Slate deposits of Vietnam and Laos

The slates of Vietnam lie in the northernmost part in the province of Lai Chau. The most important quarries are Nam Ho, Nam Ban and Lai Chau.

The area of Lai Chau lies in roughly N-S oriented Dien Bien Phu fault zone with a length of 160 km (107 mi.) and a width between 6 - 10 km (4-7 mi.). The geology is charcterised by sediments and metamorphic rock of proterozoic, paleozoic and mesozoic age.
The 400 m (1,312 ft.) thick slate deposits of Lai Chau have an extension of about 10 km (7 mi.). The slate shows a good fissility with a thickness of resulting shingles between 2-3 mm. Six slate units with a thickness between 20-150 m and an extension of 2-5 km occur in Man Ho. The slate deposits of Nam Ban have an extension of over 20 km (13 mi.). The resulting thickness of slate shingles varies between 2-3 mm.

Overview of the slate deposits of Vietnam and Laos.

In Laos slate occurs in the area of Nakadok. This blue-black slate with intercalations of sandstone is of the "Nam Houay Formation" and has a thickness of 2-3 m. The slate shows a good fissility and the resulting thickness of slate shingles varies 0,4 - 1 cm.
The geological report by Tran van Ban (editor, 2000) states a bending strength of 31 MPa. The test of the resistance against sulphuric acid showed no changes or alterations of the slate. The water absorption is 0.49 % and the porosity is 2.17 %.

In accordance to the geological map, the area comprise Cambro-Silurian units and rocks of the Lower Devonian. Here also phyllites are listed which could be the mentioned roofing slates.
Another and more detailed geological map assigns the "Nam Houay Formation" to the Ordovician - Lower Silurian. Coloured shales, ribboned slates and black slates occur in the lower subformation. In the middle and upper subformation, sericitic schists occure among other rocks.