Vol. 69.] .PETKOLOGY OF THE KALGOOKLIE GOLDFIELD. 641 



The original rock was, therefore, in all probability a poecilitic 

 hornblende-dolerite or gabbro. This view is confirmed by the study 

 of a rock found by Dr. Maclaren 10 miles south-east of Kanowna. 

 It is a hornblende-dolerite of the Careg-Llefain type, showing 

 partial uralitization, and, where most altered, reproduces the 

 features of the Kalgooiiie type. 



The following is an analysis of a lustre-mottled amphibolite from 

 Kalgoorlie, the only example of this class from Western Australia 

 that has been analysed. The high percentages of carbon-dioxide, 

 combined water, and soluble bases show that the rock had suffered 

 much surface-decomposition, accompanied by the production of 

 chlorite and carbonates. 



jY Bases soluble in 



aqua regia. 



Si0 2 44-23 



Ti0 2 0-06 



A1 2 3 10-89 4-11 



Fe 2 3 0-13 0-13 



FeO 14-22 5-00 



MnO 1-60 113 



MgO 11-42 3-15 



CaO 10-43 0-59 



Na 2 1-02 



K 2 0-20 



H 2 0+ 4-25 



H 2 0- 0-22 



COs 1-29 



FeS 2 0-26 



Total 100-22 



Sp.gr 3-00 



Analyst C. G. Gibson. 



G.S.M. 2117. Main Shaft, Great Boulder, No. 2, South. G.M.L. 1219 E. 

 Bull. Geol. Surv. W. Austral. No. 6 (1902) p. 67 



Lustre-mottled amphibolites have not been found abundantly so 

 far in Western Australia ; but one was described by me, in 1909„ as 

 almost a hornblende rock after a basic hornblende-olivine-gabbro. 1 

 The former presence of olivine was inferred from the presence of 

 colourless ellipsoids of tremolite within the large poecilitic crystals 

 of brown hornblende, but this phenomenon could be equally well 

 explained by the uralitization of enclosed augite. In the case of 

 the Glendalough rocks previously mentioned, the olivine of the 

 hornbleude-peridotite is partly altered into chlorite and tremolite, 

 and the last-named has grown inwards from the enclosing brown 

 hornblende in parallel position upon it, while the chlorite has 

 developed along cracks in the olivine. In the Glendalough amphi- 

 bolite, where the olivine has completely disappeared, the abundance 



1 Bull. Geol. Surv. W. Austral. No. S3 (1909) pp. 132 & 142. 



