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1.
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.  相似文献   

2.
Abstract Sodic amphiboles are common in Franciscan type II and type III metabasites from Cazadero, California. They occur as (1) vein-fillings, (2) overgrowths on relict augites, (3) discrete tiny crystals in the groundmass, and (4) composite crystals with metamorphic Ca–Na pyroxenes in low-grade rocks. They become coarse-grained and show strong preferred orientation in schistose high-grade rocks. In the lowest grade, only riebeckite to crossite appears; with increasing grade, sodic amphibole becomes, first, enriched in glaucophane component, later coexists with actinolite, and finally, at even higher grade, becomes winchite. Actinolite first appears in foliated blueschists of the upper pumpellyite zone. It occurs (1) interlayered on a millimetre scale with glaucophane prisms and (2) as segments of composite amphibole crystals. Actinolite is considered to be in equilibrium with other high-pressure phases on the basis of its restricted occurrence in higher grade rocks, textural and compositional characteristics, and Fe/Mg distribution coefficient between actinolite and chlorite. Detailed analyses delineate a compositional gap for coexisting sodic and calcic amphiboles. At the highest grade, winchite appears at the expense of the actinolite–glaucophane pair. Compositional characteristics of Franciscan amphiboles from Ward Creek are compared with those of other high P/T facies series. The amphibole trend in terms of major components is very sensitive to the metamorphic field gradient. Na-amphibole appears at lower grade than actinolite along the higher P/T facies series (e.g. Franciscan and New Caledonia), whereas reverse relations occur in the lower P/T facies series (e.g. Sanbagawa and New Zealand). Available data also indicate that at low-temperature conditions, such as those of the blueschist and pumpellyite–actinolite facies, large compositional gaps exist between Ca- and Na-amphiboles, and between actinolite and hornblende, whereas at higher temperatures such as in the epidote–amphibolite, greenschist and eclogite facies, the gaps become very restricted. Common occurrence of both sodic and calcic amphiboles and Ca–Na pyroxene together with albite + quartz in the Ward Creek metabasites and their compositional trends are characteristic of the jadeite–glaucophane type facies series. In New Caledonia blueschists, Ca–Na pyroxenes are also common; Na-amphiboles do not appear alone at low grade in metabasites, instead, Na-amphiboles coexist with Ca-amphiboles throughout the progressive sequence. However, for metabasites of the intermediate pressure facies series, such as those of the Sanbagawa belt, Japan and South Island, New Zealand, Ca–Na pyroxene and glaucophane are not common; sodic amphiboles are restricted to crossite and riebeckite in composition and clinopyroxenes to acmite and sodic augite, and occur only in Fe2O3-rich metabasites. The glaucophane component of Na-amphibole systematically decreases from Ward Creek, New Caledonia, through Sanbagawa to New Zealand. This relation is consistent with estimated pressure decrease employing the geobarometer of Maruyama et al. (1986). Similarly, the decrease in tschermakite content and increase in NaM4 of Ca-amphiboles from New Zealand, through Sanbagawa to New Caledonia is consistent with the geobarometry of Brown (1977b). Therefore, the difference in compositional trends of amphiboles can be used as a guide for P–T detail within the metamorphic facies series.  相似文献   

