Metallogenic importance of the New England Fold Belt: A Promising Opportunity for Metals Exploration, especially Molybdenum Mineralisation and Intrusive Related Gold Systems (IRGS)

Hikmat Salam - Masters in Geology (National University of Malaysia and National Centre of Excellence in Geology, University of Peshawar, Pakistan)

A wide range of mineral deposit types are hosted in the New England region of New South Wales (NSW), Australia.  As of the present-day Himalayan-Tibet and Andes mountains, the New England Orogen (NEO) is one such amalgamated tectonic block where the subduction of the ocean, emplacement of ophiolite, accretionary complex, development of serpentinite belt, and intrusion of plutons with a wide range of metallic precipitations have worked and loaded the New England orogen with a broad range of natural commodities (Figure 1). 

The plutonic intrusions, ophiolite, serpentinised peridotites, chromitites, and eclogites suggest collisional settings and high-pressure metamorphic conditions in the New England and New South Wales region (Fig. 1).  Such types of settings lead explorationists to study metallogenic provinces. 

Therefore, the NEO region was historically under investigation and exploration for mineral commodities including copper, silver, gold, tin, molybdenum, tungsten, bismuth, lead, and zinc.  Industrial minerals including limestone, and gemstones including sapphire, ruby, diamond, quartz, emerald, and topaz were yet another natural commodity in the New England region.

Fig. 1. Figure showing the geologic units and divisions in the New England Orogenic system. The geology and tectonic setting of NE orogenic system favour the mineralisation of important mineral suits. (Source: [1])

The major natural deposit systems such as magmatic, hydrothermal, hybrid magmatic-hydrothermal and metamorphic-hydrothermal systems dominate in the southern New England Orogen (sNEO). The Great Serpentinite Belt (GSB) of the sNEO along the Peel Fault and the ophiolite patches host the ancient mineral deposit systems where the dominant rock units include magmatic chromitite and sparse amounts of platinum group metals.

The GSB extends to Port Macquarie, where lateritic weathering has produced elevated nickel, cobalt and scandium values, proving assets for further exploration.  The accretionary complex and basement sediments of Carboniferous host massive sulphide base metal deposits and manganese horizons.  Since the New England is an orogenic system (Palaeozoic) and multiple episodes of deformation have deformed the rocks, exploration for base metal deposits in the accretionary complex and basement sediments is therefore complicated.  In addition to base metal deposits, these host rocks also contain several intermediate orogenic (metamorphic) gold and antimony deposits.

The gold-antimony-tungsten system at Hillgrove is a thick stockwork-type deposit with over 200 individual veins and has been exploited for over 110 years (Fig. 2).  The favourable geologic setting of these deposits is characterised by the concentration around major structures and intrusive (contact metamorphosed rocks). Late-stage lamprophyric and felsic dykes in the same structures occur as the hydrothermal gold - antimony rich veins.

Fig. 2. Figure showing the location of the Hillgrove project in the New England Fold belt. (Source: [2])

The magmatic, hydrothermal, and magmatic-hydrothermal systems host a wide range of metallic minerals including tin (i.e. veins and disseminations in and around the Mole Granite), Mo-W-Bi pipes (e.g. Kingsgate, Deepwater) and Intrusive-Related Gold Systems (Timbarra and possibly Glen Elgin).  Most of the mineralising granites are highly fractionated I-type granites and most are Late Permian to Early Triassic in age.

Molybdenum

The Australian government listed Molybdenum and Bismuth in the list of 30 critical minerals, which are essential for energy and security purposes. Molybdenum has a broad range of applications including heavy use globally in the development of digital technologies, electronic appliances and electrical vehicles, and computer gadgets, and is aimed to boost the green energy transition.  The prices are going higher as per the hike in demand. Molybdenum-based materials have attracted widespread attention as they are a novel type of green energy storage devices in the superconductors.

The historic Kingsgate Molybdenum project is still an asset for investors to put their financial and scientific efforts into revolutionising this globally demanded natural commodity.  The historical work on the Kingsgate project in the late 1880s and early 1900s was revived by Auzex Resources Limited between 2005 and 2010.  This has led to the recent interest by Taiton Resources Limited (ASX: T88) to look at the project again as market conditions have changed significantly with the decarbonisation and electrification evolution (Fig. 3).

"The Kingsgate high-grade molybdenum project has a lot of historical work completed by Auzex Resources Limited and this will allow Taiton to work more efficiently to take the project to the ultimate goal of creating a producing asset." - Executive Director, Noel Ong.

Fig 3. Figures (a and b) show the location of the Kingsgate Molybdenum project in the NEFB executed on the two leased blocks (ELA/6702, ELA6699/EL/9636). (Source: [3] and [4])

The Geologic and tectonic setting of the NSW and NEO promise resource potential for high-grade molybdenum in the thick hydrothermal and magmatic-hydrothermal settings.  A broad range of plutonic rocks, extrusive and dykes including lamprophyres, granites, granitoids, dacites and andesites are pockets for such metallic mineralization (Fig. 4), especially for the Intrusive Related Gold Deposits.

