The Elements Unearthed

Borneo Day 2: Saturday, July 22, 2017

Panning for diamonds at the Cempaka diamond mine. The pans are very similar to panning for gold in California, but instead of flat bottoms they have conical bottoms.

After visiting the haunted house on the hill, we drove further toward Martapura on the Trans Kalimantan Highway. We needed to meet up with a colleague of Nazar’s, whose father works in the diamond mines, so we stopped at a convenience store called Indomaret. There are many of these throughout the country. I was getting hungry and thirsty, so I bought some Minute Maid Pulpy tropical punch and a Hungry Cow ice cream bar, which was really good.

A monument to the famous (and lost) Trisakti Diamond, found near this location.

Nazar’s friend arrived and he climbed into the car with us. We traveled a short distance further on the road, then turned off onto a smaller road leading into an open area with rice fields and swampy ground. On one side of the road was a monument in the shape of a large diamond: the famous Trisakti diamond discovered near here. Its whereabouts is not known.

Digging in the mud. The first step is to dig out the mud and stones at the proper level where the diamonds are located, about 30 feet down from the mean ground level. This area has been reworked so many times that it has all been mixed up.

The first step is to dig mud and rocks from the side of the hill and shovel down to the bottom of the pit, where water is pumped and sprayed to remove the larger stones. The smaller stones and mud are sucked up a pipe to a sluice box above.

We parked by the side of the road and I took a few moments to spray myself with insect repellent, figuring I would need it here if anywhere. We walked along a narrow path through small hillocks to where the ground opened up into a large pit. Like everywhere in Indonesia, bright green vegetation grows everywhere, but underneath the soil is an orangish tan color. A group of men were working at the edge of this depression in a freshly dug pit. One man at the top was shoveling muddy soil down to the bottom and two men at the bottom were spraying the soil with water to wash out the larger rocks, then sucking it all up into a pipe under pressure. This pipe delivered the mud and gravel to a large wooden sluice box, where a man removes medium sized pieces.

Sluice boxes. The mud slurry is pumped from the pit and washing down the rills where the larger stones are separated.

The smaller stuff and mud is carried by hand in a conical washing pan (just like the gold pans in California except with a pointed instead of flat bottom) to a walled-in area filled with water. Several men inside the water pit were sloshing the water around in the pans, gradually separating out the small gravel from the mud and searching through it for any diamonds.

A sluice box. Larger stones are separated out by hand in the sluice and the mud and smallest stones are dropped into a filter box.

An older gentleman showed us a plastic bag with several small diamonds in it, about 1/10 carat each. He said they find quite a few of these each day, but larger diamonds are much more rare.

Searching for diamonds in the pan. The small stones, still with some mud mixed in, are carried to this walled pit filled with water where the slurry is swished around with water and the smaller stones settle to the bottom. The panner searches for a glint of light that indicates a diamond. The remaining pebbles are placed to the side and eventually worked again to look for gold and platinum.

In my research on this area, I found out that it has been worked and reworked for almost a thousand years; certainly the pits and hummocks look like they have been dug through many times. In years past, the pits had to be dug about 30 feet down to reach the diamond bearing gravels, and they would flood because this is a swamp, so wood was used to barricade the pits, tamped with grass to prevent the water from oozing in. Even so, they would often collapse. Now they have created a dam to wall off the swamp water so that the large pit doesn’t flood, but the soil is still very muddy.

A bag with small diamonds found at the Cempaka mine. Although very small, at bout 1/10 carat, these diamonds are discovered fairly frequently here. Most of the larger stones have been discovered after a thousand years of digging.

It took some jumping over streams and hoses and climbing around to get to the panning pit. I was worried about getting mud on my new camera, but I did manage to get good photos and video of the whole process. Nazar’s friend told us that the miners are superstitious and that we should avoid doing certain things, or we would scare away the diamonds. One was to swear or use bad language. Another was to stand with our hands on our hips like a boss. I was trying not to do this, but in the photos taken of me, there I am with my hands on my hips. I hope I didn’t scare away the diamonds.

David Black standing like a boss at the Cempaka diamond mine. This is supposed to be bad luck to stand like this, with hands on hips, and will scare the diamonds away. Oops!

Before coming to Indonesia I researched this mine and discovered that the diamonds came from kimberlite deposits in the Meratus Mountains. They were washed here in rivers during the Cretaceous Period, when sea levels were higher. This area was at sea level and formed a delta into the ocean. In the over 66 million years since then, there hasn’t been much tectonic change in Borneo (unlike Java and Sumatra) and this area has remained largely intact, except that as sea levels dropped during the ice ages, the delta was subsequently buried under further sediment washed from the mountains. So now the miners have to dig down through 30 feet of mud. The gravel layer also has small deposits of gold and platinum in it. We could see the foothills of the Meratus Mountains in the distance. I wondered if there were any diamonds still in them thar hills. I don’t think the mother lode was ever found, just as the mother lode in California was never found.

The source of the Cempaka diamonds is the Bobaris Ophiolite, which contains kimberlite deposits. Kimberlite is a volcanic vent that lifts the diamonds from deep in the earth (where pressure and heat are great enough to form them) to the surface. The diamonds were then eroded out of the kimberlite and deposited in a Cretaceous delta in what is now the Barito River basin.

There were several groups of men digging in separate locations along the walls in the larger pit, using diesel powered pumps belching smoke to pump the water and mud from the holes onto the wooden sluices. Other than diesel power, their techniques have remained largely unchanged over a thousand years. This mine may be the second oldest diamond mine in the world, after the famous Golconda mines in India. It hasn’t produced as many famous stones, but from time to time larger stones are still found. About ten years ago, a rare three-carat blue diamond was discovered here. This is just one pit of many in the general area, and they still find small diamonds. I know some commercial groups have studied areas near here and say there is quite a bit of potential even now.

The geology of Borneo during the Cretaceous Period was just right for diamond formation and uplift. Subduction along the proto-Indonesian margins carried graphite deep, where it formed into diamond. The volcanic activity produced large cratons and calderas with mantle plumes that lifted the diamonds toward the surface. Now Borneo is stable without volcanoes, compared with the rest of Indonesia.

From here the diamonds are sold to buyers in Martapura who polish and set the stones into jewelry. We were to visit that part of the process next.