Staged formation of the supergiant Olympic Dam uranium deposit, Australia

The origins of many supergiant ore deposits remain unresolved because the factors responsible for such extreme metal enrichments are not understood. One factor of critical importance is the timing of mineralization. However, timing information is commonly confounded by the difficulty of dating ore minerals. The world’s largest uranium resource at Olympic Dam, South Australia, is exceptional because the high abundance of U allows U-Pb dating of ore minerals. The Olympic Dam U(-Cu-Au-Ag) ore deposit is hosted in ca. 1.59 Ga rocks, and the consensus has been that the supergiant deposit formed at the same time. We argue that, in fact, two stages of mineralization were involved. Paired in situ U-Pb and trace element analyses of texturally distinct uraninite populations show that the supergiant size and highest-U-grade zones are the result of U addition at 0.7–0.5 Ga, at least one billion years after initial formation. This conclusion is supported by a remarkable clustering of thousands of radiogenic 207Pb/206Pb model ages of Cu sulfide grains at this time. Upgrading of the original ca. 1.59 Ga U deposit to its present size at 0.7–0.5 Ga may have resulted from perturbation of regional fluid flow triggered by global climatic (deglaciation) and tectonic (breakup of Rodinia) events.

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OPENING THE MAGMATIC-HYDROTHERMAL WINDOW: HIGH-PRECISION U-Pb GEOCHRONOLOGY OF THE MESOPROTEROZOIC OLYMPIC DAM Cu-U-Au-Ag DEPOSIT, SOUTH AUSTRALIA

Economic Geology ◽

10.5382/econgeo.4772 ◽

2020 ◽

Vol 115 (8) ◽

pp. 1855-1870 ◽

Cited By ~ 5

Author(s):

Liam Courtney-Davies ◽

Cristiana L. Ciobanu ◽

Simon R. Tapster ◽

Nigel J. Cook ◽

Kathy Ehrig ◽

...

Keyword(s):

High Precision ◽

Volcanic Rocks ◽

South Australia ◽

Ore Deposits ◽

Magmatic Zircon ◽

Ionization Mass ◽

Temporal Window ◽

Precision Data ◽

Iocg Deposit ◽

Olympic Dam

Abstract Establishing timescales for iron oxide copper-gold (IOCG) deposit formation and the temporal relationships between ores and the magmatic rocks from which hydrothermal, metal-rich fluids are sourced is often dependent on low-precision data, particularly for deposits that formed during the Proterozoic. Unlike accessory minerals routinely used to track hydrothermal mineralization, iron oxides are dominant components of IOCG systems and are therefore pivotal to understanding deposit evolution. The presence of ubiquitous, magmatic-hydrothermal U-(Pb)-W-Sn-Mo–bearing zoned hematite resolves a range of geochronological issues concerning formation of the ~1.6 Ga Olympic Dam IOCG deposit, South Australia, at up to ~0.05% precision (207Pb/206Pb weighted mean; 2σ) using isotope dilution-thermal ionization mass spectrometry (ID-TIMS). Coupled with chemical abrasion-ID-TIMS zircon dates from host granite and volcanic rocks within and enclosing the ore-body, a confident magmatic-hydrothermal chronology is defined. The youngest zircon date from the granite intrusion hosting Olympic Dam indicates magmatism was occurring up until 1593.28 ± 0.26 Ma. The orebody was principally formed during a major mineralizing event following granite uplift and during cupola collapse, whereby the hematite with the oldest age is recorded in the outer shell of the deposit at 1591.27 ± 0.89 Ma, ~2 m.y. later than the youngest documented magmatic zircon. Hematite dates captured throughout major lithologies, different ore zones, and the ~2-km vertical extent of the deposit support ~2 m.y. of hydrothermal activity. New age constraints on the spatial-temporal evolution of the formation of Olympic Dam are considered with respect to a mantle to crustal continuum model. Cyclical tapping of magma reservoirs to maintain crystal mushes for extended time periods and incremental building of batholiths on the million-year scale prior to main mineralization pulses can explain the ~2-m.y. temporal window temporal window inferred from the data. Despite the challenge of reconciling such an extended window with contemporary models for porphyry deposits (≤1 m.y.), formation of Proterozoic ore deposits has been addressed at high-precision and supports the case that giant IOCG deposits may form over millions of years.