3.
The Zvishavane Ultramafic Complex (ZUC) in the south central part of the Zimbabwe craton is comprised of coarse-grained serpentinites, metadunites and metagabbros and hosts Africa's largest reserves, and largest mine, of high-grade chrysotile asbestos. Magnesiohornblende, actinolite, plagioclase (An0.6–41.9), augite, diopside and clinozoisite constitute the mineralogy of the ZUC. Forsteritic olivine (>Fo90) was altered to form chrysotile and antigorite minerals, although some primary olivines are preserved. Contents of Al2O3 range from <1 to >2.5 wt% at TiO2 values of <0.7 wt% consistent with an island arc setting for the ZUC that originated from tholeiitic magmas. The Zvishavane Ultramafic Complex was metamorphosed at relatively high temperatures (542-779 °C) and low pressures (1.2-2kbars), consistent with contact metamorphism. Intrusion of several granitic batholiths relatively close to the ZUC likely triggered hydrothermal fluid migration which metamorphosed the ZUC. The associated asbestos deposits likely formed during hydrothermal circulation events. Zoned amphiboles, the occurrence of magnesiohornblende and actinolite, as well as cross-cutting serpentine veins are consistent with at least two stages of alteration and/or metamorphism of the ZUC. The lack of a thrust contact between the ZUC and its country rocks is consistent with the ZUC having intruded into the host Zvishavane Gneiss Complex and possibly acted as a feeder to the nearby Mberengwa greenstone belt (MGB). However, the occurrence of near end-member forsteritic olivine, the presence of zoned amphiboles, and faulting within the ZUC are all suggestive of an ophiolitic origin although forsteritic olivines also occur in intrusive layered complexes. Metamorphism of the ZUC, ascribed to intrusion of multiple batholiths and possibly the MGB, likely led to the formation of ZUC chrysotile asbestos deposits.  相似文献   

4.
In recent years, the high incidence of harmful health effects through inhalation of airborne asbestos from amphibole-bearing rock mélanges has been thoroughly documented. Here, we present a field-based, multi-scale geological approach aimed at illustrating the occurrence of amphibole fibrous mineralisation in an ophiolitic suite from the Ligurian Alps (Italy) and discussing the implication on in situ determination of the asbestos hazard. The rock mélange is composed of plurimetre-sized blocks of different lithotypes (metagabbro, serpentinite, chloritoschist) juxtaposed by the meaning of tectonic structures. The geological-structural survey revealed that the fibrous mineralisation is localised in specific structural sites of the rock volume, including veins and schistosity. Both micro-chemical and crystal structure analyses on selected fibrous samples revealed that actinolite fibres grow in veins within the metagabbro and in chloritoschists, while fibrous tremolite occurs in serpentinite schistosity. The morphological features of these amphibole fibres have been analysed in TEM images and used for classifying them as “asbestiform” or “non-asbestiform”. The results show that the asbestos hazard determination is not unequivocally identified when different procedures for asbestos fibre identification and classification are applied. This may have impact on normatives and regulations in defining environmental hazards due to asbestos occurrence.  相似文献   

5.
Based on the results of microprobe analyses, six groups of calcium amphiboles were distinguished for the Tyrnyauz deposit. Group I (mainly edenite) includes amphiboles of hornfels and periskarn rocks. Groups II-VI (actinolite-hastingsite series) are related to post-skarn metasomatic rocks of the productive stage after hornfels (II), the tonalite and plagiogranite complex (III), ultrabasic rocks (IV), pyroxene-plagioclase periskarn rocks (V), and skarn (VI). Group IV is represented by actinolite; group VI, by hastingsite; groups II, III, and V, by hornblende varieties.  相似文献   

6.
Maria Dorling  Jack Zussman 《Lithos》1987,20(6):469-489
In terms of morphology there are four major types of calcic amphibole; massive, prismatic, finely acicular and asbestos. Representatives of each of these types have been examined by optical microscopy, X-ray diffraction, scanning and transmission electron microscopy, and electron probe microanalysis. Massive specimens (nephrite) consist of randomly oriented clusters of fine, roughly lath-shaped, sub-microscopic crystals; within each cluster the lath lengths (z) are approximately aligned but neighbouring laths are rotated with respect to one another. Finely acicular specimens (“byssolites”) have well-formed crystals bounded mainly by {110} (100) and (010) faces and characteristically have striations parallel to their lengths. Asbestiform varieties range from finer (flexible) to coarser (more brittle) specimens and many specimens contain a mixture of fine and coarse fibrils. The fibrils in a bundle are aligned parallel to z but are in a range of azimuthal orientations. It is inferred that they are formed by multiple independent nucleation and growth parallel to z rather than through parting or cleavage on {110} planes. (100) defect or twin planes, or on (010) planar defects.

