Alicja M Lacinska, Michael T Styles. British Geological Survey. NERC All rights reserved

Transcription

1 Silicified serpentinite and the Barzaman Formation in the United Arab Emirates: a natural analogue for CO 2 sequestration through mineral carbonation of ultramafic rocks. Alicja M Lacinska, Michael T Styles British Geological Survey

2 (ex situ) CCSM PROCESSES AND TECHNOLOGIES

3 CCSM INDUSTRIAL PROCESSES Pre-treatment Mg extraction Mg 2+ Carbonation Mg + CO 2 Silica residuum Carbonate Silicified serpentinite CCSM NATURAL PROCESSES UAE Barzaman Formation Dolomite-cemented, ophiolitederived conglomerates

4 Local extent and associated lithologies Silicified serpentinite Barzaman Formation Silicified serpentinite

5 Silicified serpentinite >95% of quartz +- haematite/goethite, chromite, forsterite, amphibole

6 Silicified serpentinite

7 Serpentinite Silicified serpentinite microtextures and origin Silicified Serpentinite Qtz Ol Chr Chr Mesh texture in serpentinite Origin: incongruent dissolution of serpentinite, formation of siliceous micro-seeds that subsequently were overgrown by silica leached from weathered horizons elsewhere seasonal fluctuation of water table, mixed meteoric and groundwater (~neutral ph for silica precipitation) a palaeo-weathering surface, developed in temperate climate during middle Eocene to late Miocene produced a silcrete residuum result Mg completely leached out of serpentinite Ghost mesh texture after serpentinite Lacinska & Styles, in press

8 Barzaman Formation Dolomite-cemented ophiolite-derived conglomerate Minor carbonate cementation and clast alteration

9 Extensive carbonate cementation in NERC restricted All rights zones reserved

10 Extensive carbonate cementation and alteration of clasts

11 Barzaman Formation microtextures

12 Carbonate cement in Bzm Frm CO 2 captured in dolomite and calcite Barzaman Formation: alluvial fan deposits formed as a result of the rapid erosion of the Oman-UAE Ophiolite chemically and physically changed by fluid/rock interaction in the near surface environment the silicate-carbonate reaction is active due to instability of the original minerals : a) extensive replacement of fine fraction of the matrix; b) preferential replacement of harzburgite and serpentinite rather than more stable gabbro covers an area c. 5000km 2, thickness c. 60m, 25% carbonate = 1.5x10 11 tonnes of CO 2 captured equivalent of 300 years of total CO 2 emission from the UK Lacinska et al, in press

13 Conclusions Silicified serpentinite and the Barzaman Formation formed on a vast scale in the near-surface environment due to extensive fluid/rock interaction The textures observed on a macro and micro-scale show: i. Complete leaching of Mg - the reaction between serpentinite and aqco 2 (acid Mg leaching) followed by precipitation of silica, mimicking the serpentine mesh texture, resulted in silicified serpentinite ii. Carbonation in the Bzm Frm - extensive dissolution of serpentinite sand and clasts and subsequent precipitation of dolomite. The process was sequential: a) small particle size (large surface area) enhances the carbonation b) serpentinite is much more reactive than gabbro in the given conditions Silicified serpentinite CCSM NATURAL ANALOGUE CCSM INDUSTRIAL PROCESSES Barzaman Formation Mg extraction via acid leaching silicate carbonate The newly formed dolomite has proved to be stable over a geological time scale, 10 myr The Bzm Frm is a natural analogue of CO 2 sequestration via mineral carbonation using ultramafic rocks The Bzm Frm captured vast amounts of CO 2 that is equivalent to 300 years of total CO 2 emission from the UK

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