SWIR Case Study: Mineral Exploration

Delivering unprecedented geologic information.

Revolutionising the remote sensing mineral exploration market, WorldView-3 will deliver detailed geological maps to clients in a rapid, cost-effective manner.

In many countries, mining can account for up to 90 percent of a country's gross domestic product and provide employment for a significant percentage of the population. Billions are invested yearly in mineral exploration, but traditional ground survey methods are expensive, potentially restricted by social, political or environmental issues, weather or access and are unable to thoroughly explore large areas in a timely manner.

WorldView-3's multispectral and SWIR data make it possible to generate spectral reflectance maps which show accurate and detailed geology for optimised field exploration at a high resolution, without being affected by adverse developments in the political climate or weather conditions allowing mining companies a scalable, cost-effective, qualitative and continuous way to explore for minerals.

The following case study is an example of the use of WorldView-3's multispectral and SWIR data to identify lithology with a high potential for uranium mineralization, adjacent to the Rӧssing Uranium Mine in Namibia. The higher resolution WorldView-3 imagery is directly compared to lower resolution ASTER imagery over a test site south west of the mine.

Previous interpretation work by Anderson and Nash (Reference 1) using Landsat and aeromagnetic and airborne radiometric data is included in this case study and showcases the unprecedented detail available in the WorldView-3 imagery. Geoimage gratefully acknowledges the contributions by Dr Colin Nash to this paper.

Namibia: Southwest of Rӧssing Uranium Mine

Excerpts from www.rossing.com/history.htm:

"Uranium was discovered in the Namib Desert in 1928, but it was not until intensive exploration in the late 1950s that much interest was shown in the area. After discovering numerous uranium occurrences, Rio Tinto secured the rights to the low-grade Rӧssing Uranium deposit in 1966. Ten years later, Rӧssing Uranium, Namibia's first commercial uranium mine, began operating.

Today, Namibia has two significant uranium mines, which together provide for 5.8 per cent of the world's uranium oxide mining output. Rӧssing Uranium produces 2.3 per cent of the world's uranium oxide production. The mine has a nameplate capacity of 4,500 tonnes of uranium per year and, by the end of 2014, had supplied a total of 127,405 tonnes of uranium oxide to the world.

The mine is located 12 km from the town of Arandis, which lies 70 km inland from the coastal town of Swakopmund in Namibia's Erongo Region. Walvis Bay, Namibia's only deep-water harbour, is located 30 km south of Swakopmund.

The mine site encompasses a mining licence and accessory works areas of about 180 km2, of which 25 km2 is used for mining, processing and waste disposal. Mining is done by blasting, loading and hauling from the open pit, referred to as the SJ Pit, before the uranium-bearing rock is processed to produce uranium oxide. The open pit currently measures 3 km by 1.5 km, and is 390 m deep."

The alaskite type Rӧssing uranium deposit contains the largest uranium deposit in the world associated with an igneous rock and lies within the 400 to 500 km-wide Upper Proterozoic Damara orogenic belt, which extends from the Atlantic Ocean north-easterly across south western Africa before submerging beneath the post-Palaeozoic Kalahari Basin. Rӧssing is located on the south western flank of a regional oval NE-SW trending dome, about 2km from the contact of a gneissic Proterozoic basement and meta-sediments consisting of schist and graphite- and sulphate-rich marble (Reference 2).

Location of test site outlined in red.
Rӧssing Uranium Mine lies to the north east of the test site.
Background image is a natural colour composite of Landat8 data acquired 30 August 2015.

;

Geological interpretation by Anderson and Nash (Reference 1), based on LANDSAT imagery, and aeromagnetic/airborne radiometric data

WorldView-3 image.
False colour composite over the test site - vegetation is shown in red.
Pixel resolution is 0.5 metres.

ASTER image.
False colour composite over the test site - vegetation is shown in red.
Pixel resolution is 15 metres.

WorldView-3 image.

True colour composite over the test site - equivalent to a Landsat 742 composite. Geological boundaries are from interpretation of LANDSAT, aeromagnetic and radiometric data by Anderson and Nash (Reference 1).

Uranium mineralisation occurs in the Rӧssing (R) and Khan (N2) Formations. Strongly foliated pelitic schists and gneisses of lower Nosib Gp (N1) contain abundant white concordant pegmatitic granites. The massive pyroxene/hornblende gneisses of the Khan Fm (N2) show up as red/brown.  Abundant white pegmatitic granites east of Khan Mine appear to be both concordant to foliation and locally transgressive. Rӧssing Fm carbonate/schist unit (R) forms low outcrops.

