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... The weathering front separates the saprolith and the fresh rock (Philips et al. 2019). The bottommost saprock layer located in the saprolith is the least chemically altered zone and typically shows signs of the most recent weathering (McQueen and Scott 2008). Widdowson (2007) describes the plasmic zone as the mesoscopic portion containing a significant amount of clay, without a lithic fabric of the saprolite or any significant development of secondary materials, such as pisoliths and nodules. ...
The role of a landfill liner in the waste management process cannot be overemphasized. They are usually made of clay soils or geosynthetic materials or both with the sole purpose of controlling the migration of leachates into underlying aquifers and soils thereby preventing contamination. The limited availability of clay soils and high cost of geosynthetics have necessitated the search for and use of different locally available materials. Lateritic soils are one of the most commonly used materials for landfill liners in the tropical areas, where they commonly occur. However, a comprehensive review of literature on the utilization of lateritic soils as landfill liners has not been reported. Conducting a systematic review of lateritic soils for landfill liner applications enables an enhanced understanding of their inherent characteristics and appropriateness. This, in turn provides vital insights for the design and construction of effective and economically sustainable waste containment systems. Hence, this paper reviews the nature and characteristics of lateritic soils and assesses their suitability for landfill lining applications through a thorough evaluation of the desirable geotechnical, geological and geochemical properties based on available literature and data. Data on the index and geotechnical characteristics of lateritic soils at two hundred and seventy-eight locations from different countries were collected from literature and assessed based on standard specifications for landfill liners. Furthermore, their leachate attenuation characteristics and improving their suitability for landfill liners through property amendments are presented. The review results indicate that lateritic soils possess suitable engineering properties with some interesting clay mineralogical compositions for lining applications. In addition, the desirable geotechnical properties of lateritic soils can also be improved by blending it with bentonite, fly-ash, sawdust and mine tailings. Although mineralogical transformations occur after permeation with landfill leachates, lateritic soils possess contaminant attenuation characteristics such as low diffusion, good sorption and cation exchange properties that are needed for landfill liner applications.
... Al 2 O 3 displays contradicted behavior in APGG and BKG profiles, where it is substantially depleted in APGG (72 % loss in soil zone) and significantly enriched in the latter (up to 50 % in soil zone). In GJG, Al 2 O 3 is used for normalization, where it shows immobility behavior in weathering profile developed on Godhra granite, which is considered as the normal trend of Al where it is highly incorporated in secondary minerals, such as clays, oxides, and hydroxides (McQueen and Scott, 2009). Thus, the depletion behavior of Al in the APGG profile is related to the specific environmental conditions prevailing in Bomdila, Lesser Himalaya, such as intense precipitation (flood occurrence), high permeability of weathering profile (fractures and joints), etc. ...
In an attempt to constrain the micro-scale factors during weathering, large number of samples from four weathering profiles developed on granite and basalt rocks under different climatic conditions from western (Gujarat, GJ) and central (Bundelkhand, BK) India are reported in this study and compared these profiles with profiles from north eastern (Arunachal Pradesh, Lesser Himalaya, AP) India. In granitic profiles, the chemical index of alteration (CIA) values ranges from 50 to 85 whereas 42–90 CIA values are observed for basalt profiles.
This highlights the significance of climate conditions (i.e., precipitation) over lithology in controlling weathering advancement. The results of the mass-transfer coefficient (τ) of major oxides significantly vary among the three granite and basalt profiles. The trace elements distribution in weathering profiles seems to be strongly controlled by the degree of weathering and formation of secondary minerals. Regardless of the nature of parent rocks, HFSEs (high field strength elements) tend to be enriched in the upper portion of all the weathering profiles; whereas REEs (rare earth elements) display variable behavior in each profile. The principal component analysis (PCA) reveals that three components are accounted for 89.14% of the variance. PC1 is attributed to weathering intensity and formation of secondary minerals, PC2 can be related to the lithology of parent material, and PC3 might be a location-specific factors. The present study shows that the geochemical characteristics of weathering profiles cannot be explained by the influence of a single weathering agent rather, there seems to be a significant role of local (or micro-scale) factors that controls the weathering and soil formation.
... The weathering of carbonate rocks involves the dissolution of the calcitewith the loss of the Caand accumulation of the insoluble components (McQueen and Scott, 2009). This process has a direct relationship with the water table. ...
... Due to the drastic reduction of the C content in weathered rock, the rock C/N and C/P ratio also decreased sharply by weathering. It was well-proven that carbonate dissolution is fast under acid and humid conditions in the study areas [33]. In addition, the metal elements of carbonates may be retained in soil by the inner-and outer-sphere-exchangeable complex (clays + humus) and can effectively, at least in part, be taken up by microbes and plants. ...
