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Icelandic Hyaloclastite Tuffs Petrophysical Properties, Alteration and Geochemical Mobility

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Icelandic Hyaloclastite Tuffs Petrophysical Properties, Alteration and Geochemical Mobility Icelandic Hyaloclastite Tuffs Petrophysical Properties, Alteration and Geochemical Mobility Hjalti Franzson Gudmundur H. Gudfinnsson Julia Frolova Helga M. Helgadóttir Bruce Pauly Anette K. Mortensen Sveinn P. Jakobsson Prepared for National Energy Authority and Reykjavík Energy ÍSOR-2011/064 ICELAND GEOSURVEY Reykjavík: Orkugardur, Grensásvegur 9, 108 Reykjavík, Iceland - Tel.: 528 1500 - Fax: 528 1699 Akureyri: Rangárvellir, P.O. Box 30, 602 Akureyri, Iceland - Tel.: 528 1500 - Fax: 528 1599 [email protected] - www.isor.is Report Project no.: 540105 Icelandic Hyaloclastite Tuffs Petrophysical Properties, Alteration and Geochemical Mobility Hjalti Franzson Gudmundur H. Gudfinnsson Julia Frolova Helga M. Helgadóttir Bruce Pauly Anette K. Mortensen Sveinn P. Jakobsson Prepared for National Energy Authority and Reykjavík Energy ÍSOR-2011/064 December 2011 Key page Report no. Date Distribution ÍSOR-2011/064 December 2011 Open Closed Report name / Main and subheadings Number of copies Icelandic Hyaloclastite Tuffs. Petrophysical Properties, Alteration 7 and Geochemical Mobility Number of pages 103 Authors Project manager Hjalti Franzson, Gudmundur H. Gudfinnsson, Julia Frolova, Hjalti Franzson Helga M. Helgadóttir, Bruce Pauly, Anette K. Mortensen and Sveinn P. Jakobsson Classification of report Project no. 540105 Prepared for National Energy Authority and Reykjavík Energy Cooperators Moscow University, University of California in Davis, Natural History Museum in Iceland Abstract This study attempts to define the properties of hyaloclastite formations which control their petrophysical characteristics during their progressive alteration. It is based on 140 tuffaceous cores from last glaciation to 2–3 m y. The water content shows a progressive increase with alteration to about 12%, which mainly is bound in the smectite and zeolite alteration minerals. It diminishes when altered to chlorite and disappearance of zeolites indicating the dehydration of the alteration minerals. CO2 content appears to increase stepwise, firstly at about 30%, secondly at 65% and thirdly near 100% alteration. The rock oxidation increases concomitantly with the water content in the rock. This is reflected in the grain density which also diminishes with increasing alteration but increases again when entering into the chlorite-epidote alteration. Changes in porosity show that larger pores (macro porosity) are filled as alteration proceeds, while secondary micro porosity increases, mainly at palagonite/glass margins and not the least within the smectite clays. Micro porosity in fully altered tuffs ranges from about 7–35%. This type of porosity may explain the “aquiclude character” of hyaloclastites. Permeability ranges from 0.1 to about 12000 mD and a close correlation is shown between porosity and permeability. This correlation, however, is stronger between macro porosity and permeability than the micro porosity. Chemical analysis of fresh glass and palagonite shows the notable leaching of Na2O in the latter and to some extent the CaO, while FeO and TiO2 are slightly enriched. Other oxides do not show obvious tendencies for mobility. The assessment of chemical mobility during alteration, taking into account the filling of macro pores, was unsuccessful, and may be due to the formation of secondary micro porosity which is not the case in alteration of crystallized rocks. A geochemical comparison of the variably altered tuffs with the compositional field of equivalent fresh rocks indicate the limited mobility of the chemical components, except for CaO, Na2O and Rb which show clear indication of being removed. Key words ISBN-number Hyaloclastite tuffs, petrophysics, alteration, palagonite, grain density, geochemistry, mobility, Project manager’s signature Reviewed by HMH Table of contents 1 Introduction ....................................................................................................................... 13 2 Sample collection, measurements and chemical analyzes ........................................ 14 3 Sample description ........................................................................................................... 15 4 Alteration ............................................................................................................................ 16 5 Volatile content ................................................................................................................. 17 6 Grain density ..................................................................................................................... 19 7 Porosity ............................................................................................................................... 20 7.1 Changes in porosity ................................................................................................... 20 7.2 The sources of micro porosity .................................................................................. 21 7.3 Permeability and porosity ........................................................................................ 22 8 Chemical transfer .............................................................................................................. 22 8.1 Chemical mobility in basaltic glass caused by palagonitization ........................... 23 8.2 Changes in whole-rock chemical composition by palagonitization ..................... 23 8.3 Composition of hyaloclastite tuff samples compared to crystallized whole- rock samples ................................................................................................................. 24 8.4 Chemical changes with increasing secondary mineralization .............................. 25 8.5 Evidence for element mobility from geochemical trends....................................... 27 8.6 Evidence for element mobility from the relationship between Zr and some major and trace elements ............................................................................................ 28 9 Conclusions ........................................................................................................................ 29 10 Recommendations for further work .............................................................................. 30 11 References ........................................................................................................................... 31 12 Figures ................................................................................................................................. 33 List of figures Figure 1. SiO2 content versus MgO content of the hyaloclastite tuff samples. The samples are classified according to petrological series. ........................................................................ 33 Figure 2. Histogram showing sample frequency depending on the original amount of glass as a proportion of solid rock. .................................................................................................. 33 Figure 3. Histogram showing sample frequency depending on the abundance of unaltered glass as a proportion of solid rock. ......................................................................................... 34 Figure 4. Histogram showing sample frequency depending on the abundance of altered glass as a proportion of solid rock. ......................................................................................... 34 Figure 5. Histogram showing sample frequency depending on the extent to which the primary glass has been altered. .............................................................................................. 35 - 5 - Figure 6. Histogram showing sample frequency depending on the abundance of primary minerals as a proportion of solid rock. ................................................................................... 35 Figure 7. Histogram showing sample frequency depending on the abundance of altered primary minerals as a proportion of solid rock. ..................................................................... 36 Figure 8. Histogram showing the sample frequency depending on the proportion of pores in the samples as determined by point counting in thin sections. ............................................. 36 Figure 9. Histogram showing sample frequency depending on the original proportion of pores in the samples as determined by point counting in thin sections. ................................ 37 Figure 10. Histogram showing sample frequency depending on the amount of porosity in the samples as measured in air. .............................................................................................. 37 Figure 11. Histogram showing sample frequency depending on the abundance of secondary minerals as a proportion of solid rock. ................................................................................... 38 Figure 12. Histogram showing sample frequency depending on the abundance of clay as a proportion of solid rock. ......................................................................................................... 38 Figure 13. Histogram showing sample frequency depending on the abundance of zeolites as a proportion of solid rock. ....................................................................................................... 39 Figure 14. BEI photograph of a slightly palagonitized hyaloclastite tuff sample from Vigdísarvellir on Reykjanes Peninsula. ................................................................................. 40 Figure 16. BEI photograph of a moderately
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