Naturally Occurring Asbestos (NOA) in Granitoid Rocks, A Case Study from Sardinia (Italy)

Abstract

All six minerals defined as “asbestos” by the existing regulation on asbestos hazard, i.e., actinolite, tremolite, anthophyllite, crocidolite and amosite amphiboles, and the serpentine-group mineral chrysotile are typical constituents of mafic and ultramafic magmatic rocks of ophiolitic sequences. However, little is known about the presence and distribution of naturally occurring asbestos (NOA) in plutonic felsic rocks. The Isadalu magmatic complex outcropping in central Sardinia and belonging to the post-variscan Permian volcanic cycle, is described here as an interesting occurrence of fibrous amphiboles in granitoid rocks. Field work and collected mineralogical/petrological data show that NOA fibers from the Isadalu complex belong compositionally to the actinolite-tremolite series. They were generated by metasomatic growth on pristine magmatic hornblende, at ca. 470 °C at 1 kbar, during sodic-calcic hydrothermal alteration. In terms of environmental hazard, the Isadalu complex represents a high-value case study, since the actinolite-bearing felsic rocks outcrop in a strongly anthropized area. Here, towns with local and regional strategic infrastructures (dams, pipes, hydroelectric power plants, water supply, roads) have been developed since the last century, also using the granitoid asbestos-rich stones. The aim of this study is to demonstrate that NOA and relative hazard are not univocally connected to a restricted typology of rocks. This result should be taken into account in any future work, procedure or regulation defining asbestos occurrences in natural environments.

Naturally Occurring Asbestiform Minerals in Italian Western Alps and in Other Italian Sites

“…Several spot investigations, carried out during both the asbestos investigation and specific mineralogical researches, show that NONA are present in many Italian areas (8 Italian Regions) and abundant in some places. Except Piedmont and Aosta Valley Regions which we will discuss later, the NONA identified in Italy are the following (in alphabetic order): asbestiform antigorite, asbestiform Ca-erionite (with Ca-levyne), asbestiform F-edenite, asbestiform gedrite, asbestiform Mg-horneblende, asbestiform offretite, asbestiform polygonal serpentine, asbestiform sepiolite (e.g., Cattaneo et al, 2011;Bloise et al, 2014;.Bloise et al, 2016;Bloise et al, 2017;Giordani et al, 2017;Lucci et al, 2018;Mattioli et al, 2018) The Italian Regions where these asbestiform minerals have been detected are shown in Figure 2.…”

Mineralogical Characterization and Dissolution Experiments in Gamble’s Solution of Tremolitic Amphibole from Passo di Caldenno (Sondrio, Italy)

“…Simplified classification diagram [29] showing the amphibole composition determined by EPMA (12 spot analyses). Hbl indicates hornblende.…”

Hydrothermal genesis and growth of the banded agates from the Allumiere-Tolfa volcanic district (Latium, Italy)

“…Obtained results agree with the few existing literature exploring the genetic scenario of the Allumiere-Tolfa ore basin characterized by hydrothermal/metasomatic processes at low-depth due to late-magmatic hydrothermal fluids at T 120-140 ± 25 °C (from oxygen isotope data in Lombardi and Sheppard 1977), which produced an extensive alteration of the pre-existing rocks with consequent formation of the sulfates (alunite group) + kaolinite + silica paragenesis (Lombardi and Sheppard 1977). This mineral assemblage was indicated by Hedenquist et al (2000) to be typical of the "silicic" to "advanced argillic" alteration zones characterized by a depth of 0-150 m and a temperature ranging from 100 to 200 °C and capping the deeper potassic and sodic-calcic alteration zones (e.g., Lucci et al 2018) of an epithermal ore deposit.…”