Geoheritage of the Precious Opal Bearing Zone in Libanka Mining District (Slovakia) and Its Geotourism and Geoeducation Potential

Abstract

The northern part of the Slanské Vrchy Mountains, in Slovakia, within the territory of Dubnik Opal Mines, is considered to be the historical source of opal, including the opal known to the Romans. Dubnik precious opal mineralization originating from post-magmatic hydrothermal fluids based on its values should be recognized as an area of global importance. Geological processes that are connected to Neogene volcanic activity took place in the territory of the Dubnik Opal Mines and resulted in the formation of various geological products and processes represented by polymetallic mineral formation, opal formation, antimonite formation, and mineralization of the supergene stage, as well as the stratovolcano rock environment, which are of geoheritage significance. Remnants of intensive mining activity that took place during the past 2000 years provide opportunities for visitors to explore, study, and appreciate this unique geological heritage of international importance. However, geo-interpretation aimed at the general public (the largest group of potential visitors from sustainable geotourism development) and research on (geo)tourism and/or geoheritage for tourism purposes, as discussed in this paper, are lacking.

1. Introduction

The Libanka mining district, as a part of Dubnik Opal Mines, is an area with significant abiotic and biotic values [1,2,3]. Volcanism that took place in this area approximately 12.2 to 10 million years ago (Ma) created specific conditions within the rock environment together with its mineralization and associated processes [1]. Due to the exposure of rock faces from mining activities, this unique geological heritage can be viewed predominantly through historical mining works. The geoheritage has made the Libanka district (Eastern Slovakia) unique in its mineralization, specifically its precious opal mineralization. This outstanding gem has aroused people’s interest for thousands of years. The first written mention of precious opal mining in the area dates back to 1597 [1]. Emperor Rudolph II authorized the search for precious opal in the entire territory of the Hungarian Monarchy. The Dubnik opal mines are thought to have the earliest mention of opal mining in the world [1]. While underground mining activities commenced in the 18th century, it can be assumed that the primitive mining of opal could have taken place around the year 1299 [4]. This area can be recognized as one of global importance when taking into account other opal mines open to visitors in the world (e.g., Lighthing Ridge Area in Australia or Royal Peacock Opal Mine in Nevada, USA) and considering the unique origin of precious opals located in the territory of Dubnik Opal Mines (Rondeau et al. 2004) [5], its cultural-historical values [1,4] and more.

While the geology and the deposit characteristics of the Dubnik opal mines have already been described by several authors [1,6,7,8], the objective of this article is to describe the geological heritage within the mining district of Libanka for the purpose of geotourism and geotourism-related geoeducation. The article, therefore, highlights two key principles of geotourism: geology-based activities and (geo)education [9,10,11,12,13,14]. Geoeducation refers to the process of learning about the geoheritage through the geosites. Such use of geoheritage can benefit not only education but also protection and management [14]. Brocx and Semeniuk introduced the notion of the ‘8Gs’ covering geology, geoheritage, geoconservation, geosites/geoparks, geomanagement, geoeducation, geotourism, and geodiversity [14], where each of the fields, in turn, affects one another. Furthermore, education in geological heritage can have beneficial aspects on geoethics which is a great tool for raising public awareness of geological and environmental issues. Geoethics through geoeducation is one of the pillars for the development of any UNESCO Global Geopark through education [15,16], leading to an increase in an appreciation of geoheritage values, responsibility to maintain those values, and public awareness for sustainable development [17,18,19]. The Libanka mining district is included in the official concept of geoparks in Slovakia adopted by the Slovak government as a part of an area with the potential to be integrated into the proposed Solivar-Dubník geopark [20]. Therefore, a comprehensive description of the area’s geological heritage can be crucial in the actual establishment of the geopark. In this regard, the aim of this paper is to bring an overall view of geoheritage located in this unique location in light of its potential for geotourism and related geoeducation.

2. Methods

The study area of the Libanka mining district (as a part of the Dubnik Opal Mines) was selected based on its global importance [4], unique geoheritage [1,4,5], and related mining history [1].

The authors undertook fieldwork, a review of the literature, and obtained relevant data and information for analysis and synthesis.

Brilha [21] was used to assess the potential of the study area from geotourism and geoeducation perspectives. This method allows an assessment of individual sites from scientific, educational, and tourism perspectives. For the purpose of this paper, only the last two perspectives were considered. Brilha [21] argues that, due to the fact that there are distinct criteria for different values of the site (scientific, educational, tourism), their quantitative assessment must be performed separately. As this paper primarily focuses on the geotourism and geoeducation potential of the area, scientific values do not have to be assessed.

3. Geographic and Geological Overview

The Libanka mining area belongs to the wider historical area of the Dubnik opal mines and to the protected area of the Dubnik mines under the second and fourth degrees of protection [2]. Moreover, Dubnik mines also earned the title of an area of European importance within the system of protected areas of the European Union Natura 2000 (at 2008/01/25 European meeting of the Commission No. 2008/218/EC). The objectives of this area are based on the protection of biotopes and species of European importance which occur here. At the same time, the entire territory falls under the protected bird territory Slanské Vrchy Mts. [3].

