Metal source and tectonic setting of iron oxide-copper-gold (IOCG) deposits: Evidence from an in situ Nd isotope study of titanite from Norrbotten, Sweden

Abstract

Titanite occurs as a widespread accessory phase in mineralized zones and alteration associated with iron oxide-copper gold (IOCG) and iron oxide-apatite (IOA) deposits of Norrbotten County, Sweden, and is a major host of the REE in these deposits. In situ analyses of Sm-Nd isotope ratios in titanites previously analysed for U-Pb geochronology and trace element composition confirms previous interpretations of grain scale isotopic heterogeneity. Initial Nd-isotope ratios expressed relative to CHUR range from ~-3 to -8 in IOA deposits, from ~-1 to -9 in IOCG deposits, and from +2 to -4 in the most Cu-rich, deformed IOCG deposits of the Nautanen Deformation zone. Within individual IOA deposits at Valkommen (Malmberget), from -1.4 to -5.7 in grain cores, and -7.2 to -8.2 in grain rims rim at Gruvberget; and from -3.0 to -6.0 in grain cores and from -5.8 to -7.1 in grain rims at Luossavaara. In IOCG deposits at Rakkurijärvi IOCG dpeosits at Nautanen from -1.3 to -2.3. These values are consistent with the derivation of the REE, and potentially economically enriched metals, from the local volcanic sequence, either via granitic melts, or directly by leaching by metasomatic fluids. The most Cu-rich deposits reflect the involvement of more basic protoliths. The age distribution of these deposits suggest IOA deposit formation during the collisional phase of the Svecofennian orogeny (~1.9-1.8 Ga), and IOCG mineralization during this phase and during post-orogenic collapse (~1.8-1.7 Ga), whilst model ages indicate the ultimate enrichment of the continental crust in these metals during pre-collisional extensional and subduction-related basic magmatism. These processes underscore the importance of continental cycles both in producing the preserved geological record of orogenic ore deposition, and in the generation of fertile continental crust, from which metals can be mobilised by subsequent events.Nd varies relative to CHUR: from -3.1 to -4.0Nd varies from -6.1. to -7.1, and in deformed IOCG dpeosits at Nautanen from -1.3 to -2.3. These values are consistent with the derivation of the REE, and potentially economically enriched metals, from the local volcanic sequence, either via granitic melts, or directly by leaching by metasomatic fluids. The most Cu-rich deposits reflect the involvement of more basic protoliths. The age distribution of these deposits suggest IOA deposit formation during the collisional phase of the Svecofennian orogeny (~1.9-1.8 Ga), and IOCG mineralization during this phase and during post-orogenic collapse (~1.8-1.7 Ga), whilst model ages indicate the ultimate enrichment of the continental crust in these metals during pre-collisional extensional and subduction-related basic magmatism. These processes underscore the importance of continental cycles both in producing the preserved geological record of orogenic ore deposition, and in the generation of fertile continental crust, from which metals can be mobilised by subsequent events

Energy Drive for the Kiruna Mining District Mineral System(s): Insights from U-Pb Zircon Geochronology

“…Importantly, while the Rakkurijärvi deposit has been constrained radiometrically to the early Svecokarelian mineralizing period (Re-Os molybdenite, U-Pb allanite, rutile; [5,26,27]), the age of the Pahtohavare deposits is unknown. However, previous studies have found evidence for a partial contribution of magmatic fluids on the ore formation at both localities studied (fluid inclusions [5,34,36,37], Cl/Br ratios and δ 37 Cl on scapolite [38], C and O isotopes on carbonate [26], Sm-Nd on titanite [39]), indicating the magmatism likely served as an energy driver and possibly a metal and fluid supplier for the mineral systems.…”

