The exact reason behind them being present at the mine is yet to be established.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/nagaland-four-dead-abandoned-rat-hole-coal-mine
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/indian-express-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/nagaland
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/coal
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/mining
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/assam
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/meghalaya