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New geochronological data provide evidence for Permo-Triassic low-sulfidation epithermal gold-silver mineralization in the Cordillera Frontal, Argentina. The U-Pb sensitive high-resolution ion microprobe (SHRIMP) analyses on zircons and titanite gave the following results: (1) andesite and rhyolite volcanic host rocks of the Casposo Au-Ag deposit yielded a range of ages between 267.1 ± 0.7 and 241.7 ± 2.2 Ma; (2) two composite plutons located near Casposo yielded ages of 268.2 ± 1.5 and 265.1 ± 1.5 Ma for the Colorado syenogranite-granite pluton and 266.6 ± 1.4 and 254.0 ± 2.4 Ma for the Casposo granodiorite-tonalite pluton; (3) a trachyandesite dike emplaced at 265.7 ± 1.2 Ma that is crosscut by mineralized quartz-adularia-calcite-gold veins in the Kamila East area; (4) felsite intrusions, interpreted to be temporally related to the emplacement of mineralized veins at 261.1 ± 3.5 Ma; and (5) composite rhyolite/andesite dikes that crosscut all other lithostratigraphic units and mineralized veins at 238.4 ± 1.6 Ma. The 40Ar/39Ar dates on hydrothermal adularia within quartz-adularia-calcite-gold veins of the Casposo deposit revealed at least three, likely discreet, hydro-thermal fluid pulses and associated periods of vein formation during extensional events between 280–274, 262–258, and 250–246 Ma. Relative and absolute timing of volcanic host rocks, plutons, postmineralization felsic dikes, and gold-bearing veins of the Casposo epithermal vein system suggest the presence of significant Permian (Cisuralian)-Lower Triassic low-sulfidation epithermal-style gold-silver mineralization at the eastern flank of the Cordillera Principal in Argentina. The existence of this epithermal Au-Ag system opens the potential for a significant magmatic-hydrothermal system in a part of the Andes that previously was considered to be of low prospectivity.

Field mapping, drill-core logging, petrography, laser ICP-MS analysis on pyrite, chlorite geothermometry and geochemical analysis of hydrothermally altered rocks reveal two distinct styles of gold mineralisation at Mt. Percy. The first style is D2 shear zone-hosted and correlates with Fimiston-style mineralisation documented in the Golden Mile. Laser ICP-MS analyses on pyrite indicate high As concentrations (average of 5823 ppm for pyrite in Hannans Lake Serpentinite and 635 ppm in feldspar-quartz porphyry). Chlorite geothermometry reveals average temperatures of 262 ± 50 °C and 357 ± 50 °C in distal and proximal alteration zones, respectively. Geochemical analyses reveal (1) positive gold-silver and gold-antimony relationships; (2) lack of a base metal-gold relationship; (3) systematic increase of carbonatisation and alkali saturation indices from distal to proximal alteration zones; and (4) addition of K, Ca, Na and V, with corresponding depletion of Mg, Fe, P and REE. The second style is related to D4 sheeted quartz vein sets and correlates with Mt. Charlotte-style mineralisation documented in the Mt. Charlotte deposit. Laser ICP-MS analyses on pyrites reveal low As concentrations (average of 51 ppm for pyrites in feldspar-quartz porphyry and 870 ppm in Devon Consols Basalt). Chlorite geothermometry reveals an average temperature of 325 ± 50 °C on vein selvage in the Devon Consols Basalt. High-grade gold mineralisation (> 50 g/t Au) and extensive (

The Kalgoorlie district in the Archean Yilgarn Craton of Western Australia contains two world-class gold deposits: the giant Golden Mile shear-zone system and the Mt Charlotte quartz-vein stockworks. Mineralization occurs in three styles: (a) Fimiston style is characterized by ankerite-pyrite ± hematite-magnetite-gold replacement, (b) Oroya style overprints Fimiston ore in the shear zones and is characterized by silica-ankerite-V-muscovite-pyrite ± pyrrhotite-gold-telluride replacement and (c) Mt. Charlotte style is characterized by veins with ankerite-sericite ± albite-pyrite-pyrrhotite-gold selvages. Hydrothermal pyrite is ubiquitous in all styles and occurs in several stages. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) spot analyses (n = 652) were collected on 54 representative samples of pyrite from three deposits. Smooth sections in the ablation spectra were selected for quantitative analysis excluding peaks caused by micron-sized inclusions. Linear mixed effects (LME) modeling of the analytical results indicates no systematic differences between the Fimiston, Oroya and Mt Charlotte styles. The variance introduced to the dataset by geological variability reflected in random differences between samples and deposits is large. This may be a major reason for difficulties in distinguishing the differences due to mineralization style. However, there are clear differences between pyrites co-existing with different mineral assemblages. These indicate a strong control on pyrite chemistry by the composition of the hydrothermal fluids. Finally, Au-Te-As systematics show that a substantial proportion of the analyzed pyrites in all deposits fall into the field of gold saturation consistent with the known metallurgical character of the ores. Mineralogical studies, ultra-fine grinding and recovery by cyanide leach show that > 82% of all gold is present in native grains or in Au-Ag-tellurides. The refractory nature of the Fimiston pyrite concentrates is due to clusters of micron- to nano-sized inclusions rather than due to abundant lattice-bound gold.

The Golden Mile deposit (1767 t Au) in the Archean Yilgarn Craton, Western Australia, is controlled by D2 strike-slip and D3 reverse faults displacing folded tholeiitic greenstones. Granodiorite and monzodiorite dykes emplaced into the faults predate and are synchronous with propylitic and sericite–ankerite alteration overprinted by the ore. Arsenopyrite and chlorite thermometry and fluid-inclusion data indicate ore formation at 420 ± 30 °C and 300 MPa and cooling to the ambient temperature at 10 km depth (250–300 °C). Fimiston refractory ore (7 g/t Au) in propylitic Golden Mile Dolerite is zoned from inner albite–ankerite to outer ankerite–phengite–quartz replacement. Pyrite–magnetite is overprinted by pyrite–hematite ± anhydrite. Arsenical pyrite encloses chalcopyrite, tennantite, gold and tellurides. Gold thio-sulfide complexes, buffered by magmatic SO2 and H2S in the fluid, were destabilised during the ankerite–pyrite replacement of propylitic chlorite, a reaction releasing hydrogen ions for the hydrolitic alteration of adjacent albite. Gold deposition was assisted by declining gold, silver, tellurium and sulfur solubility as the fluid cooled. Dissolved sulfate is recorded in pyrite by negative δ34S (− 10 to − 5‰) at magmatic Δ33S (0–0.2‰). Oroya ore bodies are subdivided into oxidised pyrite lodes (5 g/t Au) in propylitic GMD and reduced lodes (30–120 g/t Au) characterised by Stage 1 silica–pyrite and siderite–chlorite replacement in ankerite-rich wall rocks. Rapid cooling, an acidic fluid and the retrograde solubility of ankerite facilitated replacement and the deposition of minor arsenopyrite, pyrrhotite, chalcopyrite, sphalerite and gold. Locally, the H2S-rich fluid (log fS2 = − 5.8 ± 0.5 bar at 420 °C) was reduced by organic methane. Oroya Stage 2 ore fills crosscutting veins and cements breccia. Quartz, chalcedony, dolomite–ankerite, calcite, V-muscovite, V-chlorite and V-tourmaline form the gangue of pyrite–telluride ± magnetite ore. Altaite–tellurium myrmekites were deposited at ≥ 400 °C as melt droplets together with tellurantimony, altaite, calaverite, montbrayite and petzite. As fluid temperature and tellurium fugacity declined, free gold, krennerite, coloradoite and melonite also crystallised joined by sylvanite and hessite below 350 °C. Finally, trace covellite and digenite precipitated at high fluid sulfidation states.

The Juomasuo (Co-Au) and Hangaslampi (Au-Co) deposits are located in the Kuusamo Schist Belt, part of the 1.9–1.8 Ga Svecokarelian Orogenic Belt, central Finland. The deposits are hosted by metasedimentary and mafic rocks, and structurally controlled by the F2 Kayla-Konttiaho Antiform. Hydrothermal alteration is spatially zoned, from early albite through biotite and then chlorite and late muscovite alteration. Pipe-like chlorite-quartz-pyrrhotite bodies plunge parallel to the F2 fold axis and are cut by tabular quartz-muscovite-pyrite gold lodes in the S2 axial plane orientation. The chlorite alteration zone contains 10–40 vol.% pyrrhotite containing approximately 0.25 wt% Co but whole-rock Co grades are enhanced by the late-stage and heterogeneous enrichment of minor pyrite (up to 3% Co) and introduction of cobaltian pyrite and cobalt pentlandite. Cobaltite formed where muscovite replaces chlorite within metres of the gold lodes. Cobaltite and Co-enriched pyrite formed because Co and S were mobilized from pyrrhotite in relatively S-poor gold lodes by an As-rich gold ore fluid, during late-D2. Potassium, cobalt, sulfur and arsenic were transported into the mainly chlorite-rich wallrocks, via veinlets and fractures, by the now depleted gold ore fluid. Approximately 5 vol.% pyrite in the gold lodes displays extremely variable cobalt contents, which is interpreted to reflect mobility of Co during formation of the gold lodes. The origin of the gold ore fluid is enigmatic but is most plausibly an orogenic gold fluid, despite the paucity of carbonate minerals in the gold lodes.

This study is the first to constrain the absolute timing of hypogene iron mineralization in Archean BIF located in the Yilgarn Craton. In situ SHRIMP U–Th–Pb geochronology on xenotime and monazite grains has been used to constrain the age of hypogene magnetite replacement ores at the Beebyn deposit and hypogene magnetite vein ores at the Madoonga deposit in the Weld Range study area. The Beebyn magnetite replacement ores (c. 2627 Ma) are younger than the published maximum depositional age of the BIF hosts of the Wilgie Mia Formation (2792 ± 9 Ma) and partially overlaps crystallization ages of granitic rocks (2757–2606 Ma) that intrude supracrustal rocks throughout the study area. These plutons, and their probable subvolcanic expressions, are considered to be likely sources of energy and fluids responsible for magnetite replacement ores. In contrast, Madoonga magnetite veins record multiple dates: the first at 2857 ± 41 Ma, followed by events at c. 2775 Ma through 1812 Ma. The two oldest monazite dates of 2857 ± 41 and 2832 ± 51 Ma are interpreted to be mineralization ages for magnetite veins, possibly related to subseafloor volcanism and base metal VMS systems; whereas the younger dates (i.e. 2775–1812 Ma) probably represent multiple episodes of phosphate mineral precipitation related to reactivation of structures and overprinting by discrete pulses of hydrothermal fluids. The Madoonga BIFs are genetically distinct from the Beebyn BIFs and are the oldest dated BIFs at Weld Range, being older than c. 2857 Ma, but younger than the c. 2970 Ma felsic volcanic rocks in the stratigraphic footwall to the Madoonga BIFs. Hydrothermal events at the Madoonga deposit (2215–2120 Ma) coincide with published dates for rifting, mafic–ultramafic magmatism, and basin development along the northern margin of the Yilgarn Craton (2215–2145 Ma), whereas the younger phosphate mineral dates correspond with the Glenburgh (2002–1947 Ma) and Capricorn Orogenies (1817–1772 Ma). Tectonic activity along the northern margin of the Yilgarn Craton coincides with reported ages for hematite mineralization in BIF-hosted iron-ore deposits in the Hamersley Basin and Pilbara Craton, suggesting the far-reaching effects of tectonism along paleocratonic boundaries as drivers for iron mineralization in BIF.

