134 ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



7. — COPPER STOCKWORKS IN GRANITE. 



Wheal Vyvyan. This ancient mine is in the Parish of Con- 

 stantino. A belt of the granite, some 5 to 10 fathoms in width, 

 was found to contain disseminated copper-pyrites, iron-pyrites, a 

 little grey-ore, and a little tin. This belt was traversed by 

 numerous veins or strings, which consisted of minute crevices 

 lined with tin-ore. Certain veins of granite in the " lode " 

 heaved or displaced these strings, as did also a series of cross- 

 courses.* 



A somewhat similar mass was formerly worked at Trumpet 

 Consols, in Wendron. In this instance the copper was argentifer- 

 ous, each per cent, of copper carrying from 2 to 4 ounces of silver 

 per ton.f 



Sec. 4. — Impregnations, Sfc. 



Tinder this head it will be convenient to refer to certain 

 deposits, known as Carbonas, pockets, floors, bedded veins, and 

 gash-veins which differ decidedly on the one hand from true 

 metalliferous beds, and on the other from true fissure lodes — 

 and which are usually much more concentrated and defined 

 than stockworks, and also in general much smaller. Like 

 stockworks they are often though not invariably connected with 

 definite lodes. 



Carbonas. These have so far only been found in West 

 Cornwall, and in granite. The great carbona at St. Ives Consols 

 was connected with the standard lode at the 78 fathom level by 

 a kind of pipe only a few inches in width and height. — (See fig. 

 2, Plate III). " It has been traced about 120 fathoms in length, 

 and in that distance dips 40 fathoms, but it is nowhere more 

 than 10 fathoms either in vertical thickness or in breadth, and 

 is generally much smaller. It sends of£ lode-like shoots or 

 branches laterally, and terminates in the standard lode."| Very 

 similar bodies have been worked at Rosewall Hill Mine, at 

 Wheal Speed, Balnoon, and many other places. The chief lodes 



*See Henwood, Trans. Eoy. Geol. Soc, Corn., v, 73. 



fit is worthy of note that most of the copper of this side of the Stithians 

 granite mass is argentiferous. Thus some grey-ore found at Trumpet Consols in 

 1885, contained at least 3 ounces of silver per ton for each per cent, of copper. 



X Henwood, Trans. Eoy. Geol. Soc. of Corn., V, p. 237. 



