I am currently working in a flat terrain area with no rock outcrops for determining the geology of the area. Also, the said area has no detailed lithology map and therefore am looking at developing one. However, the only information i have at my disposal are the XRF and XRD aanalysis results from soil samples collected across the study area.
Dear Ngula Niipele,
You can determine the bulk/clay mineralogy of the soil/sediments from your study area using XRD. This will help you understand the mineralogical compositions of the sediments. This information you can use to decipher the possible sources of the potential parent rocks that could have supplied these sediments to your study area. However XRF data can also be used to know about the broad source rock characteristics.
If the region is like without exposures/outcrops you have to raise manual or machine operated sediment core for temporal records if you are interested in.
Moreover, without knowing some more details about the kind of environment, broad geological settings of your area under investigation it is difficult to comment more.
Good luck!
Nitesh
From the results of DRX of the oriented glass slides you can determine the main clay minerals such as Kaolinite, smectite, chlorite...... and from the bulk, you can determine the accessory minerals associated
Do you require to determine lithological type or soil types? Make yourself clear.
Rough estimations on lithology/soil type can be made from XRD and XRF data
You can arrive at tentative mineralogy there by the rock types by combining analysis of both XRD and XRF results.
you can use NORM defined as the calculation of a theoretical assemblage of standard minerals for a rock based, on the whole rock chemical composition as determined by analytical techniques
XRD gives the mineralogy...based on which you can arrive at felsi/ mafic rock
XRF gives major oxides based on silica content you can know whether its acidic, basic, intermediate or ultrabasic rock. You can use alumina saturation index by which you can tell whether the rock is per aluminous, meta-aluminous, sub aluminous or alkaline.
XRF and XRD measurements are used to determine the chemical and mineralogical constituents in the rocks. With the help of Core hole (diamond core) drilling, we can know the vertical extension of the rock formation. Core samples give immense information for lithological assessment.
The answer from Asoori Latha is a good way to go. Your assumption that the soils are formed in situ rather than transported is a start. Recognising that much of Namibia is a desert, depending where your study area is, chemical weathering to produce clays is likely to be limited. An XRD pattern will tell you what minerals are present, besides clays and can give a crude estimate of their proportions. The non-clay minerals defined by XRD can be compared to an appropriate NORM calculation. eg CIPW, Barth meso or catanorm. Comparison of these results with adjacent geology if any can help. Another source of information may be radiometric images of the area (particularly K band), probably available from the Namibian Geological Survey.
Your question is not clear. Do you want to know the lithologies in bed rocks? Do you wish to infer the bed rock composition from soil? Or do you want to prepare a map on the basis of soil types? Inferring the composition of bed rocks from the soil analyses may have pitfalls. The soil may be in situ weathering of the bed rocks or it may be a mixed weathering product of the bed rocks and transported sediment cover.
For in situ soil samples, you may have some geological information about the underlying bedrock.
For eroded soil samples, you may have information about the provenance of lithology.
Sim. Pois, através da análises mineralógica você poderá identificar o tipo litológico. Lembrando que para isso você terá de saber qual o tipo de rocha se sedimentar, metamórfica ou ígnea, portanto, não é um processo direto ou rápido.
If I were you, I would start from as oarse gravel samples as possible, make XRF and use for lithological classification the R1-R2 diagram (de La Roche et al. 1980) and the Na2O+K2O vs SiO2 diagram (Cox et al. 1979).
Ref: Cox, K. G., Bell, J. D. & Pankhurst, R. J. 1979. The Interpretation of igneous rocks. London: Allen & Unwin. 450 p.
de la Roche, H., Leterrier, J., Grandclaude, P. & Marchal, M. 1980. A classification of volcanic and plutonic rocks using R1-R2 diagram and major-element analyses – its relationship with current nomenclature. Chemical Geology, 29, 183–210.
Dr Tapio Ruotoistenmäki,
Your references are good and widely used for igneous rocks classification.
But why do you assume the soil in question is derived from igneous precursor(s)?
Guess. Even if not, these diagrams can nicely give preliminary view of possible source rock variations.
Please refer :
PREDICTIVE BEDROCK AND MINERAL PROSPECTIVITY MAPPING IN THE GIYANI GREENSTONE BELT, SOUTH AFRICA
Thank you everybody for the constructive recommendations. Indeed I derived useful methodologies on how to go about my lithological assessement.
If we want to assess the lithological units, core hole sampling is the best way.
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