... N can be in the form of NH4+ and can replace K in microcline [34]. In other words, a lot of rock N will be kept in weathering products and may serve as the original N source of soil [33,35]. ...
... In particular, phosphorus was converted from the dissolved form into organic or particulate inorganic forms and hence fixed in weathered rock [6]. As the leaching rate of apatite is lower compared with other minerals abundant in the studied rocks, such as carbonates, and despite the fact that some P can be released, the rock loses in proportion more of the other elements, and thus P concentration remains stable or even increases despite the potential release of some P. On the other hand, within the weathered rock, the mineral voids (including fissures) were replaced by apatites, which showed significant enrichment of P within weathered minerals [33]. The enrichment of P is more likely due to the transformation of apatitebound P into more stable secondary P forms [41]. ...
Carbon (C), nitrogen (N), and phosphorus (P) stoichiometry and their allometric relationships in soil and plants are hot topics that attract a lot of attention, while those rocks that form soils are often neglected. Weathering is a common geological phenomenon that may significantly influence the nutrient composition and release of nutrients from rock and its inherent soils. This study presents C, N, and P concentrations data as well as microscope petrological photographs of fresh and weathered sandstones from Longhushan World Geopark in SE China, in an attempt to investigate C, N, and P stoichiometry of rocks before and after weathering and discuss the driving mechanisms. The results show that weathering significantly decreased rock C, C/N, and C/P concentrations, slightly decreased N and N/P concentrations, and slightly increased P concentration. Microscope observations show that fresh sandstones contain calcite, apatite, microplagioclase, and organic matter, while weathered sandstones feature apatite and organic matter. The flexible allometric relationships and mineral changes before and after rock weathering indicate that chemical mechanisms, such as dissolution of carbonate and hydration of microplagioclase, have changed the existence form of C, N, P and, thus, significantly influence rock C, N, and P stoichiometry. This stoichiometry feature can be in turn used to reflect the regulation effect of rock weathering.
... Al 2 O 3 displays contradicted behavior in APGG and BKG profiles, where it is substantially depleted in APGG (72 % loss in soil zone) and significantly enriched in the latter (up to 50 % in soil zone). In GJG, Al 2 O 3 is used for normalization, where it shows immobility behavior in weathering profile developed on Godhra granite, which is considered as the normal trend of Al where it is highly incorporated in secondary minerals, such as clays, oxides, and hydroxides (McQueen and Scott, 2009). Thus, the depletion behavior of Al in the APGG profile is related to the specific environmental conditions prevailing in Bomdila, Lesser Himalaya, such as intense precipitation (flood occurrence), high permeability of weathering profile (fractures and joints), etc. ...
... Thus, it is reasonable to consider the upper sequence to be the result of resurfacing since around 1.6 Ga. Long-term weathering and repeated impacts are two surface processes possibly involved in the Amazonian resurfacing and potentially responsible for the upper fining-upwards sequence 32,33 (Fig. 3b). Either of these two processes, or a combination, have been proposed for the formation of similar near-surface fining-upwards sequences on Mars 34 and the Moon 17 . ...
Exploring the subsurface structure and stratification of Mars advances our understanding of Martian geology, hydrological evolution and palaeoclimatic changes, and has been a main task for past and continuing Mars exploration missions1–10. Utopia Planitia, the smooth plains of volcanic and sedimentary strata that infilled the Utopia impact crater, has been a prime target for such exploration as it is inferred to have hosted an ancient ocean on Mars11–13. However, 45 years have passed since Viking-2 provided ground-based detection results. Here we report an in situ ground-penetrating radar survey of Martian subsurface structure in a southern marginal area of Utopia Planitia conducted by the Zhurong rover of the Tianwen-1 mission. A detailed subsurface image profile is constructed along the roughly 1,171 m traverse of the rover, showing an approximately 70-m-thick, multi-layered structure below a less than 10-m-thick regolith. Although alternative models deserve further scrutiny, the new radar image suggests the occurrence of episodic hydraulic flooding sedimentation that is interpreted to represent the basin infilling of Utopia Planitia during the Late Hesperian to Amazonian. While no direct evidence for the existence of liquid water was found within the radar detection depth range, we cannot rule out the presence of saline ice in the subsurface of the landing area.
... The limited spectral resolution of the ASTER bands within the SWIR region makes it impossible to discriminate between MgOH minerals and carbonate minerals (Gozzard, 2006b). Both products are particularly useful for mapping weathered mafic rocks and propyllitic hydrothermal alteration in the regolith because carbonates such as calcite and dolomite are some of the first minerals to dissolve during chemical weathering (McQueen and Scott, 2008;Cudahy, 2013). ...
