The Tasmanian Geologist - Geological Society of Australia
The Tasmanian Geologist - Geological Society of Australia
The Tasmanian Geologist - Geological Society of Australia
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<strong>The</strong><br />
<strong>Tasmanian</strong><br />
<strong>Geologist</strong><br />
NEXT MEETING:<br />
Monday 16 th February<br />
7.30 pm<br />
Hotel Cecil, Zeehan<br />
Speaker:<br />
Pr<strong>of</strong>. Ross R. Large<br />
CODES<br />
ARC Centre <strong>of</strong> Excellence in Ore Deposits<br />
University <strong>of</strong> Tasmania<br />
Pyrite:what it can tell us<br />
about ore deposits<br />
Abstract inside<br />
Newsletter <strong>of</strong> the<br />
Tasmania Division<br />
Royal <strong>Society</strong> <strong>of</strong> Tasmania<br />
Charles Darwin bicentenary activities<br />
DARWIN SYMPOSIUM<br />
7.00 pm. Wednesday 11 th February<br />
Stanley Burbury <strong>The</strong>atre,<br />
University <strong>of</strong> Tasmania<br />
Speakers are Mr Peter Stevenson, Dr David<br />
Leaman, Dr Peter McQuillan, Pr<strong>of</strong>. Michael<br />
Roe and Dr Robert Banks.<br />
ADMISSION FREE<br />
Also-<br />
Saturday 14 th February-<br />
Excursion to Queen’s Domain (cost $10)<br />
Sunday 15 th February-<br />
Excursion to Mt Wellington (cost $10)<br />
Further enquiries to<br />
royal.society@tmag.tas.gov.au or Ph 62114177<br />
February 2009<br />
ADVANCE NOTICE<br />
Thursday 19 th March<br />
Joint meeting with the <strong>Australia</strong>n Institute <strong>of</strong><br />
Geoscientists (AIG):<br />
Speaker- Dr. Greg Corbett<br />
Topic, time and venue to be announced<br />
ALSO INSIDE<br />
• King Island field symposium<br />
• Proposed Twelvetrees Medal<br />
• <strong>Geological</strong> Evolution <strong>of</strong> Tasmania<br />
volume- progress.<br />
<strong>The</strong> <strong>Tasmanian</strong> <strong>Geologist</strong>, 10th February 2008
King Island Field Symposium<br />
13 th -16 th March 2009<br />
This is now fully booked, with<br />
arrangements made for 24 registrants and 2<br />
reserves. Eight participants have chosen an<br />
add-on trip to visit possible <strong>Tasmanian</strong><br />
correlates at Waratah Bay, Victoria on 16 th -<br />
17 th March (organized by David Taylor,<br />
GSV).<br />
Further details are available on the<br />
GSA website: www.gsa.org.au<br />
For further inquiries contact the Secretary<br />
andrew.mcneill@utas.edu.au<br />
Organizing committee: Nick Direen, Clive<br />
Calver, Andrew McNeill.<br />
W. H. Twelvetrees Medal<br />
<strong>The</strong> Committee has proposed that a<br />
medal be struck in honour <strong>of</strong> the memory <strong>of</strong><br />
the eminent <strong>Tasmanian</strong> government<br />
geologist, William Harper Twelvetrees<br />
(1848 – 1919).<br />
<strong>The</strong> suggestion is that the medal be<br />
awarded at the discretion <strong>of</strong> the <strong>Tasmanian</strong><br />
Division <strong>of</strong> the <strong>Geological</strong> <strong>Society</strong> <strong>of</strong><br />
<strong>Australia</strong>, usually annually, to recognize<br />
either:<br />
• important contributions to the Earth<br />
Sciences with Tasmania (including<br />
Macquarie Island); or<br />
• outstanding contributions to Earth<br />
Sciences while resident in Tasmania.<br />
In the spirit <strong>of</strong> W. H. Twelvetrees,<br />
contributions shall be considered to include<br />
meritorious feats <strong>of</strong> geological exploration<br />
in Tasmania or elsewhere; significant<br />
published works; or meritorious service to<br />
the Earth Sciences.<br />
Two or more members <strong>of</strong> the <strong>Society</strong><br />
can nominate a member for the award by<br />
submitting to the Divisional Committee the<br />
name <strong>of</strong> the candidate, biographical data,<br />
and a citation in about 300 words describing<br />
the candidate’s work and its significance.<br />
Nominations will be valid for up to five<br />
years after the nomination date. <strong>The</strong> medal<br />
may be awarded posthumously if the<br />
