In my e-mail correspondence I found some lines from Scandivanadium’s CEO David Minchin, where he writes that since the Vanadium bearing Dictyonema Formation sits on top of the Cambrian Alum Shale, Scandivanadium will not have to dig up the Alum Shale. He also writes that the layers that are on top of the Dictyonema Formation do not contain metals and can be used as fill for the future mine.
Both statements are correct. However, the Dictyonema Shale or Formation is an Alum Shale. I have earlier written a blog about this and tried to explain that although the lower Ordovician Dictyonema Shale (or Formation) is younger than the Cambrian Alum Shale, it is still an Alum Shale.
I was curious to hear a bit more details from Scandivanadium, so I sent them the following letter:
Dear Mr Minchin,
I have been in e-mail contact with Mr XX, who forwarded me your e-mail address.
I am curious about your definition of the Dictyonema Formation and its relationship to the Alum Shale. As I understand it – and as it is stated in the geological literature, the Dictyonema Formation is part of the Alum Shale and has the same properties and almost the same geochemical composition as the underlying shale. I have however heard that Scandivanadium believes that the Dictyonema Shale is very different from the Alum Shale.
Therefore it would be great to hear from you directly how you look at the Dictyonema Shale. Do you regard it to be different from the rest of the Alum Shale? And if so, what would be your arguments for this.
Kind regards
Barbara Wohlfarth
The answer I got after about a week was not from Scandivanadium, but from one of their contracted geologists:
Good day Professor Wohlfarth
I have been forwarded your question on geology by David Minchin, CEO of ScandiVanadium. Micon is an international geological consultancy, we are acting as Qualified Person for ScandiVanadium.
With regards to your query, Micon’s understanding is that the Ordovician Dictyonema shale shares many physical similarities with the Cambrian Alum Shale, and hence are often grouped together. However the Dictyonema shale presents a number of subtle paleontological and geochemical differences which reflect the gradual freshening of the basin from anoxic conditions in the Mid-Cambrian.
The Dictyonema shale hosts the return of benthic bivalve communities, an indication that oxygenated oceanic conditions continued to the sea floor. Changing oceanic conditions are also reflected in the geochemical differences, with increased biogenic contribution of elements such as vanadium and decreased chemical precipitation, best reflected in the lower sulphur.
This geological interpretation has been based on a number of published and unpublished datasets as well as personal communication with experts in the field. Additional information on the Dictyonema shale, including distribution of various metals, will be collected by drilling the seam as part of ScandiVanadium’s planned exploration programme.
Kind regards
Andrew de Klerk, B.Sc.(Hons.), Pr.Sci.Nat., SAIMM
Senior Geologist, Micon International Co Limited
adeklerk@micon-international.co.uk | www.micon-international.com
This answer was a bit confusing. Also, I could not understand why Scandivanadium’s geologist did not answer my question directly and needed a separate geological consultancy firm to answer me. But I have now spent some hours reading up to at least find out how correct the above statement from Micon International is.
Let’s start with sulphur issue. Westergård’s (1944) investigation of drill cores in Andrarum and Gislövshammar shows the following: In the lowest part of the Alum Shale, average sulphur contents are 4-5%. The sulphur content increases in the middle part to a mean of 6% and decreases again in the Dictyonema Shale to a mean of 3%. Buchardt et al. (1997) analysed a later Gislövshammar drill core and measured a sulphur content of between 2-4% in the Dictyonema Shale. The sulphur content is highest in the part where the Vanadium content is very high, but decreases to less than 2% in the uppermost part. So yes, the sulphur content is lower in the Dictyonema Shale, as compared to the underlying shale. But it is still much higher than in the overlying shales and limestones.
And now a few sentences regarding “the return of the benthic bivalve communities and oxygenated oceanic conditions”. Schovsbo (2007) writes: The Scandinavian Alum Shale Formation (Middle Cambrian to Lower Ordovician – this includes the Dictyonema Shale) accumulated under generally low oxygen concentrations. And the popular science article by Buchard et al. (1997) (PDF available below – in Danish though) suggests that the sediments that would later become Alum Shale accumulated on the shelf and in a water depth of between 50 and 200 m. Bottom waters in this former ocean experienced alternating shorter anoxic (oxygen-starved) conditions and longer dysoxic (= very low oxygen content) conditions. Thus, the ocean, where the sediments were deposited, was not oxygenated.
Regarding the fossil content of the Dictyonema Shale, I could not find much evidence for a return of benthic bivalves. The shale is dominated by graptolites, whereas trilobites and brachiopods (benthic animals) are rare. It could be however that the latter were more common, but that their preservation was poor. Maybe a paleontologist reads my blog and can comment on the occurrence and frequency of these fossils?
Barbara Wohlfarth 