vimineral sand <strong>deposits</strong> (beach, dune, <strong>of</strong>fshore marine,and channel), carbonatite intrusions, (per)alkalineigneous rocks, iron-oxide breccia complexes, calcsilicaterocks (skarns), fluorapatite veins, pegmatites,phosphorites, fluviatile sandstones, unconformityrelateduranium <strong>deposits</strong>, and lignites. <strong>The</strong> distributionand concentration <strong>of</strong> REE in these <strong>deposits</strong> areinfluenced by various rock-forming processes, includingenrichment in magmatic or hydrothermal fluids,separation into mineral species and precipitation, andsubsequent redistribution and concentration throughweathering and other surface processes. <strong>The</strong> lanthanideseries <strong>of</strong> REE (lanthanum to lutetium) and yttriumshow a close genetic and spatial association withalkaline felsic igneous rocks, but scandium in laterite isassociated with ultramafic-mafic igneous rocks.A mineral-systems approach has been used in thisreview to classify the <strong>major</strong> <strong>Australia</strong>n REE <strong>deposits</strong>according to various mineralising criteria and/or associated <strong>geological</strong> events. This hierarchicalclassification framework has the advantage over moretraditional descriptive classifications in that it attempsto understand the <strong>geological</strong> processes consideredcritical to the formation <strong>of</strong> a particular deposit type.It also has a more predictive capacity for identifyingpotential new areas and types <strong>of</strong> REE mineralisation.<strong>The</strong> highest level <strong>of</strong> the classification comprisesfour general ‘Mineral-system association’ categories —Regolith, Basinal, Metamorphic, and Magmatic—andtheir sixteen ‘Deposit Type’ members, namely:1. Regolith—carbonatite-associated; ultramafic/maficrock-associated;2. Basinal—heavy-mineral sand <strong>deposits</strong> in beach,high dune, <strong>of</strong>fshore shallow marine tidal, and tidalenvironments; phosphorite; lignite; unconformityrelated;3. Metamorphic—calc-silicate; and4. Magmatic—(per)alkaline rocks; carbonatite;pegmatite; skarn; apatite and/or fluorite veins; andiron-oxide breccia complex.<strong>The</strong> most commercially important REE <strong>deposits</strong> in<strong>Australia</strong> are related to magmatic and weatheringprocesses associated with carbonatites and alkalineigneous rocks, and secondary placer <strong>deposits</strong>, such asheavy-mineral sand <strong>deposits</strong>. <strong>The</strong>re is considerablepotential for the discovery <strong>of</strong> high-grade, large tonnagepolymetallic REE <strong>deposits</strong> in residual lateritic pr<strong>of</strong>iles<strong>of</strong> carbonatites and within alkaline igneous rocks inthe Precambrian terranes <strong>of</strong> <strong>Australia</strong>. Residual laterite<strong>deposits</strong> associated with carbonatites are typicallyenriched in other metals, such as zirconium, niobium,and tantalum. <strong>The</strong>y also have the advantage <strong>of</strong> beingeasily mined by open-pit methods and they do notrequire extensive crushing and milling. Mesozoicalkaline volcanic provinces <strong>of</strong> eastern <strong>Australia</strong> providescope for lower-grade, polymetallic <strong>deposits</strong> in theprimary zones <strong>of</strong> trachytic and associated alkalinerock complexes. <strong>The</strong> discovery <strong>of</strong> scandium-bearingnickel-cobalt laterites associated with Phanerozoicultramafic-mafic rocks, and REE-bearing phosphoritesin Cambrian basinal successions have recently createdexploration interest throughout eastern <strong>Australia</strong>. Largeiron-oxide breccia complexes (e.g., Olympic Dam,SA) may be an important source <strong>of</strong> by-product REEthat could be exploited in the future. <strong>The</strong> economicsignificance <strong>of</strong> less conventional exploration targetswhere the REE are hosted by lignite and bauxiteaccumulations is yet to be established. In addition,ionic-adsorption clay <strong>deposits</strong> that are mined insoutheastern China represent a potential explorationtarget in <strong>Australia</strong>.