THE HEEMSKIRK MASSIF 173 



Some confirmation of this view is afforded by tlie general 

 parallelism of distribution of the consolidation products of an 

 earlier igneous invasion — that of Cambro-Ordovician time. The 

 keratophyric tuffs and the spilite of Zeehan^, the keratophyric 

 tuffs and breccias of North Dundas^, the schistose keratophyres 

 or porphyroids and porphyrites of North Dundas, North-east 

 Dundas, Rosebery, and Mt. Farrell are on this belt. The granite 

 porphyry which extends from the north-west of Granite Tor to the 

 Dove River, the schistose porphyry of Mt. Roland, and possibly 

 even the epidote porphyrite of Beaconsfield, are to be taken into 

 consideration with these others. The distribution of these related 

 rocks is, at least, significant in support of this hypothesis. Along 

 this line, or rather zone, are situated some of the most important 

 mining fields of western Tasmania. 



The relation of other mining fields and igneous rocks to those 

 which have been mentioned demands passing notice.^ 



A prominent feature in the geology of the west coast region is 

 the distribution of certain old igneous rocks — schistose tuffs, 

 porphyries, porphyrites, syenites and granites, some of which occur 

 along a meridional zone which extends from Mt. Darwin to the 

 north of Mt. Black. Plutonic, intrusive, and effusive phases are 

 all represented in this group (that of Cambro-Ordovician age already 

 mentioned), the present distribution of which is clearly axial, even 

 if the lineal arrangement has been accentuated by orogenic 

 disturbances subsequent to consolidation. 



The distribution of the Mt. Darwin, Mt. Jukes, Mt. Huxley, 

 Mt. Lyell, Mt. Read and Chester mineral fields is, in general, 

 coincident with that of this belt, but in the opinon of the author 

 the ore-bodies belong to the Devonian metallogenetic epoch. The 

 reasons for this statement cannot be here fully discussed. It 

 suffices to state that the author believes that the mineralogical 

 character of the ores of this belt of orogenic disturbance points 

 most strongly to the necessity for classifying them with the 

 Devonian ore-bodies. Hitherto there have not been found any 

 igneous rocks along this belt which may be assigned to the Devonian 

 intrusion. The author anticipates that these will yet be recognised, 

 but he believes that the characters of the ore-bodies themselves 

 are sufficient evidence of the existence of the Devonian granitic 

 magma along this zone below the surface. 



The two zones already mentioned appear to miite in the 

 neighbourhood of Rosebery, not far from Mt. Black. 



These two zones do not include within their hmits a number 

 of the important outcrops of gi'anite and granite porphyry of 

 Tasmania, nor do they embrace some well-known mining fields. 

 Of these other mining fields the author has no detailed knowledge. 



Having, however, indicated that there is one very well defined 

 zone of intrusion and mineralisation between Heemskirk and 



1 Geol. Surv. Tas., Bulletin No. 8, pp. 15-19. 



2 Geol. Surv. Tas., Bulletin No. 6, pp. 16-18. 



3 For they too e.xtend along restricted zones. Between the zones of intrusion by igneous 

 materials there are no known mineral fields. 



