﻿304 



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



III. The Yein- Solutions. 



The composition of the vein-solutions on the one hand and their 

 source on the other are cognate subjects, and may therefore be 

 considered under the same head. 



Nature of the solutions. — A clue to the chemical composition 

 of the vein-solutions is given in the first place by the hydrothermal 

 alteration of the wall-rocks, an examination of which was made 

 during this investigation. A series of analyses, tabulated below, 

 was made of fresh and altered rocks from five different localities : — 





Ax. 



A 2 . 



Bi. 



B 2 . 



Ci. 



Co. 



Di. 



D 2 . 



Ex. 



E 2 . 



H,0 



2-0.5 

 64*45 

 13-31 

 0-51 

 2-32 

 3-62 

 5-73 

 324 

 2-21 

 1-55 

 0-24 



1-24 



2-35 

 60-42 

 13-45 

 0'33 

 1-42 

 1-23 

 7*24 

 1-15 

 3-35 

 0-94 

 0-40 



8-73 



1*04 

 75-64 

 8-79 

 0-68 

 3-24 

 1-61 

 1-09 

 0-28 

 2-31 

 3-67 

 0-46 



0-31 

 1-05 



1-21 

 80-67 

 6-23 

 0-65 

 0-19 

 0-45 

 2-48 

 0-21 

 2-45 

 1-38 

 0-35 



3-24 

 1-33 



1-95 

 50-46 

 13-89 

 2-26 

 3-69 

 9-02 

 8-81 

 5-03 

 1-33 

 2-85 

 0-22 

 0-37 

 0-19 



1-65 

 62-29 

 12-27 

 1-13 

 1-29 

 8*65 

 3-29 

 2'45 

 2-66 

 0-23 

 0-27 

 0-32 

 4-34 



0-89 

 75-46 

 12-68 



0-85 

 0-34 

 1-21 

 1-68 

 5-46 

 2-48 



nil 



1-24 

 65-68 

 13-49 



056 

 0-28 

 6-28 

 0-31 

 5-85 

 0-13 



5-28 



2-12 

 2-34 



0-57 



0-65 



51-18 

 1-24 



42-27 



2-48 

 15-25 

 0-61 



6*42 



42-83 

 5-37 



32-66 



SiO.> 



A1>0 3 



TiOo 



Fe.>0 3 



Feb 



CaO 



; MgO 



! k.,o :.. 



Na.,0 



MnO 



P.,0, 



CO, 



FeS., 





Totals 



100-47 



101-01 



100-17 



100-84 



100-07 



100-84 



101-05 



99-10 



100-37 



99-62 





Specific gravities. 



2-564 



2-490 



2-522 



2-318 



2-853 



2-648 



2-621 



3-213 







Ai : Leadhills slate, fresh. 

 A 2 : Do. do. altered. 

 Bi : Conway volcanic ash, fresh. 

 B 2 : Do. do. do. altered. 



C{: Whin Sill diabase, fresh. 

 C^: Do. do. altered. 



D x : Foxdale granite, fresh. 

 D 2 : Do. do. altered. 

 E x : Halkyn limestone, fresh. 

 E 2 : Do. do. altered. 



It will be seen from the foregoing analyses that the different rocks 

 show much variation in the changes of constituents. The Lead- 

 hills slate (A x & A 2 ) shows a loss of iron oxides, balanced by an 

 increase in lime, potash, and carbon dioxide. Under the microscope 

 the altered slate shows a great development of dusty sericite, with 

 some secondary calcite and siderite. The alterations in this rock 

 have been sericitization and carbonatization. 



The rhyolitic ash from Trecastell, Conway (B 1 & B 2 ), shows 

 some loss of alumina as well as of iron oxides and soda, with an 

 increase in lime, potash, carbon dioxide, and silica. The fresh rock 

 contains abundant orthoclase and plagioclase phenocrysts, and much 

 secondary quartz-mosaic. The altered rock shows further silicifica- 

 tion, while the felspars are replaced by sericite and calcite aggregates. 



The Whin Sill (C x & C 2 ) was examined at Rotherhope, near Alston, 

 where it is intersected by a vein now being worked. The unal- 

 tered rock consists largely of andesine-labradorite and ophitic augite, 

 with a good deal of magnetite and ilmenite. Near the vein much 

 ' secondary quartz and sericite has been produced, with patches of 

 secondary carbonates. The augite is altered to pale-green chlorite, 

 with separation of magnetite. On the vein-walls the rock is white 



