Abstract Among the Cu-Ni-PGE occurrences hosted by the footwall units of the Sudbury Igneous Complex, low-sulfide systems possess the lowest sulfide content while being significantly enriched in Pd and Pt. Although the contribution of hydrothermal processes to the formation of this type of mineralization has already been recognized, no detailed studies have previously focused on the mineralogy and zonation of mineralization-related silicate assemblages and their distinction from regional processes postdating ore formation. Here, the results of detailed alteration mapping carried out on two recently discovered low-sulfide occurrences in the footwall of the Wisner area in the North Range of the Sudbury Igneous Complex are described to address these questions. In both areas, disseminated sulfides, S-shaped sulfide veins, and extensional silicate veins trending northwest-southeast to north-northwest−south-southeast formed from hydrothermal activity driven by the heat of the Sudbury Igneous Complex. Hydrothermal vein assemblages in mafic to intermediate host rocks are dominated by actinolite whereas epidote and quartz predominate in granitic host rocks. Compositional similarity (high Ni, low K, and relatively low Mg contents) of actinolite rims of vein-filling amphiboles and actinolite in ore-bearing assemblages, coupled with anomalous PGE contents of amphibole veins and their spatial proximity to mineralized zones, suggest a direct genetic relationship between silicate veining and low-sulfide mineralization. Shear-type epidote veining postdates the Sudbury Igneous Complex-related hydrothermal alteration and slightly redistributes metals from the low-sulfide footwall ores on a local scale. Both Sudbury Igneous Complex-related and regional hydrothermal assemblages of the Wisner area show characteristics identical to similar occurrences elsewhere in the Sudbury structure.

Abstract The NE Tokaj Mountains at Pálháza in NE Hungary are made up of a complex association of Miocene rhyolitic shallow intrusions, cryptodomes and endogenous lava domes emplaced into and onto soft, wet pelitic sediment in a shallow submarine environment. The intrusive–extrusive complex shows a range of interaction textures with the host muddy sediment, ranging from blocky peperites, formed on a 0.1 m-scale, through to irregular contacts closely resembling globular mega-peperites, on a >10 m-scale. The over 200 m-thick igneous succession is interpreted to result from the pulsatory growth of shallow cryptodomes through muddy saturated host sediment. The intrusions eventually breached the sedimentary cover to build up thick in situ hyaloclastite piles in the shallow subaqueous environment. The coherent rhyolitic cryptodome facies is surrounded by intrusive hyaloclastite in the contact zone to the pelitic host sediment. In the upper level of the complex, rhyolitic dome rock is capped and surrounded by hyaloclastite formed due to quench fragmentation upon contact of the lava surface with sea water.

Abstract km 0 The first Shell gas station on the M3 motorway after the end of Budapest sign. From here, the M3 motorway crosses the Gödöllő Hills during the next 35–40 kilometers. This area consists of a 2 km thick Tertiary-Quaternary sedimentary sequence underlain by Mesosoic carbonate rocks. On the present surface, loess from the Pleistocene glaciation and drift sand deposits are the most common sediments. 60 On the left side ahead the first view of the Western Mátra Mtns. appears. They are the highest mountains of Hungary with 1014 m elevation at the Kékes summit. The visible part of the Western Mátra Mts. is composed of Miocene andesitic-rhyolitic rocks forming a caldera structure with approximately 15 km diameter. The Mátra Mtns. is the object of the field programme on the fourth day and details of regional geology can be found in the guidebook. In front of the mountains the town of Gyöngyős can also be seen. 69 The M3 motorway crosses one of the traditional wine-producing area of Hungary. The vineyards covering 28 000 acres on the southern foreland of the Mátra Mts. are famous for various white vines. The center of the wine region is Gyöngyős. Behind the vineyards to the left (north) the Eastern Mátra Mtns. can be seen. This part of the Matra Mtns. is built up by andesitic rocks of Miocene age. In contrast to the Western Matra Mts., large caldera structures cannot be found here and the area is very poor in hydrothermal mineralisation.

