199 



Radium at Moonta mines, south Australia. 



Bv S. Radcliff (communicated by Prof. W. II. Bragg, 



M.A.). 



[Read September 4, 1906.] 



The ore deposits of Wallaroo and Moonta tnines present 

 many features of interest. Occurring as they do in rocks 

 of extreme antiquity, and containing a very wide range of 

 mineral species, as well as traces of many of the rare ele- 

 ments, it seemed just possible that one of the radioactive ele- 

 ments might be present in them. 



The present investigation was comm.enced in June, 1905, 

 to see if this were the case, and as the results so far obtained 

 are of considerable interest, it seemed desirable to give some 

 preliminary account of them. 



In testing for radioactivity, I used a gold leaf electro- 

 scope sufficiently sensitive to detect anything possessing an 

 activity approaching one-hundredth of that of uranium oxide 



After a good deal of preliminary work, giving negative 

 results, faint signs of activity were detected in one of the 

 smelting work's bye-products, and this activity was subse- 

 quently traced back to some "concentrates" from Moonta. 

 The fact that the bulk of the ore from Moonta mines passes 

 through the crushing and concentrating plant before being 

 forwarded to the smelting works rendered the identification 

 of the active mineral a matter of some difficulty. Experi- 

 ments on the concentrates indicated that the active mineral 

 was probably of rather low specific gravity, and of such a 

 character that it powdered readily when crushed. On put- 

 ting the concentrates through a series of sieves of different 

 degrees of fineness, the activity was found to concentrate to 

 some extent in the finest product. Elutriation tests gave 

 some indications as to the specific gravity. Further search 

 resulted in a few specimens of activity, about one-twelfth of 

 that of XJaOf,, being found in a heap of rough ore from 

 Moonta, and following up the clue afforded by their general 

 physical character a small deposit of active ore was ulti- 

 mately located in the upper workings of a shaft at Moonta 

 Mines, known as Treuer's Shaft. Shortly afterwards a sec- 

 ond deposit was found in the workings connected with Tay- 

 lor's Shaft, also at Moonta Mines. 



The specimens from these two deposits are about equally 

 active, but differ considerably in appearance and composition ; 



