In other active geothermal systems

Transcription

1 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

2 In other active geothermal systems example of Milos Aegean arc : Subduction of the african plate under the hellenic one

3 example of Milos HT: C Fluids : sea water = main component

4 example de Milos

5 Example de Milos Mainly trioctahedral clay minerals: Saponite Talc/Saponite Talc (Actinolite)

6 In other active geothermal systems Ill/Sm Smectite Aluto-Langano (Teklemariam et al., 1996)

7 In other active geothermal systems Long Valley caldera (Flexser, 1991)

8 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 )

9 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)

10 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

11 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 )

12 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

13 Lesser Antilles Guadeloupe : Bouillante geothermal field

14 Ilet igeon Malendure N Mineralogy Recognition of geothermal area by surface investigation example ofbouillante geothermal field Pointe Lézard Bouillante Bay Bouillante Caribbean Sea Thomas Duché km Rocroy Outside the Bouillante Bay: Kaolinite/smectite (± halloysite, allophanes) Weathering in tropical environnement + Fd q, Cu Ka 3 4 5

15 Mineralogy Morne Lézard Main area of thermal manifestations Hot springs Geothermal wells BO1, BO2, BO3, BO4 1 km Surface investigations Bouillante Pointe Lézard Bouillante Bay BO3 BO2 Bouillante BO1 3 BO4 Fd Fd 4 5 Prospection guide Cheap and easy q, Cu Ka - In hydrothermalized area : Smectite : beidellite (montmorillonite)

16 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

17 In depth Temperature ( C) Calcite Quartz Heul-clinopt. Wairakite Epidote Prehnite Pyrite Hematite Kaolinite Smectite I/S R=1 Illite + I/S R>1 Corrensite Chlorite BO5 300 Drilling depth (m) BO6 400 BO Upper permeable zone (damage zone of the Plateau fault) Example de Bouillante BO6 Lower permeable zone - top of the reservoir (damage zone of the Cocagne fault) Lahars Argilized fractured rocks Massive lavas Aerial and hyaloclastic tuffs

18 Subst. in octahedral sheet 75 m 9.04Å 60M40B 100M 9.7Å m 8.70Å 30M70B 60M40B 9.01Å m 8.57Å 5M95B Subst. in tetrahedral sheet 40M60B 8.81Å Position ( 2theta, CuKa) Figure 8, Guisseau et al.

19 stretching bending Fe-Al-OH Mg-Al-OH Fe-Al-OH and/or Mg-Al-OH 40 m 75 m 125m 160 m 190 m 230 m 260 m Wavenumber (cm -1 ) Figure 4, Guisseau et al

20 In hole temperature ( C) Tetrahedral layer charge (%) Figure 10, Guisseau et al. Bouillante

21 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) ln α minéral-eau = 18 Ominéral - 18 Oeau, pour 18 Ominéral - 18 Oeau< O of smectites and equilibrated fluids ( SMOW) boiling: vapor phase C geothermal fluid 260 C meteoric water seawater + boiling:fluid phase C

22 Beidellite Surficial clay mineral in equilibrium with the geothermal fluid Ascending hydrological regime (ancient and present hydrothermal vents)

23 Montmorillonite Surficial clay mineral in equilibrium with the geothermal fluid mixed with meteoric water hydrological regime : downward infiltrations Hydrostatic pressure

24 31.1 Å Cor Å Cor Å Chl.± exp I/S R 1 sme Å Chl. illite 7.60 Å Cor. kaol 7.11 Å Chl Å Chl. ± exp I/S R 1 a 4.75 Å Chl. ± exp 4.73 Å Chl. b c In depth Bouillante q Cu Ka

25 17.15 Å sme 1.49 Å sme In depth Å I/S R= Å 13 Å sme I/S R= Å 7.17 Å I/S R=1 kaol Å illite Chl Chl q Cu Ka 5.68 Å sme 5.39 Å I/S R=1 5 Å illite Chl a b c d Bouillante

26 Temperature ( C) Calcite Quartz Heul-clinopt. Wairakite Epidote Prehnite Pyrite Hematite Kaolinite Smectite I/S R=1 Illite + I/S R>1 Corrensite Chlorite BO5 300 Drilling depth (m) BO6 400 BO5 500 Upper permeable zone (damage zone of the Plateau fault) 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

27 Air dried EG

28 Depth (m) Reservoir zone: weak argilization Position of the (001) reflection (Å) of the illitic phases E.G. A.D. BO productive zone ill productive zone Specific textural and microstructural properties (interstratification rate, ) clay minerals approached equilibrium with the geothermal fluids N/G rates

29 Reservoir zone: weak argilization Specific textural and microstructural properties (cristallinity ) High CSD size High CSD size

30 Depth (m) Massive argilization in impervious zones Position of the (001) reflection (Å) of the illitic phases 650m Py E.G. A.D. BO6 Ill productive zone Ancient permeable levels Paragenesis richer in smectite productive zone In the past: Strong oversaturation of geothermal fluids (boiling, confirmed by bladed calcite)

31 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)

32 General sketch : example of Bouillante geothermal field Opening : dramatic change in flow regime (extensive fracturing, tectonic reactivation) Per ascendum hydrological regime

33 General sketch Progressive sealing Progressive collapse

34 General sketch Collapsing of the hydrothermal activity in the system lead to a change in heat flow regime

35 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

36 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

37 Montagne Pelée Fort-de-France Carbet Martinique Island Le Lamentin In low enthalpy hydrothermal systems 0 20 km 1618 North 1618 Californie La La10 La La12 La01 La101 La Pte Desgras La09 La05 La La07 Carrère La Lamentin area Lamentin Bay La New well Thermal springs Ancient well Mas et al, KM

38 Depth (m) Temperature ( C) LA LA LA Lamentin

39 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

40 - 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) q Cu Ka

41 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

42 Present day paragenesis - kaolinite C very high high (1) (2) 50 C medium 3600 wave length (cm -1 ) (3) 890

43 - Microstructural properties of kaolinites vary with hydrothermal fluid temperatures - Different properties than supergen kaolinites kaolinite crystallinity well LA02 LA03 LA03 LA03 depth (m) FWHM ( 2q) HI P 1 and P 2 medium medium very high very high T fluid ( C)

44 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

45 Ready to explore hydrothermal systems