135 research outputs found
The Wirrda Well and Acropolis prospects, Gawler Craton, South Australia: insights into evolving fluid conditions through apatite chemistry
No full textAbstract not availableSasha Krneta, Nigel J. Cook, Cristiana L. Ciobanu, Kathy Ehrig, Alkis Kontonikas-Charo
Destabilisation of titanite in the Roxby Downs Granite surrounding the Olympic Dam Fe-oxide Cu-U-Au-Ag deposit
No full textAlkiviadis Kontonikas-Charos, Kathy Ehrig, Nigel J. Cook, Cristiana L. Cioban
Neubau Atmospheres: East German Cultural Remediations of Modernist Architecture
No full textThe artistic potential modern, urban housing (“Neubau”) offered to writers and directors in East Germany from the 1960s to 1980s remains underexplored. Neubau Atmospheres seeks to bridge that gap by providing an incisive analysis of East German cinematic, literary, and architectural case studies, highlighting how the modernist housing of the GDR provided a potent vehicle for mediating the emotional and social experience of its denizens. Considering how these cinematic and literary representations focalized ideas of class, gender, and age, author Stephan Ehrig makes a compelling case for viewing this engagement with the urban environment as a cultural genre in its own right
Chemical zoning and lattice distortion in uraninite from Olympic Dam, South Australia
No full textCompositionally zoned uraninite from the Olympic Dam iron oxide-copper-gold deposit is rarely preserved, but represents an early product of in situ transformation of primary uraninite. Electron backscatter diffraction data (inverse pole figure, image quality, and grain reference orientation deviation mapping) reveal formation of zoned uraninite to be the result of a sequence of superimposed effects rather than from primary growth mechanisms alone. This is the first known microstructural analysis of uraninite showing crystal-plastic deformation of uraninite via formation and migration of defects and dislocations into tilt boundaries. Defining grain-scale characteristics and microstructural features in radiogenically modified minerals like uraninite carries implications in better understanding the processes involved in their formation, highlights limitations in the use of uraninite for U-Pb chemical ages, as well as for constraining the incorporation and release of daughter radioisotopes, especially where zoning, porosity, fractures, and microstructures are present.Edeltraud Macmillan, Cristiana L. Ciobanu, Kathy Ehrig, Nigel J. Cook, and Allan Prin
Mafic mineral clots and microgranular enclaves in A-type Hiltaba Suite granites from the Gawler Craton, South Australia: Origins and implications
No full textThe origins of mafic mineral clots and microgranular enclaves in Mesoproterozoic granites were investigated in a case study of felsic A-type Hiltaba Suite granites from the Gawler Craton, South Australia. Mafic mineral clots display interlocked textures comprising plagioclase, amphibole, biotite, apatite and magnetite and occur interstitial to coarse rapakivi feldspar, compositionally zoned plagioclase, and quartz phenocrysts. The microgranular enclaves, which may be partly disaggregated, are rounded, contain partially resorbed K-feldspar xenocrysts and have a similar mineralogy to the clots. Whole-rock geochemistry, mineral chemistry and textural features (e.g., rapakivi and granophyric textures, quartz-amphibole ocelli, multiple generations of biotite, xenocrysts, evidence of undercooling) indicate that mineral clots and enclaves may have similar origins and were sourced via multistage magma mixing. Magma rejuvenation caused mingling with a partially crystalline and ductile mush resulting in the formation of microgranular mafic enclaves which contain numerous xenocrysts. Prolonged input of mafic magma and elevated F within the residual melt promoted partial disaggregation of enclaves and recrystallization of mineral clots. Geochemically distinct biotite generations show this evolution from initially Fpoor annite to F-rich phlogopite dispersed throughout mineral clots and as ‘free’ grains within the Hiltaba Suite granites. Annite-bearing mineral clots formed at higher pressures than phlogopite clots, corresponding to crystallization at greater depths. The abundance of Cu and S in mineral clots and enclaves within Hiltaba Suite granite studied here indicates that repeated magma mixing processes may have provided a source of metals for the formation of the nearby Olympic Dam Fe-oxide Cu-U-Au-Ag deposit.Alkiviadis Kontonikas-Charos, Kathy Ehrig, Nigel J. Cook, Cristiana L. Cioban
Replacement of uraninite by bornite via coupled dissolution-reprecipitation: Evidence from texture and microstructure
No full textThe occurrence and nature of rhythmically intergrown crystals of uraninite and bornite from the Olympic Dam iron oxide-copper-gold (IOCG)-U-Ag deposit, South Australia, is reported. Distinct zones within primary, euhedral uraninite crystals have been replaced by bornite and minor fluorite leaving a skeleton of uraninite, infilled with these minerals. The partially replaced uraninite crystals are always closely associated with locally abundant bornite and fluorite. The textural features of the intergrowth are consistent with partial replacement of uraninite by bornite via a coupled dissolution-reprecipitation reaction driven by a F-rich and Cu-Fe-sulfide-bearing hydrothermal fluid rather than a form of oscillatory growth or exsolution from a U–Cu–Fe–S solid solution. The crystallographic relationship between the parent uraninite and the daughter bornite and fluorite were explored by electron backscattered diffraction, as all three minerals share common crystal structural features, despite their chemical diversity. Generally speaking, the crystallographic orientation of the uraninite parent is initially inherited by the replacing bornite, but later the orientation of the bornite changes.Edeltraud Macmillan, Cristiana L. Ciobanu, Kathy Ehrig, Nigel J. Cook, Allan Prin
Trace elements in minerals: where do we stand on the road between the Holy Grail and a can of worms?
