Summary:
Atlas
Atlas is hosted in the Perth Basin, in surficial marine sediments eroded into Cretaceous basal sediments during the Pleistocene marine transgressions.
The host sediments consist of unconsolidated well sorted sands and clayey sands, sitting over basal sediments of very fine to granular or pebbly, poorly sorted sands and clayey sands.
Atlas has one major strandline of heavy minerals, with seven minor strandlines interpreted to the north, east and west of the main strandline and a small area of mineralisation above the main strandline.
The basement to the strandline mineralisation is identified by an increase in slimes and or oversize and/or coarser gain size.
Dimensions
The main strandline mineralisation has been shown from drilling to extend for approximately 5.3 km north/south. The mineralisation extends from surface to 16 m depth, has an average thickness of 3.4 m and a maximum thickness of 12 m.
Seven additional zones of strandline mineralisation have been interpreted to the east, west and north of the main strandline. These additional strandlines are not as continuous along strike as the main strandline and are thinner and narrower. They are oriented north-south and strike lengths range from 0.1 km to 3.7 km. The top of the strandlines ranges in depth from surface to 14 m and the mineralisation extends to a depth of up to 18 m, with an average thickness that ranges from 1.4 m to 3.5 m.
Boonanarring
Boonanarring is hosted in the Perth Basin, in the Pleistocene Yoganup Formation on the eastern margin of the Swan Coastal Plain.
The Yoganup Formation is a buried pro-graded shoreline deposit, with dunes, beach ridge and deltaic facies. This formation lies unconformably over the Lower Cretaceous Leederville Formation and is overlain by the Pleistocene Guildford Formation and the Quaternary Bassendean Sand.
The Yoganup Formation consists of unconsolidated poorly sorted sands and gravels, with local interstitial clay and heavy minerals that occur sporadically along the Gingin Scarp, which is interpreted to be an ancient shoreline that was stable during a period of marine regression.
Boonanarring has three major strandlines of heavy minerals, which are interpreted to have been deposited during the Pleistocene in a notch in the local basement rock that may represent an ancient sea cliff. Lower grade mineralisation is present in the sands proximal to the higher-grade strandlines. Two additional strandlines, to the south-west of the main strandlines, are present in the southern part of the project area.
The basement to the strandline mineralisation is identified by the increased slimes content of the Leederville Formation or at the base of the Yoganup Formation. Mineralisation within this has high zircon concentrations.
The mineralisation of the Boonanarring deposit is hosted by the Yoganup Formation. The main geological units identified include:
- Surface sands: low clay, yellowish coloured and generally unconsolidated sands that occur from surface to depths of 4 – 10 m and which are interpreted as belonging to the Bassendean Sand unit. In some areas, lateritic surface gas formed at the base of this unit;
- Red cover sands: red to brown coloured iron-rich sands that have varying levels of induration and which often contain clayey lenses towards the base of the unit. Oversize material is common and goethite/limonite chips can report as heavy mineral concentrates. The sands are often coarse, suggesting a high energy depositional environment, and interpreted to correlate to the Guildford Formation;
- Host sands: brown to light grey, fine to medium grained sands that are well sorted and generally increase in grain size towards the base of the unit. This unit is correlated with the Yoganup Formation and contains heavy mineral accumulations associated with strandline deposition.
The heavy minerals within the Yoganup Formation have been concentrated in two main strandlines that coalesce in the south and are continuous over a strike length of 13.2 km. An additional strandline to the west is present in the southern part of the Premises. The basement to the strandline mineralisation is demarcated by the increased slimes content of the clay-rich Leederville Formation.
Dimensions
The heavy minerals within the Yoganup Formation have been concentrated in two main strandlines that are continuous over a north-south strike length of 10 km. The strandlines are separated by sands with low concentrations of heavy minerals of 50 m to 100 m in the north and the strandlines coalesce in the south. The eastern strandline has a strike length of 9 km and is approximately 100 m wide and extends further north than the western strandline. The western strandline has a strike length of 9.6 km and is up to 220 m wide.
An additional strandline of mineralisation is present to the east that has a strike length of 3.6 km and is up to 100 m wide and merges with the eastern strandline to the north.
Two additional strandlines, to the south-west of the main strandlines, are present in the southern part of the project area. These extend for approximately 3 km and 2.7 km north-south and have across strike widths of up to 120 m. These are overlain by a shallow sheet of mineralisation with dimensions of 350 m east-west and up to 600 m northsouth.
The strandlines are up to 15 m thick and have an average thickness of 4.5 m. The average depth to the top of the mineralised strandlines is 28 m.