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Lambina Opalfield
...a gem in South Australia's Far North
Jack
Townsend (Consulting Geologist and Gemmologist)
Important!
We have been advised that access is not permitted to the field unless a notice of entry has been served to the station owners 21 days in advance.
Details are available from PIRSA.
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 Introduction
Lambina Opalfield, 100km south of the Northern Territory border in South Australia's
remote Far North, is Australia's most recently worked source of precious opal.
Although diggings on this field have been worked intermittently for at least 30
years, it has only been in the last decade that production of precious opal has
become significant. This update of Lambina includes information on the opalfield's
history, geology, production, and characteristics of the opal.
When hypothesising
the formation of opal at Lambina, the author emphasises the possible influence
of Tertiary palaeochannels as conduits for water movement, and hence silica movement,
and the deposition of opal in immediately adjacent areas. |
Location
Lambina Opalfield is 58km northeast of the town of Marla, 90km northeast of Mintabie
Opalfield, and 10km south of Lambina Homestead (See map inset). Access to this
remote area is either from the Stuart Highway eastwards along the road to Granite
Downs and Lambina, and then along the old Oodnadatta Road that leaves this road
~60km east of Granite Downs and 5km south of Lambina Homestead, or east from Marla
11km then northeast to Broken Leg diggings and generally northwards to Lambina
Opalfield. The latter access is the preferred route taken by miners. Tracks from
the Seven Waterholes area lead to various 'diggings' around Lambina (Barnes et
al., 1992). Large map locates the opalfield and its surrounding 'diggings'. |
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Background
Lambina opalfield was probably discovered in the 1930s, but was not reported on
until 1956. It was visited and worked only intermittently in the 1950s, 1964,
1978 (Flint, 1980;Hiern, 1967), and then worked seriously from 1989 to the mid
1990s when available opaliferous 'ground' at Mintabie appeared to be diminishing.
A few miners tried their luck at the Seven Waterholes diggings (at the western
end of the opalfield) and, when word spread of their success, many others attempted
to take out opal claims over this occurrence which appeared to spread eastwards.
As Lambina Opalfield was located on a pastoral lease, the legislation required
to take out a mineral claim for opal was cumbersome and gaining access was not
easy.
Barry Lindner, President of the Mintabie Progress
Association, and later the South Australia Opal Miners' Association (SAOMA) and
former Department of Minerals and Energy Resources, became guarantors for rehabilitation
of 'diggings', with funds collected from a bond levied on each miner taking out
a lease near Lambina. This streamlined the process, but there was still much paperwork
involved. Native title issues were solved by having the appropriate Aboriginal
community make a native title claim, providing a group with whom the miners could
negotiate. The Lambina Native Title Agreement between SAOMA and the traditional
owners - the Antakirinja and Yunkuntjatjara people - was signed on 1 June 1998.
Lambina and its surrounds therefore became more accessible to opal miners, and
over 200 claims were registered in the next four months (see MESA Journal 11,
pp.28-29 for further information).
The Aboriginal people
negotiated first rights to noodle (fossick) for opal on the bulldozed dumps from
open-cut operations, and miners were allowed to camp on an area set aside for
camping. But it was agreed that no permanent residences would be allowed on the
opalfield.
As Lambina was not to be proclaimed a Precious
Stones Field, no officer from PIRSA was stationed on site, and miners had to travel
to Marla to register claims. Operations at Lambina and Mintabie are now coordinated
from Coober Pedy.
An exclusion zone was proclaimed over
Lambina in the mid-1990s to allow miners access to potential opal-bearing areas.
Mineral exploration licence holders cannot include exploration for opal in the
terms of the licence (See maps) |
Production
Opal production from fields
throughout Australia is difficult to estimate, but by using a formula determining
the amount of mining activity via the number of active claims, and documenting
the amount of equipment on particular opalfields, an estimate of production is
made in South Australia every six months and then combined into either a
calendar
or financial year total. Table 1 provides annual estimates of Lambina opal production
taken from the PIRSA Division of Minerals and Energy records. |
Table 1 | Estimates
from 1989 to 1998 are unknown, as all estimates to were included in the Mintabie
figures However, since 1999 Lambina other Far North opal diggings been treated
as a separate entity, that the estimates from 1995 to are deduced only from discussions
PIRSA's Coober Pedy Area Officers
Production increased through
late 1990s and peaked in 2001, with slight decrease in 2002. Total production
from Lambina and near surrounds has been estimated to exceed A$43 million. Production
prior to 1989 is assumed to be minor in comparison to that of recent years, when
large mining equipment was introduced. |
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| Geology
and Formation of Opal
Opal at Lambina
and other Far North opal 'diggings' is hosted mainly in rocks of Cretaceous age.
The age of the opal throughout the Great Artesian Basin (GAB) has been a point
of speculation, and claimed ages range from Cretaceous through to Recent. This
has led to a variety of geological models being proposed for opal formation because,
if the age of the formation cannot be dated, then the models for formation are
likewise many and varied. It is generally thought that Lambina opal formed during
Tertiary times.
The factors common to most South Australian
deposits (and the same appear to apply to other opalfields in Australia) are that
opal is associated with weathered sediments of the GAB, and generally with host
rocks of Cretaceous age. Mintabie is the exception, in that the opal-hosting rocks
are much older; but they are also weathered and do have onlapping Cretaceous sediments
(Townsend, 1981), although much of these sediments has been eroded away leaving
only remnants around Mintabie, and outliers further west.
