IOCG Deposit Research Articles

Origin and tectonic environment of the Longbohe Fe-Cu-(LREE) deposit in the Ailao Shan–Red River shear zone, Southwest China: a Neoproterozoic subduction-related IOCG deposit?

Origin and tectonic environment of the Longbohe Fe-Cu-(LREE) deposit in the Ailao Shan–Red River shear zone, Southwest China: a Neoproterozoic subduction-related IOCG deposit?

Magnetite texture and trace element evolution in the Shaquanzi Fe-Cu deposit, Eastern Tianshan, NW China

The Shaquanzi deposit is an important Fe-Cu deposit in the Yamansu Fe mineralization belt, Eastern Tianshan. Three types of magnetite were distinguished based on the textural and mineral assemblages, including the platy mushketovite (TA), granular magnetite coexisting with K-feldspar and epidote (TB), and granular magnetite intergrown with pyrite (TC). TA magnetite consists of three generations, including a bright core (TA-1), a dark-gray inner rim (TA-2), and a light-gray outer rim (TA-3), under BSE observations. TA-1 magnetite was transformed from the primary hematite due to a sharply reduced oxygen fugacity and retains its platy pseudomorph. With the changing temperature (increase or decrease), TA-1 magnetite underwent dissolution and re-precipitation (DRP) processes to form TA-2 and TA-3 magnetite. TB magnetite consists of two generations (TB-1 and TB-2). TB-1 magnetite contains abundant mineral inclusions and microporosity. With the decrease of fO2 and temperature, TB-1 magnetite underwent a fluid-assisted recrystallization process to form TB-2 magnetite with foam texture. TC magnetite consists of four different generations (TC-1, TC-2, TC-3, and TC-4). TC-1 magnetite with densely-distributed oscillatory zonings (generally smaller than 1 μm) is surrounded by the darker TC-2 magnetite. TC-2 magnetite with foam texture may be formed by recrystallization of TC-1 magnetite. TC-3 magnetite replaced or cut TC-2 magnetite, indicating that it was formed by the DRP process of TC-2 magnetite. Following periodic changes of fO2 and temperature, TC-4 magnetite with oscillatory zones formed around TC-3 magnetite.This study proposes a new Fe/(Mg + Al + Mn) vs Ti discrimination diagram to distinguish hydrothermal and magmatic magnetite. Magnetite compositions of the Shaquanzi deposit are quite different from those of magmatic magnetite, but very similar to those observed in the hydrothermal system such as IOCG and skarn deposit, indicating that magnetite of the Shaquanzi deposit was formed by hydrothermal process rather than magmatic differentiation.

A HR-TEM study on two generations of magnetite from the Alemao IOCG deposit, Carajás, Brazil: Implication for Fe-Cu mineralization

Multiple generations of magnetite are common in many magmatic-hydrothermal Fe deposits, which can be formed by different mechanisms. This study investigates magnetite from the Alemao IOCG deposit (Brazil) characterized by inclusion-rich cores (Mag-1) and inclusion-poor rims (Mag-2), using electron probe microanalyzer and high-resolution transmission electron microscopy (HRTEM), to understand its formation mechanism and implications for Fe and Cu mineralization. Electron probe microanalysis shows that Mag-1 has Si and Mg contents of 0.28–1.15 wt% and 0.11–0.49 wt%, respectively, higher than Mag-2. Mineral nanoinclusions of minnesotaite, chlorite, quartz, and minor Ti-rich magnetite in the Mag-1 account for the relatively high Si and Mg in the Mag-1, as measured by electron probe microanalysis. The crystal orientation of nanoinclusions relative to the host Mag1 indicates formation by growth entrapment, where they crystallized from boundary layer supersaturated fluids under non-equilibrium conditions.Identification of a reaction front, spatial coupling of parent and product phases at micro- and nano-meter scales support the formation of Alemao Mag2 by coupled dissolution and reprecipitation (CDR). Variations in fluid composition rather than fluctuations in conditions such as temperature and oxygen fugacity are the factors inducing CDR. A conceptual model is proposed for the formation of Alemao magnetite where Fe-rich fluids formed inclusion-rich primary magnetite and CDR reactions modified the texture and chemical composition of primary magnetite to form a core rich, and a rim poor, in nanoinclusions. During CDR, impurities of Si, Ca, Al, Mn, and Mg and nanoinclusions are removed from the primary magnetite and formed product magnetite with higher Fe. The progressive enrichment of Cu from Mag-1 to Mag-2 during CDR indicates that a Cu-rich fluid related to the Cu-Au mineralization is responsible the formation of Cu-rich Mag-2 and chalcopyrite. Therefore, micron- to nano-scale characterization of magnetite with multiple generations can provide important constraints on fluid evolution in ore system.