No full textAccelerating advances in analytical technologies enable the study of trace elements in minerals at ever improving sensitivity and spatial resolutions. Trace element concentration data are increasingly used to support petrogenetic interpretations, constraining ore-forming conditions, and development of distribution models for potentially valuable minor ore components. Although many datasets for minerals from mineral deposits of different types have been published, there is a growing recognition that without ultra-careful multi-technique characterization of the analyzed material, interpretations of the observed trace element patterns may be questionable. Nanoscale studies have shown that commonly held assumptions about the state of elements in minerals do not always hold true and that fluid- assisted reaction may drive nano- to micron-scale trace element remobilizationNigel J Cook, Cristiana L. Ciobanu, Max R. Verdugo-Ihl, Liam Courtney-Davies, Kathy Ehrig, Wei Li, Wenyuan Liu, Jing X
Rare earth element behaviour in apatite from the olympic dam Cu–U–Au–Ag deposit, South Australia
No full textApatite is a common magmatic accessory in the intrusive rocks hosting the giant ~1590 Ma Olympic Dam (OD) iron-oxide copper gold (IOCG) ore system, South Australia. Moreover, hydrothermal apatite is a locally abundant mineral throughout the altered and mineralized rocks within and enclosing the deposit. Based on compositional data for zoned apatite, we evaluate whether changes in the morphology and the rare earth element and Y (REY) chemistry of apatite can be used to constrain the fluid evolution from early to late hydrothermal stages at OD. The ~1.6 Ga Roxby Downs granite (RDG), host to the OD deposit, contains apatite as a magmatic accessory, locally in the high concentrations associated with mafic enclaves. Magmatic apatite commonly contains REY-poor cores and REY-enriched margins. The cores display a light rare earth element (LREE)-enriched chondrite-normalized fractionation pattern with a strong negative Eu anomaly. In contrast, later hydrothermal apatite, confined to samples where magmatic apatite has been obliterated due to advanced hematite-sericite alteration, displays a conspicuous, convex, middle rare earth element (MREE)-enriched pattern with a weak negative Eu anomaly. Such grains contain abundant inclusions of florencite and sericite. Within high-grade bornite ores from the deposit, apatite displays an extremely highly MREE-enriched chondrite-normalized fractionation trend with a positive Eu anomaly. Concentrations of U and Th in apatite mimic the behaviour of ∑REY and are richest in magmatic apatite hosted by RDG and the hydrothermal rims surrounding them. The shift from characteristic LREE-enriched magmatic and early hydrothermal apatite to later hydrothermal apatite displaying marked MREE-enriched trends (with lower U, Th, Pb and ∑REY concentrations) reflects the magmatic to hydrothermal transition. Additionally, the strong positive Eu anomaly in the MREE-enriched trends of apatite in high-grade bornite ores are attributable to alkaline fluid conditions.Sasha Krneta, Cristiana L. Ciobanu, Nigel J. Cook, Kathy Ehrig and Alkis Kontonikas-Charo
Coupled Microstructural EBSD and LA-ICP-MS Trace Element Mapping of Pyrite Constrains the Deformation History of Breccia-Hosted IOCG Ore Systems
No full textElectron backscatter diffraction (EBSD) methods are used to investigate the presence of microstructures in pyrite from the giant breccia-hosted Olympic Dam iron–oxide copper gold (IOCG) deposit, South Australia. Results include the first evidence for ductile deformation in pyrite from a brecciated deposit. Two stages of ductile behavior are observed, although extensive replacement and recrystallization driven by coupled dissolution–reprecipitation reaction have prevented widespread preservation of the earlier event. Laser ablation inductively coupled plasma mass spectrometry (LAICP-MS) element maps of pyrite confirm that many pyrite grains display compositional zoning with respect to As, Co, and Ni, but that the zoning is often irregular, patchy, or otherwise disrupted and are readily correlated with observed microstructures. The