Before this series of post’s about the geological map of the Liskeard area launches into the ‘main event’, of the lodes it will have a pause at feature with the best sounding name, Elvan.
Elvans are intrusions of a quartz porphyry rock; the word is used for both the intrusion and the rock itself. Elvan is a very hard rock that can add greatly to the cost of driving levels and sinking shafts. Elvan patches near lodes were also thought to be associated with increased mineral richness. Its hardness made it a sought after building material.
Brenton Symons in his 1863 map shows elvans as red colour washed areas. He has shown eight setts in Caradon Hill area with elvan patches, as opposed to the British Gelogical Survey’s moderm map not indicating any.
No Elvan patches are shown at all by BGS.
“There are also several strong elvans or dykes generally running about parallel with the lodes, and which so far as seen, have had a beneficial effect.”
Webb and Geach
West Sharp Tor
There is a very large elvan course, north of, and adjoining the lode; the thickness of which though driven into 6 fathoms, is not yet known.
There is a beautiful white elvan, 50 fathoms east of the engine shaft, about 3 fathoms wide.
At the 11 an elvan course came in and heaved the lode south.
The elvan, of which there are two channels, is harder than general in the district.”
East Wheal Agar
“There is a beautiful white regular elvan course 70 fathoms south of the shaft, whilst the Junction of killas and granite occurs between it and Dunsford’s Shaft”
“There is a large elvan course north of and accompanying the caunter, and in the same elvan a little north, occurs Fawcett’s Lode, which has been opened on for some distance:”
“There are two elvan courses; one occupying the whole space between the north and middle lodes, and the other in the south portion of the sett; white porphyritic dykes almost destitute of mica, composed chiefly of feldspar and quartz.”
“It should be noticed that two elvan courses of felspatic granite run parallel to the lodes.”