1.38 THE PEOGRESS OF GEOLOGICAL RESEARCH IN TASMANIA, 



is that of a series of irregular domes and basins, so that at 

 any mine level the outline of the ore-bodies is irregularly 

 lenticular. 



The origin of the ore-bodies is ascribed to ascending 

 magmatic waters genetically associated with the Epi-Silurian 

 quartz-porphyry and granite-porphyry dykes in the vicinity. 



(4). The Tin Deposits of North-East Dundas. 



These were examined in detail by L. K. Ward in 1908, 

 and their structural features, composition, and genesis are 

 described in Bulletin No. 6 of the Geological Survey. Some 

 of the later developments in the various mines are dealt with 

 by Hartwell Conder, M.A., in Bulletin No. 26. 



The tin deposits are grouped by Ward under two 

 heads — Pyritic-Cassiterite deposits and Quartz-Tourmaline- 

 Cassiterite Veins. The composition and structural features 

 have been somewhat completely elucidated, and the genesis 

 referred to the associated granite-porphyry and quartz- 

 porphyry dykes of Epi-Silurian age. However, it cannot 

 be stated that the exact relationship to the pyritic-lead de- 

 posits, the garnet actinolite veins or the axinite veins, which 

 occur associated with the tin-deposits, has been demonstrated. 

 Neither can it be claimed that the mineralography of the 

 pyritic-cassiterite ores has been closely studied, especially in 

 regard to those of dense stanniferous pyrrhotite. 



(5). The Ore Deposits of the Mount Farrell 

 District. 



The investigation carried cut by Ward in 1907 on the 

 ore-deposits of this district was an elaboration of previous 

 examinations by Twelvetrees and Waller. 



Ward's description of these deposits, contained in Geo- 

 logical Survey Bulletin No. 3, shows three types of lead 

 deposits — Sideritic-Galena lodes, Pyritic-Galena lodes, and 

 Barytic-Galena lodes. No attempt, however, is made at a 

 zonal classification similar to that evolved for the Zeehan 

 field. 



Certain types of copper ores, as well as iron ores, are 

 described, and the genesis of all of the ore deposits is ascribed 

 to the Epi-Silurian plutonic period. However, the relation- 

 ship between the lead-deposits, those containing copper, and 

 the haematite and magnetite deposits is not elucidated, so 

 that a common genetic origin for them all is by no means 

 certain. 



