Image: Storm clouds over the Jundee pit.
DESCRIPTIONS of ORE DEPOSITS
The deposits on the itinerary were:
Golden Cities - New Discovery.
Sunrise Dam & Sunrise -
New Mine, oxide & primary ore.
Chatterbox Shear Zone - Whisper, Rumour, Inuendo - New Discovery.
Granny Smith - Mature Project
(same district as Sunrise Dam, Chatterbox & Wallaby).
Wallaby - New Discovery.
Jundee - New Mine.
This tour of 4 days, commenced with an introductory meeting in Perth,
Western Australia at 6:00 pm on Tuesday 23 November, 1999, and finished in the
late afternoon of Saturday 28 November, 1999 at Perth airport.
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Ghost Crab & New Celebration
The Ghost Crab discovery is part of the greater New Celebration
operation. The main New Celebration plant is located some 35 km south east of
Kalgoorlie, while Ghost Crab is around 15 km to the west of this. Development of
the recently discovered shallow oxide resource at Ghost Crab commenced in mid 1997 to
exploit high grade oxide ore and reduce production costs of the New Celebration
operation. However this work established the potential for a larger body of ore and an
underground resource was delineated, extending beyond a depth of 400 m. Underground
mining, known as the Mt Marion Mine, began in 1999. In December 1997 reserves
totalled 3.5 mt @ 5.1 g/t Au. Mineralisation is associated with zones of strong
deformation in the north trending Karramindie Shear Zone which follows a regional
contact between mafic-ultramafic rocks (mainly talc-tremolite) and the Archaean Black
Flag Group sediments (quartz-veined biotitic greywackes). At Area 1 ore is hosted by
veined quartz-biotite greywackes, while Area 2 is in strongly sheared and altered
ultramafics with mafics (dolerites and magnesian basalt) and minor sediments.
The mine is operated by the majority shareholder Newcrest Mining Ltd, for the minority
partners of Croesus Mining NL and Sons of Gwalia Ltd.
The New Celebration gold project was established in 1986, with total
mineral resources in 1990 of 12.3 mt @ 2.65g/t Au in a number of separate bodies.
The majority of the resource was contained in a series of semi-continuous deposits
hosted by the NNW trending regional Boulder-Lefroy shear zone. The ore zone is within
the Kalgoorlie-St Ives Greenstone Belt in a sequence very similar to that at Kalgoorlie.
Within the main project area gold occurs in all stratigraphic units with the exception
of the Kapai Slate. Structure exerts the prime control on mineralisation at all
localities, although some rock type properties provide conditions more favourable to
ore grade mineralisation. The most important of these are the brittleness of the host,
and the availability of iron to assist in sulphide formation and gold precipitation.
There are three main categories of ore style, namely 1). those hosted by brittle
porphyries, within the shear zone and adjacent to the iron rich Kapai Slate; 2).
shear controlled mineralisation within basic volcanics and intrusives; and 3).
quartz-vein related ores within basic volcanics and intrusives (particularly the
gabbros/dolerites). The plant capacity at New Celebration is 1.7 mtpa. The operation
is controlled by Newcrest Mining Ltd.
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The Golden Cities group of deposits are located some 30 km to the
north of Kalgoorlie, in the south-western section of the Scotia-Kanowna Granitoid
Complex. It comprises a cluster of at least 12 prospects spread over an area of
100 km2. At the most advanced of these, Suva-Havana, drilling has intersected gold
bearing laterites, supergene oxide-gold and disseminated primary-gold mineralisation
associated with quartz veins and sulphides within fresh granite and basalt. At the
London prospect, gold is found within granite associated with quartz veining and
pyrite alteration, while at Lisbon it is related to weakly foliated
carbonate-silica-pyrite altered granite. Testing of the other prospects in the area
has revealed similar mineralisation. The first drilling was in late 1996. By mid
1998 the total resource at a 0.5 g/t Au cut-off was 17.6 mt @ 1.9 g/t Au, with
potential for substantial increases. The project is controlled by AMX Resources
NL - 100%.
