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Abstract

Mineralisation in the Rendeep area occurs below 1700m RL (>550m from surface) at
the northern end of the Renison Tin Mine, Renison Bell, western Tasmania. Probable
reserves of the Rendeep area are .3.3Mt at 1.96% Sn (Thomas, 1994), compared to
remaining proven and probable reserves of 6.4Mt at 1.41% Sn for the upper mine
(Thomas & Roberts, 1994).
The Renison deposit is hosted by supratidal to intertidal dolomitic and siliciclastic
sediments of the Renison Mine Sequence which comprises the upper —80m of the late
Precambrian Success Creek Group and the lower —60m of the Cambrian(?) Crimson
Creek Formation. Minor facies variations occur in the Rendeep area but gross thickness
variations are the result of structural processes. The strongly layered Renison Mine
Sequence tends to deform by interstratal slip in contrast to the rigidity of the relatively
massive underlying and overlying formations. Devonian D3 deformation, which dominates the Rendeep area, resulted from the radial
stress field produced by the forceful emplacement of the Pine Hill Granite into the D2
Renison Bell Anticline axis (Ktto, 1994). The granite surface plunges northeast under the
Rendeep area from its local high beneath the central part of the Renison deposit. The
Federal-Bassett Fault developed over the local granite high and is transitional to a
monoclinal fold in the Rendeep and North Bassett areas. Syn-intrusive, sub-vertical
extension produced 770m vertical displacement of the Renison Mine Sequence in the
North Bassett/Rendeep area by combined ductile and brittle processes, with ductile
processes favoured by elevated temperatures and pressures(?) closer to the granite.
The North Bassett Fault formed by layer-parallel extension of the Renison Mine
Sequence close to its contact with overlying Crimson Creek Formation. Conjugate subvertical
brittle-ductile extensional structures, Faults A and Z, formed subparallel to the
principle stress direction. Strain transferral from the North Bassett Fault onto Faults A
and Z produced a broad, concave-east open fold in the North Bassett Fault and Renison
Mine Sequence north of 66400m N. The fold axial region, which plunges —700 S,
became a major upflow zone for hydrothermal fluids during later brittle reactivations.
Draping of the Renison Mine Sequence along Fault Z and normal movement on the
antithetic Csar Fault produced the Rendeep Graben/Syncline. Dilation of the North
Bassett Fault above the Rendeep Graben/Syncline focussed hydrothermal fluid flow.
Brittle dip-slip reactivation of the Federal-Bassett Fault occurred late in the D3
deformational event, faulting the crystalline carapace of the cooling Pine Hill Granite and
releasing hydrothermal fluids.
D3 dextral wrench deformation accompanied the decay of the radial stress field
associated with the Pine Hill Granite intrusion and a return to the regional Tabberabberan
stress field (Ktto, 1994). Brittle strike-slip reactivations occurred on all major faults and a weak dextral kink fold formed in the Renison Mine Sequence interstitial to Fault A and
the North Bassett Fault, the hinge zone of which became a local focus for hydrothermal
fluid flow.
Rendeep mineralisation is predominantly "stratabound", consisting of dolomite horizons
of the Renison Mine Sequence replaced by an assemblage of pyrrhotite ± talc ±
cassiterrte and minor arsenopyrfte. Stratabound mineralisation becomes more localised
about feeder structures on approaching the Pine Hill Granite, due to the effect of
increasing temperatures and pressures(?) on the brittle/ductile transition in dolomite.
Ductile behaviour in dolomite may inhibit fluid/rock interaction by restricting fracture
propagation. A radius of 400m from the Pine Hill Granite is proposed as the minimum
distance to economic stratabound tin mineralisation based on sparse drilling information
in the Rendeep area.
Hydrothermal fluid flow paths are identified by integrating the modelled tin grade
distribution, sulphur and oxygen isotope data, and fluid inclusion data with the structural
interpretation. Possible extensions to Rendeep mineralisation are predicted by
extrapolating the hydrothermal fluid flow paths along controlling structural features.

Item Type:	Thesis - Coursework Master
Authors/Creators:	McQuitty, BM
Keywords:	Tin ores, Hydrothermal deposits
Copyright Holders:	The Author
Copyright Information:	Copyright 1995 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (M.Econ.Geol.)--University of Tasmania, 1995. Includes bibliographical references (p. 146-152)
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