FLUID INCLUSION VOLATILE ANALYSIS BY HEATED CRUSHING, ONLINE GAS-CHROMATOGRAPHY - APPLICATIONS TO ARCHEAN FLUIDS

Eighteen fluid inclusion volatile peaks have been detected and identified from 1-2-g samples (quartz) by gas chromatography using heated (approximately 105-degrees-C) on-line crushing, helium carrier gas, a single porous polymer column (HayeSep R; 10' x 1/8"; 100/120#; Ni alloy tubing), two temperature programme conditions for separate sample aliquots, micro-thermal conductivity (TCD) and photoionization detectors (PID; 11.7 eV lamp) and off-line digital peak processing. In order of retention time these volatile peaks are: N2, Ar, CO, CH4, CO2, C2H4, C2H6, C2H2, COS, C3H6, C3H8, C3H4 (propyne), H2O (22.7 mins at 80-degrees-C), SO2, +/- iso-C4H10 +/- C4H8 (1-butene) +/- CH3SH, C4H8, (iso-butylene), (?) C4H6 (1,3 butadiene), and +/- n-C4H10 +/- C4H8 (trans-2-butene) (80-degrees-C and -70-degrees-C temperature programme conditions combined). H2O is analysed directly. O2 can be analysed cryogenically between N2 and Ar, but has not been detected in natural samples to date. H2S, SO2, NH3, HCl, HCN and H-2 cannot be analysed at present. Blanks determined by crushing heat-treated Brazilian quartz (800-900-degrees-C/4 hrs) are zero for 80-degrees-C temperature programme conditions, except for a large, unidentified peak at approximately 64 mins, but contain H2O, CO2 and some low molecular weight hydrocarbons at -70-degrees-C temperature conditions due to cryogenic accumulation from the carrier gas and subsequent elution. TCD detection limits are approximately 30 ppm molar in inclusions; PID detection limits are approximately 1 ppm molar in inclusions and lower for unsaturated hydrocarbons (e.g. approximately 0.2 ppm for C2H4; approximately 1 ppb for C2H2; approximately 0.3 ppb for C3H6). Precisions are approximately +/- 1-2%, except for H2O (approximately +/- 13%). Major fluid inclusion volatile species have been successfully analysed on a approximately 50 mg fluid inclusion section chip (approximately 7 mm X approximately 10 mm X approximately 100-mu-m). Two distinct end-member Archean fluids, one internal and one external, have been found related to the Tanco zoned, granitic pegmatite, SE Manitoba. The former is an H2O (approximately 96%)-CO2 (approximately 4%)-CH4N, fluid (S species not included) with a moderate salinity of 6.6 +/- 1.3 eq. wt.% NaCl which is interpreted to be magmatic in origin, whereas the latter is an H2O (approximately 97%)-CH4 (approximately 2%)-CO2 (approximately 0.4%)-C2H6-N2 fluid with a distinctly higher salinity of approximately 10-20 eq. wt.% NaCl which is interpreted to be of metamorphic/lower crustal (approximately 2,900 bar/approximately 10 km) origin. The volatile compositions of H2O (approximately 87-94%)-CO2 (approximately 6-13%)-CH4-N2 fluids with approximately 5-6 eq. wt.% NaCl from primary inclusions from three structurally controlled, mafic-ultramafic rock hosted Archean Au-quartz vein deposits in the Barberton greenstone belt, southern Africa (n = 9) are distinctly different from the composition of the Tanco external fluid, but similar to the composition of primary fluids of interpreted magmatic origin from the Boss Mtn. MoS2 deposit, central British Columbia (approximately 97% H2O- approximately 3% CO2-N2-CH4) and to the compositions of high-temperature (approximately 400-900-degrees-C) volcanic gases from four active, calc-alkaline volcanoes, which contain approximately 88-95% H2O and approximately 1-10% CO2 (White Island, New Zealand; Mt. St. Helens, U.S.A.; Merapi, Indonesia; Momotombo, Nicaragua). Fluid inclusion volatile data for the Hollinger - McIntyre Archean Au-quartz vein system, Timmins, N. Ontario show a significant upward decrease in CH4/(CH4 + CO2) X 100 values in the upper preserved approximately 460 m (approximately 1500 ft.) from approximately 10-25% to approximately 0.3-1.5% at surface (n = 12; two duplicates). This trend is interpreted to reflect partially open system CH4 loss during H2O-CO2 phase separation illustrating one mechanism for the production of oxidised Archean Au fluids. These inclusion volatile data for Archean fluids show possible applications in improved genetic and geometrical understanding of Archean hydrothermal ore systems, and as a lithogeochemical method for discriminating quartz veins of different origins.