candidate was alive at the time <strong>of</strong><br />
nomination.<br />
Comments and suggestions from<br />
members are invited. <strong>The</strong> proposal will be<br />
put to a meeting in early 2009.<br />
“<strong>Geological</strong> Evolution <strong>of</strong><br />
Tasmania” Volume<br />
<strong>The</strong> committee met with the editors<br />
on 22 nd January to review progress. <strong>The</strong><br />
majority <strong>of</strong> contributions have been<br />
received, and letters have been sent to the<br />
remaining contributors. <strong>The</strong> following<br />
timetable will be implemented:<br />
30 th June: final deadline for all submissions<br />
15 th August: deadline for return <strong>of</strong> peer<br />
reviews<br />
15 th September: deadline for author<br />
corrections<br />
15 th October: deadline for completion <strong>of</strong><br />
editorial content.<br />
Dr Clive Calver has been appointed<br />
joint editor, in addition to Dr Keith Corbett<br />
and Pr<strong>of</strong>. Patrick Quilty.<br />
<strong>The</strong> committee has also resolved that<br />
the book will be produced in electronic, as<br />
well as printed form.<br />
Membership<br />
New applications<br />
Jafar Taheri<br />
Lindsay Clarke (student)<br />
J. Moye (student)<br />
Students remember- the <strong>Tasmanian</strong><br />
Division will pay your $10 membership fee<br />
in full!<br />
<strong>Geological</strong> <strong>Society</strong> <strong>of</strong> <strong>Australia</strong> website:<br />
www.gsa.org.au<br />
2009/2010 Divisional<br />
Committee<br />
Speakers wanted<br />
<strong>The</strong> Annual General Meeting is planned for<br />
Please April. contact All executive the Secretary and if you committee know <strong>of</strong><br />
any positions visitors will or returning fall vacant. <strong>Tasmanian</strong>s To assist willing in<br />
and planning, able to present expressions a talk at <strong>of</strong> a GSA interest meeting. from<br />
members willing and able to serve are<br />
sought by the current Secretary. Please<br />
consider if you are able to assist in your<br />
society!<br />
<strong>The</strong> role <strong>of</strong> diagenetic and metamorphic<br />
processes in the multi-stage concentration <strong>of</strong><br />
<strong>The</strong> <strong>Tasmanian</strong> <strong>Geologist</strong>, 10th February 2008
gold, arsenic and vanadium in black shale<br />
and turbidite-hosted gold deposits.<br />
Ross R Large<br />
Organic-rich mudstones or shales, within thick<br />
packages <strong>of</strong> calcareous or siliciclastic turbidites,<br />
have long been recognised as important host rocks<br />
for major gold deposits (e.g. Victorian Goldfield,<br />
Carlin District, Lena Gold Province, Otago Schist<br />
belt). Many <strong>of</strong> the deposits in these districts are<br />
referred to as orogenic gold deposits, emphasising<br />
the tectonic and metamorphic processes involved in<br />
the concentration <strong>of</strong> gold (Groves et al., 2003;<br />
Goldfarb et al., 2005). <strong>The</strong> current genetic models<br />
propose that the organic-rich sedimentary host rocks<br />
are the trap-rock for gold precipitated during<br />
deformation-related fluid flow, with the gold being<br />
transported by deep-sourced fluids <strong>of</strong> mantle or<br />
lower crustal origin, or in some cases from felsic<br />
magmas. Recent research at CODES (Wood and<br />
Large, 2007; Large et al., 2007) suggests the<br />
possibility that organic-rich black shales are<br />
potential source rocks for gold, arsenic and<br />
vanadium, and that the gold was originally trapped<br />
on seafloor organic material by chemical process<br />
during sedimentation and concentrated in arsenian<br />
pyrite during diagenesis.<br />
Research on the giant black shale-hosted Sukhoi<br />
Log deposit in the Lena gold province <strong>of</strong> Siberia<br />
(Large et al. 2007, Scott et al, 2007) has revealed a<br />
multi-stage process <strong>of</strong> gold concentration and<br />
release that occurred throughout the 50 million year<br />