Geographically, the Libanka mining district is part of the Dubnik Opal Mines, located in the Prešov Self-government Region, 18 to 19 km southeast of the city of Prešov. The area itself is located approximately three to four kilometers northeast of the village of Červenica and also belongs to its cadastral territory (Figure 1). It is approximately one kilometer from the abandoned mining settlement Dubník. In addition, the Libanka mining district is the largest mining district of precious opal mining districts within the territory of Dubnik Opal Mines and, in the past, had the highest mining production. Smaller mining districts of the Dubnik Opal Mines are Dubník, Šimonka, Prítok, Tancoška-Gunderov, Kameň, and Paseky [1].

Geologically, the area belongs to the area of the Zlatá Baňa stratovolcano (Figure 2), which is the largest stratovolcano in the Slanské Vrchy Mts. The volcanic activity of the Zlatá Baňa stratovolcano, as well as the other volcanoes in the Slanské Vrchy Mts, took place within the Neogene sea basin fill of the East Slovakian Lowland and the Košice basin. The Zlatá Baňa Formation is characterized by andesite volcanism, which began in the Upper Badenian but reached its peak only in the Middle Sarmatian. In age, this stratovolcano formation ranges from Lower Sarmatian to Lower Pannonian, with an age of 12.2 to 10.0 million years. Structurally, the stratovolcano is divided into three volcanic zones: central, transitional, and peripheral [8,22,23].

The central volcanic zone, taking the shape of a cirque-like depression, is on the surface comprised mostly of hydrothermally altered Miocene rocks. Rhyolite-derived volcanic clastics and sediments of the Lower Baden are present in its basement [8].

The transitional volcanic zone is located around the central volcanic zone and is formed by alternating deposits of andesite lava flows and volcaniclastic rocks. The lava flows of fine-porphyritic to medium-porphyritic pyroxenic andesite form a significant part of the volcanic cone and outer layers. The andesite has a porphyritic structure in this zone, and its phenocrysts are minerals such as plagioclase, hypersthene, augite, and rarely amphibole. Due to its style of formation, there are tectonic faults in this zone, which created a void for mineralization and, thus, for the formation of precious opal. In the Libanka mining district, the lava flows of medium-porphyritic pyroxenic andesite (Libanka type) and fine-porphyritic pyroxenic andesite (Ošvárska type) adjoin along an opalized fault [6,8].

The peripheral volcanic zone forms the southern part of the stratovolcano and is mainly composed of volcanic clastics such as epiclastic volcanic breccias or pyroclastics of pyroxenic andesites and sedimentary rocks [8,22].

4. Geoheritage of the Study Area

Precious opal deposits are located on the southeastern slopes at an altitude of 736 m above sea level, ending at the crest of Tancoška mountain. The location is at the meeting point of two types of lava flows: the Libanka and Ošvárska types, which caused the formation of the opalized fault running in the NW–SE direction and other faults, fissures, and cracks associated with it during massive eruptions in Baden to Central Sarmatia. The richest opal accumulations were in places where these faults were connected. The main part of the deposit is concentrated in the basement of the fault. Based on documents from 1952, the deposit is divided into upper and lower parts. The upper deposit is approximately 600 m long and 15 m thick, with a depth interval of 100 m. The lower deposit is also approximately 600 m long but 10 m thick and 200 m deep. As mentioned by Semrád [4], the deposit was divided into five opal-bearing zones, namely Kráľov Laz, Bučina, Stráne, Leština, and Predbaňa. In this case, however, precious opal mineralization was tied to the so-called mineralized columns (or pillars) with a star cross-section, tilted south of the inclination of tectonic lines, mirroring the tectonic character of the area. The pillars are most often found in breccias and pyroclastics in sizes from 5 × 10 m to 10 × 20 m, and their depth reaches from 20 to 80 m. The position of the opal-bearing rock and opal accumulations in the area, despite this, is irregular, and accurate localization is almost impossible [4,6,8].

From the geotourism perspective, the presence of geological heritage is essential as an integral part of the primary offer to tourists. In the Libanka mining district, features of geoheritage value are represented by the rocks of the stratovolcano Zlatá Baňa and several mineralization zones linked to these rock formations. From the beginning, in the Middle Miocene age, volcanic activity took place in the Slanské Vrchy Mts under the influence of vertical and lateral compression of the Neogene sedimentary rocks. This process later, in the Badenian to Middle Sarmatian period, was reflected in massive acid volcanism with a highly explosive character. It was the pressure released during these explosive episodes that caused the disintegration of the territory into several blocks, which were bounded by significant faults [7,23]. Along with other tectonic processes, the rocks were fractured by several significant faults. The Libanka area passes through the so-called opal fault, which is accompanied by other lower-order faults. During the decadent volcanic activity, ideal conditions for the formation of another geological heritage (specific mineralization) were present. Hot saturated gasses enriched with various elements and compounds penetrated through cracks and rock cavities from the greater depths of the stratovolcano to the surface, during which they also reacted with elements and minerals of the rock environment itself. Further, as they ascended to the surface, they also mixed with meteoric water in higher parts which created the conditions for the formation of several minerals. Minerals could thus crystallize on the walls of cavities or form vein fillings. Mineralization in the Libanka mining district can be divided based on the stage of its formation to the post-magmatic and supergene stage [6,7,22,23].

