Stable carbon isotopes as indicators for micro-geomorphic changes in palsa peats

Palsa peats are unique northern ecosystems formed under an arctic climate and characterized by a high biodiversity and sensitive ecology. The stability of the palsas are seriously threatened by climate warming which will change the permafrost dynamic and induce a degradation of the mires. We used stable carbon isotope depth profiles in two palsa mires of Northern Sweden to track environmental change during the formation of the mires. Soils dominated by aerobic degradation can be expected to have a clear increase of carbon isotopes (δ13C) with depth, due to preferential release of 12C during aerobic mineralization. In soils with suppressed degradation due to anoxic conditions, stable carbon isotope depth profiles are either more or less uniform indicating no or very low degradation or depth profiles turn to lighter values due to an enrichment of recalcitrant organic substances during anaerobic mineralisation which are depleted in 13C. The isotope depth profile of the peat in the water saturated depressions (hollows) at the yet undisturbed mire Storflaket indicated very low to no degradation but increased rates of anaerobic degradation at the Stordalen site. The latter might be induced by degradation of the permafrost cores in the uplifted areas (hummocks) and subsequent breaking and submerging of the hummock peat into the hollows due to climate warming. Carbon isotope depth profiles of hummocks indicated a turn from aerobic mineralisation to anaerobic degradation at a peat depth between 4 and 25 cm. The age of these turning points was 14C dated between 150 and 670 yr and could thus not be caused by anthropogenically induced climate change. We found the uplifting of the hummocks due to permafrost heave the most likely explanation for our findings. We thus concluded that differences in carbon isotope profiles of the hollows might point to the disturbance of the mires due to climate warming or due to differences in hydrology. The characteristic profiles of the hummocks are indicators for micro-geomorphic change during permafrost up heaving

Detection of trace elements/isotopes in Olympic Dam copper concentrates by nanoSIMS

Many analytical techniques for trace element analysis are available to the geochemist and geometallurgist to understand and, ideally, quantify the distribution of trace and minor components in a mineral deposit. Bulk trace element data are useful, but do not provide information regarding specific host minerals—or lack thereof, in cases of surface adherence or fracture fill—for each element. The CAMECA nanoscale secondary ion mass spectrometer (nanoSIMS) 50 and 50L instruments feature ultra-low minimum detection limits (to parts-per-billion) and sub-micron spatial resolution, a combination not found in any other analytical platform. Using ore and copper concentrate samples from the Olympic Dam mining-processing operation, South Australia, we demonstrate the application of nanoSIMS to understand the mineralogical distribution of potential by-product and detrimental elements. Results show previously undetected mineral host assemblages and elemental associations, providing geochemists with insight into mineral formation and elemental remobilization—and metallurgists with critical information necessary for optimizing ore processing techniques. Gold and Te may be seen associated with brannerite, and Ag prefers chalcocite over bornite. Rare earth elements may be found in trace quantities in fluorapatite and fluorite, which may report to final concentrates as entrained liberated or gangue-sulfide composite particles. Selenium, As, and Te reside in sulfides, commonly in association with Pb, Bi, Ag, and Au. Radionuclide daughters of the 238U decay chain may be located using nanoSIMS, providing critical information on these trace components that is unavailable using other microanalytical techniques. These radionuclides are observed in many minerals but seem particularly enriched in uranium minerals, some phosphates and sulfates, and within high surface area minerals. The nanoSIMS has proven a valuable tool in determining the spatial distribution of trace elements and isotopes in fine-grained copper ore, providing researchers with crucial evidence needed to answer questions of ore formation, ore alteration, and ore processing.Mark Rollog, Nigel J. Cook, Paul Guagliardo, Kathy Ehrig, Cristiana L. Ciobanu and Matt Kilbur

Intermobility of barium, strontium, and lead in chloride and sulfate leach solutions