The Mina Justa Iron Oxide Copper-Gold (IOCG) Deposit, Peru: Constraints on Metal and Ore Fluid Sources

Abstract Iron oxide copper-gold (IOCG) deposits are major sources of Cu, contain abundant Fe oxides, and may contain Au, Ag, Co, rare earth elements (REEs), U, and other metals as economically important byproducts in some deposits. They form by hydrothermal processes, but the source of the metals and ore fluid(s) is still debated. We investigated the geochemistry of magnetite from the hydrothermal unit and manto orebodies at the Mina Justa IOCG deposit in Peru to assess the source of the iron oxides and their relationship with the economic Cu mineralization. We identified three types of magnetite: magnetite with inclusions (type I) is only found in the manto, is the richest in trace elements, and crystallized between 459° and 707°C; type Dark (D) has no visible inclusions and formed at around 543°C; and type Bright (B) has no inclusions, has the highest Fe content, and formed at around 443°C. Temperatures were estimated using the Mg content in magnetite. Magnetite samples from Mina Justa yielded an average δ56Fe ± 2σ value of 0.28 ± 0.05‰ (n = 9), an average δ18O ± 2σ value of 2.19 ± 0.45‰ (n = 9), and Δ’17O values that range between –0.075 and –0.047‰. Sulfide separates yielded δ65Cu values that range from –0.32 to –0.09‰. The trace element compositions and textures of magnetite, along with temperature estimations for magnetite crystallization, are consistent with the manto magnetite belonging to an iron oxide-apatite (IOA) style mineralization that was overprinted by a younger, structurally controlled IOCG event that formed the hydrothermal unit orebody. Altogether, the stable isotopic data fingerprint a magmatic-hydrothermal source for the ore fluids carrying the Fe and Cu at Mina Justa and preclude significant input from meteoric water and basinal brines.

Recognising Mineral Deposits from Cover; A Case Study Using Zircon Chemistry in the Gawler Craton, South Australia

Detrital zircon grains preserved within clasts and the matrix of a basal diamictite sequence directly overlying the Carrapateena IOCG deposit in the Gawler Craton, South Australia are shown here to preserve U–Pb ages and geochemical signatures that can be related to underlying mineralisation. The zircon geochemical signature is characterised by elevated heavy rare-earth element fractionation values (GdN/YbN ≥ 0.15) and high Eu ratios (Eu/Eu* ≥ 0.6). This geochemical signature has previously been recognised within zircon derived from within the Carrapateena orebody and can be used to distinguish zircon associated with IOCG mineralisation from background zircon preserved within stratigraphically equivalent regionally unaltered and altered samples. The results demonstrate that zircon chemistry is preserved through processes of weathering, erosion, transport, and incorporation into cover sequence materials and, therefore, may be dispersed within the cover sequence, effectively increasing the geochemical footprint of the IOCG mineralisation. The zircon geochemical criteria have potential to be applied to whole-rock geochemical data for the cover sequence diamictite in the Carrapateena area; however, this requires understanding of the presence of minerals that may influence the HREE fractionation (GdN/YbN) and/or Eu/Eu* results (e.g., xenotime, feldspar).

Relationship between Selected Major, Minor, and Trace Elements in Iron Oxide–Copper–Gold Deposits, an Example from the Unique Sin Quyen Deposit (Lào Cai Province, North Vietnam)

Abstract —We study the relations between several selected elements present in the Sin Quyen IOCG deposit, Lào Cai, North Vietnam, and interpret the obtained correlations, especially with a coefficient higher than 0.7. The correlations with high coefficients are mainly observed for the elements belonging to the chalcophile group (Cu, Ag, Au, Te, and Bi) and for the relation between uranium and Ag, Au, Cu, Pb, and Bi. Although the S-, Fe-, and REE-bearing minerals are predominant in the studied deposit, no strong correlation between them and the other elements was observed, even with Cu. The phenomena are primarily explained based on the geochemical properties of the mentioned elements and the characteristics of IOCG deposits.

