Distributed acoustic sensing for mineral exploration: a pilot study from central Sweden

The iron-oxide mine of Blötberget in the Bergslagen mineral-endowed district in central Sweden has been the target of several geophysical studies in recent years. Among these studies, a series of seismic surveys aim to delineate the lateral and depth extent of the deposits for methodological and technological testing given the wealth of borehole data available for validation. The ore in Blötberget primarily comprises high-quality iron-oxides in the form of magnetite and hematite, partly enriched with apatite. The deposits occur in sheets, ranging from 10-50 m in thickness, with an approximately 45° eastward dip along an NNE-trending zone.

In June 2022, an additional seismic dataset was acquired to investigate the potential of distributed acoustic sensing (DAS) measurements in imaging the iron-oxide deposits. The use of DAS data presents several challenges, one of the most important being the directional sensitivity of the DAS cable. To date, there are only limited borehole and surface DAS applications for mineral exploration and in hardrock settings, and there is hence good potential to develop new how-to solutions for these purposes.

This study presents the seismic data generated by a vibrator truck and recorded by a 2200 m long straight fiber cable, deployed on the downdip of the mineralization. The cable was covered with gravel to improve its coupling to the ground. While complex, the results are promising, revealing distinct seismic signatures generated from the mineralization in specific data segments. 

Acknowledgments

This work is partly sponsored by the Smart Exploration Research Center. The center has received funding from the Swedish Foundation for Strategic Research (SSF) agreement no. CMM22-0003. This is publication SE25-001.