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The Sunrise Dam mine is located approximately 55 km to the south of
Laverton, and 250 km north of Kalgoorlie in the Eastern Goldfields of WA. It exploits
the section of the Sunrise ore deposit that falls within the leases held by Acacia
Resources Ltd. The Sunrise section of the deposit, which straddles the title boundary,
is within the adjacent leases of Placer (Granny Smith) Pty Ltd, a joint venture between
Placer Dome Inc (60%) and Delta Gold NL (40%). The pits of the two operations overlap,
with Acacia at present mainly mining oxide ore, while the Placer (Granny Smith)
operation is currently in primary ore. Acacia also operates the Cleo pit adjacent to
the combined Sunrise pit. The ore at Sunrise-Cleo is developed within both the
Archaean sequence and the overlying transported cover. The basement ore lies within
the Laverton Tectonic Zone which is characterised by major north-south shears and
associated faults. The hosts comprise a strongly deformed sequence of
mafic-ultramafics, acid to intermediate volcano-sedimentary units and BIFs, intruded by
granitoids. Gold mineralisation is found intermittently within a NE trending corridor
over a length of 4.5 km, coincident with a strongly magnetic BIF sequence. In the
transported cover gold occurs within two distinct horizons, each of 2 to 12 m in
thickness over a 600x200 m area and at a depth of 5 to 40 m. These are related to
water table associated iron redox fronts. Below the unconformity ore is developed in
both oxidised and fresh bedrock, occurring as a shallow west dipping zone covering a
plan area of 1600x700 m, and extending to more than 700 m below the surface. In the
primary zone, gold is found in association with pyrite replacements of BIF, as shear
mineralisation in quartz-ankerite-pyrite veining and pervasive alteration, and as thin
In March 1999 the Acacia resource totalled 28.7 mt @ 3.5 g/t Au, while in December
1998 the Placer (Granny Smith) section of the deposit had a resource of 11.3 mt @ 3.2
g/t Au. Together these total more than 135 t Au. Production from both operations was
around 23 t of Au (0.75 Moz) making it one of Australia's largest and lowest cost
mines with cash operating costs at Acacia of $A148/oz. Recent extensions of the ore
at depth comprise the Sunrise Deeps discovery.
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The Chatterbox Group
The Chatterbox group of deposits of Whisper, Rumour and Innuendo predominantly comprise oxide gold occurrences spread over
an 11 km section of the Chatterbox Shear which extends for more than 25 km along the
western boundary of the Laverton Tectonic Zone. The rocks within the zone are largely
a mafic-ultramafic association, commonly basalt, with thin layers of BIF or
ferruginous chert. It is extensively intruded by adamellite and porphyry and is
deformed into tight upright folds with extensive strike-slip faulting. There is a
widespread regolith blanket composed of superficial cover to depths of up to 60 m,
underlain by oxidation extending to more than 100 m below the surface. The bulk of the
resource occurs as extremely soft, intensely weathered rock types, to depths of less
than 125 m. In December 1998, resources amounted to 9.65 mt @ 2.2 g/t Au.
Exploration has been undertaken under the Laverton Exploration Joint Venture,
comprising Delta Gold NL (50%) and Metex Resources NL (50%).
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The Granny Smith operation is also located within the Laverton
Tectonic Zone of the Eastern Goldfields. The main plant is some 25 km to the south of
Laverton. Gold is associated with structurally controlled dilatant sites on a major
NNW trending, east dipping, brittle-ductile shear zone. The weathered profile extends
to a depth of 50 to 80 m with gold being significantly depleted in the upper 20 m.
Historically mining has been within three orebodies, the Granny, Goanna and Windich
zones. Mineralisation is continuous over a 3500 m interval, being more intensely
developed at the three ore zones. To the north at Goanna the shear
and mineralisation are entirely within oxidised and weathered meta-sediments as a
500x50x8 m body dipping at 50 degrees to the east. Granny is 1500 m
further to the south where the shear marks the contact between the overlying sediments
and a composite diorite-granodiorite intrusive. The ore zone here is 600x250x30 m,
dipping east at 25 degrees. The third zone, Windich, is another 800 m to the south, on
the south-eastern corner of the intrusive-sediment contact. It is blind and lies
within a partially oxidised granodiorite with dimensions of 400x150x30 m dipping
north-east at 10 degrees. Gold is present as discrete interstitial grains, blebs and
clusters locked in late quartz and minor ankerite filled micro-fractures. Visible gold
is rare. There is a close relationship between gold and the quartz-diorite body, while
the gold is intimately associated with carbonate.
