Summary Introduction (definitions, generalities) 1-Alteration parageneses 2- Clay alterations used as paleocondition indicators limitations 3- General functioning of geothermal systems 4- Methodology to use clays as a guide 5- Some examples 6- Clay genesis and transformations 7- Signature of clay minerals Conclusion
In other active geothermal systems example of Milos Aegean arc : Subduction of the african plate under the hellenic one
example of Milos HT: 200-300 C Fluids : sea water = main component
example de Milos
Example de Milos Mainly trioctahedral clay minerals: Saponite Talc/Saponite Talc (Actinolite)
In other active geothermal systems Ill/Sm Smectite Aluto-Langano (Teklemariam et al., 1996)
In other active geothermal systems Long Valley caldera (Flexser, 1991)
Experimental synthesis... - Smectites frequently formed outside their thermodynamic stability domain (Kloprogge et al, 1999) They evolve towards more stable phases Ex. Saponite talc/saponite, chlorite/saponite 200 days at 400 C - Mixed layer minerals = transitory metastable state (Jiang et al., 1994 ; Essene et Peacor, 1995 )
Experimental synthesis... Yamada et Nakazawa (1993): - Beidellite stable at higher temperature than montmorillonite Favored in environments of high energy Beaufort et al (2001) : hydrothermal treatment of Mt at 200 C (with sanidine, + quartz)
Summary Introduction (definitions, generalities) 1-Alteration parageneses 2- clay alterations used as paleocondition indicators - limitations 3- General functioning of geothermal systems 4- Methodology to use clays as a guide 5- Some examples 6- Clay genesis and transformations 7- Signature of clay minerals Conclusion
Study of active geothermal systems Distribution and properties of clay minerals are controlled by the dynamic of the systems crystallisation kinetics (time x temperature) must be handled Very important factor in these contexts where fluids mixing, boiling often generate strong disequilibria Inadequacy between models based on thermodynamic equilibria and the mode of functioning of these systems Numerous informations can be deduced from clay minerals (reactivity, N/G, duration of the conversion series )
Clay minerals... Textural, crystal-chemical, microstructural properties... - Recognition of geothermal areas by surface investigation - Location of permeable levels, characterization of the hydrological regime - Nature of hydrothermal fluids + fluid state - History of the hydrothermal activity (location, duration ) - Better understanding of ancient systems
Lesser Antilles Guadeloupe : Bouillante geothermal field
Ilet igeon Malendure N Mineralogy Recognition of geothermal area by surface investigation example ofbouillante geothermal field 18.25 Pointe Lézard Bouillante Bay Bouillante Caribbean Sea Thomas 7.64 3.52 Duché 4.46 1 km Rocroy 1 2 - Outside the Bouillante Bay: Kaolinite/smectite (± halloysite, allophanes) Weathering in tropical environnement + Fd 3 7 11 15 19 23 27 31 2q, Cu Ka 3 4 5
Mineralogy Morne Lézard Main area of thermal manifestations Hot springs Geothermal wells BO1, BO2, BO3, BO4 1 km Surface investigations Bouillante 17.03 Pointe Lézard Bouillante Bay BO3 BO2 Bouillante 8.52 5.61 3.37 1 2 BO1 3 BO4 Fd Fd 4 5 Prospection guide Cheap and easy 3 5 7 9 11 13 15 17 19 21 23 25 27 29 2q, Cu Ka - In hydrothermalized area : Smectite : beidellite (montmorillonite)
Morne Lézard Main area of thermal manifestations Hot springs Geothermal wells BO1, BO2, BO3, BO4 1 km Recognition of geothermal area by surface investigation Pointe Lézard Bouillante Bay Bouillante BO3 BO2 BO1 BO4 - Epithermal breccia Illite/smectite mixedlayers Record of the opening stage
In depth Temperature ( C) 80 120 160 200 240 Calcite Quartz Heul-clinopt. Wairakite Epidote Prehnite Pyrite Hematite Kaolinite Smectite I/S R=1 Illite + I/S R>1 Corrensite Chlorite 100 200 BO5 300 Drilling depth (m) BO6 400 BO5 500 600 700 Upper permeable zone (damage zone of the Plateau fault) Example de Bouillante 800 900 BO6 Lower permeable zone - top of the reservoir (damage zone of the Cocagne fault) Lahars Argilized fractured rocks Massive lavas Aerial and hyaloclastic tuffs
Subst. in octahedral sheet 75 m 9.04Å 60M40B 100M 9.7Å 7 8 9 10 11 12 125 m 8.70Å 30M70B 60M40B 9.01Å 7 8 9 10 11 12 236 m 8.57Å 5M95B Subst. in tetrahedral sheet 40M60B 8.81Å 7 8 9 10 11 12 Position ( 2theta, CuKa) Figure 8, Guisseau et al.
