Vol. 69. j PETROLOGY OK TILE KALGOORLIE G0LD1TELI). 



661 



arisen from the schists and not from the porphyry; but the 

 presence of the latter can hardly be accidental, for in a railway- 

 cutting about 3 miles east of C( nlgardie Dr. Maclaren has observed 

 an analogous phenomenon. A narrow dyke of quartz-porphyry is 

 intrusive through an amphibolite, and on each side, of the dyke 

 there is a band of graphitic schists about 5 feet wide. Unfor- 

 tunately, neither the amphibolites nor the schists are fresh enough 

 for microscopic study. 



The impregnation of schists with graphite is not confined to 

 bands traversed by porphyry -dykes. It is found, for instance, 

 along fault-planes in the calc-schists. There can be no doubt 

 whatever that the schists are of igneous origin, and that the 

 graphite is of inorganic origin. Probably it has arisen from 

 emanations given off by the porphyry magma, although the 

 exact mechanism of its formation remains obscure. 



Although in some places the graphitic schists crop out at the 

 surface without much alteration, in others they are oxidized to 

 a depth of over 100 feet, giving rise at the surface to white 

 quartz-sericite schists. To this category, apparently, must be 

 ascribed the rocks classed by Mr. Simpson as ' older sediments,' of 

 which three analyses have been made. 1 The absence of contact- 

 minerals in them militates against a theory of sedimentary origin 

 for rocks so closely associated with intrusives, while the low mag- 

 nesia and high soda percentages of the analyses make their deriva- 

 tion from albitized rocks probable. The analyses are as follows: — 





XXXII. 



XXXIII. 



XXXIV. 



SiOo 



84-07 

 1-16 

 903 

 0-42 

 0-45 

 tr. 

 0-24 

 0-21 

 1-64 

 2'21 

 1-05 

 0-20 

 0-07 

 0-04 



100-79 



2-66 

 E. S. Simpson. 



70-25 



0-34 

 15-22 



1-00 



0-87 

 tr. 



0-12 



0-14 



3-46 



1-28 



1-34 



0-42 



0-02 



5-93* 



100-39 



2-73 



E. S. Simpson. 



6001 

 0-05 



17-82 

 0-54 

 1-65 

 0-09 

 1-69 



Ti0 2 



AI2O3 



Fe-^O-i 



EeO . 



MnO 



MgO 



CaO 



5-86 



Na-,0 



2-79 

 1-85 

 1-65 

 0-15 

 5-50 

 1-88 



101-53 



2-71 

 C.G.Gibson. 



KoO 



H-0 + 



h.;o- 



CO-, 



FeS 2 



Totals 







* Including 0"50 Cu. 



XXXII. G.S.M. 1731. 'Dark-grey slate' from G.M.L. 917 E, Paringa Con- 

 solidated Mines, Ltd., Bowlder. 



XXXIII. G.S.M. 1732. ' Davk-grey sandstone' from the same lease. 



XXXIV. G.S.M. 1739. 'Light-grey sandstone' from the 400-foot level, G.M.L. 



3625 E, Hawk's View G.M., Kalgoorlie. 



1 Bull. Geol. Surv. W. Austral. No. 6 (1902) p. 77. 

 Q.J.G.S. No. 276. 2x 



