Geochemical anomalies from a survey of stream sediments in the Maquelab area (Oecusse, Timor-Leste) and their bearing on the identification of mafic-ultramafic chromite rich complex

Vicente, Victor A.S.; Pratas, João; Santos, Frederico C.M.; Silva, Maria M. V. G.; Favas, Paulo J.C.; Conde, L.

doi:10.1016/j.apgeochem.2020.104868

Cited by 9 publications

(2 citation statements)

References 34 publications

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“…However, in another areas of Timor-Leste and the Indonesian west Timor region, Audley-Charles [13] and Barkham [114] have reported the existence of altered carbonate sedimentary rocks of the Aitutu Formation by silicification processes. Meanwhile, Vicente et al [120] have presented the discovery of hydrothermal mineralization associated with Gondwana Megasequence in the Maquelab area (Oecusse -Timor-Leste). Further regional geochemical investigations in the study area are warranted, and the findings of this study could have implications for future lithological mapping research.…”

Section: Discussionmentioning

confidence: 99%

Modern River-Sand Geochemical Mapping in the Manufahi Municipality and Its Surroundings, Timor-Leste: Implications for Provenance

Vilanova,

Ohtani,

Kojima

et al. 2024

Geosciences

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A geochemical mapping of regional modern river-sand is performed to clarify geological information in the study area of Timor-Leste. Several areas of Timor-Leste including the study area in particular have limited geological information due to limited accessibility and dense vegetation coverage, and deformed, weathered, and erosion-covered materials. A total of 53 modern river sand samples were collected and analyzed. Ten major elements were determined by using wavelength-dispersive X-ray fluorescence. Areas characterized by clastic sedimentary rocks are recognized clearly by elevated concentrations of SiO2, Al2O3, and K2O. Meanwhile, areas covered by carbonate sedimentary rocks are detected by significant concentrations of CaO and MnO. The occurrences of the altered clastic and carbonate sedimentary rocks of the Wailuli and Aitutu Formations due to metamorphic, silicification and other alteration processes were responsible for the elevated concentrations and positive correlation between SiO2, CaO, K2O, and MnO, and CaO, TiO2, and MnO in the midstream and near the downstream areas of the Clerec and Sahe River catchments. The positive correlation observed between TiO2, CaO and MnO may be ascribed to the presence of carbonate components associated with secondary Ti-bearing minerals, which are potentially formed through hydrothermal alteration processes.

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Section: Discussionmentioning

confidence: 99%

Modern River-Sand Geochemical Mapping in the Manufahi Municipality and Its Surroundings, Timor-Leste: Implications for Provenance

Vilanova,

Ohtani,

Kojima

et al. 2024

Geosciences

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“…This approach assumes that rivers efficiently mix the components of rocks outcropping in their basins, transporting this mixture toward their outlets. Sampling of alluvial sediments has been widely used to generate geochemical maps with a range of different sampling densities on regional, national and continental scales (e.g., Johnson et al 2005;Caritat and Cooper 2016;Bastrakov et al 2018;Vicente et al 2020;Wang et al 2022).…”

Section: Contextmentioning

confidence: 99%

Geochemical mapping by unmixing alluvial sediments: An example from northern Australia

Lipp¹,

Caritat²,

Roberts³

2023

Preprint

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Alluvial sediments have long been used in geochemical surveys as their compositions are assumed to be representative of areas upstream. Overbank and floodplain sediments, in particular, are increasingly used for regional to continental-scale geochemical mapping. However, during downstream transport, sediments from heterogeneous source regions are carried away from their source regions and mixed. Consequently, using alluvial sedimentary geochemical data to generate continuous geochemical maps remains challenging. In this study we demonstrate a technique that numerically unmixes alluvial sediments to make a geochemical map of their upstream catchments. The unmixing approach uses a model that predicts the concentration of elements in downstream sediments, given a map of the drainage network and element concentrations in the source region. To unmix sedimentary chemistry, we seek the upstream geochemical map that, when mixed downstream, best fits geochemical observations downstream. To prevent overfitting we penalise the roughness of the geochemical model. To demonstrate our approach we apply it to alluvial samples gathered as part of the Northern Australia Geochemical Survey. This suvey gathered samples collected over a ~500,000 km2 area in northern Australia. We first validate our approach for this sample distribution with synthetic tests, which indicate that we can resolve geochemical variability at scales greater than 0.5 - 1° in size. We proceed to invert real geochemical data from the total digestion of fine-grained fraction of alluvial sediments. The resulting geochemical maps for two elements of potential economic interest, Cu and Nd, are evaluated in detail. We find that in both cases, our predicted downstream concentrations match well against a held-out, previously 'unseen' subset of the data, as well as against data from an independent geochemical survey. By performing principal component analysis on maps generated for all 46 available elements we produce a synthesis map to identify the significant geochemical domains in this part of northern Australia. This map shows strong spatial similarities to the underlying lithological map of the area. Finally, we compare the results from our approach to a geochemical map produced by kriging. We find that, unlike the method presented here, kriging generates geochemical maps that are both dampened relative to expected magnitude, as well as being spatially distorted. We argue that the unmixing approach is the most appropriate method for generating geochemical maps from regional-scale alluvial surveys.

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Carbon, nitrogen, and sulphur isotope analysis of the Padanian Plain sediments: Backgrounds and provenance indication of the alluvial components

Salani

Brombin

Natali

et al. 2021

Applied Geochemistry

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Geochemical anomalies from a survey of stream sediments in the Maquelab area (Oecusse, Timor-Leste) and their bearing on the identification of mafic-ultramafic chromite rich complex

Cited by 9 publications

References 34 publications

Modern River-Sand Geochemical Mapping in the Manufahi Municipality and Its Surroundings, Timor-Leste: Implications for Provenance

Modern River-Sand Geochemical Mapping in the Manufahi Municipality and Its Surroundings, Timor-Leste: Implications for Provenance

Geochemical mapping by unmixing alluvial sediments: An example from northern Australia

Carbon, nitrogen, and sulphur isotope analysis of the Padanian Plain sediments: Backgrounds and provenance indication of the alluvial components

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