Day 7: Properties of Gold

We're all up early for a 45-minute drive down to the river - no helicopters today, unfortunately. Unlike yesterday, it's tipping it down, and what's worse, it's the kind of rain you get in the Lake District in the UK - unremitting drizzle that soaks you through to the bone. We are, after all, in a tropical rain forest, so I guess you'd expect a bit of rain. In fact, Kate H told us yesterday that this part of New Zealand gets 5m of rain a year. Looks like today's the day all 5m are due to fall. To make matters worse, the air is thick with sand flies, whose bites are vicious, and even draw blood. The balaclavas and insect repellant we've been given provide little defence against them. We're just going to have to grin and bear it. Nothing else for it.

Mikey L's joined us this morning, which is a relief, because there's lots of shovelling to be done if we're to recover any gold. The aim is to revisit those sites on the riverbank that showed the highest number of flakes during the panning process yesterday. This is where we're most likely to find the yellow stuff. Ellen and I have decided to try a technique that's commonly used by gold prospectors - sluicing. It involves shoveling sediment from the riverbank onto the top of a sluice box, and passing water down the inclined box so as to fluidize the sample. It's a gravity separation technique much like the panning process, in that the lighter sedimentary material is swept down the sluice by the water, while the gold, being much heavier, falls to the bed of the box. Ellen's found a large fern on the riverbank, called a punga tree, whose ‘bark' will make an excellent trap for the gold. It has the same kind of fibrous consistency as a loofah. By laying pieces of punga bark across the sluice bed, we'll be able to filter off the rough-edged gold grains.

Mike sets about building us a sluice box, while Ellen and I prepare the punga baffles. An hour later, we carry our sluice box down to the river, and we're ready to start shovelling. This is a high-throughput process - the higher the better. By the end of the day, it feels like we've turned the entire riverbank over. My back's aching, and I'm soaked through. We're all still smiling though, probably because we're surrounded by some beautiful, forested countryside. The river water's crystal clear, and, thankfully, not too cold.

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