Metallogenesis of the Rhyacian Lavra Velha gold-rich IOCG deposit in the São Francisco Craton, Brazil

• The Lavra Velha deposit represents a new gold-rich IOCG mineralization at the São Francisco Craton . • The gold mineralization is associated with a hydrothermal breccia system with co-existing iron oxides and sulfides. • IOCG mineralization is related to the Rhyacian period of the northern São Francisco Craton. • Mineralization is marked by decreasing temperatures from the bottom to the top of the deposit. Lavra Velha is a newly discovered Rhyacian IOCG deposit in the northern portion of the São Francisco Craton, in the Bahia state of NE Brazil. Gold and copper mineralization is hosted by epigenetic hydrothermal breccia with large amounts of iron oxide. Multiple phases of breccia formation and hydrothermal alteration caused zoning from the base to the top of the deposit. The alteration is mainly characterized by hydrothermal calcite-epidote-magnetite, tourmaline-chlorite-magnetite, and sericite-hematite hydrothermal alteration styles. Tourmaline and chlorite chemistry indicates that low temperature alkaline fluids had variable Fe 2+ , Mg, Al, and Na contents throughout the evolution of the breccia complex. Magnetite and hematite display low vanadium content (≤0.24 wt%) and very low titanium content (≤0.06 wt%). The sulfide minerals are pyrite (with up to ~ 3 wt% Co), chalcopyrite, bornite, arsenopyrite, and covellite, in decreasing order of abundance. Coarse muscovite that is related to the latest stages of breccia displays a high barium content with an average of ≥ 1.27 wt%. Isotopic compositions of carbon and oxygen in calcite from the calcic breccia indicate that early mineralizing fluids were derived from a mixed magmatic/non-magmatic reservoir (δ 13 C ~ −2‰ and δ 18 O from 9.95 to 13.09‰ in calcite). The sulfur isotopic compositions of chalcopyrite and pyrite demonstrate that sulfur in the mineralized breccia was derived from cooling magmas that underwent weak contamination from oxidized fluids or host rocks (δ 34 S from 2.22 to 3.89‰). New U-Pb zircon ages indicate that mineralization occurred at approximately 2100 Ma, coeval with tourmaline-bearing porphyritic granite dikes that yield ages of 2098 ± 8 and 2112 ± 12 Ma respectively. Despite being considered a small deposit in relation to known reserves, Lavra Velha may be the first IOCG deposit recognized in the São Francisco Craton, particularly in the Gavião Block. Thus, it represents an important indicator for future precious and base metal exploration in the São Francisco Craton.

High REE and Y Concentrations in Mo-Au Ores of the Kis-Kuel IOCG Deposit, East Yakutia (Russia)

This paper presents the results of an updated from 2008-2019 study of the Kis-Kuel promising area and is devoted to the discovered unusual molybdenite + gold bearing mineralizing system of the Kis-Kuel Iron Oxide Copper-Gold deposit in Eastern Yakutia (Russia). Economic mineralization is localized within the apical zone of a granodiorite-diorite stock and represented by hematite, goethite, quartz, chalcopyrite, molybdenite, arsenopyrite, pyrite, native gold and bismuth (no signs of any ore mineralization were found outside the Kis-Kuel intrusive). The intrusive has a Late Cretaceous crystallization age (K-Ar) of 103 Ma. The Mo-bearing quartz vein yields a mineralization age (Ar-Ar) of 99.9±1.1 Ma and genetically relates to the granodiorite. Kis-Kuel breccia complex (KKBC) consists of a manto-type irregular shaped breccia body with arrays of variably mineralized veins and veinlets inside. The KKBC has a complete gradation from hematite-goethite altered granodiorites and more locally -diorites to intensely brecciated and hematite-goethite breccias. Multiple episodes of brecciating and veining with Fe-oxide-Cu-Au±Ag, porphyry Cu-Au±Bi, Ag-Pb and Mo+REE±Au mineralization occur in Kis-Kuel intrusive. In order to obtain more resources, the research Kis-Kuel target with IOCG mineralization was studied for molybdenum and rare earth minerals. Mainly, ore is quartz-bearing, Mo-Au-mineralized and strongly enriched in the rare earth elements (REE) material. The textures of REE minerals indicate crystallisation of monazite-(Ce) and xenotime as hydrothermal phases together with molybdenite and arsenopyrite. Analysis of quartz-molybdenite ore from the Kis-Kuel diorite-granodiorite intrusive shows previously unknown high concentrations of REE and Y, averaging 4.76 wt percent ∑REE + Y. Ore additionally contains 2.42 wt percent Mo, 8.8 g/t Au and 231 g/t Ag. We propose that one of the basic factors for mineralization styles at Kis-Kuel consists in the granitoids evolution and strongly differs from unevolved and mantle compatible compositions to highly evolved and fractionated intrusive rocks. The calc-alkaline evolution trend of the Kis-Kuel magmatic rocks is influenced by the accumulation of iron in ore. A significant part of the iron did not fractionated into high-iron melts, and separated into hydrothermal solutions with high grade gold concentrations. An extensively revised paragenetic model for Kis-Kuel deposit incorporates next four stages. Stage 1 dominated by widespread brecciating and iron metasomatism, which converted granodiorite rocks to Fe-oxide-Cu-Au ore. Stage 2 comprises chloritic and sericitic alteration and associated systems of linear quartz veins with Cu-Au-porphyry and Au-Bi mineralization. Stage 3 includes sericitic alteration and veining with quartz-molybdenite-native gold-REE minerals. Stage 4 consists of Ag-Pb veins.

