Anthony R Milnes
The University of Adelaide, Department of Earth Sciences, Department Member
- PhD on Cambrian granites and metamorphics in 1973. Post-doctoral research on phosphate ores (1973-78; Monash Universi... morePhD on Cambrian granites and metamorphics in 1973. Post-doctoral research on phosphate ores (1973-78; Monash University, CSIRO Mineral Chemistry) and later studies (1978-onwards; CSIRO Land & Water) on the mineralogy and geochemistry of weathering in soils and landscapes (silcretes, calcretes, ferricretes). Initiated research on mine wastes and mine landforms focussing on rehabilitation strategies from mid-1980's until 2010 while in CSIRO (Chief Research Scientist) and, later, Rio Tinto (General Manager, Environmental Strategy). Now Visiting Research Fellow in Earth Sciences at the University of Adelaide. Current research interests in weathering and landscape evolution. ORCID 0000-0003-4283-4428edit
A suite of soft-sediment deformation structures occurs within the basal sands and gravels in the non-marine Pleistocene succession in the Noarlunga Embayment of the Cenozoic St Vincent Basin south of Adelaide, South Australia, the... more
A suite of soft-sediment deformation structures occurs within the basal sands and gravels in the non-marine Pleistocene succession in the Noarlunga Embayment of the Cenozoic St Vincent Basin south of Adelaide, South Australia, the significance of which has hitherto gone unrecognised. The inclusion of large, isolated blocks of well-bedded sands randomly encased within fluidised, structureless clayey sands indicates that the soft-sediment deformation was intense, occurring soon after deposition by liquefaction of a still saturated sediment. Seismic activity has been, and continues to be, a regular occurrence along the adjacent Adelaide fold belt. The intensity of the deformation is comparable to the thixotropic response to earthquake activity observed during the Christchurch (New Zealand) earthquakes of 2010 and 2011, the earthquakes and aftershocks near Quorn, South Australia, in January 1887, in the southeast of South Australia in May 1899, and west of Adelaide in April 1954. This, however, is the first record of an interpreted seismite in the St Vincent Basin, although its full extent is yet to be mapped.
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Syn-and post-depositional alterations are distinguished in a detailed lithological and mineralogical study of the largely unconsolidated Plio-Pleistocene non-marine succession in coastal cliff sections in the St Vincent Basin south of... more
Syn-and post-depositional alterations are distinguished in a detailed lithological and mineralogical study of the largely unconsolidated Plio-Pleistocene non-marine succession in coastal cliff sections in the St Vincent Basin south of Adelaide. At its base, the sequence interfingers with Late Pliocene estuarine marine sediments in places but mostly unconformably overlies older Cenozoic marine sediments or Neproterozoic bedrock. The fluvial and alluvial siliclastics have bioturbation, blocky-prismatic macro-peds and subtle Fe-mottling indicators of hiatuses in deposition, and imprints of soil and shallow groundwater environments. A relative abundance of kaolinite, illite and randomly interstratified illitesmectite reflects both sediment source and conditions in the local depositional environment. A thick deposit of aeolian calcareous silt with associated pedogenic calcretes blankets the succession. Conspicuous bleached Fe mega-mottled intervals and zones of alunite-halloysite within the sequence record post-depositional, groundwater-related alterations in regolith environments. These formed during incision and erosion of the sedimentary fill in the basin in response to regional falls in base level. Each marks a different time and specific geomorphic environment according to the chemistry of the discharge of local groundwaters from aquifers that were intersected by incision and scarp retreat.
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In this paper, and in previous works, quartzites within the Sable de Fontainebleau are clearly shown to occur only near outcrops in Plio-Pleistocene plateau landscapes and are related to groundwater flows. These arrangements, together... more
In this paper, and in previous works, quartzites within the Sable de Fontainebleau are clearly shown to occur only near outcrops in Plio-Pleistocene plateau landscapes and are related to groundwater flows. These arrangements, together with dating of encased calcites, led us to consider that silicification occurred during Plio-Pleistocene glacial stages. The precipitation of silica was most likely triggered by cooling of groundwaters as they approached cold zones in the regolith close to points of discharge. We describe the arrangement and morphologies of quartzites in Tertiary sand formations in the Paris Basin to demonstrate how cold climates could have influenced hydrologic regimes and promoted silicification. The coeval precipitation of calcite and silica in gypseous formations at the edges of plateaux-bordering valleys, along with the dissolution of gypsum, also points to interactions between silica-laden groundwater and carbonate host rocks during cold periods. In parallel, the distribution and micromorphology of silicifications in associated Tertiary limestone formations suggests that they formed during cold climates in the Quaternary. These are key pointers to the role of groundwater in regolith environments in controlling silicification processes. We detail a link to palaeosurfaces of the distinctive meulières facies in the Paris Basin. Geotropic structures and micromorphological organisations are the basis of new ideas about their origin in a combination of vadose and phreatic environments and proximity to impervious cold horizons. The active zone in a permafrost landscape is a good hydrological example. All silicifications in Tertiary formations in the Paris Basin can be linked to the hydrology of Quaternary periglacial environments in a single model. This could apply more widely to similar silicifications elsewhere and be tested using new analytical techniques that date silicifications and unravel the isotopic relationships between silicification, groundwater composition and the prevailing climate.
