Police have detained eight people involved in an illegal gold mining incident in Shanxi province last month that killed six people, and 12 officials involved have been punished, authorities said on Sunday.

Six miners, who were attempting to illegally obtain gold in an abandoned mine, were found dead on Dec 27 about 2,700 meters inside a cave in a mountainous area boasting rich mineral resources in Weizhuang township, Yuncheng.

The mine they went into had been closed in 2018, with a warning posted at the sealed cave, according to a notice issued on Sunday by a work group focused on cracking down on illegal mining in Yuncheng.

In early December, a person surnamed Liu organized a group of people from Songxian county in neighboring Henan province in an attempt to commit theft in the abandoned mine, according to the statement. Liu allegedly paid off five people from Liceyu village, near the mine, on Dec 6 to keep them from tipping off authorities.

On Dec 14, the group arranged for local people to carry items brought from Henan to the cave, including a gold-dressing agent, a chemical product used to extract gold.

On the night of Dec 22, four members of the group went missing in the cave. The next night, another two went missing.

Local authorities launched a search and rescue mission after the six, including Liu, were reported missing near the abandoned mine on Dec 27.

At 3:30 pm that day, the rescue team found their bodies in the mine. Tests showed that they died of carbon monoxide poisoning.

The statement said that during a countywide investigation of production safety risks and illegal mining in late December, authorities discovered the abandoned mine had been illegally opened on Dec 21 and required the Weizhuang government to reseal it. Because it was not resealed in time, the six people were able to enter it.

Police have detained eight suspects involved in the case.

Twelve local officials who were suspected of being involved have been disciplined. They were either expelled from the Communist Party of China, given severe warnings or received other administrative punishment.

Of the 12, five from Weizhaung－including the town's Party chief, surnamed Hou－were removed from office. Two Liceyu officials were also removed, including one who was arrested on theft charges.

The city will draw lessons from the incident and hold those who did not fulfill their duties accountable, the statement said.