Papers by Patricia M J Durance
Journal of Petrology, Aug 19, 2004
Melt inclusions are small portions of liquid trapped by growing crystals during magma evolution. ... more Melt inclusions are small portions of liquid trapped by growing crystals during magma evolution. Recent studies of melt inclusions have revealed a large range of unusual major and trace element compositions in phenocrysts from primitive mantle-derived magmatic rocks [e.g. in high-Fo olivine (Fo > $85 mol %), spinel, high-An plagioclase]. Inclusions in phenocrysts crystallized from more evolved magmas (e.g. olivine Fo < $85 mol %), are usually compositionally similar to the host lavas. This paper reviews the chemistry of melt inclusions in high-Fo olivine phenocrysts focusing on those with anomalous major and trace element contents from mid-ocean ridge and subduction-related basalts. We suggest that a significant portion of the anomalous inclusion compositions reflects localized, grainscale dissolution-reaction-mixing (DRM) processes within the magmatic plumbing system. The DRM processes occur at the margins of primitive magma bodies, where magma is in contact with cooler wall rocks and/or pre-existing semi-solidified crystal mush zones (depending on the specific environment). Injection of hotter, more primitive magma causes partial dissolution (incongruent melting) of the mush-zone phases, which are not in equilibrium with the primitive melt, and mixing of the reaction products with the primitive magma. Localized rapid crystallization of high-Fo olivines from the primitive magma may lead to entrapment of numerous large melt inclusions, which record the DRM processes in progress. In some magmatic suites melt inclusions in primitive phenocrysts may be naturally biased towards the anomalous compositions. The occurrence of melt inclusions with unusual compositions does not necessarily imply the existence of new geologically significant magma types and/or melt-generation processes, and caution should be exercised in their interpretation.
&amp;amp;lt;p&amp;amp;gt;Geochemical mineral prospecting approaches are mostly point-base... more &amp;amp;lt;p&amp;amp;gt;Geochemical mineral prospecting approaches are mostly point-based surveys which then rely on statistical spatial extrapolation methods to cover larger areas of interest. This leads to a trade-off between increasing sampling density and associated attributes (e.g., elemental distribution). Airborne hyperspectral data is typically high-resolution data, whilst being spatially continuous, and spectrally contiguous, providing a versatile baseline to complement ground-based prospecting approaches and monitoring. In this study, we benchmark various shallow and deep feature extraction algorithms, on airborne hyperspectral data at three different spatial resolutions, 0.8 m, 2 m and 3 m. Spatial resolution is a key factor to detailed scale-dependent mineral prospecting and geological mapping. Airborne hyperspectral data has potential to advance our understanding for delineating new mineral deposits. This approach can be further extended to large areas using forthcoming spaceborne hyperspectral platforms, where procuring finer spatial resolution data is highly challenging. The study area is located along the Rise and Shine Shear Zone (RSSZ) within the Otago schist, in the South Island (New Zealand). The RSSZ contains gold and associated hydrothermal sulphides and carbonate minerals that are disseminated through sheared upper green schist facies rocks on the 10-metre scale, as well as localized (metre-scale) quartz-rich zones. Soil and rock samples from 63 locations were collected, scattered around known mineralised and unmineralized zones, providing ground truth data for benchmarking. The separability between the mineralized and the non-mineralised samples through laboratory based spectral datasets was analysed by applying Partial least squares discriminant analysis (PLS-DA) on the XRF spectra and laboratory based hyperspectral data separately. The preliminary results indicate that even in partially vegetated zones mineralised regions can be mapped out relatively accurately from airborne hyperspectral images using orthogonal total variation component analysis (OTVCA). This focuses on feature extraction by optimising a cost function that best fits the hyperspectral data in a lower dimensional feature space while monitoring the spatial smoothness of the features by applying total variation regularization.&amp;amp;lt;/p&amp;amp;gt;
Preliminary steps of mineral exploration have always included drilling and other destructive and ... more Preliminary steps of mineral exploration have always included drilling and other destructive and expensive exploration techniques to quantify ore-deposits underground. This study examines how we can access information on the sub-surface geology by looking at the surface vegetation. We have targeted gold-mineralization along the Hyde-Macraes Shear Zone as a development site, which is located in the Otago Schist belt in southern New Zealand. Deep rooted plants, of the Pinus radiata species, were sampled on the field to quantify the element concentrations focusing on the pathfinder elements such as As and Fe in the host rock, in conjunction with airborne and laboratory based hyperspectral remote sensing data. In order to predict the elemental concentration from hyperspectral data Partial Least Squares Regression (PLSR) was executed.
