Companies search globally for mineral deposits that can be economically mined and processed. Mineral exploration is made up of a variety of different activities and techniques that are used to find a potential discovery – which may one day become an operating mine.
Going from a previously unexplored piece of land ("greenfield exploration") to a well-defined mineral deposit can take years of work and huge sums of money. The chance of success is slim, but the right find can yield large benefits for stakeholders.
In 2017 alone, companies spent roughly $8 billion on global exploration efforts to find new precious and base metal, diamond and uranium deposits.
There are three main groups of techniques that may be utilized during mineral exploration programs, depending on the mineral deposit type and stage of exploration that is being pursued – as well as the location and budget of the program. These techniques include:
From geological mapping to rock sampling and trenching, geological techniques can provide key clues of a potential discovery at surface.
Generally built on existing maps from government or other sources, geologists will spend time in the field looking at rocks and mineral showings, then recording their interpretations in order to create high-quality maps on a small scale.
Typically a topographic map will be used at first, and a geology map will be produced once enough information on the area has been collected. This geology map will be used as a starting point for further exploration activities.
Stripping and Trenching
When mineralization is discovered on a property, the team will want to sample it to determine its characteristics and accurately map where it is on the property. Stripping and trenching may be required to remove overburden that is covering the mineralization.
Stripping involves removing a shallow amount of dirt, gravel or sand that may lay on top of the rock, and trenching makes use of blasting or digging to get into the rock and expose a vertical section of mineralization.
Chemical analysis of material, from rocks and soil to vegetation and sediment in lakes and streams.
Analysis at Assay Labs
Samples that are collected from an exploration property are sent to third-party labs for assaying. At the lab, the samples (rocks, soil, etc) will be prepared for analysis by going through drying, crushing and/or milling to create a small, fine material that is then run through various tests to determine the chemical elements that make up the sample – and in what concentrations.
An example of a common test is to dissolve the sample in an acid mixture and analyze it using an inductively coupled plasma (ICP) device that can measure the relative mass of each element using a technique called mass spectrometry (MS). These tests can detect up to 40 different elements.
Geology teams will collect rocks during the process of mapping and evaluating surface mineralization, which will be documented and assayed to increase the exploration knowledge of the property.
There are three types of samples of rocks:
Grab – Pieces of rock collected on a property. These samples may be collected randomly, or by the highest degree of visible mineralization, and so the resulting metal concentrations are not to be taken as a representation of the overall potential of the property. Grab samples are simply indicators to simply help define further exploration work.
Chip – A composite rock sample made up of chipping fragments of rock continuously along a width of exposed rock, with the goal of accumulating an equal size of rock along the length of the rock exposure. Chip samples can give grade and width information of a potential mineralization.
Channel – Similar to a chip sample, the goal of a channel sample is to collect a continuous sample of rock along the length of a sample. For a channel sample, this is done by using a rock saw and chisel and making several cuts into the chosen rock. Channel samples can give the most accurate information of any rock sample, and the data provided can be used in resource estimates.
Sampling by Other Means
If there is not enough exposed rock on a given property to sample, the next best bet is to collect soil, till and stream sediment samples that may give clues as to potential mineralization.
Geophysical methods are a set of analytical techniques that define the physical properties of minerals and rocks, including:
- Magnetism – Testing for differences in the amount of magnetite/pyrrhotite in a given rock. Typically useful for finding VMS deposits and kimberlites.
- Electromagnetic (EM) – Generally used to find deposits hosting sulphide minerals of interest (e.g. Cu, Ni)
- Induced Polarization (IP) – Method that measures the response of the ground after charging it with an electrical current. Can be useful in identifying certain porphyry copper, VMS and precious metal vein deposits.
- Radioactivity – Used to detect uranium, thorium or potassium, elements that can lead to the discovery of uranium, iron oxide copper gold (IOCG), porphyry copper, VMS and epithermal gold deposits.
Geophysical techniques can be especially useful on properties that have a large amount of overburden, making it difficult or impossible to access mineralized rock for geochemical analysis. Certain geophysical methods can detect anomalies 500 metres below surface.
Drilling, the most expensive method of exploration, typically occurs in the later stages of exploration after other methods have identified a potential deposit (an "anomaly").
Diamond and RC (reverse circulation) drilling programs are used to collect rock samples at greater depths than surface methods allow. RC drilling returns rock samples in the form of chips, akin to chip sampling but at greater depths. This method limits the amount of information that can be derived from the sample, whereas diamond drilling allows a solid piece of rock core to be collected.
An interval of core allows for much more data to be accurately interpreted. These samples are then assayed, and the results will help build a model of the entire deposit. Drilling can eventually lead to the entire resource being defined within the boundaries of a chosen cut-off grade (e.g. 0.5% copper).
The goal of exploration
Many different types of exploration techniques are used in conjunction in order to get enough information to accurately define a mineral deposit. Once enough high-quality geological data has been gathered from exploration activities, a project can be analyzed for economic feasibility.
Management will use this data to make a decision on whether to continue exploration, establish or update a mineral resource estimate, proceed with mine feasibility studies and permitting in order to reach production, or pursue other strategic initiatives with the property.
Exploration never stops
After a mine begins production, exploration activities may continue to further define the deposit and potentially extend the life of the mine (by adding more mineral resources and reserves).
Exploration work may identify opportunities outside of the current mining area, but that are located within the same regional area or along the same geological belt as the original deposit.
As reserves are depleted each year, exploration work must always continue across the world in order to replace dwindling material at current mines and stockpiles – and so exploration efforts are vital to ensure our continued supply of raw materials like copper, iron ore, coal and other minerals that are critical to our modern standard of living.