4.1. Post-Magmatic Mineralization

The post-magmatic stage in the district represents the primary mineralization, and in the Libanka mining district, it is present in three formations: polymetallic, antimonite, and opal. While the polymetallic and antimonite formations are included in the ore mineralization period, the opal formation is classified as non-ore. The oldest formation in the area is probably polymetallic, followed by antimonite formation and, later, opal. While the opal and antimonite formation took place as low-thermal mineralization up to 150 °C, the temperature interval of the polymetallic formation was from 300 to 200 °C. The cooling of saturated solutions in the rock environment was partly caused by rising to the Earth’s surface but mainly by circulating meteoric waters [7,22].

4.1.1. Polymetallic Formation

The polymetallic formation is the most important ore formation in the central region of the stratovolcano. In the territory of the Libanka district, it is not so important, but it is very widespread. There is a stringer-vein and impregnation type of mineralization which is represented by several chaotically-distributed veins of millimeters to centimeters sizes. The formation here is characterized by the formation/precipitation of marcasite and pyrite. These are iron disulfide minerals that have the same chemical composition (FeS₂) but differ in their crystal structure [6,7,8,23].

Marcasite and pyrite mineralization is visible throughout the mining area. This mineralization is often present together with antimonite and opal mineralization. The occurrence of marcasite and pyrite with opals has been associated with the Libanka deposit for centuries, viz., when opals were searched for on the surface and underground, the orange-yellow rocks in which they were found were used as criteria for their occurrence. In the Jozef tunnel, it is possible to observe several veins of orange-brown color, which are filled with marcasite and pyrite together with oxidic compounds of iron. Such veins can be 10 to 20 cm thick. Thicker veins were even locally mined in the past. Local mining of marcasite, or pyrite, was confirmed by the report of Prof. Slavík from 1920 [26] when 25 q of marcasite was mined in his presence. In the past, several thicker veins were found on the Libanka deposit where marcasite occurred in a kidney-like habit. However, most of the thicker veins had been mined or weathered to the secondary mineral limonite. The limonite in thick veins often fell or leached out due to the acidic product of weathering. This phenomenon can be seen today in the Jozef tunnel, where vein fillings are missing [6,7,8,23].

4.1.2. Antimonite Formation

Antimonite formation is represented by antimonite mineralization (Figure 3) which is in Slanské Vrchy Mts, widely spread around the tectonic structures, and related to the final stage of hydrothermal activities in the northern part of the mountains. The occurrence of the antimonite in the Libanka mining district is, however, quite rare [14]. It does not form any deposit structure, only rarely a crystalline one, therefore lacking mining potential. Despite this, there are few historical records of local mining of the antimonite as a side activity during primary opal mining. This activity generated extra money for miners working there. In addition to the general absence of this mineral, the present structures seen in the Jozef adit form very interesting star-shaped (or beam-like) crystals of needles with a width of up to 1 cm. This crystalline form occurs in rock cavities, in the past also found in direct contact with opals [8]. In the Jozef adit, many antimonite crystals were covered by secondary minerals such as cervantite or valentinite [6,7,8].

4.1.3. Opal Formation

The opal formation of the Libanka district is characterized by specific opal mineralization (Figure 4). It mainly includes precious opal mineralization, which is the most significant and unique geological heritage in the entire area. Opal is the lowest thermal member of the post-magmatic mineralization stage, with a temperature of only up to 100 °C [7,23]. Caucia et al. [27] assume, based on isotopic data of Rondeau et al. [5], relatively low (lower than 45 °C) temperature of formation of opals in this area, similar to that of Australian opals of sedimentary origin [28,29], but very different from that of volcanic opals from Mexico [30]. Such origin (low-temperature hydrothermal fluids associated with the volcanic environment) is unique and refers to geoheritage values of global importance. Precious opal accumulations occur within the opal fault located at the junction of two above-mentioned types of lava flows (Libanka and Ošvárska). Precious opal mineralization (Figure 4b) occurs on Libanka-type andesites, which are located in the fault basement. In the vicinity of the main fault, several faults, fissures, and cavities of a lower order were created, providing an ideal environment for opal formation. Mineralization occurred near the surface from relatively cold solutions. The hot steam that passed through the cracks in the rock was saturated with silica which is the building element of precious opals. In addition to silicon dioxide, however, there were also other elements and metals. These could be part of solutions from greater depths or come from already existing minerals in the adjoining rocks (e.g., pyrite and antimonite). Meteoric water cooling these gasses is also present in the very composition of opal and represents an important component. Precious opals from Libanka contained water, approximately 5 to 10% of their weight. Therefore, they were ideal for further processing and grinding for the purpose of jewel-making [22,23].

