The term asbestos is a commercial term referring to six silicate minerals, listed as human carcinogen by world hearth authorities. Asbestos was banned in France since 1996 but since a decade, a new focus was done on Naturally Occurring Asbestos (NOA). NOA are fibrous minerals that occur as natural components in some rocks and soils, as opposed to asbestos in commercial products. Human activities (such as mining, agriculture, construction or urban development) and natural weathering processes are likely to release NOA in the air. Because NOA forms in specific rocks and geologic conditions, it is possible to predict geologic environments that may host NOA. A multi-scale geological mapping program is going on in France to identify lithologies that are likely to contain asbestos-like minerals leading to the establishment of maps of potential asbestos-bearing rocks at different scales. Major occurrences concern ultrabasic, basic and dolomitic rocks affected by greenschist to amphibolite-facies metamorphism and/or hydrothermal metasomatism. Unusual occurrences were also identified, as in alkaline metagranitoids, dolerites and talcschists. To manage NOA-related risks and control worker exposures to asbestos, new upcoming regulations will come into force in France, including the prior identification of asbestos in natural soils or rocks likely to be impacted by the execution of works. Maps of potential NOA occurrences will therefore constitute reference documents for such studies. Moreover, regulations will lead to the standardisation of protocols for sampling, analysis and characterization of natural materials likely to contain asbestos.

Asbestos is a commercial term which refers to six minerals that crystallize as fibrous bundles made of very thin and easily separable fibrils. Asbestos fibers have been exploited for a long time and voluntary added in a very large set of manufactured products. In France, asbestos is prohibited since an official decree published in 1997 that prohibits the manufacture, processing, sale and import of asbestos. The asbestos ban has been the subject of an European directive published in 1999. Following this ban, a standard was defined in order to specify the sampling, preparation and identification methods for asbestos fibers in samples of commercial origin (ISO 22262-1). For natural materials, no specific analytical protocol is currently defined in France. Searching for asbestos in a rock sample, the commonly used protocols require the reduction of the sample, the grinding of a sub-sample (1 to 2 g) and its calcination in order to eliminate organic matter, then an acid attack to dissolve some constituents (calcite, gypsum). The final test portion (~ 20 mg) is mixed in water, stirred using ultrasound, filtered through a metallized membrane and covered with a new layer of carbon before it can be examined using a transmission electron microscope. The protocols currently used are long and complex and require the grinding of the sub-sample. This grinding operation is a critical step because it can lead, starting from non-asbestiform minerals, to the artificial formation of more or less fine and elongated fibriform particles (cleavage fragments), quite similar in some cases to asbestos fibers. Grinding is therefore an operation liable to affect the quality of the final diagnosis. The new protocol presented here was built with the aim of developing an analytical approach specific to coherent rock samples. This protocol does not involve the grinding of the sample and allows the in-situ morphological and chemical characterization of fibrous minerals. It is based on the use of combined analytical techniques (MOLP, EPMA, FESEM-EDS, FIB-SEM, and confocal RAMAN in SEM) from a single support corresponding to a polished thin section. This protocol allows to observe the natural morphologies of the fibers, to measure their dimensions, to characterize the relationships between fibers and the other mineralogical constituents while preserving the texture of the rock and to acquire precise chemical analyzes of the fibers. It also overcomes problems related to the grinding of the sample and the formation of cleavage fragments. This protocol has been tested through the study of several types of massive rock samples. It provides a representative and reliable in-situ diagnosis of the initial state of the fibers in solid rocks.

The event geological maps consist in innovative numerical maps that were just designed and produced for the first time, as part of the RGF (“French Geological Referential”) mapping program in the Pyrenees. Rocks acquire their mineralogical, structural and textural characteristics through a complex geological history reflecting successive stages of transformation (i.e. metamorphism, deformation, alteration…), so called “geological events”. Classical geological maps can only represent some of these events. In the Pyrenean orogenic belt, which results from a polyphase tectono-metamorphic history over 600 Ma (from Precambrian to present), 3400 geological events were identified. Such geological events were classified by types (e.g. deposit, volcanism, intrusion, metamorphism, weathering, hydrothermal alteration…) and time periods. They were referenced into a database and associated to mapped features (120,000 polygons and lines), coming from a compilation of 60 geological maps at 1: 50,000 scale. In the Pyrenees, Naturally Occurring Asbestos (NOA) mostly occur in specific lithologies such as ultrabasic, basic and intermediate plutonic rocks, and meta-limestones. These rocks may be affected by different metamorphic events (i.e. hydrothermal alteration, greenschist and/or HT-LP regional metamorphism, contact metamorphism). We performed a GIS treatment to produce a predictive map of potential NOA hosting lithologies. This treatment crosses lithological and selected geological event informations (e.g different metamorphic and alteration events). Subsequent geological field investigations with associated sampling and laboratory analyses (combining optical microscopy, microprobe and SEM analyses) allowed us to identify and characterize fibrous and asbestiform mineralogical species. Results of this work particularly emphasize: (i) the importance of actinolite-asbestos in doleritic rocks, and (ii) the occurrence of fibrous actinolite/tremolite in different marbles and skarns. Finally, we present a 1: 50,000 scale map of potential NOA occurrences in the Pyrenees. Conversely, field observations allowed us to improve both the lithostratigraphic and the event geological maps, in particular with the identification of geological domains where intense hydrothermal alteration was not previously mapped. All the data (maps of potential NOA occurrences, field observations and results of laboratory analyses) are stored in a geospatial database, partly accessible to the public. This work illustrates a possible use of geological event maps as a powerful innovative and predictivity tool. This approach will be useful in the context of the evolution of French regulations now imposing the search for asbestos before all types of works in natural environments.

