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ECONOMIC GEOLOGY

Mt. Lyell schists (porphyrite lavasand volcanic ash which have
been crushed into sericite schist), with the massive conglomerates
 and quartzites of the West Coast Range of Tasmania.
The conglomerates are
probably Devonian and
occur E. of the Mt. Lyell
schists, which are thrust
over the conglomerate by
a long and complex fault,
associated with crossfaults
 and thrustplanes.
In places wedges of conglomerate
 have been
thrust into the schists.
The Mt. Lyell Mine is in
a bay of schist which has
been nipped between
three faults, and was so
shattered that it was
completely permeated by
ore-bearing solutions.
The ore is an irregular
boat-shaped mass of iron
pyrites which contained
over seven million tonsa
It was at the surfac: 800
feet long by 200 feet
broad; it widened below
to 300 feet, but at lower
levels decreased in size,
and ended abruptly, at
the depth of about 750
feet, over the underthrust
 conglomerate. The
ore on the footwall side
contained about 2-35 per
cent. of copper with a
little gold and silver; its richness was probably due to the
solutions being nearly stagnant and giving time for the
precipitation of the metals. The ore along the hanging
wall was so low grade that it only paid to mine as fuel and

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