Production of radionuclide-free copper concentrates is dependent on understanding and controlling the deportment of daughter radionuclides (RNs) produced from 238U decay, specifically 226Ra, 210Pb, and 210Po. Sulfuric acid leaching is currently employed in the Olympic Dam processing plant (South Australia) to remove U and fluorine from copper concentrates prior to smelting but does not adequately remove the aforementioned RN. Due to chemical similarities between lead and alkaline earth metals (including Ra), two sets of experiments were designed to understand solution interactions between Sr, Ba, and Pb at various conditions. Nanoscale secondary ion mass spectrometry (NanoSIMS) isotopic spatial distribution maps and laser ablation inductively coupled-plasma mass spectrometry transects were performed on laboratory-grown crystals of baryte, celestite, and anglesite which had been exposed to different solutions under different pH and reaction time conditions. Analysis of experimental products reveals three uptake mechanisms: overgrowth of nearly pure SrSO4 and PbSO4 on baryte; incorporation of minor of Pb and Ba into celestite due to diffusion; and extensive replacement of Pb by Sr (and less extensive replacement of Pb by Ba) in anglesite via coupled dissolution-reprecipitation reactions. The presence of H2SO4 either enhanced or inhibited these reactions. Kinetic modelling supports the experimental results, showing potential for extrapolating the (Sr, Ba, Pb)SO4 system to encompass RaSO4. Direct observation of grain-scale element distributions by nanoSIMS aids understanding of the controlling conditions and mechanisms of replacement that may be critical steps for Pb and Ra removal from concentrates by allowing construction of a cationic replacement scenario targeting Pb or Ra, or ideally all insoluble sulfates. Experimental results provide a foundation for further investigation of RN uptake during minerals processing, especially during acid leaching. The new evidence enhances understanding of micro- to nanoscale chemical interactions and not only aids determination of where radionuclides reside during each processing stage but also guides development of flowsheets targeting their removal.Mark Rollog, Nigel J. Cook, Paul Guagliardo, Kathy Ehrig, Sarah E. Gilbert and Matt Kilbur

Radionuclide-bearing minerals in Olympic Dam copper concentrates

Olympic Dam hosts >80 million tonnes of copper, as copper‑iron sulphides, within hematite-dominant gangue. Processing of the relatively fine-grained copper ore is complicated by the presence of by-product uranium and its radiogenic isotopes, in particular ²²⁶Ra, ²¹⁰Pb and ²¹⁰Po, which partially recover to the final copper sulphide concentrates. Although the majority (~85%) of the U-bearing minerals (uraninite, coffinite, brannerite, thorianite, thorite) are recovered to flotation tailings, the remaining ~15% occurs in copper concentrates as sulphide-gangue composite particles and micron- to nanoscale grains occluded within sulphide minerals. Sulphuric acid leaching of copper concentrates significantly reduces the concentration of U but has only a minor impact on the daughter isotopes. Further reduction of these isotopes may be achieved through selective targeting and removal of specific minerals known to be radionuclide (RN) hosts, but fine-grained, micro- to nanoscale ore textures preclude easy direct identification of these RN host phases. Nanoscale secondary ion mass spectrometry (nanoSIMS) has proven to be an excellent platform for in situ mapping of ultra-trace RN distributions, with sub-micron spatial resolution, in individual mineral grains. Uranium and thorium minerals are, as expected, the major hosts and display significant concentrations of the entire ²³⁸U decay chain. Although the majority of these minerals are removed via acid leaching of copper concentrate, sufficient RNs remain in the concentrate as micron- to nanoscale grains within sulphides and gangue minerals or along particle microfractures. Results show that brannerite, potentially more problematic due to its lower solubility in sulphuric acid than uraninite, does not appear to contain appreciable amounts of daughter isotopes. The insolubility of ThPO₄ produces the potential for sequestration of ²³²Th and ²³⁰Th in rare earth phosphates such as xenotime, which then retain the respective decay chains. Likewise, the insolubility of certain sulphates (Sr, Ba, Pb, Ra) provides a mechanism for precipitation and entrapment of RNs. Baryte was shown to accumulate Ra and Pb naturally in the deposit, and it can upgrade its RN content substantially during sulphuric acid leaching through coupled dissolution-reprecipitation mechanisms involving Pb²⁺ and Ra²⁺ liberated from dissolved uranium minerals. Identification and prioritization of RN host minerals is crucial for the development of a more efficient processing flowsheet.Mark Rollog Nigel J. Cook, Paul Guagliardo, Kathy J. Ehrig, Matt Kilbur

