El Valle-Boinás/Carlés Geology

The 45 Km long and four kilometre wide Río Narcea Gold Belt is characterised by the alignment of mineral occurrences, Paleozoic sediments, Tertiary Basins, fracture Zones, and igneous intrusions.

High angle faults striking sub-parallel to the regional north-northeast trend of older structures pre-date igneous intrusions and Tertiary sediments which partly cover the anticlinal axis zone of the southern portion of the Río Narcea Gold Belt. Reactivation of older structures during the Tertiary Alpine Orogeny in the southern part of the belt has been found to cut and displace some mineralisation.

In the N20ºE trending part of the Río Narcea Gold Belt, the anticline is overturned. The structure is affected by a number of relatively low angle reverse faults that produced strong brecciation. Reactivation of the northeast trending fault structure during an extensive period of erosion was accompanied by hydrothermal activity occurring periodically through the end of the Paleozoic.

Metamorphism in the Río Narcea Gold Belt is related only to intrusion of the igneous rocks, which produced contact metamorphism in the sedimentary rocks. They produce hornfels in the clastic units and skarn in the carbonate units.

Gold mineralization consists mainly of two types:

  • Gold bearing cooper skarn: related to the interaction between late Hercynian intrusions, mesothermal solutions; and carbonate host rocks.
  • Jasperoid type: related to subvolcanic dykes and ephitermal solutions which cause silicification with argilisation and sericitisation, plus epigenetic, hypogene oxidation. This type of mineralisation may overprint, remobilise, and enrich gold mineralisation within the skarn deposits.

EVBC - General Geology

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El Valle-Boinás Cross-Sectionn

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