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Detrital minerals provide valuable insights into the tectonic history of continents. Uranium-lead dating of detrital zircon is widely used to characterize the magmatic history of continents but is generally insensitive to metamorphism... more
Detrital minerals provide valuable insights into the tectonic history of continents. Uranium-lead dating of detrital zircon is widely used to characterize the magmatic history of continents but is generally insensitive to metamorphism accompanying the production and reworking of crust during orogenesis. Garnet is the most important mineral for recording prograde and peak orogenic metamorphism and can occur as a common detrital phase. Here, we demonstrate laser-ablation lutetium-hafnium (Lu-Hf) geochronology of detrital garnet as a provenance tool for reconstructing orogenic histories at (super) continental scales. Detrital garnet (n = 557) from modern sands and Permo-Carboniferous glacial strata in South Australia faithfully record local garnet-grade metamorphic events but also include a major population at ca. 590 million-years with no known source in South Australia. We trace the ca. 590 million-year-old detrital garnets to a largely ice-covered orogenic province in East Antarctica, uncovering the inception of convergent margin tectonism along the palaeo-Pacific margin of Gondwana.
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Although more than 2000 shelters with non-figurative carvings ascribed to a Mesolithic style are known within the quartzitic sandstone megaclast lag deposits in the southern Paris area, only three shelters with figurative representations... more
Although more than 2000 shelters with non-figurative carvings ascribed to a Mesolithic style are known within the quartzitic sandstone megaclast lag deposits in the southern Paris area, only three shelters with figurative representations of Late Paleolithic style have been recognized. Upright megaclasts are rare in the regional lag deposits but two upright quartzitic sandstone megaclasts occur close to two of these Late Paleolithic shelters. Detailed morphological surveys of these megaclasts allow us to suggest that they were erected by humans. The fortuitous conjunction of finding an upright megaclast close to two Late Paleolithic shelters is infinitesimally small in term of probabilistic considerations. Thus, the Late Paleolithic engraved shelterupright megaclast pairs are not likely to be independent but are probably linked by culture, and so the megaclasts are expected to date from the Late Paleolithic. We suggest that they were 'engineered landmarks' erected to mark places that had cultural significance for Late Paleolithic hunter-gatherer people. The energy dedicated to erect the megaliths is an indication that shelter-megalith pairs probably had important spiritual and symbolic significance. We suggest that both contributed to locate and anchor stories to landscape features. Indeed, these shelter-megalith pairs were in the hinterland of the large open-air camps settled on fords on game migratory routes crossing the Seine River. These specific markers could have encompassed a storyline about landscapes as the support for learning routes through them. One possibility is that they had a timed relationship with herd migration.
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Coloured heavy mineral sands are a conspicuous yet somewhat ephemeral feature on the surface of many beaches around Gulf St Vincent and in Encounter Bay in South Australia. The ultimate origin of the minerals continues to be investigated,... more
Coloured heavy mineral sands are a conspicuous yet somewhat ephemeral feature on the surface of many beaches around Gulf St Vincent and in Encounter Bay in South Australia. The ultimate origin of the minerals continues to be investigated, but they are known to be important constituents of an extensive suite of Carboniferous to Permian glacigene sediments deposited over most of the region. They occur in Palaeogene palaeochannel sands as well as within overlying Pleistocene alluvial sediments and soils. It is the continued erosion of these sediments that has fed the heavy minerals into modern terrestrial landscapes and concentrated them in small-scale placer sands on the beaches around Gulf St Vincent.
