52 PROCEEDINGS OF THE ROYAL SOCIETY OF QUEENSLAND. 
in sinking shafts and driving crosscuts to develop some of the principal 
abandoned mines. However, the objective of getting mica to pay for this 
work was not attained, because the mining methods adopted were 
quite unsuitable, much valuable mica being damaged or destroyed by 
indiscriminate machine-drilling and the excessive use of explosives. 
The experienced mica miner always examines his drillings, and he 
also knows when his drill touches a mica-book by the toughness of the 
boring. 
It may be wondered why there are no productive mica mines in the 
far northern portions of the Territory, as in the Pine Creek to Maranboy 
region. The rocks there are also very old Pre-Cambrian, and numerous 
pegmatite dykes from adjoining granite masses occur in them. The 
explanation is that the Pre-Cambrian rocks of the far north consist of 
slates, fine-grained sericitic and mica-schists, quartzites and related rocks, 
but they seldom contain any coarsely crystalline rocks, like the gneisses 
and amphibolites of Central Australia. The Pre-Cambrian rocks of the 
far north belong to Grubenman’s Middle Zone series of metamorphic 
rocks. They were cool and much fractured at the time of the granitic 
invasions, and therefore the gases and solutions escaped easily instead 
of playing the intricate part involved in producing book mica. 
VI. THE FUTURE OF MICA MINING. 
There are many who think that Australian mica deposits will soon 
become worked out. There is nothing to warrant this outlook. As the 
Hart’s Range region becomes more accessible, and cost of transport lower, 
and as scientific methods of searching for mica become more and more 
adopted, a large number, if not most, of the abandoned mines will yield 
new lenses, and many of the pegmatitic deposits may be worked to great 
depths. 
Diamond drilling may also greatly help in the discovery of new 
lenses. 
The mica deposits cannot be worked out, but they can be worked to 
a standstill and become abandoned through continuing the old system 
of surface scratching without developing on intelligent lines. 