A Continuum from Iron Oxide Copper-Gold to Iron Oxide-Apatite Deposits: Evidence from Fe and O Stable Isotopes and Trace Element Chemistry of Magnetite

AbstractIron oxide copper-gold (IOCG) and iron oxide-apatite (IOA) deposits are major sources of Fe, Cu, and Au. Magnetite is the modally dominant and commodity mineral in IOA deposits, whereas magnetite and hematite are predominant in IOCG deposits, with copper sulfides being the primary commodity minerals. It is generally accepted that IOCG deposits formed by hydrothermal processes, but there is a lack of consensus for the source of the ore fluid(s). There are multiple competing hypotheses for the formation of IOA deposits, with models that range from purely magmatic to purely hydrothermal. In the Chilean iron belt, the spatial and temporal association of IOCG and IOA deposits has led to the hypothesis that IOA and IOCG deposits are genetically connected, where S-Cu-Au–poor magnetite-dominated IOA deposits represent the stratigraphically deeper levels of S-Cu-Au–rich magnetite- and hematite-dominated IOCG deposits. Here we report minor element and Fe and O stable isotope abundances for magnetite and H stable isotope abundances for actinolite from the Candelaria IOCG deposit and Quince IOA prospect in the Chilean iron belt. Backscattered electron imaging reveals textures of igneous and magmatic-hydrothermal affinities and the exsolution of Mn-rich ilmenite from magnetite in Quince and deep levels of Candelaria (>500 m below the bottom of the open pit). Trace element concentrations in magnetite systematically increase with depth in both deposits and decrease from core to rim within magnetite grains in shallow samples from Candelaria. These results are consistent with a cooling trend for magnetite growth from deep to shallow levels in both systems. Iron isotope compositions of magnetite range from δ56Fe values of 0.11 ± 0.07 to 0.16 ± 0.05‰ for Quince and between 0.16 ± 0.03 and 0.42 ± 0.04‰ for Candelaria. Oxygen isotope compositions of magnetite range from δ18O values of 2.65 ± 0.07 to 3.33 ± 0.07‰ for Quince and between 1.16 ± 0.07 and 7.80 ± 0.07‰ for Candelaria. For cogenetic actinolite, δD values range from –41.7 ± 2.10 to –39.0 ± 2.10‰ for Quince and from –93.9 ± 2.10 to –54.0 ± 2.10‰ for Candelaria, and δ18O values range between 5.89 ± 0.23 and 6.02 ± 0.23‰ for Quince and between 7.50 ± 0.23 and 7.69 ± 0.23‰ for Candelaria. The paired Fe and O isotope compositions of magnetite and the H isotope signature of actinolite fingerprint a magmatic source reservoir for ore fluids at Candelaria and Quince. Temperature estimates from O isotope thermometry and Fe# of actinolite (Fe# = [molar Fe]/([molar Fe] + [molar Mg])) are consistent with high-temperature mineralization (600°–860°C). The reintegrated composition of primary Ti-rich magnetite is consistent with igneous magnetite and supports magmatic conditions for the formation of magnetite in the Quince prospect and the deep portion of the Candelaria deposit. The trace element variations and zonation in magnetite from shallower levels of Candelaria are consistent with magnetite growth from a cooling magmatic-hydrothermal fluid. The combined chemical and textural data are consistent with a combined igneous and magmatic-hydrothermal origin for Quince and Candelaria, where the deeper portion of Candelaria corresponds to a transitional phase between the shallower IOCG deposit and a deeper IOA system analogous to the Quince IOA prospect, providing evidence for a continuum between both deposit types.

