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

Geophysics ◽  
1989 ◽  
Vol 54 (2) ◽  
pp. 158-170 ◽  
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.

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

2020 ◽  
Vol 115 (8) ◽  
pp. 1855-1870 ◽  
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.

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

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 61 ◽  
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.

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

Minerals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 311 ◽  
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.

Observations of the lineament-ore relation

1986 ◽  
Vol 317 (1539) ◽  
pp. 195-218 ◽  
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.

HEAT FLOW IN A “BLIND” GEOTHERMAL AREA NEAR MARYSVILLE, MONTANA

Geophysics ◽  
1973 ◽  
Vol 38 (5) ◽  
pp. 941-956 ◽  
Author(s):  
David D. Blackwell ◽  
Czang‐Go Baag
Keyword(s):  
Heat Flow ◽  
Magma Chamber ◽  
Mineral Exploration ◽  
High Heat ◽  
Geothermal Area ◽  
High Heat Flow ◽  
Thermal Fluids ◽  
Continental Divide ◽  
Drill Holes ◽  
Anomalous Heat

A unique geothermal area has been discovered during the course of a regional heat‐flow study using holes drilled for mineral exploration. There are no surface manifestations of abnormal subsurface temperature in spite of the fact that at one locality a temperature of 58°C was measured at a depth of only 220 m. The area of anomalous heat flow straddles the Continental Divide near the old gold mining camp of Marysville, Montana about 30 km northwest of Helena. Measured values of conducted heat flow range from 3.2 to [Formula: see text] sec. The immediate source of the high heat flow is either an unexposed reservoir of thermal fluids or a very shallow still‐cooling magma chamber. At the present time the magma chamber model is preferred. The presence of additional similar areas in the western U.S. is suggested by the data from regional heat‐flow studies. However, in most of the other areas only single anomalous heat‐flow value is available, whereas at Marysville a region of several tens of [Formula: see text] is known to have abnormal heat‐flow values. It is suggested that temperature measurements should be made in available drill holes deeper than 30 m in the high heat‐flow regions of the western U.S. as an inexpensive way to explore for other “blind” geothermal reservoirs.

scholarly journals Staged formation of the supergiant Olympic Dam uranium deposit, Australia

Geology ◽  
2021 ◽  
Author(s):  
Kathy Ehrig ◽  
Vadim S. Kamenetsky ◽  
Jocelyn McPhie ◽  
Edeltraud Macmillan ◽  
Jay Thompson ◽  
...  
Keyword(s):  
Uranium Deposit ◽  
South Australia ◽  
Ore Deposits ◽  
Ore Deposit ◽  
Timing Information ◽  
Ore Minerals ◽  
Extreme Metal ◽  
Two Stages ◽  
Olympic Dam

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.

An anomalous heat flow layer at London, Ontario

1967 ◽  
Vol 3 ◽  
pp. 167-170 ◽  
Author(s):  
A.S. Judge ◽  
A.E. Beck
Keyword(s):  
Heat Flow ◽  
Anomalous Heat

scholarly journals Heat Flow, Geotherms, Density and Lithosphere Thickness in SW of Iberia (South of Portugal)

2018 ◽  
Vol 1 (1) ◽  
pp. 18-22 ◽  
Author(s):  
Maria Rosa Alves Duque
Keyword(s):  
Heat Flow ◽  
Thermal Structure ◽  
Average Density ◽  
Ore Deposits ◽  
Flow Density ◽  
The South ◽  
Lithosphere Thickness ◽  
Structure Density ◽  
Using Data ◽  
Lateral Variations

Thermal structure, density distribution and lithosphere thickness in the SW part of the Iberian Peninsula are studied using data obtained in the South Portuguese Zone (SPZ) and SW border of the Ossa Morena Zone (OMZ) in the South of Portugal. Five different regions were defined, and models were built for each region. Geotherms were obtained using average density values from data published. The high values of heat flow density in these regions are attributed to occurrence of anomalous heat sources due to radioactivity content and exothermic chemical reactions associated to ore deposits in the zone. The results obtained with models based on isostasy in the region led to lithosphere thickness values between 95 and 96 km in the SPZ and a lower value of 94.5 km in the SW border of the OMZ. Analysis of geotherms shows lateral variations of temperature at the same depth. These lateral variations are compared with information obtained with seismic data.

The ecology of sympatric scincid lizards (Ctenotus) in arid South Australia

1998 ◽  
Vol 46 (6) ◽  
pp. 617 ◽  
Author(s):  
J. L. Read
Keyword(s):  
Home Range ◽  
Environmental Conditions ◽  
Plant Material ◽  
Reproductive Effort ◽  
Arid Zone ◽  
South Australia ◽  
Early Summer ◽  
Home Ranges ◽  
Local Species ◽  
Olympic Dam

Ctenotus skinks are the most diverse and abundant diurnal reptile genus at Olympic Dam, in the South Australian arid zone. The home range, demography, reproduction and diet of five syntopic Ctenotus species was studied over a 6-year period in chenopod shrubland. Longevity frequently exceeded three years in C. regius, four years in C. schomburgkii and five years in C. leonhardii, with a 7-year-old specimen of C. leonhardii being recorded. Females of most species tended to be larger and lived longer than males. Two eggs were typically laid by each species in early summer. Annual reproductive effort, particularly in C. leonhardii, varied considerably depending upon the prevailing environmental conditions. All local species apparently occupied home ranges, with maximum recapture radii in different species of 40–60 m. Ctenotus appear to be unspecialised insectivores, although plant material and lizards are sometimes eaten by the larger species.

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