Yol. 69.] PETROLOGY OP THE KALGOOELIE GOLDFIELD. 



653 



The practice adopted by the chemists of the Western Australian 

 Geological Survey of giving, in addition to the complete analysis, 

 a statement of the part of the rock that is soluble in aqua regia, is 

 highly commendable in the case of rocks containing much chlorite 

 and carbonates : for thus it is possible to make an approximate 

 estimate of the quantitative mineralogical composition. In these 

 calculations one method is to employ arbitrary molecules for 

 chlorite and sericite ; and this has been adopted by Dr. W. Lindgren l 

 for the calculation of two of the analyses of the foregoing table. An 

 alternative method, adopted by me, assumes an arbitrary choice of 

 disposal of the soluble bases between carbonates and chlorite, and 

 attempts to calculate the various molecules postulated by Tschermak 

 for chlorite and sericite according to the ratios between combined 

 water and the available bases. The latter method Avould be more 

 exact if the analyses were absolutely reliable ; but, in the absence 

 of estimates of fluorine and chlorine, the figures given for combined 

 water cannot be accepted as quite accurate. Nevertheless, it is 

 interesting to note the close agreement of the calculations, par- 

 ticularly as it is evident from the slight divergences in the fixed 

 molecules that slightly different atomic weights have been used. 

 The estimates for the rocks in the foregoing table are as follows 

 (XXV a and XXVI a being the estimates of Lindgren) : — 





XXII. 



XXIII. 



XXV. 



XXVa. 



XXVI. 



XXVI a. 





2-14 

 •7-45 



1-51 



6-36 

 0-22 



28-72 

 0-97 



6-45 

 16-39 

 11-94 



27-85 



0-34 



' 0-48 

 2-25 



15-56 

 0-50 



21-73 

 2-85 

 31-35 

 25-13 



0-47 

 2-25 

 15-70 



21-52 



2-76 

 31-48 

 25-20 



1-98 



3'55 

 0-34 

 22-16 

 0-44 



9-71 



1-24 



38-27 



21-23 



353 

 0-30 

 22-12 



9-58 

 2-94 

 38-24 

 21-44 







Pyrite 





Albite 



33-12 



8-43 

 3-06 

 1-04 



1382 

 4-18 



25-26 











Chlorite 







Totals 



98-50 



100-41 



100-19 



99-38 



98-92 



98-15 













No. XXIV could not be thus calculated, as the analysis shows 

 much insoluble iron and alumina that cannot be accounted for. 

 While it is frankly admitted that the results can only be accepted 

 as approximate, the above table reveals several interesting points. 

 The first is the thorough nature of the albitization, for little or 

 no insoluble lime remains in any of the rocks, except the epidotic 

 greenstones. The second is that, as the amount of sericite and 

 carbonates increases, the proportions of albite and chlorite decrease. 

 Apparently, after the production of the greenstones by albitizing 

 solutions, in which process chlorite was freely formed, a further 



1 'Metasomatic Processes in the Gold Deposits of Western Australia' Econ. 

 Geol. vol. i (1906) p. 538. 



