Limestone and dolomite are exposed in the 900 crosscut of the Central Zeballos Mine (92L 212), 7 kilometres northeast of the community of Zeballos, 110 kilometres due west of the town of Campbell River.

The deposit lies within a discontinuous belt of limestone of the Upper Triassic Quatsino Formation (Vancouver Group) that extends from Quatsino Sound southeastward to Tlupana Inlet for 120 kilometres. The belt is locally intruded along its southwest flank by quartz diorite and granodiorite of the Jurassic Island Intrusions. Underlying basaltic flows of the Upper Triassic Karmutsen Formation (Vancouver Group) outcrop to the northeast. The limestone strikes northwest and dips moderately southwest.

The 900 crosscut is situated near the west end of a mass of medium to coarse grained, recrystallized limestone that extends westward from the Nomash River for 2000 metres along the northern margin of a stock of granodiorite. The crosscut exposes grey calcium limestone intermingled with white dolomite and magnesian limestone along its 314 metre length. Most of the white carbonate is confined to a zone between 46 and 122 metres from the portal. Microscopic studies indicate the white carbonate is comprised mostly of dolomite with a little interstitial calcite. The dolomite and magnesian limestone occur as white streaks commonly ranging from a few centimetres to 10 metres thick, with one streak attaining a thickness of 21 metres. These streaks are likely the result of metasomatic activity associated with the emplacement of nearby intrusives. Samples taken along a section of white carbonate between 57.9 metres and 85.3 metres from the portal averaged 36.2 per cent CaO, 17.0 per cent MgO, 0.93 per cent insolubles and 0.28 per cent R2O3 (E.M.P.R. Bulletin 27, p. 47). Samples from a section of grey limestone between 182.9 and 201.2 metres from the portal averaged 47.3 per cent CaO, 7.26 per cent MgO, 1.8 per cent insolubles and 0.25 per cent R2O3 (E.M.P.R. Bulletin 27, p. 48). Various grab samples collected by Impact Resources Inc. analyzed as follows (in per cent) (Calcium Carbonate Co., 1981, Econotech Services Ltd., 1981, 1982):

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Sample A Sample B Sample C Sample D

CaCO3 87.9 61.95 61.2 93.0

MgCO3 9.5 37.35 38.5 1.76

SiO2 - - - 0.50

Insol. 2.6 0.78 - -

Water - - 0.13 -

Brightness

- Blue light 90.4 90.8 84.6 -

- Green light 91.25 92.1 - -

- Unspecified - - - 89.6

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Dolomite reserves are estimated at several million tonnes (R.F. Kent, 1989). Zones of garnet-diopside skarn sometimes containing magnetite and sulphides are frequently formed along the intrusive contacts.

The deposit was sampled in 1981 and diamond drilled in 1982 by Impact Resources Inc.