The {110} cleavage in amphiboles is well reported but (100) features are rarely mentioned in the literature. Our observations reveal the importance of (100) as a cleavage or parting as well as the tendency in nephrites, byssolites and asbestos towards a lath-like (parallel to z) morphology with flattening on (100). In the latter varieties therefore, the y-direction is that of second fastest crystal growth, after z.

When subjected to moderate grinding, the comminution of asbestos fibres proceeds more by separation of fibrils and less by fracturing to shorter lengths as compared with prismatic and byssolite specimens. Prolonged grinding does, however, shorten lengths of even the least brittle asbestos.

Transmission electron microscopy revealed extensive sub-grain boundaries and dislocation networks (suggesting a deformation history) in all prismatic and nephrite specimens. Fine multiple (100) twinning was observed in asbestos but not in other varieties. Although chain-width defects [on (010)], with visibility enhanced by beam damage, were most abundant in nephrites and fibrous tremolites, there appears to be no completely consistent relationship between such features and morphological type.

Electron probe analyses showed that specimens that contain more than a very small amount of aluminium do not have asbestiform habit. Asbestos specimens also have lower contents of Mn, Na and K and have formulae closer to the ideal Ca2(Mg,Fe)5Si8O22(OH)2. Small departures from this in asbestos involve Na in the A site compensated by Na for Ca rather than Al for Si whereas the reverse is true in byssolites. Chemical substitutions in prismatic specimens are much less constrained.

The characteristics of the four morphological sub-groups correlate reasonably well with what is known of their geological environments.  相似文献   


7.
Abstract Crystal-chemical relationships between coexisting sodic and calcic amphiboles have been studied in eclogitic metagabbros from the Aosta Valley, Western Alps. Textural analysis gives evidence of three successive high-pressure parageneses:
1. Pre-kinematic high-grade blueschist assemblages, preserved as polymineralic inclusions in garnet cores and made of glaucophane and actinolite (stage A).
2. Synkinematic eclogite assemblages, composed of garnet + omphacite + glaucophane ± actinolite ± white mica ° Clinozoisite + quartz + rutile (stage B).
3. Post-kinematic epitactic overgrowths of barroisitic amphibole on glaucophane and actinolite (stage C).
P–T conditions of the eclogitic metamorphism have been estimated at around 500–550°C, 16 kbar.
Glaucophane and actinolite coexist as discrete grains in stage A and B assemblages. This texture and the chemistry of the amphiboles unambiguously denotes the existence of a miscibility gap between sodic and calcic amphiboles (from NaM4= 0.80 in actinolite to NaM4= 1.70 in glaucophane at T = 500–550°C). A comparison with published analyses allows a new solvus along the glaucophane–actinolite join to be drawn.
The later barroisitic amphibole (stage C) exhibits strong chemical zonation indicating disequilibrium growth. This amphibole cannot either be used to define a miscibility gap with glaucophane or actinolite or be considered as an intermediate stage between these two end-members.  相似文献   

8.
中国夕卡岩矿床中的角闪石   总被引：6，自引：3，他引：6       下载免费PDF全文
赵一鸣  李大新 《矿床地质》2003,22(4):345-359
文章综合分析研究了中国21个夕卡岩矿床中的130个角闪石的成分分析数据。根据夕卡岩类型及其伴生金属矿化的不同，把角闪石分为4大类：钙夕卡岩中的角闪石多属钙角闪石，包括绿钙闪石、铁角闪石、镁绿钙闪石、铁浅闪石、阳起石、铁阳起石、铁镁钙闪石和铁韭闪石等；镁夕卡岩中的角闪石以透闪石为主，局部有浅闪石或韭闪石；锰质夕卡岩中的角闪石有锰质阳起石、锰质透闪石、锰直闪石和锰镁闪石；碱质夕卡岩中的角闪石属钠-钙角闪石或钠角闪石类，包括钠透闪石、镁亚铁钠闪石、亚铁钠闪石、镁铝钠闪石和镁钠闪石。碳酸盐围岩和有关侵入岩的成分对角闪石的类型、成分及其伴生金属矿化起重要的作用。  相似文献   