The Maranon Valley, located in the Eastern Cordillera of the northern Peruvian Andes, represents a 160-km-long section of the continental margin that was mainly active during the Paleozoic. A combination of whole rock geochemistry, and U-Pb, O and Hf isotope microanalysis of zircon on selected igneous rocks, reveals the timing and magmatic source variations along and across-strike of the Paleozoic proto-Andean margin. The igneous rocks exhibit a typical arc-related continental margin signature, with strong enrichment in LILE (e.g., Cs, Rb and Th), depletion of HFSE (e.g., Nb) and a negative Ti anomaly. The overlapping Hf-O isotopic compositions, together with similar inherited zircon ages, are consistent with the Lavasen Volcanics, the Esperanza Subvolcanic Complex and the Pataz Batholith sharing the same crustal source components, in about the same proportion. A genetic relationship is further supported by the strong depletion in Sr, Nb, Ta, Ti and Eu in the subvolcanic and volcanic rocks from the Esperanza Subvolcanic Complex and Lavasen Volcanics compared to the intrusive rocks from the Pataz Batholith, which is consistent with evolution of the erupted magmas by fractional crystallization. The new zircon U-Pb (LA-ICP-MS) age determinations, in combination with previously published geochronological data, suggest that the Pataz Batholith, the Esperanza Subvolcanic Complex and the Lavasen Volcanics were emplaced contemporaneously between ca. 342 Ma and 332 Ma. The new Mississippian U-Pb (zircon U-Pb LA-ICP-MS) age determination for the Lavador Pluton (336–332 Ma) and the Callangate-Enaben Pluton (341–337 Ma) suggest that magmatism was coeval with the emplacement of the Pataz Batholith. The Lavador Pluton is aligned with the main N-NW trend of the Pataz Batholith, and shares a similar range of Hf-O isotopic values (i.e., eHf (t) values from −5.3 to −1.3 and δ18O values from 6.4 to 7.1‰), and is therefore believed to represent a northern extension of the Pataz Batholith. The isotopic geochemistry and lithogeochemistry record in the Maranon Valley illustrates the regional scale tectonic switches that occurred during arc formation, from syn-collisional and compression in the Pataz-Parcoy district between ca. 342 Ma and 332 Ma, to post-collisional and extensional in the Montanitas district between ca. 332 Ma and 319 Ma. The delineation of the timing and location of tectonic regime switches in the Maranon Valley may provide a basis for future mineral exploration.

Quantitative analysis of publicly reported quarterly cost data from 23 Australian underground gold mines in the period 2014–2017 identifies consistent, statistically significant, relationships between gold grade and costs at the individual mines. Higher gold grades are associated with lower production costs throughout the dataset. The resultant regression lines for individual mines in their simplest mathematical form are a power function (f(x)=axb), where a is the scaling factor and b the rate of growth or decay in the grade-cost relationship. The general formula for the relationship between average feed grade and All-in Sustaining Costs (AISC) on a mine-by-mine basis is: AISC=exp(scaling coefficient) × Average Feed Grade(AISC decay rate) The specific grade-cost regressions are, however, markedly different between mines. For the typical grade-range of underground gold mines, costs at some mines, ‘Type 1’, display greater sensitivity to feed grade (AISC decay rate ≤ −1.0). At other mines the grade-cost relationship, although still indicating that higher grades are linked with lower costs, reveals lesser cost sensitivity to feed grade. We term these mines either ‘Type 2’ (AISC decay rate −0.6 to −1.0), or ‘Type 3’ (AISC decay rate > −0.6) where changes in feed grades correspond with lesser sensitivity to changes in costs. Although the underlying causes of the different grade-cost relationships remain uncertain, the contrasting relationships are clear and statistically significant. The identification of these contrasting grade-cost functions has major implications for the gold industry. For example, the data imply that asset-level mine transactions in the gold industry have inherently different risk characteristics depending upon whether the transacted asset is a Type 1, Type 2 or Type 3 gold mine in grade-cost terms. Disparities between recently mined grades and remaining Ore Reserve grades represent one dimension of the risk implications and the potential increase or decrease in mine value. At a steady gold price, the future cost performance of a gold mine will differ markedly based on the Ore Reserve grade to recently mined grade difference and the Types 1, 2 or 3 mine-type.

The Horto-Baratinha (HBD) iron ore deposit is located at the eastern border of Sao Francisco Craton, comprising BIF-hosted high-grade bodies (>60 wt.% Fe) associated with polydeformed quartz-mica-schists, amphibole-schist of Statherian maximum deposition age, enclosed by Statherian granitoids of the Borrachudos Suite and Neoarchean gneiss. All the sequence is crosscut by undeformed dikes and sills of pegmatitic bodies probably formed during Late Ediacaran-Cambrian. The metasedimentary sequence is stratigraphically correlatable with the Orosirian-Statherian Serra da Serpentina and Serra de Sao Jose Groups that comprise the basal units of the Espinhaco Supergroup and was intensively segmented into distinct tectonic blocks. The sedimentary/diagenetic bedding of the metamorphosed BIF (itabirite) is generally transposed by an axial planar schistosity. The lamellar hematite from itabirite is the oldest iron oxide generation, which was formed during the syn-deformational stage, parallel-oriented to the rock foliation. The (keno)magnetite grains from itabirite, iron ore and pegmatite bodies developed as idioblasts that grew over the foliation formed during late and post-deformational stages. Magnetite oxidizes subsequently to martite and granular hematite. Coarse lamellar hematite crystals randomly oriented in the border of the pegmatitic bodies also formed during the post-deformational stage due to hydrothermal reaction with itabirite. The country rocks have undergone at least three stages of deformation developed during the syn-collisional and late-collisional (Ediacaran to early-Cambrian) phases of the Brasiliano Orogeny: stage 1 with the development of a pervasive foliation (S1), parallel to axial plane to tight folds and transposition of all sedimentary structures; stage 2 with folding of S1; stage 3 with refolding of S1. Both fold systems interfere with each other making up a dome and basin refolding shape. During the late-collisional (Ediacaran to early-Cambrian) and post-collisional/gravitational collapse (Cambrian) the sequence was intruded by anatectic pegmatitic bodies, which are part of the Eastern Brazilian Pegmatite Province, one of the most significant pegmatitic regions worldwide. The fluid related with these intrusions could be related with the Si leaching, crystallization of magnetite and granular hematite, and consequent formation of high-grade iron bodies.

The Andean margin of the South American continent has been magmatically and tectonically active for over 330 million years. It is the type location where “Cordilleran-type” magmatism and orogenesis are manifest. In Argentina and Chile, between the latitudes of 28° and 40° S, magmatism related to the Gondwanan “Cordilleran-type” orogeny is reflected in a series of Carboniferous to Triassic intrusions. A comprehensive model exists for the petrogenesis of such magmas in Chile, however there is relatively little understanding of the nature and timing of Permo-Triassic magmatism in the Frontal Cordillera and Precordillera in Argentina. To address this, we present a new dataset of in situ zircon U–Pb, O and Hf isotopes from 15 felsic intrusions from Argentina. Zircon geochronology shows that magmatism in this region commenced at ca. 285 Ma and continued until ca. 250 Ma. Zircon O and Hf isotopes suggest that the oldest Permian magmas were derived from young supracrustal sources, with elevated δ18O (~ 8.5 to 7.5‰) and negative eHf values (~ − 1 to − 3 eHf). The emplacement of these magmas was coeval with the formation of mantle-derived magmas characterised by mantle-like δ18O (~ 6.0 to 5.5‰) and moderately positive eHf values (~ 4 to 1 eHf). As magmatism continued, transitional isotope signatures became predominant as melts of these disparate sources interacted and hybridised. It is proposed that under a compressional regime, mantle-derived magmas were halted in the lower continental crust, where they exchanged heat and volatiles with an older fertile lithosphere to generate melts from supracrustal sources. A shift in the stress regime at ca. 285 Ma permitted both crustally derived and juvenile mantle-derived magmas to exploit newly formed conduits to rise into the upper crust. A regional compilation of zircon O and Hf isotopes from felsic igneous rocks reveals a coherent secular trend over ~ 100 million years, where the oldest magmatism exhibits a dominant supracrustal component and younger magmas progressively (over 50 Ma) transition towards juvenile mantle-like isotopic compositions. This new dataset from Argentina fills a significant gap in the previous regional models between 285 and 250 Ma and documents the isotopic response of magmas produced in back-arc regions to a transition between compression and extensional/neutral stress regimes. These results give insight into the generation of new, or recycling of, continental crust in a back-arc setting and how the transition from compression to extension is imperative for ore-forming magmas to reach the upper crust.