Opal formation can be divided into three basic associations: limnoquartzites, ordinary opal, and precious opal-hyalite association [7]. The association of limnoquartzites is usually part of the sedimentary filling of the marginal zones of a volcano. Ordinary opal is more common in several outer volcanic zones, including wood, meat, and wax opal, which are not found in the Libanka mining area. However, the most interesting association is precious opal-hyalite. Here belongs the greatest gem of Libanka, the precious opal, together with milk and glass opal. Precious, milky, or glass opal are most often seen here as part of vein fillings and cavities, occasionally as a matrix. The forms of hyalite, which are often found in a kidney or even drop-shaped habitus, can also be appealing. According to Ďuďa et al. [7], black opal was allegedly also found in the wider area, which is mentioned in the quantitative representation of minerals in the localities of the post-magmatic stage in the northern part of the Slanské Vrchy Mts. The opal formation is often accompanied by the mineralization of chalcedony [7,22].

Opal mineralization is present primarily in pyroclastics of pyroxenic andesites [4,6,7,8]. All tunnels and shafts connected to the Libanka mining complex have shown the occurrence of the precious opal. Nowadays, opal mineralization is rarely seen in its natural environment. This geological heritage is exposed mainly in the Jozef adit, which is also the only one accessible. In the Jozef adit can be seen mainly veins of milky opal in the parent rock, rarely veins of precious opal [8]. Current accumulations of opal mineralization in the other tunnels are not completely known due to their recent state.

A unique find geologically was a 3.5 kg milk opal geode found in 1908 on the 15th horizon of the Viliam adit. Due to its shape, the 12.5 cm wide and 7 cm thick geode was named Peasant’s Slipper. The geode of such a dimension made of glass opal in the middle and milk opal in the outer part was a world rarity, which is why it was requested for an exhibition in London and the National Museum in Budapest [6]. However, in 1956 the museum caught fire, and the current existence of the geode is unknown. It is certain that, before the fire, the museum had 366,923 Dubnik opals of 58,645 carats, a third of today’s amount [31]. The last worth-mentioning find of precious opal was found in a tunnel near the Viliam adit on 12 September 1914, just before the First World War, thus named the World War opal [1].

4.2. Mineralization of the Supergene Stage

The supergene stage of mineralization in the Libanka mining district accompanies all primary mineralization (post-magmatic stage) and is often the only early indicator of primary mineralization underground [6]. These minerals are also called secondary and are formed by weathering, mostly by meteoric water (occasionally by compounds from the air) containing dissolved oxygen or carbon dioxide, which changes the chemistry of primary minerals while penetrating the rocks [8].

Secondary minerals in the Libanka mining district are mainly: limonite, alunogen, halotrichite, fibroferrite, melanterite, copiapite, pickeringite, Co-pickeringite, gypsum, elemental sulfur, and others [6]. The most visible in the area is limonite, which was formed due to the water enriched with iron from primary polymetallic minerals. This water saturated with Fe flows and drips from the walls of the mine and thus creates the so-called limonite pseudokarst, seen in the form of drops, drips, but also small cascades. Limonite is mostly brown-orange, brown to black in color, and tourists can see it again in the Jozef gallery almost everywhere [6]. There is also a 100 m-long corridor of limonite decoration that covers almost the entire exposed surface of the parent rock. In the Apolonia gallery, there was even found the largest 1 m tall limonite stalagmite named Veľký Maugli (Great Maugli), as well as a 2-m stalagnate, many stalactites, curtains, and straws [8].

There are other secondary minerals on the walls of mines as well. While the water flowing through the rocks has decomposed the iron sulfides FeS₂ (marcasite, pyrite), new compounds can be generated, such as sulfuric acid (H₂SO₄), which has been passing saturated in water through the veins in the rock and reacting with possible trace elements. Thanks to this, minerals such as alunogen, epsomite, gypsum, or kasparite (co-pickeringite) (Figure 5) are visible in mines [32].

Gypsum is commonly found on the walls of corridors or on another mineral like limonite. In the Jozef adit, there is also the gypsum corridor (Sadrovcova chodba), where this mineral is prominently represented. A clearly visible occurrence of gypsum is also found in the tunnel above the Richard gallery [8].

One of the most interesting examples of the supergene stage mineralization is the short dead-end passage in the Jozef gallery, the Alunogenka tunnel (Figure 6) with the dominating mineral alunogen. A deep yellow sulfur mineral crystallizes on the walls of this passage and thus creates a crystalline crust with imperfectly developed crystals [6], together with other secondary minerals like co-pickeringite (also called kasparite). Kašparite is a mineral that was first described in Libanka. It occurs as very interesting light pink needle-like crystals up to 2 cm long on the walls. Crystallization of these very fine minerals takes place directly from the compounds in the air. A high concentration of sulfur can be smelt even before the tunnel’s entrance. In the Jozef adit, it is also possible to observe needle-like crystals of hexahydrate, which, due to its appearance, is popularly called grandfather omniscient’s hair. Furthermore, drops of the green mineral melanterite are also present [8] (Figure 6).

