376 ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



away too from tin and from tourmaline. Even when it is 

 directly associated with these substances it seems to have had 

 quite a different origin. 



Copper as a rock-constituent, apart from definite veins, is 

 almost non-existent, and the absolute quantity of copper in the 

 West of England must be far less than that of tin. 



Zinc in Cornwall scarcely occurs at all except as the sulphide 

 (blende), and it is almost exclusively confined to the veins in 

 which iron, copper, or lead ores are found. Occasionally it is 

 met with in the tin-veins as at Wheal Metal in Breage, but only 

 in small quantities, unless notable quantities of copper are also 

 present. In such eases it is of course near the granite junctions ; 

 but when it occurs in lead veins, like copper ores under similar 

 conditions, it is found far away from such junctions. 



Some of the zinc veins have been very large, as for instance 

 at Great Eetallack and Duchy Peru in the parish of Perran. 

 Yery much blende was thrown away in the old burrows, or left 

 behind in the u.pper levels of many of the mines, and especially 

 in those between Truro and St. Agnes ; there having been 

 formerly no sale for blende. Many of these old mines and 

 burrows have been re-worked in comparatively recent times. 

 Still the product of zinc ore in our district has never been really 

 large even as compared with cojDper. 



As a rock-constituent zinc is very rare, and the absolute 

 quantity of zinc in Cornwall has probably not much exceeded 

 the absolute quantity of tungsten. 



Lead. This element also occurs almost exclusively in veins, 

 and as a sulphide (galena), and almost always at considerable 

 distances from the granite. The best deposits, as at East Wheal 

 Rose and the Menheniot mines, have mostly been associated 

 with sedimentary rocks of a fossiliferous series. As already 

 mentioned ores of zinc and copper are often found with lead 

 ores in the veins. Tin however occurs near lead only very 

 rarely,* and even then is not intimately associated with it. 



* The most notable exception is at Budnick in Perranzabuloe, described by 

 W, J. Henwood. Trans. Boy. Geol, Soc. Corn., V. 