Fig. 4. Figure showing the geologic units and positions of key metals under exploration at the Kingsgate high-grade molybdenum project. (Source: [3] and [4])

Intrusive Related Gold Systems (IRGS) 

Intrusive Related Gold Systems (IRGS) are newly defined gold deposits associated with moderately reduced, I-type, intermediate to felsic intrusions. The deposit style is zoned and centred on a central mineralising intrusion. The hydrothermal fluids mineralising such types of gold deposits are usually carbonic to rarely saline. These systems are commonly associated with convergent plate margins and the New England Fold Belt (NEFB) is a typical convergent tectonic setting favouring the development of IRGSs (the Tooloom project) (Fig. 5).

The IRGSs are characterised by variably a combination of Au with Bi, Mo, Te, W, As, Sn with low sulphide content i.e. <5%, and lack of iron ores (magnetite and haematite). The mineralisation styles are commonly in the form of sheeted veins and stockworks, breccia pipes, disseminated deposits, skarns, and distal base metal-bearing fissure veins. 

The gold and molybdenum contents vary along the vertical zonings, with gold anomalies concentrated at shallower depths and molybdenum anomalies at deeper depths. The shallower systems are characterised by breccias and carbonate alteration zones are associated with depths. Laterally, Bi and stibnite are concentrated close and at distal parts of the deposits, respectively. However, these criteria for IRGS and its characteristics are significantly in contrast to the Cu-Au porphyry deposits, though some overlap in the orogenic settings.

Fig 5. Figures (a and b) showing the defined gold deposits in the NEFB of Eastern Australia with proven IRGS deposits (the Tooloom project) and the IRGS zoned deposit style with lateral variable anomalies of metals (i.e., Au, Bi, Sb, etc), disseminations, breccias, contact metamorphosed zone, and veins network. (Source: [5])

The IRGS model is defined in a few orogenic belts around the world including the Paleo-Tethys closure (deposits in China, and Kazakhstan) and in the NSW (in the NEFB).

Some examples of the intrusion bodies in the NEFB are the Nundle Supersuite, the Uralla Supersuite, Moonbi Supersuite, the Gundle Belt, the Clarence River Supersuite, the Coastal Belt and various unnamed leucogranite intrusions. Veins, stockworks, greisens, pipes, skarns and disseminations are some common deposit styles associated with these intrusions. 

The Kingsgate Mo-Bi deposit (pipes, veins, and dissemination), the Glen Eden Mo-W-Sn deposit (breccia pipes and stockworks) and the Taronga Sn deposit (sheeted veins) are examples of intrusion-related deposits in the NEFB. The widespread occurrence of IRGS-affiliated mineral deposits and the presence of gold systems with the IRGS association, combined with the favourable granite geochemistry, highlights the IRGS prospectivity of the NEFB.

Gold stocks as an important part of any investment portfolio, can offer investors exposure to the market without holding any physical gold. Most investors are not familiar with intrusion-related gold systems. 

These gold deposits are lower grade, but their large tonnage makes them some of the most productive assets in the world. That means they can be highly attractive prospects for gold-focused companies. However investing in gold-focused companies requires due diligence, as well as an understanding of the factors that can bring these entities success.

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Reference:

1. Hugo K.H. Olierook, Jasmine Gale, Franco Pirajno, Fred Jourdan, Christopher L. Kirkland, Noreen J. Evans, Bradley J. McDonald, Mark Krejci, Qiang Jiang, Anusha Shantha Kumara, Celia Mayers, R. Adam Frew, Hugo Kaag, Brent I.A. McInnes, Terminal tectono-magmatic phase of the New England Orogen driven by lithospheric delamination, Gondwana Research, Volume 106, 2022, Pages 105-125,

2. Larvoto Resources Limited: https://www.larvottoresources.com/projects/hillgrove-gold-antimony

3. Investing News: https://m.au.investing.com/news/stock-market-news/taiton-resources-ltd-eyes-production-path-at-the-kingsgate-highgrade-molybdenum-project-3147246

4. The Market Bull: https://themarketbull.com.au/2024/01/16/taiton-resources-submits-application-to-acquire-the-kingsgate-project/amp/

5. McKay, B. A.. “Intrusion-Related Gold Systems in the New England Fold Belt – The Tooloom Example.” (2006). https://www.semanticscholar.org/paper/Intrusion-Related-Gold-Systems-in-the-New-England-%E2%80%93-McKay/78e44d8e2794b71bd71f52e725bcbf7020bf9ff5d71f52e725bcbf7020bf9ff5