Vol. 69.] PETROLOGT OF THE KALGOOULIE GOLDFIEXD. 669 



treatment of the mineralogy of the lodes. The earlier strongly 

 albitizing solutions affected only the quartz-dolerites, the por- 

 phyrites, and the porphyries, which were probably the rocks that 

 had consolidated last. The later solutions, while ascending most 

 freely in the old channels, also found new planes of weakness 

 in the older rocks : namely, the fine-grained amphibolites and the 

 serpentines, and brought about their alteration into the fine-grained 

 greenstones and ' calc-schists,' and the talc-carbonate schists and 

 mao-nesite-rocks. 1 



(c) The Connexion of Gold and Tellurides with 

 Igneous Magmas.. 



At this point a digression may be made, to indicate the widely- 

 different kinds of igneous rocks with which gold and tellurides 

 are genetically associated. Dr. J. M. Maclaren 2 has rendered this 

 discussion easy by his ingenious and illuminating classification of 

 goldfields on grounds of geological occurrence and geographical 

 distribution. His first basis of classification of primary gold 

 deposits is, however, petrological. They arc divided into : — 



1. Those connected with the extrusion of intermediate or basic rocks (ande- 



sites or diabases). 



2. Those connected with the extrusion of acid rocks of granoclioritie type. 



The first group is again divided into : — 



(i) Archrean goldfields of hornblende- schists and amphibolites: for 



instance, Western Australia (Kalgoorlie), India (Jvolar), etc. 

 (ii) Pre-Oambrian goldfields, where diabase- or diorite.-dykes penetrate 



Archaean schists: for instance, Western Australia, India (Dharwar), 



South Africa, etc. 

 (iii) Tertiary andesite goldfields: for instance, Transylvania, 2\ew Zealand, 



California, Colorado (Cripple Creek), etc. 



Petrologists will at once demur to a classification which brings 

 the phonolite and related rocks of Cripple Creek into the same 

 •division as the andesites of Transylvania and New Zealand. If a 

 preliminary classification on petrological grounds is sought, it must 

 be based in the first place on the fundamental divisions of igneous 

 rocks into the Pacific, Atlantic, spilite, and charnockite suites. 

 Unfortunately, petrology has not reached finality in the definition 



1 The development of the theory of the spilitic suite in Great Britain took 

 place some time after I had left Kalgoorlie, and when I had no longer access 

 to most of the microscopic slides. Consequently, there are some points in 

 ■connexion with it that have not received the attention which otherwise might 

 have been given to them. Of these, the most important are the relative dates 

 of uralitization and albitization of the quartz-dolerites, and the proof that the 

 intrusion of the albite-porphyries preceded the formation of the lodes. These 

 points must be left to subsequent investigators. 



2 'Gold: its Geological Occurrence & Geographical Distribution ' London, 

 1908, pp. 44-45. 



