Fluid inclusions - Petrography and genetic interpretation of fluid inclusions Dr. Alfons M. van den Kerkhof Geowissenschaftliches Zentrum der Universit ät Göttingen (Germany) Course handout: 1 http://www.uni-goettingen.de/de/26174.html Program Day 1 9:00-12:00 Introduction Classification of fluid inclusions, mechanisms of fluid inclusion forming, primary and secondary inclusions, modification of fluid inclusions 14:00-17:00 Training Microscopy exercises (COLTAN pegmatites) Day 2 9:00-12:00 Working procedure (sample preparation, equipment), destructive and non- destructive fluid inclusion analysis, principles of microthermometry, isochore definition, fluid inclusion petrography, application of cathodoluminescence 14:00-17:00 Water-salt systems Training: Microthermometry, Crushing stage, Software (isochore calculation), videos. Day 3 9:00-12:00 Water-gas systems, clathrate stability, fluid-mineral equilibria and graphite stability, COHN equilibria calculations, non-aqueous systems, working with VX diagrams 14:00-17:00 Training: Microthermometry, Software (COHN), videos. Day 4 9:00-12:00 Selected examples: Fluid inclusions in the granitic-pegmatitic system, Fluid inclusions in granulites, Fluid inclusions in ore deposits 14:00-17:00 Free exercises, presentations of participants and discussion. 2 Fluid inclusion study short working plan I. Sample preparation Doubly polished sections II. Documentation 1. Microscopy and fluid inclusion selection 2. Drawings and photos 3. Classification of fluid inclusions a. Description (one-phase, 2-phase, multiphase, daughter crystals etc.) b. Relative phase volumes (fill degree) c. Inclusion size, morphology d. Relative age (primary, pseudosecondary, secondary) III. Microthermometry 1. Cooling experi3ment (until ca. -180°C) observation of phase nucleations (Tn V, CO 2 S, etc. ) 2. Warming experiment (-180 until about 35°C) detection of phase transition temperatures (Te, Tm CO 2, Tm ice, Th CO 2, Tm ice, Tm hydrate) 3. Heating experiment (aqueous inclusions) Th total, Tm salt IV. Data treatment Calculation of compositions and densities, isochore calculation 3 Working procedure of a fluid inclusion study (revised after Van den Kerkhof, 1988) 4 Optical properties of solid phases in fluid inclusions in order of increasing refractive index name composition refract. birefringence crystal habit comments index system liquid carbon dioxide CO 2 (liq.) 1.195 o carbon dioxide CO 2 (s.) ? M? translucent, microcrystalline T<-56.6 C; usually forms a single mass aggregates euhedral crystals can be formed in liquid CH 4-CO 2 ICE H2O 1.31 negligible H rounded plates or globules anisotropic but appears isotropic Tm<0 oC, sometimes yellowish appearance WATER H 2 O 1.32-1.33 3 o CO 2-clathrate CO 2.5 /4H2O ~ negligible rhombic or rounded grains Tm = about 6 C; colourless, RI very close to water (gas hydrate) RI very close to H 2O and therefore difficult to recognize villiaumite NaF 1.33 isotropic C cubes sometimes yellow/pinkish pleochroism cryolite Na 3AlF 6 1.34 negligible M alkaline rocks elpasolite K2NaAlF 6 1.37 isotropic C topase from Volynia USSR mirabilite /Glauber´s s.Na 2SO 4.10H 2O 1.39-1.40 negligible M prismatic, acicular HYDROHALITE NaCl.2H 2O ~1.41 negligible M tiny grains giving a speckled high relief relative to ice; colourless appearance Tm (incongruent) = +0.1 oC o natron (soda) Na 2CO 3.10H 2O 1.40-1.44 low M platy crystals Tm (incongruent) = +32 C FLUORITE CaF 2 1.43 isotropic C cubes rarely octahedral, fluorescence hexahydrite MgSO 4.6H 2O 1.45 low M fibrous, tabular trona Na 3H(CO 3)2.2H 2O 1.41-1.54 moderate M fibrous, acicular NAHCOLITE NaHCO 3 1.37-1.58 very high M tabular commonly twinned; marked relief changes on rotation in pol. light carbonic fluids in granulite facies alum (Na,K)Al(SO 4)2.12H 2O 1.44-1.46 isotropic C sulfohalite Na 6(SO 4)2ClF 1.45 isotropic C thermonatrite Na 2CO 3.H 2O 1.42-1.52 moderate O borax Na 2(B 4O5(OH) 4).8H 2O 1.45-1.47 low M gaylussite Na 2Ca(CO 3)2.5H 2O 1.44-1.52 moderate M elongated or flattened crystals epsomite MgSO 4.7H 2O 1.43-1.46 low O(T) acicular alunogen Al 2(SO 4)3.18H 2O 1.46-1.48 low T(H) fibrous thenardite Na 2SO 4 1.46-1.48 low O bipyramidal or tabular c.f. gypsum CARNALITE KMgCl 3.6H 2O 1.47-1.49 low O(H) tabular pickeringite (Mg)- (Mg,Fe´´)Al 2(SO 4)4.22H 2O mean 1.48 very low M acicular, radiated aggregates halotrichite (Fe´´) SYLVITE KCl 1.49 isotropic C cubes often rounded cube edges, solubility at higher temp. increases more rapidly compared to halite burkeite Na 6CO 3(SO 4)2 mean 1.49 moderate O arcanite K2SO 4 1.49-1.50 low O massive, tabular rarely "octahedral" crystals pseudo-bischofite MgCl 2.6H 2O 1.49-1.53 low to M moderate (hydro-)bischofite MgCl 2.12H 2O 1.50-1.53 negligible M like hydrohalite identification difficult; colourless wavellite Al 3(PO 4)2(F,OH) 3.5H 2O 