173 



Notes on Some occurrences of Silica near 

 mount painter, flinders ranges. 



By A. C. Broughton. 

 [Read October 10, 1912.] 



The locality from which the examples referred to. were 

 obtained is situated in the Far North-Eastern portion of 

 South Australia, the north-easterly termination of the Flin- 

 ders Ranges. 



The specimens were collected from an area occupying 

 about 24 square miles, extending from the divide of the 

 ranges near Mount Pitt, 12 miles across the eastern slopes, 

 to Parallana, on the edge of the great eastern plain. 



The country rocks of the area examined have been deter- 

 mined as Pre-Cambrian by Dr. Mawson. They consist of 

 granites, gneiss, schists, altered porphyries, and a felspathic 

 and siliceous rock having the features of an eutectic mix- 

 ture. The area has abundant evidence of having been sub- 

 jected to great earth movements, as indicated by great 

 crushed zones, faults, and slicken-sided faces exposed on 

 excavating. 



These fissures and crushed belts perniitted the easy cir- 

 culation of highly mineralized waters rich in silica and iron. 

 The waters were evidently hot and from deep-seated sources. 

 The final traces of such activity are probably to be found to- 

 day at the hot springs at Parallana. 



This water, travelling along the cracks and faults, 

 deposited its mineral contents, cementing the crushed frag- 

 ments into a solid whole. It is with some of the results of 

 this cementation and deposition from solution that the paper 

 deals. 



These belts of iron-and-quartz-cemented zones have a 

 greater resistance to the action of the weather than the more 

 alkaline felspathic country rock, and their outcrops, with the 

 crystal-lined cavities and caves, are a feature of the country. 



The greater part of the cementing material consists of 

 iron and quartz. The iron mineral being either specular and 

 micaceous haematite, a porous ironstone, or a very massive 

 tough iron rock. The quartz is either distributed irregularly 

 throughout or else lining cavities. 



Along Radium Ridge there are small aggregates of 

 amethyst in the centre of a large mass of dense ironstone ; 

 cavities, lined with beautifully developed crystals of ordinary 



