Table 3.

Chemical and mineralogical changes brought about by anthropogenic modification of the subsurface

Material typeChemical alteration processes and effectsNatural analogueReferences
BricksSwelling on absorption of water (bricks include swelling clays, lime and elements including Na and K).
Swelling due to salt efflorescence.
Conditioning factors: mineralogical composition, method of manufacture, firing temperature and duration
Thermally metamorphosed sandy clayDunham (1992), Elert et al. (2003), Hughes & Bargh (1982), Sena da Fonseca et al. (2013)
ConcreteCement mineralogical changes include precipitation of gypsum, carbonation produces carbonate minerals and leached ions
e.g. Portlandite → CaCO3,
Ca-silicate hydrates → CaCO3 +  SiO2,
Ca-aluminate hydrates → CaCO3 + gibbsite (CaCO3 = calcite, aragonite or vaterite depending on supersaturation of fluid).
Short-term (less than 100 years) porosity decrease associated with mineral-phase transformation, followed by porosity increase due to loss of primary cement and re-dissolution of secondary minerals, e.g. zeolite. On 1ka timescale alteration product is carbonated, low-porosity layer like that occurring naturally.
Leaching from lime mortars and cement-grouting increases groundwater pH.
Rapid growth of speleothems in cellars and tunnels.
Portland cement has generally been in wide use for <150 years so its long-term durability and preservation potential is uncertain.
Low-temperature serpentinization of ultrabasic rocks; high temperature–low pressure metamorphic aureoles in calcareous or carbonaceous sedimentsAlexander (1992), Attard et al. (2016), Gherardi et al. (2012), Liu & He (1998), Milodowski et al. (2009), Rochelle & Milodowski (2013), Waters & Zalasiewicz (2018)
Drilling fluids and structures in wells and pipesCirculation of bentonite-rich drilling fluid and concrete grout used to seal wells may result in injection of CaCO3 and sulphate into surrounding fractured rock.
Drilling mud injectites distinguished by presence of flow structures, abraded cuttings, wedge-shaped geometries with sharp tops and bases, cross-cutting bedding relationships and absence of trace fossils, stylolites and concretions.
Drilling muds may contain water-emulsifying, suspending and filtration-control agents, a suspension of clay and barite, salts (sodium chloride and calcium chloride), various detergents and flocculants and organic polymers.
Accelerated corrosion of steel drill casing through oxidation produces iron oxides, or precipitation of siderite or iron sulphide in O2-poor environment.
Potential chemical degradation of plastic polymers in pipes and liners by molecular alteration by hydrolysis or heating in conditions of high or low pH.
Introduction of polymer-based drilling fluids and chemical additives and proppants designed to keep open fractures.
Contamination from Underground Coal Gasification or waste disposal via bore.
Natural hydraulic fractures; natural neptunean dykesBurton et al. (2013), Caenn et al. (2011), Daemen (1996), Enning & Garrelfs (2014), Hilbrecht & Meyer (1989), Hodgkinson & Hughes (1999), Legarth et al. (2005), Rochelle & Milodowski (2013), Savage (2011)
Rocks adjacent to Geological Disposal FacilityCaverns filled in part with radioactive waste stored in concrete cells or vitrified form, in turn placed in copper canister filled with lead (Swedish method), or in steel canister (Swiss method) and surrounded by bentonite. Bentonite buffer designed not to significantly degrade within the first million years of operation. Steel canisters may degrade within 10 ka of operation and de-vitrification of glass between c. 100 ka and 10 million years.
Fluid could be produced from cement dissolution, resulting in an alkaline plume migrating into bedrock, in turn causing mineral dissolution and precipitation of amorphous Ca-aluminosilicate mineral phases.
Elevated temperature-induced clay-mineral phase transition, e.g. >100°C smectite is modelled to transform to illite in less than a million years.
Low grade metamorphism of mud-rocks; Natural nuclear fission reactors, e.g. Oklo (Gabon)Alexander & McKinley (1999), Berry et al. (1999) Eikenberg & Lichtner (1992), Hodgkinson & Hughes (1999), Milodowski et al. (2015), Savage & Rochelle (1993), Weaver (1979)
Rock part of Carbon Capture and StorageTrapping of CO2 as a free phase in geological structural traps.
Dissolving CO2 into local groundwater to form a supercritical CO2 plume reaching 5 m radius around the injection well after 10 years and a two-phase zone of c. 650 m radius.
Residual trapping along the migration path of CO2.
Mineral trapping through dissolution of mineral phases, e.g. feldspar, dolomite and anhydrite, and precipitation of clay and calcite phases.
Bravo Dome CO2 field, New Mexico; Fizzy Horst, Southern North SeaAndré et al. (2007), IPCC (2005), Rochelle et al. (1999, 2004)
Mining leachateProduction of acidic groundwater commonly from oxidation of FeO2 and subsequent incorporation of dissolved metals including Fe3+.
Subsequent precipitation of minerals dominated by iron oxyhydroxides, oxysulphates such as ferrihydrite (Fe(OH)3), goethite (FeOOH) and iron sulphate polymorphs.
Natural oxidation of sulphide-bearing rocksAkcil & Koldas (2006), Bowell et al. (1999)
Rocks/soils at atomic weapon test sitesProduction of durable, but localized conversion of sand into a glass-like substance known variably as trinitite and kharitonchik, with unmelted quartz grains, metallic chondrules and radionuclides.Meteorite impact sitesEby et al. (2010), Shoemaker (1959)