338 ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



mingled in most cases with, more or less of siliceous substance, 

 this latter being frequently in the brittle form of quartz, known 

 as "sugary-spar," or of the highly cavernous form known as 

 " floatstone." Sometimes there is also a whitish or reddish clay 

 present (prian), also partially oxidised masses of pyrites, marca- 

 site, and other sulphides, with in many cases crystals of oxide of 

 tin. 



Grozzan is peculiarly characteristic of copper-lodes, as was 

 long ago observed by Pryce, often extending to great depths, 

 and even below the sea-level, as at the United Mines in Grwennap, 

 North Grrambler near Redruth (85 fathoms), Fowey Consols (100 

 fathoms below adit), the Phoenix Mines, Devon Great Consols, 

 and Wheal Friendship. Many of these gozzans contained 

 occasional sprigs of native copper ; more frequently considerable 

 quantities of the black and red oxides and blue and green 

 carbonates of copper, together with smaller quantities of the 

 various phosphates, arseniates, uranates, and other rare mineral 

 compounds. 



A good gozzan even in Cornwall does not of course neces- 

 sarily imply the existence of a valuable copper deposit beneath, 

 since it may be merely the result of an oxidation and hydration 

 of ordinary iron pyrites of little or no commercial value ; yet so 

 generally is it the case that rich deposits are thus indicated, that 

 no miner would hesitate to follow a really good gozzan, especially 

 if it contained mere traces of copper ; on the other hand, no 

 miner would be disposed to place much confidence in any copper 

 lode, unless it had a " good gozzan" in some part of its course. 



Iron ore has been obtained, not only from iron lodes proper 

 such as those of Eestormel, Pawton, and Brixham, but also from 

 the "backs " of very many copper, lead, and tin lodes: indeed 

 the great Perran lode itself is thought by many to be merely the 

 upper portion of an immense copper lode 



Some lode-gozzans have for many years yielded quantities 

 of ochre, either by simple stamping and washing, or, in some 

 instances by merely settling the outflowing waters. It is worthy 

 of note that the ochre thus obtained usually contains some notable 

 proportion of sub-sulphate of iron, indicating clearly its origin 