9.
Actinolite, hornblende and biotite coexisting in greenschist mafic metagreywackes have been analysed with the electron microprobe to obtain information on their chemical relationship during metamorphism. As in some other parts of the world, the two calcic amphiboles coexist in the greenschist facies because of a miscibility gap between them which is observed under conditions of low-pressure regional metamorphism; it is thought that the two amphiboles are in equilibrium, or at least that the actinolite participated in hornblendeforming reactions. Contact metamorphism by granitic intrusives of these metagreywackes has converted them to hornblende hornfelses with the assemblage hornblende, andesine, quartz, biotite±cummingtonite; the hornblendes of the hornfelses are found to have compositions between actinolite and hornblende of the greenschists, and frequently show fine exsolution lamellae of cummingtonite as a result of oversaturation in this component. The distribution of Fe-Mg between hornblende and biotite changes from the greenschist to the hornblende hornfels facies, and the K D is probably dependent on AlVI in the hornblende.  相似文献   

10.
An Early Palaeozoic (Ordovician ?) metamudstone sequence near Wojcieszow, Kaczawa Mts, Western Sudetes, Poland, contains numerous metabasite sills, up to 50 m thick. These subvolcanic rocks are of within-plate alkali basalt type. Primary igneous phases in the metabasites, clinopyroxene (salite) and kaersutite, are veined and partly replaced by complex metamorphic mineral assemblages. Particularly, the kaersutite is corroded and rimmed by zoned sodic, sodic–calcic and calcic amphiboles. The matrix is composed of actinolite, pycnochlorite, albite (An ≤ 0.5%), epidote (Ps 27–33), titanite, calcite, opaques and, occasionally, biotite, phengite and stilpnomelane. The sodic amphiboles are glaucophane to crossite in composition with NaB from 1.9 to 1.6. They are rimmed successively by sodic–calcic and calcic amphiboles with compositions ranging from magnesioferri-winchite to actinolite. No compositions between NaB= 0.92 and NaB= 1.56 have been ascertained. The textures may be interpreted as representing a greenschist facies overprint on an earlier blueschist (or blueschist–greenschist transitional) assemblage. The presence of glaucophane and no traces of a jadeitic pyroxene + quartz association indicate pressures between 6 and 12 kbar during the high-pressure episode. Temperature is difficult to assess in this metamorphic event. The replacement of glaucophane by actinolite + chlorite + albite, with associated epidote, allows restriction of the upper pressure limit of the greenschist recrystallization to <8 kbar, between 350 and 450°C. The mineral assemblage representing the greenschist episode suggests the P–T conditions of the high-pressure part of the chlorite or lower biotite zone. The latest metamorphic recrystallization, under the greenschist facies, may have taken place in the Viséan.  相似文献   

