450 



PROCEEDINGS OP SECTION C. 



In " Dana's Mineralogy " there is a list of analyses of tantalite- 

 columbite from the Etta Mine in the Black Hills of South Dakota, 

 which show to what a large extent the ore in a single mine may vary 

 in grade owing to the mutual replacement of tantalum by niobium, and 

 vice versa. As has already been stated, this is not characteristic of 

 most of the Wodgina deposits. The exception that proves the rule, 

 however, is a small parcel of crystalline stream ore, individual fragments 

 of which gave the following specific gravities : — 5-98, 6-10, 6-55, 6-92, 

 7-03, 7-75, 8-03. These figures show that this ore ranges from nearly 

 pure niobate of manganese to a nearly pure tantalate of iron. 



Tin oxide appears to exist as an essential constituent of all tanta- 

 lates and niobates. The amount thus present seldom exceeds 1 per 

 cent., and, not being recoverable by any simple process, is of no impor- 

 tance to the miner. A mechanical mixture, however, of cassiterite 

 and tantalite or columbite is readily separated by an electro magnet, 

 so that the cassiterite which thus occurs with almost all Wodgina 

 stream ores is not to be overlooked. The following figures give an 

 idea as to the extent to which the tin thus occurs :- 



Microlite (pyrotantalate of lime) occurs in association with man* 

 ganotantalite in a stream ore received from Wodgina. The exact 

 locality from which this ore was derived has so far not been discosed, 

 but, judging from the associated minerals, it is from the immediate 

 vicinity of Wodgina itself. The mineral, constituting about 2 per cent, 

 of the whole parcel, is in irregular water-worn fragments up to lin. 

 in diameter. By the courtesy of Mr. A. 0. Watkins I have been supplied 

 recently with about an ounce in weight of this mineral, and a pre- 

 liminary physical and chemical examination of it has been made. 



The specific gravity of five fragments was respectively 5-37, 5-76, 

 5-61, 5-42, 5-73, evidencing a somewhat small variation in tantalum 

 contents (probably about 15 per cent.). No evidence of crystallisation 

 is apparent, the fragments being roughly rounded and water-worn. 

 Parts of the surface are covered with a very thin black coating, which 

 sends out what one may call small rootlets into the mass of the mineral. 

 This coating, as well as more or less numerous minute black inclusions 

 in the centre of the pebbles, appears to consist of tantalate of manga- 

 nese. Where not covered with this black coat the microlite pebbles 

 are grey or light pinkish brown. On fresh fractures the mineral is 

 opaque and usually light pinkish grey, sometimes a little darker, and 

 inclined to liver-color The internal structure as seen in a thin slice 

 under a microscope is very interesting, being reminiscent of olivine 

 largely altered to serpentine. It consists of numerous cores of clear 



