Mining and Mineral Exploration

Geode Seismograph

For coal exploration, a greater density of data is needed compared to other seismic applications, and the increase in resolution requires higher frequencies and larger wave numbers. Seismic Reflection is the method of choice here, and the Geode Exploration Seismograph with its distributed architecture and fast sample rate meets the requirements needed for coal exploration. A 48-channel or greater Geode Seismic system can be used to generate a model for the overall structural geology of the area based on fault identification. A typical survey arrangement is 475 to 550 meter in length with a geophone spacing of 10 m. With this high resolution structural geology data now available, miners can then construct a mine which best fits the geology in order to achieve maximum coal extraction, saving a significant amount of time and money in the process.

For more information on best surveying practices read the paper A Simple Approach to High-Resolution Seismic Profiling for Coal by A. Ziolkowski and W. E. Lerwill, published in the Official Journal of the European Association of Exploration Geophysicists, ISSN 0016-8025 Volume 27, Number 2, June 1979.

Geode EM3D

Whereas seismic reflection is a good method for determining the structural geology of an area already identified as being coal-bearing, and therefore the high-resolution structural geology information can be used to most efficiently mine the coal, electrical resistivity methods can be used to identify to contain coal deposits in the first place. The Geode EM3D, a distributed electromagnetic system, is perfect for this application.

Capable of performing electrical soundings to depths of 1000+ meters, if the strike of the coal seam is known, a number of vertical electrical soundings can be carried out over the seam in two directions. With this survey arrangement, the two soundings can then be compared, and a nice 3D effect can be observed. The very resistive coal (compared to the surrounding matrix) shows up well in one direction versus the perpendicular direction, and from there more soundings can be performed to collect more data points, or other geophysical methods can then be used to better quantify the identified coal deposit.

G-859 Magnetometer

Magnetometers measure perturbations in the ambient magnetic field caused by contrasts in magnetic susceptibility – the ability of a substance to take on an induced magnetism caused by its immersion in the Earth’s magnetic field. The magnetic susceptibility of a rock or soil is directly proportional to its iron content, usually in the form of the minerals Hematite (Fe2O3) or Magnetite (Fe3O4). Hence, magnetometers are only sensitive to ferrous metals. However, iron is often present in accumulations of non-ferrous ores, such as gold and copper, making magnetometry a staple in mining exploration.

The G-859AP Cesium Magnetometer has features that are streamlined for small-scale mineral exploration. Its ergonomic backpack, GPS, hands-free operation, and fast sampling rate make it the best choice for large scale mining exploration surveys. Geometrics’ cesium magnetometers are sensitive to changes in the parts-per-million range, making magnetometry one of the most sensitive of all geophysical techniques. The G-864 Magnetometer is also well suited for mineral exploration endeavors.

MagArrow Magnetometer

Cesium vapor magnetometers can resolve changes in the magnetic field as small as 0.004nT. This high resolution is important for mineral exploration where the observed magnetic anomalies tend to be broad and subtle. Large-scale mining surveys traditionally involve multiple surveyors walking for hours in sometimes undesirable weather and harsh landscapes with heavy equipment on their backs. The MagArrow UAS-Enabled Magnetometer is a new solution for making magnetic surveying faster, easier, and more economical.

With the MagArrow, large scale surveys can be performed about 10 times faster than walking surveys. The MagArrow may be deployed from any small Unmanned Aerial System (sUAS) with a specified minimum payload of 1kg. The system will run for two hours on a fully charged battery, outlasting most sUAS batteries. Control of the MagArrow is done wirelessly. Connect to the MagArrow’s WiFi using your phone, tablet, or PC and wirelessly control new survey creation, data logging, and data download. The MagArrow opens up new avenues for mineral exploration.

Geode EM3D

The Geode EM3D is an electromagnetic exploration tool used to provide high-resolution, high-quality resistivity maps of subsurface geology. The instrument can employ three techniques, each advantageous under different conditions. The Geode EM3D can perform AMT (audio magnetotellurics), HSAMT (hybrid-source AMT), and CSAMT (controlled-source AMT). AMT uses naturally occurring currents in the Earth’s subsurface. HSAMT also measures natural fields but enhances the signals in a frequency band where the natural fields are weak. CSAMT does not use natural fields, but instead uses a high-power transmitter generating source signals in the AMT band (0.125 Hz to 10,000 Hz).

The color depth sections created by the GEM3D are interpreted for changes in resistivity of economically exploitable mineral deposits. For example, diamond-bearing Kimberlites are readily identified from the surrounding materials by the dike-like structure and resistivity contrast from the surrounding materials. Hard rock gold deposits are very often found in mineralized zones that are more resistive than the surrounding sediments. Chromite deposits, copper porphyry deposits, and many other mineral deposits are often characterized by strong resistivity contrast from the other geologic structures in the area.

G-824, G-864, and MagArrow Magnetometers

Although magnetic surveys are used to measure ferrous objects or minerals, they may also be used to locate minerals that are not magnetic, such as diamonds or gold. Pyrrhotite and magnetite are the primary magnetic minerals, and they are naturally found in both host rocks and some forms of alteration associated with mineral deposits. Kimberlite, the host rock to most of the world’s naturally occurring diamonds, is composed primarily of carbonate, mica, olivine, and pyroxene. Of these, olivine is the primary magnetic mineral gives the kimberlite its magnetic signature. Researchers believe that diamonds do not form in the kimberlite, but are instead carried upward in the high-pressure eruptions. Kimberlite pipes are thought to originate in the mantle and are the result of explosive eruptions traveling upward through the crust at approximately 400 meters per second. At a depth of a few kilometers beneath the land surface, the lateral earth pressures decrease enough to allow the kimberlite magma, rich in CO2 gas, to start expanding, with the resulting ore body being roughly carrot shaped.

Magnetic surveys are the primary geophysical technique used in kimberlite exploration. The magnetic signature is typically recognized as 3 to 10 circular or elliptical pipes clustered closely together. Typically, exploration begins by collecting magnetic data using a magnetometer mounted on a fixed-wing helicopter or airplane. The G-824A Magnetometer, our most sensitive airborne magnetometer, has the highest possible standards for airborne, land or marine surveys, meeting rigorous vibration and environmental testing standards. The system’s high performance and multi-function capability are excellent for mapping geologic structure or for mineral exploration.

For higher-resolution magnetic surveys across areas too small to fly but too large to cover on foot, the MagArrow UAS-Enabled Magnetometer fills the gap. The MagArrow can be flown over areas typically inaccessible to high-resolution magnetic surveys, and all while collecting data up to 10x faster than a traditional walking survey.

After targets are identified, land-based magnetic surveys allow for closer line spacing and higher data resolution. The G-864 Magnetometer is our latest land magnetometer, incorporating Geometrics’ quality with the latest in modern technology. The G-864 works with our Android Acquisition software and allows the user to collect data using any Android device. Save time in the field by defining your geometry in advance, and then visualize your data on a color map before leaving the site. A modern user interface allows you to cover more area faster, lowering your survey costs while still providing top quality data.