In its latest update (23rd of April 2019), Scandivanadium, the company which is exploring Österlen’s Alum Shale for mining of Vanadium, no longer calls the Dictyonema shale (where most of the Vanadium is located) a shale (or an Alum Shale), but now describes it as the ‘Dictyonema seam’. This sounds probably much more appealing and nicer than calling it an Alum Shale. But choosing a different name does not change the geochemical composition and properties of the Dictyonema seam/shale/formation. It remains the same, even if Scandivanadium decides to call it something different.
The geochemical composition of the Alum Shale (and of all its sub-formations) has been well-known for a long time. Several publications detail with the geochemistry of these rocks and of the underlying and overlying bedrock. To illustrate this I summarize some of the data that was presented in a table in Erlström et al. (2004):
It is easy to see in this Table that the Alum Shale (and the Dictyonema Shale) contain very high concentrations of Vanadium (414 ppm and 3880 ppm, respectively) and high concentrations of Uranium (25,4 ppm and 23,9 ppm, respectively). Moreover both shales are rich in organic material and sulfides. Once the Alum Shale and/or the Dictyonema shale are subject to weathering, oxygen and water oxidize the sulfide minerals. This generates sulphuric acid and leads to a release of metals. Uranium especially is very soluble and eventually ends up in the ground water.
The geochemical composition of the Alum Shale, which is very different from a sandstone or a limestone – as seen in the Table above, thus makes it a very special rock type. If its mining waste or spoil is not correctly taken care of (and so far I have not seen any examples of this), weathering of the remaining processed shale will cause severe pollution of agricultural land and groundwater for a long time.
This last statement is not based on my own ideas, but on numerous publications and analyses that were made in the surroundings of former Alum Shale mines in Sweden, such as in Andrarum, Degerhamn or Kvarntorp. Weathering of the mine spoil from these former mines is today of great environmental concern.
Barbara Wohlfarth 