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Finding and Assessing Mineral Resources

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  • 0:01 Finding & Assessing…
  • 1:02 Target Identification…
  • 3:34 Resource Evaluation
  • 5:50 Development & Production
  • 7:02 Lesson Summary
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Lesson Transcript
Instructor: Amy Lange

Amy has taught university-level earth science courses and has a PhD in Geology.

Because mineral resources are so rare, they are not easy to locate. In this lesson, we'll learn the process that geologists use to find and assess valuable mineral deposits.

Finding and Assessing Mineral Resources

When you think of mining, you probably think of giant pits in the Earth where workers remove valuable metals or gemstones. However, that is the end of a long, difficult, and very expensive process. Before companies can begin to pull valuable metals like copper out of the Earth, geologists must first locate these deposits, determine whether they are cost-effective to extract, and commit a large amount of capital to opening a new mining operation.

The process of locating new minerals is called mineral exploration, which can be divided into three large stages: target identification and investigation, resource evaluation, and development and production. Very few projects make it through all of these stages and get to production. Instead, most are abandoned due to insufficient resources at a particular location. In this lesson, we'll delve further into these stages to learn how geologists locate valuable mineral deposits.

Target Identification and Investigation

In the past, mineral deposits were found by geologists mapping the surface of the Earth looking for clues of valuable mineralization. However, because we have been searching for these deposits for hundreds of years, traditional prospecting methods are rarely used, except in some remote locations such as Alaska and Russia. Now most mineral exploration is performed by specialized teams of geologists using modern geophysical techniques, including magnetic and gravity surveys, which we will look at in greater detail later in this lesson.

Before companies can begin paying for costly surveys, geologists decide on a large area that is likely to have the mineral deposit of interest. This area is normally several thousands of miles across and can stretch across multiple countries. Geologists examine regular maps, geologic maps, and any other geologic data at this stage to attempt to narrow down the area.

In the case of valuable metals, geologists are often looking for specific clues, such as minerals and high concentrations of certain elements. For instance, copper often forms from hydrothermal fluids near volcanic activity. Hydrothermal fluid is hot groundwater that circulates through the bedrock, enriching it in valuable metals. This circulation of hot fluids severely alters the nearby rocks. Thus, geologists will often look for this type of alteration as a clue that there may be copper nearby.

Once geologists are certain that there is a good potential for valuable economic deposits to be in a certain area, they will begin a more targeted reconnaissance mission. This stage can involve some quick sample collecting and analysis, geologic mapping, airborne surveys, and geophysical surveys. The geophysical survey tools developed in modern times are a powerful way to quickly determine whether an area is a likely source of valuable deposits. These methods look for variations in gravity, magnetism, and seismic behavior.

Since the majority of magnetic mineral deposits are more dense than average bedrock, all of these methods are basically looking for physical anomalies that may suggest that a dense metal-rich deposit is present at depth. Other survey tools, such as magnetic surveys, allow geologists to map the underlying structures of the Earth. If an exploration team is tracking a particular geologic unit, they may want a magnetic survey to understand the underlying structures in the area.

Resource Evaluation

Once our geologist teams have targeted a specific area for having all of the required clues of valuable mineral deposits, they then begin a greater detailed investigation into the economic potential of the area. As we learned in a different lesson in this course, we only care about mineral deposits because they have economic potential in our society, meaning they are useful enough to become valuable.

One way we classify the economic potential of a mineral deposit is by determining its grade. Grade is the concentration of the metal in a body of rock and is normally expressed as a percent. It can be understood as the amount of metal per unit rock. For instance, if a deposit has 50 lbs. of copper per 1,000 lbs. of rock, the grade would be 0.05 or 5%.

But how do geologists estimate this grade before they start mining? We know they have already chosen an area that is a likely target and have performed geophysical surveys. The next step is to actually begin to drill holes into the Earth to test whether their hypotheses are correct. These samples are rigorously logged and examined by geologists for the presence of valuable mineralization or further clues.

Cores will be drilled at multiple locations surrounding and within the target area to allow geologists to best pinpoint the exact location of the deposit. Imagine that you are trying to locate the extent of filling in a jelly doughnut using only a straw. Each time you pull out the straw, you'd either have just doughnut or layered doughnut and jelly. By poking the doughnut multiple times, you could eventually figure out where the edges of the jelly are within the doughnut. In much the same way, geologists have to drill these cores to probe inside the Earth and learn where the boundaries of the deposit are.

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