Rapid, competitive radium uptake in strontium, barium, and lead sulfates during sulfuric acid leaching

Uranium- and thorium-bearing base metal mineral deposits contain daughter radionuclides which must be monitored and preferably removed or reduced during the process of generating base metal sulfide concentrates. Understanding the behavior of these radionuclides (focusing on 226Ra in this study) is critical for minimizing their concentrations in final economic products. To this end, Ra uptake into Sr, Ba, and Pb sulfates was evaluated experimentally under various conditions, including those approximating processing plant environments. Lead activity was also monitored, as 210Pb is also a radionuclide of concern. To simplify experiments, synthetic crystals of celestine (SrSO4), baryte (BaSO4), and anglesite (PbSO4) were grown in silica gel and subsequently exposed to RaCl2 solution at both low and neutral pH, for both 40 and 210 h. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) transects were performed across the grains to determine uptake of Ra (as well as trace Sr, Ba, and Pb) in the sulfates. Results indicate that Ra uptake in celestine is efficient when Ba and Pb are absent but is reduced to nearly zero when competing with baryte and anglesite. High acid sulfate activity inhibits uptake. Baryte incorporates significant Ra under all conditions. Anglesite is affected by coupled dissolution-reprecipitation mechanisms, resulting in dissolution of PbSO4 followed by precipitation of a mixed (Pb,Ba,Sr,Ra)SO4 phase in its place. Again, high sulfate activity inhibits this reaction. With this knowledge, it may be possible for process engineers to purposefully stimulate precipitation of Ra (and possibly Pb) onto a sulfate matrix, given the right conditions. Precipitation of RaSO4 (and 210PbSO4) onto a removable phase during processing would result in sulfide concentrates with natural background concentrations of radionuclides. Results from this study, including semi-quantitative Ra concentration data obtained via in situ LA-ICP-MS analysis add to data pertinent to management of Ra in boiler scales, oil and gas pipelines, environmental remediation, nuclear medicine, nuclear fuel processing and waste storage, among other industrial and research applications.Mark Rollog, Nigel J. Cook, Kathy Ehrig, Sarah E. Gilber

In situ spatial distribution mapping of radionuclides in minerals by nanoSIMS

Published online November 19, 2018The nanoSIMS (nanometre-resolution secondary ion mass spectrometry) microanalytical platform is used, for the first time, for direct in situ visualization of medium half-life radionuclide (RN) distributions (²²⁶Ra – 1602y; ²¹⁰Pb – 22.3y) in copper sulphide-bearing ore and copper sulphide flotation concentrate samples. More than 200 grains have been mapped, all with an Hyperion (H200) RF plasma oxygen ion source. Sufficient counts for masses of interest allowed the generation of maps that stand as a proof of concept for further detailed work to address the physical locations of radionuclides of main interest. The issue of potential isobaric interfering masses has been addressed and partially resolved. The distribution of the studied radionuclides, both in relation to host minerals and in relation to each other, is logical and clearly supported by well-established theories of deportment, diffusion, and redistribution. Isotope maps for ²¹⁰RN (²¹⁰Pb, ²¹⁰Po and ²¹⁰Bi) and ²²⁶Ra maps tended to show RN distribution either within minerals (evenly distributed or zoned), as ‘hot spots’ on grain surfaces/mineral boundaries, or between cleavage planes of micaceous minerals. NanoSIMS element mapping of radionuclides may have widespread application for the disposal and long-term storage of nuclear waste, radioisotope monitoring, forensic science, nuclear and materials science, nuclear medicine, minerals engineering, and isotope geochemistry.Mark Rollog, Nigel J. Cook, Paul Guagliardo, Kathy Ehrig & Matt Kilbur

