Project progress in November 2023:
Technical and environmental historical archives
Progress of the work • Published on November 29, 2023
During the months of November and December 2023, the Compagnie des Mines Arédiennes (CMA) will use available archives to carry out 3D modeling of the exploration work and historical mining infrastructures present on the Exclusive Exploration Permits granted by the French government. The aim is to produce a synthesis of this work, which will enable CMA to target its future research more effectively.
The study of these archives also makes an important contribution to the knowledge of the sensitivity of the environment, fauna, flora and water.
The program announced for 2023
| Updated mid-November 2023 | Realized | In progress | Coming soon |
|---|---|---|---|
| Consultation and study of existing archives | |||
| Precise terrain mapping and topography | |||
| Geological hammer sampling and rock analysis | |||
| Ground or airborne measurements | |||
| Environmental studies over three years (from 2023 to 2025) |
Illustration of work in November 2023
Geological and mining historical archives => 3D modeling of historical technical archives
During the months of November and December 2023, the Compagnie des Mines Arédiennes will produce a 3D model of the exploration work and historical mining infrastructure on the state-granted Permis Exclusifs de Recherches, based on available technical archives.
The goal is to achieve a synthesis opportunities, exploration and exploitation work carried out in the past during the three periods of mining that the Saint-Yrieix-la-Perche district has experienced:
- The Gallic period
- The beginning of the 20th century
- 1980 to 2000.
The compilation of a very large volume of data, including in particular the cumulative 25 years of modern research and exploitation, will allow CMA to better target its future research for 2024. These paper archives were fully scanned in high definition in order to save them in PDF format. Each document is then inventoried, then its processing is prioritized according to its level of importance.
Historical data are of various natures. They include:
Geological maps provide information on the nature and structuring of outcropping rocks. These maps allow us to formulate hypotheses on the nature of the rocks constituting the subsoil and to better understand the chronological relationships between the rocks. These maps are produced from point data which correspond to the geologist's observation points. See the news from October 2023 on this subject.
Geophysical maps bring information on the organization of the subsoil and the nature of the rocks that are there.
Several geophysical methods have been used in the past, including:
- Electromagnetism: mainly allows to measure the ability of rocks to conduct current, called conductivity and measured in ohm-meters (Ω⋅m). Usually, it is resistivity, the inverse of conductivity, which is used in geology. A low resistivity can indicate the presence of clay, graphite and sulfide rocks. A high resistivity can indicate the presence of unaltered rocks or quartz veins.
- Magnetism: allows measure the total magnetic field which reflects the magnetic susceptibility of the underlying rocks, it is measured in nanotesla (nT). High magnetic values may indicate the presence of magnetic rocks or minerals: ultrabasic rocks, sulfides, graphitic rocks. Low magnetic values may indicate the presence of weakly magnetic rocks or minerals: granites, schists, gneisses, quartz veins.
- Gamma spectrometry: allows measure the abundance of uranium, thorium and potassium in the subsoil by measuring the gamma radiation they emit. The unit of measurement is the number of photons detected during the measurement. High gamma spectrometry values can indicate the presence of granites, pegmatites, clays. Low values are indicative of quartz veins, ultrabasic rocks or schists.
The combination of these methods and the different information they provide makes it possible to know the nature of the subsoil with greater precision. Historical geophysical data are digitized and reinterpreted using the Geosoft Oasis Mount software.
Geochemical maps provide information on soil composition which reflects the nature of the rocks present in the subsoil. In the past, several geochemical sampling campaigns have been carried out at different scales => samples are taken regularly every 200 m or every 50 m or every 10 m following a grid of the area studied.
About ten chemical elements were measured: gold, silver, lead, antimony, arsenic, lithium, bismuth, vanadium, copper, nickel.
The reinterpretation of these data allows us to better target the trajectory of mineralized structures in the subsoil and to guide future CMA's research.
The cartographic treatments are carried out with the
QGIS SIG software.
Borehole logs are documents that summarize information relating to these boreholes: borehole GPS coordinates, borehole deviation, description of rocks encountered, geochemical analyses and logs (geophysical measurements in the borehole).
Numerous historic boreholes have been drilled in the Saint-Yrieix-la-Perche district, totalling over 200 km in length. The 3D modelling of all these boreholes will enable us to create a high-resolution 3D geological model of the entire district .
Historical mining infrastructure maps show all the galleries in the Saint-Yrieix-la-Perche district in 2 dimensions.
Digitizing this data and converting it into 3D will make it possible to obtain a
3D model of these infrastructures.
This work will help to better locate these works and also to reconstruct the geometry of the mineralizations exploited in the past to find their lateral and deep extensions. Ultimately, a 3D printing of the model is planned to better visualize these elements.
3D modeling is performed using
Micromine software.
The 3D modelling and reinterpretation of historical data are carried out jointly by CMA and Gexplore teams.
Historical environmental archives:
The available archives also contain environmental data before, during and after miningin the areas where modern mining took place in the 20th century. The study of these archives makes an important contribution to our knowledge of the sensitivity of the environment, fauna, flora and water. It is a useful complement to the field observations that CMA has entrusted to the ANTEA et Ecosphère over a period of three years. See the news from May 2023 on this subject.