Exploring for minerals is a challenge that miners need to approach with as much information as possible. Rare metals and minerals can easily be missed, and the process of searching for them is an expensive risk.
That is why remote sensing in mineral exploration is so important. Remote sensing involves gathering information about the physical world by measuring the radiation, particle and field signals that emanate from objects. The data can be used to identify and categorize different objects — all without needing to make physical contact.
Remote sensing isn’t a specific technology, but rather an umbrella term for a number of techniques and tools. These include radar, geographical information systems and sonar, to name a few. These tools are used to gather valuable visual and spectral data. That data can then be analyzed to create insights throughout the mineral exploration process.
Remote sensing images are used for mineral exploration in two key ways:
- Mapping the geology, faults and fractures of an ore deposit.
- Recognizing hydrothermally altered rocks by their spectral signature.
Images are gathered either through optical sensors, or through synthetic aperture sensors. Optical sensors measure the spectral data of sunlight reflected from the Earth’s surface. Synthetic aperture sensors are able to sense electromagnetic data by transmitting microwaves and receiving the back-scatter waves from the Earth’s surface.
Remote sensing benefits
Remote sensing is a valuable tool in mineral exploration, thanks to its ability to save time and money while providing helpful information. It is best used for the discovery of high-value commodities such as diamonds and gold, which are becoming more difficult to locate. While it may not show exactly where major deposits are, data gathered through sensors can be used to narrow field surveys to smaller areas.
Remote sensing also provides value by reducing the risk of a project and helping prioritize which sites to explore first. Expensive operations like drilling and field work can come after information is gathered.
The greatest advancement in mineral exploration has been the ability to synthesize various forms of data. Known drill results can be integrated with topographic maps, air photos, structural maps and ore grade data. Data synthesis can greatly increase the accuracy and effectiveness of an exploration program.
The history of remote sensing
Remote sensing has been around since before World War II, but has rapidly advanced in recent years. Initially, the primary use of remotely gathered data was comparative. If gold was found in a particular area, aerial photos of that area would be compared with aerial photos of other locales in order to find places with similar surface features. The hope was that they too would cover a valuable gold deposit.
Once satellite imagery became commercially available, the same compare-and-contrast method was used with satellite images. To date, aerial photography is still used as an exploration tool. Aerial photographs are used to identify topographic surface features that may imply the subsurface geology. Surface features like differential erosion, outcropping rock, drainage patterns and folds can be identified. Faults and contacts often provide a conduit or depositional environment for hydrothermal or magmatic fluids in regions of known mineralization. This makes them excellent targets for deeper exploration.
The advent of multispectral imaging and thematic mapping has allowed surface mapping to be performed remotely. This enables vast areas to be mapped in a short time, at a fraction of the cost of traditional geologic mapping. Different scanning spectrums have enabled researchers to begin cataloguing various reflection and adsorption properties of soils, rock and vegetation.
These spectra can be utilized to interpret actual surface lithologies from remote images. Among the most valuable data collected are the weathering and alteration products of mineral deposits, especially clays. Clays and oxides can be readily differentiated by the spectra utilized for remote sensing. By correlating the alteration products to parent materials, potentially valuable ores may be distinguished without the need for extensive soil sampling programs.
Spectral signatures and classifying images
Collecting data in the field is just the first step in coming up with a product that is useful in exploration. The next step is to translate the data into a form that is presentable to explorers, and one way to do that is through image classification. Remote sensing makes use of spectral signature. For any given material, the amount of solar radiation that it reflects, absorbs, transmits and emits varies with wavelength. When the amount of radiation from an object is plotted over a range of wavelengths, the connected points produce a curve called the material’s spectral signature.
All objects have a unique spectral signature, and similar objects share a spectral signature. Once a company has identified the spectral signature of an object, the same signature can be searched for in other data sets to find patterns and similar objects. To determine an object’s spectral signature, sensor data needs to be manipulated and processed. Most of this manipulation is accomplished by altering spectral color bands in the image.
Popular techniques and technologies
While remote sensing in mineral exploration is a rapidly advancing field, currently most remote sensing is performed through the following technologies:
Remote sensing is a mainstay in mineral exploration and for good reason. Advances in data processing and sensor technology will continue to allow explorers to take more calculated risks and gauge their mining progress with a sense of accuracy.
What else would you like to know about remote sensing, or other exploration technologies? Let us know in the comments below.
Don’t forget to follow us @INN_Resource for real-time updates!
This is an updated version of an article originally published by the Investing News Network in 2011.
Securities Disclosure: I, Amanda Kay, currently hold no direct investment interest in anything mentioned in this article.