SUPPLEMENTARY NOTE ON LIMURITE IN 



TASMANIA. 



By W. H. Twelvetrees, F.G.S., and W. F. Petterd 



C.M.Z.S. 



In this paper the authors refer to their Note on the same 

 rock presented to the Societj' last year, since when they 

 have further examined it microscopically', and have studied 

 its occurrence on the spot. They acknowledge their in- 

 de])tedness to Mr. R. Williams, the Manager of the Cole- 

 brook, for many useful and interesting specimens. The 

 mine is between Rosebery and Ringville, on the saddle of 

 a hill about 1500 ft. above sea-level, and is remarkable for 

 the quantity of pyrrhotite occurring in the rock, associated 

 with copper pyrites in relatively small quantities. The 

 authors do not regard the occurrence as a lode, but rather 

 as a rock mass, in the form of an irregular djke or intru- 

 sion. Generally, the country to the west is serpentine, 

 and to the east slates ; and the rock in question has been 

 intruded along or near the line of contact, though at the 

 top of the ridge it appears to have come up through the 

 slates in several branches or bodies, leaving horses of 

 metamorphic slate standing in its mass. Viewing the rock 

 as a mass, it is composed of augite (altered largely to uralite 

 and actinolite), axinite, calcite, datholite, danburite, with 

 secondary chlorite and sphene. Essentially it is an ultra- 

 basic rock (pyroxenite), which here and there receives the 

 addition of other boric minerals and then becomes limurite,^ 

 a composite rock, consisting practically of augite and 

 axinite. How^ were the boric emanations introduced ? 

 Were they escapes from a neighbouring acid basin ? That 

 there was an acid reservoir not far off is shown by the 

 tourmaline quartz porphyry at the Renison Bell Mine, and 

 by the axinite quartz veins found on the West Coast 

 Prospecting Association Section, and bj' the granite near 

 the latter. A slide prepared from this vein-rock is referred 

 to, and mention made of the association of tourmaline 

 with axinite in other parts of the world. The authors 

 arrive at the conclusion that the West Coast granite, or its 

 elvan dykes, consolidated at the same time as the limurite 

 dyke at the Colebrook. The action of boron vapours in the 