In the Pataz-Parcoy district, current mining activity is focused on the mesothermal quartz-carbonate-sulfide veins hosted by the Pataz batholith. Total gold production yielded approximately 8 Moz with grades in the mined ore shoots varying between 7 and 15 g/t Au, and locally reaching up to 120 g/t Au. High-grade ore shoots are extraordinarily enriched in sulfides, representing 10 to 20 modal vol% of the vein. Ore mineralogy is characterized by a complex paragenesis of pyrite, arsenopyrite, galena, sphalerite, chalcopyrite, and gold. Gold occurs mostly as electrum in equilibrium with base metals sulfides filling fractures of pyrite and arsenopyrite. A novel combination of secondary ion mass spectrometry, laser ablation inductively coupled plasma mass spectrometry, and electron probe microanalysis is used to track the compositional evolution of ore fluid(s) and to investigate the mineralization processes occurring in the Pataz-Parcoy district. Contrasting with the classical two-stage ore sequence previously proposed for the Pataz-Parcoy district, we suggest a revised paragenetic sequence, i.e., (1) deposition of pyrite core (PyI) with homogeneously distributed base metal sulfide inclusions, (2) progressive replacement of PyI by arsenian pyrite (PyII) and arsenopyrite associated with invisible gold deposition, and (3) deposition of sphalerite – galena ± chalcopyrite − electrum in fractured pyrite and arsenopyrite. We propose two models for the formation of base metal sulfide inclusions in PyI, i.e., (1) co-precipitation of base metal sulfide with PyI and later redistribution in cracks driven by partial As replacement of PyI to PyII and arsenopyrite and (2) preferential replacement of the PyI along crystallographic planes by percolation of the fluid responsible for base metal sulfide deposition in fractured pyrite and arsenopyrite.

The Golden Mile and Mount Charlotte deposits in the Kalgoorlie Terrane, Western Australia, display three main mineralization styles: Fimiston, comprised of interconnected shear zones associated with ankerite-pyrite ± hematite- ± magnetite-gold-telluride alteration; Oroya, made up of breccia bodies with V-muscovite-ankerite-pyrite ± pyrrhotite-gold-telluride alteration; and Mount Charlotte, which consists of vein arrays with symmetrical ankerite-sericite-albite-pyrite ± pyrrhotite ± gold alteration. Pyrite is in equilibrium with gold in all three mineralization styles and has been selected as a proxy to record the sulfur source of the mineralizing fluids as well as the nature of the hydrothermal processes. The δ34S, Δ33S, and Δ36S analyses on pyrite grains from the different mineralization styles, including oxidized and reduced sulfide-oxide assemblages, reveal (1) a large variation in δ34S (from − 12.6 to + 23.5‰), and (2) a previously unrecognized occurrence of anomalous Δ33S and Δ36S signatures (from − 1.0 to + 1.1‰ and from − 2.3 to + 0.9‰, respectively). It is argued that the mineralizing fluids that formed the Golden Mile and Mount Charlotte deposits record mixing among three components: mantle sulfur, oxidized seawater sulfur (e.g., SO4), and reduced elemental sulfur (e.g., S8). Petrographic evidence in conjunction with Δ33S and Δ36S data suggest that MIF-S was acquired during the deposition of shales and basalts present in the Kalgoorlie Terrane and later mixed with mantle-derived sulfur during the mineralization events. The negative δ34S values that predominate in Fimiston style mineralization are consistent with a prevalence of oxidized fluids during the ore-forming process, as reflected by the presence of hematite-pyrite-magnetite-gold assemblages. Conversely, the positive δ34S values that dominate in the Mt Charlotte and Oroya mineralization styles reflect a reducing environment, as reflected by the presence of pyrite-pyrrhotite-gold assemblages.

Textural, chemical and multiple sulfur isotope analyses of sulfides from the Archean world-class Cuiaba orogenic Au deposit, Quadrilatero Ferrifero district, Brazil, were conducted to track distinct trace element signatures from syngenetic to epigenetic-hydrothermal pyrite types in different host units, and to deduce the nature and source of the mineralizing fluids. Gold mineralization in Cuiaba is hosted in greenschist facies volcanic and sedimentary host rocks belonging to the Archean Rio das Velhas Supergroup, especially in association with quartz veins and sulfide minerals. The BIF-hosted Fonte Grande Sul orebody is controlled by quartz veins and disseminated gold-bearing pyrite, pyrrhotite and arsenopyrite in the wall rocks. Five pyrite types are classified based on textural relations as spongy, syngenetic (Py1), porous early-(Py2), smooth main-(Py3) and smooth isolated and overgrown late-stage (Py4 and Py5) types variably present in metamorphosed carbonaceous pelites, BIF and andesite . Besides pyrite, pyrrhotite and arsenopyrite are also defined according to textural and paragenetic differences, and they display significant trace element contents. Trace element abundance maps and LA-ICP-MS analyses display trace element incorporations in Py1 (present only in carbonaceous pelite), Py2 and Py3 (in all host rocks), and Py4 and Py5 (only in BIF). Py1 yields high As, Co, Ni, Pb and Ag concentrations, whereas Py2 (formed by agglomeration of Py1) maintains high trace element concentrations with slightly less of those elements. Trace element incorporation in Py3 is similar to Py1 in carbonaceous pelite. Early-stage Py2 and main-stage Py3 in BIF and andesite have increased Co and Ni, but have less Au and As. Late-stage Py4 is characterized by lower trace element concentrations, whereas Py5 is further enriched in As, Bi, Co, Ni and Pb. The hydrothermal alteration is divided into early-, main- and late-stage, which correlate to the sulfide hydrothermal evolution. The study shows that carbonaceous pelite is pre-enriched in Co, Ni and Pb, whereas certain elements like Ag, Au, Bi and As are only hydrothermally concentrated either during the early, main or late stage in BIF and andesite. This geochemical pattern supports a syngenetic versus hydrothermal origin of distinct elements, including some trace elements now in the ore zones. Multiple sulfur isotope data suggest that mineralizing fluids at the Cuiaba gold deposit reflect a complex mixing of sulfur evolved from three possible sources: seawater, mantle, and reduced elemental sulfur. Spongy, syngenetic Py1 yields Δ 33S values ranging from −2.28 to −0.25‰, separated into two ranges, the first from −2.28 to −1.97‰, and the second from −0.96 to −0.25‰. The first range suggests Py1 in the carbonaceous pelite was deposited in a seawater environment. These pyrites probably mixed with later mantle sulfur carrying a near-zero Δ33S signature, which is indicated by the second Δ33S range, or could have mixed with fluids sourced from sedimentary rocks at depth carrying a positive Δ33S signature. The second scenario is more common in sedimentary and diagenetic pyrites. An unequivocal contrast is shown by early-, main- and late-stage pyrite types (Py2, Py3, Py4 and Py5) in carbonaceous pelite, BIF and andesite, which present a continuous process of crustal assimilation values towards increasingly positive δ34S and Δ33S values. This confirms evidence for a sedimentary-derived sulfur source as also indicated by fluid inclusion data of the andesite-hosted orebody at the Cuiaba deposit.

Archean alkali-rich (Syenitic Group) intrusions in the Eastern Goldfields Superterrane, Yilgarn Craton, are chemically similar to intrusions associated with Phanerozoic alkali porphyry systems. High-temperature potassic and ferruginous alteration associated with the Yilgarn intrusions are also similar to those in Phanerozoic counterparts but these are generally not well mineralized. Disseminated and fracture-controlled gold mineralization associated with Syenitic Group intrusions is commonly hosted by mesothermal albite-carbonate-pyrite assemblages, the origin of which is ambiguous. This communication aims to stimulate discussion on the origin of gold in and around Syenitic Group intrusions and the apparent absence of significant gold or copper mineralization in associated high-temperature alteration. Gold associated with Syenitic Group intrusions in the Yilgarn Craton has many similar characteristics to disseminated gold deposits associated with syenitic intrusions in the Abitibi greenstone belt, Canada, and may be present in other Archean greenstone belts.

The Picarrao and Liberdade deposits contain high-grade iron orebodies (>65% Fe) hosted in the Guanhaes Group itabirite, that are associated with pegmatite veins and bodies. Fluid inclusion studies in quartz veins associated with the high-grade orebodies show that medium to high salinities (25–28 wt% NaCl eq.) and temperatures (275–375 °C) fluids are associated with the silica leaching that led to the iron enrichment. Mineral chemistry studies by LA-ICP-MS in the iron oxides demonstrate that metasomatic processes were responsible for the mineralogical transformations of magnetite to hematite and for subsequent hematite recrystallization. These processes are related to the iron upgrade in the itabirite and the formation of high-grade orebodies. The oxidation of the magnetite to martite is associated with an enrichment in P and As, and depletion in Mg, Ti and Co; as observed in martite crystals compared to their matching kenomagnetite rims. On the other hand Ti and Mo are enriched in hematite crystals that recrystallized from martite. In this case Ti behaved as an immobile element, and its enrichment is accompanied by the depletion of most of the trace elements. A second stage of magnetite formation precipitated with quartz in discordant veins and is oxidized to martite-II. These quartz-martite-II veins contain low salinity and temperature fluid inclusions that record an episode of meteoric fluid influx. The results of the LA-ICP-MS analyses on the fluid inclusions from pegmatite and quartz veins associated with the high-grade iron bodies indicate the contribution of anatectic fluids in the evolution of the metasomatic events.

Iron ore deposits hosted by Archean banded iron-formation (BIF) in the Weld Range greenstone belt are representative of most of the documented iron ore deposits in the Yilgarn Craton. They include near-surface, supergene goethite-hematite orebodies that overlie and partly modify deeper occurrences of hypogene magnetite and specular hematite ores. The Cenozoic goethite-hematite-rich orebodies in these deposits are unequivocally the product of meteoric fluid alteration affecting BIF in the near-surface supergene environment; however, the deeper and likely older magnetite- and specular hematite-rich orebodies have a more contentious origin. This study is the first to present a fluid-alteration model for hypogene iron mineralization in the Yilgarn Craton that uses fluid inclusion and mineral chemistry data to constrain the physical-chemical characteristics and source of hypogene fluids responsible for mineralization. High-grade (>57 wt% Fe), magnetite-rich iron ore at the Beebyn deposit defines a discontinuous series of 440 °C) and CO2-rich. Paired O and C stable isotope data for Stage 1 ferroan dolomite suggest that these fluids had a magmatic source, while Stage 1 magnetite chemistry (e.g. enrichments in Mg, Mn, Ca, and Na) indicates chemical exchange took place between the fluids and mafic igneous rocks prior to crystallization of magnetite. The presence of monophase carbonic fluid inclusions in Stage 1 ferroan dolomite suggest that phase separation of a bicarbonate-rich aqueous fluid took place in deeper parts of the hydrothermal system, which led to the separation of the resultant volatile-rich and brine phases during transport of the Stage 1 fluid to shallower crustal levels. Cooling of the hydrothermal system during the Stage 2 fluid event involved (i) an early brine (>275–327 °C; 36–40 equiv. wt% NaCl) with Cl/Br and C and O isotopes values that overlap the ranges for magmatic fluids, with minor involvement of Archean seawater, and extensive chemical exchange with country rocks; followed by (ii) pulses of moderate- and lower-temperature Stage 2 brines (>125–260 °C; 2–24 equiv. wt% CaCl2) with Cl/Br, O and C isotope, Na/Br, and Ca/Ca + Na signatures that suggest cooling of magmatic-derived fluids that mixed with Archean seawater and reacted with mafic igneous country rocks in areas more distal to fluid pathways. The last stage of formation of magnetite-rich ore at the Beebyn deposit involved the flow of Stage 3 fluids through the existing fault network that controlled earlier fluids. Stage 3 fluids are lower-temperature (>98–175 °C), low to high-salinity brines with Cl/Br values that overlap reported ranges for 3.2 Ga vent fluids and seawater. Thus, they are likely the product of heated Archean seawater that was chemically-modified through interaction with mafic country rocks. Magnetite-talc veins at the Madoonga deposit have fluid halogen ratios for fluid inclusions hosted by magnetite that are compatible with a range of possible sources, including low-grade metamorphic fluids, geothermal brines, or oil field formation waters. Although, their common spatial association with semi-massive sulfides suggests their likely precipitation from brines derived from heated Archean seawater. More locally developed specular hematite-quartz veins that cut folded magnetite-rich ores at the Beebyn and Madoonga deposits are the product of iron redistribution in BIF by heated meteoric fluids or seawater, with precipitation of specular hematite as a consequence of oxidation and cooling of the fluid.

