FLUID INCLUSIONS STUDIES

What is a fluid inclusion ?

Fluid inclusions represent entrapped microgeochemical samples of mineralizing fluids – whose studies can provide important clues to an understanding of their nature and P-V-T-X conditions of mineralisation.

Fluid inclusions are minute amount of liquid/gas/dissolved solids entrapped in a crystal during crystallisation.

Could be used to establish the environment in which rock/mineral might have formed (Sorby, 1958).

Fluid inclusions range in size from 2 to 20 microns with fluid content of 10-9 ml.

What are applications of fluid inclusions ?

Mineral Exploration Understanding the physical and chemical environment of ore deposition Igneous Petrogenesis Evolution of ore bearing fluids providing information on-

ancestary of fluids, its evolutionary pathway through precipitation/dissolution/cooling/boiling/mixing, mechanism of metal transport

Information on T, P, density, salinity and composition of fluids. Use as geothermometer and geobarometer To chart pathways of fluid flow-possible to delineate areas

where fluid activity is more pronounced Providing information on the nature of volatiles in the mantle

(CO2- carbonic magmatism)

What are applications of fluid inclusions ?

Sedimentary Petrography Recognising the nature of provenance of detrital clasts of

various sediments Metamorphism Recognising pressure and temperature changes during

metamorphism and metasomatism of sediments Gemnology Identifying valuable natural gemstones from the

inexpensive synthetic stones Lunar rocks and Meteorites Reconstucting various extraterrestrial processes in the

study of lunar and meteoritic samples Site selection for Nuclear Reactors and Repositories Providing valuable evidence on suitability in safety site

selection

What are applications of fluid inclusions ?

Geothermal Energy Fluid inclusion measurements of cores during drilling of active

geothermal systems which provide data on deep temperature in exploration in geothermal fields

Mining Assessing concentrations of high pressure gas inclusions in domal salt

deposits to avoid rock blasts/blowouts by natural decrepitation of such fluid inclusions

Oil Exploration HC inclusions help in finding migration pathways or even possible

reservoir rocks Paleoclimatology Reconstucting paleotemperature, paleoclimate and paleoconcentrations

of CO2 and isotopes of rare gases (He,Ne,Ar,Xe) in atmosphere from the study of dated polar sheets, cave deposits and bedded salt deposits

Which minerals are favourable for fluid inclusion studies ?

Quartz Fluorite Apatite Calcite Halite Dolomite Sphalerite Barite Topaz Cassiterite

FLUID INCLUSION WAFERS [Doubly polished 0.5 - 1mm thick]

What are the various phases in fluid inclusions ?

Gas, Liquid, Solid, Glass Monophase Liquid L=100% Liquid rich two phase L>50% Vapour rich two phase V=50 to 80% Monophase vapour V=100% Multiphase solid L=variable, S<50% Immiscible liquid L1 , L2

Glass Gl>50%

What is the classification scheme for fluid inclusion studies ?

Primary (P) inclusions are formed during primary growth of a mineral

Secondary (S) inclusions are those incorporated into host mineral after crystal formation

Psuedosecondary (PS) inclusions are assumed to develop in a similar way to S-inclusions, the only difference is that fracturing and healing take place before crystal growth has terminated.

What is the instrument used for fluid inclusion studies ?

CHAIXMECA microthermometry heating/freezing stage with a temperature range of -180oC to +600oC

Heating- Freezing chamber connected to an electronic console for monitoring temperature.

Dewar flask for Liquid Nitrogen for carrying out cryogenic studies.

The assembly is fixed on to the microscope stage for direct observation.

Fluids in metamorphism

Role of carbonic fluids in granulite evolution from Southern India (Srikantappa)

Carbonic fluids in high P granulites in E Himalaya, Tibet of China (Kun Shen et. Al.)

Metamorphic evolution in Bastar Craton (A Dutta et.al)

Information Obtained

Generally, assumed FI are significant in upper parts of Earth crust, but FI of CO2, N2, CH4 in high grade metamorphic rocks, deep seated granites, mantle derived material --- solid solution in silicates, as carbonatites, as disseminated carbonate, graphite and diamond.

Granulite xenoliths in basalt and ultramafic nodules (dunite and peridotite) in alkali basalt intrusions

Fluid inclusions contain high content of CO2

To establish relationship between metamorphic zonation and

uplift – by relating to content of CO2 (Using slope of P-T space) Decipher role of CO2 in evolution of earth

Fluids in tectonism

Evolution in Garhwal Himalaya (R Sharma) P-T-X evolution around MCT, Kumaon Himalaya (S.N.Lal)

Early quartz present as mineral inclusions in garnet, host garnet, late quartz in metapelites, granite gneisses and quartz veins

Information Obtained

Evolution of fluids during metamorphism and syn/post-thrust migration with imprints of retrogression

Fluid inclusion planes (FIP’s) used as structural markers Information used to reconstuct the tectonic evolution of

a specific area Used as thermobarometric, structural and tectonic

markers

Fluids in mineral exploration

Geothermometry of quartz veins in BHQs in BIF, N Goa (Jadhav et al)

Concordant veins, discordant veins, two generations of hydrothermal phenomenon show ranges of temperature—resulting in secondary enrichment

Fluids in mineral exploration

Variations in C-O-H-N fluid chemistry in Zawar deposits, Rajasthan (Pandalai et al)

Methane production-early in clasts of arkose, later during interaction of a CO2-rich fluid with carbonaceous sediment – led to precipitation of galena and spalerite ores

Fluids in mineral exploration

Involvement of high temperature brine in pre-shearing hydrothermal alteration: evidence from FI in tourmaline in feldspathic schist from Pathargora, STB.

Melt Inclusions

Comendites (Russian workers) Behaviour of Na, F, Li, Zr and REE in melt and their

partitioning processes, Composition of magmas

Experimental Fluid Inclusion Studies

High Pressure studies Permitting observations of phase behaviour of inclusions

at high temperature and pressure in designing difficult laboratory studies of synthetic systems

What are the case studies in uranium exploration in AMD ?

Ladi-Ka-Bas, Sikar District, Rajasthan

Multiphase (L+V+S -Halite) FI 250-350 oC, 34-40 wt% eNaCl,

NaCl-KCl-H2O composition

What are the case studies in uranium exploration in AMD ?

Sirsoti, Sonbhadra District, U.P. - Uraniferous migmatite rocks

H2O(L) + H2O(V); H2O (L) +CO2 (L) + CO2 (V) 150oC to 350oC

What are the case studies in uranium exploration in AMD ?

Lambapur, Nalgonda District, A.P. Quartz 100 to 200oC 23 wt% eNaCl Quartzite 150 to 250oC 5 to 23 wt% eNaCl Granite 150 to 300oC 22 wt% eNaCl Dulapali, Raigarh District, Chattisgarh Altered uraniferous breccias 200 to 335oC, 18wt%eNaCl, NaCl rich, KCl rich Garda, Bastar District, Chattisgarh Pegmatites-barren, mineralised (Nb, Cassiterite) High saline 23 wt%eNaCl, 450 to 500oC, H2O-CaCl2

Low saline 14 wt%eNaCl, 200 to 250oC, H2O-NaCl-KCl

What kind of equipment required for advanced work ?

Linkam 600 heating and freezing stage linked to a petrographic microscope.

What kind of equipment required for advanced work ?

Raman Laser Ion Microprobe (Non-destructive, high

senstivity on small samples, identification of individual phases of multiphase inclusions)