Gravimetric Mapping Of An Abandoned Underground Limestone Mine In Clark County, Indiana

An underground limestone mine near the center of Clark Military Grant 48 in Clark County, Indiana, was in<br>operation from 1892 to 1896. This mine, here referred to as the Gheen’s Mill Cementville Mine, was abandoned and<br>became flooded before the slope shaft entrance was back-filled. The roof of the mine is at a depth of about 8.2 m (27<br>feet). An interval of 4.3 m (14 ft) or less of limestone was mined to make a natural cement. A map of the mine was<br>needed because undermined areas might be unsafe for buildings. The area is presently being developed as a business<br>park. Fifty-six holes were drilled several years ago to map the mine, but their precise locations were unknown.<br>Seventeen holes found cavities, 32 holes penetrated the mined interval but did not encounter cavities, and 7 holes did<br>not find bedrock within a depth of 11 m (33 ft). A gravity survey was made to help locate these holes and to better<br>define the bounds of the mine. One hole was successfully exhumed and identified on the basis of the gravimetry.<br>Gravity was measured at 837 stations in nineteen east-west and north-south profiles with 3.05-m (loft) station<br>spacing. Inflection points of a negative 140~pgal Bouguer gravity anomaly located edges of the mine. First and second<br>horizontal derivatives of the gravity profiles helped locate these edges. Gravity profiles around the mine perimeter<br>did not detect any tunnels extending between the boreholes. A large negative residual Bouguer gravity anomaly south<br>of the mine defines a buried valley that limited the area available for mining. The gravity method should be practical<br>in mapping similar underground mines in the region. Approximately 40 percent of one of these mines, the Falls City<br>Mine, has collapsed (Ren6, et al., 1994). The gravity survey of the Gheen’s Mill Cementville Mine probably indicates<br>that a lesser proportion of the limestone was mined within the perimeter of this mine than in the case of the Falls City<br>Mine.