The Yilgarn Craton results from three major mantle input events (at ca 3.0–2.9, 2.8 and 2.7 Ga) that have interacted with > 3.0 Ga continental crust. Zircon geochronology and Sm-Nd isotopic data subdivide the craton into an older Yilgarn proto-craton and the younger, more primitive Eastern Goldfields Superterrane (EGST). Formation of the Kalgoorlie-Kurnalpi Rift (KKR) within the EGST was associated with the 2.7 Ga event, which exploited weakened crust at the eastern margin of the Yilgarn proto-craton where thick sequences of komatiite and basalt were erupted between ca 2710 and 2690 Ma in the Kalgoorlie Terrane. Calc-alkaline volcanism in the Kurnalpi Terrane began at ca 2730 Ma and continued to ca 2690 Ma, overlapping rifting and plume-related volcanism in the Kalgoorlie Terrane. Deposition of siliciclastic sedimentary rocks within basins at ca 2660 resulted from an intra-orogenic extensional event and coincided with the transition from High-Ca to Low-Ca granite magmatism and peak emplacement of intrusions with a metasomatised mantle source component. Most aspects of the KKR are satisfied by broadly coincident plume-related magmatism in the Kalgoorlie Terrane and westward subduction to the east of the Burtville Terrane. Geochemical characteristics of 2730–2700 Ma calc-alkaline volcanism and 2685–2630 Ma low-SiO2 and alkali-rich intrusions support models for a continental margin subduction zone setting. World-class gold deposits formed in reactivated margins of the KKR, which became flux zones for mantle-derived magmas, hydrothermal fluids and heat during 2675–2620 Ma orogenesis. The orogenic gold mineralisation can be subdivided into proximal intrusion-related and distal-source deposits.

“Magmato-Hydrothermal Space” is a new mathematical construct where 24 ore and pathfinder elements are used to quantify ore-element signatures. Quantification allows relationships between ore deposit samples to be mapped. The broad-scale view of Magmato-Hydrothermal Space reveals three important trends: (1) Zn-Pb sediment-hosted mineralisation to igneous-associated Cu-Au mineralisation, (2) Cu-Au mineralisation to Au-only mineralisation, and (3) ultramafic associated magmatic Ni-Cu-PGE mineralisation through Cu-Au mineralisation to granitoid-associated Mo, W and Sn mineralisation. The view provided by Magmato-Hydrothermal Space reveals that there is a spectrum of ore element signatures that mirrors the spectrum of ore deposit classes described in the literature. Geochemical variations within individual ore deposit classes are examined for orogenic-Au, VHMS, epithermal and sediment-hosted Cu samples. Sub-groups within each of these classes are compared on element enrichment diagrams and described in the context of Magmato-Hydrothermal Space. Orogenic Au samples are divided into two sub-groups of As-Sb rich mineralisation and four sub-groups of relatively As-Sb poor mineralisation. The As-Sb poor sub-groups include a Te-Cu-Ag rich sub-group that overlaps with the porphyry Cu class and a Te-W-(Bi-Mo) rich class dominated by granitoid hosted deposits. The VHMS class ranges from a Cu-rich sub-group that overlaps with porphyry Cu and IOCG classes through a Cu-Zn sub-group to two Zn-Cu sub-groups, one of which overlaps with the SHMS class. The epithermal class is divided into Zn-rich, Cu-rich and base metal – poor sub-groups.

This study examines the whole-rock geochemistry and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) iron oxide chemistry of itabirite and related iron ore, as well as underlying phyllitic wall rock, of the Pau Branco iron ore deposit, Quadrilatero Ferrifero, Brazil. The phyllite and iron ore of Pau Branco extend from hypogene deep-seated into supergene weathered zones. The phyllitic sequence that underlies the itabirite-hosted iron ore along a sheared contact includes (from the bottom to top) carbonaceous and carbonate-, chlorite-, and Fe-rich zones, which likely reflect distal to proximal alteration halos. The Fe-rich phyllite and iron ore comprise a complex iron oxide mineralogy: (1) magnetite-martite is hosted in itabirite and related medium-grade iron ore and present as disseminated minerals in phyllite; (2) microplaty hematite replaces chlorite and carbonate in the phyllite; (3) granoblastic hematite is a recrystallization/precipitation product and the dominant iron oxide of the hard iron ore; (4) schistose specular hematite overgrows earlier iron oxides; and (5) goethite replaces earlier hematite and amphibole within the weathering horizon. Whole-rock geochemistry and related mass balance calculations reveal that, unlike the itabirite-hosted iron ore, interpreted to be the result of a solely residual iron enrichment via depletion of most major oxides and trace elements, the iron enrichment of the phyllite is caused by addition of Fe 2 O 3 . The Fe 2 O 3 is likely sourced from the overlying itabirite/iron ore and is mineralogically reflected in the replacement of carbonate and chlorite by hematite. The rare earth elements (REE) abundances of the different ore and phyllite zones reveal seawater-like REE signatures and Y/Ho ratios of the itabirite, hypogene and supergene iron ore, shale-atypical REE patterns in the unaltered phyllite, and Eu fractionation trends. This suggests a distinct input of hydrothermal fluids during the Fe enrichment of the phyllite. Locally, restricted Ce fractionation is attributed to distinct (e.g., Mn-rich) lithostratigraphic intercalations within the itabirite. Laser ablation-ICP-MS mineral chemistry of phyllite-hosted martite and microplaty hematite suggests a strong chemical inheritance by the host rock and precursor mineral. Positive Ce anomalies are restricted to phyllite- and itabirite-hosted martite only and, therefore, may reflect the highly oxidative conditions during martitization. At Pau Branco, the fluid-rock interaction affected not only the itabirite, but also the underlying phyllite, resulting in distinct alteration halos that extend beyond the itabirite toward the footwall. The significant chemical influence and importance of country-rock lithologies as a possible elemental source, for example, must be taken into account when interpreting whole-rock geochemical data and investigating an itabirite-/banded iron formation-hosted iron ore system.

The world-class Cuiaba gold deposit of the Archaean Rio das Velhas greenstone belt in Brazil is hosted in banded iron formation containing carbonaceous matter and carbonate, within the reclined, isoclinal Cuiaba fold. Mineralised quartz veins are hosted in andesite in the stratigraphic footwall of the banded iron ores and form some of the more recently discovered ore bodies. Fluid inclusion data of the quartz vein–associated “Veio de Quartzo” ore body are obtained from four quartz types (Qz1, Qz2, Qz3, Qz5) in gold-mineralised V1 shear vein and V2 extensional veins, barren V3 extensional vein array, and V4 breccia-style veins, all developed during the Archaean D1 event. Three fluid types are distinguished: (i) aqueous fluids of low salinity (1.8–3.8 wt% NaCl equiv), homogenisation (into liquid) at 220 to 230 °C; (ii) aqueous fluids of moderate salinity (5.3–12.7 wt% NaCl equiv), and homogenisation at 250 to 290 °C; and (iii) aqueous-carbonic fluids of moderate salinity (6.0–15.1 wt% NaCl equiv), with 30–91 mol% CO2, 8–41 mol% CH4 and up to 28 mol% N2 and decrepitation (into vapour) at 280 to 310 °C. Based on an independent pressure estimate, a pressure correction was applied to aqueous fluid inclusions, resulting in minimum trapping temperatures at 360 °C for V1 veins, 330 °C for V2 veins, 300 °C for V3 veins and 270 °C for the late-stage V4 veins. Ion chromatography analyses reveal a Br/Cl ratio of 0.7 × 10−3 in Qz1-V1, from 1.4 to 1.5 × 10−3 in Qz2-V2, 0.3 to 0.4 × 10−3 in Qz3-V3 and 0.7 to 0.9 × 10−3in Qz5-V4 veins. Zinc, Pb and Cu are relatively enriched with ~ 100 to 1000 ppm in aqueous and aqueous-carbonic fluid inclusion assemblages in all vein and quartz types, which is similar to other orogenic gold deposits hosted in the Rio das Velhas greenstone belt. The fluid inclusion data are consistent with a model invoking a metamorphic origin for the mineralising fluid. A two-step model of hydrothermal fluid flow and gold enrichment is suggested to have developed during the Archaean D1 event, with an early, aqueous-carbonic fluid pulse of relatively high temperature (from V1 up to V3) and an evolved, aqueous-carbonic fluid pulse of lower temperature (V4, breccia-style veins). The Rio das Velhas greenstone belt is dominated by regionally metamorphosed metasedimentary rocks, resulting in a complex hydrothermal fluid evolution and related gold mineralisation such as the shear zone–controlled Veio de Quartzo ore body.

Several iron-ore deposits hosted within Mesoarchean banded iron formations (BIFs) are mined throughout the North Pilbara Craton, Western Australia. Among these, significant goethite±martite deposits (total resources >50 Mt at 55.8 wt% Fe) are distributed in the Wodgina district within 2 km of the world-class pegmatite-hosted, tantalum Wodgina deposits. In this study, we investigate the dominant controls on iron mineralisation at Wodgina and test the potential role of felsic magma-derived fluids in early alteration and upgrade of nearby BIF units. Camp-scale distribution and geochemistry of iron ore at Wodgina argue against any significant influence of identified felsic intrusions in the upgrade of BIF. Whereas, the formation of BIF-hosted goethite±martite iron ore at Wodgina involves: (i) early (ca 2950 Ma) metamorphism of BIF causing camp-scale recrystallisation of pre-existing iron oxides to form euhedral magnetite, with local enrichment to sub-economic grades (∼40 wt% Fe) within or proximal to ...