Abstract Epithermal ore deposits form in the shallow portions of hydrothermal systems, from the surface to less than about 1-km depth. The hydrothermal activity is associated with contemporaneous volcanism and related magma intrusions, and the ore is hosted typically by volcanic rocks. There have been many major exploration successes since the late 1970s, e.g., El Indio (Chile), Hishikari (Japan), Ladolam (Papua New Guinea) and Yanacocha (Peru). As a result, epithermal deposits have become increasingly important producers of gold during the past 20 years and are now one of the main targets of gold exploration in volcanic belts of any age. Compared to other types of gold deposit, epithermal deposits are among the best understood in terms of diagnostic characteristics, variations in styles of mineralization and genetic processes. Part of this understanding, particularly of the basic geological and mineralogical features, comes from early studies that were detailed and insightful (e.g., Ransome, 1907; Lindgren, 1933). However, our understanding of the nature of the fluids responsible for metal transport, and the processes that lead to epithermal mineral deposition and associated wallrock alteration is due to recent detailed geological and geochemical studies both of ore deposits and, importantly, active hydrothermal systems and volcanoes. For example, hydrothermal systems that have been explored and developed for their geothermal energy potential provide direct evidence on the composition, distribution, and flow of fluids, the patterns of temperature and pressure, and processes such as boiling and mixing (Henley and Ellis, 1983). More recently, the study of discharges from volcanoes and

Abstract Volcanic-hosted ore deposits of the Carpatho-Pannonian region have been well known since the time of the Celtic and Roman empires. These deposits played an important role in the precious-metal, copper and base-metal production of these empires over their long histories. The essential volcanological and geological aspects of these deposits have been recognized only recently thanks to advances in paleovolcanic reconstructions and geotectonic analysis using principles of plate tectonics. Paleovolcanic reconstructions (e.g., Konecný, 1971; Konecný et al., 1995a; Szakács and Seghedi, 1995) have demonstrated that volcanic-hosted ore deposits are intimately related to andesite stratovolcanoes, dacite-rhyolite flow-dome complexes and subvolcanic intrusive complexes in regions of continental margins and island arcs. Geotectonic analysis (e.g., Lexa and Konecný, 1974; Horváth and Royden, 1981; Royden, 1988; Csontos, 1995; Nemcok et al., 1998) points to the Carpathians and Pannonian basin as a coupled Tertiary orogenic arc and related back-arc basin whose evolution was terminated by collision with the European platform margin. The metallogeny of the region can be interpreted using models developed for volcanic-hosted ore deposits of plate margins, and it also contributes to the body of knowledge on such deposits. As mentioned above, the Carpathian orogenic arc along with the Pannonian Basin is one of several Tertiary arcs in the Mediterranean region coupled with a back-arc extensional basin, (Fig. 1), here located in the northern branch of the Alpine orogenic belt. The relative movement of the European and African plates was responsible for the early stages of the Alpine orogeny owing to Early Tertiary continent-continent

Abstract The Tokaj Mountains are situated in northeastern Hungary and host one of the oldest Au-Ag-base metal mining districts of the Tertiary-Quaternary volcanic arc of the Carpathians. The first documentation of mining activity of the Telkibánya area in the northern Tokaj Mtns. (Fig. 1) was a 14th century order from the Hungarian Royal Court, in which the borders of the mining field — coincident with the presently known distribution of mineralization — were defined (Benke, 1988). During the Medieval Ages Telkibánya reached the rank of a ‘Royal Mining Town’ and was a regular member of the Council of the Lower-Hungarian Mining Court. In addition to the mining of precious metals, the Tokaj Mtns. have attracted several generations of Hungarian and foreign geologists, not only because of the world famous ‘Tokaji Aszu’ wine, but because of the volcanological, petrological and mineralogical interest of the area. Desciptions of mining sites and mineral occurrences can be found in old geological publications such as Beudant (1822). Petrological work on volcanic rocks carried out by József Szabó, the ‘Father of Hungarian Geology’ in th Tokaj Mtns. and similar areas of the Carpathians during the second part of the 19th century led to the revision of the classification of ‘trachytes’ (the old name of volcanic rocks) on the basis of plagioclase composition, rock-fabric and genesis. During the 20th century the Tokaj Mtns. were intensively explored for precious metals and exploited for raw materials such as clays (kaolinite, illite, bentonite), zeolites, pure silica and alunite, as well as

