Table 5.6 - Field and petrographic characteristics of formations belonging to the Repulse Bay Volcanic Group
REPULSE BAY VOLCANIC GROUP
'Rhyolitic' Subgroup
| UNIT | Mount Davis Formation | Long Harbour Formation |
|---|---|---|
| Colour | light grey to grey | light grey to pinkish grey |
| Composition | rhyodacite to rhyolite | rhyodacite to rhyolite |
| Lithologies | crystal tuff and tuffite | crystal tuff and rare eutaxite |
| Dominant texture | lapilli-bearing coarse ash | lapilli-bearing coarse ash |
| Crystals | feldspar, quartz and biotite | pink feldspar, quartz and biotite |
| Lithics | lava and tuff | tuff and rare granite |
| Glass/Pumice | rare | rare |
| Fabric | massive | massive to crudely bedded |
| Thickness | 950 m | >600 m |
'Trachytic' Subgroup
| UNIT | Ngo Mei Chau Formation | Ap Lei Chau Formation | Che Kwu Shan Formation | Mang Kung Uk Formation | Pan Long Wan Formation |
|---|---|---|---|---|---|
| Colour | pale bluish grey | pale grey | pale grey | black to brown | bluish grey |
| Composition | trachyte to rhyolite | trachyte to rhyolite | trachyte to rhyolite | trachydacite to rhyolite | trachydacite to rhyolite |
| Lithologies | vitric tuff, tuffite, limestone, lava | vitric tuff, tuff-breccia, tuffite | vitric tuff, tuff-breccia | crystal tuff, tuffite, epiclastic breccia | lava, vitric tuff |
| Dominant texture | welded fine ash | welded fine ash | welded fine ash | fine ash | porphyritic and fine ash |
| Crystals | quartz and feldspar | quartz and feldspar | quartz and feldspar | feldspar and quartz | feldspar and quartz |
| Lithics | - | - | - | rare accretionary lapilli | - |
| Glass/Pumice | common | common | common | rare | rare |
| Fabric | ± eutaxite | ± eutaxite | ± eutaxite | well-bedded | ± eutaxite and flow-banded |
| Thickness | >450 m | >1250 m | 500 m | 300 m | 420 m |