176 D6. Noble Gases and Halogens to Unravel Crustal Processes and Their Control on Energy Resources

Tuesday, 11 October 2022
1:30 PM - 5:30 PM
601

HIGH HELIUM CONCENTRATIONS IN WELL GASES FROM THE DULUTH COMPLEX, MINNESOTA, USA

Paper number: 176-16
Program: Technical Sessions
Time: 5:00 PM – 5:15 PM

Authors

Abstract

Helium is an important industrial gas with a wide array of applications. It is used extensively in medical magnetic resonance imaging (MRI) scanners, for scientific and cryogenic research, welding, refrigeration, gas for aircraft and as a coolant for nuclear reactors. Over the past decade, the global supply chain has struggled to meet increasing demand. This has led to significant disruptions to the global helium market, resulting in volatile helium prices.

Radiogenically produced 4He accumulates in ancient crust during quiescent periods and is subsequently released during periods of active tectonism or volcanism, or gradually via diffusion1. Gas reservoirs can trap and store 4He that is produced by radiogenic decay of U and Th in the crust. This occurs as another gas (CH4, CO2 or N2) or fluid (i.e., groundwater) interacts with a 4He rich source rock, which acts to concentrate the helium in subsurface reservoirs2,3. Helium is most commonly extracted as a byproduct of natural gas production, when CH4 is the dominant gas in the crust, but can also be concentrated by CO2 and N2 when stable continental cratonic regions interact with volcanic systems or become tectonically active.

We report gas chemistry data from an exploration borehole recently drilled in the Duluth Complex (DC), Minnesota, USA . We find that well gases contained 10.5% He, 13.2% N2, 73.8% CO2 and 2.4% CH4. The DC is the major intrusive component of the 1.1 Ga Midcontinent Rift System, composed predominantly of 1096 Ma anorthositic to troctolitic mafic intrusions emplaced into the 1108-1083 Ma North Shore Volcanic Group (NSVG) and above 1.85 Ga Animikie Basin sediments4. The DC has been tectonically quiescent since emplacement of the youngest intrusion, but was proximal to the longer duration NSVG thermal anomaly5.

These findings are an example of how helium can be focused in continental settings. The continental crust provides the source of 4He and intrusive volcanics provide the source of CO2 and heat to release and concentrate the helium6. The major element chemistry of the gases from the Duluth well is consistent with their release from the crystalline basement following interaction with a CO2 rich magmatic body.

1Warr et al., 2022

2Ballentine and Burnard 2002

3Ballentine and Sherwood Lollar, 2002

4Miller et al., 2002

5Schmidt et al., 2021

6Danabalan et al., 2022

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-382740

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