With growing interest in the application of in situ multiple sulfur isotope analysis to a variety of mineral systems, we report here the development of a suite of sulfur isotope standards for distribution relevant to magmatic, magmatic-hydrothermal, and hydrothermal ore systems. These materials include Sierra pyrite (FeS2), Nifty-b chalcopyrite (CuFeS2), Alexo pyrrhotite (Fe(1 − x)S), and VMSO pentlandite ((Fe,Ni)9S8) that have been chemically characterized by electron microprobe analysis, isotopically characterized for δ33S, δ34S, and δ36S by fluorination gas-source mass spectrometry, and tested for homogeneity at the micro-scale by secondary ion mass spectrometry. Beam-sample interaction as a function of crystallographic orientation is determined to have no effect on δ34S and Δ33S isotopic measurements of pentlandite. These new findings provided the basis for a case study on the genesis of the Long-Victor nickel-sulfide deposit located in the world class Kambalda nickel camp in the southern Kalgoorlie Terrane of Western Australia. Results demonstrate that precise multiple sulfur isotope analyses from magmatic pentlandite, pyrrhotite and chalcopyrite can better constrain genetic models related to ore-forming processes. Data indicate that pentlandite, pyrrhotite and chalcopyrite are in isotopic equilibrium and display similar Δ33S values + 0.2‰. This isotopic equilibrium unequivocally fingerprints the isotopic signature of the magmatic assemblage. The three sulfide phases show slightly variable δ34S values (δ34Schalcopyrite = 2.9 ± 0.3‰, δ34Spentlandite = 3.1 ± 0.2‰, and δ34Spyrrhotite = 3.9 ± 0.5‰), which are indicative of natural fractionation. Careful in situ multiple sulfur isotope analysis of multiple sulfide phases is able to capture the subtle isotopic variability of the magmatic sulfide assemblage, which may help resolve the nature of the ore-forming process. Hence, this SIMS-based approach discriminates the magmatic sulfur isotope signature from that recorded in metamorphic- and alteration-related sulfides, which may not be resolved during bulk rock fluorination analysis. The results indicate that, unlike the giant dunite-hosted komatiite systems that thermo-mechanically assimilated volcanogenic massive sulfides proximal to vents and display negative Δ33S values, the Kambalda ores formed in relatively distal environments assimilating abyssal sulfidic shales.

The Boulder Lefroy-Golden Mile (BLF-GMF) fault system is the most intensely mineralized structure (>2150 t Au to 2015) in the Archean Yilgarn Craton, Western Australia. The fault system links the Kalgoorlie and Kambalda mining districts in the Eastern Goldfields Province, a continental-margin orogen subdivided into the western Kalgoorlie ensialic rift and the eastern Kurnalpi volcanic arc. After rifting, the 2.73–2.66 Ga greenstone-greywacke succession in the Kalgoorlie-Kambalda area underwent five phases of orogenic deformation, predominantly during ENE-WSW shortening: D1 upright folding at ca. 2680 Ma, D2 sinistral strike-slip faulting at 2678–2663 Ma, D3 folding of late conglomerate-turbidite successions at 2665–2655 Ma, D4 dextral strike-slip faulting at 2655–2640 Ma and D5 east-northeast-striking normal faulting. Regional prehnite-pumpellyite to greenschist facies burial metamorphism took place during D1 and D3 crustal thickening, and amphibolite facies aureoles formed around granite batholiths during and after D3 at 400 ± 100 MPa pressure. The D2 BLF offsets D1 folds by 12 km SW-side south and contains a porphyry dyke (2676 ± 7 Ma) boudinaged by transtensional oblique-slip along a line pitching 21° southeast. The BLF is linked by transverse D2 thrusts to other sinistral faults recording strike-slip until 2663 ± 7 Ma. Late D2 strike-slip movement alternated with early D3 shortening. D3 thrusts accommodated strain in fault blocks of rigid mafic-ultramafic volcanic rocks consolidated during D1, while the sedimentary rocks in D3 synclines were foliated at high strain. Biotite-sericite alteration and gold-pyrite mineralization in the BLF-GMF system took place at 11 ± 4 km burial depth in faults active during D2 and D3. The Golden Mile (1708 t Au) and other deposits are associated with stocks and dykes of high-Mg monzodiorite-tonalite porphyry, part of a late-orogenic (2665–2645 Ma) mantle-derived suite of adakitic affinity. Hornblende and apatite compositions indicate that these intrusions are characterized by high water contents (5–6 wt% H2O in melt), by high oxidation states (δNNO +1.0 to +2.4 log units) and by igneous anhydrite. Some stocks contain pervasive anhydrite-pyrite mineralization of low gold grade (0.4 g/t). Biotite-sericite-pyrite ore bodies such as those at Kanowna Belle (140 t Au) also replace faulted metamorphic rocks above batholith domes cored by plutons of the monzodiorite suite. The D4 strike-slip faults are barren at Kambalda but control gold quartz-vein ore at Kalgoorlie (2651 ± 9 Ma), and Au-Ag breccia ore at Black Flag (

The concept of a mineral system was first formally introduced in 1994, two decades after the analogous petroleum system concept had been developed. Mineral systems involve: (1) tectonic events that trigger and define temporal windows for mineralising events, (2) geochemical and tectonic processes that produce ‘source regions’ often enriched in metals and hydrothermal fluids and magmas capable of mobilising these metals, (3) tectonic, sedimentary, diagenetic and structural processes that produce conduits that can act as pathways for fluid/magma flow at lithospheric, crustal, province and district scales, (4) processes that drive fluid flow, (5) focussing mechanism that concentrate (or throttle) the flow of fluids or magmas into depositional ‘trap’ sites at the camp to deposit scales, (6) chemical and physical processes that cause metal deposition at the trap site, (7) post-depositional geochemical processes that produce geochemical and geophysical features that allow later detection, and (8) processes that enhance exhumation, preservation and upgrading of mineralised material. Although mineralising events are generally short-lived, important features of mineral systems can develop well before, or well after the mineralising event, and the evolution of a mineral system can extend over hundreds of millions to billions of years. For example, the architecture of mineral systems, which controls the location of source regions and conduits, is commonly established (long) before the mineralising event, and exhumation and upgrading through metamorphism and/or supergene enrichment occur (long) after the mineralising event. The advantage of the mineral system approach is that it focusses on the critical geological processes necessary to form a major mineral deposit and is not restricted to descriptive elements of a specific mineralisation style. Mineral systems can explain the spatial and temporal co-occurrence of mineral deposits within a specific mineral province. The mineral system concept can also explain families of coeval mineral systems that potentially formed in the same or adjacent terranes or provinces. Presently, mineral systems are broadly subdivided into orthomagmatic and hydrothermal classes, with several transitional systems between these end-members not well defined (e.g., sediment-hosted deposits with hydrothermal overprints or enrichment). Coeval, or nearly coeval, mineral systems, such as IOCG and porphyry Cu–Au systems in Chile or orogenic Au and Cu–Au porphyry systems in the Lachlan Orogen in eastern Australia, can develop during the tectonic evolution of a given terrane. Overprinting mineral systems, potentially separated by tens of millions of years, can also develop where products of early-formed mineralising events (e.g. syn-volcanic or syn-sedimentary events) can be overprinted at a later stage by mineralisation formed during orogenesis or basin inversion (e.g., orogenic Au system). The mineral system concepts and models can be translated into effective exploration targeting criteria and serve as the basis of robust, testable exploration models. Arguably, this is the main practical purpose for a systematic mineral system analysis and its main advantage over traditional descriptive deposit models. This advantage is enhanced in under-explored areas, particularly covered areas with poor or no outcrop, where known existing deposits, from which empirical models are developed, are lacking. Defining and mapping expressions of the critical elements of mineral systems can effectively focus exploration targeting. Major deep-crustal domain boundaries, often overlain by younger geological provinces and not clearly expressed in many traditional geological datasets, provide steep crustal zones of focused regional fluid flow for many orthomagmatic and hydrothermal mineral systems. Significant challenges in the development of mineral system models and their effective practical applications remain. For example, there is not enough information on the tectonic setting of productive mineral systems and the existing information is commonly conflicting. This is often caused by a short-lived transient nature of specific tectonic conditions favourable for triggering and driving a productive mineral system, exacerbated by a lack of outcrop and/or lack of high resolution geophysics, geochemistry and geochronology in poorly explored geological terranes. An important challenge that mineral system geoscience can help to address is exploration area selection at the district to camp scale. At larger scales, conceptual understanding of the relationships between tectonism and metallogeny can identify potentially mineralised provinces, and at smaller scales, well established empirical relationships between deposits and geochemical and geophysical anomalies provide vectors to ore at the camp to deposit scale. It is the intermediate, district to camp scale where both conceptual- and empirical-based targeting commonly fail, providing a challenge to mineral exploration, particularly in greenfields terranes. Finally, mostly end-member hydrothermal and orthomagmatic mineral systems have received much attention in recent years; sedimentary deposits (e.g., placers, phosphorites) have yet to be defined within the mineral system framework. However, recent developments in the mineral system geoscience provide an increasingly robust framework for more effective predictive regional exploration targeting.

