AEM Survey at Pitfield Copper-Gold Project

Empire Metals Limited / LON: EEE / Sector: Natural Resources

21 September 2022

Empire Metals Limited

Airborne Electro-Magnetic Survey at Pitfield Copper-Gold Project

Empire Metals Limited (LON: EEE), the AIM-quoted resource exploration and development company, is pleased to announce the results of the airborne electro-magnetic ('AEM') survey covering a total of 1,664 line-km over the majority of the 615 km² Pitfield Copper-Gold Project ('Pitfield'), located in Western Australia. 

Highlights

·    The AEM survey has identified a suite of anomalous conductive features, many of which are located in unexplored areas or areas not explored with modern techniques.

·    30km long regional alteration feature, considered highly prospective for sediment hosted copper, defined from interpretation of AEM survey and aeromagnetic data.

·    Successfully mapped variations in the bedrock conductivity response, providing very useful new basement geological information, particularly over large areas of the project area of low magnetic intensity.

·    Of particular interest is that some previously defined copper anomalies based on historical regional stream sediment sampling and/or the proximity to old copper workings lie along distinct boundaries in conductivity response.

·    The survey confirms that the Yandanooka Basin contains geological features that make this an attractive sediment-hosted copper exploration target.

Shaun Bunn, Managing Director, said: "Combined with the highly successful airborne magnetic survey, Empire now has a clear sense of the significant mineralised potential of Pitfield. We set out to map the geology of the Yandanooka basin and in particular to highlight potentially preferred host rocks for copper. When matched with the aeromagnetic data, a coincidence of elevated magnetic signature and more resistive rocks in the EM occurs within the upper Mt Scratch siltstone sequence and defines a 30km long regional alteration feature. The large area contained within and around the margins of this feature is considered highly prospective for sediment hosted copper. In addition, the survey has highlighted specific anomalous conductive areas that may relate to sulphide accumulations or native copper associated with mineralised systems.

"The new data clearly provides important new geological insights that will be used in formulating an exploration strategy and work programme for Pitfield."

Airborne Electro-Magnetic Survey at Pitfield

AEM data is used in minerals, energy, and groundwater resource exploration. The AEM technique takes advantage of natural variations in electrical conductivity beneath the surface which results from variation in rock and pore fluid properties. The presence of electrically conductive minerals such as graphite, clays, and sulfide minerals, or electrically conductive fluid such as saline groundwater, results in greater conductivity relative to non-conductive mineral assemblages or non-conductive fluid (typically fresh ground water). Due to the influence of both rock and pore water properties on the AEM response, AEM datasets are normally interpreted in conjunction with other spatial and airborne datasets including surface geology, soil geochemistry and magnetics and gravity.

AEM data is collected by transmitting an electromagnetic signal from a system attached to a plane or helicopter. The signal induces eddy currents in the ground which are detected by receiver coils towed below and behind the aircraft. AEM techniques can detect variations in the conductivity of the ground to a depth of several hundred metres, depending on the acquisition system and geological and hydrogeological stratigraphy. AEM surveys require complex processing to allow interpretation and therefore are usually designed to detect particular subsurface targets which are based on a perceived conductivity contrast, for example:

·      the spatial extent of geological features, such as a clay-rich unit in a sedimentary sequence or a graphite-bearing unit in a metamorphic complex

·      the depth of an unconformity between sedimentary cover and the underlying basement rock

·      the location of groundwater resources, such as fresh or saline aquifers.

The AEM survey was flown by New Resolution Geophysics Australia Pty Ltd ('NRG') using the well-known, very capable heliborne 'Xcite' electro-magnetic acquisition system (Figure 1). NRG's Xcite™ systems are towed arrays, using high performance AS350 B-series helicopters (or similar). The AS350 is ideal for the close terrain following required for geophysical surveys.

Figure 1:  NRG's Xcite™ system

The AEM survey covered the entire project area on a 400m line spacing.  A survey altitude of 30 to 40m (Transmitter-Receiver array) and 60 to 70m (helicopter) was employed. The magnetometer sensor was located mid-way between the bird and the helicopter.

