According to the summary report of the Inspectors of Mines the 3 were killed by an explosion of blasting gelatine 74%NG. They were sinking a shaft in very wet conditions, two rockdrills working side by side two men in each. One drill pierced a concealed unexploded charge from a previous blast. The report concentrates on the reason for the failure of the previous charge, suggesting it was due to excess moisture caused by failure of the waterproofing of the explosive.
It is highly likely a fuller report will be found in local newspapers at the time.