GRSG 34th Conference 2023

Title: Multi-scale approach to remote sensing mineral exploration for expansion of a Moroccan silver mine – the Imiter case study

Author: Alfie Baines

CGG Satellite Mapping carried out a multi-sensor, multi-scale remote sensing study over the Imiter silver mine in the Bou Azzer district (Ouarzazate, Morocco) and surrounding areas to identify potential targets for mine expansion. The Imiter silver mine represents a typical low-sulphidation epithermal, with some evidence of Iron Oxide Copper Gold (IOCG) style mineralization. Epithermal deposits are typically evident at surface, showing strong structural controls and association with characteristic alteration mineral assemblage, making them ideal targets for remote sensing studies. Sentinel-2, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and WorldView-3 (WV-3) multispectral satellite data were integrated with various Digital Elevation Models (DEMs) of increasing spatial resolution.

A team of specialist remote sensing and structural geologists mapped the geology at regional (1:25,000) and local (1:5,000) scales, producing a complete lithostratigraphic database and structural interpretation; this geological interpretation is based on true color composites, false colour RGB composites and DEM derivative layers. Spectral geologists derived detailed ‘mineral maps’ from multispectral SWIR data (ASTER and WV-3), identifying three families of intrusive dikes with distinct alteration haloes. High resolution (2.5 m spatial) DEM data and WorldView-3 optical (VNIR – SWIR) data also identified regions of massive quartz veining. Mine operators provided insights on structural controls and mineral associations to assist with mapping and target identification.

Mineralisation occurs as infill in m-scale wide, 10 – 100 m-scale long pull apart structures related to transtensional stress. Mineralised structures are generally restricted to the footwall of a regional E-W trending normal fault and associated with strong propylitic (especially chloritic) alteration. High resolution WV-3 data enabled a more consistent structural interpretation, leading to the identification of many more pull apart structures capable of hosting mineralization. Spectral mineral maps highlighted zones of hydrothermal alteration related to previously unidentified intrusive dykes, potential veining, and more typical (non-linear) alteration haloes, all of which are indistinguishable in true colour imagery.

Spectral geologists developed new methods to investigate alteration signatures and interpret RGB false color composites. Integration of new insights from specialist mapping, structural reinterpretation and spectral processing identified high-priority targets for further study. In particular, deposit-scale structural mapping complemented the regional-scale reinterpretation and identified a number of structures with high mineralization potential at both scales. Furthermore, most intrusives identified in WV-3 mineral maps were indistinguishable in ASTER data, highlighting the importance of datasets optimized for the deposit scale.

CGG Satellite Mapping carried out a multi-sensor, multi-scale remote sensing study over the Imiter silver mine in the Bou Azzer district (Ouarzazate, Morocco) and surrounding areas to identify potential targets for mine expansion. The Imiter silver mine represents a typical low-sulphidation epithermal, with some evidence of Iron Oxide Copper Gold (IOCG) style mineralization. Epithermal deposits are typically evident at surface, showing strong structural controls and association with characteristic alteration mineral assemblage, making them ideal targets for remote sensing studies. Sentinel-2, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and WorldView-3 (WV-3) multispectral satellite data were integrated with various Digital Elevation Models (DEMs) of increasing spatial resolution.

A team of specialist remote sensing and structural geologists mapped the geology at regional (1:25,000) and local (1:5,000) scales, producing a complete lithostratigraphic database and structural interpretation; this geological interpretation is based on true color composites, false colour RGB composites and DEM derivative layers. Spectral geologists derived detailed ‘mineral maps’ from multispectral SWIR data (ASTER and WV-3), identifying three families of intrusive dikes with distinct alteration haloes. High resolution (2.5 m spatial) DEM data and WorldView-3 optical (VNIR – SWIR) data also identified regions of massive quartz veining. Mine operators provided insights on structural controls and mineral associations to assist with mapping and target identification.
Mineralisation occurs as infill in m-scale wide, 10 – 100 m-scale long pull apart structures related to transtensional stress. Mineralised structures are generally restricted to the footwall of a regional E-W trending normal fault and associated with strong propylitic (especially chloritic) alteration.

High resolution WV-3 data enabled a more consistent structural interpretation, leading to the identification of many more pull apart structures capable of hosting mineralization. Spectral mineral maps highlighted zones of hydrothermal alteration related to previously unidentified intrusive dykes, potential veining, and more typical (non-linear) alteration haloes, all of which are indistinguishable in true colour imagery. Spectral geologists developed new methods to investigate alteration signatures and interpret RGB false color composites. Integration of new insights from specialist mapping, structural reinterpretation and spectral processing identified high-priority targets for further study. In particular, deposit-scale structural mapping complemented the regional-scale reinterpretation and identified a number of structures with high mineralization potential at both scales. Furthermore, most intrusives identified in WV-3 mineral maps were indistinguishable in ASTER data, highlighting the importance of datasets optimized for the deposit scale.