A short walk visiting 3 waypoints that should take you about half an hour. Please note that to log this cache it is not necessary to pay for the guided tour around the ancient mines. All the information can be found around the site without having to pay a penny, but the mines are well worth a visit if you have the time. See the related web site for details on opening times and tours etc.
During the period of time that geologists call the Carboniferous era, approximately 340 million to 280 million years ago, North Wales, like many other parts of Britain lay underneath a shallow tropical sea, with similar conditions to present day Bermuda or Florida. Skeletons of plankton, and shells settled on the bottom of the sea and were broken up by the motion of the waves into tiny particles. Plankton skeletons and shells are made almost completely out of lime so over millions of years, beds of lime, hundreds of feet thick accumulated on the sea bed, solidified, and turned into limestone.
1) Dead animals sink to the sea bed and break up into tiny particles
2) The layers of sediment turn into rock, some of the skeletons and shells remain complete and harden to form fossils
3) The rock is folded and parts are eroded
4) The fossils are exposed on the surface. Many can be seen on the Great Orme today
Sometime after this, most likely between 280 million and 200 million years ago earth movements put a great deal of pressure on the limestone and caused it to crack. Many of these cracks would have been very small, but some of them would have penetrated deep into the earth’s crust. Within the earth’s crust there are pockets of boiling hot minerals, liquids and gases which are under immense pressure. These would have forced their way towards the surface through the cracks; some of the liquids and gases would have dissolved areas of limestone around the cracks to form cavities. The minerals, which in this case were copper minerals would fill these cavities, cool down, solidify and form veins of copper ore.
Fissures or Faults appeared in the rock due to the pressure it was under
Mineral rich magma from the earth’s core, under great pressure, forces its way up through the crack
The veins of copper are wider when going through various layers of rock as some are more soluble than others
During this time the limestone rock surrounding the veins would have undergone a chemical change. Some of the lime in the limestone would have been replaced by magnesium turning it into magnesium limestone or Dolomite.
This Dolomite would have been slightly softer than the limestone, and combined with the fact that the copper ores were exposed on the surface would have provided favourable conditions for early miners.
To log this Earthcache email the CO the answers to the following questions, please do not include your answers in your logs.
Waypoint 1 (Copper Rock)
1. What colour is evident on the rock, explain what mineral you think this is (clue in the title) but why has it turned this colour.
2. Photograph of you or your GPS at this rock (optional of course)
Waypoint 2 (Information Board)
3. Name the 2 metals mentioned on the information board?
Waypoint 3 (Limestone Rock)
4. Look closely at the rock and you will see some fossils, these are Crinoids. By what other name are Crinoids commonly known?
5. Estimate the height, length and width of this rock.
Research required
6. What year was the copper mine discovered?
7. What other metal is added to Copper to make Bronze?
I am happy for you to log this Earthcache before your email but if I haven't received an email within a few weeks of your visit I will delete your log.
Many thanks to the management at the Great Orme Ancient Mines for permission and helping me with this Earthcache.