Field trip to the Harz Mountains

Rammelsberg
Rammelsberg Mine

October 24th to 28th 2013

The Harz Mountains are a fault block mountain range in northern Germany, situated at the junction of the states of Lower Saxony, Saxon-Anhalt and Thüringen. Known in Latin as Herzynia which gave its name to the alternative term for the Variscan Orogeny, namely the Hercynian Orogeny.

The area is famous for its rich and varied geology and historical/archaeological mining. Therefore the aim over the following three days was to see as much as possible from the varied geological exposures, and visit some of the mining sites that make this area so well known.

Day 1, Friday October 25th

Rammelsberg Museum & Besucherbergwerk (mining museum) situated on the outskirts of Goslar.

After a hearty breakfast in the Lodge Hotel Goslar, which was to be our base for the weekend, we set off on foot to the Rammelsberg Mining Museum. Gerd said “it’s only a gentle 10 minute walk”, however over the weekend we were to learn that Gerd’s idea of distance and time varied somewhat to what the majority of us considered gentle and not too far.

Gerd’s gentle walk was a steady uphill climb of around 1 km and took more like 20 minutes to complete. The Rammelsberg is actually 635 metres high; fortunately for us the mine is not at the peak but some 450 metres below it. But what awaited us there was well worth the after-breakfast exercise!

Rammelsberg
Outside Dr Lothar Klappauf's office

Within the mining museum complex are the offices of the “Niedersächsisches Landesamt for Denkmalpflege” (something like a Federal Heritage Agency). There the man in charge, Dr Lothar Klappauf, gave us a tour of his department and a brief explanation of their work, before taking us to the site of the archaeological dig that was discovered within the grounds of the Rammelsberg Mine.

This again consisted of another uphill walk of around 1 km through the mine surface buildings and road ways to the edge of what originally was the opencast mine, in use before mining at the Rammelsberg was continued underground.

excavations at Rammelsberg
Rope found at the excavation site

At the dig we were shown were they had found a leather shoe sole, which after radio carbon dating gave an indication that it was from the beginning of the 11th centuary. This would indicate that the site was being actively mined from possibly around the 10th centuary.

Another of their interesting finds was a length of rope thought to have been used to pull the ore wagons by horses, as evidence of hoof and wagon wheel prints have been found in the ground.

The thought is that this site was being worked through old opencast mining debris, by driving shafts and tunnels to get to the copper rich veins which had become unworkable using opencast mining methods.

weathered mining debris
Old mining debris that was covering the excavation

This was due to the depth of the vein and also the danger of the working face collapsing on the miners. This debris is rich in lead but was not of interest to the early miners. Copper was their goal, the ore was then transported to smelting sites all over the Harz Mountains, this was easier than moving the large amounts of timber that were required to smelt the ore to the mine itself. This timber had then to be converted to charcoal before use.

The Rammelsberg Ore body was formed by the escape of hot metal bearing thermal springs on the sea floor which today we call “Black Smokers”, during the Devonian period.

excavated mining tunnel
Tunnel remains all original

Two large lenses of ore were formed which were later caught up in the folding of the rocks during the Variscon or Hercynian orogeny and now lie overturned at an angle to the mountain.

The ore body is a sulphidic microcrystalline copper and lead/zinc composition, and within the upper Harz are also found coarse sulphidic lead/silver ores. The mining of these ores started in the 10th and 11th century at opencast sites (old bed) and after the discovery of the (new bed) in the 19th century continued with tunnels and shafts into the mountain.

Industrial extraction continued at the Rammelsberg Mine until June 1988 when the mine closed. Officially this was because deposits were mainly worked out, but the local version is slightly different, in that they believe it was the difficulty in finding sufficient young miners to continue the extraction of ore, which was the reason for closure.

In 1992, the Rammelsberg Mines and the historic influenced Old Town of Goslar were entered on the UNESCO World Cultural Heritage List.

Ore-bearing rock, Rammelsberg
Rammelsberg ore rich in copper

Industrial extraction continued at the Rammelsberg Mine until June 1988 when the mine closed. Officially this was because deposits were mainly worked out, but the local version is slightly different, in that they believe it was the difficulty in finding sufficient young miners to continue the extraction of ore, which was the reason for closure.

It is estimated that in this 1000 years of mining, 30 million tonnes of Rammelsberg ore have been extracted. A typical ore body is around 14% zinc, 6% lead and 2% copper with some traces of gold and silver. The picture which is a sample of Rammelsberg ore shows on the right hand side how the ore can be polished due to the high copper content.

After lunch Dr Klappauf’s good friend Herr Friedrich-Albert Linke showed us how to find some of the 3000 year old smelting sites used by early man to extract tin, lead and copper from surface ore deposits exposed by erosion.

After a short bus journey from Goslar up into the surrounding forest area, we arrived at the location of our attempts to discover a smelting site. The method used is very simple, but as we were to find out, 100% successful.

