Table 5.4 - Field and petrographic characteristics of formations belonging to the Tsuen Wan Volcanic Group

TSUEN WAN VOLCANIC GROUP
UNIT Yim Tin Tsai
Formation
Shing Mun
Formation
Tai Mo Shan
Formation
Sai Lau Kong
Formation
Colour grey grey grey purplish grey
Composition rhyodacite to rhyolite rhyodacite to rhyolite rhyodacite to rhyolite rhyodacite to rhyolite
Lithologies crystal tuff crystal tuff, tuff breccia, tuffite crystal tuff dacite lava, tuff breccia, tuffite
Dominant texture coarse ash coarse and fine ash coarse ash porphyritic and coarse ash
Crystals quartz and feldspar quartz and feldspar quartz and feldspar feldspar and quartz
Lithics rhyolite lava, volcanic rock fragments rhyolite lava, marble, tuff, volcanic rock fragments - rhyolite lava, volcanic rock fragments
Glass/Pumice - rare - -
Fabric massive to crudely bedded massive to crudely bedded ± eutaxitic massive bedded, flow-banded
Thickness 200 m 600 m >600 m >300 m

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