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.
A volcanic star is born
When our globe was 20 million years younger, a warm sea spread over this area. The seabed was a thin layer of the earth’s crust that any stronger earthquake was able to tear up. And, there was no shortage of those in the Tertiary time period. Through deep cracks, hot magma surged to the surface – in some places, there was more magma, in others, less. In the area of the Štiavnica hills, there was more of it. About 16.5 million years ago, countless eruptions formed the volcanic cone of a gigantic stratovolcano. It was about 4 kilometres tall (almost like the Matterhorn) and covered the area from Levice to Zvolen, and from Nová Baňa to Krupina. The southern part of the stratovolcano bathed in the sea and had no idea it was the largest volcano in central Europe, for no Europe existed at that time.
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.
Had there been no erosion, the hike up to the top of Mount Sitno would have been four times longer than it is today. The appearance of the stratovolcano today and the discovery of almost 150 minerals within its area are the result not only of a frequent alteration of the volcano’s active and quiet periods, but also of erosion. Wind, storms, water and glaciers transported the eroded rocks away and wore about 3 kilometres off the volcanic cone. Thanks to that, ascending Mount Sitno is a pleasant hike today, not a fight for life. In addition, particles of gold from eroded veins settled in the alluvia of creeks and rivers to delight the eyes of every person walking up-stream to for pan gold.
How did people learn that they would find gold in Štiavnica?
Forget about the lizards. Also, about any other animal carrying a glistening golden nugget in its mouth, which is said to have alerted people to the deposits of precious metals in the surroundings. To discover a golden vein in Štiavnica was harder than following in the footsteps of an animal to find a golden treasure.
If you have carefully read the part on tourist-friendly erosion, then you know that the Štiavnica stratovolcano eroded for hundreds of thousands of years and that water was gradually washing away the gold. Small streams carrying the gold flowed into rivers, and those into other rivers. And those other rivers (for example, the Danube) were, therefore, richly gold-bearing. This did not escape the attentive eyes of the first gold hunters. We do not know when this happened, nor have we any idea as to why the first gold hunters decided to become gold hunters. What we know for sure is that they were called prospectors, and that they panned for gold, travelling upstream in the rivers. And as they explored, they went from one river to another, eventually reaching the place where the washing-away of gold began. It is assumed that prospectors came to this area from both the Ipeľ River and the Hron River sides. And this is how the tale of Banská Štiavnica began.
Why is there gold where it is not supposed to be?
According to various estimates, from 55 to 200 tonnes of gold have been extracted from mines in Štiavnica and its surroundings. It is said that about 100 tonnes are still underground. However, nobody knows where exactly. Will you set off on a search? We will help you a little.
As we have already mentioned, both gold and silver minerals crystallised very near the earth’s surface; at depths of 100 – 150 metres at the most. Therefore, it was a great surprise when, in the nearby town of Hodruša, gold was discovered 500 metres below the surface. How is it possible? Some experts assume that the centre of the stratovolcano is surrounded by an outer ring, in which there are great deposits of gold. The latest geological survey has found that, at a certain stage of the Štiavnica stratovolcano’s development, a giant lump of granodiorite lava began to be formed in the stratovolcano’s centre. Due to strong pressures pushing up from the bowels of the earth, this fiery potato ascended higher and higher, melting everything that got in its way. However, it managed to cool before reaching the surface. Now it is stuck inside the stratovolcano, having golden embellishments at some parts of its edges. Where these places are remains a secret.
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.