<strong>The</strong> complex spatial distribution and concentration<strong>of</strong> REE in many <strong>Australia</strong>n <strong>deposits</strong> reflect the subtledifferences in physical and chemical behaviours <strong>of</strong>many <strong>element</strong>s (17 REE and associated metals) in theprimary host rock and in the secondary weatheringpr<strong>of</strong>ile. Each orebody is ‘unique’ with different<strong>geological</strong> and metallurgical challenges. <strong>The</strong> pathwayto production is project specific, and involves manyintricate processing stages that <strong>of</strong>ten need to adaptduring the life <strong>of</strong> the project. Some REE-bearingores have associated abundances <strong>of</strong> uranium andthorium, thus environmental and competing land-useissues (e.g., heavy-mineral sand <strong>deposits</strong> along thecoastal zone and National Parks) may also have to beconsidered. <strong>The</strong> development <strong>of</strong> a REE deposit fromdiscovery to production may therefore be a protractedprocess involving many technical challenges andexpensive commitments. Ideally, mining companiesneed a REE orebody with favourable <strong>geological</strong>geochemical-processingparameters, a careful approachto environmental considerations, high levels <strong>of</strong> differentskills, and access to processing technologies andsignificant amounts <strong>of</strong> capital.THE MAJOR RARE-EARTH-ELEMENT DEPOSITS OF AUSTRALIA: GEOLOGICAL SETTING, EXPLORATION, AND RESOURCES
CONTENTSSCOPE AND OBJECTIVESACKNOWLEDGEMENTSEXECUTIVE SUMMARYCONTENTSiiiivvviiChapter One: What are Rare-Earth Elements? 11.1. Introduction 11.2. Discovery and Etymology 61.3. Major Properties and Applications 141.3.1. Properties and applications <strong>of</strong> individual <strong>rare</strong>-<strong>earth</strong> <strong>element</strong>s 141.4. Global Production and Resources 221.5. <strong>Australia</strong>’s Resources 261.6. Exploration History <strong>of</strong> Rare-Earth Elements in <strong>Australia</strong> 27viiChapter Two: Geochemistry <strong>of</strong> Rare-Earth Elements—Behaviour in the Geochemical Cycle 292.1. General Chemistry 292.2. Abundances <strong>of</strong> Rare-Earth Elements on Earth 312.2.1. <strong>The</strong> mantle 312.2.2. <strong>The</strong> crust 322.3. Rare-Earth-Element Concentrations in Major Rock Types 322.3.1. Igneous rocks 322.3.2. Sedimentary rocks 352.4. Rare-Earth-Element Abundances in Major Rock-Forming and Minor Minerals 372.5. Rare-Earth Elements in Hydrothermal Fluids 402.5.1. Fluid-melt partitioning 402.5.2. Rare-<strong>earth</strong> <strong>element</strong>s in fluids at temperatures below 350 o C 412.5.3. Rare-<strong>earth</strong>-<strong>element</strong> mobility in surficial fluids 42Chapter Three: Geological Settings <strong>of</strong> Rare-Earth-Element Deposits in <strong>Australia</strong> 453.1. Introduction 453.2. Classification <strong>of</strong> Rare-Earth-Element Deposits 483.3. Geological Settings <strong>of</strong> Rare-Earth-Element Deposits in <strong>Australia</strong> 523.3.1. Type examples <strong>of</strong> <strong>major</strong> <strong>rare</strong>-<strong>earth</strong>-<strong>element</strong> <strong>deposits</strong> in <strong>Australia</strong> 52Deposit Type 3.1: Rare-<strong>earth</strong>-<strong>element</strong>-bearing laterite with carbonatite complexes 52CONTENTS
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