11.
Textural and chemical relationships in the Ca-amphibole serieshave been examined in progressively metamorphosed mafic schistfrom the Povungnituk Group, northern Qubec. In the hornblendezone, coexisting actinolite and hornblende are characterizedby sharp optical and chemical boundaries. They also displayan epitaxial intergrowth texture, consistent with contemporaneouscrystallization and the presence of a miscibility gap (solvus)between actinolite and hornblende. At higher grade, in the oligoclasezone, actinolite is always rimmed by hornblende. Across theoligoclase isograd, the compositional break between actinoliteand hornblende remains relatively constant in width (6–10wt.% Al2O3). Accordingly, the concentric texture and the lackof chemical gradients are interpreted as a local equilibriumat the scale of the interfaces between the two amphiboles. Throughoutthe hornblende zone and the lower part of the oligoclase zone,both amphiboles are characterized by a progressive Mg-enrichment,with no consistent change in edenite and Tschermak components.The hornblende zone can be characterized by a continuous reactionwith Mg-enrichment of reactants (biotite and chlorite) and products(actinolite and hornblende). However, this reaction requiresa mixed-volatile phase with a much higher XCO2 ({small tilde}0.5) than those calculated from equilibrium curves in the NCMASH—CO2system. The oligoclase isograd can be represented by a discontinuousoligoclase—hornblende-forming reaction which coincideswith the change from epitaxial to concentric texture at theoligoclase isograd. At the upper limit of the oligoclase zone,gradational boundaries and a continuous solid solution betweenhornblende and actinolite document a disequilibrium texture.Although a miscibility gap can be documented in the hornblendezone, its closure at higher grade is not observed, based onequilibrium crystallization of actinolite and hornblende. Theresults of this study suggest that the crest of the solvus mustbe crossed between the oligoclase and actinolite-out isograds,based on zoned profiles between hornblende rims and relic actinolite. "The term exsolution refers to the process whereby an initiallyhomogeneous solid solution separates into two (or possibly more)distinct crystalline minerals without the addition or removalof material to or from the system. Exsolution generally, althoughnot necessarily, occurs on cooling. The miscibility gap representsa temperature—composition field in which solid solutionbetween the end members decreases gradually from higher to lowertemperatures."  相似文献   

12.
Vermiculites with impurities of amphibole, a dry fine residue and calcined materials from three deposits in the province of Córdoba, Argentina, were studied. From a commercial perspective, amphiboles are considered as “asbestos”, a group of silicate minerals with strong and flexible fibres that are heat resistant and chemically inert, and thus well suited for heat insulation. These fibrous particles have provoked controversies about the toxicity impact on human health and the development of diseases such as mesothelioma, asbestosis or lung cancer. Their commercialization and exploitation are currently prohibited. The sampled minerals were identified with a petrographic microscope, chemical analyses, SEM and XRD. It was concluded that amphibole minerals are present in all the deposits studied and in every phase of plant production, but not all of them have asbestiform characteristics.  相似文献   

13.
An exceptionally well-exposed part of the Flin Flon Greenstone Belt (Manitoba/Saskatchewan) is used to characterize the mineral assemblage evolution associated with prehnite–pumpellyite through amphibolite facies metamorphism of basalts. Data from these rocks are combined with a large literature data set to assess the ability of current thermodynamic models to reproduce natural patterns, evaluate the use of metabasic rocks at these grades to estimate pressure–temperature (P–T) conditions of metamorphism, and to comment on the metamorphic devolatilization that occurs. At Flin Flon, five major isograds (actinolite-in, prehnite- and pumpellyite-out, hornblende-in, oligoclase-in, and actinolite-out) collectively represent passage from prehnite–pumpellyite to lower amphibolite facies conditions. The evolution in mineral assemblages occurs in two narrow (~1,000 m) zones: the prehnite–pumpellyite to greenschist facies (PP-GS) transition and greenschist to amphibolite facies (GS-AM) transition. Across the GS-AM transition, significant increases in the hornblende and oligoclase proportions occur at the expense of actinolite, albite, chlorite, and titanite, whereas there is little change in the proportions of epidote. The majority of this mineral transformation occurs above the oligoclase-in isograd within the hornblende–actinolite–oligoclase zone. Comparison with thermodynamic modelling results suggests data set 5 (DS5) of Holland and Powell (1998, Journal of Metamorphic Geology, 16 (3):309–343) and associated activity–composition (a–x) models is generally successful in reproducing natural observations, whereas data set 6 (DS6) (Holland & Powell, 2011, Journal of Metamorphic Geology, 29 (3):333–383) and associated a–x models fail to reproduce the observed mineral isograds and compositions. When the data from Flin Flon are combined with data from the literature, two main pressure-sensitive facies series for metabasites are revealed, based on prograde passage below or above a hornblende–albite bathograd at ~3.3 kbar: a low-pressure ‘actinolite–oligoclase type’ facies series, characterized by the appearance of oligoclase before hornblende, and a moderate- to high-pressure ‘hornblende–albite type’ facies series, characterized by the appearance of hornblende before oligoclase. Concerning the PP-GS transition, the mineral assemblage evolution in Flin Flon suggests it occurs over a small zone (<1,000 m), in which assemblages containing true transitional assemblages (prehnite and/or pumpellyite coexisting with actinolite) are rare. This contrasts with thermodynamic modelling, using either DS5 or DS6, which predicts a wide PP-GS transition involving the progressive appearance of epidote and actinolite and disappearance of pumpellyite and prehnite. Patterns of mineral assemblages and thermodynamic modelling suggest a useful bathograd (‘CHEPPAQ bathograd’), separating prehnite–pumpellyite-bearing assemblages at low pressures and pumpellyite–actinolite-bearing assemblages at higher pressures, occurs at ~2.3 to 2.6 kbar. Observations from the Flin Flon sequence suggests devolatilization across the GS-AM transition (average: ~1.8 wt% H2O) occurs over a very narrow interval within the actinolite–hornblende–oligoclase zone, associated with the loss of >75% of the total chlorite. By contrast, modelling of the GS-AM transition zone predicts more progressive dehydration of ~2 wt% H2O over a >50°C interval. Observations from the field suggest devolatilization across the PP-GS transition occurs over a very narrow interval given the rarity of transitional assemblages. Modelling suggests fluid release of 1.0–1.4 wt% resulting from prehnite breakdown over a ~10°C interval. This fluid may not be entirely lost from the rock package due to involvement in the hydration of igneous mineralogy across the PP-GS transition as observed in the Flin Flon sequence.  相似文献   

