ASTER

How modern technologies can help us?

As consultant geologists always looking for new targets and expanding existing ones, we are constantly trying to cover more ground in less time, and to deliver useable product to our clients. Time allocated for fieldwork is sometimes limited, and will probably become more constrained in the future (the excuses being dollars and safety). Thus, we need to address the case of how we maximise efficiency, maintaining production of high-quality deliverables. How to do that? Personally I am seeing this as a situation where we need to utilise modern technologies to help us. The particular emphasis here is on the word “HELP”. Some outside our professional niche of greenfields mineral exploration believe modern technology is capable of replacing many tasks (in other words, take our jobs away). SJS believe that technology should not be used to replace fieldwork, but rather to augment, streamline, and ­­­­improve the process, resulting in time efficient workflows and high-quality deliverables.

At SJS we implement the newest, state-of-the art products and trends in order to make our workflow time-efficient. When exploring on greenfield ground, we promote classic structural geological methodology to analyse and interpret data, but also there are certain techniques and products which allow us to get there faster and can be used to augment the exploration process.  One of these products is ASTER, multispectral satellite imagery. Australia is a great place to implement it in a workflow, because the products are already processed and publically released (thanks to CSIRO, Tom Cudahy and others - link). Utilising ASTER before going into the field helps focus, pinpoint exploration targets, and reduce time spent in the field.

What is ASTER?

ASTER stands for Advanced Spaceborne Thermal Emission and Reflection Radiometer. ASTER is collaboration between The Japanese Ministry of Economic Trade and Industry, and NASA. The first instrument was launched on board NASA's Terra satellite in 1999. Simply put, ASTER measures reflected light and emitted EM radiation from the Earth surface and atmosphere. The ASTER multispectral satellite system consists of three separate sub-systems with a total of 14 spectral bands. Bands span from visible, near-infrared (VNIR), shortwave infrared (SWIR), thermal infrared (TIR). The pixel resolution is dependent on the band, but in general ranges from 15 to 90m.  For more information please refer to CSIRO website and their product notes (link).

The ASTER spectral bands do not have sufficient spectral resolution to accurately detect specific minerals, contrasting with hyperspectral systems (hundreds of channels), but ASTER is good enough for detection of important rock forming and alteration-related minerals such as muscovite, chlorite, carbonates, iron oxides, clays and quartz as well as mineral groups such as AlOH group, MgOH group, and FeO group. As I mention before, ASTER data was processed by CSIRO, using a methodology proposed by Hewson et al. (2005) and Cudahy et al. (2008) and released to the public as different vegetation and mineral groups, and content/composition products available from CSIRO and GSWA websites.

So... does it work and how does it work?

Does it work? The short answer is: YES, it does! ...well, anyway, in most cases.

ASTER has been used successfully across different deposits, such as Pb-Zn-Au (Broken-Hill), Cu-Mo (Infiernillo deposit), Mn (Woodie Woodie), Fe (Weld Range), and a VMS deposit of the Panorama Formation (Van Ruitenbeek et al., 2011).

As showed at Panorama (Van Ruitenbeek et al., 2011), hyperspectral/multispectral studies are effective in exploration for VMS deposits. Detection of potassium-alteration zones and Al-rich (e.g. muscovite) and Al-poor mica (e.g. phengite) mineral groups may provide important constraints in order to reconstruct the palaeo-fluid pathways related to VMS-mineralisation systems. At Panorama and elsewhere, the reconstruction of Al-poor white mica domains indicated mineralisation areas and proximity of the ore-body position (e.g. Van Ruitenbeek et al., 2011).

Conceptual model of palaeo-fluid flow (recharge and discharge cells) and associated hydrothermal alteration. Panorama area, Pilbara, WA. From Van Ruitenbeek et al., 2011. The cells are usually detectablle by multispectral (ASTER) and hypespectral imagery.

SJS use ASTER to augment exploration for base metals in different terranes with differing structural and mineralisation styles. In most cases, the ASTER signal is subsequently confirmed on the ground.

In spite of its limited spatial (in average, 30m pixel size) and spectral resolution (multispectral, 14 bands) ASTER offers a cost- and time-effective tool for mineral deposit exploration. That said, ASTER-defined targets require field verification, but ASTER data interpretation provides one more important constrain and thus reduces overall time (and thus money) spent on field-work. Combined with structural, geological and geochemical data collected in the field, and a geologist's knowledge and experience, multispectral imagery has great potential in greenfields exploration, and certainly “helps” especially in times when consultants are required to produce high-quality and precise exploration programmes under strict time constraints.

SJS has necessary experience and effective workflow with ASTER analysis in Australia to streamline workflows and constrain exploration targets.

Mario Zelic, SJS Resource Management 13-Mar-2014
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Julian Vearncombe

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