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9.7 Option — Mining and the Australian Environment: 4. The exploration and evaluation of a named ore deposit
Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002. © Board of Studies, NSW.
[Edit:7 Aug 08]
gather information to describe the impact of improvements in technology on exploration techniques
outline the common exploration methods used to identify the ore deposit (including satellite imagery, aerial photograph interpretation, geophysics, geochemistry and drilling)
Both the above dot points are covered below.
Use the information below on improvements in technology on exploration techniques and see if you can, add to this information by looking on the Internet as new technologies are developed fairly regularly.
Geological mapping, satellite imagery and aerial photography
- A geological map is a pictorial representation of surface or underground geological information.
- Certain types of ores are only associated with certain rock outcrops. So geophysicists need to know what types of rocks are present in the exploration site to evaluate its potential.
- Various geological structures reveal the presence of an ore body, eg the Kimberlite pipe at the Argyle Diamond Mine was discovered using satellite imagery.
Geochemical exploration
- Geochemical testing of soil, sediments and rock leads to identifying areas with certain useful types of mineralisation.
- Often the ore deposit is detectable chemically at some distance from the deposit.
Geophysics
- Geophysicists measure the physical properties of rocks such as elasticity, gravity, magnetism or electrical properties.
- Gravitational Anomalies may indicate the presence of some denser materials, like metal, in the search area.
Electrical methods
- Sulfide minerals are better conductors of electricity.
- Higher conductivity of the earth may indicate the presence of ore bodies.
Seismic Surveys
- Artificial seismic pulses are generated to get reflections from the layers beneath the earth.
- Repeating this process at close intervals enables the scientist to get a three dimensional image of the geological structures beneath.
Radiometric Surveys
- Gamma rays emitted by some ores may be useful data.
- Particularly useful in the search for uranium.
Drilling
- Drilling cores enables the geologists to get the best picture of the rocks below.
- Cores also bring samples of the rock to the surface for testing.
- Scientists in the CSIRO’s Heavy Ion Analytical Facility (HIAF) have developed the AUStrAliS (accelerator mass spectrometry for ultra sensitive trace element and isotopic studies) system and proton microprobe to study exploration methods and reduce discovery and evaluation time.
plan and perform first-hand investigations to test for the presence of ore minerals or metals using:
- a geophysical method
- a geochemical method
- To plan the investigation discuss with fellow
class mates and your teacher how you could simulate testing for the presence
of ore minerals or metals under the ground using the two methods listed above.
- When you have decided on a method make sure you have the required equipment, then perform the investigation. You could divide tasks among yourselves. An example of an investigation is given below.
A Geophysical method
- Magnetise a large steel nail (say a 3" nail) and bury it in sand in a large plastic sand tray.
- Orient the tray so it runs along a north-south line.
- Sprinkle a small amount of iron(II) sulfate on the sand over and around the location of the nail. You can sprinkle some in other locations too.
- Thoroughly dampen the sand.
- Measure up a grid over the sand tray (say a 10 cm x 10 cm grid)
- Get an ordinary compass and "fly" it over the sand tray (about 5cm above the surface) along grid lines, taking readings of the magnetic declination each 10cm (at grid line intersections).
- On a plan, plot declinations, noting any anomalies. This simulates aeromagnetic survey.
A Geochemical Method
- On the same grid system, take small sand samples (equal size) at each grid intersection point.
- Put each sample into labelled (with grid reference) test tubes, add about 10 mL of water and shake. Then add 1 mL of 0.1 mol/L potassium hexacyanoferrate(III) (potassium ferricyanide) solution to each test tube.
- A blue colour will indicate the presence of iron(II) ions in the sand sample - ie a geochemical anomaly. This simulates soil geochemical exploration.
- Plot any geochemical anomalies on the plan. Locations where aeromagnetic anomalies coincide with geochemical anomalies are potential drilling targets.
- You could use a plastic drinking straw as a drill to drill into the sand at the target(s). Hitting the nail is finding the orebody - exploration program successful!
- Variations include: building some topography onto the sand model; tightening the exploration grid around potential targets and doing more magnetics or geochemical sampling; having some sort of buried topography as well to record drilling depth to a boundary.
describe the role of drilling in determining the size and grade of the deposit
- Mineral exploration can be basically divided into
3 major stages:
- Area selection.
- Data collection.
- Data evaluation which includes drilling.
- Drilling is undertaken to identify the size and quality
of the deposit, and a feasibility study is conducted. If the deposit is
too small, not concentrated enough or too isolated, then mining of the area
is abandoned.
- The NSW Department of Mineral Resources Core
library
at Londonderry, near Sydney, provides a range of catalogued drilled
cores from areas all over NSW. This library is an important resource for sampling
or inspection of the rock strata of previously drilled areas, to evaluate
whether further mining can proceed.
gather information from secondary sources to analyse the processes used to determine the feasibility of mining the deposit
Information can be gathered by going to the Internet or by contacting local
mining companies by telephone. A website that has information about how to
determine feasibility is Mining Feasibility for Mining Company Project Australia. Another website is Feasibility GemCom, Mine Production Management Solutions, Vancouver, BC, Canada
analyse the process of determining the feasibility of mining the deposit, referring to the stages involved in its development from a resource to a reserve
Once a deposit has been detected by drilling, a feasibility study is carried out to determine whether it is viable to mine the site. If the deposit is too small, not concentrated enough or too isolated, then mining of the site will not continue. On average, about ten potential mine sites out of every thousand will reach drilling stage, and of these, only one will lead to the development of a mine.
