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The Snapper and Ginkgo heavy mineral sand zircon, ilmenite deposits are 11 km apart, located in the Tertiary Murray Basin, ~40 km west of Pooncarrie, 85 km NNE of Mildura and 170 km SSE of Broken Hill in southwestern new South Wales.
(#Location: Snapper - 33° 26' 48"S, 142° 9' 19"E; Ginkgo - 33° 22' 4"S, 142° 13' 36"E).
The Murray Basin covers an area of approximately 0.3 million km2 in NSW, Victoria, Queensland and South Australia, and is a low relief, saucer-shaped intracratonic basin, filled by a Cainozoic sequence of marine and terrestrial sediments. These sediments are weakly consolidated, near horizontally bedded sands that were deposited during marine transgressions and regressions in the Late Miocene to Late Pliocene period.
Both the Ginkgo and Snapper mineral deposits are hosted within the Pliocene Loxton-Parilla Sands, which lie within the third and upper sequence of the Tertiary succession of the Murray Basin. These are two of a series of elongate, NW-SE trending deposits in the northwestern part of the Murray Basin.
For the regional setting, stratigraphy and distribution of heavy mineral deposits in the basin, see also the separate Murray Basin Heavy Minerals and Mindarie records.
The Ginkgo deposit extends over a NW-SE strike length of ~14 km, and varies in width from 250 to 900 m and in overall thickness from 20 to 50 m. It is elevated between 0 and 65 m above present sea level. Along strike, the heavy mineral grade and total amount of heavy minerals of the deposit is vartiable. The richest grades (>10% HM) occur in the central part over a distance of ~4 km. HM grades decrease away from the central sector toward the ends. The decrease is fairly gradual to the NW, but to the SE, there is a sharp transition in heavy minerals grade and content. This discontinuity coincides with a marked change in thickness and attitude of the deposit, and with a well-developed NE-SW oriented lineament visible on satellite and Digital Elevation images of the Murray basin. This lineament is a fault which is aligned approximately normal to the palaeo-shoreline (Roy and Whitehouse, 2003).
The most extensive ad highest grade part of the deposit is on the northwestern side of the fault, coinciding with the upthrown block that appears to tilt gently to the NW. Both the base of the heavy minerals deposit and the overlying ground surface show vertical displacements of about 15 m, indicating the fault has been active subsequent to the heavy minerals deposit formation in the early Pliocene, ~6 m.y. ago, and is evidence for very slow rates of denudation in the Murray basin (Roy et al., 2000).
The base of the Ginkgo deposit is generally planar, is sharply defined by an abrupt change in grade, and slopes basinward to the SW at about 1°, probably representing an erosional discontinuity. The upper surface is more irregular. The maximum thicknesses is towards the back of the deposit, whilst its front typically steps down between 10 and 15 m and appears to be erosional in most places (Roy and Whitehouse, 2003).
Sections through the main part of the deposit show an overall gradation in mineralisation from low grade (1 to 2% HM) at its rear (NE side) to high grade (20 to 30% HM) at the front (SW side). The internal structure of the deposit is characterised by as many as five SW-dipping zones with varying degrees of mineralisation. Mineral-rich zones, which are separated by less mineral rich sand, are 5 to 10 m thick, 40 to 70 m wide, and inclined at 10 to 13°, dipping towards the front of the barrier. They extend over intervals of 30 to 40 m vertically, and 300 to 400 m in the inclined plain. Correlations between interpreted lithofacies and heavy mineral distributions, show that the mineral-rich zones in the front of the Ginkgo deposit correspond to the laminated heavy minerals-rich beach sand facies. The beach sand units are interbedded with non-laminated sand, that contain comparatively lower heavy minerals grades (Roy and Whitehouse, 2003).
Reserves at Ginkgo (after Geol. Survey of NSW, 2014) are Measured reserve: 135 Mt @ 2.9% HM + Indicated reserve 43 Mt @ 1.99% HM.