“…C and O isotopes of calcite from veins, breccia matrices, and marble indicate that the Rakkurijärvi ore-related calcite derived isotopic signatures from both magmatic and marine carbonate sources [26]. Furthermore, εNd isotope data from titanite at Rakkurijärvi indicate an overlap with the regional values for granitoids from the early Svecokarelian [26,39]. The deposit is dated by Re-Os (molybdenite: 1862 ± 6 Ma and 1853 ± 6 Ma) and U-Pb (laser ablation (LA)-ICP-MS on allanite: 1854 ± 18 Ma, and TIMS on rutile: 1859 ± 2 Ma) constraining the timing of formation to ca.…”

Silicate, Iron Oxide and Copper-Gold-Silver Microspherules in Ores and Pyroclastics of the Kostenginskoye Iron Ore Deposit (Russian Far East)

“…[6,75,105] и геохимические (особенно изотопные) характеристики существенно магнетитовых (часто с медью и золотом) руд и вмещающих их изверженных горных пород [22,55,101,103]. В рамках этой модели рудообразующие флюиды имеют существенно мантийное происхождение, что подтверждается данными по распределению радиогенных (Nd, Hf, Pb) и стабильных (Fe, O, Cl) изотопов в рудах и вмещающих их породах и минералах [35,94,103]. Собственно гидротермальный класс моделей можно разделить на две подгруппы.…”

“…Вторая группа исследователей полагает, что осаждение железа и других металлов происходило из экзогенных флюидов с высокими содержаниями галогенов, связанных с эволюцией осадочно-вулканогенных и метаморфических толщ [23,46,51] или смешанных мантийно-коровых флюидов [33,50,91,95]. Многие исследователи также предполагают многоступенчатую архитектуру долгоживущих коровых рудообразующих систем, в которых железо-фосфорные месторождения с магнетитом и апатитом (так называемый Кирунский тип) занимают наиболее глубинные их горизонты, а железооксидно-медно-золотое (собственно IOCG Андийского типа) оруденение ассоциируется с субвулканическими системами и тесно связано с медно-золотыми порфировыми и высокосульфидными эпитермальными месторождениями [15,77,88,89,92,94,100]. Основным связующим звеном в этих долгоживущих (до 100 млн лет [58,59]), многоуровневых коровых рудно-магматических системах являются обогащенные металлами субдукционные и постсубдукционные магмы, возникающие, согласно современным изотопно-геохимическим данным, из флюидов и расплавов, образовавшихся при дегидратации или плавлении погружающейся океанической плиты под перекрывающий ее перидотитовый мантийный клин [47,57,58,73,87].…”

Geochemical characterization of mineralized albitite from Paleoproterozoic Bhukia IOCG‐IOA deposit of Aravalli‐Delhi Fold Belt, Rajasthan, western India: Genetic linkage to the gold (±Cu ± U) mineralization

“…Iron‐oxide copper gold–Iron Oxide Apatite (IOCG‐IOA) deposits attracted profound interest during recent times for their shallow depth of occurrences, abundant and wide variety of mineral species, and large resource potentials (Kontonikas‐Charos et al, ; Li et al, ; Li, Santosh, & Li, ; Mark, Wildem, Oliver, Williams, & Ryan, ; Marschik & Fontboté, ; Martinsson, Billstrom, Broman, Weihed, & Wanhainen, ; Megan, Williams, Holwell, Lilly, & Iain, ; Michelle, Tappert, Giles, Tappert, & Mauge, ; Mukherjee, Venkatesh, & Fareeduddin, ; Sillitoe, ; Storey & Smith, ). These deposits are characterized by the preponderance of iron oxides (low‐Ti magnetite, hematite), Cu‐sulfides, gold, apatite, Light Rare Earth Elements (LREE), silver, and radioactive elements (U and Th) that are derivatives of a large hydrothermal system (Barton, ; Chen, ; Heidarian, Lentz, Alirezaei, Mcfarlane, & Peighambari, ; Hitzman, Oreskes, & Einaudi, ; Meyer, ; Mukherjee, Venkatesh, & Fareeduddin, ; Porter, ; Sillitoe, ; Williams et al, ).…”