Tectono-metallogenic systems are geological systems that link geodynamic and tectonic processes with ore-forming processes. Fundamental geodynamic processes, including buoyancy-related processes, crustal/lithospheric thinning and crustal/lithospheric thickening, have occurred throughout Earth's history, but tectonic systems, which are driven by these processes, have evolved as Earth's interior has cooled. Tectonic systems are thought to have evolved from magma oceans in the Hadean through an unstable “stagnant-lid” regime in the earlier Archean into a proto-plate tectonic regime from the late Archean onwards. Modern-style plate tectonics is thought to have become dominant by the start of the Paleozoic. Mineral systems with general similarities to modern or geologically recent systems have been present episodically (or semi-continuously) through much of Earth's history, but most of Earth's present endowment of mineral wealth was formed during and after the Neoarchean, when proto- or modern-style plate tectonic systems became increasingly dominant and following major changes in the chemistry of the atmosphere and hydrosphere. Changes in the characteristics of some mineral systems, such as the volcanic-hosted massive sulphide (VHMS) system, reflect changes in tectonic style during the evolution towards the modern plate tectonic regime, but may also involve secular changes in the hydrosphere and atmosphere. Whereas tectono-metallogenic systems have evolved in general over Earth's history, specific tectono-metallogenic systems evolve over much shorter time frames. Most mineral deposits form in three general tectono-metallogenic systems: divergent systems, convergent systems, and intraplate systems. Although fundamental geodynamic processes have driven the evolution of these systems, their relative importance may change as the systems evolved. For example, buoyancy-driven (mantle convection/plumes) and crustal thinning are the dominant processes driving the early rift stage of divergent tectono-metallogenic systems, whereas buoyancy-driven processes (slab sinking) and crustal thickening are the most important processes during the subduction stage of convergent systems. Crustal thinning can also be an important process in the hinterland of subduction zones, producing back-arc basins that can host a number of mineral systems. As fundamental geodynamic processes act as drivers at some stage in virtually all tectonic systems, on their own these cannot be used to identify tectonic systems. Moreover, as mineral systems are ultimately the products of these same geodynamic drivers, individual mineral deposit types cannot be used to determine tectonic systems, although mineral deposit associations can, in some cases, be indicative of the tectono-metallogenic system. Ore deposits are the products of geological (mineral) systems that operate over a long time frame (hundreds of millions of years) and at scales up to the craton-scale. In essence, mineral systems increase the concentrations of commodities through geochemical and geophysical processes from bulk Earth levels to levels amenable to economic mining. Mineral system components include the geological (tectonic and architectural) setting, the driver(s) of mineralising processes, metal and fluid sources, fluid pathways, depositional trap, and post-depositional modifications. All of these components link back to geodynamic processes and the tectonic system. For example, crustal architecture, which controls the spatial distribution of, and fluid flow, within mineral systems, is largely determined by geodynamic processes and tectonic systems, and the timing of mineralisation, which generally is relatively short (commonly The geochemical characteristics of many mineral systems are a consequence of their geodynamic and tectonic settings. Settings that are characterised by low heat flow and lack active magmatism produce low temperature fluids that are oxidised, with ore formation caused largely by redox gradients or the provision of external H 2 S. The characteristics of these fluids are largely governed by the rocks with which they interact, rocks that have extensively interacted with the hydrosphere and atmosphere, both environments that have been strongly oxidised since the great oxidation event in the Paleoproterozoic. In settings characterised by high heat flow and active magmatism, ore fluids tend to be higher temperature and reduced, with deposition caused by cooling, pH neutralisation, depressurisation and fluid mixing. Again, the characteristics of these fluids are governed by rocks with which they interact, in this case more reduced magmatic rocks derived from the mantle or lower crust.

The BIF-hosted iron ore system represents the world's largest and highest grade iron ore districts and deposits. BIF, the precursor to low- and high-grade BIF hosted iron ore, consists of Archean and Paleoproterozoic Algoma-type BIF (e.g., Serra Norte iron ore district in the Carajas Mineral Province), Proterozoic Lake Superior-type BIF (e.g., deposits in the Hamersley Province and craton), and Neoproterozoic Rapitan-type BIF (e.g., the Urucum iron ore district). The BIF-hosted iron ore system is structurally controlled, mostly via km-scale normal and strike-slips fault systems, which allow large volumes of ascending and descending hydrothermal fluids to circulate during Archean or Proterozoic deformation or early extensional events. Structures are also (passively) accessed via downward flowing supergene fluids during Cenozoic times. At the depositional site the transformation of BIF to low- and high-grade iron ore is controlled by: (1) structural permeability, (2) hypogene alteration caused by ascending deep fluids (largely magmatic or basinal brines), and descending ancient meteoric water, and (3) supergene enrichment via weathering processes. Hematite- and magnetite-based iron ores include a combination of microplaty hematite–martite, microplaty hematite with little or no goethite, martite–goethite, granoblastic hematite, specular hematite and magnetite, magnetite–martite, magnetite-specular hematite and magnetite–amphibole, respectively. Goethite ores with variable amounts of hematite and magnetite are mainly encountered in the weathering zone. In most large deposits, three major hypogene and one supergene ore stages are observed: (1) silica leaching and formation of magnetite and locally carbonate, (2) oxidation of magnetite to hematite (martitisation), further dissolution of quartz and formation of carbonate, (3) further martitisation, replacement of Fe silicates by hematite, new microplaty hematite and specular hematite formation and dissolution of carbonates, and (4) replacement of magnetite and any remaining carbonate by goethite and magnetite and formation of fibrous quartz and clay minerals. Hypogene alteration of BIF and surrounding country rocks is characterised by: (1) changes in the oxide mineralogy and textures, (2) development of distinct vertical and lateral distal, intermediate and proximal alteration zones defined by distinct oxide–silicate–carbonate assemblages, and (3) mass negative reactions such as de-silicification and de-carbonatisation, which significantly increase the porosity of high-grade iron ore, or lead to volume reduction by textural collapse or layer-compaction. Supergene alteration, up to depths of 200 m, is characterised by leaching of hypogene silica and carbonates, and dissolution precipitation of the iron oxyhydroxides. Carbonates in ore stages 2 and 3 are sourced from external fluids with respect to BIF. In the case of basin-related deposits, carbon is interpreted to be derived from deposits underlying carbonate sequences, whereas in the case of greenstone belt deposits carbonate is interpreted to be of magmatic origin. There is only limited mass balance analyses conducted, but those provide evidence for variable mobilization of Fe and depletion of SiO2. In the high-grade ore zone a volume reduction of up to 25% is observed. Mass balance calculations for proximal alteration zones in mafic wall rocks relative to least altered examples at Beebyn display enrichment in LOI, F, MgO, Ni, Fe2O3total, C, Zn, Cr and P2O5 and depletions of CaO, S, K2O, Rb, Ba, Sr and Na2O. The Y/Ho and Sm/Yb ratios of mineralised BIF at Windarling and Koolyanobbing reflect distinct carbonate generations derived from substantial fluid–rock reactions between hydrothermal fluids and igneous country rocks, and a chemical carbonate-inheritance preserved in supergene goethite. Hypogene and supergene fluids are paramount for the formation of high-grade BIF-hosted iron ore because of the enormous amount of: (1) warm (100–200 °C) silica-undersaturated alkaline fluids necessary to dissolve quartz in BIF, (2) oxidized fluids that cause the oxidation of magnetite to hematite, (3) weakly acid (with moderate CO2 content) to alkaline fluids that are necessary to form widespread metasomatic carbonate, (4) carbonate-undersaturated fluids that dissolve the diagenetic and metasomatic carbonates, and (5) oxidized fluids to form hematite species in the hypogene- and supergene-enriched zone and hydroxides in the supergene zone. Four discrete end-member models for Archean and Proterozoic hypogene and supergene-only BIF hosted iron ore are proposed: (1) granite–greenstone belt hosted, strike-slip fault zone controlled Carajas-type model, sourced by early magmatic (± metamorphic) fluids and ancient “warm” meteoric water; (2) sedimentary basin, normal fault zone controlled Hamersley-type model, sourced by early basinal (± evaporitic) brines and ancient “warm” meteoric water. A variation of the latter is the metamorphosed basin model, where BIF (ore) is significantly metamorphosed and deformed during distinct orogenic events (e.g., deposits in the Quadrilatero Ferrifero and Simandou Range). It is during the orogenic event that the upgrade of BIF to medium- and high-grade hypogene iron took place; (3) sedimentary basin hosted, early graben structure controlled Urucum-type model, where glaciomarine BIF and subsequent diagenesis to very low-grade metamorphism is responsible for variable gangue leaching and hematite mineralisation. All of these hypogene iron ore models do not preclude a stage of supergene modification, including iron hydroxide mineralisation, phosphorous, and additional gangue leaching during substantial weathering in ancient or Recent times; and (4) supergene enriched BIF Capanema-type model, which comprises goethitic iron ore deposits with no evidence for deep hypogene roots. A variation of this model is ancient supergene iron ores of the Sishen-type, where blocks of BIF slumped into underlying karstic carbonate units and subsequently experienced Fe upgrade during deep lateritic weathering.

The Neoproterozoic Telfer deposit, one of Australia’s largest gold-copper deposits, is located in the Paterson orogen. Several highly differentiated calc-alkaline to alkali-calcic peraluminous granites intruded the metasedimentary rocks near (5–20 km) Telfer contemporaneously with structurally controlled gold-copper mineralization. Fluid inclusion assemblages with different fluid inclusion types were identified in samples from a range of different vein types. These inclusion types range from three-phase aqueous Laq + Vaq + Shalite, high-salinity (≤50 wt % NaCl equiv), high-temperature (≤460°C) inclusions to two-phase aqueous or two-phase aqueous carbonic, low- to moderate-salinity (2–22 wt % NaCl equiv), moderate- to high-temperature (≤480°C) fluid inclusions. Fluid inclusion trapping mechanisms and interpreted precipitation mechanisms for gold and copper include (1) adiabatic cooling between 450° and 200°C in all veins and, (2) locally, fluid phase separation at about 300°C. The trapping pressure of fluid inclusion assemblages trapped during phase immiscibility was calculated to be approximately 1.5 kbar. For fluid inclusion assemblages that lack evidence for phase immiscibility, a pressure at the temperature of final homogenization of up to 3 kbar was calculated. This high pressure value is interpreted to be related to local fluid overpressure, as a consequence of fault zone movement, in faults and fractures that localized gold at Telfer. Phase immiscibility and gold precipitation were induced during sharp pressure decrease accompanying fault zone movement. In situ laser inductively coupled plasma-mass spectrometry (ICP-MS) analyses of fluid inclusions revealed high trace element contents in all fluid inclusion assemblages. Manganese/Fe ratios of 0.24 is observed. Given the high temperatures and salinities of up to 480°C and 42 wt % NaCl equiv, Au and Cu were likely transported as chloride complexes. This interpretation is supported by the observation that the highest base metal contents occur in the highest-salinity fluid inclusion. Potassium/Ca ratios of >1 in most assemblages, the high homogenization temperatures (≤480°C) in many fluid inclusion assemblages, and the high trace element contents (e.g., Fe, Mg, K, Na) in most of the fluid inclusion assemblages are compatible with involvement of a magmatic hydrothermal fluid during gold-copper mineralization. This fluid was probably derived from the coeval granites in the Telfer area and, thus, Telfer is interpreted to be a distal, intrusion-related, metasedimentary rock-hosted, gold-copper deposit type.