Radionuclide distributions in Olympic Dam copper concentrates: the significance of minor hosts, incorporation mechanisms, and the role of mineral surfaces

Some iron oxide-copper-gold (IOCG) deposits contain variable amounts of uranium. Developing mineral deportment models for the radiogenic isotopes resulting from decay of ²³⁸U presents a singular technical challenge, as concentrations of ²²⁶Ra, ²¹⁰Pb, and ²¹⁰Po fall far below the detection limits achievable for most in situ analytical methodologies. The nanoscale secondary ion mass spectrometry (nanoSIMS) platform combines low detection limits with sub-micron resolution, revealing previously unseen spatial distribution patterns of radionuclides (RNs) in (and on) particles of copper sulphide concentrates. Many potential host minerals for these radionuclides can be readily predicted based on chemical behaviour, periodic table trends, and published studies documenting likely host minerals. Using nanoSIMS data for ores and metallurgical products from the Olympic Dam IOCG deposit and associated processing facilities, we present compelling evidence for the ability of certain minerals within the copper concentrates to host daughter radionuclides derived from uranium decay. Many of these minerals had not traditionally been considered or previously documented as such. These include high-abundance minerals hosting low concentrations of radionuclides, and several relatively low abundance minerals exhibiting remarkable radionuclide enrichment. Rutile, fluorapatite, fluorite, hematite, zircon, covellite, and molybdenite are all proven to be minor hosts of at least some members of the ²³⁸U decay chain, and are, collectively, important for establishing the overall RN budget. Surface effects are found to play a significant role, with elevated levels of ²²⁶Ra and ²¹⁰Pb found on most available surfaces, irrespective of mineral, in acid-leached concentrate. Some rRNs, particularly ²²⁶Ra and ²¹⁰Pb liberated from uranium minerals during sulphuric acid leaching, can become extensively redistributed throughout the concentrate, creating newly-formed RN hosts. This new mineralogical deportment information can be used in developing new flowsheets to enhance radionuclide removal without a corresponding loss of Cu. NanoSIMS has proven invaluable for elucidating the mineral-scale deportment of ultra-trace radionuclides throughout the processing circuit at Olympic Dam.Mark Rollog, Nigel J. Cook, Paul Guagliardo, Kathy Ehrig, Matt Kilbur

Uptake of trace elements by baryte during copper ore processing: a case study from Olympic Dam, South Australia

Baryte is a common gangue mineral in many ore systems. Here, we report on a study of baryte chemistry in samples of ore and processing materials (flotation feed, flotation concentrate, flotation tailings, concentrate leach discharge, and tailings leach discharge) from the Olympic Dam Cu-U-Au-Ag deposit, South Australia. Elements that commonly substitute for Ba in the baryte lattice, including Sr and Ca, are measured in variable concentrations reflecting grain-scale zonation and heterogeneity at the scale of the deposit but appear unaffected during processing. Variation in the concentration of some other elements, notably Cu, reflect both the heterogeneous nature of flotation feed and the intimately intergrown character of the sulfide-sulfate assemblage. Measured Pb concentrations in baryte progressively increase during processing from flotation feed to flotation concentrate, and particularly in concentrate leach discharge. Such data suggest that, during sulfuric acid leaching, baryte contained within the concentrate is able to incorporate quantities of Pb that have been mobilized during break-down of Pb-bearing minerals (notably U-minerals containing radiogenic lead). This takes place via surface adsorption followed by rapid coupled dissolution-replacement driven incorporation throughout the grain. Results suggest that baryte may scavenge non-target elements during processing and contribute to an understanding of mobility, mineralogical location, and evolution in the deportment of radionuclides through the processing cycle.Danielle S. Schmandt, Nigel J. Cook, Kathy Ehrig, Sarah Gilbert, Benjamin P. Wade, Mark Rollog, Cristiana L. Ciobanu, Vadim S. Kamenetsk

