viii
Table of contents
Acknowledgements……….. ... ii
Abstract ………. ... iii
Riassunto ………. ... v
Chapter 1: Thesis Overview 1.1 Introduction ………..………… ... 1
1.2 The Montecastelli and Querceto outcrops………...………… ... 3
1.3 The goals of the study ………. ... 4
1.4 Thesis structure and content ………...………… ... 5
Chapter 2: Brucite-driven CO2 uptake in serpentinized dunite from Ligurian Ophiolites (Montecastelli, Tuscany) 2.1 Introduction ……… ... 10
2.2 Geological background …………..……….… ... 12
2.3 Local geology ……… ... 15
2.3.1 The escarpment ……….………... ... 18
2.3.2 The mine dump ...……….…...……… ... 21
2.4 Petrography, mineral chemistry and geochemistry of host rocks... ... 23
2.4.1. Type 1 - Serpentinized harzburgites ……….. ... 23
2.4.2 Type 2 - Serpentinized dunites ...……….…... ……… ... 25
2.5 Petrography and mineral chemistry of carbonate assemblages…… ... 32
2.5.1 Mg-Fe LDHs: replacement and fracture infill……… ... 32
2.5.2 Hydrous Mg carbonates: replacement, fracture infill and free-surface coating ……… ... 36
ix
2.6.1 The Montecastelli ophiolite complex ………. ... 40
2.6.2 The serpentinization process...……….…... ... 41
2.6.3 The carbonation process...……….…... ... 43
2.7 Conclusions……… ... 48
Chapter 3: A genetic model for hydromagnesite precipitation by isotopic signatures at the Montecastelli mine (Tuscany, Italy) 3.1 Introduction ……….. ... 55
3.2 Geological background ……… ... 57
3.3 Montecastelli copper mine ………. ... 59
3.4 Results ……….. ... 61
3.4.1 Petrography and geochemistry of the host rocks ………. ... 61
3.4.1.1 Serpentinized harzburgites...……….…... ... 61
3.4.1.2 Serpentinized breccias ………. ... 64
3.4.2 Carbonate and aragonite precipitation………. ... 67
3.4.2.1 Carbonates...……….…... ... 68
3.4.2.2 Mg-rich clays………. ... 73
3.4.3 Mineral-microbe interactions……….. ... 73
3.4.4 Isotopic compositions of carbonate minerals……….. ... 76
3.4.5 Hydrogeochemistry………. ... 79
3.5 Discussion ………... ... 84
3.5.1 Mineral carbonation into copper mine……….. ... 84
3.5.1.1 Hydromagnesite ± kerolite ± aragonite crusts ...…………... 85
3.5.1.2 Aragonite flowstone ………. ... 87
3.5.2 Fluid evolution………... ... 88
3.5.2.1 PHREEQC modeling ...……….…... ... 89
x
3.5.3 Carbonate genetic model……….. ... 96
3.6 Conclusions ……… ... 98
Chapter 4: Flow paths of the interacting fluids in the Montecastelli serpentinites outcrops: constraints from the stable isotope (O, C, H) 4.1 Introduction ……… ... 104
4.2 Geological background and local geology …………..……….. ... 106
4.3 Results ……… ... 107
4.3.1 Isotope composition of serpentinite host rocks……… ... 109
4.3.2 Carbonate precipitates……… ... 111
4.3.3 Mineral-microbe interactions……….. ... 112
4.3.4 Isotope composition of carbonates……… ... 115
4.3.5 Hydrogeochemistry……….. ... 119
4.4 Discussion ………. ... 123
4.4.1 Path flow of the rainwater……….. ... 123
4.4.2 Aragonite precipitation....……….…... ... 126
4.4.3 Rayleigh-type isotope distillation model……….. ... 127
4.4.4 PHREEQC modeling……….. ... 129 4.5 Conclusions ………. ... 138 Chapter 5: Querceto 5.1 Introduction ……… ... 142 5.2 Previous study …………..………. ... 144 5.3 Results ……… ... 146 5.3.1 XRD characterization………... 146 5.3.2 Mineral-microbe interactions……….. ... 147 5.3.3 Isotopic characterization………. ... 150 5.4 Discussion ………. ... 153
xi
5.4.1 Origin of the fluid………. ... 153
5.4.2 Modelling of the fluid evolution ……… ... 154
5.5 Preliminary genetic model ……….. ... 157
5.6 Conclusions ……….. ... 158
Chapter 6: DNA preliminary investigations 6.1 PCR amplification of extracted DNA ……… ... 161
6.2 Analyses of 16S sequences …………..………. ... 163
6.3 Microbial activity ………. ... 167
Chapter 7: Conclusions 7.1 Summary of the research ……….. ... 169
7.2 Suggestions for future researches……….. ... 174
Appendices Analythical methods ………... 175
Appendix to Chapter 2……….. ... 194
Appendix to Chapter 3……….. ... 205