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Multivariate Statistical Analysis of Trace Elements in Pyrite: Prediction, Bias and Artefacts in Defining Mineral Signatures

Minerals ◽

10.3390/min10010061 ◽

2020 ◽

Vol 10 (1) ◽

pp. 61 ◽

Cited By ~ 3

Author(s):

Marija Dmitrijeva ◽

Nigel J. Cook ◽

Kathy Ehrig ◽

Cristiana L. Ciobanu ◽

Andrew V. Metcalfe ◽

...

Keyword(s):

Trace Elements ◽

Statistical Analysis ◽

Trace Element ◽

South Australia ◽

Large Datasets ◽

Ore Deposits ◽

Partial Replacement ◽

Multivariate Statistical ◽

Wide Range ◽

Olympic Dam

Pyrite is the most common sulphide in a wide range of ore deposits and well known to host numerous trace elements, with implications for recovery of valuable metals and for generation of clean concentrates. Trace element signatures of pyrite are also widely used to understand ore-forming processes. Pyrite is an important component of the Olympic Dam Cu–U–Au–Ag orebody, South Australia. Using a multivariate statistical approach applied to a large trace element dataset derived from analysis of random pyrite grains, trace element signatures in Olympic Dam pyrite are assessed. Pyrite is characterised by: (i) a Ag–Bi–Pb signature predicting inclusions of tellurides (as PC1); and (ii) highly variable Co–Ni ratios likely representing an oscillatory zonation pattern in pyrite (as PC2). Pyrite is a major host for As, Co and probably also Ni. These three elements do not correlate well at the grain-scale, indicating high variability in zonation patterns. Arsenic is not, however, a good predictor for invisible Au at Olympic Dam. Most pyrites contain only negligible Au, suggesting that invisible gold in pyrite is not commonplace within the deposit. A minority of pyrite grains analysed do, however, contain Au which correlates with Ag, Bi and Te. The results are interpreted to reflect not only primary patterns but also the effects of multi-stage overprinting, including cycles of partial replacement and recrystallisation. The latter may have caused element release from the pyrite lattice and entrapment as mineral inclusions, as widely observed for other ore and gangue minerals within the deposit. Results also show the critical impact on predictive interpretations made from statistical analysis of large datasets containing a large percentage of left-censored values (i.e., those falling below the minimum limits of detection). The treatment of such values in large datasets is critical as the number of these values impacts on the cluster results. Trimming of datasets to eliminate artefacts introduced by left-censored data should be performed with caution lest bias be unintentionally introduced. The practice may, however, reveal meaningful correlations that might be diluted using the complete dataset.

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Ore minerals down to the nanoscale: Cu-(Fe)-sulphides from the iron oxide copper gold deposit at Olympic Dam, South Australia

Ore Geology Reviews ◽

10.1016/j.oregeorev.2016.08.015 ◽

2017 ◽

Vol 81 ◽

pp. 1218-1235 ◽

Cited By ~ 27

Author(s):

Cristiana L. Ciobanu ◽

Nigel J. Cook ◽

Kathy Ehrig

Keyword(s):

Iron Oxide ◽

Gold Deposit ◽

South Australia ◽

Copper Gold ◽

Ore Minerals ◽

Olympic Dam

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Geothermal signatures and uranium ore deposits on the Stuart Shelf of South Australia

Geophysics ◽

10.1190/1.1442640 ◽

1989 ◽

Vol 54 (2) ◽

pp. 158-170 ◽

Cited By ~ 15

Author(s):

G. A. Houseman ◽

J. P. Cull ◽

P. M. Muir ◽

H. L. Paterson

Keyword(s):