14.
This study examined commercial talc deposits in the U.S. and their amphibole-asbestos content. The study found that the talc-forming environment directly influenced the amphibole and amphibole-asbestos content of the talc deposit. Large talc districts in the U.S. have mined hydrothermal talcs that replaced dolostone. Hydrothermal talcs, created by siliceous fluids heated by magmas at depth, consistently lack amphiboles as accessory minerals. In contrast, mineable talc deposits that formed by contact or regional metamorphism consistently contain amphiboles, locally as asbestiform varieties. Examples of contact metamorphic deposits occur in Death Valley, California; these talc-tremolite deposits contain accessory amphibole-asbestos. Talc bodies formed by regional metamorphism always contain amphiboles, which display a variety of compositions and habits, including asbestiform. Some industrial mineral deposits are under scrutiny as potential sources of accessory asbestos minerals. Recognizing consistent relations between the talc-forming environment and amphibole-asbestos content may be used in prioritizing remediation or monitoring of abandoned and active talc mines.  相似文献   

15.
Abstract Compositions of actinolite, hornblende and cummingtonite, together with pyroxene and plagioclase, are studied in basic intrusions in the Dalradian of north-east Scotland, and the Glen Scaddle complex in the West Moine. Amphibolitization is due to influx of water from the country rocks. Pyroxene compositions are found to have adjusted to the regional metamorphic environment. Owing to the difficulty of diffusion of Al and Si, calcic amphiboles are zoned and commonly contain quartz blebs. Discontinuities in zoning give rise to actinolite-hornblende pairs. Compared with north-east Scotland, disequilibrium is less strong in the Glen Scaddle area: in the latter, plagioclase compositions have been greatly changed, Na partition between hornblende and plagioclase is close to equilibrium, the maximum Al content of hornblende is lower and zoning patterns are more consistent. The Fe/Mg ratio in calcic amphiboles varies with Al content, while approaching equilibrium partition with other minerals. Both zoning patterns and Fe/Mg partition with cummingtonite suggest that Fe/Mg of the calcic amphiboles increases more strongly with increasing (Alvi+Fe3+) than can be explained simply by substitution of Al,Fe3+ for Mg on M2. Model reactions for amphibole formation are constructed. Cummingtonite formed at lower chemical potential of CaO than actinolite: Ca was exchanged for Mg,Fe between orthopyroxene-derived and clinopyroxene-derived local systems. Both cummingtonite and actinolite were formed because of kinetic constraints, as intermediate reaction products: actinolite-hornblende pairs represent disequilibrium. This work suggests that many occurrences of actinolite with hornblende, where the minerals are zoned, may also be due to diffusion kinetics.  相似文献   

