136 THE PHOGRESS OF GEOLOGICAL EESEARCH IN TASMANIA, 



VIII. ORE-DEPOSITS. 

 (1.) The Development of the Investigations. 



It is in this domain that our greatest advance has been 

 made. This is not surprising, in view of the fact that the 

 study of our deposits of economic minerals is the raison d'etre 

 of the Geological Survey. 



The earlier portion of the period under review witnessed 

 intense mining activity in Tasmania, and it is to the develop- 

 ments resulting from such work, together with the concur- 

 rent demand for geological examinations, that we owe the op- 

 portunities for research which have been productive of ap- 

 preciable results. 



The year 1902 saw the late W. H. Twelvetrees and his 

 assistant, G. A. Waller, busily engaged examining active 

 mining fields and preparing incomplete geological maps of 

 those areas. The v/crk performed by Waller in the Zeehan 

 field constitutes the first complete geological mapping of a 

 mining field executed in Tasmania. There was gradually 

 evolved at this period by both investigators the conception 

 of a genetic connection between the plutcnic igneous rocks 

 and our ore-deposits, particularly between the granitic rocks 

 and our tin, lead, zinc, and iron deposits. 



After the resignation of Waller in 1904 the late W. H. 

 Twelvetrees continued the examination of ore deposits, with- 

 out, however, having the opportunity of carrying out de- 

 tailed mapping. With the appointment in 1907, however, 

 of L. Keith Ward as Assistant Government Geologist, an op- 

 portunity was afforded of initiating systematic studies of 

 our ore-deposits, accompanied by the detailed geological re- 

 search which is essential to an understanding of their gene- 

 sis. The old ground traversed by Twelvetrees and Waller 

 was retraced and new ground broken as opportunity offered, 

 and these repeated examinations of our more important min- 

 ing fields and their ore-deposits have continued up to the 

 present time, with the result that the knowledge we now 

 possess of these ore-deposits is considerable. 



(2). The Galena Lodes of Zeehan. 



The earlier investigations by G. A. Waller on the ore 

 deposits of the Zeehan field were elaborated in detail by 

 Twelvetrees and Ward, and the composition, structural fea- 

 tures, and genesis thoroughly elucidated. The galena-bear- 

 ing lodes are grouped into two belts — the Pyritic Belt and 

 the Sideritic Belt. The difference in mineralogic composition 