Abstract The Mátra Mtns. cover an area of 570 km 2 in the western part of the Tertiary-Quaternary volcanic belt of the Carpathians. The average elevation of this region varies between 600 to 700 m; however, the highest peaks in Hungary, Galyatetõ (965 m) and Kékestetõ (1015 m), are found here. The Mátra Mountains consist of two major volcanic units (Fig. 1). The Paleogene Unit covers an area of about 25 km 2 in the northeastern part of the Màtra Mtns. in the vicinity of Recsk village. The Paleogene Unit consists of an Upper Eocene calc-alkaline volcanic sequence intercalated with sedimentary rocks. It formed along the internal island arc part of asubduction zone that was located between the Northern and Southern Alps during the Laramian-Pyrenean orogeny (50–70 Ma). The emplacement of the Paleogene Unit into its present position in the Western Carpathians was caused by a large-scale (ca. 300 km) northeastward movement of crustal units along the re-activated Periadriatic-Darnó strike-slip fault during the lower Miocene (Zelenka, 1973, 1975; Csontos et al, 1992). The ore complex containing high- and low-sulfidation type epithermal, porphyry copper, skarn and metasomatic replacement deposits and is genetically related to this Paleogene Unit. Mining activities around Recsk go back presumably as far as prehistoric time. However, documentation of prospecting is available only since the 18th century. In the early times copper ores and silver-bearing galena and fahlore were exploited, whereas the alunitized and pyritized wallrock was used for alum production. The enargite-luzonite-grey-ore-Au-pyrite massive/stockwork mineralization was discovered in the middle of the

Abstract The Central Slovakia Volcanic Field (CSVF), of Badenian through Pannonian age (16.5–8.5 Ma), is related to both subduction of the flysch belt oceanic/suboceanic basement underneath the advancing Carpathian arc and to back-arc extension processes. Hercynian basement including Late Paleozoic and Mesozoic sedimentary rocks shows a distinct Basin and Range (horst and graben) structure. Volcanic rocks resemble medium- to high-K orogenic volcanic suites of evolved arcs and continental margins. Intrusive rocks show a granodiorite trend, locally with a slight shift towards monzonite. Petrography and geochemistry indicate mantle source magmas with variable crustal contamination and differentiation in shallow magma chambers. Late stage rhyolites indicate crustal melting and magma mixing. Initial Early Badenian andesite volcanic activity (16.5–16.3 Ma) is represented by scattered andesite (often garnet-bearing) extrusive domes and related extrusive and reworked breccias. Two andesite pyroclastic volcanoes were subsequently formed in the SE part of the CSVF, while large andesite stratovolcanoes were built up in the remaining parts of the CSVF during Early to Middle Badenian times (16.3–1.5 Ma). During Middle and Upper Badenian times (15.8–14.5 Ma) evolution of stratovolcanoes continued by subsidence of grabens and caldera associated with activity of both: 1) relatively mafic undifferentiated basaltic andesites, and 2) andesites and differentiated volcanic rocks, — mainly hornblende and biotite-bearing andesites to dacites. Granodiorite, diorite and various porphyritic rocks were emplaced at deeper levels and in the basement. Rhyodacite domes and related pumice tuffs of Early Sarmatian age occasionally occur. Renewed activity of less differentiated andesites during Sarmatian time (14.5–12.5 Ma) formed discontinuous complexes on the slopes of older stratovolcanoes in the south, while it formed new volcanoes in the northern part of the CSVF, with centers situated on marginal faults of grabens. An extensive Late Sarmatian rhyolite volcanic activity (13–10.5 Ma) gave rise to a dome/flow complex and related volcanoclastic rocks in the western part of the CSVF along a N-S to NE-SW trending fault system; A small basalt/basaltic andesite stratovolcano of Pannonian age in the north and scattered basalt flows and intrusions in the central part of the CSVF were the latest products of the calcalkali volcanism. Sporadic nepheline basanite/trachybasalt volcanic activity took place during the Pliocene and Quaternary.

