Iron Oxide Copper-Gold (IOCG) Deposits through Earth History: Implications for Origin, Lithospheric Setting, and Distinction from Other Epigenetic Iron Oxide Deposits

Abstract

The iron oxide copper-gold (IOCG) group of deposits, initially defined following discovery of the giant Olympic Dam Cu-U-Au deposit, has progressively become too-embracing when associated deposits and potential end members or analogs are included. The broader group includes several low Ti iron oxideassociated deposits that include iron oxide (P-rich), iron oxide (F-and REE-rich), Fe or Cu-Au skarn, highgrade iron oxide-hosted Au ± Cu, carbonatite-hosted (Cu-, REE-, and F-rich), and IOCG sensu stricto deposits. Consideration of this broad group as a whole obscures the critical features of the IOCG sensu stricto deposits, such as their temporal distribution and tectonic environment, thus leading to difficulties in developing a robust exploration model.The IOCG sensu stricto deposits are magmatic-hydrothermal deposits that contain economic Cu and Au grades, are structurally controlled, commonly contain significant volumes of breccia, are commonly associated with presulfide sodic or sodic-calcic alteration, have alteration and/or brecciation zones on a large, commonly regional, scale relative to economic mineralization, have abundant low Ti iron oxides and/or iron silicates intimately associated with, but generally paragenetically older than, Fe-Cu sulfides, have LREE enrichment and low S sulfides (lack of abundant pyrite), lack widespread quartz veins or silicification, and show a clear temporal, but not close spatial, relationship to major magmatic intrusions. These intrusions, where identified, are commonly alkaline to subalkaline, mixed mafic (even ultramafic) to felsic in composition, with evidence for mantle derivation of at least the mafic end members of the suite. The giant size of many of the deposits and surrounding alteration zones, the highly saline ore fluids, and the available stable and radiogenic isotope data indicate release of deep, volatile-rich magmatic fluids through devolatization of causative, mantle-derived magmas and variable degrees of mixing of these magmatic fluids with other crustal fluids along regional-scale fluid flow paths.Precambrian deposits are the dominant members of the IOCG group in terms of both copper and gold resources. The 12 IOCG deposits with >100 tonnes (t) resources are located in intracratonic settings within about 100 km of the margins of Archean or Paleoproterozoic cratons or other lithospheric boundaries, and formed 100 to 200 m.y. after supercontinent assembly. Their tectonic setting at formation was most likely anorogenic, with magmatism and associated hydrothermal activity driven by mantle underplating and/or plumes. Limited amounts of partial melting of volatile-rich and possibly metal-enriched metasomatized early Precambrian subcontinental lithospheric mantle (SCLM), fertilized during earlier subduction, probably produced basic to ultrabasic magmas that melted overlying continental crust and mixed with resultant felsic melts, with devolatilization and some penecontemporaneous incorporation of other lower to middle crustal fluids to produce the IOCG deposits. Pre...

Multiple Stage Ore Formation in the Chadormalu Iron Deposit, Bafq Metallogenic Province, Central Iran: Evidence from BSE Imaging and Apatite EPMA and LA-ICP-MS U-Pb Geochronology

“…The deposits are characterized by large masses of Ti-rich to Ti-poor Fe oxides (essentially magnetite) and subordinate phosphates, in particular apatite, and are known as Kiruna-type magnetite-apatite (e.g., [1]) or iron oxide-apatite (IOA) deposits [2]. Some researchers (e.g., [3][4][5][6] included the Kiruna-type apatite-bearing Fe-oxide deposits in the wide range of the iron oxide copper-gold (IOCG) deposits. However, the deposits are considered by other researchers (e.g., [7,8]) as a distinct type of iron deposits, known as iron oxide-apatite (IOA) ores.…”

Unraveling the origin of the Andean IOCG clan: A Re-Os isotope approach

“…1). Although each one of these deposit types have distinctive characteristics, the common presence of iron oxides (magnetite and/or specular hematite) has led several authors to group them together in what has been termed the IOCG clan (Hitzman et al, 1992;Sillitoe, 2003;Williams et al, 2005;Groves et al, 2010). The Andean IOCG deposits are characterized by abundant presence of magnetite, with chalcopyrite and minor bornite with important amounts of gold and silver.…”

Mesozoic Iron Oxide Copper-Gold Mineralization in the Central Andes and the Gondwana Supercontinent Breakup

“…With improved geochronological methods and better plate tectonic reconstructions (e.g., Condie, 2005), the temporal distribution of mineral deposits associated with supercontinent assembly and breakup have been documented for many important ore types, such as orogenic gold deposits (Goldfarb et al, 2001), volcanic-hosted massive sulfide deposits , and sediment-hosted lead-zinc deposits (Leach et al, 2010). Most Precambrian IOCG deposits are believed to have been distributed in intracratonic settings, typically 100 to 200 km inland from cratonic margins, and appear to form during episodes of supercontinent breakup (Groves et al, 2010). In the case of the Central Andes, Mesozoic IOCG mineralization was associated with an active continental margin (Sillitoe, 2003;Chen et al, 2010a).…”

“…In the case of the Central Andes, Mesozoic IOCG mineralization was associated with an active continental margin (Sillitoe, 2003;Chen et al, 2010a). The remelting of mafic crust generated by upwelling mantle was inferred in both Central Andean and Precambrian IOCG tectonic regimes Mesozoic Iron Oxide Copper-Gold Mineralization in the Central Andes and the Gondwana Supercontinent Breakup (Atherton et al, 1983;Pollard et al, 1998;Groves et al, 2010). With the help of recent precise geochronological data, in this paper we reconstruct the tectonic evolution of the Central Andes during Gondwana breakup and examine its relationship with Mesozoic IOCG mineralization in detail.…”