Is there hidden potential in Carajás? Insights through the geophysical signature of Cristalino deposit

Geophysical methods are fundamental to exploration of IOCG deposits because they are associated with magnetite, hematite, and sulfides, which can produce different and significant geophysical responses. Because of the frequent occurrence of ferromagnetic minerals, magnetic data have been used extensively in exploration for IOCG deposits. The geophysical data at the Cristalino IOCG deposit in Carajás, Brazil, provide two important insights: 1) magnetic rocks are not fully mapped by total gradient data when these rock units have the same strike direction as the declination of the Earth’s magnetic field in low latitude areas, and 2) deposits that are mainly composed of brecciated to massive sulfide minerals are only weakly magnetic or even non-magnetic. These characteristics are important for exploration programs because qualitative analysis of magnetic data , especially by the commonly used total gradient calculated from total field anomaly, is the main tool for selecting prospects in low latitude regions, and important targets could be undetectable by this method. Gravity data have been extensively applied recently to exploration programs in Carajás, but similarly to magnetic data, the core of the brecciated to massive chalcopyrite mineralization can have lower densities than the surrounding alteration with hematite and magnetite and, therefore, be associated with low gravity anomalies that are not usually targeted in mineral exploration. The electromagnetic response will increase with the increasing connection between sulfides, varying from moderate in vein systems, to moderate to high in stringer and stockwork systems, to high anomalies in massive systems. To better understand the impact of these features on exploration programs, we show in this study that the magnetic, gravity, and electromagnetic responses vary with mineralization end-members. From a vein system formed at greater depths that produce high magnetic and gravity anomalies (associated with iron oxides from alteration) and moderate electromagnetic anomaly (poor connection between sulfides), to stringer, stockwork, and massive systems formed at shallower depths that exhibit lower magnetic and gravity anomalies but a high electromagnetic anomaly. Our analyses indicate that it is possible that the deposits mostly associated with massive sulfide could have been missed, and there could be significant hidden potential in the Carajás region. We illustrate that the detection of such potential depends on the quantitative integration of magnetic data with gravity and electromagnetic data through the inversion and multiphysics approach.

New insights into the genesis of IOCG deposits: From a case study of the Yinachang deposit in SW China

The Yinachang Fe-Cu-Au-U-REE deposit is hosted by the lower part of the Paleoproterozoic Kunyang Group in the central Yunnan Province of SW China in an area known to contain iron-oxide Cu-Au mineralisation. The deposit includes: (i) the sulphide assemblage chalcopyrite – pyrite – magnetite – cobaltite – molybdenite – cassiterite; (ii) Rare Earth Element assemblage bastnaesite – parasite – fergusonite – xenotime – monazite; (iii) the uranyl hydroxide mineral vandendriesscheite; (iv) gold commonly hosted by ankerite; and (v) the gangue mineral assemblage apatite – biotite – fluorspar – quartz – calcite. The ore is commonly massive, disseminated, banded, or in calcite veins. The banded mineralisation contains high concentration of Au, Co, Mo, U, Fe, Cu and REE, and the vein-type mineralisation has abundant REE minerals of bastnaesite, parisite, fergusonite and xenotime. Monazite exists as inclusions in apatite or as discrete grains on the surface of magnetite, and the uranium is associated with chalcopyrite. The mineralising process can be divided into an initial Na-alteration followed by the ore-forming assemblages of Fe-REE and Cu-Au-U-REE mineralisation. The average δ18OH2O values in the quartz and calcite change are between 3.5 and 10.7‰, with δDV-SMOW values ranging between −98.2 and −47.7‰. The calcite, siderite and ankerite have δ13C isotope composition ranges from –14 to +1‰ and δ18O compositions of +6.9 to +22‰. The H–O–C isotope systematics indicate that the mineralising fluids have mixed magmatic and metamorphic sources, whereas the carbon is sourced from marine carbonate, and the low temperature alternation of polyphase mantle material. In situ δ34S sulphide value ranges between 1.1 and 11.9‰, and the bulk δ34S value ranges between −4.7 and 10.5‰. In situ Pb isotopes of sulphide samples have 206Pb/204Pb values of 18.58–18.76, 207Pb/204Pb values of 15.51–15.66 and 208Pb/204Pb values of 37.47–38.06. These values plot in the upper crust Pb-evolution curve, indicative of a complex source of Pb in the deposit. The Pb is interpreted to have a deep-seated magmatic source with a contribution from the crust. It is also proposed that the REE-mineralised fluids are derived from a late stage of alkaline magma differentiation. The 40Ar-39Ar biotite date indicates that the Precambrian rocks in the Kangdian region were regionally metamorphosed at ca. 900 Ma. The Yinachang Fe-Cu-Au-U-REE deposit is interpreted as an IOCG deposit based on geological and isotopic studies. The banded ore and vein type ore are the main exploration targets for uranium, gold and REE. This study helps us better understand IOCG deposits in China.