In the Snapper deposit, which is ~11 km to the SSW of Ginkgo, the Loxton-Parilla Sands have been subdivided into various sub-units:
• Lower Loxton-Parilla Sands, the immediate host to both deposits, composed of fine to medium grained quartz sands which are generally unconsolidated, well sorted and contain little clay. The deposit is generally overlain by 30 to 35 m of overburden, increasing to the north where the orebody dips to the NW, comprising the following:
• Mica Sands, which are fine to very fine micaceous sands.
• Upper Loxton-Parilla Sands, barren sand otherwise similar to the Lower Loxton-Parilla Sands.
• Shepparton Formation, a sandy clay unit which outcrops in places where the uppermost stratigraphic layer, the Woorinen Formation, is absent.
• Woorinen Formation consists of very fine to coarse sand and silty sand, sandy clay and minor calcrete.
The Snapper heavy mineral deposit occurs as a series of stacked beach deposits that dip at a shallow angle to the NW. The base of the deposit is generally flat and ~40 to 50 m below the surface. The high grade core of the deposit within the area to be mined is ~6 km long and up to 700 m wide.
The deposit has been divided into six domains.
Domain 1 is a high grade lens that runs the full length of the deposit, characterised by good rutile values and relatively low zircon, and is thickest in the south. It is in the stratigraphic centre of the deposit, underlain by Domain 3 that occupies the full width of the deposit, and is overlain by Domain 5. It passes laterally to the west into Domain 4, whilst to the east, both Domains 1 and 5 are replaced by Domain 6.
Domain 2 is a deep, thin, high grade lens at the base of the deposit, below Domain 3 on the far western side of the deposit.
Domain 3 represents lower-grade material , and is characterised by high levels of titanium silicates.
Domain 4 is a thin, discontinuous high grade lens, the western continuation of Domain 1.
Domain 5 is the low grade material overlying Domain 4 and although of low-grade, has relatively high zircon levels.
Domain 6 is a wide, high grade lens on the eastern side of the deposit, and is mineralogically the best domain.
This tabular package of domains overlay unmineralised mica-rich, fine to very fine offshore facies sands of the Lower Loxton-Parilla Sands.
The measured + indicated reserve for the Snapper Mine comprises ~117 Mt @ 5% heavy minerals. This represents some 5.9 Mt of heavy minerals composed of ilmenite, leucoxene, rutile and zircon. Snapper Mine ore grades are especially high (typically 8 to 9% heavy minerals) in the early years of production.
The Snapper summary is drawn from a report by BEMAX Resources Limited dated 2007 - Snapper Mineral Sands Project, Environmental Assessment, Section 2
Production commenced at the Ginkgo mine in 2005 and at Snapper in 2010.
Both mines utilise conventional tractor scoops for topsoil handling, truck and shovel operation for overburden and wet dredge mining and floating concentrator plants to recover and separate the heavy minerals in the ore deposit. The Heavy Mineral Concentrate (HMC) obtained by the wet-dredging process is pumped ashore to the mineral concentrate stockpiles. The stockpiled HMC is processed at the onsite Wet High Intensity Magnetic Separation (WHIMS) plant which separates the HMC into three streams. The first stream, Mags 1, is comprised primarily of Ilmenite. The second stream, Mags 2, is comprised mainly of Secondary Ilmenite and Leucoxene while the third stream contains the non magnetic minerals of Rutile and Zircon. The three mineral streams are transported separately by road train to the mineral separation plant in Broken Hill for further refinement before transport via rail to Port Adelaide in South Australia. From there it is shipped to Bunbury in Western Australia and elsewhere for further processing and refinement into final products (Cristal Mining website, 2016). The operator (2016) was Cristal Mining Australia, a subsidiary of subsidiary of the National Titanium Dioxide Company Limited (Cristal), a private company with headquarters in Jeddah, Kingdom of Saudi Arabia.
The most recent source geological information used to prepare this summary was dated: 2007.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
References to this deposit in the PGC Literature Collection:
Roy P S, Whitehouse J 2003 - Changing Pliocene sea levels and the formation of heavy minerals beach placers in the Murray Basin, southeastern Australia: in Econ. Geol. v98 pp 975-983|
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