The True Blue mine shaft dates back to the 1890s. The shaft is located today in the car park of the True Blue Motel.

The mine closed in 1925. The shaft is understood to extend to a depth of 800 feet and is linked to the workings that extend to about 1200feet below ground level. In the 1970s the shaft was capped with a viewing platform and opened as a tourist attraction, but from late 1970s progressive erosion of the soil and ashhalt surrounding the cap caused subsidence of the concrete apron and the viewing portal, and large voids opened between the concrete apron and the surrounding soil. Instability of the cap threatened the structural integrity of the rooms 30 and 32 of the motel.

In 2013 the NSW Government sought tenders to stabilise the shaft and attempts were made in 2014 but were unsuccessful. In 2015 the NSW Department of Industry's Derelict Mine program engaged Mainmark to plug and seal the mineshaft.

The dimensions of the main shaft is 3m x 1m separated into three compartments and shored with timber. Mainmark filled the void beneath the cap with 500m3 of Terrefill lightweight cementitious grout. Mainmark then created a bespoke buoyant grout which was injected through 20m deep boreholes around the shaft to create a plug. The shaft was then filled with Terrefill.

GFWAust provided expertise to carry out the secondary grouting to fill unknown surface voids surrounding the shaft.