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The Tate Museum (The University of Adelaide) holds a large collection of (tektites) australites including the Pens Collection from the Florieton area in east-central South Australia. Many of these specimens are intact or near-so and have... more
The Tate Museum (The University of Adelaide) holds a large collection of (tektites) australites including the Pens Collection from the Florieton area in east-central South Australia. Many of these specimens are intact or near-so and have the various forms ascribed to their behaviour as they entered the Earth's atmosphere. However, a significant number, some of which may have been initially fractured and broken by erosional processes on the Earth's surface, were later reworked by Aboriginal Australians to form small tools and hence are important artefacts. Of the Florieton specimens, 6.5% have been reworked into microlithic flakes. This note points to the historical value of the Pens Collection, discusses the nature of the environment in which they were found, and speculates about the collecting and adaptation of australites by Aboriginal Australians.
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We tested the potential for sand calcites to serve as a novel paleoclimate archive by investigating their age and formation conditions. Fontainebleau sand calcites are Pleistocene in age (based on 14 C and U-Th dating) and were primarily... more
We tested the potential for sand calcites to serve as a novel paleoclimate archive by investigating their age and formation conditions. Fontainebleau sand calcites are Pleistocene in age (based on 14 C and U-Th dating) and were primarily formed during glacial periods. δ 13 C values increase with the depth at which these sand calcites formed, consistent with open and closed CO 2 systems. Interpretation of the δ 18 O-T relationship in sand calcites points primarily to their formation at a low temperature, around 2°C in shallow ground water and at about 9°C in deeper groundwater settings. Their occurrence, characteristics, and compositions suggest crystallization from paleo-ground waters in permafrost environments. Crystallization of sand calcites was triggered by degassing of cold carbonate-containing surface waters as they infiltrated warmer subsurface groundwater environments. We consider sand calcites to be important indicators of interactions between meteoric water and ground water in Pleistocene periglacial landscapes. Their disposition may point to specific features of periglacial landscapes, and their ages could permit an assessment of landscape incision rates. Large crystals and zoned spheroliths may, in fact, encapsulate continuous high-resolution records of continental glacial and periglacial paleoenvironments.
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Silcretes are clearly observed and abundant as components of paleolandscapes on several continents. Mechanisms for the formation of several varieties of silcrete, with specific relationships to paleolandscapes, are described. Each type of... more
Silcretes are clearly observed and abundant as components of paleolandscapes on several continents. Mechanisms for the formation of several varieties of silcrete, with specific relationships to paleolandscapes, are described. Each type of silcrete displays particular morphological features in its profile in the paleo-regolith, and these features provide pointers to its origin via mechanisms of absolute or relative accumulation of silica in specific environments relating to groundwater or soil-water hydrology. The characters of silcrete varieties that may have triggered the interest of prehistoric peoples to exploit them for manufacturing stone tools, and which control knappability, include granulometry and the specific nature of silica cements. The successions of silica precipitation and recrystallisation events are clearly evident as a complex of micromorphological features that provide clues to the hydrological environment and its geochemistry at the time or times of silicification. Examples are given of the distribution of different silcrete facies, which could have had differing values for exploitation for stone tool production, in modern-day landscapes in France and Australia.
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Ranger Mine is located about 260 kilometres east of Darwin, the capital city of the Northern Territory, Australia. The mine lease is surrounded by Kakadu National Park which is designated a World Heritage Area. The mining operations are... more
Ranger Mine is located about 260 kilometres east of Darwin, the capital city of the Northern Territory, Australia. The mine lease is surrounded by Kakadu National Park which is designated a World Heritage Area. The mining operations are heavily regulated by Government authorities and representatives of community groups. As a result, rehabilitation planning has been an important component of mine operations since they commences in the late 1970's. Long term security and effective rehabilitation of tailings is one of the principal rehabilitation goals for Ranger Mine. Since 1996, tailings have been deposited in a mined-out pit. In-pit disposal has the advantages of relocating the mine wastes to the site from which the original ore was mined, as well as secure containment due to the low possibility of structural failure of the pits. There are issues relating to the prevention of groundwater contamination from transport of tailings pore fluids during mine operations and after decommissioning and rehabilitation. In addition, post-deposition settlement of the tailings mass is likely to be large unless adequate settled densities can be achieved during the life of the mine. Strategies that are being investigated and implemented to ensure that the tailings deposits achieve high settled densities during operations to reduce the residual settlement are described. In addition, techniques for measuring and monitoring the key properties of the in-pit tailings deposits are reported.
