Vol. 69.] PBTKOLOGY OF THE KALGOORLIE GOLDFIELD. 651 



gradual passages. Here it may be observed that, although there is 

 always an inherent probability of finding granophyresin association 

 with quartz-dolerites, I have failed absolutely to discover any trace 

 of them in Kalgoorlie, every suspected rock proving on microscopic 

 study to be a metasomatized quartz-dolerite. 



In hand-specimens the coarser rocks are white or various shades 

 of pink, and present much outward similarity to granites ; but they 

 always reveal their doleritic origin by the presence of leucoxene. 

 Microscopically they exhibit in many cases their original structure 

 much' better than the greenstones, for the absence or paucity of 

 chlorite (an obscuring element in the greenstones) makes the 

 distinction between the various pseudomorphs much sharper. The 

 pyroxenes are represented by dense aggregates of carbonate grains 

 disposed around the partly- or completely-sericitized felspars. 

 Micrographic and micropegmatitic intergrowths of quartz and 

 albite are often beautifulty displayed, and in such abundance as to 

 make it evident that the rocks thus altered were slightly more 

 siliceous than those parts of the same intrusion that are now repre- 

 sented by amphibolites. The felspars, wherever identifiable, are 

 albite, as in the greenstones. The leucoxene is frequently replaced 

 by rutile, a process that becomes more marked with advancing 

 schistosity. 



As in the case of the greenstones, however, many of the rocks 

 are not such obvious derivatives of quartz-dolerites, owing to 

 a greater development of carbonates and sericite. They consist 

 apparently of coarse-grained structureless aggregates of secondary 

 minerals (chiefly quartz, carbonates, and sericite), but there are 

 few in which the presence of leucoxene or of archipelagos of 

 quartz does not betray the original character. Most of them 

 contain a large amount of pyrite, the iron of which appears to 

 have been furnished largely by the chlorite, for a disappearance of 

 chlorite goes hand in hand with the appearance of pyrite. 1 Secon- 

 dary magnetite is fairly common, while haematite and arsenopyrite 

 are occasionally found. 



In the immediate vicinity of the lodes these rocks are represented 

 by pale-grey schists with silvery foliation-planes, often rough by 

 reason of imperfect shearing or from the projection of octahedra 

 of magnetite. In microscope-sections the schistosity is less evident 

 than the hand-specimens would suggest. Sericite is the first mineral 

 to assume a parallel development, and next to it comes chlorite 

 (if any exists in the rock), then the carbonates, which are drawn 

 out into lenticular streaks. The large magnetite-crystals seem to 

 be posterior to the shearing : for their edges are quite sharp, and 

 they are never flattened or drawn out. The ultimate products of 

 the shearing are fine-grained schists with a granular quartz base, 

 in which certain bands are very rich in rutile. These quartz- 

 carbonate-sericite schists are the rocks regarding which Mr. 

 L. J. Spencer 2 expressed doubts concerning their relationship with 



1 The alumina of the chlorite is probably utilized in the formation of 

 sericite, while the magnesia is removed or goes into the carbonate. 



2 See p. 629. 



