While first movers with satellite mapping methods have known since the early 1970s the benefits of being able to quickly process huge imagery datasets, the recent squeeze on exploration budgets may inspire the further proliferation of the often-ignored tool.
For explorers, one of the most essential remote sensing tools is Japan’s advanced spaceborne thermal emission and reflection radiometer, or ASTER.
ASTER collected shortwave infrared information on the earth’s surface from NASA’s Terra satellite between 1999 and 2008, amassing an enormous archive of accessible and potentially efficiency-improving geological data covering the entire planet.
It is the only satellite system specifically designed for the mapping of mineral groups such as clays and iron oxides commonly occurring in alteration zones associated with mineralisation.
Image processing algorithms applied to ASTER data can map mineral alteration from porphyry copper-gold-moylbdenum systems, epithermal gold-silver systems, volcanic-hosted massive sulphide systems and mesothermal gold systems.
It allows explorers to identify the best places within large alteration zones where mineralisation is determined more likely to occur, saving time, money and a number of unnecessary permitting headaches.
To get a better idea of how ASTER image processing can streamline exploration in the mining industry, MiningNewsPremium.net spoke with Global Ore Discovery geologist Daryl Nunn.
Global Ore Discovery specialises in remote sensing, structural interpretation, database manipulation and mineral systems analysis, with an aim of putting explorers on the ground in the best locations.
Through the processing and targeting of ASTER imagery, the consultancy has been able to position clients’ field teams onto outcropping mineralisation in various parts of the world, including the Tien Shan area of the central Asian gold belt, the well-explored porphyry copper belt of northern Chile and the Santa Cruz epithermal gold-silver province of southern Argentina.
“The alternative requires having a geologist on the ground and it takes a lot of time and capital to map a large area,” he said.
“Whereas an ASTER scene is 60 kilometres by 60 kilometres and we can process and target that in less than a week and identify the best areas of alteration for field follow-up.
“You’re doing a non-invasive technique that doesn’t require ground clearance.
“You don’t need to go through the processes of indigenous ground clearance, landowner negotiations or any of those other things that take time away from exploration.
“This satellite data is there and ready to be used without having to go through the process of clearance for acquisition – and one of the biggest costs of exploration at the moment is getting on the ground.”
Specifically, ASTER is best at reading spectral responses from iron oxides, carbonates, silica content, kaolinite, white micas, alunite, pyrophyllite, chlorite, epidote and jarosite.
It can also be used in night-time thermal imaging for groundwater, palaeochannel uranium and geothermal exploration.
Image processing of this kind can be especially useful in vast, overseas locales where logistics can be difficult and mineral data is scarce but tantalising.
“ASTER’s a great tool, particularly in places like west Africa where to fly an airborne survey you have to get expensive equipment overseas and you’ve got all the added mobilisation costs,” Nunn said.
“When you’re looking at bang for your buck, ASTER can be a great filtering tool for the initial stages of exploration.
“We have also found new outcropping mineralisation in near mine situations where it has been overlooked or unrecognised by ground crews after years of exploration.”
In Australia, ASTER has an archive of more than 35,000 scenes, 3500 of which make up a web-accessible continental overview through Geoscience Australia’s national ASTER mosaic.
A recent application at Orion Gold’s Connors Arc project in Queensland resulted in the identification of five new targets.
Global Ore conducted the processing for Connors Arc’s ASTER data, confirming the technique as serviceable for broad-scale, grass-roots style targeting methods, which improves confidence in on-ground follow-up.
“ASTER is not a magic bullet technique but is invaluable when integrated with other regional datasets such as magnetics, gravity, stream sediments and geological mapping,” Nunn said.
“Through integrating this technology with other datasets, we have helped focus our clients’ field teams into the higher priority target areas.
“This makes for better exploration efficiency and has in a number of cases led to ‘discovery outcrops’ that with further exploration have turned into significant precious metal resources.”