period <strong>of</strong> sedimentation, diagenesis and<br />
metamorphism in the Bodaibo trough. We have used<br />
the rapidly developing laser ablation ICP-MS<br />
technology to study the siting and partitioning <strong>of</strong><br />
gold, arsenic, vanadium and other metals during<br />
diagenesis and metamorphism <strong>of</strong> the black shales.<br />
During periods <strong>of</strong> extreme euxinic conditions on the<br />
seafloor, gold and a range <strong>of</strong> other trace elements<br />
(As, Zn, Ag, V, Ni, Mo, Pb, Se, Te, Cu, Cr, U) are<br />
trapped on organic-surfaces forming strong organometallic<br />
ligands, leading to a concentration <strong>of</strong> metals<br />
in the most organic-rich facies <strong>of</strong> the sediments (e.g.<br />
Algeo and Maynard, 2004; Rimmer, 2004). During<br />
diagenesis, pyrite framboids, and clusters <strong>of</strong> pyrite<br />
micro-crystals <strong>of</strong> various textural forms, grow<br />
within the organic-rich sediments, commonly<br />
mediated by the biological reduction <strong>of</strong> marine<br />
sulfate to H 2 S. A portion <strong>of</strong> the gold and arsenic,<br />
plus many other trace elements (particularly Ni, Mo,<br />
Se, Pb, Ag, Te, Cu) are partitioned into the<br />
diagenetic pyrite. Other trace elements remain in the<br />
organics or form insoluble oxy-hydroxides<br />
(particularly V, U, Cr, Algeo and Maynard, 2004).<br />
<strong>The</strong> arsenic content <strong>of</strong> the diagenetic pyrite is a<br />
critical control on the amount <strong>of</strong> gold that is trapped<br />
within the sediment (Reich et al., 2005). <strong>The</strong> more<br />
arsenic-rich the black shale package, the more gold<br />
that is likely to be trapped during early diagenesis,<br />
thus contributing to form a more suitable gold<br />
source rock.<br />
With the onset <strong>of</strong> late diagenesis, the early<br />
forms <strong>of</strong> micro-crystalline gold-bearing arsenian<br />
pyrite, recrystallise to larger crystals ( commonly <<br />
0.2 mm) <strong>of</strong> subhedral to euhedral pyrite, or in some<br />
cases pyrite nodules, developed parallel to bedding.<br />
Some gold and selected other trace elements are<br />
released during this process forming a gold-bearing<br />
diagenetic fluid, that may migrate and deposit free<br />
gold in late diagenetic structures. As the sediment<br />
passes through the oil window, mobile organics<br />
migrate along structures and may transport further<br />
gold, dissolved within the organic-rich fluid<br />
(William-Jones and Migdisov, 2007). <strong>The</strong>se<br />
processes have also been observed in the Carlin<br />
district (Emsbo and Koenig, 2005).<br />
Deformation and metamorphism is<br />
accompanied by further recrystallisation and growth<br />
<strong>of</strong> pyrite in the black shales. <strong>The</strong> syn-deformation<br />
pyrite is commonly coarser grained (0.2 to 20 mm),<br />
with less sediment inclusions, and a significantly<br />
lower dissolved trace element content (Large et al.,<br />
2007). Gold originally dissolved in the diagenetic<br />
pyrite is released during metamorphism to form free<br />
gold, which concentrates in preferred structural sites<br />
(anticlinal zones or shears) associated with either<br />
metamorphic pyrite or syn-deformation quartz veins.<br />
Not only is the gold released from the diagenetic<br />
pyrite during metamorphism, but other trace<br />
elements, in particular, Cu, Zn, Pb, Ag, Bi, Te, are<br />
also released to form minor discrete sulfides<br />
(sphalerite, chalcopyrite, galena and various goldsilver-tellurides)<br />
which commonly form inclusions<br />
within the metamorphic pyrites. Certain elements,<br />
that are strongly held within the structure <strong>of</strong> pyrite<br />
(e.g. As, Ni, Co, Se), remain to become concentrated<br />
in the metamorphic pyrite. Vanadium which was<br />
originally concentrated in organic matter in the<br />
sediments, by reduction <strong>of</strong> V 5+ to V 4+ (Wood, 1996),<br />
is subsequently incorporated into gold-bearing<br />
