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The Mindarie heavy mineral sand zircon, ilmenite deposits are located in the lower south western corner of the Murray Basin, 60 km south-west of Loxton and 150 km east of Adelaide in South Australia (#Location: centred on 34° 47' 18"S, 140° 13' 9"E).
The Murray Basin covers an area of approximately 0.3 million km2, low relief, saucer-shaped intracratonic basin, filled by a Cainozoic sequence of marine and terrestrial sediments which is up to 600 m thick in the west-central Renmark Trough area, but is generally 200 to 300 m elsewhere in the basin (Brown and Stephenson 1991). It is bounded to the west by basement rocks of the Mount Lofty and southern Flinders Ranges; to the north by late Palaeozoic rocks of the Darling Basin; and to the east and south-east by sedimentary and metamorphic rocks of the Lachlan Fold Belt and the Victorian Highlands. The Cainozoic sediments overlie the Permian Nadda Basin and Cretaceous Berri Basin within the confines of the basin.
For the regional setting, and other deposits in the basin, see also the separate Murray Basin Heavy Minerals record.
The Murray Basin succession is divided into three Tertiary sequences, overlain by a thin cover of Quaternary and Recent sediments:
i). The first sequence of sedimentation commenced with the deposition of the non-marine dominated Palaeocene Renmark Group. A minor marine incursion took place in the western and south-western section of the basin while terrestrial deposition continued elsewhere into the middle Miocene.
ii). The second phase was mainly composed of Oligocene to Middle Miocene marine sediments of the Murray Group, mainly clays and limestones.
iii). The third sequence started in the late Miocene to early Pliocene with a marine transgression that commenced with the deposition of green, grey and brown calcareous clays and silts and minor sands of the Bookpurnong Beds. These are conformably overlain by a the marginal marine sands of the Loxton-Parilla Sands, comprising a series of transgressive and regressive marine units deposited in environments that range from offshore to shallow marine and beach/strandplain, with minor intercalations of fluvial and back beach lacustrine deposits. A large number of strandlines have been preserved within the Loxton-Parilla Sands throughout the Murray Basin, many of which host significant concentrations of heavy mineral sands, including the Mindarie deposits.
The Loxton-Parilla Sand unit is made of four main lithotypes: i). micaceous clays, ii). silts, iii). silty sands, iv). cross-bedded micaceous sands with minor sandy conglomerate and pebble conglomerate. It is overlain by a sequence of non-marine late Pliocene to Recent sediments above a disconformity that is commonly marked by a lateritic, locally siliceous, weathering profile known as the Karoonda Surface.
In the centre of the basin, the disconformity is overlain by fluvio-lacustrine green and red brown clays of the Blanchetown Clay, which range in age from 2.4 to 0.7 Ma. Where the Blanchetown Clay is absent, as in the Karoonda district, the Loxton-Parilla Sand is disconformably overlain by a thin succession of unconsolidated red-brown siliceous silty sand, sandy clay and clay-pellet aggregates, forming extensive east-west oriented dunes of the 0 to 30 m thick Woorinen Formation. The Karoonda Surface is also locally marked by the development of pedelogical calcrete known as the Bakara Formation or the Ripon Calcrete which locally forms massive sheets. Where present it sits disconformably above the Loxton-Parilla Sand and the Blanchetown Clays and underlies, or is intercalated with, the Woorinen Formation.
The uppermost unit developed is the late stage crescent shaped dunes known as the Lowan Sands, which are white to light brown and form high dune systems.
In the vicinity of the Mindarie HMS deposits, the Loxton-Parilla Sands are often exposed at surface, or thinly covered by low dunes interpreted to be part of the Woorinen Formation. Calcrete and possible Blanchetown Clays are preserved on hills and mesas, mainly to the north west of the deposit area, while thick accumulations of Woorinen Dunes occur to the north.
From the surface, the top 0 to 5 m is variable, comprising unconsolidated fine to medium sands with occasional layers of sandy clay, clayey sand or clay. Calcrete is also present over the same interval, usually immediately underlain by clay units.
Within the ore zone, sands are usually fine to medium grained, with a basal layer of very coarse to granular and occasionally pebbly sands usually up to 5 m thick. Below the granular sand layer, the sands become very fine to fine and are often micaceous, with thin intercalations of coarse to very coarse granules or pebble horizons, interpreted to represent a deeper water facies, with storm surge deposits. Towards the north-western end of the deposit, the granular layer often thickens and may overlap the tail of the mineralised deposits. The sands below the mineralised interval often contain fossil fragments, with shell fragments and echinoderm spines being the most commonly observed. Goethite occurs as replacements of the fossil casts and is also often observed in the heavy mineral fractions.
