Picture of Flätsbo mine

Flätsbo mine is a sulphide mineralisation with copper, zinc and some lead as dissemination. It is located just outside the surveyed area.

Photo: SGU

19 January 2024

Insights on the Ockelbo domain may affect future exploration

230 versus 6,099. That's how big a difference it is in the number of iron mineralisation between two areas in Bergslagen with otherwise comparable bedrock. But what is it due to? A new report from the Geological Survey of Sweden (SGU) tries to answer that. The answer is important for the planning of future exploration.

The bedrock within what is known as the Bergslagen lithotectonic unit contains many mineralisations, but one area in the northern part stands out. In the so-called Ockelbo domain, located in Dalarna and Gävleborg counties, the frequency of mineralisation is significantly lower despite similar bedrock. Here, the iron mineralisation is 27 times less than in the investigated reference area.

Instead, the magmatism in the area is chemically and possibly also age-wise more related to that in the Los area a little further north. This means that future exploration efforts in the Ockelbo domain need to have a different focus than those in Bergslagen, says Magnus Ripa, geologist at SGU.

The lower frequency of mineralisation may be related to the fact that there are fewer occurrences of suitable host rocks, such as original limestone, in the Ockelbo domain. Another explanation could be the differences in the degree of sodic and potassic alteration of the volcanic rocks in the areas. Both factors may indicate that the supracrustal rocks in the Ockelbo domain to a lesser extent were formed in a marine environment.

Between the rock types of the two areas there are also differences in the distribution of silica contents and the content of aluminum, iron, titanium, phosphorus, strontium, barium, zirconium and heavy rare earth elements.

Bergslagen, etapp 2. Malmförutsättningar i norra delen av Bergslagens litotektoniska enhet, SGU-rapport 2024:01

Last reviewed 2024-01-19