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Welcome to the volcano

When you came to Banská Štiavnica, you, in fact, found yourself within the territory of one of the largest volcanos in Europe. It is called the Štiavnica stratovolcano. And although dormant at the moment, it can talk in its sleep about why large deposits of gold were created right here and why a great part of them has not yet been discovered. The only thing that the volcano keeps a secret is its next wake-up date.

When a series of volcanic eruptions occurred in the shallow warm sea which once covered our region, a ring of volcanic mountains arose approximately 50 to 100 kilometres from the then Fatra-Tatra mountainous coast. Today, this ring spreads from the Kremnica Hills, through the Štiavnica Hills, the Poľana and Cerová Mountains in Slovakia, the Matra, Bükk, and Tokaj Mountains in Hungary, and ends again in Slovakia in the area of the Slanské Hills. Resource: Dušan Kočický

Lost (strata) and found (gold)

A stratovolcano consists of ‘strata’, which means ‘layers’ in Latin. They are formed when periods of lava eruptions alternate with times when ash and volcanic fragments are blown out of the volcano. In this way, layers of hardened lava and softer tuffs (light, porous volcanic rock) are created. When the stock of magma was partly used up, the Štiavnica stratovolcano fell asleep for hundreds of thousands of years. While it slept, the inside of the volcano cooled down and collapsed, thus creating something like a cauldron (caldera). At the same time, cracks were created, through which water seeped deep into the cauldron. At those great depths, it was as if the water was in a pressure cooker; high pressure and temperature caused minerals to dissolve, and as this mineral water rose to the surface, it gradually cooled and the minerals crystallised – each at a different temperature and depth. Gold and silver solidified closest to the Earth’s surface.

Three main stages in the Štiavnica stratovolcano’s development. Resource: Dušan Kočický

This is the way Gregorius Agricola (1494 – 1555), considered the founder of mineralogy, depicted gold panning at a river. The picture is from his publication Twelve Books on Mining, which was the most used guide for ore mining and smelting for about 200 years. Resource: Boston Library Consortium Member Libraries

Gold-bearing gangue in Hodruša mine – at a depth where, theoretically, no gold was supposed to be found. Resource: Lubo Lužina

The hill beneath the Calvary: a cone pastry without the egg liquor filling

You already know that the Štiavnica stratovolcano fumed volcanic clouds mainly in the Tertiary period (65 - 2.5 mil years BCE). One more wave of volcanic activity shook future Slovakia in the Quaternary period, too. Fortunately, thanks to it, Štiavnica’s Calvary can tower atop the hill of Scharffenberg.

Approximately 2.5 mil years ago, when the Štiavnica stratovolcano had been ground down almost to what it looks like today, things began to happen in its territory, and elsewhere, again. Experts call these things the basaltic wave of volcanic activity. As a result of this activity, Cerova Mountain near the town of Rimavská Sobota, Putikov vŕšok Hill near the village of Tekovská Breznica, and the Scharfenberg of Štiavnica developed. This is how it happened for the Scharfenberg: In the middle of a sleeping volcano, underground forces pushed up a smaller, basaltic volcano. For a while, it gushed everything a good volcano could, but at a certain moment, lava ceased to flow out of the volcano, and it began to look like the chocolate-coated cone pastry (called “špic”), which is so popular in Slovakia. Instead of the chocolate coating and cream filling, the volcano was covered by less tasty volcanic ash and, instead of the egg liquor inside, the volcano contained basaltic lava. The lava solidified, like pastry cream put in the freezer. Our little volcano in the middle of a bigger one began to be weathered, until only a basaltic thumb, covered by debris, remained. At that time, it did not even remotely remind anyone of the tasty cake. Only when the Calvary was built on the little weathered volcano was it given the kind of decoration that any confectioner would be proud of.

Contours of the caldera (volcanic cauldron). They are best seen from the treeless locations on the Tanád ridge or from the Farárova hôrka site. Resource: Lubo Lužina

Occurrence of veins in Banská Štiavnica and its surroundings. Resource: Lubo Lužina