4.3. Rock Environment of the Zlatá Baňa Stratovolcano

Even though mineralization is geotouristically the most attractive part of the geological heritage in the area, the rocks of the Zlatá Baňa stratovolcano, where the mineralization is located, also fall under geological heritage. The Libanka district is located in the transitional zone of the stratovolcano, in the so-called mantle volcanism, which is characterized by alternating lava flows of andesite and pyroclastic strata. Ošvárska-type andesite is present in the area in the form of monotonous andesite, where its lava flows are separated by zones of lava breccias. The Libanka-type andesite, within which opal mineralization occurs, is very irregular and often brecciated. In the Libanka mining complex, these andesites differ both in structure and color. The difference between lava flows and lava breccias is also visible in the Jozef adit. The lava flows are dark gray to slightly dark red in their entirety. They are located in several dead-end corridors due to their mining disadvantages. Monotonous andesite does not contain many defects, and thus the probability of finding precious opal is very low. It is also much more difficult to mine in this type of andesite, and therefore, mining in tunnels like this was usually stopped. The brecciated andesite can be seen as a gray to dark gray color and is composed of fragments of pyroxenic andesite, sediment particles, and sulfide impregnations, which are glued together by a fine-grained matrix [23].

Further, hydrothermal processes have affected underground water. The high mineralization or thermal properties are the results of post-volcanic processes within the body of the Zlata Bana stratovolcano, where several mineral springs are located, especially in its central volcanic zone [23]. Mineralizing waters are of the Ca-Mg-HCO₃-Cl type, and in the deeper zones (1000 m), thermal water is also found with temperatures up to 59 °C. However, the water of pH 3.16 saturated with heavy metals like antimony has a negative impact on the nearby village Červenica (peripheral zone) [33]. In addition to the water, the stratovolcano had an impact on biotuc nature. The andesites affect the composition of the derived sediments and thus have enriched the soil with their acidity. More acidic soils created conditions for today’s beech and fir-beech forests which, in the past, replaced intensively logged original oak-beech forests. Moreover, endangered species like Sphagnum fimbriatum are found there [21]. Within the fauna, the abandoned mining areas become important wintering grounds for up to 16 species of bats [8,21]. The combination of solid volcanic rocks of the stratovolcano with sediments of the Paleogene and Neogene ages causes processes that deform the subsoil and thus create conditions for landslide failures [23]. The risk of slope deformation of such heaps is also increased by opal searchers who have to dig up these heaps with the aim of finding precious opal overlooked during the mining in the past [22].

5. Geoeducation and Geotourism Potential of the Area—Discussion

Nowadays, it is possible to see geological heritage as part of tourism, primarily in the Jozef adit (Figure 7) and exceptionally also in the Viliam adit. The current state of mines does not allow using the other adits and tunnels (Figure 8) for tourism due to safety concerns. The surroundings of the Jozef adit have markedly improved in recent years. The area around the Jozef adit operated by Slovak Opal Mines s.r.o., for instance, includes a large parking lot, access to the gallery from the main road, a small outdoor mining exhibition in the form of three mining carts, signs, and a few interpretation panels, outside tables, a fireplace, offices for employees, a newly constructed visitor information center with a café, and a restroom. Slovak Opal Mines further organizes activities for children, such as searching for opals. The next well-known Hereditary adit Viliam, which was the subject of a project to restore mining and develop tourism 10 years ago, is now abandoned, and its surroundings are in a neglected state. Geological heritage, as well as other mining works scattered throughout the forest, are poorly marked and difficult to access due to the lack of maintenance of tourist trails, their absence or lack of promotion, and the lack of general information.

Following the principles of geotourism [9,10,11,12,13,14] by providing (geo)education, it is important to provide and interpret information on geological heritage in a way tourists will gain knowledge. Based on the information provided in this article so far, it is certain that the mining district Libanka, as a part of Dubnik opal mines, has significant geotourism potential. Before the development of any geoheritage and/or geotourism related activity or product, proper research aimed at geological heritage and (geo)sites is required.

For the Libanka mining district, despite its undeniable values and potential, there is a lack of diverse scientific materials devoted to this topic. Books covering the geological heritage of Dubnik opal mines tend to be too old [6,7,23,26,34], but there are the four most recent publications of Peter Semrád, whose books are extensive and the most accessible [1,4,8,32]. However, there is a relatively small portion of the scientific literature and almost no publications devoted to the tourism potential of the area. It is important to provide more study materials and sources to support the information to educate visitors. Furthermore, from the perspective of geotourism development, it is crucial to collect and select geologically significant sites, characterize them, and determine their condition and values, e.g., via quantitative and/or qualitative evaluation [35,36,37,38]. Adopting the Brilha method [21], assessment results show that this area has relatively high educational and touristic potential (

Table 1. Assessment of potential educational use of the Jozef adit according to Brilha [21].