A total of 147 lines was flown for an overall 1,664 line km (Figure 2).

Figure 2:  Project Location with extent of recent AEM survey shown.

AEM Survey Results

The AEM data mostly concerns the off-time when the transmitter current is off, leaving only the secondary eddy currents in the receiver. Because the EM responses exponentially decay after the turn-off, the off-time is usually divided into  intervals (called time gates, which exponentially expand as moving from early to late time), and the samples within each time gate are averaged to produce time channel data. The averaging over time further smooths out outliers and other noise, making the data more robust for interpretation.

A time domain EM data map is produced by contouring data at a particular time channel as a function of the horizontal location.  Early time channels are most sensitive to the near-surface features, while the late time channels average over a larger volume.  By way of example, in Figure 3, the airborne EM results for gridded Channel 15 (mid-time) response was selected with warm colours showing areas of higher conductivity, annotated with historic stream sediment sampling results and salt lake domain in the south east of the project.

Figure 3: AEM results showing gridded Channel 15 (mid-time) response.

The AEM survey has confirmed that the Yandanooka basin contains geological features that make this an attractive sediment-hosted copper exploration target.  Some of the key findings include:

·    the survey has been successful in mapping significant variations in rock conductivity within the Yandanooka Formation, and has confirmed conductive stratigraphy associated with the Mt Scratch siltstone or its lateral facies equivalent;

·    the large area of magnetite-altered Mt Scratch siltstone is less conductive overall, and more variable in its conductivity containing both conductive anomalies due to potential association with sulphides, and more resistive domains which may reflect rock alteration, both of which are of exploration interest;

·    in general, the more resistive rocks are associated with the older Mullingarra gneiss basement and the sandstone mafic conglomerate bearing lower parts of the Yandanooka Group, the latter having a thickness of at least 1,000m; and

·    the mapped drainage and salt lake domain in the south east sector of the project corresponds closely with high conductivity in the AEM and is interpreted to be a mainly surficial response to saline groundwater, thus the AEM survey has been less effective at mapping basement geology in this area.

The outline of the magnetic anomalism closely matches the more resistive domain within the Mt Scratch siltstone succession, which forms the upper part (up to 9,000m thick) of the Yandanooka basin. Outside the magnetic anomaly domain, the Mt Scratch siltstone is more consistently conductive indicating a component of reduced, possibly graphite-bearing sedimentary units.

The lower +1,000m includes substantial thicknesses of sandstone and mafic clast conglomerate which may provide copper-bearing source rocks for the basin outcropping adjacent to and overlying the Mullingarra gneiss (refer Figure 4), while the overlying reduced Mt Scratch siltstone can be the redox trap for the copper fluids mobilised from deeper in the basin. This fits the reduced sediment hosted copper model very nicely.

Figure 4.  Historic BHP stratigraphic section focussed on the lower Yandanooka Group, 1984.

Geophysical consultant Newexco has evaluated and identified a suite of anomalous conductive features which are annotated on Figure 5 as violet squares. Many of these features are located in  areas unexplored by modern techniques, some with empirical support in regional stream sediment sampling or proximity to old copper workings. The areas of interest are defined by anomalies lying along distinct boundaries in conductivity response.

Figure 5: Central part of the project area showing Channel 15 of the AEM survey along with historic stream sediment sampling and historic copper workings

In the central part of the project area, a cluster of conductivity anomalies were defined from the AEM survey. CRA completed stream sediment sampling over parts of this area some 30 years ago identifying significant copper anomalism as shown in Figure 5, along with broadly coincident zinc, silver and nickel, all elements likely to be elevated in sediment-hosted copper systems. The stream sediment sampling was completed over relatively subdued topography with extensive shallow cover, so is likely to have only been partially effective in evaluating the bedrock potential. Nonetheless, a broad target area of coincident EM conductivity anomalies and Cu-Zn-Ag metal anomalism can be defined for further exploration. A conductivity anomaly defined over some 1.5km at the southern end of the Mt Scratch workings is also of interest, along with several features closely associated with the linear contact between high conductivity units to the east and variable conductivity units to the west, and coinciding with the margin of the regional alteration feature.