Journal of Geochemical Exploration, 2022
Abstract Biogeochemistry is an effective and fast approach for orientation studies in mineral exp... more Abstract Biogeochemistry is an effective and fast approach for orientation studies in mineral exploration. Vegetative cover has been used in a range of geological environments to gain insight into the composition of sub-surface soils and bedrock found at depth; however, there is little to no records of biogeochemistry being coupled within a remote sensing and spectroscopy framework in the domain of mineral exploration. The study uses lab- and airborne hyperspectral remote sensing to localize gold mineralisation using the concept of biogeochemistry. This pilot study uses plant species, Pinus radiata in close proximity to a mineralised shear zone. This study used a 2 m spatial resolution airborne hyperspectral data, captured by AisaFENIX sensor and was complimented with lab-based hyperspectral data of the sampled vegetation and soil/rock exposed along the Hyde-Macraes Shear Zone, within the Otago schist belt in the South Island, New Zealand. The hyperspectral data, and the biogeochemistry data was explored using several statistical approaches to determine significant relationships between the underlying soil and rock substrate and biogeochemistry of the sampled vegetation with a focus on pathfinder elements to gold-mineralisation. Three commonly used multivariate predictive regression models, were tested, including partial least squares regression (PLSR), kernel based PLSR (kPLSR) and random forest regression (RFR) modelling. The results suggest that hyperspectral scanning can discriminate samples from a mineralised zone spectrally. Furthermore, the lab-based hyperspectral data outcompetes the airborne hyperspectral data for vegetation to identify areas of potential mineralisation. The model performances vary depending on the part of the plant analysed, and bark samples are found to be promising to explore underlying geological resources in the future. The regression model that show up to R2cv > 0.7 using bark samples decreases to R2cv ~ 0.2 when trained with needle samples. The airborne data is significantly more complex, which is observed in poorer model performances with R2cv ranging from 0.2 to 0.5.
Australian Journal of Earth Sciences, Sep 3, 2020
New age and geochemical data are used to investigate the origin of a ∼670 km-long line of eight s... more New age and geochemical data are used to investigate the origin of a ∼670 km-long line of eight seamount volcanoes along the western side of the Norfolk Ridge between New Caledonia and New Zealand. Altered lavas and limestones were dredged from three volcanoes during the 2015 Volcanic Evolution of South Pacific Arcs cruise of N/O l'Atalante, so a total of four, including the northernmost and southernmost, have now been directly sampled and analysed. Dating of lava and volcanic breccia clasts by Ar-Ar methods gives north-to-south ages from these sites of 31.3 ± 0.6, 33 ± 5, 21.5 ± 1.0 and 26.3 ± 0.1 Ma. These ages, along with supporting stratigraphic data on a fifth seamount from IODP borehole U1507, provisionally refute the hypotheses that the seamounts represent a southward-younging, age-progressive, intraplate volcanic chain on the Australian Plate or a subduction-related chain of restricted age range. Geochemically, the upper Eocene to lower Miocene lavas have alkaline and subalkaline basaltic compositions, and some could be shoshonitic. The location of the volcanoes along the western side of the Norfolk Ridge suggests an origin related to late Eocene and early Miocene melting near an intracontinental lithosphere-asthenosphere step. Involvement of a deep slab in petrogenesis is also possible. Key points 1. Eight seamounts form a line along the Norfolk Ridge. 2. Dating and geochemistry indicate the seamount line is not a hotspot track. 3. A rift-related origin, possibly with influence by subduction, is proposed.
