Kieselkalke der Schweiz: Charakterisierung eines Rohstoffs aus geologischer, petrographischer, wirtschaftlicher und umweltrelevanter Sicht

In Switzerland, predominantly three types of rock are used for the fabrication of hard rock products: siliceous limestone, Flysch sandstone and Molasse sandstone. Not all varieties of these rocks show hard rock characteristics. Potential hard rock deposits are concentrated on localities along the northern Alpine rim where 11 open cast mines are in service. Problems in choice of site for hard rock quarries often occur due to conflicts between industrial use and environmental protection. This study investigates siliceous limestones in Switzerland. Because of their geographical extension and industrial usability, these rocks have the highest potential for high quality hard rock products. Siliceous limestones are analysed petrographically, mechanically characterised and compared. Thereby, mineralogical-petrological as well as technical methods are applied. Depending on the paleogeographical origin and the time of deposition the Swiss siliceous limestones can be divided into four varieties which are important for their use. Out of these, two varieties are found along the Helvetic rim of the Alps and were deposited during Early Cretaceous. More precisely these are the siliceous limestones of the Helvetic Kieselkalk-Formation (Hauterivian) and those of the Helvetic Valanginian. Two other varieties formed during Early Jurassic and occur in the Moltrasio-Formation of the Southern Alps and in different Liassic nappes of the Prealpes medianes. Macroscopically, specific characteristics of the fine grained siliceous limestones can be observed. The distinction of the varieties by thin sections, X-ray diffractometry (XRD) and scanning electron microscope (SEM) is more difficult. In oriented thin sections, the siliceous limestones can be classified by their sedimentary texture according to DUNHAM (1962), independent of the variety. This method allows to distinguish three kinds of textures: mudstones, wackestones and packstones. Furthermore, factors influencing the behaviour of the rocks under mechanical stress are observed in thin sections. Among these, the quantification of potentially weak zones oriented parallel or oblique to the sedimentary layering and accompanied by secondary pyrite is the most significant factor. The investigation of the qualitative mineral assemblage by XRD reveals up to six phases. Besides calcite and quartz, ankerite, partly substituted by dolomite, as well as muscovite 2 M1, pyrite and regionally chlorite are observed. Quantification by the Rietveld-Method shows that calcite and quartz represent the largest amounts in all the varieties. Locally, however, these amounts can vary strongly which makes a regional forecast of the mineralogical composition of these rocks impossible. For the analyses by SEM, mineral amounts have to be considered. Etched samples of siliceous limestones containing < 30 wt% authigenic quartz show local, partial silification. With an increasing proportion of silica, quartz-rich areas are connected in a tight 3-dimensional mesh. In samples with more than 30 wt% authigenic quartz, unsilicified areas are seldom larger than 100 μm. Independent of the content of authigenic quartz, the silicified parts serve as framework and therefore they contribute to the resistance to mechanical stress. Moreover, the uniaxial compressive strength is influenced by authigenic quartz. Between silification and compressive strength, a linear correlation can be observed. Thus, siliceous limestones (up to 340 MPa) can achieve almost twice the rupture strength of pure limestone (160 MPa). Furthermore, the LCPC abrasion and refractivity test according to AFNOR P 18-579 also mirrors the silification grade. Compared to limestones, in siliceous limestones already a small amount of authigenic quartz leads to an increased refractivity. Compared to other hard rocks used in Switzerland, three of the four considered varieties of siliceous limestone show lower average refractivity coefficients. In this test, especially wackestones prove to be the most durable kind of siliceous limestone. The comparison between the refractivity test and the Los Angeles test for ballast according to EN 1097-2 reveals that these hard rocks can be viewed in a more sophisticated way. In conclusion, the refractivity test could serve as a single testing method for the classification of hard, medium hard and soft rocks.



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Date (Creation)
2012-01-01
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https://www.mica-project.eu/ / MICA_B3-110

MICA WP3 2018-11-03T15:16:00 Record extracted from Batch 3 spreadsheet

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Completed
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SGTK - Schweizerische Geotechnische Kommission

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  • MICA

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  • Mixture of historic (up to 2005) and recent (2006 onwards)

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  • Requirement for data generation: Voluntary
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  • Method of data or information generation: Academic research

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  • Geochemical

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  • Geology

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  • Mineralogical

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  • Production

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  • Resources

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  • Sand and gravel

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Switzerland - Distribution of siliceous limestones in Switzerland
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Reviewed by: British Geological Survey
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Commission Regulation (EU) No 1089/2010 of 23 November 2010 implementing Directive 2007/2/EC of the European Parliament and of the Council as regards interoperability of spatial data sets and services
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2010-12-08
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Organisation source implies that information should be of good quality

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2ba45cd8-71cb-4c70-9465-969ec3632870 XML
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English
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MD_CharacterSetCode_utf8
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Non geographic dataset
Date stamp
2024-11-07
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ISO19115
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2003/Cor.1:2006
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British Geological Survey

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