Gas shows in Glyde sub-basin

Abstract

Anecdotal evidence from drillers indicated the presence of decimetre-thick bitumen seams and gas flows from waterbores and mineral exploration holes within 50 km of Merlin diamond pipes and McArthur River base metal deposit in the McArthur Basin. Bitumen and oil fluorescence has since been confirmed in many holes. In the late 1970s and early 1980s, Amoco Minerals and Kennecott Explorations drilled the so-called Glyde Sub-basin, 15 km south of the Merlin pipes, for a HYC/McArthur River look-a-like. To quote from page 25 of open-file CR1981-0028: {drillhole} 'GR9 was located towards the northern end of the southern sub-basin, and encountered 42.5m of Cambrian sandstone before passing into 413.7m of dolomitic bituminous Barney Creek Formation. Towards the base of the Barney Creek Formation interbedded tuffaceous siltstones and vitric tuffs increased. The prospective pyritic section occurred from 456.2m to 501.75m and contained about 8% disseminated pyrite and rare sphalerite. Within the pyritic section, the interval from 483m to 493.85m consisted of bedded and partly brecciated, porous bituminous dolomite. The top 2m of this unit consisted of brecciated fragments from the lower 8.75m section. Underlying the pyritic section was the Coxco Dolomite, the W-Fold Shale unit not being present. The Coxco Dolomite was, very porous and fractured, often containing bitumen clots in open fractures. In GR9, gas flows became evident towards the base of the drill hole. Very small gas flows were evident in all {holes} drilled in the Glyde River Basin but in GR9 they were more significant. A gas sample was taken for analysis and assayed by Amdel. The sample contained 0.78% Oxygen as air contaminant and in the following analysis this had been deleted to give results on an air free basis. The gas contained 10.75% nitrogen, 0.2% carbon dioxide, 74.25% methane, 10.25% ethane 3.25% propane, 0.175% iso butane, 0.6% N-butane, 0.105%. N-pentane, 0.165% hexanes and 0.08% heptanes and higher. Due to the high gas flows from GR9 the hole was plugged with cement.? Core from this hole, called GRNT-79-9 in COREDAT, is available for study in the Darwin core library. Note that it is over 100 km from the nearest petroleum well and in an area not normally considered prospective for hydrocarbons. Geophysical interpretation would suggest that much more of the McArthur Basin is prospective for oil and gas than previously thought and, given the proximity to a ready market at mines, the matter warrants further study. The extensive bitumen in this area also opens up the possibility of a Century-style base metal deposit.