16.
The town of Biancavilla, located on the lower flanks of Mt. Etna volcano, eastern Sicily (Italy), showed high mortality rates owing to malignant pleural neoplasms, a cause of death specifically related to exposure to asbestos fibres. An environmental survey indicated the stone quarry site of Il Calvario as a possible source of asbestos fibre exposure, while a mineralogical study allowed to identify the new asbestiform mineral fluoro-edenite. A joint epidemiological and environmental study was conducted to assess the characteristics of the outbreak of malignant mesothelioma and to test the assumption of a causal relation with exposure to fluoro-edenite. Due to the lack of awareness of fluoro-edenite releases, Il Calvario may not be the only source of the fibre, but is probably the main one. The evolution of the volume of material quarried from Il Calvario was studied on the basis of maps printed from 1896 to 1995, by using a digital elevation model. The natural and anthropogenic causes of the territorial spread of the newly discovered amphibole fibres are discussed relatively to a geo-volcanological, territorial and environmental evolution of the area affected.  相似文献   

17.
20世纪,越来越多的证据使人们意识到,吸入含石棉的灰尘会使从事与石棉有关的几种职业(如石棉采矿、造船和石棉产品组装)的工人患上几种严重的呼吸道疾病(石棉沉着病,肺癌和mesotheliuma)。为此已经制定了若干规定,以控制工人们在特殊的制造、采矿和其他工作地点与石棉尘埃的接触。比较间接的是控制和管理"天然产生的石棉"(NOA),这一问题近年来也引起了管理机构、健康机构和居民团体的注意。NOA包括在自然状态下原地找到的被描述为石棉的矿物,例如在基岩或土壤中的这种矿物。NOA之所以引起关注,是因为如果含石棉的岩石受到自然侵蚀或人类活动(例如修路、城市开挖、农业、采矿、压碎和碾磨)的影响,就有可能暴露并变成空中尘埃的微小纤维。天然石棉矿床的规模差异很大,从薄的四散的细脉一直到大的矿体。它们的地理分布与地质条件直接有关。石棉产出的地质背景是含镁丰富的主岩,这些岩石受到低压低温的变质作用蚀变而成。已知的容矿主岩包括变质的和已被交代的超基性岩(尤其是蛇纹岩)、一些基性火成岩、变质白云岩和变质的铁建造。石棉形状的角闪石在几种热液蚀变型的碱性火成侵入体中也能作为副矿物存在。石棉形成于可预见和可鉴别的地质环境。这种认识是一种信息,而这种信息使公众健康机构可以执行有情报根据的屏蔽和管理规划。第一步是在区域的或国家规模的尺度上确定和描述已知的(报道过的)石棉矿床。第二步是对容纳已知石棉矿的单位进行填图,以划定可能的其他石棉矿化的范围。这种地质研究使有关机构对遇到石棉的可能性做出规划,而尽量节省在不太可能遇到石棉矿的地区的管理费用。对石棉地质条件的认识可以事先应用于岩石和土壤的挖掘项目,而不管挖掘的规模有多大。这种对石棉管理的科学探索能有助于缓解对挖掘所发现的自然石棉矿床的连续不断地做出反应。因此,通过对很可能含有石棉矿床的地区做填图,规划者可开发出一些控制尘埃的程序,这些程序适用于工人和附近居民最容易暴露于空气携带的石棉的地区。  相似文献   

