Geology & History of the Gastein Healing Gallery

The rock deposited in the Pennine Ocean (the ancient Mediterranean Sea) between Europe and Africa prior to the formation of the Alps as a result of continental erosion could only escape the enormous pressure exerted by the northward thrust of Africa by rising upward (folding) and moving sideways (east and west). The resulting east-west stretching of the rocks created numerous north-south-oriented, steep faults, which cut the new mountain range into several sections at great depths. One of these rifts also divided the later Gastein Radhausberg mountain into two halves forever, which were also moved horizontally relative to each other. This rift ultimately formed the geological prerequisite for a massive mineralization process (hydrothermal sulfide mineralization) in the final phase of the Alpine orogeny.

The great pressure from the weight of the overlying gneisses mobilizes non-ferrous metals from the underlying Paleozoic shales of the Habach Formation. The precious metals contained therein are pulled upward solely due to the existence of this deep fissure (zone of complete pressure relief), with the predominant transport medium being silicic acid (SiO2), which is also squeezed out of the rock. As the metal solutions rise, they cool and crystallize, filling the cavities of the vein fissures with ore. The outgassing of silicic acid in the uppermost areas leads to the formation of sulfide-rich quartz druses with isolated free gold crystals (glass ore).

After mineralization was complete, the entire Radhausberg was torn apart a second time by the alpine mountain-building forces, which were now slowly coming to an end. This resulted in the formation of shallow relaxation fractures close to the surface in the gneiss, whose fracture surfaces were completely ground down by strong relative movements. The abrasion forms a fine-grained and largely watertight, clayey sediment in the fracture zones. Pressure and temperature are no longer sufficient for the possible migration of ores into these structures, which remain largely barren. (Miners would later refer to these structures as "foulings").

This was followed by a long period without any further significant geological events. It was not until the end of the last global glaciation about 10,000 years ago that the formation history of the Gastein healing springs continued. The melting of the kilometer-thick ice sheet quickly led to a huge supply of free surface water, which on the one hand began to slowly erode the flanks of the mountain, but on the other, especially along the western slopes, was relatively quickly diverted into the interior of the mountain. The porous gneiss can absorb large quantities of meltwater in this way and slowly channel it deep underground along its eastward-sloping schist surfaces. The underlying schist, on the other hand, forms a natural water barrier. The high rock temperature at great depths has time to take effect, the water warms up, reduces its specific weight, and thus rises again. As it rises, it cools down once more (decrease in rock temperature, mixing effects with cooler water flowing in, etc.), so that a large-scale cycle can eventually develop.

A major part of the meltwater is thus trapped in the gneisses of the Radhausberg for a long time and dissolves the trace elements it contains, such as radium, chromium, and fluorine. The metallic radium salts dissolved in the water decay into gaseous radon, but only after enrichment with fluorine salts can the waters attack and dissolve the metals in the ore vein. Suddenly, an excellent path emerges for the radon water to rise along the emptied vein back towards the surface. However, a layer of clayey sediments, which is insurmountable for the water rising from the depths, stops this process and protects the ore vein from further leaching.

At the same time, at the end of the Ice Age, the geometry of the mountain also begins to change significantly. The valley flanks are heavily eroded and deepened by the melting glaciers, so that the hot waters can now emerge and flow away via numerous springs, especially on the western flank. A first natural spring horizon forms, the remaining ore vein above it is saved from further leaching and is once again at rest.

Several thousand years later. The Radhausberg has essentially taken on its present form. Further erosion of the valley flanks also causes the exit points of the thermal water (altitude of the springs) to sink steadily until the thermal water level in the mountain finally reaches its present height. The surface water that continues to seep in on the western flank of the mountain pushes the thermal water out of the springs, similar to a bucket filled to the brim and overflowing. This bucket was filled during the Ice Age, and its rim is the current spring horizon.

But the long period of rest for the residual ore vein is already over. Now that word has spread about the healing powers of the springs at the foot of its mountain, its rusty brown head (oxidized outcrop zone) is attracting numerous adventurers and miners to the valley, who are now going at the mountain and its precious metals from the surface. The vein defends itself with all its might (trapped mine water, harsh and long high-alpine winters, complicated ore transport, etc.) – but nevertheless: historical mining mercilessly snatches its treasures from depths of approx. 400 meters. Then the hand-operated technology of that time reaches its limits; further advancement into the depths is impossible, even though the precious metals continue to beckon. In some places, the miners had already reached the great decay zone, and they secretly puzzled why the rich ore suddenly came to an end here. While most seemed to attach little importance to the question, others were certain that the mineralization must continue deeper down.

The Radhausberg and its treasures have now been annexed and are part of the German Reich. Using state-of-the-art technology, a new access tunnel to deeper sections of the ore vein is being driven from the eastern flank of the valley. This promising attempt, known as the Paselstollen, takes just under two years and, at the end of 1944, after 1,840 meters, actually reaches the ore vein approximately 400 meters below the historic mine.

However, the Berlin Reich Ministry of Economics at the time was greatly disappointed to learn that no ore could be found in the vein. Even a 120-meter-high excavation shaft in the vein revealed only empty, depleted cavities filled with hot steam, which had heated all the rock in its vicinity to over 40 °C. Shaking their heads, the German miners left this tunnel, which they considered worthless; once again, the mountain had prevailed.

It was not until the early 1950s that the radon content of the hot steam in the Paselstollen mine was discovered and the connection with the famous Gastein thermal springs was recognized.