Potential Educational Use
Criteria/Indicator	Score	Weight	Weighted Score
Vulnerability:
The geological elements of the geosite present no possible deterioration by anthropic activity	4	10	40
Accessibility:
Site is located less than 100 m from a paved road and with bus parking	4	10	40
Use limitations:
The site has no limitations to being used by students and tourists	4	5	20
Safety:
Site with safety facilities (fences, stairs, handrails, etc.), mobile phone coverage, and located less than 25 km from emergency services	3	10	30
Logistics:
Lodging and restaurants for groups of 50 persons less than 50 km away from the site	3	5	15
Density of population:
Site is located in a municipality with less than 100 inhabitants/km2	1	5	5
Association with other values:
Occurrence of several ecological and cultural values less than 10 km away from the site	3	5	15
Scenery:
Site is currently used as a tourism destination in local campaigns	2	5	10
Uniqueness:
The site shows unique and uncommon features considering this and neighboring countries	4	5	20
Observation conditions:
All geological elements are observed in good conditions	4	10	40
Didactic potential:
The site presents geological elements that are taught at all teaching levels	4	20	80
Geological diversity:
There are three types of geodiversity elements in the site	3	10	30
Total score			345

and

Table 2. Assessment of potential touristic use of the Jozef adit according to Brilha [21].

Potential Touristic Use
Criteria/Indicator	Score	Weight	Weighted Score
Vulnerability:
The geological elements of the geosite present no possible deterioration by anthropic activity	4	10	40
Accessibility:
Site is located less than 100 m from a paved road and with bus parking	4	10	40
Use limitations:
The site has no limitations to being used by students and tourists	4	5	20
Safety:
Site with safety facilities (fences, stairs, handrails, etc.), mobile phone coverage, and located less than 25 km from emergency services	3	10	30
Logistics:
Lodging and restaurants for groups of 50 persons less than 50 km away from the site	3	5	15
Density of population:
Site is located in a municipality with less than 100 inhabitants/km2	1	5	5
Association with other values:
Occurrence of several ecological and cultural values less than 10 km away from the site	3	5	15
Scenery:
Site is currently used as a tourism destination in local campaigns	2	15	30
Uniqueness:
The site shows unique and uncommon features considering this and neighboring countries	4	10	40
Observation conditions:
All geological elements are observed in good conditions	4	5	20
Interpretative potential:
The public needs to have some geological background to understand the geological elements of the site	3	10	30
Economic level:
The site is located in a municipality with a household income lower than the national average	1	5	5
Proximity of recreational areas:
Site located less than 15 km from a recreational area or tourist attraction	2	5	10
Total score			300

).

The recent state of the location, especially the mine (Jozef adit), presents an excellent example of the historical mining of precious opal in this area. The site is accessible by car or bus directly from the road nr. 3440 with the possibility of car and bus parking at the site, as mentioned above. There are no specific limitations of site use, except the requirement to reserve the visit via an online form (available at: https://slovenskeopalovebane.simplybook.it/v2/#book (accessed on 11 September 2022)). However, the Libanka mining district is located in an area of relatively low-density occupation between two small villages (Červenica and Zlatá Baňa). The closest bigger cities are Prešov (24 km by car) and Košice (30 km by car). From a geodiversity perspective, three types of diversity are present on the site of Jozef adit, including mineralogical and volcanological geodiversity elements and elements of general geology. However, from a general perspective (including all types of the public), to fully understand phenomena present in the territory, some geological background is required in that information on regional geological evolution, and general geological processes are insufficient. So, visitors without geological backgrounds may find some ambiguities in the current geo-interpretation. In this regard, for sustainable geotourism development in the area, effective interpretational methods should be adopted, e.g., interactive models and maps. Such improvement in geointerpration will lead to an increase in attractiveness, the number of visitors, and overall awareness of this geoheritage site. The attractiveness of precious opal mines shows growing numbers of visitors per year (

Table 3. Numbers of visitors in the Jozef adit (source: internal material of Slovenske Opalove Bane).

Month/Year	2022	2021	2020	2019
January	0	0	251	8
February	0	0	262	34
March	369	0	228	346
April	806	0	0	822
May	1338	979	597	1231
June	1886	1226	1500	1684
July	4616	5412	7509	2969
August	6200	6885	8688	3810
September	1834	1866	1766	1069
October	2084	967	332	1316
November	N/A	387	0	424
December	N/A	0	0	271
Total	19,133	17,722	21,133	13,984

). In 2016, the number of visitors to the Jozef adit was 12,022 [39]. In 2020 the number reached more than 21,000 visitors. However, the years 2020 and 2021 were significantly affected by the COVID-19 pandemic and related measures and restrictions, and, as such, the numbers could be even higher. So, the positive trend showing an increase in the number of visitors indicates a growing interest in visiting this site. However, a more detailed analysis of visitors was not possible due to the unavailability of structured data based on education level, age, etc. From the perspective of effective management of (geo)tourist products and visitors, such information is crucial. Data on the visitation clearly show that, from the perspective of visitor numbers, the most significant months are May to October, with the majority of visits during July and August (Figure 9). A relatively short distance from Prešov and Košice positively affects mine visits by students from these two cities. School-organized excursions predominantly take place at the end of May, during June, September, and the first half of October—during the start and/or end of the school or academic year at primary schools, secondary schools, and universities. Considering this fact, the months of July and August represent the most important period of the tourist season in the area from the general public perspective. Recently, there has been no inventory of geosites located in the area or geoproducts (excluding mine visits mentioned above). A brief overview of the geosites of national and international significance located close (up to 30 km) to the Libanka mining district is provided in

Table 4. Geosites near the Dubnik Opal Mines.