stretching bending 940 914 Fe-Al-OH Mg-Al-OH 880 840 3660 3630 3600 Fe-Al-OH and/or Mg-Al-OH 40 m 75 m 125m 160 m 190 m 230 m 260 m 975 925 875 825 3750 3700 3650 3600 3550 Wavenumber (cm -1 ) Figure 4, Guisseau et al
In hole temperature ( C) 170 150 130 110 90 70 50 0 20 40 60 80 100 Tetrahedral layer charge (%) Figure 10, Guisseau et al. Bouillante
Drilling depth (m) Figure 9, Guisseau et al. Isotopic composition of clay phases 10 3 ln α smectite-eau = 2,55 * 10 6 * T -2 4,05 (Sheppard et Gilg, 1996) 10 3 ln α illite-eau = 2,39 * 10 6 * T -2 3,76 (Sheppard et Gilg, 1996). 10 3 ln α minéral-eau = 18 Ominéral - 18 Oeau, pour 18 Ominéral - 18 Oeau<10. 0 50 18 O of smectites and equilibrated fluids ( SMOW) -10-5 0 5 10 15 20 boiling: vapor phase 100-160 C geothermal fluid 260 C 100 150 200 250 300 meteoric water seawater + boiling:fluid phase 100-160 C
Beidellite Surficial clay mineral in equilibrium with the geothermal fluid Ascending hydrological regime (ancient and present hydrothermal vents)
Montmorillonite Surficial clay mineral in equilibrium with the geothermal fluid mixed with meteoric water hydrological regime : downward infiltrations Hydrostatic pressure
31.1 Å Cor. 15.24 Å Cor. 14.43 Å Chl.± exp I/S R 1 sme 14.31 Å Chl. illite 7.60 Å Cor. kaol 7.11 Å Chl. 7.14 Å Chl. ± exp I/S R 1 a 4.75 Å Chl. ± exp 4.73 Å Chl. b c In depth Bouillante 4.5 6.5 8.5 10.5 12.5 14.5 16.5 18.5 2q Cu Ka
17.15 Å sme 1.49 Å sme In depth 60 61 62 63 64 27 Å I/S R=1 8.55 Å 13 Å sme I/S R=1 9.05 Å 7.17 Å I/S R=1 kaol 2.5 4.5 6.5 8.5 10.5 12.5 14.5 16.5 18.5 10 Å illite Chl Chl 2.5 4.5 6.5 8.5 10.5 12.5 14.5 16.5 18.5 2q Cu Ka 5.68 Å sme 5.39 Å I/S R=1 5 Å illite Chl a b c d Bouillante
Temperature ( C) 80 120 160 200 240 Calcite Quartz Heul-clinopt. Wairakite Epidote Prehnite Pyrite Hematite Kaolinite Smectite I/S R=1 Illite + I/S R>1 Corrensite Chlorite 100 200 BO5 300 Drilling depth (m) BO6 400 BO5 500 Upper permeable zone (damage zone of the Plateau fault) 600 700 800 Lower permeable zone - top of the reservoir (damage zone of the Cocagne fault) 900 BO6 Lahars Argilized fractured rocks Massive lavas Aerial and hyaloclastic tuffs
Air dried EG
Depth (m) Reservoir zone: weak argilization Position of the (001) reflection (Å) of the illitic phases 300 400 E.G. A.D. BO6 500 600 productive zone ill 700 800 900 950 productive zone Specific textural and microstructural properties (interstratification rate, ) clay minerals approached equilibrium with the geothermal fluids N/G rates
Reservoir zone: weak argilization Specific textural and microstructural properties (cristallinity ) High CSD size High CSD size
Depth (m) Massive argilization in impervious zones Position of the (001) reflection (Å) of the illitic phases 650m Py. 300 400 E.G. A.D. BO6 Ill. 500 600 700 productive zone Ancient permeable levels Paragenesis richer in smectite 800 900 950 productive zone In the past: Strong oversaturation of geothermal fluids (boiling, confirmed by bladed calcite)
Reservoir zones : 2 argilization schemes Rapid ascending of geothermal fluids and abrupt changes in physical and chemical conditions Strong argilization Rapid nucleation and growth Parageneses rich in smectites controlled by fluid chemistry, independant of temperature beidellite (saponite) Ancient reservoir zones of Bouillante... Examples of Milos, Chipilapa Slow ascending of geothermal fluids which are close to equilibrium with the host rock Weak argilization - Parageneses controlled by T Predicted clay phases : mixed layers, chlorite, illite... Present reservoir of Bouillante... Texture and crystal structure of clay minerals could be a potential indicator of the hydrodynamic of fluids in the reservoir zones (past and recent)
