OF THE EIO-TINTO MINES. 259 



Quebranto Huesos are, I think, connected with the eastern end of 

 the South lode, while San Dionisio may be regarded as an extension 

 westwards of the South lode. This and the j^orth lode have been 

 entirely opened up by the present proprietary, nothing having been 

 done upon them since the Eoman times until about the year 1878. 

 The Valley lode is not yet opened up. The North, South, and 

 San Dionisio lodes all show abundant evidence of very extensive 

 work by the Romans, and even of still more ancient works ; but 

 as this paper is designed to deal only with the geological and 

 mineralogical features of the district, and not with the mining 

 operations which have been carried on from time to time, or with 

 those which are now being carried on, I need not further refer to 

 these points, except to draw attention to the series of enlarged 

 sections given (figs. 3-8, p. 260), all of which refer to what is 

 known as the South lode *. 



O T? S T TT 



Sulphur 33-04 24-03 52-81 15-82 40-89 



Selenium trace. 0-10 0-13 



Iron 34-72 12-21 46-12 2-21 36-24 



Copper 31-68 62-50 0-11 0-01 4-30 



Arsenic O'Ol 0-03 0-23 0-01 0-10 



Lead 0-02 0-14 trace. 80-41 11-37 



Antimony trace. . . . 0-40 0-20 



Zinc 0-10 trace. trace. 0-14 6-66 



Bismuth trace 0-21 0-04 



Silica and insol.. 0-15 0-02 0-10 0-02 0-21 



99-72 98-93 99-37 99-33 100-14 



Silver 0-033 0-010 0-005 0-015 0-015 



Gold . In all a few grains only to the ton. 



The Manganese-lodes. — A system of fissures having the same 

 general directions as those larger ones which contain pyrites, occurs 

 in the immediate neighbourhood of these latter ; indeed, the man- 

 ganese-fissures often seem to be merely branches of the pjTites- 

 fissures. Like them, they are frequently bounded by slate on one 

 side and by porphyry on the other ; but pretty often they have slate 

 on both sides, although they are never found far from masses of 

 porphyry. Occasionally they are entirely in porphyry. The veins 

 vary in width from an inch or less up to several yards. Unlike the 

 pyrites-veins, in which siliceous deposits are conspicuously absent, the 

 manganese-veins are generally very highly silicified, the walls being 

 often converted into excellent jasper to a considerable depthf. 



The manganese-ore itself is sometimes very siliceous, but otherwise 

 a fairly pure but hard variety of pyrolusite, assaying over 80 per cent, 

 of peroxide of manganese. A great number of these veins occur in 



* A list of the various minerals which have been met with at the Rio-Tinto 

 mines, comprising thii-ty -three species, is given by me in the ' Mineralogical 

 Magazine,' vol. iv. pp. 211-216. 



t An analysis of one of these jasper bands from Bella Vista has been given 

 supra, p. 249. 



