The Tailings Tephra zeolite prospect outcrops on the abandoned Copper Mountain railway, 1 kilometre southeast of the Similkameen River and 4 kilometres south of Princeton.
The deposit is situated near the eastern margin of the Princeton Basin, a northerly striking fault-bounded trough filled by Eocene volcanic rocks of mainly intermediate composition, comprising the Lower Volcanic Formation, and an overlying Eocene sedimentary sequence of sandstone, shale, waterlain rhyolite tephra (tuff) and coal, up to 2000 metres thick, comprising the Allenby Formation.
Zeolite mineralization is contained in a zeolitized, waterlain, rhyolite crystal-vitric tuff in the upper part of the Allenby Formation (Princeton Group), known informally as the Tailings ash. A roadcut along the southeast side of the railway exposes a section of vitric-crystal tuff, 3 to 4 metres thick, overlain by at least 6 metres of mainly vitric rhyolite tuff. The beds strike 087 to 105 degrees and dip 20 to 40 degrees north. The upper and lower contacts of this zeolitized horizon are not exposed in the section. The deposit is estimated to contain inferred reserves of 54,000 tonnes over a southeasterly strike extension of 70 metres (Assessment Report 21235, page 5). The horizon continues west for 1650 metres, across the Similkameen River, along the south flank of the west-trending Tailings syncline.
Zeolite alteration is in the form of clinoptilolite, which is accompanied by plagioclase, potassium feldspar, quartz, clay, biotite, cristobalite and sanadine. Fourteen chip samples taken across the section contained between 56 and 77 per cent clinoptilolite (Geological Fieldwork 1988, page 513). Exchangeable cation analyses and cation exchange capacity (CEC) in milli- equivalents per 100 grams on two samples are as follows (Open File 1987-19):
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Sample Magnesium Calcium Potassium Sodium CEC
Z7 1.5 27.2 31.1 32.9 102.8
TA9 3.0 32.5 29.8 22.5 101.0
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Both samples were taken along the railway exposure. Sample Z7 is a grab sample, while sample TA9 is a composite chip sample.
