﻿320 MR. A. M. FINLAYSON ON ORE-DEPOSITION [May I9IO, 



hand, where no silver was removed by amalgamation in Roswag's 

 experiments, and where ore-dressing does not affect the silver-value 

 of the ore, it is probable that the silver exists in its primary state 

 of combination with the galena. 



In conclusion, the general order of deposition of the vein- 

 minerals, exclusive of calcite and quartz, may be stated as follows :— 



1. Chalcopyrite. 



2. Fluorspar. 



5. Pyrite and arsenopyrite. 



It may be mentioned, for comparison, that a common order of 

 deposition in the Upper Mississippi district has been : blende, 

 galena, marcasite. 1 



These conclusions are generally supported by the vertical dis- 

 tribution of ore in the veins. Chalcopyrite generally occurs in the 

 deeper parts of the veins, with galena above, as at Ecton in 

 Staffordshire. 2 Similarly, in the Alston Moor district, chalcopyrite 

 is chiefly found in the 'Copper Hazles ' between the Upper Scar 

 and Tynebottom Limestones, which are on a much lower horizon 

 than the lead and zinc ores of the Great Limestone and adjoining 

 strata. Blende replaces galena in the deeper levels of several 

 British mines, as is also the case at Freiberg below 1600 feet. 3 

 A similar vertical succession has been recorded in the Castle 

 Mountain and Elkhorn districts (Montana). 1 The silver-content of 

 galena becomes distinctly poorer in the deep levels of Foxdale, 

 Leadhills, and other mines. This is in agreement with the obser- 

 vations of A. W. Stelzner and F. Kolbeck at Freiberg, 5 and of 

 Zirkler in the Upper Harz. c Finally, fluorspar is chiefly confined 

 to the upper horizons of the veins. This has been pointed out 

 by Mr. C. B. Wedd in North Derbyshire, 7 and the same pheno- 

 menon is seen in the Weardale and Alston Moor districts, where 

 it is confined to the upper 300 feet of the metalliferous strata 

 of the Carboniferous Limestone Series. This feature of the occur- 

 rence of fluorspar, which is apparently at variance with the fact 

 that fluorspar is one of the earlier minerals deposited, is probably 

 due to the instability of the mineral at high temperatures, since it 

 is decomposed by superheated steam, 8 and could not therefore exist 

 at greater depths. 



1 C. R. Van Hise, 'A Treatise on Metamorphism ' Monogr. xlvii, U.S. Geol. 

 Surv. 1904, p. 1145. 



2 ' Geology of North Derbyshire' Mem. Geol. Surv. 2nd ed. (1887) p. 158. 



3 R. Beck, ' The Nature o'f Ore-Deposits ' (transl. W. H. Weed) New York, 

 1905, p. 362. 



4 W. H. Weed & L. V. Pirsson, 'Geology of the Castle Mountain Mining 

 District, Montana' Bull. U.S. Gei>l. Surv. No. 139, 1896; W. H. Weed, 

 ' Geology & Ore-Deposits of the Elkhorn Mining District, Jefferson Co., 

 Montana' 22nd Ann. Rep. U.S. Geol. Surv. pt. ii (1900-01) p. 503. 



5 R. Beck, op. siipra cit. p. 362. 



u * Ueber die Ganguehaltnisse der Grube Bergmannstrost bei Clausthal ' 

 ' Gliickauf ' Essen, 1897, p. 84. 



7 ' The Fluorspar Deposits of Derbyshire ' Trans. Inst. Min. Eng. vol. xxxv 

 (1908) pp. 517-21. 



8 Ibid. p. 525; also Henry Watts, 'Dictionary of Chemistry' London, 

 vol. i (1863) p. 718. 





