IOCG Mineralization Research Articles

Gold metallogeny in Iran; implications for gold exploration and conceptual modelling

Significant progress in the classification, definition and understanding of the main Au deposit types could significantly aid improvements in Au exploration. Because of the wide occurrence of Au in the central part of the Tethyan Eurasian Metallogenic Belt, Iranian structures composed of more than 17 zones (arcs and blocks) are considered as having one of the largest Au reserves in the Middle East. Without attempts at understanding the tectono-magmatic evolution of Iran and the geodynamic settings of Au deposition, the establishment of a reliable predictive exploration model for Au-type deposits in Iran and other parts of the world will be unsuccessful. By considering a total of 33 Au deposits and prospects in Iran, a mineralization sequence is revealed from orogenic and volcanogenic massive sulfide (VMS), orogenic, Carlin-type, epithermal/porphyry Cu–Au/skarn, epithermal/iron oxide–copper–gold (IOCG). The trend of deposition gradually changes in the SW–NE axis to intrusion-related, epithermal and porphyry Cu–Au deposits at the Urumieh–Dokhtar Magmatic Arc (UDMA) and post-arc magmatism. VMS deposits occur adjacent to the NE Zagros Fold and Thrust Belt, at the Sanandaj–Sirjan Zone. The Zagros Orogeny and associated post-collisional magmatism at UDMA host many porphyry, epithermal and intrusion-related Au deposits, with a major magmatism peak in the Miocene. This work reveals that orogenic and Carlin-type Au mineralization are linked genetically. After each associated subduction for Palaeotethys (286–215 Ma) and Neotethys (210–68 Ma) in Iran, VMS and orogenic Au-deposits are formed in the border of the subduction (±obduction) zone. The porphyry, intrusion-related, epithermal and IOCG mineralization are emplaced in appropriate formations and structures during collision and post-collision processes.

Linking Pacific Plate formation and Early Cretaceous metallogenic response on the circum-Pacific continental margins

Hydrothermal mineralization along the circum-Pacific continental margin is genetically linked to the motions of the Pacific Plate. Compiled geochronological results of ore deposits, coupled with the newly reconstructed geometry of the late Early Cretaceous subduction zones in East China, North America, and the Central Andes using GPlates and I2VIS software, were applied to investigate the relationships between mineralization and Pacific Plate formation. The ∼120-m.y.-old orogenic Au provinces in East China and North America are related to transpression caused by high-rate oblique subduction with intermediate−high dip angles of the Izanagi and Farallon plates, respectively. In contrast, the ∼105-m.y.-old porphyry-epithermal belt in Southeast China was produced by oblique subduction of the Izanagi Plate with low−intermediate subduction rates and intermediate−high dip angles. In the Central Andes, the oblique subduction of the Farallon Plate with low−intermediate rates and low dip angle accounted for iron oxide−copper−gold ore (IOCG) deposit mineralization in South Peru at ca. 110 Ma; whereas the high rate and low dip-angle subduction of the paleo-Phoenix Plate, which caused mild compression, was responsible for Fe, porphyry Cu, and IOCG mineralization in North Chile at ca. 110 Ma. The late Early Cretaceous metallogenic response in the circum-Pacific region coincides with superplume events that triggered the significant growth of the modern Pacific Plate. The forward simulations reveal that different subsequent styles of subduction and associated magmatism are likely responsible for the distinct mineralization types present in the region, including orogenic Au, porphyry-epithermal, Fe, and IOCG deposits. The precise dynamics of the subduction zone determined by this study led to the improved metallogenesis models in the Pacific margin.

