Why prospect and explore for minerals? What do you search for, and how?
Mineral exploration
New deposits are found by prospecting. Geologists work to find clues as to where there are important metals such as copper, gold and nickel, and minerals such as apatite (needed in fertiliser) in large quantities. Deposits are hard to find, and prospecting takes a long time.
Ore is a naturally occurring material from which minerals of commercial value can be extracted at a reasonable cost. A deposit can contain several ores and many different metals, which need to be concentrated in quantities 100-10,000 times greater in the deposit than in the surrounding bedrock. Ore is created deep in the earth’s crust through different geological processes. Prospecting activities aim to locate the ore, which can be detected by its properties. Many ore minerals are heavy, magnetic or electrically conductive, and their presence in the bedrock shows in geophysical measurements. You can often see high metal content in surrounding ground and groundwater due to the ore.
During the most recent ice age, the inland ice lifted small sections from the ores at the surface and transported them along its routes. Geologists need to find these routes and interpret them to find the ore.
Drill core logging. Photo: Niclas Dahlström.
THE LONG PROCESS FROM PROSPECTING TO A MINE
Prospecting activities usually begin in an office, where all existing data on the bedrock and its chemical and physical properties are reviewed to determine whether the area is favourable to certain types of mineralisation and ore. Different types of rock concentrate different metals, so that if a company is looking for gold, it looks for rock types that are favourable to gold deposits. If the company’s interest is in industrial minerals, such as calcite or dolomite, it looks for other rock types.
Field investigations in prospecting projects usually start with geological mapping and sampling to get a perception of the rock types and their composition in the area.
The investigations are carried out by geologists who walk around in the area, hammering small pieces of stone from rock surfaces. Geophysical measurements are made either by ground personnel walking with measuring instruments, or from the air from low-flying aircraft. Geophysical measurements are needed to steer mapping and sampling to the most favourable areas.
After the first mapping and sampling phase, which usually takes several years, all the collected data are analysed. If nothing interesting is found, the area is abandoned. If there are signs that something interesting can be hidden in the ground, the next phase of field investigations is initiated. Based on the collected information, the investigations usually target a more limited area with high potential for discovering ore. Heavier and more expensive methods such as diamond drilling are used to gain information from deeper down in the ground. Based on drilling results, the prospecting activities are either stopped or again steered more exactly to the area with the most favourable indications.
Out of 1,000 prospecting projects, only about one gives sufficient indications of the existence of ore in the area. The entire process from the initial field mapping stage to the start of mine planning usually takes several decades, even if there are favourable geological indications of ore in the area. Most prospecting projects fail to find ore.
Mineral exploration can sometimes mostly be desk work. Photo: Niclas Dahlström.
Facts: The exploration process
Exploration takes a long time, and few projects lead to mines. The reason may be several, for example, that the find is too small or low grade, the prices are too low or there is difficulty in obtaining a permit. If everything goes as the company thinks and you manage to find a mineral resource and get all the permits, then the process can take between 20-30 years in general. The process is illustrated in a simplified manner below. Between the steps, a number of permits are required, which you can read about in Chapter 3.