The Granny Smith mine is operated by Placer (Granny Smith) Pty Ltd and is a joint
venture between Delta Gold NL (40%) and Placer Dome Inc (60%). The initial resource
when the mine commenced operation was approximately 27 mt @ 1.6 g/t Au. Annual
production is just over 4 mt of ore at grades of from 2 to 4 g/t Au. Current
production is almost exclusively from the Sunrise pit, 30 km to the south.
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The Wallaby deposit and its continuation to the south,
Just in Case, are located within the Laverton Tectonic Zone, some
11 km to the west of Granny Smith. Three sub-horizontal to flat dipping and
sub-parallel mineralised lodes have been delineated over an area of 400 m along
strike and 600 m down dip by early 1999, although all were still open on two sides.
The main lodes have numerous, associated, smaller, less continuous, sub-parallel and
cross linking zones. Two main sets of granitic intrusions are found within the
mineralised zone. These are also mineralised where cut by the lodes, although the
mineralisation tends to be disseminated and of lower grade. The main host is a
series of Archaean polymict conglomerates. The bodies are masked by 15 to 70 m
of lake sediments. Intersections include 18 m @ 4.1 g/t Au, 10 m @ 19.1 g/t Au,
28 m @ 10.3 g/t Au and 38 m @ 2.3 g/t Au. The resource in mid 1999 was 41.7
mt @ 2.8 g/t Au for 115 t Au (3.7 Moz) to a depth of 400 m. With Just in Case,
the total resource is around 130 t Au (4.2 Moz). The Wallaby discovery was the
result of drilling in mid 1998. Wallaby is held by the Granny Smith Joint venture
(40% Delta Gold NL, 60% Placer Dome Inc), while the smaller Just in Case is in a
Homestake Mining-Abednego lease.
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The Jundee and adjacent Nimary gold deposits are
located 500 km to the north of Kalgoorlie and 50 km north-east of Wiluna in the Yandal
Greenstone Belt of WA. This greenstone belt has few historic gold workings, sparse
outcrop and a truncated lateritic profile. Mining at Jundee commenced in mid 1995.
At the end of 1998 the total resource at Jundee-Nimary was 41 mt @ 5.1 g/t Au,
for 210 t (6.75 Moz) of contained gold. It is being exploited from at least 5 open
pits and an underground mine, and treated by a 3 mtpa capacity plant. Regionally the
host sequence of the greenstone belt comprises lower BIFs and mafic to ultramafic
units, overlain by tholeiitic and high-Mg basalt and dolerite with minor sediments.
These are followed in turn by a sequence of felsic to intermediate volcanics with
minor chert, basalt and shale. On a regional scale, Jundee-Nimary is part of an
80 km line of anomalies defining an inferred south-east trending shear zone.
Jundee is at the contact between the mafic to ultramafics and the overlying acid to
intermediate volcanics. On a district scale, basalt and dolerite are important
hosts due to their brittle behaviour during low grade metamorphism, and their iron
content. The ore is localised in numerous quartz-carbonate-pyrite brittle veinlets
in four main orientations. The main host rocks are mafic in composition, and include
tholeiitic basalts, dolerites and spatially associated feldspar rich porphyry dykes.
Jundee-Nimary is operated by Great Central Mines Ltd.
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For more information contact: T M (Mike) Porter, of Porter GeoConsultancy (firstname.lastname@example.org)
This was another of the International Study Tours designed, developed, organised and escorted by T M (Mike) Porter of Porter GeoConsultancy Pty Ltd (PGC) in joint venture with the Australian Mineral Foundation (AMF). While the reputation and support of the AMF contributed to the establishment of the tours, after it ceased trading at the end of 2001, PGC has continued to develop, organise and manage the tour series.
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