378 



ingredients from without and the depletion of silica is evidenced, we have no very- 

 definite explanation of these formations. 



In other localities, still in the central belt, appear zones of weakness along 

 which intense pneumatolitic and hydatogenous processes have been active. The 

 great reef formation culminating in Mount Gee is the principal example of this 

 kind. In this reef the most persistent constituents are quartz, often in drusy 

 amethystine vughs, and specular iron.^^^ At intervals other ingredients appear 

 in notable quantities, including massive barytes, fluorspar (both green, blue, and 

 black varieties), and uranium ores most commonly autunite and torbernite. On 

 the eastern side of Mount Painter, in a continuation of the same mineralized 

 zone, narrow veins of turquoise are associated with the uranium phosphate ores 

 in a matrix consisting principally of micaceous and specular hematite and quartz. 

 Several veins of stilbite, associated with fluorite, about 6 inches wide and of 

 considerable horizontal extension, were found at the extremity of Mount Gee, 

 extending outwards from the region of the lode formation across the igneous 

 rocks, thus further attesting to the post-volcanic thermal character of the Mount 

 Gee formation. 



The common uranium minerals of this formation, namely, the autunite and 

 torbernite, are found as flakes and scales in the more porous portions of the 

 lode, often as a last mineral to crystallize in the vughs themselves. They are, 

 therefore, amongst the latest minerals to be introduced. So far no quantity of 

 uranium-bearing minerals of a more primary or magmatic character have yet 

 been located, though in. some areas of the lode and in the adjacent country 

 monazite is quite abundant and may be uranif erous ; also over a short distance 

 in another locality the lode formation is studded with small crystals of brown 

 fergussonite. 



As regards the specific characters of the igneous rocks, unfortunately only a 

 limited number ^''^ are available for microscopic examination. 



Mount Gee to the Bolla-Bollana Gorge. ^^^ 



The more acidic rocks of the central zone are in marked contrast to the 

 prevailing basic types of the Bolla-Bollana Creek to the southward. As an 

 exception, in the former case is a very coarse-grained, basic pegmatite outcrop- 

 ping about one mile south of Mount Gee in the small creek (Sphene Creek) 

 leading therefrom to the Bolla-Bollana Creek. This pegmatite is constituted of 

 coarse uralitic hornblende and clove-brown sphene, the individuals in each case 

 often reaching 6 inches and more in length. Such a rock would appear to 

 represent the pegmatite of a dioritic or gabbroic magma. 



Passing down Sphene Creek sundry types of gneiss are traversed, some of 

 which are clearly of sedimentary origin. Elsewhere, also, in the central belt of 



(3) "Notes on some Occurrences of Silica near Mount Painter," Trans. Roy. Soc. S. Austr., 

 xxxvi. (1912), p. 173. 



(■*) The major portion of the collection was rendered practically valueless by an accidental 

 confusion of the specimens and their labels, which occurred during my subsequent absence 

 abroad. 



(5) In my earlier paper (Proc. Austr. Ass. Adv. Science, 1911, p. 118) this has been 

 referred to as the Arkaroola Gorge. This confusion has arisen because in that paper I 

 adopted W. B. Greenwood's geography of the locality. According to him, Sphene Creek 

 junctions with the Arkaroola Creek, not the Bolla-Bollana Creek. On the most recent plan 

 published by the Lands and Survey Department it is quite the reverse. It may be that the 

 Government plan is in error, for Greenwood had an intimate knowledge of the country. In 

 the meantime, however, it is safest to adopt the Government survey. As my notes are not 

 detailed as regards the geography, I find a diflficulty in accurately placing the gorge encountered 

 in the great quartzite on the Bolla-Bollana Creek ; so that the position marked with a cross 

 on the plan herewith is but approximate. 



