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Eucla Basin - Heavy Mineral Sands Exploration, WA & SA

Overview

The Cainozoic Eucla Basin is a large onshore-offshore basin on the southern Australian passive margin. The basin extends some 350 km inland from the modern day coastline of Western Australia and South Australia and also extends seaward approximately 150 km.  It covers a vast area stretching 2,000 km from the southeast coast in Western Australia to the southwest coast of South Australia and northward through to the boundary of the Nullarbor Plain with the Great Victoria Desert . The Eucla Basin and adjacent hinterland palaeovalley system together covers ~20% of the Australian continent. 

The Eucla Basin comprises a thin passive margin succession that was deposited during the final stages of separation between the Australia and Antartica plates. The basin contains continental and marine Cainozoic sediments ranging in age from 140 million years to the near present time.

Although the Eucla Basin has long been recognised as being prospective for mineral sands, the remote location, general lack of geoscientific data and prevalence of coastal beach sand mining saw limited exploration activity. Changing conditions in the mineral sands industry resulted in extensive mineral sands exploration activity undertaken in the Eucla Basin during the last ten years, with Diatreme being one of the first exploration companies to recognise the opportunity and secure exploration tenements.

Regional Geology

The Eucla Basin, including the vast Nullarbor Plain, lies on the margins of the Yilgarn, Musgrave and Gawler cratons in southern Australia and owes its distinctive landscape to a unique set of interactions between eustatic, climatic and tectonic processes over the last ~50 Ma.

Pervasive aeolian sand and clay cover and widespread duricrusts in the present-day landscape have hampered thorough mapping of the basin but an extensive borehole dataset provides a record of marine, marginal marine, estuarine, fluvial and lacustrine environments, reflecting several major depositional events relating to eustatic sea-level variation which, during highstands, inundated the craton margins, flooding palaeovalleys to up to 400 km inboard of the present coastline.

The onshore sequence displays a number of distinct geomorphic units including the Nullarbor and Roe Plains, a series of coastal barrier ranges including the Ooldea, Barton and Paling Ranges and hinterland palaeodrainage systems now largely delineated by strings of playa lakes and lunettes developed in topographic lows on the adjacent cratons and extending inland to the Neoproterozoic Paleozoic Officer Basin. The present landscape is dominated by Quaternary sand plains and colluvial regolith, largely superimposed on and locally obscuring the older Tertiary landforms.

HM sands prospectivity

The Eucla basin in southern Australia is emerging as a major new heavy minerals province in Australia. Beach placers are associated with a series of partially buried Cenozoic coastal barrier sands formed along an arcuate 2,000-km-long basin margin, the trace of which is up to 320 km inland of the present coastline. The presence of high-grade deposits with dominant zircon over ilmenite and lesser amounts of rutile and leucoxene was established with the discovery of the Jacinth and Ambrosia heavy mineral deposits by Iluka Resources in late 2004. Additional heavy mineral prospects (including Cyclone) were subsequently identified and are at various stages of evaluation.

Four distinct constructional phases for the development of shorelines can be recognized and correlated with major third-order sea-level events, established from the marine depositional record as occurring during the middle Eocene ( 42.5 Ma), late middle Eocene (39-36 Ma), late Eocene (36-34 Ma), and Miocene-Pliocene (15-2.6 Ma). Prevailing westerly winds built extensive dune systems by longshore drift. Sediment movement was from west to east. Detrital zircons from the Ooldea and Barton barriers show a distribution of zircon age that is consistent with the Proterozoic Musgrave province to the north of the basin as the dominant primary source area of the heavy minerals, with a contribution from the Albany Fraser orogen to the west. The likelihood is that these heavy minerals have been recycled via sedimentary basins that flank the Musgrave province and include the Officer basin and deposits of the Bight basin.

The current depositional model is summarized as follows:

(1) initial rapid transgression and deposition of a shallow marine sand sheet subsequently overlain by shallow marine limestone during middle Eocene;

(2) a major Eocene transgression and deposition of a shelf barrier and lagoonal shoreface marine complex during the late middle Eocene;

(3) further transgression and highstand deposition during the late Eocene;

(4) renewed transgression of barrier lagoonal and possibly flooding deltaic sand blanket in the southeastern coastal plain with neotectonic uplift tilting in the western Eucla margin during Mio-Pliocene time.

Each stage of reworking increased the potential for heavy mineral concentration in placer deposits.

Company Exploration

Diatreme established a strategic tenement position in the Eucla Basin, initially securing extensive title over the Barton shoreline in WA near the state border, and the Ooldea shoreline in SA west from Maralinga. With the extensive exploration work completed by the company a significant area has been explored, and the company tenement holding steadily consolidated as exploration results were received and interpreted.  

Exploration to date has resulted in the identification of a significant Heavy Mineral Resource at the Cyclone Project within E69/1920 in Western Australia. The Company completed a Pre-Feasibility Study ("PFS") for Cyclone on 2012 is continuing to advance the project with a Definitive Feasibility Study ("DFS") currently in progress. Refer to Cyclone Project for further details.

Minor regional exploration is ongoing, with specific tenements discussed below.

WA E69/1920 "Wanna Lakes"

Initially granted in 2006 to cover a 35km strike extent of the Barton shoreline with a prominent headland feature within its SE corner, reconnaissance exploration in 2007 discovered the Cyclone deposit associated with an interpreted embayment feature. Regional exploration along the remainder of the shoreline was not successful in identifying significant mineralisation and the tenement was subsequently renewed and reduced to its current size of 33km2 to encompass the Cyclone deposit and immediate surrounds.

WA E69/2408 "Wanna East"

Initially granted in 2008 to cover the adjoining eastern (landward) extension of the Barton shoreline in E69/1920. Regional exploration was successful in defining the Zephyr deposit (see ASX Release 11 Oct 2010) in an estuarine setting behind (5km NE) the Cyclone deposit, but exploration within the remainder of the tenement was not successful in identifying significant mineralisation and Wanna East was subsequently renewed and reduced to its current size of 42km2 to encompass the Zephyr deposit and immediate surrounds.

WA E69/2425 "Wanna South"

Initially granted in 2008 to cover the adjoining south-western (seaward) extension of the Barton shoreline in E69/1920. Regional exploration was not successful in defining significant mineralisation associated with shallow marine / offshore sediments, but extensions of the Cyclone nearshore mineralisation were confirmed. Wanna South was subsequently renewed and reduced to its current size of 3km2 to encompass the Cyclone Nearshore resource extensions.  

 

Cyclone, Cyclone Extended (Image Resources) and Zephyr Resource extent


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