Fluid inclusion volatile analysis by gas chromatography with photoionization micro-thermal conductivity detectors: Applications to magmatic MoS 2 and other H 2 O-CO 2 and H 2 O-CH 4 fluids

Details Fluid inclusion volatile analysis by gas chromatography with photoionization micro-thermal conductivity detectors: Applications to magmatic MoS 2 and other H 2 O-CO 2 and H 2 O-CH 4 fluids Fluid inclusion volatile analysis by gas chromatography with photoionization micro-thermal conductivity detectors: Applications to magmatic MoS 2 and other H 2 O-CO 2 and H 2 O-CH 4 fluids

Jan 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992gecoa..56..261b&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 56, Issue 1, pp.261-272

Computer Science

4

Scientific paper

Eighteen fluid inclusion volatile peaks have been detected and identified from 1-2 g samples (quartz) by gas chromatography using heated (~105°C) on-line crushing, helium carrier gas, a single porous polymer column (HayeSep R; 10' × 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: N 2 , Ar, CO, CH 4 , CO 2 , C 2 H 4 , C 2 H 6 , C 2 H 2 , COS, C 3 H 6 , C 3 H 8 , C 3 H 4 (propyne), H 2 O (22.7 min at 80°C), SO 2 , ± iso- C 4 H 10 ± C 4 H 8 (1-butene) ± CH 3 SH , C 4 H 8 (iso-butylene), (?) C 4 H 6 (1,3 butadiene) and ± n- C 4 H 10 ± C 4 H 8 (trans-2-butene) (80 and -70°C temperature programme conditions combined). H 2 O is analysed directly. O 2 can be analysed cryogenically between N 2 and Ar, but has not been detected in natural samples to date in this study. H 2 S, SO 2 , NH 3 , HCl, HCN, and H 2 ca nnot be analysed at present. Blanks determined by crushing heat-treated Brazilian quartz (800-900°C/4 h) are zero for 80°C temperature programme conditions, except for a large, unidentified peak at ~64 min, but contain H 2 O, CO 2 , and some low molecular weight hydrocarbons at -70°C temperature conditions due to cryogenic accumulation from the carrier gas and subsequent elution. TCD detection limits are ~30 ppm molar in inclusions; PID detection limits are ~ 1 ppm molar in inclusions and lower for unsaturated hydrocarbons (e.g., ~0.2 ppm for C 2 H 4 ; ~ 1 ppb for C 2 H 2 ; ~0.3 ppb for C 3 H 6 ). Precisions (1 ) are ~ ±1-2% and ~ ± 13% for H 2 O in terms of total moles detected; the latter value is equivalent to ±0.6 mol% at the 95 mol% H 2 O level. Major fluid inclusion volatile species have been successfully analysed on a ~50 mg fluid inclusion section chip (~7 mm × ~10 mm × ~100 m ). Initial inclusion volatile analyses of fluids of interpreted magmatic origin from the Cretaceous Boss Mtn. monzogranite stock-related MoS 2 deposit, central British Columbia of ~97 mol% H 2 O, ~3% CO 2 , ~ 140-150 ppm N 2 , and ~16-39 ppm CH 4 (~300-350°C) are reasonable in comparison with high temperature (~400-900°C) volcanic gas analyses from four, active calc-alkaline volcanoes; e.g., the H 2 O contents of volcanic gases from the White Island (New Zealand), Mount St. Helens (Washington, USA), Merapi (Bali, Indonesia), and Momotombo (Nicaragua) volcanoes are 88-95%, >90% (often >95%), 88-95% and ~93%, respectively; CO 2 contents are ~3-10%, 1-10%, 3-8%, and ~3.5%. CO 2 /N 2 ratios for the Boss Mtn. MoS 2 fluids of ~ 190-220 are in the range for known volcanic gas ratios (e.g., ~ 150- 240; White Island). The S content of the Boss Mtn. MoS 2 fluid prior to S loss by sulphide precipitation may have been ~2 mol% since CO 2 / S molar ratios of analysed high-temperature volcanic gases are ~ 1.5. This estimate is supported by S contents for White Island, Merapi and Momotombo volcanic gases of ~2%, ~0.5-2.5%, and ~2%. COS has been determined in H 2 O-CO 2 fluid inclusions of interpreted magmatic origin from the Boss Mtn. MoS 2 deposit and the Tanco zoned granitic pegmatite, S.E. Manitoba at ~50-100 ppm molar levels, which are consistent with levels in volcanic gases. It appears that low, but significant, concentrations of C 2 -C 4 alkanes (~ 1-20 ppm), C 2 -C 4 alkenes (~ 1-480 ppb) and alkynes (e.g., C 3 H 4 ) have been detected in magmatically derived fluids (Boss Mtn. MoS 2 deposit; Tanco granitic pegmatite). Significantly higher, low molecular weight hydrocarbon concentrations have been determined in a CH 4 -rich (~ 2%), externally derived fluid of possible metamorphic or deep crustal origin trapped as inclusions in metasomatic wall-rock tourmaline adjacent to the Tanco pegmatite (e.g., 300/470 ppm C 2 H 6 ; 50/90 ppm C 3 H 8 ; 3-60 ppm C 2 H 4 / C 3 H 6 n - C 4 H 10 ).

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