diagenetic pyrite as micro-inclusions <strong>of</strong> V-bearing<br />
illite, and finally occurs as roscolite, intergrown with<br />
pyrite and free gold, in metamorphic assemblages.<br />
At higher metamorphic grades, above middle<br />
greenschist facies, much <strong>of</strong> the early diagenetic<br />
pyrite is converted to pyrrhotite. This is<br />
accompanied by the complete release <strong>of</strong> gold to the<br />
metamorphic fluid, as pyrrhotite, unlike pyrite, has a<br />
low trace element content and does not<br />
accommodate significant gold or arsenic within its<br />
structure (Buryak, 1982; Large et al, in press). For<br />
this reason pyrrhotite-rich black shales are unlikely<br />
to be good host-rocks for gold.<br />
In conclusion, organic rich black shales,<br />
especially those enriched in As, Ni, Mo, Pb, Zn and<br />
V are ideal source rocks for gold. Diagenetic and<br />
metamorphic processes are critical to releasing the<br />
gold, originally bound in organic-matter and<br />
dissolved within early arsenian pyrite, to become<br />
concentrated in later stages <strong>of</strong> syn-deformation<br />
pyrite and associated quartz veins.<br />
Full references are available from the editor or<br />
author on request.<br />
Abstracts from IAVCEI meeting<br />
<strong>The</strong> GSA (<strong>Tasmanian</strong> Division) gave financial support to<br />
assist two students attending the IAVCEI ( International<br />
<strong>The</strong> <strong>Tasmanian</strong> <strong>Geologist</strong>, 10th February 2008
Association <strong>of</strong> Volcanology and Chemistry <strong>of</strong> the Earth’s<br />
Interior) meeting in Reykjavik, Iceland in 2008. In<br />
accordance with our funding policy (see November<br />
newsletter), we reproduce abstracts <strong>of</strong> the papers<br />
presented by them.<br />
Facies analysis <strong>of</strong> a partly extrusive, basaltic<br />
submarine cryptodome, Shirahama Group,<br />
Izu Peninsula, Japan<br />
Sarah M. Gordee, J. McPhie & S. R. Allen<br />
University <strong>of</strong> Tasmania<br />
<strong>The</strong> physical evolution <strong>of</strong> modern and ancient<br />
volcanic environments can be best understood through<br />
the essential field technique <strong>of</strong> facies mapping. Detailed<br />
mapping <strong>of</strong> volcanic deposits in SW Izu Peninsula, Japan<br />
has provided information that exemplifies the importance<br />
<strong>of</strong> this method. Two main facies associations were<br />
identified that provide information on the eruption<br />
history and lateral changes in eruption style <strong>of</strong> a<br />
submarine basaltic volcanic complex<br />
<strong>The</strong> first facies association comprises massive,<br />
monomictic, jigsaw-fit basalt breccia that grades<br />
vertically and laterally into thick beds <strong>of</strong> reversely<br />
graded, clast-rotated to chaotic, monomictic basalt<br />
breccia. Clasts are angular with curviplanar margins and<br />
are interpreted to have formed by quench fragmentation.<br />
Jigsaw-fit breccia and associated breccia beds are<br />
interpreted as in situ and resedimented hyaloclastite,<br />
respectively. <strong>The</strong> succession is overlain and partly<br />
infilled by thin beds <strong>of</strong> pumiceous sand.<br />
<strong>The</strong> second facies association comprises<br />
elongate, tightly packed, coherent basalt lobes that grade<br />
into domains <strong>of</strong> monomictic, jigsaw-fit to chaotic, clastto<br />
matrix-supported basalt breccia with pumiceous sand<br />
matrix. <strong>The</strong> coherent lobes cross-cut and locally disrupt<br />
the overlying pumiceous sand beds. <strong>The</strong> clasts in the<br />
sediment-matrix basalt breccia are texturally and<br />
compositionally identical to the coherent lobes and the<br />
facies is interpreted as peperite.<br />
Collectively, the two facies associations are<br />
interpreted to represent the margin <strong>of</strong> a partly extrusive<br />
submarine cryptodome. In situ and resedimented<br />
