Zrinski mine

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The area of "Miner's garden" where Zrinski mine is located (150 m southwest from climbers' lodging «Grafičar») is formed of very old rocks, 300 million years, from Paleozoic period. They were formed deep in the earth, and they reached its current position 12 million years ago in a way that blocks of these rocks were moved along large faults in the earth's crust, and finally formed the appearance which is present today.

In the surrounding of Zrinski mine one can notice 3 types of rocks: green and clay schists and dolomites.

Some famous buildings on Medvednica are made of schists, such as Tomislavov dom, Brestovac, Sljeme chapel and many facades of houses.

Schists were named after their distinct appearance of laminated layered structure which resembles pages in a book or puffed pastry. For their genesis these rocks belong to a group of metamorphic rocks because they were formed in earth's depth through metamorphosis of other rocks under great pressure and temperature. Under the influence of pressure and temperature flattened layered minerals were formed which overlapped each other and gave a rock such a layered appearance. Green schists are green and very hard, while clay schists are brown and brittle.

Dolomites are a different type of rocks, belonging to sediment rocks, or more precisely carbonates similar to limestones, which are located in karst area, but dolomites besides calcium contain magnesium as well. Dolomites form the same mine corridors and its surrounding, and are incorporated in surrounding green schists.


Green schistMedieval miner in Zrinski mine surrounded withdolomite rocks

How did the ore get to Miner's garden ?

Similar to a well know Croatian saying «it was brought by water» - in this case it was hot underground water rich with minerals, which came from the depths of Medvednica. As the hot water approached the surface, it became cooler, and what was left as a result of cooling down the water rich with minerals are ore – beds.

For this ore deposit to develop, solutions rich with dissolved lead, zinc, and silver had to flow for a longer period of time. That is the only way a sufficient quantity of ore could develop to intrigue a medieval miner.

Millions of years later those ore – beds became an interest topic of human society, since the survival and economic standard largely depended on available mineral raw materials.

Much larger deposits of lead-zinc ore were formed in a similar way, like the ones in Mežica in Slovenia or Bleiberg in Austria . Such deposits are called hydrothermal from Greek word for water and heat.

Inhabitants of Zagreb and its surrounding probably are not aware that in the past there were silver mines on Medvednica, and Zrinski mine is a proof of mining in 16 th and 17 th century.

Silver mine

Zrinski mine is in fact a lead-zinc ore mine, but we call it silver mine although silver was only an alloy in this ore. Miners had to excavate large quantities of ore, and only after extensive treatment they would reach the valuable ore, silver.

Lead-zinc ore contains several minerals of which galena – lead-glance is most abundant, after which we find smaller quantities of sphalerit which contains zinc, and pyrite, dolomite and quartz.

Galena – the name comes from Greece word “gal” – to shine. It is a gray mineral which contains lead, and in which silver is integrated.

If we scratch the surface of the rock a bit we shall see mineral galena. It is gray, and on hard surface it leaves a gray mark. It is quite heavy but not very hard, since we can scratch it with a nail. If we hit a cluster of galena with a hammer it will crumble into many smaller cubes.

Galena is an important ore and can contain up to 2% of silver, while in Zrinski mine the content is only 0.05%.

Mineral galena

So we come to the most important question, how much silver did the miners get out of galena? Just one half of a kilogram of silver from one tone of galena, which is today considered extremely little. But we have to take into account that the value ratio of gold and silver changed through centuries. Value ratio of gold and silver in medieval ages was 1:13 , by the end of 19th century 1:28 , during 1940's 1:77, while today it is almost 1:100, which probably is the reason the demand for silver decreased.

Based on this, during centuries miners realized they don't have much use because a lot of hard work and effort had to be put in to receive a small 7 cm silver cube. Maybe those are the reasons there is not much data on mining on Medvednica.

Other minerals in Zrinski mine

Sphalerit , zinc sulfide, (ZnS), can be much more difficult to observe in samples from Zrinski mine than galena. It varies in color from gray-brown to bronze or black. It has a wax-like glow, and is somewhat harder than galena but with a smaller specific weight. It leaves brownish to white trail. Its name comes from Greek word “sfaleros”, which means deceptive. Miners often misplaced it for other materials because of its variable color.


Mineral sphaleritMineral pyrite

Pyrite (FeS₂) does not occur in large quantities in samples from Miners' garden, but generally it is one of the more common mineral ores. It takes a form of a small yellow cube with metal glow. Because of the glow and the color people in these parts call it “kitten's gold”. It got its name from Greek word “pyros” – fire.

Dolomite (Ca, Mg) CO₃ is a name of a mineral and a rock. It is related to a more known calcite (CaCO₃) which builds limestone. It is light gray and of medium hardness. It forms crystals with sharp edges, and splits well. It got its name after its finder, a French chemist Dolomieu. Mountain massive Dolomite in Italy was named after this common mineral and rock.


Mineral dolomiteMineral quartz

Quartz (SiO₂) is a very common mineral that occurs in many rock types. Most often it is grayish or white. It often brakes irregularly in shell shape. It is of high hardness, and with a piece of quartz we can scratch the surface of all above mentioned minerals. Quartz builds white quartz veins which can often be noticed on Medvednica.

Mining

Mining in a medieval mine was based on experiences of German and Check miners, and on experiences which were collected in a famous book by Georgius Agricola «De Re Metallica».

In medieval times ore seeking begun with looking for an ore vein by dowsing-rod. Dowsers would walk over a certain terrain looking for ore vein, when the rod trembled they knew they found ore (the force of an ore vein moved the rod). At that spot excavation of ore would begin. Vertical shafts were excavated first. On the surface above the shaft they would construct eaves with a pulley, and with a rope and wooden or wicker baskets they would haul the ore to the surface. Later on vertical shafts would be connected with horizontal corridors.

Work day in medieval mine would last 10 to 12 hours. Darkness and high moisture, coldness, dust and inadequate ventilation of the mines was everyday life for our and other European miners. Miners usually worked in pairs with very simple tools, a hammer and a wedge, and the underground was illuminated with oil-lamps. With these simple tools one miner would daily pick only 3-4 cm of rock in depth. It is presumed that 30 miners worked daily, and they could excavate about 10 tons of ore that contained 5 kilograms of silver.


Pictures from the book “De Re Metalica” by Agricola: Search for the ore and Transport of excavations


Exit from the mine in green schists

PUBLIC INSTITUTION "NATURE PARK MEDVEDNICA" opened this mine for tourists on St. Barbara day, December 4 th , 2004, the patroness of miners, which was under reconstruction for a long period, as to be safe and attractive for visitors. 

see Park offer – Zrinski mine