Most
of the South Australian GAB sediments are marine (Bulldog Shale), whereas in Lightning
Ridge and parts of the Winton Formation in Queensland, the GAB sediments are terrestrial
(Horton, 2002). Horton also suggested that there was gentle warping of the GAB
sediments at ~24 Ma, and that the opalisation and silcrete formation occurred
at or after this, approaching the 20-18 Ma age (Tertiary times) suggested for
much of the South Australian opal.
All Australian opalfields
have silcrete (silicified claystone, siltstone or sandstone) capping the Cretaceous
and/or Tertiary sediments; this is also interpreted as having developed during
Tertiary times. However, the timing
of opalisation is necessarily identical
that of the silicification despite there being strong association geographic locality
tweenthe two.
At Lambina, opalised sandstone occurs well
as opal introduced into cracks, nodules replacing fossils such marine snails,
belemnites and bivalves. | |
Investigator Mark 10 auger drill. |
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| Trench
digger in a bulldozer cut. |  |
| Tracked
drilling rig |  |
| Bulldozer
in an open cut |
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| Influence
of Palaeochannels
Tertiary palaeochannels(ancient
river channels) have been found on many opalfields, and these are considered important
factors in opal genesis. They are generally coarse-grained sand bodies with good
porosity that could have acted as channels or conduits for water movement, and
hence silica movement and deposition of opal in adjacent areas. Similarly, faulting
or fault zones are associated with opal formation, and are therefore also considered
to be conduits for silica-rich groundwater.
The digital
elevation model (DEM) of Lambina (Fig. 3 below) indicates the possibility of remnant
channels trending east to west, and opal occurrences in the area extending from
Lambina through to Todmorden Outstation and south to Eeavinna Hill and England
Hill occur in 'breakaway' country of mesas and eroded plains that cut into the
Early Cretaceous Bulldog Shale.
As plotted on the DEM,
many known occurrences of opal are associated with these mesas (topographic highs,
shown in red); the interpreted palaeochannels are shown in white (Fig. 3). The
palaeochannels are interpreted as having originally been topographic lows - stream
channels that were later silicified during the Tertiary and now remain as highs
caused by a reversal in topography resulting from erosion of the softer surrounding
Tertiary and weathered Cretaceous sediments since late Tertiary times. |
| A
parcel of Lambina opal |  |
| Sorting:
Left dish shows opal stained with iron |  |
| Pieces
of Lambina opal |
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Fig. 3 Digital elevation model of Lambina and
other Far North opal diggings. A number of east-west-trending mesas interpreted
as remnant palaeochannels are outlined in white.
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 | Potential
Future Sources of Opal
As the occurrence
of opal in northern South Australia is so widespread — several hundred kilometres
north of Coober Pedy on 1:250 000 map areas such as WINTINNA, ABMINGA and through
to Mintabie opalfield on EVERARD - there appears to be much potential ranging
from England Hill (Townsend and Scott, 1981) in the south and Lambina (Flint,
1980) to the north, Todmorden to the east and Mintabie to the west. This area
of at least 10,000km2
includes sporadic occurrences of opal adjacent to mesas and, more importantly,
contains remnants of palaeochannels.
Interpretation of
remote sensing data will almost certainly assist in further discoveries of opal,
as has been shown using DEM pseudocolour images of Coober Pedy, Andamooka, and
now Lambina and its surrounds. At Mintabie, Andamooka and Coober Pedy, the DEM
images were made after most of the diggings were already known, but in northern
South Australia there are only a sprinkling of known opal occurrences over a very
large area of 'breakaway' landscape. Closer-spaced airborne surveys to produce
more detailed DEM images in selected areas should assist in this exploration. |
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| Precious
Lambina opal |
Acknowledgements
The author thanks the PIRSA Division of Minerals and Energy
for assistance with the photographs generated from the Coober Pedy office, and
provision of map images from PIRSA Spatial Information Services and Publishing
Services.
For further information contact Jack Townsend (Ph: 08 8297 4799,
Email: townsend.jack@myaccess.com.au) |
| References
Barnes, L.C., Townsend,
I.J., Robertson, R.S., and Scott, D.C.— 1992
Opal:
South Australia's Gemstone
South Australia Department of Mines and
Energy.Handbook, 5
Brown,
G., Townsend, 1.J. and Endor, K.— 1993
Some
Far Northern Opal Diggings in South Australia
Australian Gemmologist,
18(8):252-256
Flint,
D.J.— 1980
Lambina Opal Diggings.
South Australia Department of Mines and Energy. Report Book, 80/103 Hiern,
M.N.— 1967
Opal Deposits in
Northern South Australia
Mining Review, Adelaide, 122:37-39
Horton,
D.— 2002
Australian Sedimentary
Opal — Why Is Australia Unique?
Australian Gemmologist, 21(8):278-294
Primary
Industries and Resources South Australia— 1998
Lambina
Native Title Agreement
MESA Journal, 11:28-29 McCallum,
W.S.— 1980
Vesuvius Opal Diggings
South Australia Department of Mines and Energy. Report Book, 80/38 Townsend,
1.J. and Robertson, R.S.— 1980
Wallatinna
Opal Diggings
South Australia Department of Mines and Energy. Report
Book, 80/34 Townsend,
I.J. and Scott, D.C.— 1981
Sarda
Bluff, Ouldburra Hill, and England Hill Opal Diggings
South Australia
Department of Mines and Energy. Report Book, 81/17 Townsend,
I.J.— 1981
Discovery of Early
Cretaceous Sediments at Mintabie Opal Field
South Australia Geological
Survey. Quarterly Geological Notes, 77:8-15 Townsend,
I.J.— 1990
Mintabie
Opal Field: Mining and Geology
South Australia
Geological Survey. Quarterly Geological Notes, 117:8-15 |
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