Fe-Zn-S system and the sphalerite geobarometer

How do we get them out?
� Carbonates: phosphoric acid -> CO 2
� Silicates: reaction w/ BrF 5, F 2, ClF 3 -> O
� O + hot graphite -> CO 2
� Sulfides: heat w/ oxidant e.g. CuO
� S + O -> SO 2
� Or S + F source -> SF 6
� OH or H 2O: reaction w/ hot U or Zn -> H 2
� Now: Direct laser fluorination
Ratios: Del/Delta Terminology
� δO 18 , δD, δC 13 , δS 34
� δ = (R sample/R std -1) * 1000
� where
� R sample = (O 18 sample /O16 sample )
� Ex: a δ of +10 => sample 1% heavier than
the standard
Standards
� Very difficult to measure absolute
amounts so always use standards
allowing ratio measurements
� O & H: referred to SMOW
� Soft rockers may refer O to PDB
� C: belemnite from the Pee Dee Fm: PDB
� S: Canyon Diablo meteorite troilite: CDT
Fractionation Factors
� See reading for relationship of the delta
notation to more rigorous derivation of the
fractionation factor between 2 minerals or
phases yielding diagrams with axis of:
� 10 3 lnα A-B
� 10 3 lnα A-B ~ δ A - δ B = Δ AB
2