Western Australia. Ill 



whicli prove, on examination, to be decomposed pyrites or ferro- 

 magnesian crystals. Especially noticeable in a few samples, 

 e.g. 12331a, are rather lenticular patches, sometimes 1^ inches in 

 length and ^in. in width, composed of a pale-green chlorite, some 

 limonitic iron-ore, and strings of very fresh needles of dark-green 

 tourmaline. In such an advanced stage of alteration are these 

 patches that it is impossible to say definitely from the evidence 

 available whether they are original or represent xenoliths that have 

 been altered partly by ordinary chemical agencies and partly by 

 a kind of pneumatolytic action. It certainly would appear that the 

 keratophyre when near the temperature of consolidation, but still 

 more or less viscous, had enclosed within its mass fragments of 

 greenstone, and that the tourmaline had been produced as a contact- 

 metamorphic product by vapours containing boron associated with 

 the intrusive. On the other hand, not only does tourmaline occur 

 in some of the slides fresh and with no connexion with chlorite, but 

 the felspars and the rock itself in these cases are quite fresh. Unless, 

 therefore, the specimens have been collected from the margins of the 

 keratophyre, and the tourmaline is, in consequence, due to a partial 

 impregnation of the rock by boric vapours, it is difficult to see how 

 in the latter case the mineral can be regarded as other than original. 



Regarding the occurrence of tourmaline, Clarke^ states: "In 

 igneous rocks it seems to have been produced by fumarole action, and 

 not as a direct sepai'ation from the magma." 



Van Hise writes^: "Tourmaline rather frequently occurs in the 

 marbles and in the calcareous schists ; it also has a rather widespread 

 occurrence in granites, gneisses, etc. In these rocks it frequently 

 occurs in such relation to dykes of igneous rocks, especially of 

 pegmatites, as to suggest that its development is promoted by contact 

 action. Because of the boron, tourmaline has generally been regarded 

 as evidence of fumarole action. Certain it is that boron is not usually 

 a constituent of the ordinary sediments, and to account for this 

 element would seem to require its introduction from an outside 

 source, either by gaseous or by aqueous solutions." 



The occurrence of the mineral in the North End is not restricted 

 to the keratophyre. Indeed, according to the field evidence the 

 mineral is especially common in the lode formation, which consists 

 of kaolin and sericitic material seamed with quartz and quartz- 

 tourmaline leaders. Moreover, in the Mystery Lode in the altered 

 keratophyre contiguous to the lode material, small nests of the 

 mineral have been found which appear to be partially moulded by 

 gold. From this it is probable that the gold is not contemporaneous 

 with the tourmaline, but has been formed at a later date by 

 percolating solutions. Further, as will be seen later on, there are 

 specimens of the quartz-carbonate-fuchsite rock, apparently on the 

 margin of which occur strings of tourmaline. 



Most noteworthy of all are specimens 12331b and 12237. These 

 are both from the same locality, viz. G.M.L., 4458 E. They are both 

 light-coloured rocks with a faint reddish tinge, and both show distinct 



^ Clark(\ Data of Geo-chemistry, p. 347. 



^ Van Hise, Treatise on Metamorphism, p. 326. 