Regolith–landform mapping of the Kimberley Science and Conservation Strategy (KSCS) project area in the west Kimberley Craton reveals an erosional landscape dominated by a plateau defined by aluminous and ferruginous residual and relict units. The rarity of deep preserved profiles suggests persistent weathering, erosion and recycling of the regolith materials. The residual regolith represent the remnants of extensive paleosurfaces reserved at the high and low Kimberley surfaces. The residual regolith dates from Late Miocene to Early Pleistocene, indicating at least two distinct periods of laterization possibly linked to changes in the climate 22.4 – 10.4 Ma and 6.7 – 2.3 Ma. The present residual duricrusts are possibly reworked duricrusts from distinct weathering periods that commenced in the Miocene. The Kimberley Plateau landscape tilts to the north as indicated by elevations of the residual units. This tilting is consistent with the northwesterly downward warping of the Australian Plate as it approaches the Sunda-Banda Arc. The tilting to the north likely contributed to the erosional process causing dissection of the Kimberley landscape. Gamma ray radiometric potassium–thorium–uranium (KTU), thorium (Th) and potassium (K), Landsat Australian Geological Survey
Organisation (AGSO) ratio, magnetic 1VD and Kimberley Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) datasets were concurrently used for mapping regolith–landforms and to provide compositional mineralogical information,
especially for areas of difficult access where remote mapping is necessary. The Kimberley ASTER products were developed to remove the issues of variable green and dry vegetation cover that affected the quality of ASTER-selected mineral maps over the
Kimberley region. The green vegetation issue was remediated by using an ‘unmixing’ approach that essentially ‘offsets’ the target mineral content by the amount of green vegetation for each pixel using the equation (a1 × X1 + b1) + c × (a2 × X2 + b2), where X1 is the target mineral content; X2 is the vegetation content, which can be either positive or negative (1 – X2); a and b are constants required to reduce the dynamic range of the selected input data to lie between 0 and 1; and c is variable, and is a value that can be
used to iteratively adjust the amount of vegetation to be unmixed. Hyperspectral validation of the regolith samples for Kimberley ASTER was not conducted. Hyperspectral validation of regolith samples for future ASTER versions is recommended, with the aim
of refining the data used for mapping specific regions or localities
... In the weathered diamictites, all chemical changes and mineral alterations are largely driven by redox reactions that play an important role in major and trace element mobility and hydromorphic metal dispersion as a function of the pH, Eh, temperature, and salinity of the ground water [47]. Oxidation-reduction, acid-base, hydrolysis, and dissolution processes are the main chemical changes occurring near and above the water table, which represent a redox boundary between the weathered and unweathered diamictites. ...
... Sulfides, together with carbonates, ferromagnesian, and opaque oxide heavy minerals, are easily oxidized and removed from the weathered diamictites above the redox boundary [11,24,[47][48][49]. The released Fe 2+ , Mn 2+ , Ca 2+ , Mg 2+ , and SO4 2-combine with bicarbonate HCO3 -and SO4 2-anions below the redox boundary to form diagenetic silicates (smectite and chlorite), carbonate (calcite and dolomite), and framboidal and massive pyrite cement. ...
Areas under a thick Permian glacial cover in Western Australia formed as glaciers gouged fresh bedrock and deposited diamictites in disconnected valleys and basins. These areas now present the greatest challenge for mineral exploration in the northeast Yilgarn Craton. At the Lancefield North gold prospect, in the southern part of the Duketon Greenstone Belt, Permian diamictites on average 40 m thick cover unweathered basalt hosting gold mineralization. The basal Permian dia-mictites consist of fresh, very poorly sorted, angular to rounded, pebble-to boulder-sized, polymic-tic clasts supported by a matrix of coarse-grained sand and mud. The framework and matrix are cemented by calcite, dolomite, chlorite, and pyrite. These diamictites are stable under alkaline and reducing conditions below the water table. Detrital; fresh sulfides; gold; and opaque oxides, such as pyrite, pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, gersdorffite, cobaltite, pentlandite, scheel-ite and galena, chromite, ilmenite, and magnetite, are identified in the framework and matrix of the fresh diamictites, and these are identical to those in the primary gold mineralization. Weathering of diamictites and oxidation of detrital and diagenetic sulfides above the water table produced several Fe-and Mn-rich redox fronts and secondary chalcocite and bornite. Interface sampling across the Archean-Permian unconformity shows Au, As, Zn, Ni, Co, and Cd anomalism over the minerali-zation compared to the background. However, these elements are low in concentration in the redox fronts, where Fe is correlated with As, Cu, Mo, and Sb and Mn is correlated with Co, Ni, and Ba. Gold shows elevated levels in the fresh basal diamictites and decreases in the weathered diamictites over the mineralization. A sampling at or near the Archean-Permian unconformity (interface sampling) only delineates gold mineralization, with no hydromorphic dispersion halo beyond the peripheries. At the Lancefield North prospect, the detrital indicator sulfides are mechanically dispersed up to 500 m to the east of the mineralization in the direction of ice flow. This dispersal distance is controlled by the rough topography of the Archean-Permian unconformity, and it may be greater, but the estimation of the actual distance of transport is limited by the distribution of drill hole locations.
