Muon radiography (muography) is an imaging technique based on atmospheric muon absorption in matter that allows to obtain two and three-dimensional images of internal details of hidden objects or structures. The technique relies on atmospheric muon flux measurements performed around and underneath the object under examination. It is a non-invasive and passive technique and thus can be thought of as a valid alternative to common prospecting techniques used in archaeological, geological and civil security fields. This paper describes muon radiography measurements, in the context of archaeological and geological studies carried out at the Temperino mine (LI, Tuscany, Italy), for the search and three-dimensional visualisation of cavities. This mine has been exploited since Etruscan times until recently (1973), and is now an active tourist attraction with public access to the tunnels. Apart from the archaeological interest, the importance of mapping the cavities within this mine lies in identifying the areas where the extraction ores were found and also in the safety issues arising from the tourist presence inside the mine. The three-dimensional imaging is achieved with two different algorithms: one involving a triangulation of two or more measurements at different locations; the other, an innovative technique used here for the first time, is based on the back-projections of reconstructed muon tracks. The latter requires only a single muographic data tacking and is to be preferred in applications where more than one site location can be difficult to access. Finally the quality of the three-dimensional muographic imaging was evaluated by comparing the results with the laser scan profiles obtained for some known cavities within the Temperino mine.
Transmission-based muography (TM) is an innovative imaging technique based on the measurement and analysis of the cosmic ray muons flux attenuation within the target under investigation. This technique allows imaging inner-body density differences and has successfully been applied in a wide range of research fields: geology, archaeology, engineering geology and civil engineering. The aim of this study is to show the reliability of TM as an innovative, noninvasive geophysical method for ore body prospecting and other mining related studies. The measurements were carried out at the Temperino mine in the San Silvestro Archaeological and Mining Park (Campiglia Marittima, Italy), where several magmatic and metasomatic geological units are embodied. Among them, a Cu–Fe–Zn–Pb(–Ag) sulfide skarn complex primarily composed by hedenbergite and ilvaite minerals. Using the acquired muon imaging data obtained with the MIMA (Muon Imaging for Mining and Archaeology) detector prototype (cubic detector of 0.5 × 0.5 × 0.5 m3), the presence of a high-density vein inside the skarn body within the rock volume above the muon detector was identified, localized and interpreted. Applying a back-projection algorithm to the obtained 2D transmission map made it possible to estimate and visualize as point cloud data, in a 2D or 3D environment, the identified high-density body and its relative distance from the detector. The results of this study highlight the potential of muography as a support tool to other geophysical methods in the field of mining exploration.
<p>Muon radiography is a non-invasive imaging technique that allows, through cosmic muon absorption measurements, to obtain two-dimensional and three-dimensional images of the internal structure and average density of very large material volumes. Its applications currently range from many fields: geological, archaeological, industrial, civil and nuclear safety. The technique of muon radiography being non-invasive represents a valid alternative to the common survey techniques in these fields of applications. In this presentation I will show some results obtained with this technique in the geological field for the three-dimensional imaging of cavities and tunnels within the Temperino mine located in the San Silvestro Archaeological Mining Park near Campiglia Marittima in the province of Livorno in Tuscany (Italy). The Temperino mine has ancient etruscan origins and still has areas which are not mapped in the available documentation. The mining activities of the area have always been focused on the search for a hard and dense rock called skarn in which there are metallic sulphides of Cu, Ag, Pb, Zn, Fe. Currently only one of the most superficial levels of the mine is accessible to the public through a tourist route. The muographic measurements on this site therefore have a dual objective, on the one hand to test the imaging technique on known cavities, on the other hand to discover new cavities whose knowledge could be useful, for example, for important assessments concerning historical and safety aspect of the site. All measurements were carried out with the muon detector MIMA (Muon Imaging for Mining and Archaeology) designed and built at the National Institute of Nuclear Physics (INFN) in Florence. MIMA is a cubic tracker of approximate dimensions (50x50x50) cm<sup>3</sup>and is equipped with a special protective aluminum mechanism that allows its altazimuth orientation. Various measurements were made within the tourist gallery located about 50 m below ground level for the observation of areas above.&#160;By comparing muon transmission measurements with simulations, it was possible to generate two-dimensional angular maps of average density of material observed in every direction within the detector's acceptance. The presence of some low-density anomalies associated with the presence of cavities was thus identified. Through algorithms based on the triangulation technique and on a track backprojection technique, the cavities were located in three-dimensions. For the known cavities it was also possible to compare the reconstructed development with their real profile that was acquired with the laser scanner technique, finding a good compatibility (average deviation below&#160;1 m for a 7 m high cavity located 20 m above the detector&#8217;s installation location).&#160;These measurements therefore validate the muon radiography technique in the geological field for the search for cavities inside mines. The technique can be applied to identify not only low-density anomalies or voids, but also high-density areas: the application of the muon imaging technique for the identification of dense ore bodies is being studied at Temperino mine.</p>
<p><span>In the last twenty years several applications of muography (or muon radiography) technique have been carried out for geological purposes. Among them, particular attention was given to underground ore bodies prospections. For thousands of years humans have been searching new methods to understand where to find underground ore bodies and how to localize it in the three-dimensional space. Often, economically useful minerals are bounded to other minerals, forming rocks of high density values that are hosted, usually, in rocks with lower density values. In literature gravimetry and magnetometry represent the most employed geophysical methods for imaging and detection of mineral-rich ore bodies. To verify the feasibility of muography as a non-invasive geophysical prospecting technique, our research group, composed by subnuclear physicists and geologists, carried out some underground measurement campaigns at the Temperino Mine (Campiglia Marittima, Italy). Here it is located a pliocenic metasomatic ore deposit, a Cu-Pb-Zn-Fe skarn complex composed by johannsenite, quartz, hedenbergite, ilvaite and accessory primary sulphides (chalcopyrite, galena, sphalerite, pyrite). These metalliferous bodies of skarn have tabular geometries with sub-vertical orientations. Currently, the first level of Temperino Mine has been equipped as a touristic path and belong to the Archeological Mining Park of San Silvestro. Along this gallery, carved both into the metamorphic and non-metamorphic rocks, it&#8217;s been installed the MIMA muon tracker (Muon Imaging for Mining and Archaeology), a small and rugged prototype (0.5 x 0.5. x 0.5 m</span><span><sup>3</sup></span><span>) developed by the physicists of the National Institute of Nuclear Physics (INFN), unit of Florence, and the Department of Physics and Astronomy of Florence. MIMA detector is able to measure the underground muon flux inside the mine gallery. Matching the simulated muon transmission rate with the experimentally measured one it&#8217;s possible to obtain a two dimensional average density angular map of the observed target. Also, using algorithms based on triangulation and back-projection techniques is possible to obtain a reconstruction of the 3D volume of high-density areas (and also low-density areas) inside the studied volume. The latter is the volume that falls within the detector&#8217;s acceptance. The aim of this research is to obtain a georeferenced 3D model of the Cu-Pb-Zn ore bodies hosted in the rocks between the top of the mine gallery and the surface of the Temperino Mine area. We want to confirm that muography technique could become a suitable and reliable tool for the mining prospections field.</span></p>
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