Heat Flow ◽

South Australia ◽

Thermal Anomaly ◽

Ore Deposits ◽

Thermal Gradients ◽

Proterozoic Basement ◽

Drill Holes ◽

Olympic Dam ◽

Homogeneous Unit ◽

Anomalous Heat

An analysis of temperature data from drill holes on the Stuart Shelf of South Australia demonstrates a major thermal anomaly associated with the Olympic Dam copper‐uranium‐gold deposit. The average heat flow on the Stuart Shelf (seven locations, excluding Olympic Dam) is [Formula: see text], but an additional heat flow of approximately [Formula: see text] is present in the sediments overlying the orebody. Although some of the anomalous heat flow appears to be generated in the mid‐Proterozoic basement at depths greater than 1 km, uranium assays indicate that approximately [Formula: see text] can be attributed to concentrations defining the orebody. Major anomalies in heat flow can be readily detected in the flat‐lying cover of Cambrian and late Proterozoic sediments. The Tregolana shale within this sequence is a widespread homogeneous unit, typically 100–200 m thick. It is easily identified on temperature logs by its high thermal gradient relative to other sections in the hole. The heat flow anomaly at Olympic Dam is clearly distinguished by measuring thermal gradients within the Tregolana shale; gradients in the Tregolana shale at Olympic Dam are close to 83 °C/km, with a standard deviation (SD) of 6 °C/km, compared to 51 °C/km (SD = 7 °C/km) elsewhere on the Stuart Shelf.

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Silician Magnetite: Si–Fe-Nanoprecipitates and Other Mineral Inclusions in Magnetite from the Olympic Dam Deposit, South Australia

Minerals ◽

10.3390/min9050311 ◽

2019 ◽

Vol 9 (5) ◽

pp. 311 ◽

Cited By ~ 13

Author(s):

Cristiana L. Ciobanu ◽

Max R. Verdugo-Ihl ◽

Ashley Slattery ◽

Nigel J. Cook ◽

Kathy Ehrig ◽

...

Keyword(s):

South Australia ◽

Dark Field ◽

Ore Deposits ◽

Spinel Type ◽

Diverse Range ◽

Scanning Transmission ◽

Copper Gold ◽

Annular Dark Field ◽

Definition Of ◽

Olympic Dam

A comprehensive nanoscale study on magnetite from samples from the outer, weakly mineralized shell at Olympic Dam, South Australia, has been undertaken using atom-scale resolution High Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF STEM) imaging and STEM energy-dispersive X-ray spectrometry mapping and spot analysis, supported by STEM simulations. Silician magnetite within these samples is characterized and the significance of nanoscale inclusions in hydrothermal and magmatic magnetite addressed. Silician magnetite, here containing Si–Fe-nanoprecipitates and a diverse range of nanomineral inclusions [(ferro)actinolite, diopside and epidote but also U-, W-(Mo), Y-As- and As-S-nanoparticles] appears typical for these samples. We observe both silician magnetite nanoprecipitates with spinel-type structures and a γ-Fe1.5SiO4 phase with maghemite structure. These are distinct from one another and occur as bleb-like and nm-wide strips along d111 in magnetite, respectively. Overprinting of silician magnetite during transition from K-feldspar to sericite is also expressed as abundant lattice-scale defects (twinning, faults) associated with the transformation of nanoprecipitates with spinel structure into maghemite via Fe-vacancy ordering. Such mineral associations are characteristic of early, alkali-calcic alteration in the iron-oxide copper gold (IOCG) system at Olympic Dam. Magmatic magnetite from granite hosting the deposit is quite distinct from silician magnetite and features nanomineral associations of hercynite-ulvöspinel-ilmenite. Silician magnetite has petrogenetic value in defining stages of ore deposit evolution at Olympic Dam and for IOCG systems elsewhere. The new data also add new perspectives into the definition of silician magnetite and its occurrence in ore deposits.

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EPITHERMAL MANGANESE MINERALIZATION, KIMOLOS ISLAND, SOUTH AEGEAN VOLCANIC ARC, GREECE

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11672 ◽

2017 ◽

Vol 43 (5) ◽

pp. 2646 ◽

Cited By ~ 2

Author(s):

N. Lykakis ◽

S. P. Kilias

Keyword(s):