Linking the Gawler Craton and Mount Isa Province through hydrothermal systems in the Peake and Denison Domain, northeastern Gawler Craton

Tectonic reconstructions of Proterozoic Australia commonly place the Peake and Denison Domain of the northeastern Gawler Craton at the interface between the North and South Australian cratons prior to the reconfiguration of Australia’s main tectonic components in the Mesoproterozoic. However, this reconstruction is largely based on palaeomagnetic data as the geological correlations between these regions are currently limited, particularly during the Mesoproterozoic. The early Mesoproterozoic period is significant as it corresponds to major IOCG mineralization in the eastern Gawler Craton between 1600 Ma and 1575 Ma, and IOCG mineralization in the Mount Isa Province largely between 1550 Ma and 1490 Ma. Therefore, determining the relationship of the Peake and Denison Domain to the Gawler Craton and Mount Isa Province during this period is essential to evaluating mineral prospectivity in the northeastern Gawler Craton. New U–Pb LA-ICP-MS geochronology on zircon and titanite improves our understanding of the tectonothermal and hydrothermal history the Peake and Denison Domain during the late-Palaeoproterozoic, early-Mesoproterozoic and the Cambrian–Ordovician periods. Titanite formed within largely calc-silicate alteration assemblages indicates the Peake and Denison Domain has a protracted history of hydrothermal activity, recording events at c. 1565 Ma, 1530–1515 Ma, c. 1500 Ma, c. 1465 Ma and c. 490 Ma. The highly calcic nature of the c. 1565–1500 Ma alteration in the Peake and Denison Domain shares strong similarities in age and character to the regional calcic-sodic alteration recorded in the Mount Isa Province. We suggest the two regions were influenced by similar hydrothermal systems during the early Mesoproterozoic, supporting reconstruction models that place the Peake and Denison Domain near the Mount Isa Province during the early-Mesoproterozoic. This highlights the prospectivity of the Peake and Denison Domain for Isan-style IOCG mineralization, but requires consideration of the post-1500 Ma rotation of prospective structures.

The southern IOCG and hydrothermal nickel mineralization trend of the Carajás Mineral Province: Airborne geophysical and remote sensing evidences for structural controls and hydrothermal signature

The iron oxide‑gold‑copper deposit (IOCG) and hydrothermal nickel deposit are globally important targets for mineral exploration due to their notable role in the clean energy transition. The Carajás Mineral Province stands out for having the highest known concentration of world-class IOCG deposits, especially within the regional Canaã shear system, which exerts a critical control in polymetallic deposit distribution. The dense regolith cover and rainforest vegetation hinder the structural mapping and recognition of host rocks and metasomatic facies. In this context, we integrated remote sensing and geological data to evaluate the influence of the structural framework on the IOCG and hydrothermal nickel mineralization location and the metasomatic footprints that envelope these mineral deposits. These deposits are spatially correlated to anomalies that have values greater than the average and standard deviation (⩾ x̄ + sx) of the gamma-spectrometry and geomorphological features (K/eTh, eU/eTh, F-parameter, K and eU deviations, and morpholineament density). The regional control is exerted by NW–SE- and N–S-trending structures, whereas NE–SW- and E–W-oriented shallow structures present the most significant mineralization control at the local scale. Structure intersections express the Carajás deep to the shallow crustal architecture of the region and the potential pathways for the hydrothermal and ore-forming fluids in multiple metallogenetic events.

Evidence for transpression during formation of the Candelaria Punta del Cobre IOCG -district and regional implications

The youngest and best exposed Iron Oxide Cu–Au (IOCG) deposits currently recognized are found in the coastal belt of the Andes. Their formation has been attributed to back-arc extension or transtension associated with the convergent Andean margin. Here we document transpressional deformation synchronous with Cu mineralization in the Candelaria-Punta del Cobre district, the largest IOCG district of the Andean belt. A northwest-southeast shortening direction is recorded by north-northwest sinistral strike-slip faults that host mineralization, northwest dikes, and north-northeast compressive structures. Batholith emplacement synchronous with mineralization formed a north-northeast oriented foliation zone parallel to the intrusive contact and associated folds in the host rock sequences that face inwards towards the intrusive contact. Age constraints indicate that transpressional deformation in the Cretaceous arc, at least locally, begun earlier than previously documented, and IOCG mineralization may have spanned the transition from extension to the initial phase of compression.

