 CONSERVATION OF
WALES' MINERAL HERITAGE:
ROAD CUTTINGS AND QUARRIES
The construction of new
roads or tracks in upland areas frequently
exposes much bedrock and it follows that there is
a reasonable prospect of interesting
mineralisation coming to light. Some important
discoveries have been made along track sections
in Wales, including the only decent exposures of
the Coed Y Brenin porphyry-copper orebody, which
are now protected as SSSI's.
Working quarries offer a challenge in
conservation terms but mineral suites may be
conserved by bulk removal
("rescue-collecting") of material to
Museum geology departments, where it can be
preserved and studied at leisure. When a quarry
closes, if there is still important
mineralisation on show, its preservation can
where safely practical be written in to the
post-closure plan.
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Here is a prime
example of a roadside exposure of
metallogenic interest. This is a forest
road in Coed Y Brenin. It has been cut
through Cambrian sedimentary rocks and
intrusions. Here, however, is a boss-like
area of harder rock... |
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Closer examination
reveals an abundance of sintery quartz
and fine-grained pyrite... |
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It is a pipelike
mass of brecciated rock cemented by
silica and iron sulphides. It is enriched
in base-metals, gold, silver, arsenic and
antimony. |
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Here is a close-up.
Repeated brecciation is evident and the
mineralisation is texturally complex even
under high magnification.
The pipe has been interpreted as a fossil
fumarolic system, representing the
altered and mineralised zone through
which superheated waters passed upwards
to exist as geysers upon reaching the
surface. The heat was supplied by the
magma chamber which underlay the early
Ordovician Rhobell volcano, which at the
time of formation would have been
somewhere overhead! This site is now a
SSSI. |
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Blasting at a quarry
in Carboniferous Limestone, NE Wales.
This area contains many metal mines, the
majority of which are so overgrown that
their mineralogical interest is difficult
to assess without substantial mechanised
excavation. However, the working quarries
freshly expose the same mineralisation on
a regular basis, making the collection of
unweathered sample suites a more
realistic possibility. This quarry was
producing some fine azurite specimens in
1998 and many are now preserved in the
National Museum of Wales' mineral
collection. |
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Azurite (dark blue)
and the copper arsenate tyrolite (light
blue) in situ at Dolyhir Quarry, on the
Welsh Border, 1996. The quarry works
Wenlock Reef Limestone and the underlying
Longmyndian (Precambrian) sedimentary
rocks. A series of Cu-Pb-As-Ba dominated
veins cuts through the sequence.
This short-lived exposure was studied and
sampled extensively and produced a great
diversity of different minerals, both
primary and secondary. Prior to the
area's removal by quarrying, many tens of
kilogrammes of samples were preserved.
The mineralisation is highly complex and
studies will be ongoing for some time to
come. |
MINES
NATURAL
EXPOSURES
EXIT
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