Geochemistry of hydrothermal tourmaline from IOCG occurrences in the Great Bear magmatic zone: Implications for fluid source(s) and fluid composition evolution

Tourmaline crystallized during iron oxide and alkali-calcic alteration and IOCG mineralization in the Great Bear magmatic zone, Canada. Within the samples analyzed, tourmaline occurs as small crystals in the groundmass of hydrothermal breccias (Southern Breccia and Contact Lake), or as large prismatic crystals in quartz (±ore-mineralogy) veins (Contact Lake, DeVries Lake, and NICO). The tourmaline from these localities is predominantly shorlitic in composition, with minor dravitic, uvitic and feruvitic components. The boron isotopic composition ranges from −15‰ to −5‰, with the majority of values between −15‰ and −10‰. The lack of variation among samples supports a common fluid source across the belt for the metasomatic-hydrothermal systems. These results are isotopically similar to global magmatic and non-marine evaporitic reservoirs, and lighter than seawater and marine sedimentary rocks. The δ11B results support a single-fluid IOCG deposit model for the systems studied, wherein metasomatic-hydrothermal fluids derived by magmatism ascend and evolve over time through fluid-rock interactions.

Mineralogy as a proxy to characterise geochemical dispersion processes: A study from the Eromanga Basin over the Prominent Hill IOCG deposit, South Australia

The Early Cretaceous interbedded sandstone, siltstone and mudstone of the Cadna-owie Formation and the reduced mudstone of the Bulldog Shale overlying the Prominent Hill IOCG deposit in South Australia (total tonnage: 140 Mt. @ 1.2% Cu and 0.5 g/t Au; OZ Minerals Limited 2017) are shown to preserve Cu concentrations up to 5043 ppm Cu. These cover sequence materials are approximately 100 m thick over the basement rocks that host the deposit. This study investigates the source of elevated Cu in the cover material by assessing the Cu deportment in these formations and focuses on understanding element migration processes resulting in development of elevated Cu concentrations. Petrographic and QEMSCAN® analysis show that Cu resides within sulphides including high-temperature Cu-sulphides (e.g. bornite) in the Cadna-owie Formation. The Cu-sulphides are associated with Fe-oxides (magnetite) and minerals including pyroxene, amphibole, garnet, chlorite and plagioclase that are interpreted to be detrital and are likely to be of metamorphic origin. Based on these observations, lateral physical processes driven by sedimentary dynamics are interpreted to be the main processes responsible for elevated Cu concentrations in the Cadna-owie Formation in the Prominent Hill area. Chemical migration processes likely had only localised influence and resulted in minor Cu redistribution. QEMSCAN® data collected on samples from the weathering profile of the Bulldog Shale shows that weathering processes (e.g. pyrite oxidation, serpentinisation and feldspar hydrolysis) mostly affect the upper Bulldog Shale and that Eh-pH conditions gradually change with depth from the oxidised and acidic upper Bulldog Shale to the reduced and slightly acidic lower Bulldog Shale. Copper speciation and Eh-pH conditions are used to interpret downward chemical migration of Cu due to weathering as the main process for development of elevated Cu concentrations within the weathered Bulldog Shale in the Prominent Hill area. Upward chemical and lateral physical migration processes may have influenced Cu concentrations within the unweathered Bulldog Shale, however the degree of influence is yet to be determined. Overall this study shows that elevated Cu concentrations in the Early Cretaceous cover sequences overlying the Prominent Hill deposit can be linked back to mineralisation itself and that processes resulting in elevated Cu concentrations include chemical and physical migration.

Structural controls of the Ernest Henry IOCG deposit: Insights from integrated structural, geophysical and mineralogical analyses.

Iron Oxide Copper-Gold deposits (IOCGs) are structurally controlled, and typically display zonation of iron oxides and sulphides, which is potentially related to redox zonation. There are three mai...

