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TASMANIA'S ORE DEPOSITS. I
In concluding his geological descrip
tion of Tasmania, 'Mr Twelvetrees re
fers to ore-deposition in this State as
follows: 'The period during which the
deposition of metalliferous ores was
most active was the interval between
the Upper -Silurian and PermoCarbon
iferous. Ore-deposition has been _ as
sociated principally with the consolida- j
t-ion of the. gabbroid ana granite
masses. Nickel sulphide and osmiri
dium owe their origin to the serpen-'
tine at the Heazlewood, Trial Harbor,
and Dundas. On the. other hand, the
granite magma is responsible f or the
lodes of silver-lead all over the islaifcj,
whether these pierce quartz-porphyry,
as at the Devon and Mount Tyndall,
slate, sandstone, and limestone, as at
Zeehan, or ultra-basic dyke rock, as at
the 'Magnet. The pyritic lead, zinc,
or copper ores of the West Coast Range
(Mount Lyell, Mount Bead, .'Mount
Black, etc.) are also most probably
due to tie action of the 'acid magma
Tin and wolfram ores are naturally re
ferred. to the .same soi ree, and the
quartz reefs of the Ordovician strata
must- be regarded as the result of the
expiring effort of the cooling magma
to get rid of its surplus available
silica. A few veins of barren quartz
occur in the Permo-Carboniferous
strata, but beyond the exceptional case
of the. alkali porphyries at Port Cyg
net; the chapter of metal-bearing lode
action closed, as it began, with the
Devonian period. Within that period,
therefore, were accumulated the great
stores of mineral rwhich the mining in
dustry of Tasmania is now drawing
upon. The mines of .gold, silver, lead,
copper, and tin rank high among the
famous mines of tlie world. Her
mineral wealth may, in fact, be con
sidered remarkable when, despite the
small area of the island (26,000 square
miles), the value of the mineral pro
duced for the year ending December
31, 1907, amounted to £2,277.159.
The industry is thriving, is on a sound
and established basis, and with the
careful administration and care -which
it receives, it may with confidence be
expected to continue a highly import
ant asset of the State for a quite in
definite period of time.
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