Geology 



the latter was present in considerable quantity in the 

 Granite Mountains. 



Carbonic acid also apparently played a part in the 

 alterations, though probably, at a later stage, acting upon 

 the felspars of the granite and producing Kaolin perhaps 

 somewhat in the manner indicated by the following 

 equation : 

 A1 2 O 3 . K 2 . 6(SiO 2 ) + 2 H 2 O + CO 2 = A1 2 O 3 . 2(SiO 2 ) . 2H 2 O 



(Orthoclase) (Kaolin) + 4 SiO 2 + K 2 CO 3 



In this particular case the element lithium also seems to 

 have been involved in the reactions, as with some of the 

 veins was associated a considerable quantity of the 

 lithia-mica, lepidolite. It would, therefore, appear that 

 the tin, fluorine, and boron originally dissolved in the 

 granite-magma were set free during its solidification at 

 a stage when its outer parts had already become solid 

 and that they found their way together with steam and 

 carbonic acid along cracks and fissures which had been 

 produced in the already solid portion. 



Here as they reached cooler regions new combina- 

 tions were entered into, the fluorides of tin and silicon 

 were decomposed by the aqueous vapours forming the 

 corresponding oxides tin-stone and quartz, while the 

 hydrofluoric acid set free by this reaction combined with 

 the minerals of the neighbouring rocks to form the 

 characteristic minerals above described. 



On tracing the mineral veins we found that though 

 they traversed the granite and the surrounding gneiss, 

 it was only near the junction of the two rocks that they 

 were at all rich in tin. 



We followed the foot of the mountains towards Tin 

 Creek without again descending to Centre Valley, and 



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