Karen Rickers1,2, Rainer Thomas2 & Wilhelm Heinrich2

1HASYLAB at DESY2GeoForschungsZentrum Potsdam, Germany

The magmatic-hydrothermal evolution

of a water-, B- and F-rich granitic

system: a melt/fluid inclusion study

2004 GSA annual meeting, November 7 – 10 2004

Sample locality

from Förster et al., 1999

type A type B

water-poor silicate meltwater-rich silicate melt

vapor

vapor

solids

solids

melt inclusion types in pegmatitic quartz (T incl> 550 °C)

daughter phases:K-feldspar, quartz, Li-bearing micatopaz, tourmaline

similar daughter phases

________20 µm 20 µm________700°C, 1 kb, 24 h

Room temperature

Homogenization

experiments

Element partitioning in type A and B melts

Thomas et al., CMP, 2000 Thomas et al., CMP, 2003

0 10 20 30 40 50

500

550

600

650

700

750single phase m elt (supercritical)

silicatem elt(A)

flu id-rich m elt (B)

m elt A + m elt B

Tem

pera

ture

(°C

)

H 2O (w t.% )0 10 20 30 40 50

1

2

3

4650°C

600o C

500o C

C.P.

B 2O3 (

wt%

)Water content (wt%)

A-type inclusions B-type inclusions

pegmatitic (Thom > 500°C) and hydrothermal (Thom < 500°C) fluid inclusions in quartz

Thom ca. 550 °C Thom ca. 480 °C

Thom ca. 480 °C Thom ca. 430 °C

DORIS-III

White SR

Beamstop

MicroscopeCCD cameraPbPb--shieldingshielding

45o

HPGeHPGe--detectordetector

XYZSamplestage

Cross Slits45o

Beammonitor

Beammonitor

Monochromator

Synchrotron radiation µ-XRF, beamline L, HASYLAB, Hamburg

Single bouncecapillary Absorber

Set-up: monochromatic excitation, capillary

trace element composition of type A & B melts

detected elements : Fe, Zn, As, Rb, Nb, Sn, Cs, Ta, ± Sb, Ag & Wconcentration range: 0.5 – 10750 ppm

Cs Rb

Nb/Ta Rb

Sn Rb As Rb

Variation of trace elementcompostion with watercontents

Cs, Fe, Mn, Nb, As

Ag, Zr

Independent from water content: W & Sb

0.0001

0.001

0.01

0.1Zn Sn As Fe Cu Cs Rb

element

mol

/kg

trace element compositions of fluid and meltsat the pegmatitic stage

detected elements in fluid inclusions of the pegmatite stage: Fe, Cu, Zn, As, Rb, Nb, Sn, Sb, Cs ± Ag

concentration range: 0.1 - 1100 ppm

type B melttype A meltvapor-rich FI

Chemical composition of fluid inclusions of thehydrothermal stage

detected elements in fluid inclusions of the hydrothermal stage: Fe, Cu, Zn, As, Rb, Nb, Sn, Sb, Cs ± Ag & W

concentration range: 2 - 10395 ppm

Fe-Cs

0

0,05

0,1

0,15

0,2

0,25

0 0,01 0,02 0,03 0,04

Cs (mol/kg)

Fe (m

ol/k

g)

Zn-Cs

0

0,02

0,04

0,06

0,08

0,1

0,12

0 0,005 0,01 0,015 0,02 0,025 0,03 0,035

Cs (mol/kg)

Zn (m

ol/k

g)

Rb-Cs

0

0,01

0,02

0,03

0,04

0,05

0 0,005 0,01 0,015 0,02 0,025 0,03 0,035

Cs (mol/kg)

Rb

(mol

/kg)

Sn-Rb

0

0,005

0,01

0,015

0,02

0 0,01 0,02 0,03 0,04 0,05

Rb (mol/kg)

Sn (m

ol/k

g)

Elemental maps of single fluid inclusion:Early hydrothermal stage

Inclusion in a quartz host of 100 µm thicknessExcitation conditions: Ni/C ML at 40 keV, sample time / pixel: 40s, pixel size 10x10 µm2

Elemental maps of single fluid inclusion:Later hydrothermal stage

Inclusion in a quartz host of 300 µm thicknessExcitation conditions: Ni/C ML at 40 keV, sample time / pixel: 30s, pixel size 5x5 µm2

chemical evolution of fluids

10

100

1000

10000

1 2 3 4 5

ZnSbMnFeCs

10

100

1000

10000

1 2 3 4 5

As

Cu

Rb

Sn

Th = 550°C Th = 480°C Th = 430°C

+ A

g, C

d, B

r

+ W

ppm

ppm

early late

summary

pegmatitic stage, melts:strong Sn-, Cs- and Rb-enrichment in the silicate-meltspositive correlation of Cs and Rb with Nb, Ta and Sn Extreme enrichment in melts close to the critical point

pegmatitic stage, fluid inclusions:preferential partitioning of Cu and Zn into the fluid phasepreenrichment of Cu, Sn, As, Zn, Fe in vapor-rich fluid inclusions

hydrothermal stage:fluids evolve from initially Cu- and Sn-rich to Cs-, Zn-, Mn- and Fe-rich brinesW only detectable in Cu- and Sn-rich fluids of the early hydrothermal stageCs enrichment is correlated with salinity