Regolith mapping of deeply weathered terrain in savannah regions of the Birimian Lawra Greenstone Belt, Ghana

Abstract

ABSTRACT:A regolith map for the Lawra Belt has been developed by categorizing the regolithlandform units by processing and interpreting remote sensing data. Regolith landform units were extracted from Landsat band ratios 3/1 and 5/4 to map ferruginous saprolite and lags; band ratio 5/7 was used to identify residual regolith and band ratio 4/2 was employed to separate ferruginous units from non-ferruginous regolith.Additional regolith landform units' discrimination was provided by compiling and interpolating radiometric data particularly for Landsat TM poorly defined areas.SRTM images were used to mark out the extent of the alluvial plains. High topographical terrains were marked from DEM image to represent the residual areas.Regolith landform unit (RLU) map that showed residual (relict and erosional), ferruginous, and depositional domains of the Lawra Belt was developed by superimposing the extractions made from the remote sensed data. Interpretive map generated from the remote sensed image analysis was validated by first creating a non-genetic regolith map through ground truth survey. The non-genetic map based on A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT2 | P a g e spatial distributions of the different regolith mapping units were classified on genetic classes or regimes based on regolith-landform similarities to develop a genetic map.The interpretive and the genetic map were superimposed to develop the regolith map for the Lawra Belt. The inliers and outliers presenting compositional overlaps within broad regolith classes were rectified from the field mapping information. The combined approach of image analysis and the ground truth mapping grouped the regolith of Lawra Belt into ferruginous (F), relict (R), erosional (E) and depositional (D) regimes.

Characterizing and Indexing Regolith Materials Using Geochemistry towards Hidden Mineral Anomaly Delineation: A Case Study of Savannah Region of NW Ghana

“…The total evaporation of 2050 mm recorded for the area exceeds the annual rainfall more than two fold. These conditions are favourable for lateritization processes to form laterites [4,9] and will contribute to the rapid changing regolith [1]. …”

“…On the contrary topographic high landscapes represent the eastern side [2]. Most parts of the landscape rises gently between elevations of 100m and 250m above mean sea level [1].…”

“…Butt and Zeegers [4] show a wide range of materials within a single regolith profile or toposequence with great variations in mineralogical and chemical composition, as well as variations in fabric and origin. Arhin et al [1] confirmed the complexities of regolith, particularly in the savannah regions of Ghana when they recognized the ferruginous regolith regime that consists of lateritic duricrust, lateritic gravel, ferruginous duricrust or ferricrete and all ferruginous materials whose origins cannot be identified easily in the field and generally called cuirasse by the French.…”

“…Regolith as known to mineral exploration geologists represents materials overlying the coherent bedrock and contains unconsolidated and secondarily cemented materials [1][2][3]. It thus forms the oxidizing environment of the earth's landscape and can have simple and/or complex weathering histories depending on the climatic and the anthropogenic activities.…”

“…Superficially the surface regolith materials look alike and require experts in regolith mapping to distinguish the differences between the various domains in regolith complex terrains. From [1,2] the regolith is found atop the bedrock and can host potential mineral anomalies of the deep seated orebody or an expression of the deep seated or hidden mineralisation can be detected in them. The climate everywhere do impact on the hydrological, weathering and geomorphic processes hence producing mosaic of different regolith units, changing rapidly and thus affecting the geochemical expressions in the surface regolith.…”