Baseline bioavailable strontium and oxygen isotope mapping of the Adelaide Region, South Australia

Strontium and oxygen isotopes provide a useful method for provenancing bioapaties, such as teeth and bone. In order for this approach to be successful, regional baseline bioavailable isotope data are required; however, few databases are currently available in Australia. This study measured stable oxygen and bioavailable strontium isotope ratios from low mobility fauna sampled from the major geological and physiographic provinces in Adelaide, South Australia in order to create a database for this region. Bioavailable strontium isotope ratios (87Sr/86Sr) obtained from the predominantly siliciclastic metasediments of the Neoproterozoic Adelaide Geosyncline have a range of 0.7122 ± 0.0001 to 0.7202 ± 0.0001. Cainozoic samples (dominantly terrestrial fluvial/lacustrine and marine carbonate sediments) from the Adelaide Plains have values in the range of 0.7098 ± 0.0002 to 0.7121 ± 0.0001. Samples from the alluvial fan sediments near the Eden-Burnside Fault at the boundary between these regions have values of 0.7131 ± 0.0001 to 0.7143 ± 0.0001. Stable oxygen isotope results range from − 9.5 to − 4.5‰ δ18OC (VPDB) and do not appear to vary systematically based on elevation, temperature, rainfall or humidity. These results demonstrate that strontium isotopes are potentially a useful tool for provenance studies within the Adelaide area. Oxygen is probably a more appropriate tool for discriminating seasonality rather than location within the study region. This research also suggests that rats are better suited for mapping strontium isoscapes than koalas, and that, while (non-systematic) offsets appear to exist between laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) and thermal ionisation mass spectrometry (TIMS) data, this effect is considerably less than the variation between geological provenances in the region.Lee Rippon, Mark Rollog, David Bruce, Juraj Farkas, F. Donald Pate, Timothy Owen ... et al

REE-, Sr-, Ca-aluminum-phosphate-sulfate minerals of the alunite supergroup and their role as hosts for radionuclides

Aluminum-phosphate-sulfate (APS) minerals of the alunite supergroup are minor components of uranium-bearing copper ores from the Olympic Dam deposit, South Australia. They typically represent a family of paragenetically late replacement phases after pre-existing REE-bearing phosphates (fluorapatite, monazite, and xenotime). Characterization with respect to textures and composition allows two groups to be distinguished: Ca-Sr-dominant APS minerals that fall within the woodhouseite and svanbergite compositional fields; and a second REE- and phosphate-dominant group closer to florencite in composition. All phases nevertheless display extensive solid solution among end-members in the broader APS clan and show extensive compositional zoning at the grain-scale. Samples representative of the deposit (flotation concentrate and tailings), as well as those that have been chemically altered during the processing cycle (acid leached concentrate), were studied for comparison. NanoSIMS isotope mapping provides evidence that the APS minerals preferentially scavenge and incorporate daughter radionuclides of the ²³⁸U decay chain, notably ²²⁶Ra and ²¹⁰Pb, both over geological time within the deposit and during ore processing. These data highlight the role played by minor phases as hosts for geologically mobile deleterious components in ores as well as during mineral processing. Moreover, Sr-Ca-dominant APS minerals exhibit preferential sorption of Pb from fluid sources, in the form of both common Pb and ²¹⁰Pb, for the first time revealing potential pathways for ²¹⁰Pb elimination and reduction from ore processing streams.Nicholas D. Owen, Nigel J. Cook, Mark Rollog, Kathy J. Ehrig, Danielle S. Schmandt, Rahul Ram, Joël Brugger, Cristiana L. Ciobanu, Benjamin Wade and Paul Guagliard