Ultra-low density geochemical mapping in Zimbabwe

Zhao, Gengxin; Fuqing, HE; Dai, Xuefu; Zhang, Surong; Yu, Rengan

doi:10.1016/j.gexplo.2013.11.001

Cited by 9 publications

(3 citation statements)

References 6 publications

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“…Iron and Mn had the highest mean concentrations of 28.325 and 442 mg/kg, respectively. When compared to regional stream sediment surveys in other Sub-Saharan Africa regions [ 26 , 77 ], the Lom Basin sediments were depleted in all examined trace metals. However, average concentrations of the non-essential trace metals As (99.40 µg/kg), Hg (5.40 µg/kg), V (963.14 µg/kg) and Pb (151.59 µg/kg) were significantly higher than the levels (As = 22.3 µg/kg, Hg ≤ 0.01 µg/kg, V = 158.5 µg/kg and Pb = 12.3 µg/kg) reported by Taiwo and Awomeso [ 37 ] for sediment from the gold city of Ijeshaland.…”

Section: Resultsmentioning

confidence: 98%

Regional geochemical baseline concentration of potentially toxic trace metals in the mineralized Lom Basin, East Cameroon: a tool for contamination assessment

et al. 2018

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The distribution of trace metals in active stream sediments from the mineralized Lom Basin has been evaluated. Fifty-five bottom sediments were collected and the mineralogical composition of six pulverized samples determined by XRD. The fine fraction (< 150 µm) was subjected to total digestion (HClO4 + HF + HCl) and analyzed for trace metals using a combination of ICP-MS and AAS analytical methods. Results show that the mineralogy of stream sediments is dominated by quartz (39–86%), phyllosilicates (0–45%) and feldspars (0–27%). Mean concentrations of the analyzed metals are low (e.g. As = 99.40 µg/kg, Zn = 573.24 µg/kg, V = 963.14 µg/kg and Cr = 763.93 µg/kg). Iron and Mn have significant average concentrations of 28.325 and 442 mg/kg, respectively. Background and threshold values of the trace metals were computed statistically to determine geochemical anomalies of geologic or anthropogenic origin, particularly mining activity. Factor analysis, applied on normalized data, identified three associations: Ni–Cr–V–Co–As–Se–pH, Cu–Zn–Hg–Pb–Cd–Sc and Fe–Mn. The first association is controlled by source geology and the neutral pH, the second by sulphide mineralization and the last by chemical weathering of ferromagnesian minerals. Spatial analysis reveals similar distribution trends for Co–Cr–V–Ni and Cu–Zn–Pb–Sc reflecting the lithology and sulphide mineralization in the basin. Relatively high levels of As were concordant with reported gold occurrences in the area while Fe and Mn distribution are consistent with their source from the Fe-bearing metamorphic rocks. These findings provide baseline geochemical values for common and parallel geological domains in the eastern region of Cameroon. Although this study shows that the stream sediments are not polluted, the evaluation of metal composition in environmental samples from abandoned and active mine sites for comparison and environmental health risk assessment is highly recommended.

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Section: Resultsmentioning

confidence: 98%

Regional geochemical baseline concentration of potentially toxic trace metals in the mineralized Lom Basin, East Cameroon: a tool for contamination assessment

et al. 2018

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“…Geochemically surveying large areas remains challenging as there is a perception that large numbers of samples must be collected and analysed. Significant effort has thus been expended in developing methods to develop geochemical maps from low-density sampling campaigns (e.g., Smith and Reimann 2008;Zhao et al 2014;Birke et al 2015;Liu et al 2021. ) A widely used low-density approach is to sample sediments from stream, overbank or floodplain deposits.…”

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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“…National‐scale geochemical mapping has been carried out for more than 40 years in other countries (Butt & Nichol, 1979; Wang, 2013; Xie, 1979; Xie, 2002; Xie, 2007; Xie & Yin, 1993); geochemists all over the world have carried out a variety of studies on geochemical mapping techniques such as sample collection, analysis and testing, and map generation, and achieved fruitful results and proved that geochemical mapping method is the most effective method for rapid exploration and evaluation of mineral resources (Cheng et al, 1997; de Caritat et al, 2009; de Caritat & Cooper, 2011; Garrett et al, 2008; Smith et al, 2013; Wang et al, 2015, 2019; Xie & Ren, 1993; Zhao et al, 2014). The Sino–Zambian Cooperation Project was implemented from 2012 to 2015, which conducted low‐density geochemical mapping over the entire country of Zambia, filling the gap in national‐scale geochemical mapping in the country.…”

Section: Introductionmentioning

confidence: 99%

Enrichment characteristics and metallogenic significance of rare elements in Zambia: Based on 1:1,000,000 geochemical mapping

Sun,

Ren,

Wang

et al. 2023

Geological Journal

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The Sino–Zambian Cooperation Project has filled the gap in Zambia national‐scale geochemical mapping, providing basic geochemical guarantees for Zambia's basic geology, mineral development, environmental protection, agricultural production and other aspects. This article aims to reveal the distribution characteristics of its rare elements (Li, Be, Nb, Rb, Sr). The median value of Li, Be, Nb, Rb and Sr is 4.94 × 10−6, 0.65 × 10−6, 7.50 × 10−6, 33.00 × 10−6 and 21.90 × 10−6, respectively. The median and average values of the Irumide Belt, Zambezi Belt, Choma‐Kalomo Block and Hook Granite Complex are higher than other tectonic belts, showing that rare elements are enriched in those areas. The distribution of element anomaly areas is mainly related to the distribution characteristics of granite type rare metal mineralization occurrences, and a small number of anomaly areas are controlled by salt lake brine‐type mineralization occurrences. A total of five rare metal geochemical anomalies have been delineated respectively based on the 85% cumulative percentage of rare elements (Li, Be, Nb, Rb, Sr). The metallogenic prospective area delineated based on the comprehensive anomaly area of rare elements will provide an important reference for searching for rare metal deposits in this area.

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Ultra-low density geochemical mapping in Zimbabwe

Cited by 9 publications

References 6 publications

Regional geochemical baseline concentration of potentially toxic trace metals in the mineralized Lom Basin, East Cameroon: a tool for contamination assessment

Regional geochemical baseline concentration of potentially toxic trace metals in the mineralized Lom Basin, East Cameroon: a tool for contamination assessment

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

Enrichment characteristics and metallogenic significance of rare elements in Zambia: Based on 1:1,000,000 geochemical mapping

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