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Structure and mineralisation of western Tasmania. AMIRA P291. Report No. 2. May 1991


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Berry, RF and Keele, RA 1991 , Structure and mineralisation of western Tasmania. AMIRA P291. Report No. 2. May 1991.

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Abstract for "An excursion guide for the Mt Lyell Mining Lease with emphasis on the Great Lyell Fault, Haulage·Unconformity and North Lyell alteration." R.F.Berry

The Devonian deformation at Mt Lyell includes early
N-S trending folds, NNW trending folds (D1), low
angle north directed thrusting and high reverse faults
with associated steep cleavage(D2). The pattern of
these structures is recognisable but where they interact
closely as in North Lyell there is still some problems
in unravelling the geometry. Many of the relationships
which were used to define these phases are exposed
on the Lyell leases.
The Haulage Unconformity is related to relatively
shallow dips to the east and the geometry is
compatible with a normal fault margin. However
regional data is supports a more active tectonic setting
in the late Cambrian and structure may vary very
rapidly in both time and space.
The age of the North Lyell alteration is less well
constrained. Both S1 and S2 are visible in the altered
Owen Conglomerate. The alteration does penetrate
into Pioneer Sandstone and possibly into Gordon
Limestone but the intensity drops off sharply at the
contact suggesting that either the alteration is nearly
finished at "Haulage time" or two stages of alteration
are required.

Introduction of "A description of the Howards Road Traverse" RA Keele.
At the western end of the traverse, the Pioneer Beds
lie unconformably over the rocks of the Lower Dundas
Formation (LDF).The angular unconformity is about
30°; considerable erosion is implied by the absence of
the Middle and Upper Dundas Formations
(equivalents of the Newton Creek Sandstone and
Owen Conglomerate to the east of the Henty Fault
The first section of the traverse (0-5 km) crosses
siltstones and shales of the LDF. These rocks
are variably cleaved and folded into two syncline-anticline
pairs. Bedding-cleavage measurements
indicate that the folds are non-cylindrical and that
the W-limbs of the anticlines (or E-limbs of the
synclines) plunge N, whilst the E-limbs plunge S.
The W-limbs of the anticlines are overturned,
indicating transport is to the west. The cores of the
anticlines are occupied by fine grained sandstones.

The second section of the traverse (5-8 km)
comprises shales, siltstones, sandstones, grits and
conglomerates of the White Spur Formation (WSF).
The folds in this formation are open to tight in style,
the hinges are generally well preserved and opposing
plunges much less marked than in the LDF. Regions
of steeply to vertically plunging bedding-cleavage
intersections are interspersed with the gentler
plunging folds.

The third section of the traverse through to the
Henty Fault (8-15 km), comprises thrusted rhyolitic
and dacitic volcanics, occasional interbedded shales
and mafic intrusives of the Central Volcanic Complex
(CVC). The WSF appears to lie conformably over the
CVC, although locally structural complications may
obscure the real contact relations; further north, the
boundary between the two domains is a sheared and
"collapsed" anticlinal hinge.

The last and final section, beyond the HF,
comprises volcanic rocks and volcaniclastic sediments
of the Tyndall Group and the basal Owen which lies
conformably over the latter. These rocks are folded
into S-plunging folds and are affected by N-directed

Proceed northwards from Queenstown on the
Zeehan Highway, crossing the Henty Bridge and
continue on for approximately 6 km to the Howards
Road turn off, which is on the right-hand side of the
highway. There is ample parking here.

Item Type: Report (Technical Report)
Authors/Creators:Berry, RF and Keele, RA
Publisher: University of Tasmania/AMIRA
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