Southern Thomson Orogen collaborations

Project date

Ongoing since 2015

Description

Following a broader study of the Thomson Orogen in Queensland, the Geological Survey of Queensland (GSQ) is now focused on the southern region of the orogen (Figure 1). This area has relatively thin cover, with inferred Palaeozoic basement rocks of the Thomson Orogen occurring in scattered small outcrops and depths typically between 100m and 1,000m below the Eromanga Basin (Figure 2).

The southern Thomson Orogen region is widely considered under-explored for mineral deposits. Known mineralisation occurs in small outcrop areas (e.g. near Tibooburra in New South Wales and possibly at Granite Springs in Queensland) while neighbouring terrains (e.g. Lachlan Orogen and northern Thomson Orogen) host a wide range of mineralisation styles (e.g. orogenic gold, VMS, Cobar-style, porphyry-related).

Outcropping Thomson Orogen rocks are shown in red; the remainder are covered by Devonian to Mesozoic basins

Figure 1: Location of the Thomson Orogen and Southern Thomson Orogen project area

Map showing depth to basement rocks

Figure 2: Depth to basement rocks in the Southern Thomson Orogen project area

Background

Exploration in the southern Thomson Orogen has been hampered by an overall lack of geoscientific data for basement rocks and uncertainty of cover thickness. Additionally, the southern Thomson Orogen is viewed as the missing link in understanding the geological and tectonic evolution of eastern Australia. These factors have driven the current focus of data acquisition and research.

Projects

The GSQ's work in the southern Thomson Orogen forms part of 2 major collaborative projects.

The Southern Thomson Orogen project

In 2015 we started a project with Geoscience Australia (GA) and the Geological Survey of New South Wales. Our aim was to generate a better understanding of the geological character and mineral potential of the southern Thomson Orogen and encourage mineral exploration. This project has involved acquisition of new regional AEM data, MT data, geochemistry, geochronology and structural and mineral systems studies. This work guided a stratigraphic drilling program (Figure 3) which was completed in September 2017 and resulted in 12 new drill cores from the Thomson Orogen below the Eromanga Basin cover. Five stratigraphic drill holes were successfully completed in Queensland (Table 1, Figure 4).

Results

We scanned the cores with the HyLogger™ and took samples for geochronology and geochemistry (Figure 5). These are now stored at the Exploration Data Centre, Zillmere. We will release the results publicly through southern Thomson Orogen workshops and the GSQ and GA websites. Reports and publications from this project include:

Drill rig at sunset at Geological Survey of Queensland site Cunnamulla 1

Figure 3: Drill rig at GSQ Cunnamulla 1

Basement geology showing location of stratigraphic holes and geological boundaries

Figure 4: Basement geology and location of stratigraphic holes

Table 1: Initial results of the southern Thomson Orogen stratigraphic drilling in Queensland
Drill holeDTB Drilled length Basement lithology
GSQ Eulo 1 299m 379.3m Multiply deformed, quartz-muscovite-biotite-chlorite schist with abundant deformed milky segregations (prelim. maximum depositional age ~460Ma)
GSQ Eulo 2 49m 135.5m Volcaniclastic boulder conglomerate with carbonate altered matrix overlying altered dacitic to rhyolitic ignimbrite (prelim. magmatic age ~385Ma)
GSQ Eulo 3 96m 171.9m Thin-bedded metasandstone and metasiltstone with abundant, locally galena-bearing quartz veins
GSQ Eulo 4 261m 357.6m Thin-bedded metasandstone and metasiltstone in fault contact with altered and deformed intermediate to mafic porphyritic intrusive rock with locally extensive carbonate veining
GSQ Cunnamulla 1 502.2m 632.4m Foliated metasandstone and metasiltstone with local magnetite-rich domains, deformed quartz veins and native copper along some foliation surfaces

Drill core showing volcaniclastic boulder conglomerate from stratigraphic drill hole Geologic Survey of Queensland Eulo 2

Figure 5: Volcaniclastic boulder conglomerate from stratigraphic drill hole GSQ Eulo 2

Southern Thomson Orogen: a missing link in the Tasmanides

A second collaborative project aims to improve understanding of the geological and structural history of the Thomson Orogen and its context in the broader tectonic evolution of eastern Australia. This is an Australian Research Council (ARC) project titled ‘Southern Thomson Orogen: a missing link in the Tasmanides’ that brings together investigators from the University of Newcastle, the University of Queensland, Queensland University of Technology, the Geological Survey of New South Wales and GSQ. Several university honours projects have already been completed while projects at the masters and PhD level continue.

Results

Results were published in a special issue of the Australian Journal of Earth Sciences, 2018, Volume 65, Issue 7 and 8, Evolution of the southern Thomson Orogen and environs: evaluating the missing link of the Tasmanides.

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Contact

General enquiries 13 QGOV (13 74 68)