186 PROCEEDINGS OF SECTION C. 



Ihat the whole process of serpentinisation — with the attendant de- 

 velopment of such minerals as chlorite, stichtite, asbestos, fibrous 

 or columnar magnetite, and occasional calcite or dolomite — may 

 be ascribed to the influence of the magmatic emanations given o^ 

 from the whole surface of the cooling acidic magma of later date. 

 Or, in other words, the water of hydration wherewith the basic rock 

 types have been converted into hydrated varieties may have been 

 of magmatic origin. In support of this suggestion may be cited 

 one pecuharly interesting occurrence. Near the summit cutting on 

 the Comstock tramway in Zeehan a mineral vein has traversed a 

 serpentinised basic (mica-gabbro) dyke in which asbestos vems 

 occurred. The asbestos veins have been converted into veins of 

 ferriferous dolomite in which the original structure is preserved. 

 The mineral veins in this district being all ascribable to a single 

 period of deposition, which immediately succeeded the acidic in- 

 vasion, and when there was apparently still a considerable thickness 

 of superincumbent rock above the point where deposition took 

 place, it is significant that the asbestos had already been formed 

 when the mineralisation occurred. In view of this known occur- 

 rence — to which will probably be found analogous examples as the 

 geological survey of Tasmania proceeds — the serpentinisation ap- 

 pears to be due to juvenile not to meteoric waters. 



How far amphibolitisation is a concomitant process with that 

 of serpentinisation is not yet apparent. While it is possible that in 

 some cases the amphiboles may have been developed in the basic 

 masses by processes akin to those which have controlled the depo- 

 sition of members of the amphibole family in the mineral veins at 

 Mt. Ramsay and North Dundas, the problem demands much more 

 detailed investigation in the field than that which it has yet received. 



Turning from the consideration of the basic rocks themselves 

 to that of the mineral veins located within their boundaries or in 

 their immediate neighbourhood, we find several phenomena which 

 have some bearing or^ the questions here discussed. 



At the Adelaide Mine in Dundas, which is situated in imme- 

 diate proximity to a considerable development of serpentine, some 

 very magnificent crystals of crocoite have been obtained from 

 the oxidised portions of the lode. These occur in the weathered 

 part of a lode of which the primary constituents are dolomite, 

 sphalerite, galena, pyrite, and a curious green mineral which appears 

 to be a chromiferous sericite. This same green mineral has been 

 found also at the Spray Mine and the Colonel North Mine at 

 Zeehan. 



The magnetite ore of the Comstock region carries traces, ^ and 

 the iron ore of Anderson's Creek carries appreciable^ quantities of 

 chromium. 



1 Vide : G. A. Waller, " Report on the Iron and Zinc-Lead Ore Deposits of the Comstock 

 District," 1903, p 0. 



2 Vide : W. H. Twelve rees, " Report on the Mineral Resources of the Districts of Beaconsfield 

 .and Salisbury," 1003, p. 26. 



