{"id":57535,"date":"2024-06-25T10:00:00","date_gmt":"2024-06-25T07:00:00","guid":{"rendered":"https:\/\/geoconversation.org\/geophysical-methods-for-mineral-exploration\/"},"modified":"2026-05-07T17:57:55","modified_gmt":"2026-05-07T14:57:55","slug":"geophysical-methods-for-mineral-exploration","status":"publish","type":"post","link":"https:\/\/geoconversation.org\/en\/geophysical-methods-for-mineral-exploration\/","title":{"rendered":"Geophysical Methods for Mineral Exploration"},"content":{"rendered":"\n

Deposits near the surface of the earth have already been found and mined or are being mined. This means it\u2019s time to look for them at great depths. Geophysics will help us here. Read our material about what geophysical methods to include in geological exploration. <\/p>\n\n

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Discovery of large and medium-sized deposits of copper, zinc, lead and nickel from 1900 to 2020 and their distribution by depth. Source: MinEx Consulting, 2020<\/figcaption><\/figure>\n\n

Geophysicists look for anomalies<\/h2>\n\n\n

The task of geophysics is to record physical anomalies. Specialists measure the Earth’s natural fields (gravitational and magnetic) or create artificial fields using generators and vibration installations (electric fields, elastic vibration fields). This is done to find deviations from the average values.\u00a0\u00a0<\/p>\n\n\n

These deviations – anomalies – are created by various properties of rocks and ores: density, magnetic susceptibility, radioactivity, seismic and electrical properties. If there is an anomaly, then perhaps an ore body lies at depth.<\/p>\n\n\n

I talk about my working day as a geophysicist and about 3D electrotomography in the note \u201cOne of my days on the other side of the Arctic<\/a>\u00bb.<\/pre>\n\n\n
From a general to an accurate picture of the field<\/h2>\n\n\n
To get general data on the physical properties of rocks<\/strong> from areas of hundreds and thousands of square kilometers, we explore the area from an airplane or helicopter. This is airborne geophysics.<\/p>\n\n\n
In the aerial version, we carry out gravity surveys, magnetic surveys, gamma spectrometry, frequency and pulsed (electromagnetic) electrical surveys. We will talk about some of them further.<\/p>\n\n\n
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Geological problems that are solved by geophysical research;<\/figcaption><\/figure>\n\n\n
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Types of geophysical work by location<\/figcaption><\/figure>\n<\/figure>\n\n\n
To get more detailed picture of the field<\/strong> and to distinguish smaller anomalies, equipment is placed on the surface. This is terrestrial geophysics.\u00a0<\/p>\n\n\n
More devices can be lowered into the well. If we study the space between several wells with a distance of 50 m or more, this is borehole geophysics. Not to be confused with logging, where we place the tool inside one well and obtain data only around it.<\/p>\n\n\n
Aerogeophysics is carried out at the regional stage of geological exploration, and ground and borehole physics is carried out at the prospecting and exploration stage. Anomalies of hundreds of meters are visible during aerial photography, and ground and borehole geophysics reveal the position and dimensions of a potential ore body.<\/p>\n\n\n
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Performing geophysical work using aerial, ground and borehole methods. Source: Geophysics for the mineral exploration scientist, Dentith, 2014<\/figcaption><\/figure>\n\n\n
Deciding whether to turn to geophysics<\/h2>\n\n\n
Before moving on to the selection of geophysical methods, it is necessary to understand whether it is even possible to solve a geological problem using geophysics. To do this, answer two questions:<\/p>\n\n\n
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  1. Do the physical properties of the search object differ from the host rocks?<\/strong> The section may be composed of different rocks, but if their physical properties are the same, then it will not be possible to separate these rocks using geophysical methods.<\/li>\n\n\n
  2. Will the search object create an anomaly that can be registered and isolated from the noise?<\/strong> Perform mathematical calculations (modeling) in a special program before going into the field. Determine what type of anomaly an orebody might create using knowledge of the physical properties of rocks, the size of the orebody, and the expected depth of the orebody.<\/li>\n<\/ol>\n\n\n
    Choosing geophysical methods<\/h2>\n\n\n
    If you answered yes to both questions, then we next select methods for searching for ore bodies.<\/p>\n\n\n
    We are looking for magnetic anomalies: magnetic prospecting method<\/strong><\/h3>\n\n\n
    You can search for iron ore deposits, identify and map intrusive bodies (dykes and batholiths), and trace faults using magnetic prospecting<\/strong>. It records deviations from the Earth\u2019s normal magnetic field\u2014magnetic anomalies. They are the ones who carry information about the magnetization of geological bodies.<\/p>\n\n\n
    An abnormal magnetic field occurs regional<\/strong> And local<\/strong>:<\/p>\n\n\n
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    1. Regional anomalies (for example, Kursk) extend over large areas. They are caused by large structures composed of rocks and iron ores with high magnetic properties.<\/li>\n\n\n
    2. Local anomalies appear due to different magnetization of geological structures or ore deposits. These anomalies are created by small ore bodies up to a few hundred meters thick, which are also noticeable in the regional magnetic field trend.<\/li>\n<\/ol>\n\n\n
      We see an example of a local magnetic anomaly over ore bodies in a profile through the Qian’an deposit in China. The deeper the iron ore, the less distinct the magnetic anomaly becomes.<\/p>\n\n\n
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      Local magnetic anomalies over an iron deposit in China. Source: Geophysics for the mineral exploration scientist, Dentith, 2014<\/figcaption><\/figure>\n\n\n
      We look at deviations in gravity: gravity survey method<\/strong><\/h3>\n\n\n
      Helps identify intrusions, faults, folds of sedimentary cover, ore bodies, oil and gas deposits and other local density heterogeneities gravity survey<\/strong>.<\/p>\n\n\n
      Gravity survey measures the change in gravitational acceleration that occurs due to different densities of rocks. But we are not interested in the force of gravity on the Earth\u2019s surface, but its variations are many orders of magnitude smaller, so in gravimetry they use the fractional unit milligal (mGal), 1 mGal = 10\u20135 m\/s2 or 9.8 m\/s2 = 980,000 mGal.<\/p>\n\n\n
      In the gravity field at the Elazig deposit in Turkey, chromite bodies with increased density values \u200b\u200bstand out as positive anomalies.<\/p>\n\n\n
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      Gravimetric anomaly over chromite ore bodies. Source: Geophysics for the mineral exploration scientist, Dentith, 2014<\/figcaption><\/figure>\n\n\n
      Thunderstorms in the service of a geophysicist<\/h3>\n\n\n
      To study deep horizons they use magnetotelluric sensing<\/strong>. It registers the Earth’s magnetotelluric field (MT field), which consists of oscillations of various frequencies. High-frequency oscillations of the MT field quickly attenuate with depth, while low-frequency oscillations, on the contrary, penetrate very deeply. High frequencies carry information about the near-surface part of the section, and low frequencies – about deep horizons. This is how we obtain data on the electrical properties of the entire mountain range – a geoelectric section.<\/p>\n\n\n
      MT fields are called:<\/p>\n\n\n