Defining early stages of IOCG systems: evidence from iron oxides in the outer shell of the Olympic Dam deposit, South Australia

The IOCG deposit at Olympic Dam (South Australia) is hosted within the Roxby Downs Granite, which displays a weakly mineralised contact to the orebody (hereafter ‘outer shell’). In a mineralogical-geochemical characterisation of Fe-oxides from the outer shell, we show silician magnetite (Si-magnetite) and HFSE-bearing hematite define the early stages of alkali-calcic alteration. This association forms in the presence of hydrothermal K-feldspar and calc-silicates via overprinting of magmatic magnetite and ilmenite breakdown. Geochemical modelling, at ≥ 400 °C, shows such reactions occur at pH-fO2 conditions coinciding with shifts from K-feldspar to sericite, and ilmenite to rutile stability. The subsequent Si-magnetite+siderite association forms down-T in the absence of K-feldspar. Transition from granular to bladed morphologies in Si-magnetite is part of a series of Fe-oxide interconversions, followed by formation of zoned, U-W-Sn-Mo-bearing hematite. Enrichment in REE, Y and U in Si-magnetite and the prevalence of U-W-Sn-Mo-bearing hematite support a granite-derived fluid. Combined, petrographic and geochemical evidence show a transition among Fe-oxides from the outer shell to the orebody attributable to the evolution of the same fluid. Unusual massive magnetite intervals and Fe-oxide nodules in granite are considered due to either the presence of inherited lithologies, metasomatic products, or the result of magnetite-rich, crystal mush forming in the melt. We propose a model, corroborated by recently published data including high-precision U-Pb dating of magmatic zircon and hydrothermal hematite, in which an ‘outer shell’ is initiated at the 6–8 km depth of granite emplacement during volatile release from fluids ponding at intrusion margins. Granite cupola collapse at shallower levels (2–3 km?) follows via uplift along faults, facilitating intense brecciation and ore formation.

The Cristalino IOCG deposit: an example of multi-stage events of hydrothermal alteration and copper mineralization

Abstract The Cristalino deposit is located 40 km east of Sossego mine, Carajas. The orebody lies along a NW-SE-striking shear zone and is mainly hosted by the Neoarchean bi-modal volcanics of the Grao Para Group. Field work and petrographic data seconded by SEM-EDS analysis allowed recognizing an early sodic metasomatism that was followed by calcic-ferric, potassic and propylitic alterations, and finally by carbonatization. The volcanic rocks were altered under deformation regimes that changed from ductile-brittle to brittle. The deposit resulted from two mineralizing stages. The early stage took place at a greater depth and produced an ore association composed chiefly of chalcopyrite, pyrite, and magnetite as disseminations, breccia and veins particularly in Ca-Fe altered rocks. The later stage occurred at a shallower depth and formed a practically magnetite-free ore association, consisting essentially of chalcopyrite ± pyrite ± hematite in breccias and veins generated mostly during the potassic alteration. These ore associations indicate that the hydrothermal system evolved with temperature decrease and increase in fO2, Cu/Fe ratio and sulfur activity. Cristalino is conceived as a multi-stage IOCG deposit similar to others lying in the Carajas E-W corridor of IOCG systems.

Characterization of the hydrothermal alteration and ore zones of The Rio Vermelho Prospect: A new iocg mineralization in The Carajás province

The Rio Vermelho prospect is located in the eastern sector of the Carajás Mineral Province, near to the contact with the metasediments of the Araguaia Fold Belt. The mineralization is located in a horse splay zone of the Carajás Fault, near to the Cristalino IOCG deposit. The ore is hosted by Archean deformed granitoids affected by multi-stages hydrothermal alteration controlled by NNW-SSE structures. Geological mapping and detailed drill core logging associated to petrographic studies allowed the identification of different hydrothermal stages. The hydrothermal alteration starts with a sodic system, preserved only in distal areas, in which albite replaces the original feldspars in regional deformed granites and fills a stockwork vein system in metadiorite/metagabbro rocks. The excess of silica after original feldspars transformation forms quartz in the sodic paragenesis. The presence of actinolite in metadiorite/metagabbro, although restricted to distal areas, might be suggestive of local coeval calcic alteration. Pervasive potassification, represented by the crystallization of microcline together with quartz, overprints the albite paragenesis and occurs proximal to the ore zone. Chloritization occurs in two different stages, pre- and syn-mineralization. The pre-mineralization is characterized by pervasive lamellar chlorite I associated with epidote and quartz. The syn-mineralization is marked by fibro-radial chlorite II, enriched in FeAl and Mn, and associated with iron oxide and copper sulfides filling veins and breccias. Before the mineralization stage, silicification marks the beginning of the brecciacion phase producing quartz veins. The copper mineralization stage, with ore filling breccias dominated by chalcopyrite with subordinate bornite, occurs associated with abundant hematite replacing early magnetite crystals. Sericitization is a continuous post-mineralization process producing pervasive finely scaled white mica that is followed by epidote and carbonate formation during the last hydrothermal alteration phase. The hydrothermalism starting with sodic-calcic phases and ending with low-k potassic phase suggests a temperature ranging from >500 to <300 °C. The transition from high temperature sodic and potassic alteration to low temperature in the ore zone in a ductil-brittle environment, suggest a possible input of externally-derived fluids. The abundant hematite derived from magnetite transformation indicates extremely oxidized fluids and suggests a depositional temperature <350° during the ore formation. The hydrothermal characteristics of the copper mineralization of the Rio Vermelho Prospect suggest a shallow IOCG type dominated by hematite. Its regional position at the borders of the Araguaia Fold Belt, possibly not affected by the Neoproterozoic processes, opens a new area for exploration in the easternmost part of the Carajás Domain.