Sea Water ◽

Metal Sulfide ◽

Ore Deposits ◽

Vein Wall ◽

Volcanic Arc ◽

Ore Minerals ◽

Manganese Mineralization ◽

Element Enrichment ◽

Low Sulfidation

Manganese mineralization is hosted by a marine monomictic, lithic volcaniclastic breccia, possibly an andesitic in situ hyaloclastite, and shallow-marine or subaerial epiclastic conglomerates, in the Korakies area, NE Kimolos, active south Aegean volcanic arc. Old mine workings (in the form of rubble, adit and shaft), and abandoned rail and ship loading facilities, exist in the area. Mineralization occurs as a quartz/chalcedony vein system filling extensional NNE-SSW–trending faults and fractures, of Pliocene age. Maximum vein width reaches 5 m; length may extend to 250 m. The ore shares strong textural analogies with volcanic-hosted epithermal-style deposits, i.e. crustiform banding, vugs, hydrothermal breccias, cockade and comb textures. Vein wall rocks are hydrothermally altered to quartz-adularia±illite, chlorite and barite. Pyrolusite, hollandite, cryptomelane, and coronadite are the main ore minerals, with quartz, chalcedony, jasper and barite gangue. Ore samples contain up to 25.8 % MnO2, 14.7 % FeOTOT, 2860 ppm Zn, 1132 ppm Pb and 136 ppm Cu; Mn and Zn show mutual positive correlation (r2=0.61). Trace element enrichment (i.e. Zn, Pb, and Cu) may suggest a proximal base metal sulfide mineralization. Concentrations of 4.3 % Na, 0.09 % Mg and barite presence may suggest genetic involvement of sea water. The mineralization studied is similar to volcanic-hosted low-sulfidation epithermal ore deposits deposited from neutral pH fluids. This is a rare example of a vein-type epithermal-style hydrothermal manganese deposit formed in a marine environment.

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Observations of the lineament-ore relation

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1986.0032 ◽

1986 ◽

Vol 317 (1539) ◽

pp. 195-218 ◽

Cited By ~ 34

Keyword(s):

North America ◽

Systematic Study ◽

Mineral Exploration ◽

South Australia ◽

Distribution Patterns ◽

Ore Deposits ◽

Floor Plan ◽

Regional Tectonic ◽

Tectonic Framework ◽

Olympic Dam

Geological and geophysical features of the Australian continental crust follow systematic distribution patterns characterized by major linear discontinuities, or lineaments. These lineaments form the floor plan of the regional tectonic framework, and appear to represent fundamental crustal thresholds and corridors of disturbance along which maximum crustal energies have been channelled. The effects are variously expressed as lineament-associated intensifications of intrusion, deposition, dislocation, deformation, metamorphism and mineralization. In Australia, over two decades of systematic study led to the recognition that major Australian ore deposits are related to major lineaments. This was a retrospective observation that established the relation for known deposits. The subsequent prospective use of the relation in mineral exploration is exemplified in the discovery of the giant lineament-related Olympic Dam Cu-U-Au deposit at Roxby Downs, South Australia. Major Australian examples of the lineament-ore relation are described in comparison with apparently similar relations in North America, and these are briefly considered in regional and global contexts.

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The Genesis of the Giant Shuangjianzishan Epithermal Ag-Pb-Zn Deposit, Inner Mongolia, Northeastern China

Economic Geology ◽

10.5382/econgeo.4695 ◽

2020 ◽

Vol 115 (1) ◽

pp. 101-128 ◽

Cited By ~ 2

Author(s):

Degao Zhai ◽

Anthony E. Williams-Jones ◽

Jiajun Liu ◽

David Selby ◽

Panagiotis C. Voudouris ◽

...

Keyword(s):

