Further adventures of our mineralogists in Cambodia: follow museum scientists Paula Piilonen and Glenn Poirier on their hunt for minerals for their research.
In Ratanakiri province, and many other regions across Cambodia, the land is covered by a dark orange red, iron- and aluminum-rich soil called laterite.
Laterites form in tropical climates and are the result of extensive, intense chemical weathering of the underlying rock—in this case, basalt.
When wet, laterite can be cut into blocks and used for construction of buildings. As it dries, it hardens to a rock-like consistency. The Angkor Wat complex, along with many other temples of Angkorian age (9th and 10th centuries) found throughout both Cambodia and Thailand, have been constructed with laterite bricks as the main foundation, covered with more aesthetic sandstone facing.
Because laterite profiles in this part of the country can be up to 50 metres thick, it is sometimes difficult to find fresh, solid rock outcrop. For this reason, our field work tends to focus on areas that provide the most likely exposure: waterfalls, rivers/creeks, boulder fields at the bottom of slopes, and quarries.
Today we visited one such quarry north of Ban Lung and the Angkor Gold office. Here, they are quarrying basalt, the rock that we are studying, for use as road fill. After poking around the waste-rock piles on the edges of the quarry near the stone crushers, we met one of the workers who, through hand gestures because he didn’t speak English and we don’t speak Khmer, told us that we could enter into the quarry itself.
At the bottom of the quarry, we made a startling discovery. Although the larger blocks are drilled off and pushed to the bottom of the quarry (explosives are not allowed here), the bulk of the work to reduce the boulders to smaller fragments (about 30 cm to 60 cm) was being done BY HAND. Workers (in flip flops) stand in the rock piles and split boulders using only a large sledgehammer. A full shift of this manual labour must be back-breaking.
The smaller fragments are then loaded into a dump truck and fed into the crushers at the top of the quarry, where they are reduced to road fill (15 cm to 30 cm).
The quarry itself was an amazing experience for a geologist: a textbook-quality volcanic section consisting of three distinct basalt flows. Having access to the quarry wall to study (and sample) this section adds important information to our study of the basalts in the region. Nowhere else can multiple, fresh flows be observed in a single locality.
We were able to collect 15 kg of rock and leave the quarry satisfied with an excellent morning of work.