The Method

> First find a small stream that has made its way down the hillside through the pine forest.

> There you look for traces of slag in the stream bed and if you are successful and find some, you then follow the stream uphill whilst continuing to look for slag deposits at regular intervals.

> Eventually the slag can no longer be found in the stream bed.

> At the point where you last found slag, start looking around for small mounds without any vegetation growth (the slag inhibits the growth of vegetation). If you spot one (which we did), start digging and low and behold large lumps of slag started to appear.

> There you have it: one more prehistoric smelting site discovered by the OUGS ME.

slag from Middle Age mining
Slag deposits found in stream bed

If the slag you find looks like the example on the left in the picture, then they managed to extract copper, lead and tin from the ore using charcoal. However, if it looks like the right example, only lead and tin were extracted, because they had only used wood as a source of heat. The temperature of burning wood is about 200 degrees short of the melting point of copper, which requires the higher burning temperature of charcoal to extract it from the ore.

Using this method, Herr Linke and his colleagues have up to now found some 1600 smelting sites in the surrounding area, well thanks to the OUGS ME that is now 1601.

As an added bonus to all the activities of the day, we had the opportunity before setting out to look for slag, to visit the Roeder Gallery at the Rammelsberg Mine.

Here we joined one of the guided tours around the 200 year old gallery system. It consists of a network of galleries, water wheels and shafts. We followed from the surface the route of the water, channelled into the mine to set four wooden water wheels in motion. Two of the wheels served to transport ore out of the mine, the rotary motion of the wheel used to drive a winding drum which allowed an empty ore bucket to be lowered down the shaft whilst at the same time hauling a full ore bucket up the shaft.

Water wheel control beams
Water wheel control beams

By using two wheels set side by side but having the paddles set in opposite directions, the water could be directed to either side of the wheel, and so the direction of rotation of the water wheel could be alternated to allow continuous movement of full and empty ore buckets up and down the shaft. The wheel also had a braking system, used to stop the ore buckets at the top and bottom of the shaft.

This was all controlled by a man at the shaft bottom, using a system of wooden beams running along a tunnel 80 metres long to the wheel itself.

The remaining two wheels were used to lift water out of the mine; water for the wheels came from the Herzberg Pond built in 1561 and created to ensure that a continuous supply of water was available even in times of drought.

This all seems very straightforward until you realise the size of these wheels: the two ore transportation ones are 7 metres in diameter and the pumping ones 8 metres. They were constructed over 200 years ago underground, using candles and crude oil lamps as the only source of light, in very wet and confined spaces using basic hand tools. Yes, as you may have guessed we were very impressed with what we saw and were told during our tour of the Roeder-Gallery.

Terry Warrington

REFERENCES:

Dr Lothar Klappauf.

Herr Friederich–Albert Linke.

Rammelsberg Museum & Besucherbergwerk literature

Wikipedia: Harz Mining.

Day 2, Saturay October 26th - Geology in the Southern Harz.

We journeyed to the south end of the Harz near Osterode and met up with Dr Firouz Vladi, a gregarious character brimming with scientific and local knowledge. He took us into the forest in Düna, a protected area he explained, which had never been clear-felled since it appeared at the beginning of the present interglacial.

The forest and indeed surrounding area sits on gypsum deposits created when the locality formed part of the famous Zeichstein Sea during the Permian.

sink hole
Fig. 1. A sink hole

During the late 80’s a severe summer storm allegedly swept through the forest and the remains of many trees still litter the forest, however it is also known that Gerd was in the locality around this time and he has never satisfactorily accounted for his whereabouts.

At first the forest appeared to contain more sink holes then mushrooms, the former are the result of collapsing gypsum caves, themselves created by anhydrite layers rehydrating and swelling as they approach the surface.

mushrooms
Fig. 2. The white slimy mushrooms

In previous centuries, cracks and channels connecting these caves were often found to contain the remains of such exotic creatures as (woolly) rhinoceros and elephants which may have been hunted by Neolithic man or escaped from a passing circus. Such finds stimulated the debate on evolution. Fortunately these creatures are no longer in the area, instead as we pressed into the forest the mushrooms became more plentiful. Apart from the old faithfuls, abundant examples of round brilliant white mushrooms were found under the leaf litter, covered in a slime with the consistency of egg white (Fig. 2.)

sluggish salamander
Fig. 3. The self-propelled mushroom (aka. a salamander)

Near a large sink hole whose water content fluctuates with the water table and appears to lag precipitation by 21 days, a large yellow and black self-propelled mushroom was spotted. Sluggish in the autumn temperatures, it obligingly posed for photographs.

