Mercury showings of the Savona Mercury Belt are associated with faulted, carbonate and/or silica altered zones within Triassic or Jurassic metasediments or metavolcanics and are spatially related to Tertiary intrusions. The Tunkwa Lake mercury prospect is believed to cap one of these Tertiary bodies and is thought to represent the upper, low temperature horizon of an epithermal system that could carry precious metal values at depth. Most of the recent work on the showing has focused on this potential.
The Tunkwa Lake property is underlain by north striking and moderately east dipping Upper Triassic Nicola Group andesitic metavolcanics with intercalated siltstone, sandstone, argillite and occasional limestone units. The volcanics comprise andesitic agglomerates, and amygdaloidal and feldspar porphyry andesite flows. The Nicola rocks are locally cut by diorite dikes and later rhyodacite dikes. Several faults are believed to pass through the property. Wide zones of brecciated rock or gouge, pervasively carbonate and/or silca replaced, mark the trace of the larger faults on surface. Elevated mercury, antimony and arsenic values accompany late ankerite, dolomite and quartz veinlets and pervasive low temperature silica replacement to depths of at least 125 metres within one major fault zone, but precious metal values are uniformly low.
The most intense carbonate/silica alteration occurs at the Tunkwa Lake showing where the metavolcanics have been highly fractured and brecciated by a fault zone. A banded andesitic tuff is altered to ankerite and veined with dolomite. The carbonate zone is mineralized with disseminated stibnite, tetrahedrite, chalcopyrite, malachite and azurite with cinnabar occurring as thin films and small masses in dolomite and quartz veins. Zones of silica replacement occur up to 5 metres in width with several small silicified breccia zones mended with chalcedony.
The Toonkwa claim was staked in about 1899 and although its exact location has not been given, it is believed to have been staked on this showing. A small amount of development work was done from 1899 through 1902. The showing was apparently staked again in about 1913 as the Summit claim by Hardie Cinnabar Mines Ltd. Development work done up to this point consisted of opencuts and a shallow shaft. The 6-metre shaft continues at the bottom as an incline shaft. Toonkwa Quicksilver Mines staked five claims in about 1934 and although their location is indefinite they are believed to have been located on this property. It was reported that two retorts were installed and some samples of mercury produced at this time. The property was restaked in 1937 as the Ridge and Bull Horn claims, owned by W.A. and Mrs. Jane Ferguson. The claims lapsed in September 1937. Restaked by J.B. and D.J. McDonald as the O.K. and Cinnabar claims, these were allowed to lapse in May 1938. The property was apparently restaked by G.F. Dickson in 1939. McLelland on a field trip to the property in November 1939 reported two retorts in operation. During 1940, Messrs. Sterritt and Hardie joined Dickson in the operation and about 45 kilograms of mercury were produced by the end of the year. The operation continued into 1941, most of the production coming from a cut driven to the east of the shaft. In 1981, the Model claims were staked to cover the Tunkwa showing which was considered to have potential as an epithermal gold prospect. The property was subsequently optioned to Placer Development Ltd. (1981-84), to Lacana Mining Corporation (1984-85) and to Mad River Resources Inc. (1988-89). Work by Placer Development in 1981 consisted of a widely spaced soil (471 samples) geochemical survey yielding inconclusive results. In 1984, Lacana Mining conducted geological and geophysical (VLF-EM and magnetometer) surveys over the immediate mercury showing, and in September of that year drilled 5 diamond-drill holes totalling 405 metres; gold mineralization was not found and the option was terminated. During 1988 and early 1989 expanded geochemical (409 soil samples), geophysical (14.7 kilometres of VLF-EM and magnetometer) and geological surveys were conducted over the Model and Anne claims which covered the showing. In 1989, Mad River Resources Inc. completed 7 percussion-drill holes totalling 733 metres on a highly fractured, carbonate/silica altered fault zone but no significant precious metal values were discovered.