Structural Evolution of the Central Kiruna Area, Northern Norrbotten, Sweden: Implications on the Geologic Setting Generating Iron Oxide-Apatite and Epigenetic Iron and Copper Sulfides

Abstract To guide future exploration, this predominantly field based study has investigated the structural evolution of the central Kiruna area, the type locality for iron oxide-apatite deposits that stands for a significant amount of the European iron ore production. Using a combination of geologic mapping focusing on structures and stratigraphy, petrography with focus on microstructures, X-ray computed tomography imaging of sulfide-structure relationships, and structural 2D-forward modeling, a structural framework is provided including spatial-temporal relationships between iron oxide-apatite emplacement, subeconomic Fe and Cu sulfide mineralization, and deformation. These relationships are important to constrain as a guidance for exploration in iron oxide-apatite and iron oxide copper-gold prospective terrains and may help to understand the genesis of these deposit types. Results suggest that the iron oxide-apatite deposits were emplaced in an intracontinental back-arc basin, and they formed precrustal shortening under shallow crustal conditions. Subsequent east-west crustal shortening under greenschist facies metamorphism inverted the basin along steep to moderately steep E-dipping structures, often subparallel with bedding and lithological contacts, with reverse, oblique to dip-slip, east-block-up sense of shears. Fe and Cu sulfides associated with Fe oxides are hosted by structures formed during the basin inversion and are spatially related to the iron oxide-apatite deposits but formed in fundamentally different structural settings and are separated in time. The inverted basin was gently refolded and later affected by hydraulic fracturing, which represent the last recorded deformation-hydrothermal events affecting the crustal architecture of central Kiruna.

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Geophysical methods used in the discovery of the Kitumba iron oxide copper gold deposit

Interpretation ◽

10.1190/int-2014-0201.1 ◽

2015 ◽

Vol 3 (2) ◽

pp. SL15-SL25 ◽

Cited By ~ 2

Author(s):

Thomas R. H. Woolrych ◽

Asbjorn N. Christensen ◽

Darcy L. McGill ◽

Tom Whiting

Keyword(s):

Iron Oxide ◽

Structural Information ◽

Geophysical Methods ◽

3D Models ◽

Induced Polarization ◽

Magnetic Data ◽

Airborne Gravity ◽

Data Sets ◽

Geologic Mapping ◽

Copper Gold

A range of geophysical techniques has been used at various stages of the discovery and delineation of the Kitumba deposit in Central Zambia. Early era magnetics, geologic mapping, artisanal Cu plays, and the application of an iron oxide copper gold (IOCG) exploration model led explorers to the area in the 1990s. An airborne gravity gradiometer (AGG) survey was flown in 2004, and it highlighted key regional elements considered to be prerequisite for prospective IOCG mineralization. The AGG survey accurately delineated the spatial extents of two target areas referred to as the Kitumba and Mutoya systems. Gravity, radiometric, and magnetic data sets acquired as part of the AGG survey have mapped geologic and structural information as well as the extent of the IOCG alteration system. Significant uranium anomalism in the radiometric data was identified at Kitumba upon which the discovery hole S36-001 was sited. In 2012, a 3D direct current resistivity and induced polarization survey was conducted over Kitumba. The survey results provided 3D models of induced polarization chargeability anomalism and allowed successful delineation of sulfide material within the known deposit. The survey also provided an enhanced understanding of the 3D geometry of the mineralization. This improved understanding allowed a refocusing of drilling activities to best target extensions to existing mineralization.

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Geologic and Structural Evolution of the NE Lau Basin, Tonga: Morphotectonic Analysis and Classification of Structures Using Shallow Seismicity

Frontiers in Earth Science ◽

10.3389/feart.2021.665185 ◽

2021 ◽

Vol 9 ◽

Author(s):

Melissa O. Anderson ◽

Chantal Norris-Julseth ◽

Kenneth H. Rubin ◽

Karsten Haase ◽

Mark D. Hannington ◽

...

Keyword(s):