Revisiting the IOCG geology and age of Alemão in the Igarapé Bahia camp, Carajás province, Brazil

The Fe oxide–Cu–Au (IOCG) mineralization at Alemão in the Carajás province of the Amazon craton occurs in a volcanosedimentary sequence, part of the Igarapé Bahia Group, at the gradational contact between a lower, volcanic-dominated sequence and an upper, predominantly siliciclastic unit. The deposit is the concealed, hypogene root of the Acampamento Norte body of the larger Igarapé Bahia camp, in which chalcopyrite-dominant associations are intimately associated with steeply-dipping, massive to semi-massive magnetite bodies that are broadly subparallel to the host strata. Chlorite, amphibole, tourmaline, quartz, biotite, albite, K-feldspar, and carbonates constitute the main alteration products accompanying mineralization, although chlorite is dominant. The broadly tabular, massive and semi-massive bodies account for the highest-grade parts of the deposit and are surrounded by voluminous halos of intensely to moderately veined host rocks, with the same accompanying opaque and silicate assemblages that, although lower grade, contribute to the large-scale Cu–Au mineralization. Locally, the central lodes at Alemão contain bornite in addition to chalcopyrite, as well as molybdenite, a feature common to all the mineralized centers in the Igarapé Bahia camp.Molybdenite from a central body of massive magnetite–chalcopyrite, and demonstrably paragenetically related to the Cu-bearing sulfides, returned a Re–Os age of 2627 ± 11 Ma, which defines the timing of the IOCG mineralization at Alemão. Geologic relationships and similarities with the rest of the hypogene Cu–Au mineralization in the area imply that this date is also valid for the entire Igarapé Bahia camp. The age confirms the epigenetic nature of the mineralization, its emplacement during or following inversion of the Carajás basin, and the protracted recurrence of IOCG mineralization throughout the Carajás province. A genetic relationship between the Cu–Au mineralization and the widespread district-scale mafic intrusive magmatism is speculated.

Copper mobilization via seawater-volcanic rock interactions: New experimental constraints for the formation of the iron oxide Cu-Au (IOCG) mineralization

The involvement of modified seawater and/or basinal brine in IOCG mineralization was documented by numerous geologic studies. Still, this process remains poorly understood. In this study, we reacted seawater with andesite and basalt, the most common arc volcanic rocks, at 150 and 240 °C and water vapor-saturated pressure to assess the Cu leaching capacity and fluid evolution due to the seawater-volcanic rock interactions. The experimental results show that Mg, Fe, Al, and SO42− in the modified seawater decreased significantly, accompanied by an increased Ca concentration. The fluid pH also decreased from 8.3 of the initial seawater to ∼7.5 and ∼7.0 after 150 and 240 °C experiments, respectively. The incongruent calcsilicate (e.g., plagioclase) dissolution and anhydrite precipitation were observed in the reacted rock samples. Thermodynamic modeling confirmed the trends of those concentration changes but predicted several alteration minerals that were not observed in the experiments. Our experiments show that Cu-leaching efficiency is much higher from the andesite than from the basalt, also higher at 240 °C than at 150 °C. The andesite contains more Cu than the basalt samples, and abundant Cu-rich (average 106 ppm) plagioclase-hosted silicate melt inclusions and Cu-bearing (average 59 ppm) groundmass are identified in the original andesite sample but not in the original basalt sample, which is considered to be the cause of the Cu-leaching differences between the two rock samples. The δ34S value of resultant fluids is dominated by seawater sulfate with a minor contribution of magmatic sulfur from the rock. Thermodynamic modeling combined with recent experimental studies show that deposition of Cu sulfides is the most effective when Cu-bearing fluids react with early-stage pyrite. Our results suggest that the seawater/(brine)-volcanic rock reactions at 150–250 °C can produce Cu-bearing fluids, which in turn can form IOCG deposits, and that Cu mineralization with sulfides zonation can result from replacement reactions between the Cu-bearing fluids and Fe-rich minerals in precursor iron ore bodies.

