Nothing speaks against that coincidence, but the brine would not be in a chemical equilibrium with the redbeds. It should reduce and bleach the flow channels. Compare the descriptions of the Kupferschiefer in Germany and Poland. 

Thank you for your answer.

It is exactly that I observed, an hematite bleaching along flow channel in my Pyrenean outcrop.

In Mc Caig et al. 2000 papers, I read that "The brine could have been derived from the Upper Triassic evaporate and stored in the lower Triassic redbeds. Some of this formation water could have been stored in a second host-rock: in the Devonian basement or in the Silurian graphitic slates".

So, if I well understand you, the brine canot be in equilibrium with redbed, so can you think its origin could be formation water as suggested by McCaig ?

I will search Kupferschiefer papers, if you have some references it would help me.

Thank you again

Vincent