The North Australian Zinc Belt (NAZB) is the largest global Zn-Pb-Ag mineral province. The mineral system that produced the NAZB lasted several hundred million years, beginning well before mineralization when the architecture that enabled mineralization was established. An essential component of this architecture was the establishment of a crustal edge, which can be seen in a range of geophysical and geochemical datasets and formed the locus of subsequent mineralizing events. The fluid and S sources were coeval evaporative brines, but the metal sources were volcanic rocks deposited 100+ Myr prior to mineralization. Mineralization occurred during a period of overlapping contraction and sedimentation, with deformation driven by out-of-area tectonic events. Topography, established during deformation and compaction, drove fluid flow into synclinal sub-basins where mineralization was caused by fluid interaction with either carbonaceous and dolomitic siltstone hosts or with a brine pool. Data from other Zn-Pb-Ag provinces suggests similar processes and controls globally.

The Heavy Mineral Map of Australia (HMMA) is the world’s first project aiming to define acontinental heavy mineral baseline. It utilises a novel sample processing workflow andautomated mineralogy techniques to rapidly generate and analyse mineralogical data from1315 archived samples of catchment outlet sediments collected from 1186 catchmentsacross the Australian continent.Heavy minerals were extracted and concentrated from the 75–425 μm fraction of eachsample via an optimised workflow to accelerate output while maintaining integrity and quality of produced heavy mineral concentrates. Automated mineralogy facilitated rapid and consistent collection of mineral data from each heavy mineral concentrate, and anassociated bespoke mineral library incorporates more than 160 unique mineral phases,including minerals that will be of interest to both researchers and mineral explorers. Apublicly accessible mineral network analysis application has been developed in parallel with the HMMA project to facilitate exploration and interpretation of the resulting >140 million mineral grain identifications dataset.Upon completion in late 2023 the HMMA will provide a heavy mineral baseline acrossapproximately 80% of Australia, with processing of samples and data acquisition undertaken in a standardised and uniform manner enabling easy replication of techniques and both internal and external comparability.

We describe a vision for a national-scale heavy mineral (HM) map generated through automated mineralogical identification and quantification of HMs contained in floodplain sediments from large catchments covering most of Australia. The composition of the sediments reflects the dominant rock types in each catchment, with the generally resistant HMs largely preserving the mineralogical fingerprint of their host protoliths through the weathering-transport-deposition cycle. Heavy mineral presence/absence, absolute and relative abundance, and co-occurrence are metrics useful to map, discover and interpret catchment lithotype(s), geodynamic setting, magmatism, metamorphic grade, alteration and/or mineralization. Underpinning this vision is a pilot project, focusing on a subset from the national sediment sample archive, which is used to demonstrate the feasibility of the larger, national-scale project. We preview a bespoke, cloud-based mineral network analysis (MNA) tool to visualize, explore and discover relationships between HMs as well as between them and geological settings or mineral deposits. We envisage that the Heavy Mineral Map of Australia and MNA tool will contribute significantly to mineral prospectivity analysis and modeling, particularly for technology critical elements and their host minerals, which are central to the global economy transitioning to a more sustainable, lower carbon energy model.

First posted June 4, 2021 For additional information, contact: Director, Geology, Geophysics, and Geochemistry Science CenterU.S. Geological SurveyMS 973, Box 25046Denver, CO 80225 A challenge for the global economy is to meet the growing demand for commodities used in today's advanced technologies. Critical minerals are commodities (for example, elements, compounds, minerals) deemed vital to the economic and national security of individual countries that are vulnerable to supply disruption. The national geological agencies of Australia, Canada, and the United States recently joined forces to advance understanding and foster development of critical mineral resources in their respective countries through the Critical Minerals Mapping Initiative (CMMI). An initial goal of the CMMI is to fill the knowledge gap on the abundance of critical minerals in ores. To do this, the CMMI compiled modern multielement geochemical data generated by each agency on ore samples collected from historical and active mines and prospects from around the world. To identify relationships between critical minerals, deposit types, deposit environments, and mineral systems, a unified deposit classification scheme was needed. This report describes the scheme developed by the CMMI to classify the initial release of geochemical data. In 2021, the resulting database—along with basic query, statistical analysis, and display tools—will be served to the public through a web-based portal managed by Geoscience Australia. The database will enable users to trace critical minerals through mineral systems and identify individual deposits or deposit types that are potential sources of critical minerals.

The accelerating pace of population growth, economic development and technological innovation drive increased demand for non-fuel mineral commodities vital for emerging and low-carbon technologies. Lists of relevant chemical elements, also considered critical to the economic and national security of the world’s major and emerging economies (often dubbed “critical minerals”) vary from country to country but commonly include REE, Ga, In, W, PGE, Co, Nb, Mg, Mo, Sb, Li, V, Ni, Ta, Te, Cr and Mn [1

Rare earth elements (REE) have gained importance due to their widening industrial applications and their use as geochemical tracers. REE sulfate complexes are some of the most stable REE aqueous species in hydrothermal fluids, and may be responsible for REE transport and deposition in a wide variety of geological environments, ranging from sedimentary basins to magmatic hydrothermal settings. However, the thermodynamic properties of most REE-sulfate complexes are derived from extrapolation of ambient temperature data, since direct information on REE-sulfate complexing under hydrothermal conditions is limited to a single study that derived formation constants for Nd, Sm and Er in sulfate solutions to 250 ˚C (Migdisov and William-Jones, 2008). In this study, we employ ab initio molecular dynamics (MD) simulations to calculate the speciation and thermodynamic properties of yttrium(III) in sulfate and chloride solutions at temperatures and pressures up to 500 ºC and 800 bar. The MD results were complemented by in situ X-ray absorption spectroscopy (XAS) measurements. Our results show that yttrium(III) forms complexes with sulfate with both monodentate and bidentate structures over the investigated temperature range (200 ˚C to 500 ˚C). In simulation boxes containing both chloride and sulfate, yttrium(III) bonds with less sulfate and forms mixed Y-Cl-SO 4 complexes. The thermodynamic properties for yttrium(III) sulfate complexes derived from MD enable a better modelling of REE transport in hydrothermal systems.

