﻿Vol. 66.1 ORE-DEPOSITION IN LEAD AND ZINC YEINS. 299 



11. Problems of Ore-Deposition in the Lead and Zinc Veins of 

 Great Britain. By Alexander Moncrieff Finlayson, M.Sc, 

 F.G.S. (Read January 26th, 1910.) 



Contents. Page 



I. Introduction 299 



II. Source of the Ores 300 



III. The Vein-Solutions 304 



IV. Metasomatic Processes 310 



V. Paragenesis 313 



VI. Influence of the Country-Rock on Ore-Deposition 321 



VII. Secondary Alteration 324 



VIII. Summary 326 



I. Introduction. 



The lead and zinc districts of Great Britain afford good opportunities 

 for the study of these ores, owing to the variety of types met with 

 and the advanced state of mining. Unfortunately, however, many 

 interesting districts have been exhausted and abandoned, with the 

 inevitable loss of much valuable information, which was not secured 

 when the mines were in operation. As Franz Posepny has truly 

 iremarked, 



' Mining, indeed, constantly furnishes fresh evidences in new openings, but it 

 destroys the old at the same time ; and if these are not preserved for science 

 before it is too late, they are lost for ever.' l 



The Geological Survey memoirs, however, have in some cases 

 preserved many data which could not otherwise be obtained. The 

 present work has been carried out on the basis of personal field- 

 work in all the chief districts, coupled with laboratory work at the 

 Imperial College of Science and Technology, where all the analyses 

 tabulated in this paper were made. 



The lead and zinc veins of Britain are chiefly of the spathic and 

 "barytic types of Freiberg mineralogists. Calcite is the predominant 

 gangue, while fluorspar, barytes, and quartz are also abundant. 

 Zeolites occur locally, as at Strontian in Argyllshire, and at Glenda- 

 lough (Wicklow). The galena is argentiferous to a varying degree, 

 and rich silver-ores have been mined at Hilderston (Linlithgow- 

 shire), at Alva (Stirlingshire), and in parts of Cornwall. These 

 veins, though small and unimportant, are of the Joachimsthal and 

 Annaberg type. The country-rock of the veins embraces nearly 

 all the Palaeozoic formations, from pre-Cambrian gneiss to the 

 Carboniferous Limestone. 



1 ' The Genesis of Ore-Deposits' Amer. Inst. Min. Eng. 2nd ed. (1902) p. 3 

 (reprinted from vol. xxiii of the Trans.). 