The feasibility study may be divided into stages:
- Economic concepts and criteria
- outlining the economic basis for exploration decisions
- investigation of the risks and returns of mining, along with exploration costs
- discussion of the role mining of such a deposit will have in the mining company
- consideration of the expected value of the deposit.
- Documentation of data
- definition of the geological regions
- estimation of the cost of exploration by considering
the exploration environment, time needed and geological region.
- Data base compilation
- listing of possible discoveries for evaluation
- projection of long term metal prices
- investigation of the net economic return from the smelter
- estimation of the deposit size and cost for the deposit based on historical data
- development of general deposit costing relationships.
- Before tax assessment of exploration
- a set of base conditions are evaluated (including
the exploration environment, geographical region, metal prices, mineral
fields and time requirements) before an analysis is given.
- a set of base conditions are evaluated (including
the exploration environment, geographical region, metal prices, mineral
fields and time requirements) before an analysis is given.
- After tax assessment of exploration
- consideration of present Australian income tax and state royalty payment systems
- overall analysis of the viability of mining the chosen site.
explain how local, state and federal government policies may affect the decision to mine the deposit
State
The Environmental Policy of the NSW Department of Primary Industry, Mineral Resources states several controls imposed on the mining industry that may affect its decision to mine a deposit. If any of the controls below are breached, sanctions may be incurred by the Department:
- The Department reviews Environmental Impact Statements and compares them to performance criteria, through a consultative process involving other government agencies and stakeholders.
- The Department reviews environmental data.
- The Department conducts site inspections and audits.
- The Department investigates incidents.
Federal
- The federal government controls the export of minerals so a mine wouldn’t go ahead if it didn’t have a licence to export the mineral they intend to mine.
- As well as the state environment laws the federal government also has environmental legislation. The current one is the Environmental Protection and Biodiversity Conservation Act, 1999. Companies must comply with federal legislation if the commodity is to be traded between Australia and another country or between states or territories. This legislation also must be complied with if the trading of the commodity involves Australia’s obligations under an agreement with one or more other countries.
The site below is for the Ranger Uranium Mine and is a special case as it is within the World Heritage Kakadu National Park. Environmental requirements of the Commonwealth of Australia for the operation of Ranger uranium mine.
gather information from secondary sources to examine methods used to extract and refine the ore from the deposit
The best place to gather information is from the Internet. Below is a link to the Minerals Council of Australia. You could also find information about overseas mines by using a search engine.
- The Minerals Council of Australia has information
on mining in NSW. Click on whichever mineral you want to research and
scroll down to 'Mining and processing'.
assess the impact of installing infrastructure or using that which already exists on determining the feasibility of mining the deposit
- The impact of the installation of infrastructure may
be very complex and very expensive.
- Decisions need to be made as to the method of mining
such as open cut, strip mining, quarrying or underground.
- If the mine is a long way from civilisation, a town
for the workers will have to be built.
- What process will be needed for the treatment of the
ore?
- How will the ore be carried to the surface or carried
to the treatment plant? A railway may be needed.
- When completed the mine will have to be rehabilitated.
- All will have an impact on the installation of infrastructure.
outline the methods and technologies used in the extraction, concentration and refining of ore from the deposit
Example: Uranium
Extraction:
Uranium is usually extracted using one of three mining methods:
- Open-cut mining methods, which involves
the topsoil being removed and stockpiled separately for rehabilitation
purposes. The deposit is simply removed by digging a large excavation
called an opencut. As the opencut increases in depth its walls are sloped
to avoid collapse. Examples of open cut mines include the Ranger, Nabarlek,
Mary Kathleen and Rum Jungle ore bodies.
- Underground mining methods are more complex
as they must consider deposit accessibility, ground support, ventilation,
blasting and haulage. Access to the underground ore body is either by
vertical, horizontal or inclined shafts. Underground mining is used where
the uranium is not near the surface. Examples of underground mines include
Olympic Dam, Radium Hill and South Alligator Valley deposits.
- In-situ leaching is used when the uranium deposit occurs within a sandstone area. This involves the pumping of an acidic or alkaline solution through the porous sandstone, which acts to dissolve the uranium deposit. The solution containing the uranium is then recovered and sent to be processed. Honeymoon and Beverley are examples of mines using in-situ leaching.
Concentration
Concentration of the uranium involves the following steps:
- The uranium ore is crushed into a fine powder
and mixed with water to produce a slurry.
- The slurry is treated with either an acidic or
alkaline solution (depending on the characteristics of the ore), which
causes the uranium to dissolve in the solution.
- Non-uranium minerals (called ‘tailings’)
which usually remain undissolved are separated from the uranium-rich liquid
by allowing them to settle out.
- The uranium-rich liquid is filtered to remove any solids before the uranium is recovered using either solvent extraction, ion exchange or direct precipitation (again depending on the characteristics of the ore).
Refining
Refining involves three steps:
- The uranium is recovered in a precipitate which
is filtered and dried to produce a yellow powder called yellowcake.
- The yellowcake is heated to 700°C, producing
dark grey uranium oxide powder.
- The powder is placed in steel drums for export.
The Uranium Information Centre
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