Pixel resolution is 7.5 metres.

ASTER image.

True colour composite over the test site - equivalent to a Landsat 742 composite.

Geological boundaries are from interpretation of LANDSAT, aeromagnetic and radiometric data by Anderson and Nash (Reference 1).

Uranium mineralisation occurs in the Rӧssing (R) and Khan (N2) Formations. Strongly foliated pelitic schists and gneisses of lower Nosib Gp (N1) contain abundant white concordant pegmatitic granites. The massive pyroxene/hornblende gneisses of the Khan Fm (N2) show up as red/brown.  Abundant white pegmatitic granites east of Khan Mine appear to be both concordant to foliation and locally transgressive. Rӧssing Fm carbonate/schist unit (R) forms low outcrops.

Pixel resolution is 30 metres.

WorldView-3 image.

Al-OH Mineralogy composite over the test site.

Geological boundaries are from interpretation of LANDSAT, aeromagnetic and radiometric data by Anderson and Nash (Reference 1).

Uranium mineralisation occurs in the Rӧssing (R) and Khan (N2) Formations.

Pixel resolution is 7.5 metres.

ASTER image.

Al-OH Mineralogy composite over the test site.

Geological boundaries are from interpretation of LANDSAT, aeromagnetic and radiometric data by Anderson and Nash (Reference 1).

Uranium mineralisation occurs in the Rӧssing (R) and Khan (N2) Formations.

Pixel resolution is 30 metres.

WorldView-3 image.

Decorrelation Stretch of SWIR bands 765 over the test site.

Geological boundaries are from interpretation of LANDSAT, aeromagnetic and radiometric data by Anderson and Nash (Reference 1).

Uranium mineralisation occurs in the Rӧssing (R) and Khan (N2) Formations. Strongly foliated pelitic schists and gneisses of lower Nosib Gp (N1)contain abundant pink concordant pegmatitic granites. The massive pyroxene/hornblende gneisses of the Khan Fm (N2) show up as brown. Abundant pink pegmatitic granites east of Khan Mine appear to be both concordant to foliation and locally transgressive. Rӧssing Fm carbonate/schist unit (R) forms low outcrops and display a greenish colour.

Pixel resolution is 7.5 metres.

ASTER image.

Decorrelation Stretch of SWIR bands 765 over the test site.

Geological boundaries are from interpretation of LANDSAT, aeromagnetic and radiometric data by Anderson and Nash (Reference 1).

Uranium mineralisation occurs in the Rӧssing (R) and Khan (N2) Formations. Strongly foliated pelitic schists and gneisses of lower Nosib Gp (N1)contain abundant pink concordant pegmatitic granites. The massive pyroxene/hornblende gneisses of the Khan Fm (N2) show up as brown. Abundant pink pegmatitic granites east of Khan Mine appear to be both concordant to foliation and locally transgressive. Rӧssing Fm carbonate/schist unit (R) forms low outcrops and display a greenish colour.

Pixel resolution is 30 metres.

The Last Word

The Rӧssing case study illustrates how well WorldView-3 delivers improved definition of geological units and particularly the uranium bearing formations, which would help exploration efforts to locate additional uranium deposits near and around the mine site.

WorldView-3 multispectral and SWIR imagery provides vastly improved capabilities in support of geological and other surface mapping applications by delineating

  • Clays
  • Carbonates
  • Iron-bearing rocks and iron oxide
  • Alteration products
  • Mica

at a higher resolution than previously available. The sharper images from WorldView-3 lead to improved analysis and interpretation, providing better discrimination of complex alteration systems.

Geoimage has expertise in processing multispectral and SWIR data and can help you to extract the most information from your data. The techniques and processes used in this Rӧssing case study can be applied to other commodities and we also offer complementary services such as Digital Elevation Model generation from stereo imagery, digital mosaics to cover large areas or remove cloud, and subscription services to online imagery.

The next topic allows you to access and analyse a SWIR sample mining dataset. Click here to read.


      

Reference 1: Anderson and Nash, Explor.Geophys. Vol. 28

Reference 2: World Distribution of Uranium Deposits (UDEPO) with Uranium Deposit Classification 2009 Edition

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