■Vol. 69.] PEXKOLOGl' OF THE KA LGOOTtLlE GOMJJflELD. 6G5 



the association of rocks at Kalgoorlie with those of St. David's 

 Head (South Wales), and the Kettlestoun Quarry, Bathgate Hills 

 (Scotland). 



The similarities displayed in these analyses are too striking to 

 be accidental, and must be explained away if the albite-porpbyries 

 are considered not to beloug to the quartz-dolerite series. 



Albitization — that is, the secondary alteration of lime-soda 

 felspars, by which albite-molecules are substituted for anorthite- 

 molecules — was first brought into prominence by Mr. E. B. Bailey 

 & Mr. G. W. Grabham l in the case of some Carboniferous lavas at 

 Arthur's Seat, and in some quartz-dolerites of the Central Valley 

 of Scotland. The secondary albite is sometimes sericitic, and is 

 accompanied by chlorite and carbonates. Unfortunately, we are 

 left in doubt as to the effect of the alteration on the pyroxenes and 

 iron-ores. The albitization is ascribed to the action of concentrated 

 solutions of sodium carbonate, which are derived from the magma 

 itself. An interesting point is, that while the most basic 

 felspars in any given rock are the first to be albitize'd, the altera- 

 tion operates with greatest freedom on the most acid rocks. 



Mr. H. Dewey & Dr. J. S. Flett i claim albitization as a juvenile 

 alteration affecting certain rocks of the spilitic suite, a series of 

 volcanic and intrusive rocks whose 



* essential characteristics are the abundance of soda-felspar and t lie remarkable 

 frequency with which they have been albitized.' {Ojj. cit. p. 2 -10. J 



If their contention, that the spilite suite is a fundamental division 

 of igneous rocks comparable with the Atlantic and Pacific suites, be 

 correct, then it will at once be conceded that the albite-porphyries 

 of Kalgoorlie, from their richness in albite and their resemblance 

 to the soda-felsites of Great Britain, find their place in the spilite 

 suite. Their contention gains considerable weight from the obser- 

 vations of Mr. AV. N. Benson, 3 who lias found spilites associated 

 with radiolarian cherts in Eastern Australia in exactly the same 

 manner as they occur in Great Britain. 



But there are other rocks in Western Australia, which on 

 chemical and mineralogical grounds must also belong to the spilite" 

 suite. These are the albite-granites and albite-pegmatites that 

 occur in some of the goldfields and in all the tin and tantalum 

 fields. The analyses in the following table (p. 66(5) are quite 

 comparable with those of the more acid members of the suite in 

 Great Britain quoted by Mr. Dewey & Dr. Flett (op. cit. p. 209). 



11 ' Albitization of Basic Plagioclase-Felspars ' Geol. Mag. dec. 5, vol. vi 

 (1909) pp. 250-56. 



- 'British Pillow-Lavas & the Rocks Associated with them' Ibid. vol. viii 

 (1911) pp. 202-209 & 241-4S. 



:i 'Spilite Lavas & Radiolarian Rocks in Xew South Wales' Ibid. vol. x 

 (1913) pp. 17-21. 