Australian Journal of Earth Sciences, Aug 1, 2012
Applied earth science, Dec 10, 2019
Environment Systems and Decisions, Apr 5, 2019
Geochemistry Geophysics Geosystems, Jan 31, 2023
The 2015 VESPA voyage (Volcanic Evolution of South Pacific Arcs) was a seismic and rock dredging ... more The 2015 VESPA voyage (Volcanic Evolution of South Pacific Arcs) was a seismic and rock dredging expedition to the Loyalty and Three Kings Ridges and South Fiji Basin. In this paper we present 33 40Ar/39Ar, 22 micropaleontological, and two U/Pb ages for igneous and sedimentary rocks from 33 dredge sites in this little‐studied part of the southwest Pacific Ocean. Igneous rocks include basalts, dolerites, basaltic andesites, trachyandesites, and a granite. Successful Ar/Ar dating of altered and/or low‐K basalts was achieved through careful sample selection and processing, detailed petrographic and element mapping of groundmass, and incremental heating experiments on both phenocryst and groundmass separates to interpret the complex spectra produced by samples having multiple K reservoirs. The 40Ar/39Ar ages of most of the sampled lavas, irrespective of composition, are latest Oligocene to earliest Miocene (25–22 Ma); two are Eocene (39–36 Ma). The granite has a U/Pb zircon age of 23.6 ± 0.3 Ma. 40Ar/39Ar lava ages are corroborated by microfossil ages from associated sedimentary rocks. The VESPA lavas are part of a &gt;3,000 km long disrupted belt of Eocene to Miocene subduction‐related volcanic rocks. The belt includes arc rocks in Northland New Zealand, Northland Plateau, Three Kings Ridge, and Loyalty Ridge and, speculatively, D’Entrecasteaux Ridge. This belt is the product of superimposed Eocene and Oligocene‐Miocene remnant volcanic arcs that were stranded along and near the edge of Zealandia while still‐active arc belts migrated east with the Pacific trench.
Social Science Research Network, 2022
AGU Fall Meeting Abstracts, Dec 1, 2018
The Waihi epithermal system is a low sulphidation epithermal system that hosts one of the largest... more The Waihi epithermal system is a low sulphidation epithermal system that hosts one of the largest high grade ore deposits in the Southern Hemisphere. The use of petrographic and EPMA analyses demonstrate there are distinctive textural zones within pyrite grains that vary in chemistry and appearance. Some of these zones contain elevated concentrations of Au and Te, and varying concentrations of Fe, S, Cu, Pb or Zn. The textural observations indicate that in some samples, pyrite growth was interrupted by periods of dissolution. Grains begin growth with overall low trace element concentrations, with the highest concentrations of trace elements occurring in the middle phase of the grain’s growth. Inclusions are rich in Pb, Ca, Se, Zn and Ni, and are attributed to the ‘dirty’ texture of some samples. Inclusion-rich areas are also high in Au. The nature of the presence of Te suggests either a single source of magmatic fluid, released in pulses, or periodical dilution of the magmatic fluid...
Applied Earth Science, 2014
Geochimica et Cosmochimica Acta, 2006
Environment Systems and Decisions, Jul 5, 2019
This paper synthesizes important elements from case studies presented in its companion paper (Qui... more This paper synthesizes important elements from case studies presented in its companion paper (Quigley et al., 2019) to define mutual and distinct characteristics and to develop a more holistic understanding of how earth science was used to support diverse examples of decision-making. We identify a suite of 28 di↵erent science actions used within the case studies that
Journal of Petrology, 2004
Melt inclusions are small portions of liquid trapped by growing crystals during magma evolution. ... more Melt inclusions are small portions of liquid trapped by growing crystals during magma evolution. Recent studies of melt inclusions have revealed a large range of unusual major and trace element compositions in phenocrysts from primitive mantle-derived magmatic rocks [e.g. in high-Fo olivine (Fo > $85 mol %), spinel, high-An plagioclase]. Inclusions in phenocrysts crystallized from more evolved magmas (e.g. olivine Fo < $85 mol %), are usually compositionally similar to the host lavas. This paper reviews the chemistry of melt inclusions in high-Fo olivine phenocrysts focusing on those with anomalous major and trace element contents from mid-ocean ridge and subduction-related basalts. We suggest that a significant portion of the anomalous inclusion compositions reflects localized, grainscale dissolution-reaction-mixing (DRM) processes within the magmatic plumbing system. The DRM processes occur at the margins of primitive magma bodies, where magma is in contact with cooler wall rocks and/or pre-existing semi-solidified crystal mush zones (depending on the specific environment). Injection of hotter, more primitive magma causes partial dissolution (incongruent melting) of the mush-zone phases, which are not in equilibrium with the primitive melt, and mixing of the reaction products with the primitive magma. Localized rapid crystallization of high-Fo olivines from the primitive magma may lead to entrapment of numerous large melt inclusions, which record the DRM processes in progress. In some magmatic suites melt inclusions in primitive phenocrysts may be naturally biased towards the anomalous compositions. The occurrence of melt inclusions with unusual compositions does not necessarily imply the existence of new geologically significant magma types and/or melt-generation processes, and caution should be exercised in their interpretation.
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Papers by Patricia M J Durance