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The environmental regulation for Ranger Uranium Mine, in the Northern Territory, Australia, requires the stored tailings (irrespective of where they are finally stored, whether in a tailings dam or in mined-out pits) be capped safely to... more
The environmental regulation for Ranger Uranium Mine, in the Northern Territory, Australia, requires the stored tailings (irrespective of where they are finally stored, whether in a tailings dam or in mined-out pits) be capped safely to minimise contamination, erosion and radon gas emission, and also to enable the site to be rehabilitated through revegetation. The hydraulically deposited neutralised tailings in the existing tailings dam have a 'gel-like' structure which hinders the consolidation process. Consequently. the in situ tailings have a high water content, low permeability and extremely low shear strength. The present paper describes the case history of a successful capping trial constructed on these extremely soft tailings. Environmental geotechnical issues are highlighted and investigated. Results, especially the characteristics of the tailings observed during the construction and subsequent monitoring, are also discussed.
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The degree of racemization of aspartic acid released by 6 mol/L HCI hydrolysis of peptides contained in a rhyolitic tephra-loess-palaeosol sequence in North Island, New Zealand, increases rapidly with depth and also with age as defined by... more
The degree of racemization of aspartic acid released by 6 mol/L HCI hydrolysis of peptides contained in a rhyolitic tephra-loess-palaeosol sequence in North Island, New Zealand, increases rapidly with depth and also with age as defined by radiocarbon and fission-track dating and by tephrochronology. D/L values for aspartic acid released from peptides still remaining in the stratigraphic materials after being subject to this procedure and only released after subsequent treatment with hydrofluoric acid also showed an increase to a depth of 5.5 m, but to a much lesser degree. The ages determined largely agree with previous estimates from tephrochronology. This technique may form a basis for dating of airfall deposits and palaeosols beyond the range of the radiocarbon method.
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The formation of iddingsite by the oxidative weathering of Fo80 olivine begins by solution of Mg from planar fissures, 20 ~ wide and spaced 200 ~ apart, parallel to (001). Oxidation of Fe within the remaining olivine provides nuclei for... more
The formation of iddingsite by the oxidative weathering of Fo80 olivine begins by solution of Mg from planar fissures, 20 ~ wide and spaced 200 ~ apart, parallel to (001). Oxidation of Fe within the remaining olivine provides nuclei for the topotactic growth of goethite. Cleavage cracks <50 ~ in diameter allow Na, AI, and Ca from adjacent minerals, particularly plagioclase, to enter the altering olivine while Mg and Si diffuse away. In the early stages of weathering, strips of Fe-rich smectite (saponite), 20-50 & wide and 1-7 layers thick, form bridges 50-100 ~. long across the planar fissures. Dioctahedral smectite crystallizes on the margins of wider cleavage-controlled fissures; with further weathering halloysite is formed away from the fissure walls. In the ultimate stages of alteration, the saponite and dioctahedral smectite are lost, leaving a porous, oriented aggregate of goethite crystals each measuring about 50 • 100 • 200 A (X, Y, Z, respectively), with sporadic veins of halloysite crossing the pseudomorph.
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The relative abundances and 234U/238U activity ratios of tetravalent and hexavalent U in 33 phosphorite nodules from the East Australian continental margin have been determined. U(IV) constitutes between 59-96% (average 80%) of the total... more
The relative abundances and 234U/238U activity ratios of tetravalent and hexavalent U in 33 phosphorite nodules from the East Australian continental margin have been determined. U(IV) constitutes between 59-96% (average 80%) of the total U in non-ferruginous Quaternary nodules, but between 11-86% (average 63%) in ferruginous Tertiary nodules. Quatemary phosphorite nodules on the East Australian continental margin form within well-oxygenated, low carbon-flux environments on the upper continental slope, generally at water depths between 350-450 m. Predictable relationships exist between the radiometric age and tetravalent U content (%U(IV)) of the nodules and their P205, Fe2O3, and labile organic carbon concentrations. The nodules probably initially form as part of a more widespread phosphatic layer which contains 7-9% P205, has Fe203/K20 ratios between 3-4, hydrogen indices (HI) >80, and is relatively uranium-rich (U/ P2O5 X l0-4 = 15-20). Virtually all the U is originally incorporated into the nodules as U(IV). The layer is subsequently broken up into discrete nodules which are periodically reworked and exposed at the sediment-water interface. During this exposure, the nodules preferentially gain both apatite and iron hydroxide. As a result, their P2O5 concentrations increase to 16-18% within 80 kyr of their formation, whereas the Fe2O3/K2O ratios increase to 8-10. Little or no U apparently accompanies this apatite, for the U/P2O5 ratios approximately halve as the P2O5 concentration doubles, and the nodules have concordant 230Th/234U and 231Pa/235U ages. Contemporaneously, exposure causes progressive oxidation of both the organic carbon (HI decreases to 20) and tetravalent uranium (U(IV) decreases to 60-70%) contents. The high U concentrations and high %U(IV) of the East Australian samples show that the presence of abundant organic matter is not necessary for the fixation of U in sedimentary apatite. Moreover, the %U(IV) in these phosphorites is not a direct function of the redox potential of the depositional environment, but rather an indicator of the amount of sea-tloor weathering experienced by the nodules.
