I'l'fro/o;/!/ (1 11(1 (u'oloijii of Qvft'iisfoivn. \'.Vi 



tuonts of tilt' rock. Tlic luicToscope, however, reveals the fact thut 

 sericite, cai hoiiates. and jtyritcs ai'e the ultiuiiite products of the 

 original minerals. It is evident that the solutions causing the 

 alteration must have been rich in alkaline carbonates and sulphides. 

 That they also contained arsenic and antimony, is apparent from 

 the abundance of arsenopyrite and stibnite neai- the veins. The 

 solutions undoubtedly were acjueous, yet the rock has probably 

 suffered dehydration, which is explained by the disappearance of 

 ■chlorite containing about 13% water, and its i-eplacement by seri- 

 cite containing only about 4%. A chemical analysis, of the wall 

 rock adjoining a quai-tz vein in the Morning Star diorite, showed 

 that the percentage of total water was 2.64 in the propylitised rock, 

 .and only 0.96 in the sericitised and carbonated facies. The efficacy 

 •of moderately strong alkaline carbonate solu^tions to dissolve rock- 

 forming minerals is well known. Therefore, the extreme metaso- 

 matic alteration undergone In- the original rock is easily explained 

 as a result of the attack of such solutions. Gold is known to be 

 soluble in alkaline sulphide solutions, and it was probably in such 

 .solutions that the gold in the veins at Yow Yow was introduced. 



D. — Quartz l'orph\ir\j, One Tree Hill. 



The eight inch to one mile geological map, published by the Vic- 

 torian Mines Department, shows an outcrop of porphyrite at 

 Smyth's Gully. The author is not aware of any such rock there, 

 and apparently the rock intended to be shown is the One Tree Hill 

 porphyry. This rock is seen on the surface, at the summit of One 

 Tree Hill, adjoining the Buck line of reef, and is here decomposed 

 to a mass of kaolin containing abundant quartz grains. It can 

 also be seen on the track leading from the hill to the battery in 

 Fern Tree Gully, and a tunnel driven from this gully into the hill 

 to cut the Buck and Swedish reef intersected it. Where seen on the 

 surface, the lock appears to l)e a dyke,i but the relations as revealed 

 by the tunnel section, although not very clear, seem more suggestive 

 of an intrusive pipe. The rock is greatly brecciated in places, and 

 xenoliths of black slate, sandstone, and quartz porphyry are often 

 included in it. Breccia and an agglomerate occur on the surface 

 near the head of Fern Tree Gully, and also in the tunnel, but 

 their relation to the normal igneous rock was not evident. The 

 pebbles of tlie agglomerate are chiefly quartz porphyry, and are 



1 The 189.") geologically coloured parish plan of Queenstown shows a diorite dyke at One Tree 

 Hill. 