Integration of Stress–Strain Maps in Mineral Systems Targeting for IOCG Mineralisation within the Mt. Woods Inlier, Gawler Craton, South Australia

The application of finite element analysis is used to simulate the relative distribution and magnitude of stress–strain conditions during a geologically brief, NNW-SSE-oriented, extensional event (1595 Ma to 1590 Ma), co-incident with IOCG-hydrothermal fluid flow and mineralisation across the Mt Woods Inlier, Gawler Craton, South Australia. Differential stress and shear strain maps across the modelled terrane highlight regions that were predisposed to strain localization, extensional failure and fluid throughput during the simulated mineralisation event. These maps are integrated with other datasets and interpretation layers, one of which is a proposed structural–geometrical relationship apparent in many world-class IOCG deposits, including Prominent Hill, Olympic Dam, Sossego, Salobo, Cristalino and Candelaria. These deposits occur at steeply plunging, pipe-like intersections of conjugate extensional systems of faults, shears and/or contacts, wherein the obtuse angle may have been bisected by the maximum principal extensional axis (viz., σ3) during mineralisation. Several other layers are also used for the generation of targets, such as distance from major shear zones, favourable host lithologies, and proximity to tectonostratigraphic contacts of markedly contrasting competency. The result is an integrated target index or heat map for IOCG prospectively across the Mt. Woods Inlier.

Skarn-style alteration in Proterozoic metasedimentary protoliths hosting IOCG mineralization: the Island Dam Prospect, South Australia

New mineralogical, geochemical, and geochronological data are presented for the Island Dam prospect, Olympic Cu-Au Province, South Australia. Skarn assemblages comprising actinolite/phlogopite + K-feldspar + magnetite suggest the presence of calcareous protoliths at Island Dam and indicate high-temperature alkali-calcic alteration in the early stages of IOCG mineralization, as seen in other deposits in the region. Dating of lamellar hematite intergrown with Cu-Fe-sulfides allows the timing of the alteration-mineralization event to be constrained at 1594 ± 28 Ma, contemporaneous with the ~ 1.59 Ga IOCG mineralization event recorded across the eastern Gawler Craton. The host metasedimentary sequence can be correlated to the Wallaroo Group based on lithology and fabrics, and stratigraphically by an underlying ~ 1850 Ma Donington Suite granite and the new U–Pb ages for superimposed mineralization. Oscillatory zoned silician magnetite in skarn displays a trace element signature comparable to that observed in the outer shell of the Olympic Dam deposit and the nearby Wirrda Well prospect and is consistent with early stages of IOCG mineralization. The geochemical signatures of hematite from skarn and banded Fe-rich metasedimentary rocks share a common enrichment in W, Sn, Mo, Th, and U seen in hematite from IOCG-style mineralization across the Gawler Craton. Relative enrichment in As, Sb, Ni, and Co is, however, specific to iron-oxides from banded Fe-rich metasedimentary rocks. These features can be attributed to pre-existing iron-rich lithologies.

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).

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.

Subduction: The recycling engine room for global metallogeny

The formation of ore deposits, within mineral systems that represent highly anomalous concentrations of economic elements in localized parts of the Earth’s crust, first requires an enriched and available source of those elements. In early Earth history, initial enrichment in the upper mantle was arguably through mantle plumes that even recycled metals from the core-mantle boundary. From the Mesoarchean onwards, the development of plate tectonics allowed subduction processes to be increasingly important in both recycling of elements from the upper mantle into the lower crust and from there into the upper crust where mineral deposits could form and be exploited. The most obvious expression of this recycling process is the direct association of porphyry-high-sulfidation epithermal-skarn Cu-Au-Ag +/- Mo systems and inboard fractionated granite-associated Sn-W systems with magmatic-hydrothermal fluids derived from subduction-related magmas in convergent margins, where epithermal Au-Ag systems also developed due to high thermal gradients. Syn-subduction VMS Cu-Zn-Pb(Au) systems were accreted at convergent margins. Most orogenic gold systems relate to fluids released through devolatilization of down-going subduction slabs and overlying metal-rich sediment wedges. More indirect associations relate to the ability of subduction zones to cause structural damage and metasomatize and fertilize sub-continental mantle lithosphere along the margins of bordering craton margins. Orogen collapse in the final stages of the subduction-related orogenic event led to asthenosphere upwelling and formation of proximal intrusion-related and more distal Carlin-type gold systems in continental basins on the craton margins. During subsequent orogenic events, previously metasomatized and fertilized mantle lithosphere was reactivated to release hydrothermal fluids to form many of the orogenic gold systems in eastern China. Reactivation of the metasomatized lithosphere also resulted in development of post-subduction hybrid or alkaline magmas that generated giant magmatic Kiruna-type Fe-P, carbonatite-related REE-Nb or Cu-P, and lamproite-related diamond systems, together with magmatic-hydrothermal IOCG mineral systems near craton margins. Subduction-damaged craton margins and their rift-related marginal basins became the sites of formation of Zambian Copper Belt-type deposits and the craton margins were reactivated during subsequent rifting allowing intrusion of giant Ni-Cu mafic–ultramafic bodies along lithosphere-tapping fault zones at those margins. Thus, subduction acts as the recycling engine room or factory responsible for many of the global giant mineral systems that are currently exploited.