hyaloclastite breccias indicate an extrusive, subaqueous<br />
environment and are consistent with expected facies<br />
associations across the quench fragmented carapace and<br />
resedimented flanks <strong>of</strong> a seafloor basaltic lava dome.<br />
Pumiceous sand infilled the interstices within the breccia<br />
pile to form a sediment-matrix breccia. <strong>The</strong> facies<br />
association comprising coherent lobes and peperite<br />
indicates an intrusive origin and is interpreted to<br />
represent the subsurface portion <strong>of</strong> the cryptodome. <strong>The</strong><br />
intrusion utilized syn-depositional micro-grabbens within<br />
the pumiceous sand that developed in response to the<br />
expanding magma body beneath the surface, and<br />
interaction <strong>of</strong> the magma with the wet, unconsolidated<br />
sand produced peperitic domains. Regionally, another<br />
similar facies association at the same stratigraphic<br />
interval includes a thick mound <strong>of</strong> basaltic fluidal clast<br />
breccia that may represent weakly explosive fire<br />
fountaining at another seafloor vent.<br />
<strong>The</strong> Luise amphitheatre, Lihir Island, Papua<br />
New Guinea: Caldera, maar crater or<br />
sector-collapse scar?<br />
Jacqueline L. Blackwell 1 , Jocelyn McPhie 1 ,<br />
David R. Cooke 1 , Kirstie A. Simpson 1 ,<br />
Jonathon Rutter 2<br />
1<br />
<strong>Australia</strong>n Research Council Centre for Excellence in<br />
Ore Deposits<br />
2<br />
LGL, Lihir Operations, Papua New Guinea<br />
<strong>The</strong> 40Moz. Ladolam gold deposit on Lihir<br />
Island, Papua New Guinea occurs in a 3.5 by 4.0 km<br />
seaward-facing, horseshoe-shaped amphitheatre.<br />
Previous workers have postulated that the amphitheatre<br />
is a caldera, a maar-diatreme crater or a volcanic sector<br />
collapse amphitheatre. Correct interpretation <strong>of</strong> the<br />
amphitheatre underpins understanding <strong>of</strong> ore formation.<br />
Our analysis <strong>of</strong> the dimensions and morphology<br />
<strong>of</strong> the amphitheatre, together with mapping and logging<br />
the bedrock facies in which it occurs, strongly favours<br />
sector collapse <strong>of</strong> the former Luise volcano. <strong>The</strong><br />
amphitheatre is much larger than maar-craters and lacks<br />
the pyroclastic facies typically associated with both<br />
maars and caldera. <strong>The</strong> bedrock mainly comprises<br />
variable altered trachyandesitic and trachybasaltic lavas<br />
and shallow intrusions, and volcaniclastic facies typical<br />
<strong>of</strong> the proximal and medial parts <strong>of</strong> andesitic cone<br />
volcanoes. Furthermore, bathymetry surrounding Lihir<br />
Island has revealed the presence <strong>of</strong> hummocky<br />
topography and marginal levees extending <strong>of</strong>fshore from<br />
the Luise harbour, interpreted to be a debris avalanche<br />
deposit. A coral-limestone unit that encircles the rest <strong>of</strong><br />
the island is absent from the Luise harbour, having been<br />
destroyed by a sector-collapse-generated debris<br />
avalanche.<br />
Sector collapse involving removal <strong>of</strong> ~ 1 km <strong>of</strong><br />
the former Luise volcano is consistent with porphyry –<br />
style alteration being overprinted by epithermal-style<br />
mineralisation and alteration.<br />
GSA Tas. Division Committee (2008-09)<br />
Chairman: Dr Nick Direen<br />
Tel 0413 030612<br />
ndireen@frogtech.com.au<br />
Secretary: Dr Andrew McNeill<br />
C/- CODES, University <strong>of</strong> Tasmania<br />
Private Bag 79<br />
Hobart 7001<br />
Tel: 03 62262487<br />
Fax: 03 62267662<br />
andrew.mcneill@utas.edu.au<br />
Treasurer: Dr Peter McGoldrick<br />
Committee Members:<br />
Dr Ron Berry<br />
Dr Garry Davidson<br />
Dr Mark Duffett<br />
Mr John Everard (newsletter editor)<br />
jeverard@mrt.tas.gov.au<br />
Dr Jacqueline Halpin<br />
Mr Michael Vicary<br />
Ms Isabella von Lichtan<br />
<strong>The</strong> <strong>Tasmanian</strong> <strong>Geologist</strong>, 10th February 2008