Municipality	Site	Distance	Main Feature(s)
Kecerovský Lipovec	rock outcrop	9 km *	andesite jointing
Herľany	geyser	16 km *	unique cold-water geyser
Šimonka	peak	6.5 km **	the highest peak of the Slanské Vrchy Mts.
Solivar	museum	19.7 km *	unique complex of technical objects dating from the 17th century used for pumping and cooking salt from brine
Zlatá Baňa	mine	6.1 km *	historical mining of antimony
Ploské	tuff canyon	19.3 km *	approx. 60 m long tuff canyon formed by water erosion with 5 to 12 m high walls
Hermanovce	rock cliffs	13 km **	the most extensive exposed rock complex in the Slanské Vrchy Mts. consisting of two andesite complexes
Rankovce	rock cliffs	17.3 km *	volcanic rock complex, unique viewpoint

Note: Distances marked by * show walking distance using marked tourist trail; other values marked by ** show road distances using car.

. To reach higher numbers of visitors in the rest of the year and attract people to stay in the area for a longer time, research, including a study on detailed geoheritage mapping and analysis, visitor expectations and needs, (geo)tourist products, and sustainable tourism development, is required.

The responsibility of application research findings and results, however, lies with governmental, research, and educational institutions [40]. So, the development of any activities related to geotourism or geoeducation should start with detailed research of the mining district of Libanka, its geological, geomorphological, ecological, historical, and cultural values, and their tourist possibilities to enhance education and arouse protection of geological heritage among visitors. These could be carried out by the government through activities such as scientific writing competitions and research grants, as seen, for example, in Geopark Karangsambung Karangbolong (Indonesia) [40], or by cooperation with academic institutions, local authorities, and stakeholders, such as Hateg Country Dinosaurs Geopark in Romania [41].

The mining district of Libanka, as a part of the Dubnik Opal Mines and its wider area, together with Saltworks in Prešov, is part of the area with the potential to become a geopark (Figure 10), as mentioned in the Update of the Concept of geoparks in the Slovak Republic, an official document adopted by the Slovak government [20,42].

The need for information on geological heritage and its interpretation is, therefore, even higher, as it could play an important role in geoeducating the general public as well as students in geosciences with the proper interpretation tools selected. The characteristics of geological heritage could be the stepping stone in doing so. The current geoheritage interpretation and further education in the area are, unfortunately, on a very low level. UNESCO Global geoparks pay major attention to education on-site as well as through websites, seminars, workshops, classes, or activities [45,46]; therefore, they can serve as an example of good practice in geoeducation, geotourism, and geoconservation for a specific area. Appropriate geoeducation, covering human and natural worlds at local, regional, and global scales, can be an essential preparation for an interconnected world [47]. The main objectives of geoeducation and the study of geoheritage, on a larger scale, are understanding how social, physical, and living systems work and interact; knowledge of various cultures, ecosystems, and natural physical systems; the ability to communicate across cultural and geographical boundaries; and analysis of various situations (especially in nature) using the tools and perspectives of different sciences [48,49]. However, considering the establishment of the geopark, including the Dubnik Opal Mines territory according to the UNESCO Global Geoparks program, much work must be undertaken to meet the standards integrating the protection and preservation of Earth heritage sites in a strategy for regional sustainable economic development. In this regard, we find regional networking to be the most important step for further development leading to the definition of future geoparks.

Most of the information provided on-site is limited to the cultural and historical values of the Libanka mining district. Geological heritage is interpreted, to a very limited extent, mainly through guided tours in the Jozef adit, whose focus is also more on the history of the mines. They provide two guided tours, namely for the basic and for the adventurous [48]. During the tour for adventurers (taking up to 5 h), visitors have a special opportunity to visit the Alunogenka tunnel and the Malý hapslik hall and descend to the horizon of the Viliam gallery [48]. Providing information about geological heritage is, however, targeted mainly at the description of heritage without a wider context of its origin and significance. The Jozef gallery, as the only open adit in the whole Dubnik opal mines area, is one of the busiest places in the area of a potential geopark. Construction of geotrails and interpretation panels explaining geological processes standing behind the origin of geological heritage would effectively contribute to geoeducation if communicated well [50,51]. In addition, panels should be simple yet thought-provoking [52] and preferably also include QR codes providing further information [47,53]. The current state of available trails is unacceptable as they can hardly be found due to not being properly marked both on-site and on maps and lacking information panels. Initiating touristic trails would trigger education and touristic development, as well as bring light to many historical mining works in the area. To arouse interest in geoheritage, nature experience trails and discovery trails could be presented [52]. According to the information from the management of Slovak Opal Mines, an educational trail along surface mine entrances (Figure 8) is planned to be (re)constructed in the area. So, the overall tourist attractiveness and geoeducational value of the area will increase. Another option for delivering the message and ensuring knowledge acquirement is via augmented reality accessible by mobile phones [54,55] and leaflets or kiosks [51,56] at the newly built tourist center. The better experience could be accomplished by using together both personal (e.g., guided visits) and non-personal (e.g., audio-visual equipment) presentations of geological heritage [53] (e.g., 4D presentations in Ipolytárnoc, Novohrad-Nógrád Geopark [57]). In addition to the educational tools on-site, there could be educational materials available online or in a tourism center before a trip to ensure the geoeducation. Such tools can be field guides (e.g., in Cuilcagh Lakelands Geopark, Ireland), geotours (e.g., in Bakony-Balaton Geopark, Hungary), field trips (e.g., in Naturtejo Geopark, Portugal), or games and experiments (e.g., Araripe Geopark, Brazil) [45]. Furthermore, activities such as opal finding (already carried out by Slovak Opal Mines) can link education to entertainment (as performed by “Rock Fossils” in Swabian Alb Geopark, Germany [58]).

