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THETFORD. 



The visit to Thetford affords further opportunities for 

 the study of the occurrence, mining, and milling of asbestos 

 — subjects which have already been discussed for the 

 occurrence at Black Lake. 



EAST BROUGHTON. 



The interest at East Broughton centres in the rock 

 types, and, the occurrence of asbestos in sills. 



Rock Types. 



The rock differs from that of Thetford and Black Lake, 

 in being much softer and more shattered. It is almost 

 completely serpentinized, the only exception being certain 

 hard blocks which carry no asbestos. The asbestos 

 recovered here rarely occurs in veins, but generally as slip 

 or parallel fibre, being, in fact, only the softer and partially 

 fibrous, outer portions of the individual pieces into which 

 the rock is shattered. A microscopic examination of these 

 rocks is still necessary in order to determine the actual 

 mineral composition of these hard blocks, and to find out, 

 if possible, whether the asbestos-bearing portion was 

 originally similar to that in the Thetford series. The 

 presence of considerable bodies of talc, and steatite or 

 soapstone, indicates that there was a good deal of pyroxene 

 in the original rock. There is very little chromite in the 

 serpentine of this class. 



The altered greenstones are chloritic and epidotic 

 schists, probably originally diabase, together with horn- 

 blende schists which grade into them. The latter may be 

 the altered, more acid parts of the primary rock, perhaps 

 corresponding to the porphyrite of the Thetford series. 

 The precise character of these rocks can only be determined 

 by detailed lithological examination, which has not yet 

 been made. 



The appearance of the rock is at first disappointing as 

 there are no signs of the cross fibre veins which are so much 

 in evidence at Thetford. However, on crushing the rock 

 to a fine powder a considerable amount of short fibre is 

 found. The asbestos produced at East Broughton is all 

 of short fibre and of low grade, no crude whatever being 