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The uranium-series disequilibria of phosphorites, sediments, and coexisting solitary corals from the outer continental shelf and upper slope off eastern Australia have been determined in an attempt to relate the genesis of phosphorites in... more
The uranium-series disequilibria of phosphorites, sediments, and coexisting solitary corals from the outer continental shelf and upper slope off eastern Australia have been determined in an attempt to relate the genesis of phosphorites in this area to an absolute time scale. The 234U/238U, 23°Th//234U, and 231pa/235U activity ratios in the phosphorites are internally consistent, and indicate that the apatite component of the phosphorites has remained a closed system with respect to U, Th, and Pa, except for very minor losses of 234U. These losses do not affect the 23°Th/234U-derived ages, and comprise only 1-2% of the total 234U activity, significantly less than the losses observed in phosphorite nodules from off Peru-Chile. A morphological subdivision of the phosphorites into either non-ferruginous or ferruginous is supported by the isotopic data. Earthy, friable non-ferruginous phosphatic nodules range in age from 2.5 to > 250 kyr; Holocene ages were obtained from five different locations in water depths ranging from 365 to 450 m. In contrast, the uranium-series isotopes in well-indurated ferruginous nodules occurring in the same general area, but in shallower (< 350 m) water, are in radioactive equilibrium, indicating that their ages exceed 800 kyr. Solitary corals (CatTophv/lia planilamellata Dennant 1906) are associated with non-ferruginous nodules on the upper slope, and commonly contain internal phosphatic molds. Several corals and their internal molds from one location were dated by uranium-series methods: the coral ages ranged from 17 to 20 kyr, and were typically 10-15 kyr older than their respective phosphatic internal molds. These results are consistent with the sedimentological observations, and provide independent evidence that geologically meaningful ages can be obtained from marine phosphorites. Phosphate deposition off eastern Australia appears to have been largely continuous throughout the late Quaternary, rather than being restricted to times of high sea-level, as reported for phosphorites off Peru-Chile.
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Stratigraphic, geomorphological, and radiometric evidence shows that the laterite of the high plains and plateau of Kangaroo Island is older than the Middle Jurassic but younger than the Early Permian. Palaeoclimatic and palaeontological... more
Stratigraphic, geomorphological, and radiometric evidence shows that the laterite of the high plains and plateau of Kangaroo Island is older than the Middle Jurassic but younger than the Early Permian. Palaeoclimatic and palaeontological considerations suggest the Triassic as the most likely age of both the laterite and the surface on which it is developed. High-level lateritized surfaces in the adjacent Mount Lofty Ranges and southern Eyre Peninsula are of similar age.
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Comprehensive surveys and mapping of the vegetation on a number of areas selected for possible future mining of phosphate on Christmas Island, Indian Ocean, in concert with an evaluation of its ecology, enabled an assessment of potential... more
Comprehensive surveys and mapping of the vegetation on a number of areas selected for possible future mining of phosphate on Christmas Island, Indian Ocean, in concert with an evaluation of its ecology, enabled an assessment of potential impacts of disturbance. The research targeted the possible impacts on forest types as well as on the occurrence and distribution of EPBC-listed and other significant flora. Mining has not proceeded but the unique dataset provides new information on the floral ecology on this isolated seamount, demonstrates the effectiveness of a rigorous strategy for establishing baseline conditions, and informs practical approaches for both protecting significant flora and re-establishing key revegetation types in areas of significant land disturbance.
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Effective and sustainable restoration of significantly disturbed landscapes, particularly mined landscapes, is technically difficult and almost never achieved. However, it is possible to generate sustainable revegetation of mined lands... more
Effective and sustainable restoration of significantly disturbed landscapes, particularly mined landscapes, is technically difficult and almost never achieved. However, it is possible to generate sustainable revegetation of mined lands if there is a suitable understanding of the key attributes of the post mining environment and of the vegetation composition and ecology of appropriate analogue areas. On Christmas Island, the mined phosphate is actually the substrate for vegetation establishment and growth. Post mining karst landscapes provide completely different environmental conditions for plant growth. A detailed review and analysis of the floristics, ecology and structure of vegetation on Christmas Island, together with data on secondary and natural successional pathways following mining and other disturbances, has been undertaken over several years and provides the basis for a self-sustaining rehabilitation strategy based on six guiding principles.