Day 6: Properties of Gold

So, here we go again, our first day of filming for the third series of Rough Science. It's great to be back with the old team. Although we arrived in New Zealand last Sunday, we're all still feeling the after-effects of the 20,000 km trip out here. My first impressions of this place are that (i) the people are all so friendly, (ii) the country is so beautiful, and (iii) I'm so damned lucky to be here.

It's going to be a fairly easy day today. Our first job is to be flown in two helicopters over the Franz Josef Glacier - now, is that a great start to the day or what? The glacier and the surrounding alpine scenery are indescribably beautiful. To see it so close up from the air leaves me speechless.

The helicopters take us to the sawmill, where we are given our challenges for Programme 1. Ellen and I are asked to locate a site where we can pan for gold - yes, gold. There are tonnes of it up there in the mountains, most of it is embedded as tiny flakes in quartz veins in the rock. Weathering and erosion release the gold from the quartz and surrounding rock, and it's washed downstream by glacial melt-waters, streams and rivers. On its journey to the sea (amazingly, the coast is only 5 km from the glacier here) the flakes are broken up into finer and finer particles. Gold is a very unreactive metal - it doesn't corrode or rust like many other metals. Its extraction is therefore just a matter of physically separating it from the rocks, gravel and sediment on the riverbed; no chemistry's necessary. However, any gold to be found here will contain copper, silver and perhaps platinum as impurities.

The site Ellen and I are looking for from the helicopter is something like a bend on a largish, fast-flowing river. Because the water flows less quickly on the inside of a bend, it's here that the heavy gold flakes and grains will be deposited in a line (anything from a few centimetres to a metre or so wide) on the riverbed. Another place to look is under large boulders in the river. As the water carries the gold and sediment over a boulder or rock, the gold grains and flakes fall to the riverbed on the downstream side.The gold eventually works its way down the clay bedrock, where it comes to rest. A drop in the water level allows access to these so-called alluvial gold deposits.

Having located a suitable site on the bank of the Whataroa River to start our search, Ellen and I agree to take samples from various positions in an attempt to locate the line where gold might have been deposited. We use an old prospecting technique called panning. This involves scooping up a handful or two of the sediment from the site in question into a wok-sized pan, and swirling it about in water, all the while agitating so as to work the heavy gold particles to the bottom of the pan. After a few vigorous swirls, the bulk of the larger pebbles and gravel can be swept off the top. The swirling process is continued, each time removing lighter and lighter material from the top of the pan. You eventually end up with the darker, heavier silt, most of which is the black mineral magnetite (a magnetic iron ore). It's at this stage that you have to be more careful and swirl the contents of the pan more gently. If you get the right action, and if there was gold in your original sample, a fleck or two of gold grains (or if you're really lucky, flakes) will separate out from the dark material. When it happens, you get the most amazing buzz - gold fever!

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