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The geology of Vulcan Ridge : Dewar Creek Area, British Columbia Zajac, Ihor Stephan


The rocks underlying Vulcan Ridge are mainly Proterozoic metasediments of the Lower and Middle Division of the Aldridge formation and Proterozoic (or later) Moyie intrusives. Most of the metasediments are fine-grained quartzites, phyllites, schists and hormfelses composed mainly of quartz, biotite, muscovite and little feldspar. Tourmaline is a minor constituent of most metasediments but in the upper part of the Lower Aldridge it commonly forms up to 30 percent of the rocks. It is believed to have formed metasomatically by solutions derived from the White Creek batholith. A lens-like deposit of breccia-conglomerates makes up the upper most part of the Lower Aldridge. Most of the deposit is composed of unsorted material - angular to subangular fragments of Aldridge type metasediments imbedded in abundant fine-grained matrix of similar composition. This deposit is believed to have formed by subaqueous slides or mudflows. The Moyie intrusives are sill-like bodies of dioritic and gabbroic rocks composed essentially of hornblende, plagioclase and variable amounts of quartz. Most of the variations in texture and composition apparent in some of the intrusives are probably due to alteration but some may also be due to magmatic differentiation and to assimilation of country-rocks. The metasediments in the southern part of the area have been subjected to regional metamorphism and are of low metamorphic grade. In the northern part of the area the rocks have been contact metamorphosed. Within approximately 1½ mile of the White Creek batholith they have been metamorphosed to phyllites, schists and hornfelses which attained or closely approached a medium grade of metamorphism characteristic of the hornblende hornfels facies. Retrogressive metamorphism is extensive in the rocks near the contact of the batholith and is attributed to hydro-thermal solutions derived from that intrusive. Structure of the rocks south of the White Creek batholith is dominated by northeasterly trending folds which have been refolded into a large anticline near the batholith, and by northeasterly striking, steep dipping faults.

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