Isotopic Lu–Hf and geochronological studies on the zircon grains of the Paleoproterozoic Borrachudos Suite provide constrains of the evolution of the tectonomagmatic events that affected the southern border of the Sao Francisco Craton and leaded to the formation of the associated iron and emerald deposits. The granite records magmatic crystallization in the 1740-1688 Ma time range, and A2-type geochemical signature. Zircon grains present hydrothermal and anatectic areas with Cambrian age that are related to the gravitational collapse of the final stages of the Brasiliano orogen. During this event the granite was deformed and metamorphosed in the amphibolite facies, leading to anatexis and the formation of large amount of pegmatite bodies. The Hf isotope data on the hydrothermal/anatectic areas indicate partial melting were accompanied by hydrothermal fluids enriched in radiogenic Hf. These fluids contributed to the formation of large volume of hydrous melts (pegmatites), the formation of the emerald deposits and the high-grade iron orebodies.

Archean metabasalts enclose the Serra Norte iron deposits in the Carajas Mineral Province, Brazil. They experienced seafloor hydrothermal alteration, regional metamorphism under low greenschist facies conditions, and hematite-associated hydrothermal alteration, characterizing (i) least-altered, (ii) chlorite, and (iii) hematite-chlorite basalts in the N4 and N5 deposits. Their petrographic and geochemical changes were caused by both chlorite and hematite hydrothermal alteration. Nevertheless, part of the original, igneous textures and some of their primary minerals (plagioclase and clinopyroxene) are commonly preserved. Geochemical investigation of the least-altered basalt indicates a calc-alkaline affinity. Trace element behavior (e.g., Nb and Th) is consistent with an arc-related setting and continental crustal contamination. Where hydrothermal alteration affects basalts the most, distal, intermediate, and proximal alteration zones are distinguished based on the amount of chlorite ± hematite (less magnetite). Chlorite composition in (i), (ii) and (iii) marks these three mafic lithotypes, with variations in the Fet/(Fe + Mg) ratios that clearly reflect buffered through unbuffered conditions. Mineralogical and textural features, such as ruptured amygdales, indicate fluid interaction with hydrothermal minerals forming veins and breccias caused by hydraulic fracturing. Both chlorite and hematite-chlorite basalts experienced renewed isotopic equilibrium due to hydrothermal alteration, showing a decrease in δ18O (7.4 to 1.9 ‰) in comparison to the least-altered basalt reflecting an increase in fluid-rock ratio. On most discrimination diagrams and MORB-normalized spidergram, the investigated rocks are comparable to a volcanic arc environment associated with subduction zone. These and other evidence such as (a) a seafloor-associated volcanogenic sequence; (b) arc-type sedimentation of the Grao Para Group indicated by hyaloclastic tufts, breccias and volcaniclastic rocks; (c) jaspilites in the Serra Norte; and (d) a large subduction signature expressed by enrichment in Th, all suggest that the Grao Para basalts overflowed on the continental crust in a back-arc environment, with the primary magma having experienced significant upper crustal contamination. The arc-association evolution and the variability of lithological, sedimentological, igneous volcanic, structural, metamorphic, and other evolutionary aspects of the Itacaiunas Supergoup is suggestive of a greenstone-belt-type setting.An arc-associated evolution and the variability of lithological, sedimentological, igneous volcanic, structural, metamorphic, and other aspects of the Itacaiunas Supergoup supports a greenstone-belt-type setting.

The Faina greenstone belt is located in central Brazil and contains the Cascavel and Sertao gold deposits (500,000 oz Au total resource and past production). The bulk of the gold is hosted in quartzite and biotite schist at Cascavel, and carbonaceous schist and banded iron formation at Sertao. The metamorphic grade of the host rocks is greenschist facies. Cascavel is a vein-hosted gold deposit with orebodies mainly controlled by F2 fold hinges, with minor mineralization in D3 shear zones. Hydrothermal alteration in quartzite is characterized by distal quartz-K-feldspar ± muscovite, intermediate quartz-fuchsitic mica-biotite-pyrite, and proximal quartz-white mica-pyrite ± chalcopyrite. The biotite schist is characterized by distal quartz-chlorite-calcite and proximal white mica-biotite-tourmaline-siderite-pyrite. Native gold is located within intensely deformed quartz veins, and locally as free gold disseminated in proximal alteration zones. Sertao is a shear zone-hosted gold deposit with orebodies controlled by D3 shear zones including gold-bearing shear veins and surrounding hydrothermally altered wallrocks. Hydrothermal alteration is characterized by distal quartz-ankerite-chlorite-pyrite ± chalcopyrite and proximal quartz-white mica-siderite-pyrite-arsenopyrite ± chalcopyrite. Gold is in equilibrium with arsenopyrite and within arsenopyrite disseminated in the proximal alteration zone. Chlorite geothermometry suggests temperatures of 335–407 °C and 328–397 °C for the gold-bearing hydrothermal fluids in the Sertao and Cascavel deposits, respectively. Arsenopyrite geothermometry on arsenopyrite within gold-bearing veins in the Sertao deposit yields temperatures between 310 and 480°C. Structures controlling hydrothermal alteration and gold mineralization in both deposits are developed during a regional D2 event and subsequently deformed during a D3 event. Hydrothermal alteration minerals are consistently replacing metamorphic minerals. The alteration assemblages in both deposits are similar, albeit their modal mineralogy is controlled by the host rock composition. Therefore, both the Cascavel and Sertao deposits are interpreted as orogenic, mesozonal gold systems comparable with other orogenic gold systems in Brazil and worldwide.

Mississippian arc magmatic suites of the Au-rich Pataz and Cu-dominated Montanitas regions in Peru reveal distinct modes of magmatic-hydrothermal petro- and metallogenesis. The distinction is remarkable due to their broad contemporaneity (336–322 Ma), arc-parallel position, and close distance ( 0 and δ18O of ~ 5.3‰) and assimilated old crust (variously low eHf and δ18O > 5.3‰). The ultimate source of Au in the mineralised Pataz batholith was oxidised (fO2 at FMQ buffer; based on zircon trace chemistry) and alkali-, LILE- and HFSE-enriched, most likely represented by the metasomatised mantle. The syn-extensional emplacement of the relatively reduced (ΔFMQ 0) and dominantly mantle derived without significant incorporation of crustal material. Samples from the Cu-mineralised suites indicate the additional contribution of a δ18O

Gold production from the northern Pataz district in the eastern Andean Cordillera of Peru has been sourced mainly from mesothermal quartz-carbonate-sulfide veins hosted by the Mississippian Pataz batholith. Gold is also found in basement-hosted veins underlying the batholith, in the Vijus-Santa Filomena area of the district. Both are located within a central horst; similar vein mineralogy and proximal phengitic white mica alteration are common to both. However, comb-textured quartz, the chemical compositions of bulk ore and sulfide minerals, and the presence of barite and siderite veins suggest that the basement-hosted veins formed at a shallower crustal level. Similar expressions of hydrothermal alteration associated with anomalous gold, As, Sb, and Tl are also present in the adjacent Lavasen graben, where alteration is intimately associated with volcanic processes that deposited the Mississippian Lavasen Volcanics. K-Ar and 40 Ar- 39 Ar ages for hydrothermal illite from all three locations range between Mississippian and Late Triassic but are consistent with a single Mississippian hydrothermal event, if the data record a minimum age for original illite formation. The geologic setting, mineralization styles, and chemical data suggest a range of crustal depths, ranging from mesothermal batholith-hosted veins through shallow to intermediate depths for the Vijus-Santa Filomena area to a near-surface epithermal setting for the Misquichilca area. Telescoping of this 10- to 13-km crustal range into a 3-km topographic section of the Andes is attributed to syn- and postmineralization uplift and erosion. Sulfide-rich high-grade ore shoots and moderately saline fluid inclusions in the batholith-hosted veins are inconsistent with the original orogenic gold model and suggest a magmatic source component for the ore fluid, consistent with stable isotope (O, H, C, and S) compositions of quartz, illite, carbonates, and sulfides. The isotopic data suggest a mixed magmatic-meteoric ore fluid in the basement-hosted deposits of the Vijus-Santa Filomena area and the volcanic-hosted Misquichilca area. Both the Pataz batholith and the Esperanza Subvolcanic Complex are of the same Mississippian age as the hydrothermal alteration and mineralization. The Esperanza Subvolcanic Complex, comagmatic with the Lavasen Volcanics, contains cognate mineral clots from which a subjacent magma chamber can be inferred. It exhibits potassic, calc-silicate, and argillic alteration, and evidence for the evolution of an Fe-rich volatile phase. The Lavasen-Esperanza magma suite is ferroan and weakly alkaline, with A-type affinities. These features provide a conceptual genetic link with hydrothermal alteration associated with gold mineralization, including Fe (±As) sulfides, phengitic white mica, celadonite, Fe-rich carbonates, and less common Fe oxides. An oxidized intrusion-related model is proposed for gold and hydrothermal alteration in the northern Pataz district.

The Lamego orogenic gold deposit (1.3 Mt measured resources at 7.26 g/t Au) is located at the south-western end of the 5 km-long Cuiaba–Lamego trend, Quadrilatero Ferrifero region, Brazil. Both Archean orogenic gold deposits are situated in the Rio das Velhas greenstone belt with the lithological succession at Lamego consisting of metamorphosed (greenschist facies) mafic volcanic rock, chert and banded iron formation (BIF), and carbonaceous and micaceous pelites. The Lamego fold, which controls the Lamego deposit, is the most visible structure related to the D1–D2 event, with a perimeter of about 4.8 km and a maximum width of 450 m. The fold is defined by the layering of the mafic unit with minor BIF and large exposures of carbonaceous and micaceous pelites. It is a rootless, reclined, isoclinal, cylindrical fold with an axial trace striking northwest–southeast dipping 20° to 30°. The hinge zone is thickened and the limbs are thinned, with the limbs dipping 20° to 30° to the SE. Orebodies consist of the Lamego BIF, where gold-mineralized zones are related to iron-rich bands, and associated silicification zones. Replacement-style mineralization is associated with sulfide bands; mainly pyrite, As-rich pyrite, and arsenopyrite. Two structural generations, G1 and G2, are recognized and encompass a set of structural elements. The G1 structural generation developed in a progressive deformation event and resulted in structures oriented from NE to SW and dipping to the SE. Structures pertaining to the G2 structural generation are oriented N–S dipping to the W. The four major high-grade gold orebodies are Carruagem, Queimada, Arco da Velha, and Cabeca de Pedra. Their gold grade shows a spheroidal pattern and a distribution that varies along the S1–2 foliation. These lenses represent the hinge zone of F2 reclined folds with the plunge of the orebodies controlled by the F2 fold axes. The lower-grade gold lenses are controlled by pinch and swell, and locally expressed quartz boudins developed during D1–D2. They have two orthogonal directions, one to the NW–SE and the other to the NE–SW, thereby defining chocolate-tablet style boudinage. Hydrothermal monazite grains in a mineralized mafic volcanic rock indicate that mineralization formed at 2730 ± 42 Ma (U–Pb SHRIMP). Younger monazite dated at 2387 ± 46 Ma, and xenotime dated at 518.5 ± 9 Ma suggest Siderian and Cambrian imprint in the Lamego deposit area. The Cambrian age reflects the late stages of the Brasiliano orogenic cycle, which is expressed in the Lamego deposit by the S3 crenulation cleavage (trend NS and dip steeply to the E). Importantly, the Cambrian structural modification is responsible for the present geometry of the Lamego orebodies, but is not associated with hydrothermal alteration; it has not introduced any new gold and also has not caused remobilization of the orebodies or ore minerals.