Within the Mindarie deposit area, a series of individual and parallel NW-SE oriented palaeo-shorelines containing strandline mineralisation of variable tenor have been identified, each separate by up to several kilometres. The bulk of the defined resource is within 8 of these strandlines, which contain mineralisation with a continuous high-grade core. The mineralised strandlines occupy an area of ~65 km in a NE-SW direction (from Karoonda in the SW to just NE of Mindarie), normal to the trend of the shorelines (Teakle, 2001) and a width of up to 70 km, parallel to the strandline trend. The individual mineralised strandlines range in length from 12 to 34 km, with widths varying from <50 m to >300 m, the longer of which have an arcuate nature with strike directions varying by up to 10° from one end to the other. The mineralised strandlines lie under about 12 m of sandy overburden, lightly bound with a clay fraction, and are some 40 m above the water table.
The main cluster of strandlines containing the bulk of the ore reserves are within a 10 km wide zone with a strike length of ~50 km, including, from NE to SW, the Amiens, Mindarie C, Mindarie A (A1 to the NW and A2 to the SE), Mercunda, Long Tan, Lone Pine and Halldon strandlines. Individual resources extend over strike length of 5 km (as at Mindarie A1), 9 to 13 km (as at Mindarie A2, Mercunda, Long Tan and Lone Pine), 15 to 20 km (as at Halldon and Amiens) to ~26 km (as at Mindarie C). Other strandlines containing resources are found within this cluster, while a further at least ten are found over the ~40 km interval to the SW to Karoonda (Teakle, 2001).
JORC compliant resource and reserve estimates at a variable ~1.0% total HM cut-off grade in October 2012 were (Murray Zircon Ltd, 2014):
Measured Resources - 39.5 Mt @ 3.6% HM containing 10.4% slimes, 21.4% Zircon, 5.8% Leucoxene, 5.1% Rutile, 64.4% Ilmenite;
Indicated Resources - 126.2 Mt @ 3.1% HM containing 10.1% slimes, 17.8% Zircon, 6.6% Leucoxene, 4.6% Rutile, 66.3% Ilmenite;
Inferred Resources - 5.3 Mt @ 3.3% HM containing 9.0% slimes, 17.0% Zircon, 5.1% Leucoxene, 3.9% Rutile, 67.2% Ilmenite;
TOTAL Resources - 171.0 Mt @ 3.2% HM containing 10.1% slimes, 18.6% Zircon, 6.4% Leucoxene, 4.7% Rutile, 65.9% Ilmenite;
Proved Reserves - 24.0 Mt @ 4.4% HM containing 10.8% slimes, 23.9% Zircon, 6.3% Leucoxene, 5.1% Rutile, 62.5% Ilmenite;
Probable Reserves - 34.1 Mt @ 4.2% HM containing 11.1% slimes, 19.3% Zircon, 6.5% Leucoxene, 4.6% Rutile, 66.4% Ilmenite;
TOTAL Reserves - 58.1 Mt @ 4.3% HM containing 11.0% slimes, 21.2% Zircon, 6.4% Leucoxene, 4.8% Rutile, 64.8% Ilmenite;
Resources estimates, revised in Oct 2013 were (Murray Zircon Ltd, 2014):
Indicated Resources - 73.4 Mt @ 1.4% HM containing 10% slimes, 9% Zircon, 16.9% Leucoxene+Rutile, 30.5% Ilmenite;
Inferred Resources - 25.9 Mt @ 2.0% HM containing 10% slimes, 9% Zircon, 22.7% Leucoxene+Rutile, 42.1% Ilmenite;
TOTAL Resources - 270.3 Mt @ 2.6% HM containing 10% slimes, 9% Zircon, 16.4% Leucoxene+Rutile, 54.0% Ilmenite;
The original resource inventory in 2005 (Australian Zircon Limited), which was very similar, was based on 45 to 63 µm grain sizes.
This summary is based on information published by the Department of Primary Industry and Regions South Australia (PIRSA/DMITRE) and reports for and by Murray Zircon Pty Ltd, Australian Zircon Limited and Southern Titanium NL.
The most recent source geological information used to prepare this summary was dated: 2012.
Record last updated: 20/10/2014
This description is a summary from published sources, the chief of which are listed below.
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