Cambrian intrusion-related copper mineralisation at the Thomas Creek prospect, Southwestern Tasmania
Reid, R (2001) Cambrian intrusion-related copper mineralisation at the Thomas Creek prospect, Southwestern Tasmania. Coursework Master thesis, University of Tasmania.
The Thomas Creek Prospect lies at the southern end of the Sorell Peninsula, western
Tasmania and consists of intrusions believed to be coeval with copper mineralisation
within a dioritic intrusive complex. The prospect is hosted by the Noddy Creek
Volcanics, which are geochemically correlated to the calc-alkaline Mt Read
Widespread (600 by 400 m) but low grade copper mineralisation is hosted by diorites
and feldspar~augite porphyritic andesite intrusions, which have been intruded by
chalcopyrite-bearing porphyritic micromonzodiorites. Early disseminated magnetite,
pyrite and chalcopyrite formed prior to and synchronous with pervasive feldsparsilicate
alteration. Various chalcopyrite-bearing vein generations (actinolite,
tounnaline, K-feldspar- smectite, epidote and carbonate) have overprinted the earlyformed
magnetite and feldspar-silicate alteration assemblages.
The "immobile" elements (Ti and P) were mostly mobilised during the fonnation of
pervasive K-feldspar hydrothermal alteration at Thomas Creek. A subset of the
geochemical data set exhibits coherent behaviour, indicating that the diorites and
porphyritic micromonzodiorites form a co-magmatic fractionation series. Coherent
behaviour ofBa, Rb, Sr and K20 has been recognised for the igneous suite. Both
primary and secondary K-feldspar appear to be intrusion-related. Fe, S, P, Zn and Cu
appear to have been lost during fractionation due to devolatilisation of the
Sulphur isotope values of sulphides at Thomas Creek range from -4.9 to 11.5%o.
Sulphides in the early formed magnetite and feldspar-silicate alteration assemblages
have similar s34s ranges (5.3 to 9.3%o). The isotopic range in the porphyritic
micromonzodiorites (8.2 to 11.5%o) is believed to have formed in response to
fractionation and devolatilisation of 32s-rich hydrothermal fluids, resulting in
isotopically lighter signatures (-4.9 to 7.7%o) in veins related to the intrusions. Sulphur isotope geothennometry, utilising co-existing pyrite-chalcopyrite pairs, indicates
mineralisation temperatures in veins ranged from 254 to 611 °C.
Four stages of mineralisation have been recognised at Thomas Creek: 1:- early
magnetite and feldspar-silicate alteration; 2:- emplacement of Cu-bearing
micromonzodiorite intrusions and precipitation of coeval actinolite and tourmaline
veins; 3:- K-feldspar- smectite vein formation; and 4:- epidote and carbonate veining_
Phases 1 and 2 represent periods of magma emplacement with some mixing of
magmatic-hydrothermal water with seawater-derived fluid. Phase 3 veins appear to be
of magmatic character, with minimal seawater influence. Phase 4 probably represents
final incursion of seawater-derived fluids as the magmatic system waned.
Thomas Creek can be correlated to Mt Lyell copper-gold mineralisation, based on
similarity of sulphur isotope distribution and ore mineralogy. Mineralisation at the
Thomas Creek Prospect is believed to represent the root zone of a Mt Lyell-type
hydrothermal system_ There are also some similarities with the alkaline porphyry CuAu
deposits of British Columbia, with Thomas Creek possibly being the submarine
analogue of a porphyry system formed in a back arc environment.
|Item Type:||Thesis (Coursework Master)|
|Additional Information:||Copyright 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).|
|Deposited By:||ePrints Officer|
|Deposited On:||23 Jun 2012 22:54|
|Last Modified:||04 Sep 2012 12:20|
|ePrint Statistics:||View statistics for this ePrint|
Repository Staff Only: item control page