We collected 38 groundwater and two surface-water samples in the semi-arid Lake Woods region of the Northern Territory to better understand the hydrogeochemistry of this system, which straddles the Wiso, Tennant Creek and Georgina geological regions. Lake Woods is presently a losing waterbody feeding the underlying groundwater system. The main aquifers comprise mainly carbonate (limestone and dolostone), siliciclastic (sandstone and siltstone) and evaporitic units. The water composition was determined in terms of bulk properties (pH, electrical conductivity, temperature, dissolved oxygen, redox potential), 40 major, minor and trace elements, and six isotopes (O-18(water), H-2(water), C-13(DIC), S-34(SO4)2-, O-18(SO4)2-, Sr-87/Sr-86). The groundwater is recharged through infiltration in the catchment from monsoonal rainfall (annual average rainfall approximate to 600mm) and runoff. It evolves geochemically mainly through evapotranspiration and water-mineral interaction (dissolution of carbonates, silicates and to a lesser extent sulfates). The two surface waters (one from the main creek feeding the lake, the other from the lake itself) are extraordinarily enriched in O-18 and H-2 isotopes (O-18 of +10.9 and +16.4 parts per thousand VSMOW, and H-2 of +41 and +93 parts per thousand VSMOW, respectively), which is interpreted to reflect evaporation during the dry season (annual average evaporation approximate to 3000mm) under low humidity conditions (annual average relative humidity approximate to 40%). This interpretation is supported by modelling results. The potassium (K) relative enrichment (K/Cl- mass ratio over 50 times that of sea water) is similar to that observed in salt-lake systems worldwide that are prospective for potash resources. Potassium enrichment is believed to derive partly from dust during atmospheric transport/deposition, but mostly from weathering of K-silicates in the aquifer materials (and possibly underlying formations). Further studies of Australian salt-lake systems are required to reach evidence-based conclusions on their mineral potential for potash, lithium, boron and other low-temperature mineral system commodities such as uranium.

The Stavely Project is a federal and state government collaboration that aims to increase greenfields mineral exploration in western Victoria across an area that preserves a number of structurally dismembered prospective Cambrian volcanic belts (collectively termed the Stavely Arc), the majority of which are under younger cover rocks. These belts developed along with eastern margin of the proto-Australian continent (Delamerian Craton) during west-directed subduction. The region contains numerous features in common with well-endowed volcanic arc terranes worldwide. The project aim was achieved by collecting new geoscientific datasets to better characterise the subsurface Cambrian geology in order to de-risk exploration efforts in the region. Restoration of the volcanic belts to Cambrian-time results in three strikepersistent (~1160 km composite length), sub-parallel belts that are prospective for a series of arc-related mineral systems (porphyry, epithermal and volcanic-hosted massive sulfide deposits). These systems may also occur outside the volcanic belts themselves – this greatly increases the exploration search space in Cambrian rocks. In addition, the region is a potential host of Ordovicianto Silurian-aged orogenic gold systems and Devonian intrusion-related gold and base metal systems. The younger cover rocks host world-class heavy mineral sand resources.

ABSTRACT Fluid inclusions provide the only direct samples of palaeofluids that may be related to mineralisation processes. In order to apply fluid inclusion data to study fluid flow on a larger scale, we have used a mineral systems approach, which regards a mineral deposit as part of a much larger system and considers all the processes that are involved in mobilising ore components from a source, transporting and accumulating them in a more concentrated form and then preserving them throughout the subsequent geological history. This not only enables a better understanding of fluid flow processes but also enables fluid inclusions to provide an exploration target that is much larger than the ore deposit itself. As an example, a study of fluid inclusions associated with gold mineralisation in the Tanami Region of Northern Australia was used to determine the temperatures and compositions of the ore fluids. Once the parameters of the mineralising fluids were established, the study was then expanded to a region of central Australia covering almost 100,000 km2. It was concluded that a high temperature (320 – 360 °C), low salinity fluid containing CO2 and other gases was circulating in the northern part of this region at around 1720 Ma. This suggests the circulation of an orogenic gold style fluid and indicates that this region has potential for other orogenic gold deposits. In the southern part of this region, a lower temperature (120 to 190 °C), high salinity fluid with no detectable gases was present and appears to represent circulation of a basinal brine. In the second example, fluid inclusion data from Cu-U-Au-Ag-REE prospects in the Olympic Copper-Gold Province in South Australia were used to constrain geochemical modelling of the mineralisation processes. By combining the inversion-generated, 3-D geophysical maps with geochemical and magnetic susceptibility values derived from the modelling, it has been possible to divide the range of observed magnetic susceptibilities into divisions that represent the various alteration assemblages within this region. This approach allows us to use geochemical modelling to relate alteration assemblages, and hence, the predicted sites of mineralisation, to the geophysical expressions of the mineral deposit.