A genetic link between albitic magmas and IOCG mineralization in the Ossa Morena Zone (SW Iberia)

A detailed geological and isotopic study of the Colmenar deposit (Ossa Morena Zone, SW Iberia) shows that the magnetite-rich mineralization formed by complex magmatic-hydrothermal processes related to the crystallization of water-rich albite-magnetite igneous rocks derived from the crystallization of unusual melts formed during anatexis in a high temperature-low pressure metamorphic regime. The most likely protolith includes a sequence of iron-rich chemical sediments, amphibolite and possible meta-evaporites of early Cambrian age. The albite-magnetite rock occurs as up to 20 cm-thick dyke and breccia bodies and show complex immiscibility relationships with an albite-K-feldspar-quartz leucogranite. Iron-rich fluids exsolved during the crystallization of these melts are responsible of the formation of hydrothermal breccias and the widespread replacement of the hosting calc-silicate hornfels by a magnetite-ferroactinolite-albite assemblage along syn-mineralization shear zones. Geochronological data obtained for mineralization and related hydrothermal alteration points to a Variscan age (ca. 340 Ma), interpreted also as the age of the high-grade metamorphism driving anatexis at the Valuengo Metamorphic Complex. Despite the low Cu and Au contents, this mineralization shares features with the IOCG systems, which in other districts show a spatial relationship with albite-rich rocks, evaporites and pre-existing iron mineralization. The observations presented from Colmenar support an alternative genetic model with prospective implications for the Ossa Morena Zone that can be extrapolated to other IOCG belts worldwide.

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.

Evolution of the Kiruna-type Gol-e-Gohar iron ore district, Sanandaj-Sirjan zone, Iran

The Gol-e-Gohar iron ore district in the Sanandaj-Sirjan zone of south-western Iran comprises six major ore bodies. The largest deposit is Gol-e-Gohar No. 3 (Gohar-Zamin) with about 643 Mt @ 53.1% Fe. The host rocks in this district are Late Neoproterozoic meta-sedimentary rocks (para-gneiss, marble), meta-basalt (ortho-amphibolite), and I-type meta-granite (ortho-gneiss). The district is characterized by potassic-sodic (albite-K-feldspar), phyllic (muscovite) and propylitic (chlorite-calcite-dolomite-magnesite with pyrite) hydrothermal alteration, and massive and brecciated Kiruna-type magnetite ± apatite mineralization. There is also boron (B) metasomatism, manifested as tourmaline blastesis. Gol-e-Gohar magnetite contains Mg, Ca and Si up to the percent range, V and Ti in the 100s ppm level, and low Cr, Co, Ni in the tens of ppm range, typical of skarn or IOCG mineralization. The oxygen isotope composition of magnetite is 4.9 ± 0.7‰ δ18O (n = 9) and the iron isotope composition is 0.49 ± 0.05‰ δ56Fe (n = 17). These data suggest that the magnetite ore formed from a magmatic-hydrothermal (high-T) fluid in equilibrium with a granitic source. The hydrothermal carbonate inclusions in late pyrite have δ11B values of 20.3 ± 2.4‰, indicating the imprint of fluids which interacted with the Early Cambrian marine country rocks of the district, such as limestone and/or evaporites. The Gol-e-Gohar iron ore district shows several similarities to the Bafq iron district, located about 400 km to the north, and seems to be a disrupted member of the Kashmar-Kerman arc.

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.