The next step is to integrate all new geophysical data into an interpreted geological map, prior to planning the Company's first phase of on-ground exploration. This will include, amongst other things:

·    access agreements with local landowners;

·    soils or auger geochemistry over key prospective areas to define drilling targets; and

·    further definition of the AEM anomalies using on ground Moving Loop EM to validate and confirm the orientation of conductive features.

Location and Regional Geology

Pitfield is comprised of a granted Exploration Licence (E70/5465) and an Exploration Licence Application (E70/5876) covering a total of 615 sq km. Pitfield is located near Three Springs, a town  313 kilometres north of Perth, Western Australia on the Midlands Road, which until the opening of the Brand Highway in 1975 was the main road route from Perth to the state's north. (Figure 6).

Figure 6- Location Map - Showing Pitfield Tenements and Major Access Roads.

Local Geology and Historical Mining Activities

Pitfield lies at a unique setting along the boundary of Western Yilgarn province, where a major craton-scale structure internal to Southwest Gneiss province intersects and offsets the Yilgarn margin and controls the position of the Neoproterozoic Yandanooka basin, the only example of this globally important copper prospective age adjacent to the western Yilgarn craton.

Major lithological contacts, either within basins or at the basement contact (particularly transitions between oxidised and reduced rocks) can focus copper deposition. Pitfield is located along strike from the historic Baxters copper mine at Arrino which produced 106 tonnes of copper at a grade between 20-30% Cu which, along with numerous other prospects, demonstrates that the copper mineralisation process has occurred in the Pitfield area.

Historical geochemical sampling by CRA (which became part of Rio Tinto Group) and others has confirmed that a previously identified magnetic anomaly associated with alteration including magnetite/hematite, epidote replacement and fractures and carbonate-quartz veinlets is host to extensive copper anomalism, extending south from Baxters and with greater than 150ppm Cu in soils identified over a strike length of 7km (refer Figure 7.).  The anomaly remains open to the south and east including over 10km of this high-intensity magnetic feature within the project which is yet to be explored. Limited exploration has been undertaken within the project outside a 5km radius from the Baxters mine.

Previous governmental regional magnetic surveys were flown at 200m line-spacing and indicated strongly magnetic stratigraphy/alteration within the project area. Empire's recently completed airborne magnetic and radiometric survey was flown on a 50m line spacing at a height of some 30m and comprising some 3,470 line-km, giving an enhanced magnetic and radiometric resolution over the main areas of interest. This identified a major magnetic anomaly extending over 20km along the western boundary of the licence area that closely aligns with the surface copper anomaly identified by CRA when conducting surface sampling in the early 1990s (Figure 6).

Market Abuse Regulation (MAR) Disclosure

Certain information contained in this announcement would have been deemed inside information for the purposes of Article 7 of Regulation (EU) No 596/2014, as incorporated into UK law by the European Union (Withdrawal) Act 2018, until the release of this announcement.

**ENDS**

For further information please visit www.empiremetals.co.uk  or contact:

About Empire Metals Limited

Empire Metals is an AIM-listed (LON: EEE) exploration and resource development company with a project portfolio comprising gold interests in Australia and Austria.

The Company's strategy is to develop a pipeline of projects at different stages in the development curve. Its initial focus has been on the high-grade Eclipse and Gindalbie Gold Projects in Western Australia.  The Company expanded its exploration licence area in April 2022 from 9.5km² to 1,728km² with the acquisition of the Pitfield Copper-Gold Project and the Walton Copper-Gold Project in Western Australia, and the Stavely Copper-Gold Project in the Stavely Arc region of Victoria. 

Empire also holds a portfolio of three precious metals projects located an historically high-grade gold production region comprising the Rotgulden, Schonberg and Walchen prospects in central-southern Austria.

The Board continues to evaluate opportunities through which to realise the value of its wider portfolio and reviews further assets which meet the Company's investment criteria.