of the metamorphic basement host quartz-sulphide veins and nests with pyrite, arsenian pyrite, fahlore, chalcopyrite and sphalerite (types 3 and 4). Pyrite is missing in type 4 and the occurrence of gold is very low. All ore types
are characterized by highly anomalous Tl content (up to 530 g/t).
The mineralization corresponds to the hot-spring style, epithermal Au-Ag mineralization model. The most important common features of Berger’s model and the Füzérradvány mineralization are: The mineralization is related to rhyolitic  volcanism and poorly-eroded parts of shallow geothermal systems. Typical mineralogical composition: native gold or electrum, Ag-selenide and/or Ag-teluride, pyrite. The ore texture is characterized by the predominance of banded veins and breccias with a silicified matrix. Hydrothermal alterations from top to bottom are as follows: silica-sinter, massive silicification, quartz-adularia veins, veinlets and breccias with a quartz matrix. The veins are mainly chalcedonic, rarely opaline. In the upper 50 to 100 m of the epithermal system increased contents of Au, As, Sb, Hg and Tl are typical, while their content is decreased by depth accompanied by significant increase of Ag contents.