Back to Seathwaite Tarn copper mine

 

We visited the upper level of Seathwaite Tarn copper mine. The spoil heap was mostly quartz. I found this paper about the mineralisation at the site. Apparently the adit that can no longer be seen here went in 100 fathoms. A fathom is 6 feet or 1.8 metres so the tunnel was 180 metres long. The copper minerals formed in veins of quartz, hence the spoil. I've known for a while that mineral veins form when faults in the rock caused by earth movements fill up with very hot mineral-rich fluid which crystalises out. If I've read it right, then quartz formed first in the faults. Then more earth movements fractured the quartz and the copper minerals formed in those cracks. Here the copper mineral also contained bismuth but I'm going to need to improve my chemistry to understand fully.