Moment Tensor ◽

Plate Boundary ◽

Structural Evolution ◽

Strike Slip ◽

Normal Faults ◽

Geologic Mapping ◽

Centroid Moment Tensor ◽

Lau Basin ◽

Fault Kinematics ◽

Back Arc

The transition from subduction to transform motion along horizontal terminations of trenches is associated with tearing of the subducting slab and strike-slip tectonics in the overriding plate. One prominent example is the northern Tonga subduction zone, where abundant strike-slip faulting in the NE Lau back-arc basin is associated with transform motion along the northern plate boundary and asymmetric slab rollback. Here, we address the fundamental question: how does this subduction-transform motion influence the structural and magmatic evolution of the back-arc region? To answer this, we undertake the first comprehensive study of the geology and geodynamics of this region through analyses of morphotectonics (remote-predictive geologic mapping) and fault kinematics interpreted from ship-based multibeam bathymetry and Centroid-Moment Tensor data. Our results highlight two notable features of the NE Lau Basin: 1) the occurrence of widely distributed off-axis volcanism, in contrast to typical ridge-centered back-arc volcanism, and 2) fault kinematics dominated by shallow-crustal strike slip-faulting (rather than normal faulting) extending over ∼120 km from the transform boundary. The orientations of these strike-slip faults are consistent with reactivation of earlier-formed normal faults in a sinistral megashear zone. Notably, two distinct sets of Riedel megashears are identified, indicating a recent counter-clockwise rotation of part of the stress field in the back-arc region closest to the arc. Importantly, the Riedel structures identified in this study directly control the development of complex volcanic-compositional provinces, which are characterized by variably-oriented spreading centers, off-axis volcanic ridges, extensive lava flows, and point-source rear-arc volcanoes. This study adds to our understanding of the geologic and structural evolution of modern backarc systems, including the association between subduction-transform motions and the siting and style of seafloor volcanism.

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Radiogenic and stable isotope evidence for age and origin of authigenic illites in the Rotliegend, southern North Sea

Clay Minerals ◽

10.1180/claymin.1994.029.4.12 ◽

1994 ◽

Vol 29 (4) ◽

pp. 555-565 ◽

Cited By ~ 11

Author(s):

K. Ziegler ◽

B. W. Sellwood ◽

A. E. Fallick

Keyword(s):

North Sea ◽

Structural Evolution ◽

Lower Permian ◽

Gas Reservoirs ◽

Gaseous Hydrocarbon ◽

Oxygen Isotope Exchange ◽

Basin Inversion ◽

Southern North Sea ◽

Evaporative Concentration ◽

Isotopic Analyses

AbstractAeolian sandstones of the Lower Permian Leman Formation (Rotliegend Group) provide the best gas reservoir in the southern North Sea, but permeability is greatly reduced by the presence of authigenic fibrous illites. New radiogenic (K/Ar) and stable (oxygen and hydrogen) isotope data are presented for fibrous illite cements (<0.1 µm), so that the absolute timing and controlling diagenetic factors for their formation can be more fully evaluated. Thus, the expected quality of gas reservoirs in the southern North Sea might be better predicted. Samples have been analysed from five wells in areas with contrasting structural evolution: the Sole Pit Basin, and the Indefatigable Shelf. The K/Ar ages of between 160 and 190 Ma have been obtained from the Indefatigable Shelf illites, and between 120 and 160 Ma for those from the Sole Pit Basin, reflecting different times of basin inversion. These K/Ar ages are interpreted by reference to burial/thermal models for each well. The temperature of illite precipitation falls between 88 and 140°C. Calculated pore-fluid compositions derived from oxygen and hydrogen isotopic analyses give values of ∼ + 1 to +9‰ (SMOW) δ18O and +1 to −50‰ (SMOW) δD. The illite δD values have probably been affected by isotopic exchange and fractionation with the surrounding gaseous hydrocarbon. The δ18O values reflect the degree to which evaporative concentration had affected Zechstein marine waters which subsequently invaded the Leman Sandstone. Comparisons between δ18O and δD values in clays and in formation water for the Leman Field suggest that oxygen isotope exchange might have taken place, and that the initial K+ and radiogenic 40Ar contents within illites may have been modified.

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Monitoring fluid chemistry in iron oxide-copper-gold-related metasomatic processes, eastern Mt Isa Block, Australia

Geofluids ◽

10.1111/j.1468-8123.2006.00127.x ◽

2006 ◽

Vol 6 (1) ◽

pp. 45-66 ◽

Cited By ~ 10

Author(s):

L. J. MARSHALL ◽

N. H. S. OLIVER

Keyword(s):

Iron Oxide ◽

Fluid Chemistry ◽

Copper Gold ◽

Mt Isa

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Noble gas and halogen constraints on fluid sources in iron oxide-copper-gold mineralization: Mantoverde and La Candelaria, Northern Chile

Mineralium Deposita ◽

10.1007/s00126-014-0548-x ◽

2014 ◽

Vol 50 (3) ◽

pp. 357-371 ◽

Cited By ~ 5

Author(s):

Robert Marschik ◽

Mark A. Kendrick

Keyword(s):

Iron Oxide ◽

Gold Mineralization ◽

Noble Gas ◽

Northern Chile ◽

Copper Gold ◽

Fluid Sources

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Iron Oxide-Copper-Gold ±Uranium in the Great Bear Magmatic Zone: Nature of Uranium in IOCG Systems

10.4095/292100 ◽

2012 ◽

Cited By ~ 1

Author(s):

E Potter ◽

L Corriveau ◽

J -F Montreuil

Keyword(s):

Iron Oxide ◽

Copper Gold ◽

Great Bear Magmatic Zone

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Stretching and Contraction of Extensional Basins With Pre-Rift Salt: A Numerical Modeling Approach