Pb-isotopic constraints on the source of A-type Suites: Insights from the Hiltaba Suite - Gawler Range Volcanics Magmatic Event, Gawler Craton, South Australia

The 1595–1575 Ma Hiltaba Suite intrusives and coeval Gawler Range Volcanics (GRV) represent a significant crustal component of the Mesoarchean-Mesoproterozoic Gawler Craton, South Australia, and one of the largest silicic igneous provinces in the world. They are also spatially and temporally-affiliated with world-class IOCG mineral deposits (i.e. Olympic Dam) thus making an understanding of these rocks important both economically, and petrologically. Here, we present the results of 177 in situ Pb-isotopic analyses of alkali feldspar in the Hiltaba Suite/GRV, which when integrated with existing SmNd isotopic and geochemical data, reveal a craton-wide isotopic zoning. Pb-isotopic zonation is controlled by the varying interaction of a parental melt derived from a sub-continental lithospheric mantle (SCLM)-like enriched mantle reservoir (238U/204Pb ≤ 9.4, 232Th/238U ≤ 3.66) and twocrustal end-member reservoirs: an unradiogenic reservoir (207Pb/206Pb ≥ 0.97, 208Pb/204Pb ≥ 35.7) and a radiogenic reservoir (238U/204Pb ≥ 10, 232Th/238U ≥ 3.95). The SCLM-like reservoir exerts a strong control on Pb-isotopic compositions around the central-western Gawler Craton (Nuyts Terrane), while the unradiogenic reservoir which represents granulitic lower crust, appears to be spatially limited to the northwest of the Gawler Craton. The radiogenic reservoir, coincident with the IOCG province and probably represented by monazite-rich metasediments, is more prevalent in the eastern Gawler Craton. Correlation between melt-source 238U/204Pb(t) and 232Th/238U(t), with LREE (i.e. La, Ce etc) and HFSE (Zr, Nb etc) which are characteristically enriched in A-type magmas, suggest the importance of hybridisation between a crustal melt component and enriched-mantle-melt component in the formation of A-type magmas.The isotopic and geochemical compositions of the ~1592 Ma Lower GRV and ~1588 Ma Upper GRV effectively bracket the Hiltaba Suite intrusive rocks, and thus provide an avenue for investigating the temporal Pb-isotopic development of a representative part of the Hiltaba Suite/GRV magmatic systems. The Pb-isotopic characteristics imply that either Lower and Upper GRV magma systems developed independently, or reflect a magmatic system evolving substantially over a ~2 Ma period, dominated by mafic input at first (3 to 8% crustal melt; Lower GRV) and moving towards homogeneous, crustal, isotopic compositions with increased crustal melt proportions (15 to 20%) in the Upper GRV.The consistency of these melt source constraints - isotopically, geochemically and proportionally - with other A-type suites around the world favours a unified petrogenetic model for A-types involving dominantly mantle-derived melts, with varying proportions of crustal material which impart characteristically LREE-HFSE enriched geochemical signatures.

Evolution of the Igarapé Bahia Cu-Au deposit, Carajás Province (Brazil): Early syngenetic chalcopyrite overprinted by IOCG mineralization

