TY - JOUR
T1 - Metal source and tectonic setting of iron oxide-copper-gold (IOCG) deposits
T2 - Evidence from an in situ Nd isotope study of titanite from Norrbotten, Sweden
AU - Storey, Craig
AU - Smith, Martin
N1 - © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
PY - 2016/9/1
Y1 - 2016/9/1
N2 - 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 -4.0Nd 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.
AB - 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 -4.0Nd 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.
U2 - 10.1016/j.oregeorev.2016.08.035
DO - 10.1016/j.oregeorev.2016.08.035
M3 - Article
VL - 81
SP - 1287
EP - 1302
JO - Ore Geology Reviews
JF - Ore Geology Reviews
SN - 0169-1368
IS - Part 4
ER -