Ore Deposits ◽

Northeastern China ◽

Granite Porphyry ◽

Time Interval ◽

Short Time Interval ◽

Sulfur Source ◽

Weighted Mean ◽

Ore Minerals ◽

Porphyry Intrusion

Abstract The newly discovered Shuangjianzishan Ag-Pb-Zn deposit, with 145 Mt of ore grading 128.5 g/t Ag (locally up to 32,000 g/t) and 2.2 wt % Pb + Zn, is located in the Great Hinggan Range metallogenic belt, northeastern China, and is currently the largest Ag deposit in Asia. The Ag-Pb-Zn orebodies occur as veins and are hosted primarily by a Permian slate. Recent drilling and core logging have identified a partially Mo mineralized granite porphyry intrusion adjacent to the Ag-Pb-Zn mineralized veins. This well-preserved magmatic-hydrothermal system therefore offers an excellent opportunity to evaluate the possible temporal and genetic relationship between Mo-mineralized porphyry intrusions and Ag-Pb-Zn veins. Three primary paragenetic stages of veining have been recognized: (I) early pyrite + quartz ± K-feldspar, (II) main ore sulfide + sulfosalt + quartz + calcite + sericite + chlorite ± epidote, and (III) post-ore quartz. The silver mineralization occurs mainly in the late paragenetic part of Stage II, in which canfieldite (Ag8SnS6), argentite (Ag2S) and freibergite [(Ag, Cu)12Sb4S13] are the dominant Ag-bearing ore minerals. A combination of ore mineral chemical and sulfur isotope geothermometers and physicochemical calculations suggest that the Ag-Pb-Zn mineralization took place at a temperature of 250° to 200°C, a pH of 6.7 to 5.6, and a Δlogfo2 (HM) of –2.4 to –8.7. A conspicuous enrichment of Sn and Se in the ore, which is represented by minerals containing the metal suite Ag-Pb-Zn-(Cu-Sn-Se-Sb), likely reflects a close genetic association between the base metal mineralization and a magma. In situ analyses show that the δ34S values of the sulfides and Ag-bearing sulfosalts from the Ag-Pb-Zn mineralized veins vary from –4.67 to +2.44‰; the mean value is –2.11 ± 1.49‰ (n = 77). The calculated mean δ34SH2S value of the ore-forming fluid is –1.65 ± 0.83‰, which is indicative of a magmatic sulfur source. In situ Pb isotope analyses of the ore minerals yielded a narrow range of values (206Pb/204Pb of 18.243–18.310, 207Pb/204Pb of 15.503–15.563 and 208Pb/204Pb of 38.053–38.203, n = 59). Comparisons to corresponding isotopic data for the various rock units in the area and sulfides from nearby ore deposits indicate that there were substantial contributions of Pb and other metals (e.g., Ag and Zn) to the Shuangjianzishan deposit from a Mesozoic granitic source. Diorite-granodiorite dikes and dacite are crosscut by the Ag-Pb-Zn veins, and therefore, predate ore formation. These rock units have zircon U-Pb ages of 250.2 ± 2.0 and 133.9 ± 1.4 Ma, respectively. A concealed, weakly Mo mineralized granite porphyry intrusion proximal to the Ag-Pb-Zn mineralized vein system yielded zircon U-Pb ages of 134.4 ± 1.0 (MSWD = 0.1) and 134.4 ± 1.0 Ma (MSWD = 0.2), for coarse- and fine-grained facies, respectively. These ages are indistinguishable within the uncertainty from the zircon ages for the dacite and a granite intrusion ~2 km north of the mineralized veins, which has a weighted mean zircon U-Pb age of 135.2 ± 1.4 Ma (MSWD = 0.78). Molybdenite from three quartz vein/veinlet samples hosted by slate immediately above the porphyry intrusion yielded Re-Os model ages from 136.3 ± 0.9 to 133.7 ± 1.2 Ma and a weighted mean Re-Os age of 134.9 ± 3.4 Ma. Finally, three pyrite samples separated from the Ag-Pb-Zn mineralized veins have a weighted mean Re-Os model age of 135.0 ± 0.6 Ma. The very similar zircon U-Pb ages for the Mo-mineralized granite porphyry and dacite, and Re-Os ages for molybdenite and pyrite in the Shuangjianzishan ore district indicate that the Mesozoic magmatic-hydrothermal activity was restricted to a relatively short time interval (~136–133 Ma). They also suggest that the weakly Mo mineralized granite porphyry was likely the source of the fluids and metals that produced the Ag-Pb-Zn mineralization. Based on our geological observations and an extensive analytical database, a model is proposed for the genesis of the giant Shuangjianzishan Ag-Pb-Zn deposit in which the ore-forming fluid and its metals (i.e., Ag, Pb, and Zn) were exsolved during crystallization of the final phase of a composite granite porphyry intrusion. This fluid transported metals to the distal parts of the system, where they were deposited in preexisting faults or fractures created by the withdrawal of magma during the waning stages of the magmatic-hydrothermal event. The present study of the Shuangjianzishan Ag-Pb-Zn deposit and those of other magmatic-hydrothermal ore deposits in the region provide compelling evidence that the widespread Mesozoic felsic magmatism and Ag-Pb-Zn mineralization in the southern Great Hinggan Range took place in an intracontinental extensional tectonic setting, which was synchronous with, and spatially associated to, Paleo-Pacific slab rollback and lithospheric delamination and thinning.

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