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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. Technical Report. University of Tasmania/AMIRA, Hobart, Tasmania,. (Unpublished)

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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 (HF). 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 thrusting. 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)
Publisher: University of Tasmania/AMIRA
Date Deposited: 18 Aug 2009 02:21
Last Modified: 18 Nov 2014 04:04
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