The Karouni deposit is located in central Guyana 35 km to the W of the former producing 5 Moz Omai mine and is interpreted to be an orogenic gold deposit. It is hosted in Rhyacian aged (2.2 to 2.1 Ga) volcano-sedimentary and intrusive rocks metamorphosed to greenschist facies. Detailed structural and crosscutting relationships, coupled with robust, new U-Pb geochronology on intermediate to felsic intrusive rocks and hydrothermal minerals from the Karouni camp have constrained the structural evolution of the deposit and provided a new age for gold mineralization with important implications for the structural framework and timing of gold mineralization throughout the region. Magmatism within the 200 km2 of the Karouni camp progressed from early, synvolcanic intermediate composition dikes at ∼2147 Ma to a major voluminous pulse of felsic magmatism coeval with regional deformation during the Trans-Amazonian Orogeny between 2120 and 2088 Ma. A late pulse of granitic magmatism at ∼1950 Ma may be related to a post orogenic event. Inherited zircons within the felsic intrusive rocks indicate assimilation of crust as old as 2223 ± 32 Ma. Gold mineralization associated with camp scale D2 deformation has been dated to 2084 ± 15 Ma on the basis of U-Pb geochronology of hydrothermal titanite. These results show gold mineralization is coeval with felsic magmatism and contemporaneous with a major pulse of orogenic gold mineralization in the Birimian Province of West Africa.

Mesoarchean Algoma-type BIF in the Yilgarn Craton are locally enriched by secondary processes to iron concentrations approaching 72 wt% Fe. While their near-surface goethite–hematite ores are unequivocally the product of supergene fluid alteration, their deeper magnetite and crystalline hematite–martite ores have a contentious origin. This study shows that magnetite ores formed after diagenesis and peak greenschist facies metamorphism of BIF, coinciding with regional deformation events. The ores formed by a multi-stage process involving initial replacement of primary quartz bands in BIF by hypogene carbonate minerals, followed by the dissolution of the carbonate and concentration of magnetite. At the Beebyn deposit, the earliest fluids were hot (∼440 °C), CO2–vapor-rich, and were likely derived from felsic magmatic fluids. In contrast, the fluids responsible for carbonate alteration at the Matthew Ridge, Koolyanobbing, and Windarling deposits were cooler (366 to 125 °C) and aqueous-rich with salinities from 0.3 to 43.9 wt% NaCl equiv. Their Cl–Br and C–O isotopic ratios suggest they are the product of mixing between magmatic fluids and heated seawater. In all deposits, later cooling (∼178 to 98 °C) of these fluids led to dissolution of carbonate minerals and concentration of magnetite. Dated monazite and xenotime from magnetite ores demonstrates that fluid alteration of BIF began in the Mesoarchean and continued episodically through to the Paleoproterozoic. Later specular hematite-rich veins that cut and modify magnetite ores crystallized from aqueous-rich fluids that are more oxidized, with salinities from 0 to 28.7 wt% NaCl equiv. and crystallization temperatures of 243 to 85 °C. Their Cl–Br and C–O isotopic fluid ratios indicate that they formed from mixing between heated seawater and meteoric waters. The BIF-hosted iron deposits in the Yilgarn Craton show remarkable similarities with the well-studied iron deposits in the Carajas Mineral Province and Hamersley Basin. They all show the same transition through time from magnetite- to hematite-rich ores. Subsequent episodic, tectonically-driven, fluid alteration events led to further iron enrichment in these deposits. The transition in ore types most likely corresponds to a common guiding process, namely the uplift of crustal rocks containing BIF – resulting in the progressive shallowing of fluid alteration pathways and the greater influence of cooler, more oxidized, hydrothermal fluids. Unlike iron deposits hosted by Algoma-type BIF in the Yilgarn and Carajas, iron deposits hosted by Superior-type BIF in the Hamersley Basin display a greater influence of oxidized marine and meteoric waters, without involvement of magmatic fluids.

The Mt Richardson deposit contains high-grade (>57 wt% Fetotal) iron ore zones hosted by several banded iron-formations (BIFs) in the c. 3504 Ma Illaara greenstone belt. The BIFs and intervening mafic igneous rocks are exposed along a 700 m-wide, 140 m-high, NNW-trending ridge that demarks the eastern limb of a greenstone belt-scale tight, upright, moderately SSE-plunging syncline. Local expressions of this fold generation include parasitic metre-scale fold hinges, an axial planar fabric, and intersection lineation in BIFs. Margins of tightly folded BIFs are commonly sheared and altered by hypogene magnetite and quartz. Although primary bands are strongly overprinted by disseminated magnetite, the concomitant growth of quartz translates to a negligible increase in the iron content of hypogene-altered BIFs. Reactivation of magnetite–quartz-altered shear zones and interaction with more oxidized fluids led to the replacement of magnetite by martite, precipitation of crystalline hematite, and recrystallization of quartz. Mafic igneous rocks are altered to fine-grained chlorite via replacement of igneous amphibole, biotite, and plagioclase within 30 m of sheared and hypogene-altered BIFs. Hypogene-altered mafic igneous rocks are enriched in Fe2O3total and W, and depleted in MnO, K2O, Ca, Na2O, and Sr compared to least altered rocks. Subsequent reactivation of shear zones and the circulation of supergene fluids led to dissolution and replacement of primary and hypogene quartz by goethite, and further oxidation of magnetite to martite. Resultant goethite–hematite ore zones are silica-poor, iron-rich, porous, and friable. Alteration indices for supergene-modified, hypogene ore zones in BIFs include hypogene magnetite and hematite in BIFs, chlorite-replacement of primary minerals in mafic igneous rocks, intense supergene goethite–hematite–kaolinite alteration, thinning of primary quartz bands in BIFs, and the presence of broad high-strain zones. Prime exploration targets in the Illaara greenstone belt are areas where these alteration indices coincide with fold-thickened BIFs. Given the friable nature of high-grade iron ore zones, mineralized occurrences are often at least partly hidden and require remote detection methods, followed by drilling, for testing. Mt Richardson differs from most iron deposits in the Yilgarn Craton by the absence of early hypogene carbonate mineral replacement of primary quartz bands in BIFs. Instead, Mt Richardson demonstrates the greater role of supergene fluids that exploit existing structures and permeability via reactivation of hypogene magnetite- and hematite-rich shear zones. In this regard, the Mt Richardson deposit has greater affinity with iron deposits in the Pilbara Craton.

The Rapitan-type banded iron formation (BIF) in the Banda Alta Formation (Fm) of the Neoproterozoic Jacadigo Group in Brazil was deposited in a redox-stratified, marine sub-basin, which was strongly influenced by glacial advance/retraction cycles with temporary influx of continental freshwater and upwelling metal-enriched seawater from deeper anoxic parts. These new finding are based on new stratigraphic, whole-rock geochemical, and stable Fe and C isotope data from the “Santa Cruz” hematite deposit near Corumba, Mato Grosso do Sul, where a stratigraphy of lower and upper dolomite-rich and intermediate chert-rich BIF facies with up to three intercalated diamictites is revealed. The Ca-Mg-Fe-Mn-carbonate-chert-hematite and chert-hematite BIF (∼30–45 wt% Fe) of the lower dolomite-rich facies shows chemical signatures consistent with well-oxidized seawater, i.e. low (Pr/Yb)PAAS, strong negative CePAAS-, and positive GdPAAS- and YPAAS-anomalies, as well as negative-δ13C carbonate typical for Neoproterozoic glaciogenic carbonates. Sedimentation in a rather shallow water depth during relatively warm interglacial periods was likely influenced by abundant freshwater from fluviatile runoff and melting icebergs. In such conditions abundant microbial activity accommodated CO2 sequestration in carbonates as spheroids and mats and fractionated δ57Fe (−2.6 and −1.2‰) in primary Fe-hydroxides. In contrast, the intermediate chert-rich facies, characterized by chert-hematite BIF (∼35–55 wt% Fe) and isolated hematite chert and hematite mud, recorded trace element signatures of non-oxidized (absence of Ce anomalies and variable YPAAS-anomalies), more metal-enriched (Fe, Mn, Si, Ni, Zn, Pb, U) seawater, thus deposition was within and below the shallow-level redoxcline during ice cover. Colder water and isolation from sunlight reduced microbial activity, and thus an almost non-fractionated δ57Fe (−0.7 to 0.0‰) fluid signature reveals that low-temperature (based on almost absence of Eu anomaly in BIF) hydrothermal (MOR) vents or (sub-) seafloor alteration of mafic or felsic rocks, or shales fertilized seawater with metals. All results lead to the model that the Jacadigo Group formed during one major marine transgression-regression cycle, and BIF facies in the Banda Alta Fm were a response to first- and second-order periodic variations of the depth of the redoxcline, induced by the juxtaposition of glacial advance/retraction cycles, active graben tectonics, and glacial isostatic adjustment or eustatic water level changes. The chert-rich BIF facies marked the maximum of transgression. Age and tectonic setting of the Jacadigo basin remains contentious: it may represent a continental back arc basin of the Brasiliano collision zone (∼590 Ma), in which submarine alteration was possibly related to low-temperature hydrothermal fluids moving through the active graben system (as an alternative to basin-wide benthic pore water flux). This would place the Jacadigo group to the suite of Ediacarian “Gaskier” glaciations, although a relationship to the Marinoan glaciation (660–635 Ma), mainly based on the published sedimentation age-bracket of 706–587 Ma, is also possible.