Mapping evaporite minerals and associated sediments in Lake Magadi, Kenya, using Hyperspectral Hyperion data

G R L Kodikara,G J Van Hummel,F J A Van Ruitenbeek,T Woldai,K D Shepherd

doi:10.4038/jur.v4i1-2.7882

Abstract

Hyperion hyperspectral (VNIR-SWIR) satellite image data was used to map the spatial distribution of mineral precipitates at Lake Magadi area, in the southernmost part of the eastern Kenya rift, Kenya. Mapping was coupled with laboratory analysis, including visible near infrared diffuse reflectance spectroscopy (VNIR) measurements and X-ray diffraction for selected rock and soil samples. The VNIR spectral responses of 92 rock and soil samples including trona, chert, diatomite, basalt/trachyte, erionite, Green bed and High Magadi bed were studied and identified. The spectral signatures of Chert samples show the broad Si-OH absorption feature at 2.2 μm while, Green bed, High Magadi bed and diatomite exhibit carbonate absorption feature at 2.35 μm with broad Si-OH absorption feature at 2.2 μm. Trona exhibits six common absorption features at 1.50, 1.74, 1.94, 2.03, 2.22 and 2.39 μm. These characteristics spectral absorption features together with the general shape of the spectral curve are used to identify the surface minerals of the area. In the mapping of different stages of evaporites and other surface minerals using Hyperion data, various image processing techniques including, the Minimum Noise Fraction (MNF), Pixel Purity Index (PPI) and Mixture Tuned Matched Filtering (MTMF) were applied. These spectral mapping methods coupled with geochemical knowledge of the area substantially improved the existing geological knowledge and enhanced the capability to derive substantial information related to the distribution and formation of precipitates and evaporites in the area.

Highlights

The Lake Magadi, in the southernmost part of the eastern Kenya rift, is one of the most interesting places to study lacustrine evaporatic sedimentation processes and their mineral reactions in the world
Are difficult to study because variations in mineralogy are not easy to recognize in the field and the large spatial extent that limits accessibility (Warren, 2006)
Different types of evaporites and solutions have been categorized as one in the published geology map, the mineral mapping process using remote sensing clearly identified and mapped the different types/stages of evaporites and solutions. patial distribution of mineral precipitates and related solutions improve the understanding of mineral formations of the area with the help of hydrogeochemical literature

Summary

Introduction

The Lake Magadi, in the southernmost part of the eastern Kenya rift, is one of the most interesting places to study lacustrine evaporatic sedimentation processes and their mineral reactions in the world. The access to relatively inexpensive satellite-borne multispectral and hyper-spectral data have created new opportunities for the regional mapping of mineralogy, geological structures and rock types including alteration products (Hewson, Cudahy et al, 2005, Vaughan, Hook et al, 2005) These techniques provide identification of different surface expressions and mapping possibilities for minerals in the hydroxyl, silicate, sulphate, carbonate and iron oxide groups covering large extents at times with inaccessible terrains. The motivation of this research is to evaluate the identification and mapping capability of different evaporites and precipitates in Lake Magadi area using space-borne hyperspectral Hyperion data with help of their spectral characteristics This output will produce a map of localities of the prospect with favourable conditions for the formation of lacustrine mineral deposits and it can be used to plan the best ground access to the prospect

Methods

Results

Conclusion