OCCURRENCE OF MICA IN CENTRAL AUSTRALIA. 
51 
here and there on the steep slopes far away from the dumps, which, when 
the sun falls at the right angle on them, glitter like diamonds. Almost 
all the principal mica mines of Central Australia are situated in the 
Hart’s Range and in similar rock formations along the Plenty River 
north of the Hart’s Range. A few pegmatite outcrops carrying a little 
book-mica have been found in odd gneissic outcrops in the region of 
Barrow Creek, and in a few places north of the Strangway Range. The 
latter have been worked to some extent and have yielded a small quantity 
of mica, but all other micaceous pegmatites have been found not worth 
working. 
The Plenty River mines (see plate III.) were only scratched until the 
Government took over the development of one of the groups, the Ajax 
Group. A strange theory existed amongst the old Italian, and other, mica 
miners to the effect that no mica mines are of any value unless they occur 
high up in the ranges. The Plenty River deposits were regarded by them 
only as pockets which would not live in depth. This idea is, of course, 
quite nonsensical, and the government work done in the Ajax Group, and 
later work by a private syndicate in the Binkum mine, show it to be so. 
In the steep ranges the mica deposits are eroded and exposed, so that they 
are easily seen and the dykes are easily traced. The quality of the mica 
is good from the outset, since there is no considerable superburden of 
decomposed rock in wdiich the mica has undergone deterioration. 
Tunnels or adits can be driven, and the waste rock slides down the 
mountain-side and does not encumber the workings. These are the 
advantages of the mountain mines. But there are serious disadvantages. 
The slopes are generally far too steep for any vehicular road to be made 
to the mine. In a number of cases it is impossible even to get a camel- 
track or a mule-track to it. There is no ground level enough to pitch a 
camp. The miners sometimes live a thousand feet or more lower down. 
Tools and timber, food and fuel have to be hauled by manpower up the 
steep slithery and rocky slopes. It is impossible to get drilling machinery, 
winches and petrol up. Consequently the work is carried on in the most 
primitive and arduous fashion. Every morning and night the men climb 
up or down carrying or dragging tools sharpened or to be sharpened, 
mica won during the day, and so on — a task more arduous than the hard 
labour in the mines. 
The mines in the low-lying flat to gently undulating country, as along 
the Plenty River, have the disadvantages of the outcrops being largely 
covered up with soil and difficult to trace, and of the pegmatite being 
acted on by wet-season water sufficiently to damage much of the mica 
down to water level, at 50 feet, or more, in depth. On the other hand 
the advantages of mines so situated are very great. Roads can be 
carried right up to them, and rock drills, engines, machinery, timber, 
tools of all descriptions, explosives and necessities for the miners, can 
be landed by truck at the very site where they are required. Conse- 
quently work can be carried out cheaply by the most labour-saving 
machinery and modern methods. It does not take long to sink a shaft 
to the undecomposed dyke rock. 
In 1943 and 1944 the government rendered good service in con- 
structing, by means of graders, a number of good roads to various 
points situated centrally to the mica mines of the Hart’s Range and 
Plenty River. It also had a number of bores sunk which gave the miners 
water supplies more reliable than those few natural holes and springs, 
which had previously supplied them. Very useful work was also done 