Frontiers in Earth Science ◽

10.3389/feart.2021.648937 ◽

2021 ◽

Vol 9 ◽

Author(s):

Pablo Granado ◽

Jonas B. Ruh ◽

Pablo Santolaria ◽

Philipp Strauss ◽

Josep Anton Muñoz

Keyword(s):

Hanging Wall ◽

Structural Evolution ◽

Extension Rate ◽

Rift Basins ◽

Basin Inversion ◽

Accommodation Space ◽

Basement Faults ◽

Original Distribution ◽

Thrust Belts ◽

Half Graben

We present a series of 2D thermo-mechanical numerical experiments of thick-skinned crustal extension including a pre-rift salt horizon and subsequent thin-, thick-skinned, or mixed styles of convergence accompanied by surface processes. Extension localization along steep basement faults produces half-graben structures and leads to variations in the original distribution of pre-rift salt. Thick-skinned extension rate and salt rheology control hanging wall accommodation space as well as the locus and timing of minibasin grounding. Upon shortening, extension-related basement steps hinder forward propagation of evolving shallow thrust systems; conversely, if full basin inversion takes place along every individual fault, the regional salt layer is placed back to its pre-extensional configuration, constituting a regionally continuous décollement. Continued shortening and basement involvement deform the shallow fold-thrust structures and locally breaches the shallow décollement. We aim at obtaining a series of structural, stratigraphic and kinematic templates of fold-and-thrust belts involving rift basins with an intervening pre-rift salt horizon. Numerical results are compared to natural cases of salt-related inversion tectonics to better understand their structural evolution.

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Evidence of multiple halogen sources in scapolites from iron oxide-copper-gold (IOCG) deposits and regional Na Cl metasomatic alteration, Norrbotten County, Sweden

Chemical Geology ◽

10.1016/j.chemgeo.2017.01.005 ◽

2017 ◽

Vol 451 ◽

pp. 90-103 ◽

Cited By ~ 10

Author(s):

Nelson F. Bernal ◽

Sarah A. Gleeson ◽

Martin P. Smith ◽

Jaime D. Barnes ◽

Yuanming Pan

Keyword(s):

Iron Oxide ◽

Metasomatic Alteration ◽

Iocg Deposits ◽

Copper Gold

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MAPPING THE MINERAL ZONATION AT THE ERNEST HENRY IRON OXIDE COPPER-GOLD DEPOSIT: VECTORING TO Cu-Au MINERALIZATION USING MODAL MINERALOGY

Economic Geology ◽

10.5382/econgeo.4915 ◽

2022 ◽

Vol 117 (2) ◽

pp. 485-494

Author(s):

Tobias U. Schlegel ◽

Renee Birchall ◽

Tina D. Shelton ◽

James R. Austin

Keyword(s):

Iron Oxide ◽

Gamma Ray ◽

Geochemical Data ◽

Iocg Deposits ◽

Mineral Mapping ◽

Gamma Ray Spectrometer ◽

Mineral Assemblages ◽

Copper Gold ◽

Host Rocks ◽

Acid Alteration

Abstract Iron oxide copper-gold (IOCG) deposits form in spatial and genetic relation to hydrothermal iron oxide-alkali-calcic-hydrolytic alteration and thus show a mappable zonation of mineral assemblages toward the orebody. The mineral zonation of a breccia matrix-hosted orebody is efficiently mapped by regularly spaced samples analyzed by the scanning electron microscopy-integrated mineral analyzer technique. The method results in quantitative estimates of the mineralogy and allows the reliable recognition of characteristic alteration as well as mineralization-related mineral assemblages from detailed mineral maps. The Ernest Henry deposit is located in the Cloncurry district of Queensland and is one of Australia’s significant IOCG deposits. It is known for its association of K-feldspar altered clasts with iron oxides and chalcopyrite in the breccia matrix. Our mineral mapping approach shows that the hydrothermal alteration resulted in a characteristic zonation of minerals radiating outward from the pipe-shaped orebody. The mineral zonation is the result of a sequence of sodic alteration followed by potassic alteration, brecciation, and, finally, by hydrolytic (acid) alteration. The hydrolytic alteration primarily affected the breccia matrix and was related to economic mineralization. Alteration halos of individual minerals such as pyrite and apatite extend dozens to hundreds of meters beyond the limits of the orebody into the host rocks. Likewise, the Fe-Mg ratio in hydrothermal chlorites changes systematically with respect to their distance from the orebody. Geochemical data obtained from portable X-ray fluorescence (p-XRF) and petrophysical data acquired from a magnetic susceptibility meter and a gamma-ray spectrometer support the mineralogical data and help to accurately identify mineral halos in rocks surrounding the ore zone. Specifically, the combination of mineralogical data with multielement data such as P, Mn, As, P, and U obtained from p-XRF and positive U anomalies from radiometric measurements has potential to direct an exploration program toward higher Cu-Au grades.

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