Information on the geological heritage of the Libanka mining district (or Dubnik Opal Mines) found on the Internet is insufficient, incomplete, or incomprehensible to the general public. The official website of Slovak Opal Mines (https://www.slovenskeopalovebane.sk/ (accessed on 10 September 2022)) shares mainly practical information. Therefore, tourists can hardly obtain any information about the geoheritage of the area and its values. An opportunity to provide more information about geological heritage could be expanding the information provided on the already existing site of Slovak opal mines or through the website of the potential geopark Solivar-Dubník [20]. Based on the examples of some UGGp geoparks websites (e.g., Molina-Alto Tajo geopark, Villuercas-Ibores-Jara geopark, Azores geopark), the information about geological heritage could be available together with educational materials such as textbooks, guide books, and others linked to educational activities [45]. Geological heritage could also be interpreted via a map placed on a website. Kohmoto [59] classified different categories of maps in UGGp geoparks. Category maps of model courses and other maps included information about geosites (already existing) or possible development of their educational use through additional data applied to them. Such maps are interactive as they show data on heritage after the interaction with the user [60]. In addition to the tools accessing the information and methods of communicating it online equally matters. To make the interpretation of geological heritage both appealing and educational, it needs to be provided via different media or platforms and with attention to its comprehension.

6. Conclusions

The importance of the geological heritage of the Libanka mining district within the area of potential geopark Solivar-Dubník is undeniable. Thanks to the mining works, the area has direct access to the geological heritage inside of the Zlata Baňa stratovolcano´s rock environment, which is represented mainly by several mineralization formations. To provide information on geological heritage of the area at specific level using specific interpretation methods, it is important to identify its most important and attractive geoheritage features and further characterize them for educational purposes within the (geo)tourism development activities. Within geoeducation, the interpretation of the geoheritage should be carried out according to the target group [50]. Brocx and Semeniuk [14] consider geo-education as a way to gain geological knowledge through visiting geological sites that can be used for primary, secondary, and tertiary teaching institutions or other geological institutions. In this regard, information about the Libanka geoheritage could be helpful to students in understanding geological matters in situ as a part of a field trip or excursion. The field trips or visits of tourists with some geological knowledge are as yet less represented than those oriented toward the general public. The general public is the largest tourist group and covers a wide spectrum of people with different educational levels [51,61]. As a potential geopark is supposed to be sustainable in the matter of its effective management, attention to the larger touristic segment and its education should be taken into account. In this case, the characteristics of geoheritage should be interpreted in an even more simplified form to be comprehensible to the majority of tourists [47,58]. Furthermore, any geological interpretation should be communicated to tourists using various methods also to entertain them [50,51,62].

In addition to arousing geological knowledge, education about the geological heritage can positively impact the visitor´s attitude toward this heritage and thus create a better understanding of its value leading to the natural need for its protection [63,64]. Characteristics of the geological heritage of the geologically-valuable area mining district Libanka, as presented in this paper, brings an educational value within the area of perspective geopark Solviar-Dubník which can arouse attention to conservation and contribute to sustainable development in the area. Further to that end, there are opal mines of high historical value, providing insights into the natural environment of continentally unique precious opal mineralization.

In this paper, the geoheritage values of the Libanka mining district located in the area of Slovak opal mines were described. Its geotourism and geoeducation potential can be considered as one of the key aspects affecting its geopark establishment. However, there is a long administrative road from one geologically significant area, even globally important, to a geopark. In the recent study, especially when discussing geoeducation, no specific structured data on the numbers of direct and indirect beneficiaries (students, schools, the general public, etc.) were available. Such data are mandatory for effective and sustainable geopark management, and attention must be paid to this aspect. Based on the findings presented in this paper, further research should be aimed at a detailed study of tourists (including their detailed age and academic structure) and their expectations, experiences, and perceptions (via, for example, the field and/or online surveys), effective geoheritage interpretation, involvement of the local community, and sustainable development.