18.
KLEIN  CORNELIS  JR. 《Journal of Petrology》1968,9(2):281-330
Chemical analyses for the following amphibole pairs are presented:anthophyllite—tremolite (or actinolite, or hornblende),cummingtonite (or grunerite)–actinolite (or hornblende),cummingtonite (or grunerite)–anthophyllite (or gedrite),and manganoan cummingtonitemagnesioriebeckite. Nineteen analyses of such pairs are quoted from the literature,and thirty-seven additional pairs have been newly analyzed byelectron probe techniques. Quantitative microprobe determinationsof Si, Al, Fe, Mn, Mg, Ca, and Na were made on polished thin-sections,using naturally occurring, analyzed, homogeneous amphibolesas standards. The literature analyses and the electron probeanalyses for metamorphic, two-amphibole assemblages are givenfor amphiboles in physical contact, which show no textural evidenceof one amphibole being a reaction or alteration product of theother. The chemical data for some of the volcanic, two—amphiboleassemblages were obtained from occurrences that probably donot represent equilibrium pairs. The chemical data are used to determine the extent of the miscibilitygaps between the various amphibole series and the fractionationof the major elements between the two amphiboles of a pair.Anthophyllite and members of the cummingtonite-grunerite seriesgenerally have a larger Fe(total)/Mg ratio than the coexistingcalcic amphibole. The maximum CaO, Al2O3and Na2O contents ofcummingtonite in metamorphic cummingtonite—hornblendepairs are 19 and 32, 02 weight per cent, respectively. Themaximum CaO, A12O3, and Na2O contents of cummingtonite in metamorphiccummingtonite-hornblende pairs are 19, 32, and 02 weightper cent, respectively. Larger CaO and Al2O3 values reportedin the literature were found to be too high because of admixtureof actinolite or hornblende in the analyzed separates. Smallamounts of MnO tend to concentrate preferentially in anthophylliteor cummingtonite of anthophyllite-hornblende and cummingtonite-hornblendepairs. Anthophyllite-cummingtonite pairs may show very similarFe(total)/Mg ratios and differ slightly in Al2O3 content only.  相似文献   

19.
郑永飞 《地质科学》1995,30(1):1-11
利用增量方法和同位素交换技术,对角闪石族矿物的氧同位素分馏进行了理论计算和实验测定。理论结果表明,不同化学成分的角闪石之间存在一定的氧同位素分馏,其13O富集顺序为:钠闪石>蓝闪石>铁闪石>阳起石=镁铁门石≥直闪石≥透闪石>普通角闪石>铝直闪石>韭闪石。高温条件下(>500℃),角闪石相对于水亏损18O达1‰至3‰。实验进行在有少量流体存在的条件下,温度为520℃至680℃。所确定的方解石-透闪石氧同位素分馏系数与理论计算值在误差范围内完全一致。理论和实验确定的石英-透闪石分馏曲线均显着低于已知的经验校准曲线,反映了变质岩中含角闪石矿物集合体内部的退化同位素再平衡。  相似文献   

20.
The Susunai Complex of southeast Sakhalin represents a subduction-related accretionary complex of pelitic and basic rocks. Two stages of metamorphism are recognized: (1) a local, low- P / T  event characterized by Si-poor calcic amphiboles; (2) a regional, high- P / T  event characterized by pumpellyite, actinolite, epidote, sodic amphibole, sodic pyroxene, stilpnomelane and aragonite. The major mineral assemblages of the high- P / T  Susunai metabasites contain pumpellyite+epidote+actinolite+chlorite, epidote+actinolite+chlorite, epidote+Na-amphibole+Na-pyroxene+chlorite+haematite. The Na- amphibole is commonly magnesioriebeckite. The Na-pyroxene is jadeite-poor aegirine to aegirine-augite. Application of empirically and experimentally based thermobarometers suggests peak conditions of T  =250–300 °C, P= 4.7–6 kbar. Textural relationships in Susunai metabasite samples and a petrogenetic grid calculated for the Fe3+-rich basaltic system suggest that pressure and temperature increased during prograde metamorphism.  相似文献   

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