... Weathering involves the chemical breakdown of rocks owing to near-surface processes and is a common overprint that can result in significant chemical modification and therefore make it difficult to differentiate from lithological change (e.g. McQueen & Scott, 2008). In drill hole MSDP11, weathering mainly effects a felsic igneous protolith and results in primary feldspar being replaced by kaolinite to varying degrees down to a depth of 74.5 m. ...
Geochemical data are frequently collected from mineral exploration drill-hole samples to more accurately define and characterise the geological units intersected by the drill hole. However, large multi-element data sets are slow and challenging to interpret without using some form of automated analysis, such as mathematical, statistical or machine learning techniques. Automated analysis techniques also have the advantage in that they are repeatable and can provide consistent results, even for very large data sets. In this paper, an automated litho-geochemical interpretation workflow is demonstrated, which includes data exploration and data preparation using appropriate compositional data-analysis techniques. Multiscale analysis using a modified wavelet tessellation has been applied to the data to provide coherent geological domains. Unsupervised machine learning (clustering) has been used to provide a first-pass classification. The results are compared with the detailed geologist’s logs. The comparison shows how the integration of automated analysis of geochemical data can be used to enhance traditional geological logging and demonstrates the identification of new geological units from the automated litho-geochemical logging that were not apparent from visual logging but are geochemically distinct.
• KEY POINTS
• To reduce computational complexity and facilitate interpretation, a subset of geochemical elements is selected, and then a centred log-ratio transform is applied.
• The wavelet tessellation method is used to domain the drill holes into rock units at a range of scales.
• Several clustering methods were tested to identify distinct rock units in the samples and multiscale domains for classification.
• Results are compared with geologist’s logs to assess how geochemical data analysis can inform and improve traditional geology logs.
... The ferric oxide (FeOx) content layer indicates the presence of iron oxide minerals (i.e. hematite and goethite) and typically represents either the end-product of weathering in regolith or residual soils on ironrich bedrock, i.e. mafic and ultramafic rocks (Anand & Butt, 2010;McQueen & Scott, 2008). Ferric oxide composition reflects the relative dominance of hematite and goethite, which can be a function of climatic conditions, i.e. hematite is often related to arid environments and goethite is more abundant in wet environments (Eggleton, 2008). ...
... Ferric oxide composition reflects the relative dominance of hematite and goethite, which can be a function of climatic conditions, i.e. hematite is often related to arid environments and goethite is more abundant in wet environments (Eggleton, 2008). The aluminium oxyhydroxide (AlOH) content layer represents the abundance of alumino-silicate minerals and may be reflect the AlOH content of the parent material (e.g. the higher AlOH content of felsic rocks compared to mafic or sedimentary rocks) or may reflect the presence of AlOH rich clays and thus the degree of weathering (McQueen & Scott, 2008). The AlOH composition layer reflects the relative abundances of Al-rich (kaolinite) and Si-rich (smectite) clay minerals and can be related to weathering and transportation, e.g., Si is typically depleted during weathering resulting in Al-rich end-products (Eggleton, 2008). ...
The primary aim of mineral exploration is to focus the search space from regional scale (1000s km²) to prospect scale (1–10 km²), identify areas that warrant further investigation, and ultimately drill a target. Mineral deposits typically display geochemical anomalism related to the conditions of their formation, or the weathering and mass transport of sediment away from a mineral deposit. However, this anomalism can be obscured in soil-sample surveys due to background variations in host bedrock chemistry and the transformation and redistribution of original minerals during surface weathering, regolith development, and supergene processes. This contribution uses machine-learnt map products to aid in the interpretation of a regional-scale soil-sample dataset. ASTER (satellite spectral) data were combined with airborne radiometric data using Self-Organising Maps (SOM) to generate a map of regolith type. A map of bedrock geology was previously derived by the authors from airborne geophysical data using Random Forests. These two products are used to classify soil samples with an objective bedrock-geology and regolith-type classification. A z-score normalisation was implemented on the soil-sample geochemical data, using two different matrices (regolith type and bedrock geology) to remove the bias of bedrock geology and regolith type from the soil sample chemistry. The signal that remains likely reflects metasomatic processes, and associated elemental anomalism, potentially linked to mineralisation. These data can then be plotted to provide maps of (pathfinder) element anomalies, thus identifying potential exploration targets. We explore this approach to normalise geochemical data in a dataset of 9,924 soil samples collected over an area of 1,028 km ², from Kerkasha, Eritrea (Nubian Shield). The Kerkasha project is an early-stage exploration project, with a limited understanding of the local geology and mineral deposit types; however, it contains many Au and Cu prospects that have received minimal exploration work.