formation of ductile microstructures in pyrite requires temperatures above ~260 ◦C, which could potentially be related to heat from radioactive decay and fault displacements during tectonothermal events. Coupling EBSD methods with LA-ICP-MS element mapping allows a comprehensive characterization of pyrite textures and microstructures that are otherwise invisible to conventional reflected light or BSE imaging. Beyond providing new insights into ore genesis and superimposed events, the two techniques enable a detailed understanding of the grain-scale distribution of minor elements. Such information is pivotal for efforts intended to develop new ways to recover value components (precious and critical metals), as well as remove deleterious components of the ore using low-energy, low-waste ore processing methods.Samuel Anthony King, Nigel John Cook, Cristiana Liana Ciobanu, Kathy Ehrig, Yuri Tatiana Campo Rodriguez, Animesh Basak, and Sarah Gilber
Chemical and textural interpretation of late-stage coffinite and brannerite from the Olympic Dam IOCG-Ag-U deposit
No full textThe Olympic Dam iron-oxide copper-gold-silver-uranium deposit, South Australia, contains three dominant U minerals: uraninite; coffinite; and brannerite. Microanalytical and petrographic observations provide evidence for an interpretation in which brannerite and coffinite essentially represent the products of U mineralizing events after initial deposit formation at 1.6 Ga. Marked compositional and textural differences between the various types of brannerite and coffinite highlight the role of multiple stages of U dissolution and reprecipitation. On the basis of petrography (size, habit, textures and mineral associations) and compositional variation, brannerites are divided into four distinct groups (brannerite-A, -B, -C and -D), and coffinite into three groups (coffinite-A, -B and -C). Brannerite-A ranges in composition from what is effectively uraniferous rutile to stoichiometric brannerite, and has elevated (Mg +Mn + Na + K) and (Fe + Al) compared to other brannerite types. It displays the most diverse range of morphologies, including complex irregular-shaped aggregates, replacement bands, and discrete elongate seams. The internal structure of brannerite-A consists of randomly-oriented hair-like needles and blades. Brannerite-B (>5 μm in size) is generally prismatic and typically associated with baryte and REY minerals (REE+Y= REY). Brannerite-C and -D are both associated with Cu-(Fe)-sulfides and are typically composed of irregular masses and blebs (10–50 μm in size) with a more uniform or massive internal structure. Brannerite-D is distinct from -C and always contains inclusions of galena. Brannerite-B to -D all contain elevated ΣREY, with brannerite-B and -C having elevated As, and brannerite-D having elevated Nb. All coffinite is typically globular (each globule is 2–10 μm in size) to collomorphic in appearance. Coffinite-A ranges from discrete globules to collomorphic bands completely encompassing quartz. Coffinite-B is always found with uraninite, and includes collomorph coffinite enveloped by massive uraninite, as well as aureoles of coffinite on the margins of uraninite crystals. Coffinite-C is associated with brannerite and REY minerals. The majority of coffinite is heterogeneous. Brannerite and coffinite have probably precipitated as part of a late-stage hydrothermal U-event, which might have involved the dissolution and/or reprecipitation of earlier precipitated uraninite, or could represent the products of a later U mineralizing event. Evidence which supports formation of late-stage coffinite and brannerite includes: (1) low-Pb contents of both minerals; (2) coffinite is commonly found on the edges of uraninite, implying later deposition; and (3) coffinite is often found on the edge of brannerite aggregates, suggestive of brannerite precipitation occurred before coffinite. Moreover, there are many features (e.g. banding, scalloped edges, alteration rinds, variable compositions etc.) indicative of hydrothermal alteration processes.Edeltraud Macmillan, Nigel J. Cook, Kathy Ehrig and Allan Prin
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