A band of limestone of the Upper Triassic Parsons Bay Formation (Vancouver Group) extends for at least 1.6 kilometres west from the shore on the southeast corner of Harbledown Island. On the north side the band is overlain and partially interbedded with argillite and minor volcanics. To the south the limestone is underlain and partially interbedded with basaltic flows of the Upper Triassic Karmutsen Formation (Vancouver Group). Bedding strikes 050 to 090 degrees and dips 20 to 90 degrees northwest. The limestone bed averages 213 metres in thickness. Dikes varying from 0.3 to 0.6 metres in width commonly intrude the limestone.

The deposit is comprised of friable, medium grained, sugary textured, dark bluish grey limestone that displays a streaked appearance. Occasional narrow bands, veinlets and lenses of white calcite are present. Scattered pyrite grains are also evident. Three chip samples of equal length taken in succession across a total width of 137 metres perpendicular to the strike of the band averaged 53.08 per cent CaO, 0.087 per cent MgO, 5.0 per cent insolubles, 0.11 per cent Fe2O3, 0.27 per cent MnO, 0.045 per cent P2O5 and 0.018 per cent sulphur (Minister of Mines Annual Report 1954, p. 184, Samples 1 to 3).

In 1954, Lease 1594 was held by R.H. Chestnut and Lease 1966 was held by J.T. Protheroe. In 1958 Chestnut leased his claim to the Granby Consolidated Mining, Smelting and Power Company Limited. The Company diamond drilled 17 holes totaling 94 metres. In 1975 the Company became Granby Mining Corporation.