GEOLOGY AND PETROLOGY OF ENOGGERA GRANITE. 157 



This sgems to have been followed by a reversion to a series 

 of dykes of a dioritic and porphyritic nature, all of which 

 show a preponderance of NajO over K„0 with comparatively 

 high values for CaO. 



In the East Moreton and Wide Bay districts to the 

 north of the Enoggera area are a number of plutonic and 

 hypabyssal rocks which have been described by Dr. H. I. 

 Jensen,-*^ and which petrologically and chemically seem to 

 have many points in common with the Enoggera rocks. Of 

 these the *'Neurum" granite of the Woodford area seems to 

 most nearly approach the Enoggera granites in age, since 

 Jensen considers it to be "post-Carboniferous, probably 

 Permian. ' '-" It is described as " a bluish, tonalitic granite. ' '' 

 Referring to this granite he says further: — "The graphic 

 granite aplites of the Delaney's Creek and Fife's Range 

 mountains are probably the last differentiation products 

 of this mass." This seems a fairly close parallel both of 

 types and events with the Enoggera area. 



Further, Jensen, in summarising the history of thi« 

 East ]\Ioretou and Wide Bay area, refers to an original 

 quartz dioritic rock which was closely followed by an aplitic 

 phase, one result being the formation of "mixed" rocks 

 referred to earlier in this paper. 



V. ECONOMIC. 



The decision at which the author arrived, that the 

 Enoggera granite was probably related to the Stanthorpe 

 and New England "acid" granites, held an economic 

 interest in addition to its geological significance, as both 

 these granites are stanniferous. However, so far as the 

 autlior can discover, no find of tin has ever been made on 

 this area. As noted on p. 152, Part I., of this paper, flakes- 

 of molybdenite were discovered while the field work was 

 being carried out, and since that time molybdenite in small 

 quantities has been found in several parts of the area. 



This sparse occurrence of molybdenite and the local 

 tourmalinisation of the granite on its north-eastern edge are 

 the only points which suggest the possible existence of tin 



="•' Geology of Parts of the East Moreton and Wide Bay 

 Districts. Proc. Linn. Soc. N.S.W. Part I. 1906, p. 73. 

 -' Op. Cit., p. 92. 



