Predictions of prospectivity based on remote sensing were developed using alteration mineral indicative hyperspectral mapping and remote sensing anomaly filtering, combined with geological characteristics and anomalous mineral field verification. Based on the results of the hyperspectral mineral mapping and the actual geological ground conditions, the results of mapping of altered minerals, such as chlorite, muscovite, kaolinite, and iron oxide were validated, and gold, silver, copper, nickel, and other geochemical anomaly areas were identified for verification work. The results of hyperspectral mineral extraction show that the mineral assemblage closely related to gold deposits in shear zones is muscovite + chlorite + epidote + kaolinite. This alteration mineral assemblage can be used as regional search criteria for shear zone gold mineralisation and was the basis for the discovery of mineralised hydrothermal alteration centres and delineation of four prospective targets. Established on a spectral prospectivity model of the study area, prospective ore-bearing areas have been delineated, which indicate the direction for further geological and mineral resource surveys.

https://www.mdpi.com/2071-1050/11/2/428/pdf

Research on Hyperspectral Identification of Altered Minerals in Yemaquan West Gold Field, Xinjiang

https://hal-brgm.archives-ouvertes.fr/hal-02160944/document

Coupling SEM-EDS and confocal Raman-in-SEM imaging: A new method for identification and 3D morphology of asbestos-like fibers in a mineral matrix.

Realization of large geo-engineering projects in rocks containing naturally occurring asbestos (NOA) must address several crucial geo-environmental issues, including the design of the construction site, the enforcement of health protection measures and the environmentally responsible spoil management. This leads to a compelling need to develop effective and standard procedures to evaluate the distribution and concentration of NOA in rock volumes. NOA petrofacies are here proposed as an innovative tool to evaluate the asbestos distribution and concentration in complex geological settings. NOA petrofacies are fundamental asbestos-bearing rock types, consisting in recurrent lithological and structural features controlling asbestos occurrence. Here we describe and discuss how the NOA petrofacies approach was utilized in a geo-environmental study for the evaluation of asbestos content in a complex meta-ophiolite suite, which will be crossed by the “Gronda di Genova” highway by-pass project (Genoa, NW Italy). NOA petrofacies were used to predict the distribution and relative abundance of NOA in geologically homogeneous zones characterized by the occurrence of specific NOA minerals.

Petrofacies for the prediction of NOA content in rocks: application to the “Gronda di Genova” tunneling project

Notice explicative carte géologique Maroc (1/50 000), feuille Al Glo'a

Abstract The tectonic evolution of Alpine Corsica and surrounding areas is described through a series of plate reconstructions from the onset of the Alpine convergence in the early Cretaceous (~ 120 Ma) to the early Miocene (~ 19 Ma). The southward subduction of Eurasian lithosphere (Alpine Tethys) beneath Adria and Iberia, and the subduction of Ligure–Piemontese Ocean (Iberian plate) beneath the Adria margin, led to the formation of a trench–trench–trench triple junction close to the northern margin of Adria. During the first phase, from the early Aptian (~ 120 Ma) to the Campanian (~ 75 Ma) the northeastern oceanic part of the Iberian plate subducted beneath Adria along an intra‐oceanic subduction zone between Corsica and Adria. This trench was linked to the eastern Iberian convergent margin (having opposite polarity) through a transform fault. Starting from the Campanian and until the Oligocene (~ 34 Ma) oceanic and transitional crust was obducted onto Hercynian Corsica and Eurasia, giving rise to HP metamorphism within the subducted continental crust. From ~ 40 Ma to the early Oligocene (~ 33 Ma) the onset of continental collision in the Alpine area led to thickening of the subducting Eurasian margin through the formation of the European lower crustal wedge. Finally, from the early Oligocene (~ 33 Ma) to the early Miocene (~ 19 Ma), during the rotation of the Corsica and Sardinia blocks, the Pyrenean–Alpine belt lost its continuity in Gulf of Lyon and Provencal area, while the western Adriatic margin (Apennine domain) became a left‐lateral transpressive belt linking the western Alpine chain with the Calabrian Arc.

Kinematic Evolution of Alpine Corsica in the Framework ofMediterranean Mountain Belts

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.

TEM and FESEM characterization of asbestiform and non-asbestiform actinolite fibers in hydrothermally altered dolerites (France)

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.

Naturally occurring asbestos in an alpine ophiolitic complex (northern Corsica, France)

\n In France, asbestos was banned by national decree (no. 96-1133) in 1996. The regulatory texts and standards adopted to implement this ban are concerned primarily with asbestos-containing manufactured products and are difficult to apply to asbestos-bearing natural materials (i.e., rocks and soils). Considering problems related to asbestos-bearing natural materials, the French Ministry of Ecology, Sustainable Development, and Energy has mandated the French Geological Survey to map locations where asbestos-bearing rocks are found. Mapping was prioritized to geological domains where naturally occurring asbestos (NOA) was predictable (e.g., the Western Alps and Corsica). These studies integrated field expertise, sampling, and laboratory analysis data to characterize the potential of geological units to contain NOA. Additionally, studies were conducted on geological formations exploited to produce aggregates. These studies were focused on quarries excavating massive, basic or ultrabasic rocks likely to contain NOA and quarries mining alluvium likely to contain asbestos-bearing rock pebbles. These studies highlight the difficulty of establishing robust analytical procedures for natural materials. The distinction between cleavage fragments (resulting from the fragmentation of non-asbestos particles) and proper asbestos fibers is particularly problematic for laboratories. Thus, a recent study by the National Agency for Health Safety, Food, Environment, and Work recommends applying the asbestos regulation to elongated mineral particles (length/depth > 3:1, length > 5 μm, depth < 3 μm) with chemical composition corresponding to one of the five regulated amphibole species regardless of their mode of crystallization (asbestiform or non-asbestiform). The upcoming regulatory changes are part of a decree published in 2017, including the prior identification of asbestos in natural soils or rocks likely to be impacted by ground-disturbing construction activities. Specific protocols will be defined for sampling, analysis, and characterization of natural materials that may contain asbestos.

Florence Cagnard

Papers

TEM and FESEM characterization of asbestiform and non-asbestiform actinolite fibers in hydrothermally altered dolerites (France)

Naturally occurring asbestos in an alpine ophiolitic complex (northern Corsica, France)

Naturally Occurring Asbestos in France: Geological Mapping, Mineral Characterization, and Technical Developments