86 Reviews — South Australia Department of Mines. 



X. — South Australia, Department of Mines, Mining Review for 

 the Half-year ended June 30, 1918. 'No. 28. Adelaide, 1918. 



AFTER the usual summary of outputs and values of minerals, 

 this issue goes ou to describe several interesting mineral 

 occurrences. 



Rores put down by the Government diamond drill on the Yelta 

 Mine, adjoining the Moonta Mines property, traversed a copper- 

 bearing lode which in one bore swelled to a rich ore body 21 feet 

 thick, with an average copper content of 27 per cent, rising in places 

 to 34*5 per cent; the lode is enclosed by the same country rock as 

 that of the Moonta Mines. 



An account is given of a graphite field on Eyre's Peninsula. The 

 soil over part of the field is covered with a crust of travertine, but 

 where this is absent flake graphite and graphite-bearing stones are 

 found in a structureless subsoil stained with limonite. Magnesite 

 is present and quartzite fragments are frequent. The nature of the 

 decomposition products shows that the graphite has been developed 

 in a series of sediments which have been greatly altered and 

 invaded by pegmatites, and are now represented by a mixture of 

 lime-silicate rocks and gneisses, such as are formed by the alteration 

 of impure dolomitic limestones. The workings have not yet been 

 carried below the zone of weathering, but the indications of workable 

 graphite are promising. 



In the county of Fergusson, on Yorke Peninsula, alunite has been 

 discovered in the sea cliffs in a bed of clay resting on polyzoal limestone. 

 The rocks are Tertiary in age and are overlaid by 50 feet of clay 

 and 20 feet of travertine or superficial limestone. The alunite 

 occurs as irregular layers, from 1 inch to 9 inches in thickness, and 

 as nodular masses arranged in layers along a total width of about 

 12 chains. 



The mode of origin of the alunite is rather obscure, but there are 

 two possible explanations : the first supposes that the mineral was 

 derived from sulphates generated from pyrites and from potash in 

 the clay, and this idea is supported by the fact that samples of the 

 same clay from a point a few miles away contain from l - 7 to 5 per 

 cent of potash and from 2 - 38 to 0'23 percent of S 3 respectively. 

 Alunite is soluble in sulphuric acid and, on coming within the 

 influence of the limestone, the excess acid would be destroyed with 

 the precipitation of the alunite immediately above the limestone. 

 On the other hand, alunite is also known to have been derived from 

 solutions rising from depth, and this may be the case here. It is 

 likely that the fault fissures in the limestone along which the 

 solutions could ascend did not extend into the clay, and that the 

 alunite was therefore deposited just above the limestone. 



The mineral is worked along adits from the shore ; the samples 

 taken contained from 60 to 87 per cent of alunite, corresponding to 

 6-3 to 9-3 per cent of K 2 0. 



W. H. W. 