The Igarapé Bahia IOCG Cu–Au deposit, located in the Carajás Domain, the northern part of the Carajás Province in the Amazon Craton, is one of the most economically important deposits in the province. The deposit is hosted in the metavolcanosedimentary Igarapé Bahia Group and the metasedimentary Águas Claras Formation. The Igarapé Bahia Group encompasses a lower unit with metavolcanic rocks and metagabbros, and metasedimentary rocks (metarhythmites, epiclastic rocks, and banded iron formation) of the upper unit. Epiclastic rocks are predominant in the Águas Claras Formation. Basement xenoliths within the lower unit yielded an U–Pb zircon age of 2935 ± 36 Ma, suggesting that a sialic crust was present prior to basin installation likely due to rifting. The U–Pb dating of detrital zircons yielded maximum deposition age at 2784 ± 27 Ma for the upper unit, and 2763 ± 32 Ma and 2774 ± 19 Ma for the Águas Claras Formation. Chalcopyrite nodules and layers are found within metarhythmites, concordant to primary structures, but without hydrothermal alteration halos and iron oxide. This chalcopyrite generation seems to have precipitated synchronously to the deposition of the Igarapé Bahia Group. Chalcopyrite nodules and layers show δ34SVCDT values ranging from +0.29 to +1.56‰. These data indicate that most of its sulfur is likely derived from the metavolcanic rocks of the lower unit. Host rocks and chalcopyrite nodules and layers were overprinted by the IOCG mineralization. The latter formed extensive halos of hydrothermal alteration and was accompanied by ductile deformation and hydrothermal brecciation. These processes resulted in (tourmaline)–carbonate–magnetite, (tourmaline)–carbonate–chlorite and (tourmaline)–(biotite)–chlorite mylonites and breccias. Chalcopyrite from magnetite-rich zones (i.e. IOCG mineralization) displays δ34SVCDT values from +1.36 to +5.35‰. In addition to magmatic sulfur, seawater-derived sulfate may have been incorporated in sulfides via thermochemical sulfate-reduction reactions. Trace element geochemistry in distinct copper ores (i.e. nodules and layers versus magnetite-rich) also point to different origins of both styles of mineralization. The timing of the IOCG mineralization was constrained at 2559 ± 34 Ma in the Alemão orebody. These data suggest that an IOCG-type metallogenetic event at ca. 2.5 Ga overprinted an older syngenetic-exhalative type copper mineralization. They also indicate that precipitation of early sulfide minerals within the Itacaiúnas Supergroup may have created Cu-rich sequences that could have been remobilized, generating the broad group of the IOCG deposits at Carajás.

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.

Lithological and structural controls on the genesis of the Candelaria-Punta del Cobre Iron Oxide Copper Gold district, Northern Chile

The Candelaria-Punta del Cobre district is the largest Iron-Oxide Cu and Au (IOCG) district in the Chilean IOCG belt with more than 13 Mt of contained copper. Candelaria is the most important deposit in the district, which includes seven other smaller producers (Carola, Punta del Cobre, Mantos de Cobre, Candelaria Norte, Granate, Alcaparrosa, Atacama Kozan, Las Pintadas). The district, which is characterized by an Early-Cretaceous volcanic-sedimentary arc sequence (∼135–132 Ma; Punta del Cobre Formation) overlain by the marine-sedimentary Chañarcillo Group, formed in an extensional back-arc basin (∼132–130 Ma). The Copiapó batholith, which occupies the western side of the district, was emplaced between ∼118 and 110 Ma during the change from extensional to transpressional tectonics. Mineralization is hosted predominately in the upper part of the Lower Andesite member and the overlying Volcano-sedimentary and Dacite members all within the Punta del Cobre Formation. Mineralization is hosted by fault zones, breccias, and specific lithologies. North-northwest faults are the dominant host for vertically extensive orebodies. Stratigraphically-controlled mineralization forms extensive stratabound ore bodies (“mantos”). Textural evidence suggest that the hydrothermal system evolved and advanced upwards over time. The earliest event was dominated by magnetite-actinolite in stratigraphically-controlled mantos and extensive zones of disseminated magnetite-actinolite below Candelaria, which were subsequently overprinted by chalcopyrite-dominant mineralization with magnetite-actinolite-biotite-K-feldspar alteration. In addition to magnetite, iron oxides include widespread mushketovite and hematite in the upper part of some deposits. Geochronological data suggest that the main phase of mineralization occurred between ∼122 Ma and ∼115 Ma (U-Pb in zircon), overlapping in age with the two major early phases of the Copiapó batholith. There is no field evidence to indicate that exposed phases of the batholith were the source of mineralizing fluids. Alteration and mineralization in the earliest phase of the batholith (La Brea) occurs in structures and is minor compared to mineralization in the Punta del Cobre Formation. Later phases of the batholith cut the main stage of mineralization. The extent of IOCG mineralization in the Candelaria-Punta del Cobre district reflects a combination of factors including changing regional kinematics and related fault architecture, multiple intrusive events, fluid access to permeable and reactive lithologies, vertical changes in redox conditions, and the potential role of multiple fluids.