Abstract The essential structural aspects and paleovolcanic reconstruction of the Central Slovakia Volcanic Field has been discussed by Konecný et al., (1995); their paper is reprinted in this volume. Volcanic rocks, especially central volcanic zones including subvolcanic intrusive complexes, host a number of mineral deposits and occurrences. Fourteen types of mineralization have been distinguished in this region (Fig. 1), including: Magnetite skarn deposits and occurences related to contacts of the granodiorite subvolcanic intrusion with Triassic limestones and dolomites. Porphyry/skarn copper ± molybdenum or gold deposits and occurrences related to granodiorite porphyry stocks and dike clusters emplaced in Triassic carbonate rocks. Porphyry copper ± molybdenum mineralogical occurrences related to diorite to monzodiorite stocks. Base metal stockwork/disseminated mineralization related to granodiorite and diorite porphyry intrusions. Barren high-sulfidation alteration systems related variably to granodiorite, diorite, monzodiorite, and granodiorite porphyry intrusions (stocks), possibly representing the tops of porphyry-type hydrothermal systems. A high-sulfidation epithermal gold deposit and occurrences related to diorite/monzodiorite stocks, showing rudimentary porphyry type mineralization at depth. A low-sulfidation epithermal gold deposit related to granodiorite subvolcanic intrusion, along with base metal stockwork/disseminated mineralization. Low-sulfidation epithermal veins situated in central zones of older stratovolcanoes; however, these are directly related to local horst uplifts and late-stage rhyolitic extrusive domes and dikes. On the basis of metal contents there are base metal, silver — base metal and precious metal epithermal veins. Where these veins coexist there is a zonation in metals. Base-metal replacement deposit and occurrences adjacent to base-metal epithermal veins in Triassic carbonate rocks. Precious-metal replacement

Abstract The paleohydrothermal systems in the central zone of the Javorie stratovolcano are represented at the surface by conspicuous outcrops of secondary quartzites (residual quartz) and much less conspicuous argillized rocks. These zones of advanced argillic alteration were assumed during the early seventies to reflect porphyry copper systems at depth. Subsequent drilling at Banisko (Konecný et al., 1997), and a systematic metallogenetic survey in the central zone of the Javorie stratovolcano (Štohl at al., 1981) confirmed this assumption and provided extensive information concerning the geology, mineralogy, geochemistry and geophysics of this area. The next stage of metallogenetic investigation (Štohl et al., 1985, 1986) was then devoted to the detailed study of individual hydrothermal systems. Geochemical sampling as well as drilling was used to explore for a possible enargite-type Cu mineralization; with the exception of a few occurrences the results were negative. Nobody was aware of the possibility for gold potential at that time. In addition, gold was not analyzed for since sufficiently sensitive analytical methods were not available to carry out systematic gold geochemistry. In the early nineties the advanced argillic zones of alteration were recognized to represent high-sulfidation epithermal systems with a possible gold potential. In February, 1996, Rhodes mining company began to explore the area. Portions of drill cores from the preceding exploration campaign which were enriched in pyrite were sampled and analyzed for gold; however, the results were mostly negative, with only two samples showing values close to 1 g/t. The discovery of gold mineralization at Klokoc —