This paper provides a field description and an analytical characterization of the fibrous minerals associated with ultrabasic and basic rocks from the Corsican Ophiolitic Complex, on the island of Corsica, in order to examine their asbestos potential. Thirty-five fibrous samples taken from serpentinites, magnesium-rich meta-gabbros and meta-basalts were studied, using combined EPMA, Ramanand FESEM methods. The results highlight that naturally occurring asbestos (NOA) are abundant in serpentinites and regularly occur in magnesium-rich meta-gabbros and meta-basalts in northern Corsica. The spatial distribution, abundance and mineralogical types of these NOA strongly depend on the petrographic nature of the hosting rocks and their structural pattern. NOA in serpentinites correspond to chrysotile vein networks in the internal parts of the thickest rocky masses and to tremolite veins and shear planes carrying tremolite fibers, both in the external parts of these masses and in highly sheared serpentinites within or close to tectonic contacts. NOA in highly deformed magnesium-rich meta-gabbros are associated with the opening and filling of albite–tremolite veins, associated with the syntectonic boudinage of the most competent meta-gabbros. In the meta-basalts, NOA are associated with late metamorphic, actinolite-bearing polymineralic veins cross-cutting the foliation planes. Fragments and pebbles of serpentinites, meta-gabbros and meta-basalts containing NOA are also present in colluvium, scree and alluvium resulting from erosion processes. Special attention should be paid to serpentinites and/or magnesium-rich meta-gabbros-bearing colluvium in which fibrous occurrences of tremolite regularly evolved into whitish clusters consisting of very long, easily separable, flexible and entangled fibers with a higher asbestos potential. The characterization of NOA in the COC serpentinites, meta-gabbros and meta-basalts leads us to consider them as hazardous materials. As these lithologies are very abundant within the whole structural edifice, they may be regularly impacted by development or construction work and thus require suitable monitoring.

Asbestos consists in natural minerals crystallized in a specific habit and possessing in particular properties. In the case of Naturally Occurring Asbestos, usual methods applied to the identification of mineral fibers and the determination of their possible asbestiform nature seems not efficient, especially in the case of mineral fibers included in mineral matrix. We present a new in-situ method based on the use of confocal Raman-in-SEM imaging implemented in a Scanning Electron Microscope as an efficient method for in-situ mineralogy. The limitation of conventional methods is discussed. We applied 2D-Raman imaging to the identification of sub-micrometric fibers included in different mineral matrix. We were able to identify actinolite fibers down to 400 nm in diameter, included in feldspar, quartz and/or calcite matrix. Moreover, Confocal Raman allows the collection of 3D data that would provide access to critical information on the morphology of the amphibole fibers in the volume, such as aspect ratio, fibers distribution and amphibole volume fraction. We performed this method on various examples of rocks containing actinolite fibers of mean structural formula is: Na-0,Na-04-0,Na-12 Mg-2,Mg-79-3,Mg-73 Al-0,Al-29-0,Al-58 K-0,K-01 Ca-1,Ca-79-1,Ca-98 Mn-0,Mn-01-0,Mn-09 Fe2+(0,99-1,91) Fe3+Si-7,Si-64-7,Si-73 O-22(OH)(2). We demonstrated that coupling confocal Raman imaging and SEM is a new and efficient in-situ method for identification and morphological characterization of amphibole fibers.

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This paper provides new mineralogical and morphological characterizations of calcic amphiboles from hydrothermally altered dolerites from France to discuss their potential to contain naturally occurring asbestos (NOA) and to release elongated mineral particles corresponding to asbestos fibers, or asbestos-like fibers, into the air. The calcic amphiboles were characterized using electron microprobe analysis, scanning and transmission electron microscopy. The results underline that fibrous occurrences of actinolite and ferro-actinolite regularly occur in hydrothermally altered dolerites, both in the groundmass and in quartz veins. In the groundmass, actinolitic amphiboles crystallize at the expense of magmatic clinopyroxenes and are rarely fibrous. Conversely, actinolite and ferro-actinolite fibers from quartz veins are potentially asbestiform to clearly asbestiform. The identification of quartz veins in hydrothermally altered dolerites is, therefore, an important parameter which should draw attention to the possible presence of asbestiform actinolite fibers. The mineralogical characterization of such veins as well as the estimation of their thickness and density is an important point to consider during studies involving NOA issues. Moreover, the degree of weathering of the dolerites, which directly affects the ability of non-asbestiform actinolite crystals to dissociate into very thin fibers, regarded as cleavage fragments instead of as asbestos, is also a key parameter to consider. Hydrothermally altered dolerites are common rocks likely to be exploited by the quarrying industry to produce aggregates or to be affected by construction works. Due to the abundance of actinolite fibers that they may contain locally, these rocks become priority targets to be monitored in terms of geological characterization and airborne fiber emission to ensure the protection of populations and workers.