650 DR. J. A. THOMSON ON THE [DeC. I913, 



significance is doubtful, and as they are geologically unimportant, 

 it will serve no useful purpose to describe them in detail here. 

 Mention should, however, be made of one specimen which might be 

 considered the result of contaet-metamorphism, as it occurs in the 

 vicinity of a dyke of albite-porphyry. It was collected in the western 

 cross-cut off the west drive, at the 300-foot level of the Hannan's 

 Star Consolidated CM. The rock has a dull-grey coloration 

 seldom seen in any other variant of the quartz-dolerites ; but, 

 in section, it differs from the ordinary greenstones only in the 

 substitution of chloritoid for chlorite in the pseudomorphs after 

 the original pyroxene. Occasionally, the chloritoid projects into 

 the sericitized felspars. Except in the occurrence of chloritoid, 

 there are no characteristics suggesting contact-alteration, and 

 greenstones, from the contact of the albite-porphyry at other 

 localities do not contain chloritoid, 



Analyses of the greenstones will be found at the end of the next 

 section (p. 652). 



C. Bleached Greenstones (Albitized Quartz-Dolerites 

 without Chlorite). 



These rocks, as mentioned above (p. 646), pass gradually into 

 the greenstones, and the distinction made is only for purposes 

 of description. They occur chiefly in ' The Mile,' and, without 

 forming exclusively the walls of the telluride-lodes or the matrix of 

 the ores themselves, they are most abundant in what may be termed 

 the lode-channels. 1 Sometimes, particularly in the ' North 

 End,' the bleached greenstones are found as thin variants of the 

 greenstones on each side of venules of quartz or albite. At other 

 times, especially in parts of ' The Mile,' they form wide bands of 

 rock alternating with similar bands of greenstone, the boundary 

 between the two being sharp and usually along a stroug joint- 

 plane. This mode of occurrence has been supposed to indicate a 

 later intrusive origin for the rocks under discussion, particularly 

 where they have been identified as granophyres. It is probably 

 due to movements along the joint-planes faulting out of sight those 

 spots where the gradation between the two rocks occurs. Such 

 gradations can be observed in innumerable cases, if very close 

 inspection be made. Mine- workings are nearly always smothered 

 with dust or slime, the lighting underground is poor at the best, 

 and, in consequence, much hammer-work and close inspection is 

 necessary before the true relationship of two adjacent rocks can be 

 made out. Sudden breaks are much more easily noticed than 



1 The lodes of ' Tbe Mile' may be divided, on geographical grounds, into three 

 groups. The western group contains the lodes of the Ivanhoe, Great Boulder, 

 and Golden Horseshoe Mines ; the central group includes those of the Kalgurli, 

 South Kalgurli, Great Boulder, Perseverance, and Lake-View Consols Mines; 

 and the eastern the lodes of the Oroya-Brownhill, Associated Northern, and 

 Associated Mines. Within each group the lodes are close together, and run in a 

 belt of sheared and mineralized country that may be termed a lod e-channel. 

 The three groups are separated by broader belts of barren greenstone. The 

 lodes of the western and central groups are in the quartz-dolerites, those of the 

 eastern group in the calc-schists. 