General sketch : example of Bouillante geothermal field Opening : dramatic change in flow regime (extensive fracturing, tectonic reactivation) Per ascendum hydrological regime
General sketch Progressive sealing Progressive collapse
General sketch Collapsing of the hydrothermal activity in the system lead to a change in heat flow regime
Clay minerals... Besides of their hypothetical use as accurate geothermometers, crystal-chemical and textural properties of clay minerals are a interesting tool to better understand the whole functioning of hydrothermal systems
In low to medium enthalpy geothermal systems Plaine du Lamentin Clay minerals poorly studied in low to medium temperature geothermal systems : - Studies focus on secondary minerals in high enthalpy reservoirs - Clays minerals are quite similar to clay minerals formed during weathering -Clay minerals superimposed on HT parageneses formed during arlier events but Most surficial part of geothermal field Interest for prospection
Montagne Pelée Fort-de-France Carbet Martinique Island Le Lamentin In low enthalpy hydrothermal systems 0 20 km 1618 North 1618 Californie La11 1616 La10 La03 1616 La12 La01 La101 La02 1614 Pte Desgras La09 La05 La04 1614 1612 La07 Carrère La06 1612 Lamentin area Lamentin Bay La08 1610 1610 1608 New well Thermal springs Ancient well 1608 710 712 714 716 718 Mas et al, 2003. 0 2 KM
Depth (m) Temperature ( C) 40 60 80 100 LA01 100 200 300 400 500 600 LA02 700 800 LA03 900 1000 Lamentin
Textural/microstructural parameters Different events of kaolinite crystallization occurred kaol sme - «Early kaolinite» Dissolution features, replacement by smectite (Mt/Bei) - «Present» kaolinite Euhedral crystals No dissolution features
- Microstructural properties of kaolinites in present circulation zones as a function of hydrothermal fluid temperatures 3 : 50 C - 2 : 70 C - 1 : 90 C 7.17 Å (001) peak of kaolinite Hinckley index, 1963 (3) (2) (1) 11 12 13 14 2q Cu Ka
Stretching bands Bending bands P 2 P 1 very high high medium low very low very high high medium low very low wave length (cm -1 ) Lietard, 1977
3667 3651 938 Present day paragenesis - kaolinite 3693 914 3620 90 C very high high (1) (2) 50 C 3720 3680 3640 medium 3600 wave length (cm -1 ) 950 930 910 (3) 890
- Microstructural properties of kaolinites vary with hydrothermal fluid temperatures - Different properties than supergen kaolinites kaolinite crystallinity well LA02 LA03 LA03 LA03 depth (m) 390.60 311.00 410.15 405.60 FWHM ( 2q) 0.32 0.15 0.11 0.10 HI 0.51 0.80 1.27 1.32 P 1 and P 2 medium medium very high very high T fluid ( C) 50 70 90 90
Conclusion According to their kinetic control, clays minerals occurring in hydrothermal systems cannot be used in most cases as absolute geothermometers Crystal-chemical, textural, microstructural properties Reaction rate, degree of transformation towards more stable phases depend on F/R (permeability), dt/dt, Dynamic of the system Prospection
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