Erzberg Mine in Austria: An iron ore reserve with a long tradition
Dr Robert Sturm (Austria)
The Erzberg Mine is situated in the Austrian county of Styria. From a geological point of view, it belongs to the so-called greywacke zone, which represents a band of Palaeozoic metamorphosed sedimentary rocks intercalated between the Northern Limestone Alps and the Central Alps. The Erzberg Mine is the world’s largest deposit of the iron mineral siderite (FeCO3), which is mixed with ankerite (CaFe[CO3]2) and dolomite (CaMg[CO3]2). Due to this mixture of different mineral phases, the concentration of iron ranges from 22% to 40% and adopts an average value of 33%. The annual output amounts to about two million tons of iron ore, which is transported to blast furnaces in Linz and Leoben-Donawitz. According to current estimations, the ore reserves will allow mining activity for another 30 to 40 years.
History of the Erzberg Mine
There are lots of myths regarding the founding date of the iron mine on the Erzberg. According to the opinion of several scholars and a few written documents of dubious veracity, the mine was already established in the year 712, which would imply a use of the deposit by Slavic peoples. However, there exists better evidence that foundation of the mine took place in 1512, which was also the inauguration year of the Oswald church in the village Eisenerz.
First documentary mention of the Erzberg Mine is from 1171. In the fourteenth century, the Reigning Prince of Styria published a decree, according to which the mining of iron ore, the production of unrefined iron and its further processing were clearly organised. The upper half of the Erzberg Mine was exploited from the village of Vordernberg, whereas the lower half of the deposit was tapped from the village Innerberg, today’s Eisenerz.
A horizontal line a heightt of 1,186m, the so-called “Ebenhöhe”, partitioned the mountain into the two mining areas. According to a further decree from the year 1448, the sales areas of the iron were subject to a division: the north of Europe was supplied by Innerberg, whereas southeast Europe, including the area ranging from Venice to the Levant, received iron from Vordernberg. The two villages, Steyr and Leoben, were advanced centres of the iron trade and thereby gained great prosperity.
Until the introduction of rock blasting by black powder in the year 1720, quarrying of the iron ore took place in a spacious system of mine-workings. Single tunnels were driven into the rock using only hammers and chisels. In the second half of the nineteenth century, black powder was successively replaced by dynamite, representing a much stronger explosive device. Nowadays, modern emulsion explosives are used for open-cast mining.
Under the reign of Archduke Johann (1807-1859), iron mining experienced a great upswing, from which the whole region benefited. Underground mining ceased in the year 1986, whereas open-cast mining is still continued, with ore exploitation taking place up to the twenty first level of the 44 levels at Erzberg.
Current mining activity on the Erzberg
Today, the Erzberg Mine represents the largest open-cast mining system in Europe. The total amount of exploited material (iron ore and country rock) is 7.2 million tons per year with an ore-to-country-rock ratio of 3 : 7. About 50% of the iron ore exploited from the mine is already present in pure form, so that it can be directly transferred from the mining level to the crushing and sieving system, and finally to the ore deposited. The other 50% has to undergo a concentration process, including magnetic and heavy liquid separation.
In a single explosion, 40,000 to 60,000 tons of rock are released. The daily amount of ore transferred to the steelworks in Linz and Donawitz is about 6,000 tons. For the transportation of the rock material, seven heavy-duty dumpers, with a load capacity of 120 tons, three medium-sized dumpers, and four large-scale wheel loaders, are available. The size of the workforce, including miners and non-mining staff, currently amounts to 220 persons.
Extraordinary mineral finds from Erzberg
The most impressive mineral find originating from the mine on the Erzberg Mine is the so-called “flos ferri”, which was described for the first time by the German physician, Georg Hieronymus Welsch, in 1675. It was also included in the second edition of JG Wallerius’ “Systema Mineralogicum” from the year 1778. According to a geological study published by K Redlich, in the year 1916, “flos ferri” corresponds to nothing else than aragonite crystallising with a fibrous or, in extreme cases, with a vermiform structure. The mineral was formed wherever cavities were available for its undisturbed crystallisation. It normally adopts a snow-white colour, but may be azure, if it contains enhanced concentrations of copper.
Besides its fibrous and vermiform appearance, aragonite may also crystallise as needles of different sizes, which are arranged to partly imposing mineral levels. Furthermore, the mineral may occur as sintered stone, which is formed by continuous sedimentation processes. Other minerals occurring as large geodes are ankerite, siderite, dolomite and calcite. Also azurite, malachite and vermilion form rather eye-catching crystals.
Less common mineral species found in the Erzberg Mine include erzbergite, ranciéite, sideroplesite, dravite, enargite, epsomite, chalcanthite and others. More detailed information on the mineral world exposed in the Erzberg Mine can be obtained by visiting the show mine, where visitors can explore the tunnel system on the mine railroad, observe the miners during their demolition work and enter the museum with its gallery of highly impressive mineral finds.
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Prochaska: Genetic concepts on the formation of the Austrian magnesite and siderite mineralizations in the Eastern Alps of Austria, Geologia Croatica 2016, Vol. 69, 31-38.
Redlich: Der steirische Erzberg, Mitteilungen der Geologischen Gesellschaft in Wien 1917, 9. Jg., H. 1-2.