Inspired by such finds and the tales from our guide, we set off to a cave where the local population took refuge during the allied advance of 1945. It is known the only villager to die was one unfortunate lady who returned to find her donkey. The fate of her donkey has never been established.

cave in Southern Harz
Fig. 4(a). The bat cave

Dissolved gypsum causes subterranean lake water to become heavily stratified and this stratification in return exerts a strong control over cave morphology, giving them uniformly flat ceilings and 45° walls. We had a look in the cave but of far more interest was the tale of Bronze Age skeletons - and the diverse mushrooms around the area.

mushrooms
Fig. 4(b). Mushrooms around the cave
mushrooms
mushrooms
Mushrooms around the cave

After this, we embarked on a long hike through the woods, stopping to gain insights on how the recent glaciations (and interglacials) have contributed to the landscape we see now. Halfway through the hike our convoy was interrupted by a herd of particularly boisterous cows (of Bavarian origin most like). In good spirits and buoyed by the warm sunshine the group decided on a route which put at least 500 extra metres between me and my sandwiches. We did however find some stones which when beaten released a strong odour of natural gas. These were identified as dolomites.

mushrooms
Fig. 5. Mushroom city

After the walk we drove off to a café next to a big white rock for lunch. Its garden contained numerous mushrooms, sheep and geese. The bockwurst and ”einbecker” beer were rudimentary but the cherry waffles were reckoned to contain some 3,000 calories. A castle used to sit atop the big white rock but the French blew it up after the “Seven Years War”.

After this we set off to look at some more rocks at the “Hammersteinklippen”, the forest around which were filled with mushrooms (Fig. 5.), more then you could shake a stick at. There was a nice view from the rocks which were almost 100% quartz – although nobody could decide on a name or a metamorphic grad, that they were indigestible was however not disputed. Despite our best efforts with hammers, some rock remained after our departure and any subsequent visit will require dynamite.

Hammersteinklippen
Hammersteinklippen
glade in a cornifer forest
Walking in the woods
mushrooms
Fig. 8. Mushrooms by the mysterious wall

Returning through the woods, we looked at a dry stonewall, possibly a Neolithic enclosure but also a fantastic location for mushrooms (Fig. 8.). There was also a block of salt nearby which hunters placed to lure deer and Gerd explained the intiricices of German hunting.

After this, all geologied out and despite the unfortunate lack of rain, we jumped in the bus and headed for the hotel and our enjoyable dinner at the “Brauhaus”.

Ciarán Costello

Sunday October 27th

After meeting our guide for this day, Dr. Friedhard Knolle, we started our trip in Goslar with a trip to the Klusfelsen (Klus rock).

This rock was being tilted from horizontal layering to nearly vertically and so you are able to look at the downside (footwall) of the strata at the back of this rock.

Klusfelsen
Fig. 1: The Klusfelsen

The structures which you can see are therefore not the boundaries of horizontal layers, they are more like bedding or cross-bedding structures.

All strata at the northern foreland of the Harz Mountains is tilted vertically and so you can walk through Mesozoic times and sediments – with every step you walk across several million years, getting to the older strata towards the northern rimof the Harz.

Doing so, we reached the Goethe-Steinbruch (Goethe quarry), named after one of the most famous German poets, Johann Wolfgang von Goethe.

Blast furnaces
Fig. 3: Blast furnaces in the Harz "countryside"

We left Goslar, heading to the historic center of the mining industry in this area, where the ore was brought to the blast furnaces.

Today, the soils of this area are highly contaminated with toxic heavy metals.

In the background of figure 3, you can see the famous Langenberg-Steinbruch (Langenberg quarry, figure 4), where the tilted strata is beautifully exposed and can thus be easily studied.

Langenberg quarry
Fig. 4: Langenberg quarry

This strata was tilted more than 90° to the west (to the right in this picture). A few years ago, a new species of dinosaurs was found at this site.

You can see our expedition group at the edge of this quarry – also looking for some nice small fossils at the ground.

Spheroidal weathering
Fig. 6: Spheroidal weathering

We then left Langenberg and the Mesozoic southwards to enter the Paleozoic and the central region of the Harz, heading to a place which showed us that granite is not as hard and resistant as you might have thought. What you can see in figure 6 is the erosion of granite from the plutonic rocks of the Brocken (the highest mountain at the Harz).

Note the hammer for scale, showing that only medium sized rounded blocks of granite are left and the rest is more or less pulverized to small grains.

This is achieved by continuous change between warm and cold temperatures and freezing water inside small fissures, cracking the rock.

outcrop of Harzburgite
Fig. 7: Harzburgite (outcrop width is ca. 4 m)
thin section of a Harzburgite
Fig. 8: Sketch of a thin section of Harzburgite

We finished this very interesting field trip with a visit to a real type locality: Harzburgite!

While our guide Dr. Knolle was explaining the peculiarities of this type of rock, we were able to collect some samples of it, which had fallen down from the outcrop. Inspecting them with our hand lenses, we were able to see olivine and pyroxene, just as this nice sketch of a thin-section (displayed next to the outcrop) is telling us.

Stefan Mohr

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