On the prospects of identifying magmatogene-hydrothermal iron-ore deposits in the Ukrainian Shield

According to the analysis of literary materials and author's own observations in different regions of the world, a specific set of iron-ore and related deposits, won the international title of "hydrothermal iron-oxide-gold-copper deposits” (IOCG — Hydrothermal Iron Oxide Copper-Gold Deposits) has been described here. The most important feature of IOCG-type deposits are large masses of iron, often forming clusters of magnetite-rich (at least hematite) ores of magmatogene and magmatogene-hydrothermal genesis. It is shown that the type of IOCG deposit can be discovered within the suture zones of the Ukrainian Shield on the example of the installation within the Krivoy Rog-Kremenchug structural and metallogenic zone of paragenetic association of hydrothermal-metasomatic mineralization of gold-polymetallic manifestations and certain types of rich iron-ore. Geophysical surveys must play the leading role.

Bio-Heap Leaching of Primary Copper Sulfide Ore by JOGMEC

JOGMEC has been carrying out the study on primary copper sulfide ores leaching for recovering copper economically and efficiently by heap leaching. In our study, we have been using the primary copper sulfide ore produced in an IOCG deposit. The ore is characterized by high iron content and high acid consumption in leaching. For the optimization of the leaching, the conditions such as ore size, agglomeration, pH and irrigation rate of leaching solution were examined with column leach tests. The best result was over 80 % extraction of copper in 150 days with leaching solution of 1 M sulfuric acid and temperature of 45 °C. In this experiment, the fines of the ore sample were removed before putting it into the column to keep the permeability of the ore bed. In these column leach tests, the Fe2+/total-Fe ratio of PLS decreased gradually by the activity of naturally grown iron-oxidizing bacteria. The bacteria in PLS, which have the ability of iron-oxidizing and sulfur-oxidizing, were identified by next-generation sequencing as Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. We also carried out bench-scale tests with about 200 tons of the primary copper sulfide ores. Iron-oxidizing and sulfur-oxidizing bacteria were identified in the leaching solution as same with column leach tests. It is considered that the bacteria worked in the leaching solution and on the surface of the ores.

Delineating the structural controls on the genesis of iron oxide–Cu–Au deposits through implicit modelling: a case study from the E1 Group, Cloncurry District, Australia

Abstract Iron oxide–Cu–Au (IOCG) deposits encompass a range of ore body shapes, including strata-bound replacement ores and hydrothermal breccias. We use the implicit method to make a detailed three-dimensional geological model of a strata-bound IOCG in the Cloncurry District, the E1 Group, to elucidate structural controls on mineralization. This model is compared with the nearby, world-class, Ernest Henry breccia-hosted IOCG deposit. Cu–Au mineralization in the E1 Group occurs as structurally controlled, mainly strata-bound, replacement bodies hosted in metasedimentary and metavolcaniclastic rocks intercalated with barren meta-andesite. Replacement bodies in the E1 Group conform to a series of NNW-plunging folds formed in regional D 2 during peak metamorphism. Folding was followed by local D 3 /regional D 4 shortening, which formed a dextral, transpressional Riedel brittle to ductile system along the regional Cloncurry Fault Zone. Modelling suggests that much of the Cu–Au mineralization is controlled by synthetic R structures associated with this Riedel system. The deformation sequence at Ernest Henry is comparable, but differences in host rock rheology, permeability and fluid pressure may explain the variation in ore body types and total Cu–Au resource between the two deposits. The results carry implications for other districts containing these styles of IOCG mineralization.