Geologists study the rocks and landscape that make up Western Australia. By looking at and sampling rocks, they can find out how and when these rocks formed. The knowledge gained by working in the bush is produced as geological maps and reports, which help the community, industry and government to plan for the future.
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Government geologists making maps
It's a big State
With a surface area of more than 2.5 million square kilometres, Western Australia is easily the largest state in Australia. Geological mapping started in the middle of the 19th century, with geological observations made during expeditions in search of mineral deposits, water and pastoral land. The Geological Survey of Western Australia (GSWA) was established in 1888, when the first full-time Government Geologist was appointed. Systematic mapping started in the 1950s, to map the whole state at 1:250 000 scale, a goal reached in 1980. More detailed mapping at a 1:100 000 scale is still in progress today. New mapping projects at GSWA are prioritised on the basis of potential for maximum benefit to the community.
Before starting a mapping project, geologists consult with Aboriginal, pastoral and mining stakeholders, along with the Department of Parks and Wildlife and other government agencies.
Geologists use airphotos, satellite images and GPS to locate outcrops. Field measurements are made with a compass, and detailed field observations are recorded on a portable tablet computer that is preloaded with satellite and geophysical imagery. Hardcopy airphotos have now been largely superseded by rectified air photos stored on the tablet computer.
In the past, camels and horses were used during geological expeditions. These were gradually replaced during the 1920s in favour of motorised vehicles, with ships and rail used for the bulk of some journeys. Occasional use of aeroplanes began in the 1930s.
Today geologists use four-wheel-drive vehicles to get to rock outcrops. They carry camping and safety equipment, as well as food and water. They may shift camp every few days as they map an area, or fly camp at a different place each night.
Helicopters are sometimes used to access remote outcrops and collect samples. They are more effective for the collection of large sample numbers in regional geochemical surveys.
Rock and soil samples
Geologists collect rock and soil samples for further studies. These typically include:
- petrography — cutting a thin slice of the rock to view under a microscope, which helps identify the different minerals that make up a rock
- geochronology — extracting key minerals from rocks in order to date them
- chemical analysis — determining the concentrations of many elements and understanding rock origins
Back at the office
The geological map takes shape as the geologist combines the information gathered during fieldwork and the subsequent analyses onto a map base. Today, geophysical imagery, particularly detailed aeromagnetic imagery, is an integral part of the interpretive process.
In the past, maps were hand drawn and hand coloured, but computers now make the job more accurate. Geological data is assembled using Geographic Information System (GIS) software that allows a better spatial accuracy. Each map typically comprises a base with topographic information with a superimposed coloured geological map. A map legend is an essential part of the geological map, and illustrates the age, lithology, stratigraphy and structural relationships of rock units in a given area.
The final map
Geological maps are plotted by computers rather than offset printed. As well as rock types and outcrops, the maps show creeks, roads, tracks, bores, mineral deposits and other landmarks. They may provide the most accurate topographic information available, as ground-truthing is part of the mapping process. Physical maps are now just one layer in a multi-layered package of intelligent digital spatial data. GSWA provides a free GIS tool, GeoMap.WA, to view, interrogate and manipulate this data. Users can take the data into the field via a laptop computer, rather than a simple paper map spread over the vehicle bonnet.
GeoMap.WA is a computer-based application that allows users to visualise, interrogate and integrate vector and raster data types and associated attribution
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