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Geology, petrology and precious metal mineralization, Toodoggone River area, north-central British Columbia

University of British Columbia

The Toodoggone River area (NTS:94E) is approximately 300 km north of Smithers, in north-central British Columbia. Early Jurassic Toodoggone volcanics consisting of calc-alkaline, intermediate extrusive rocks have a thickness exceeding 1200 m. The oldest members of the suite are andesite flows with minor agglomerate and pumice breccia. Overlying the andesites are voluminous dacitic ash flows consisting of vitric ash to lapilli tuff, vitric-lithic ash tuff, and vitric-crystal ash tuff. All andesites are characterized by porphyritic textures and phenocrysts of plagioclase, hornblende, biotite and magnetite. Dacites are distinguished by vitroclastic and devitrification textures, fragments of pumice as well as crystals of quartz, sanidine, plagioclase, basaltic hornblende, magnetite and hematite. Andesites of the Hazelton Group have a thickness of 900 m and are similar to the andesites of the Toodoggone suite. Five distinct alteration styles identified within the region include: propy.litic, zeolitic, intermediate to advanced argillic, potassic and silicic facies. In the Toodoggone suite, with, increasing silica content CaO, P₂O₅, TiO₂, FeO(total), Al₂O₃, V, Zr decrease and K₂O increases. Element mobility during low grade metasomatism is indicated by the wide scatter of points in the Na₂O, MgO, Cr, Ni, Th, Sr, Rb and Nb variation diagrams. Brecciated and silicified veins act as host to gold and silver mineralization within Toodoggone, Hazelton and Takla volcanic flows and tuffs. Fluid inclusions from the Moosehorn and Mt. Graves prospectssuggest that ore-minerals formed at temperatures of between 232°C and 267°C, with fluid salinities of between 3.3 and 6.5 equivalent weight percent NaCl. Mineral deposits formed under lithostatic pressures at depths of between 115 m and 225 m. A self-sealed throttling model accounts for variations in salinity, temperature, depth of formation, alteration types, metal zonation as well as depositional mechanisms, and can be used as an exploration guide to hidden ore shoots.

Text

2010-05-12

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http://hdl.handle.net/2429/24610

Geological Sciences

University of British Columbia

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