1.52-1.55 low O radiated aggregates, globules GYPSUM CaSO 4.2H 2O 1.52-1.53 very low M tabular, prismatic, fibrous hydromagnesite Mg 5(CO 3)4(OH) 2.4H 2O 1.52-1.54 low M(O) acicular crystals or lamellae hydroboracite CaMg[B 3O4(OH) 3]2.3H 2O mean 1.52 moderate M associated with gypsum DAWSONITE NaAl(CO 3)(OH) 2 1.47-1.60 moderate O fibrous bundles frequent in alpine fissures aggregates HALITE NaCl 1.54 isotropic C cubes rarely octahedral, same refractive index as quartz Fe-chlorides FeCl n various moderate to (T) var. tabular, often rhombic commonly light green high or hexagonal QUARZ SiO 2 1.54-1.55 low antarcticite CaCl 2.6H 2O 1.49-1.55 low/negligible T like hydrohalite but occasionally rounded crystals micas various 1.56-1.60 low to M platy extremely thin plates moderate strontianite SrCO 3 1.52-1.67 high O acicular, pseudohexagonal ANHYDRITE CaSO 4 1.57-1.61 low O prismatic associated with gypsum aragonite CaCO 3 1.53-1.69 high O prismatic, acicular whewellite CaC 2O4.H 2O 1.49-1.65 very high M prisms uranium vein deposits Ca,Mg CARBONATE (Ca,Mg)CO 3 1.49-1.66 very high T rhombohedral high relief; marked changes in relief on rotation in pol. light barite BaSO 4 1.64-1.65 low O tabular APATITE Ca 5(PO 4)3(F,OH,Cl) 1.63-1.67 low H hexogonal crystals HEMATITE Fe 2O3 (2.9-3.2) T hexagonal plates distinctive red/brown plates SULFIDES various - var. euhedral grains identification sometimes possible in refelective light GRAPHITE C - H mostly amorphous euhedral (platy) crystals rare; highly Raman active (from: Van den Kerkhof & hein, 2001, Lithos 55, 27-47) 5 Estimation of volume fractions 1 6 Estimation of volume fractions 2 7 Fluid inclusion classification Classification scheme for fluid and melt inclusions in minerals based upon phases observed at room temperature L=liquid, V= vapour, S=solid, GL=glass (from: Sheperd, 1985) Examples of phases in fluid inclusions in porphyry copper deposits (from: Nash JT, 1976, US Geol. Survey Prof. Papers 907D) 8 Eutectic properties of salt solutions (Hein, Compact course, 1990) 9 Microthermometry abbreviations „ A consensus of fluid inclusion workers on usage of microthermometric terms was reached and first printed in Vol. 10 of COFFI. It is suggested that if this terminology is used consistently in the future papers, considerable ambiguity will be avoided (For ease of typewriting and typesetting, I suggest not using subscripts) „ (Roedder 1981, Fluid Inclusion Research – Proceedings of COFFI) 10 Relative age of fluid inclusions Primary-secondary“ classification Principle sketch of inclusion classification, based on Roedder´s (1981) criteria. The stippled line denotes growth zoning. P= primary, PS= pseudosecondary and S= secondary inclusions. The P and PS inclusions in the inner growth zone are older than the P and PS ones in the outer zone. Inclusions along the growth planes are denoted as primary. The S trail, extending to the surface of the crystal, postdates all P and PS inclusions (from: Hansteen, 1988, Cand. Scient. Thesis, Univ. Oslo) 11 Primary fluid inclusions (diagnostic criteria) (a) Diagnostic criteria for classifying fluid inclusions as primary (after Roedder, 1979) 12 (b) Different occurrences of primary fluid inclusions in relation to growth zoning (compilation) (from: Van den Kerkhof & Hein, 2001, Lithos 55, 27-47) Trail terminology / Homogeneous – heterogeneous trapping Trail terminology (Vollbrecht, 1989) composed after Simmons and Richter (1976) and Kranz (1983). A main distinction is made between transgranular, intergranular, and intragranular inclusions (b) The intragranular fluid inclusions may decorate different internal grain textures and are accordingly subdivided. (below) (a) Homogeneous trapping of fluids. At room temperature (after cooling) phase separation may result from shrinkage, saturation or unmixing of the original homogeneous fluid. (b) Heterogeneous trapping of fluids. Fluid inclusions of variable composition and phase ratio are trapped at the same time (Van den Kerkhof & Hein, 2001, Lithos 55, 27-47) 13 Fluid inclusion modification (Hansteen, 1988) (Bodnar, Binns & Hall, 1989, J. Metam. Geol. 7, 229-242 14 Overview of methods for analyzing fluid inclusions NON-DESTRUCTIVE ANALYSIS 1. OPTICAL MICROSCOPY AND VIZALIZING TECHNIQUES Petrographical microscope fluid inclusion abundance, chronology CL-Microscopy /SEM-CL textural relations with host mineral, secondary quartz UV-Microscope detection of hydrocarbons IR-Microscope visualisation of fluid inclusions in semi-opaque and opaque minerals (e.g. cassiterite, chromite, sphalerite, pyrite) TEM dislocations /micro-cracks around FI 2. MICROTHERMOMETRY composition and molar volume 3. VIBRATIONAL SPECTROSCOPY Laser excited micro-Raman spectroscopy composition of non-aqueous fluids, identification of daughter crystals FT-IR detection of CO 2, H 2O, hydroxyl, ..