﻿308 ME. A. M. FlNLAYSOlir ON OEE-DEPOSITION [May I9IO, 



Barium, on the other hand, would be readily carried as the car- 

 bonate, dissolved in excess of carbon dioxide, the change to barytes 

 being effected during deposition by reaction with alkaline sulphides 

 and by oxidation. In this connexion the relations of the sulphate 

 and carbonate of barium in the veins are important. These two 

 minerals are seldom closely associated in the veins, one generally 

 occurring to the exclusion of the other. Further, there is no 

 evidence, except in local cases, of change from the one form into 

 the other. The carbonate (witherite), as at Fallowfield and Settling- 

 stones, generally appears as a direct metasomatic replacement of 

 limestone ; while the sulphate (barytes) occurs usually as a compact 

 fissure-filling. Prof. Clowes has suggested that barytes, as a cement 

 in sandstone, has been formed in situ by interaction between 

 barium carbonate and soluble sulphates. 1 Herr G. Lattermann has 

 described a deposit of barytes at Lautenthal in the Harz, which has 

 been formed by the interaction of sulphate-bearing mine-waters 

 with spring-water carrying barium chloride. 2 Mr. C. W. Dickson 

 has shown that it forms by reaction between bicarbonated solutions 

 of barium and oxidizing sulphides. 3 This last case is most probable 

 for the barytes in the British districts. The formation of the 

 sulphate seems to be, in every case, brought about during deposition. 



Fluorine was doubtless the chief agent in the primary processes 

 of magmatic extraction, forming volatile fluorides or fluosilicates 

 of the metals. As the solutions ascended, and became cooled and 

 diluted, these compounds would be hydrolysed, with the formation 

 of new combinations and release of the fluorine, which was ulti- 

 mately fixed by combination with calcium. 



Summing up, it appears that the vein- solutions carried, in 

 addition to fluorine and volatile fluorides, chiefly alkaline and 

 earthy carbonates, which transported barium in solution and 

 effected the observed alteration of the wall-rock ; also alkaline 

 sulphides, which transported the lead and zinc as sulphides. 



Source of the solutions. — The conclusion that all the ores 

 are of deep-seated origin, as well as the depth to which the veins 

 extend, indicates that the waters were, in the first place, 'juvenile/ 

 being probably hydrothermal after-effects of deep-seated igneous 

 disturbances and intrusions. This is supported by the occurrence 

 of fluorine; the processes at considerable depth were probably 

 pneumatolytic in nature. Further, it is not likely that meteoric 

 waters played any conspicuous part in the primary ore-deposition 

 in the slate and granite districts. 



In limestone areas, however, the conditions are different, and a 

 consideration of the facts strongly suggests that underground 

 atmospheric waters, mingling with the 'juvenile' waters, have 

 played an important part in ore-deposition. The facts are as 

 follows : — 



(1) The ores are almost universally distributed throughout the 



1 Proc. Roy. Soc vol. xlvi (1889-90) p. 368. 



2 Jahrb. K. Preuss. Geol. Landesanst. 1888-89, p. 259. 

 8 School of Mines Quarterly, vol. xxiii (1902) p. 366. 



