Northern Australia Geochemical Survey: Data release 1 - Total (fine fraction) and MMI™ element contents

Bastrakov, Evgeniy; Main, P.T.; Wygralak, AS; Wilford, J.; Czarnota, K.; Khan, Muhammad Saleem

doi:10.11636/record.2018.006

Cited by 2 publications

(5 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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%

“…This approach was first proposed, and validated against independent data, in a 13,000 km 2 pilot study in the Cairngorms mountains, UK using relatively high-density (1 sample per 2 km 2 ) geochemical data (Lipp et al 2021). In the present contribution we upscale this approach considerably to generate regional scale geochemical maps from a survey in northern Australia (Bastrakov et al 2018). This survey covers a region one order of magnitude larger at a density two orders of magnitude lower.…”

Section: Proposed Solutionmentioning

confidence: 99%

“…The Northern Australia Geochemical Survey (NAGS; Bastrakov et al 2018) was a collaboration between Geoscience Australia, the Northern Territory Geological Survey and the Geological Survey of Queensland, which closely followed the strategies and workflows established by the earlier National Geochemical Survey of Australia (NGSA; Caritat et al 2011;Caritat 2018) . NAGS targeted catchment outlet sediments at an average sample density of one site per ∼ 500 km 2 , approximately ten times that of NGSA, over a ∼ 500,000 km 2 area straddling the Northern Territory-Queensland border in northern Australia.…”

Section: Northern Australia Geochemical Surveymentioning

confidence: 99%

“…These are then converted into logarithmic standard deviations by taking the mean of the upper and lower bounds. Full details of sampling, analytical and quality control methods are given in Bastrakov et al (2018). Of the 47 elements that passed through this quality control procedure we analyse 46, excluding Scandium as it was found to contain large amounts of spurious variance introduced by the imputation process.…”

Section: Sedimentary Geochemical Datamentioning

confidence: 99%

“…To make sure this alignment is as accurate as possible we use the target upstream catchment polygons published alongside the NAGS dataset (Bastrakov et al 2018). For each of the catchment polygons we identify the point within it with the largest drainage area (to access its outflow point).…”

Section: Aligning Sample Sites To Drainagementioning

confidence: 99%

See 4 more Smart Citations

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

Lipp¹,

Caritat²,

Roberts³

2023

Preprint

View full text Add to dashboard Cite

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.

show abstract