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Termite mounds reveal desert gold
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that
BILL BACHMAN/WILDLIGHT
termite Want to find buried treasure? Nature’s little diggers will show you the way, says Beth Geiger
●
THE Kalahari desert in Botswana guards its geological secrets well. A layer of sand, soil and weathered rock tens of metres thick blankets all but a few outcrops of the underlying bedrock. Trying to find precious minerals embedded in the bedrock is a blind and very expensive grope. That’s why, when a geologist in the 1970s discovered a single fleck of a mineral called ilmenite on the surface, he paid attention. Ilmenite comes from a type of rock called kimberlite, and kimberlite hosts diamonds. That telltale fleck gave up an invaluable secret from the rock below: the richest diamond deposit in the world, now the Jwaneng diamond mine. But the minerals were 40 metres down, so how did a lone grain of ilmenite see the light of day? Termites hauled it. Desert termites dig deep. They need to. In hot, arid areas, termites build large mounds above ground to help air circulation and temperature control. If a mound is damaged, it must be repaired immediately to keep out predators and protect the colony. However dry the desert, termites always need wet mud for
www.newscientist.com
construction. To get it the insects tunnel 30 metres or more down to the water table, clamp bits of clay or wet rock in their jaws, then climb back home to build the mound, grain by damp grain. In doing this they not only bring up samples of the soil from that depth, but also traces of water that may have flowed through rocks containing precious ores. Termite mounds are packed with clues to what lies beneath. Now geologists and mining companies are waking up to the true potential of termite sampling. A team of Australian researchers is developing precise techniques that make the mounds, along with desert plants, reliable indicators of the rocks below. As well as scouring termite mounds for traces of gold, they are searching for chemical signatures of gold formation, brought up from the water table and concentrated in the mounds. Termites, they believe, are the ticket to new reserves of diamonds, gold and other buried treasure. Normally, to get a sample of bedrock from beneath all the accumulated sand, soil and stones, collectively known as regolith, 30 June 2007 | NewScientist | 35
STEVE HILL
geologists must drill an exploration hole. Termites do more or less the same thing for free, and the results are dotted all over the desert. “A termite mound is an inverted drill hole. It’s just what we want,” says Jon North of North Atlantic Resources in Toronto, Canada. Though some geologists, including North, have dabbled in termite mound sampling in parts of Africa, until recently many geologists and mining companies saw it as a “hobby” or complementary approach, rather than a reliable way to find gold. In Australia there was no need to try it out – most of Australia’s mineral wealth has come from the 30 per cent of the land where rocks are exposed, the geologic equivalent of low-hanging fruit. Now, though, the easy finds have run out and it’s time to explore the other two-thirds, where regolith masks the bedrock. But regolith is problematic. It can be tens or hundreds of metres thick. In Australia it is also very old and therefore has been churned and blown around for millions of years. That means it may have little geochemical connection to the rocks underneath. Still, there’s little doubt that it hides worthwhile targets. In the Tanami desert of
Samples Anna Petts of the University of Adelaide takes from termite mounds can show telltale signs of gold 36 | NewScientist | 30 June 2007
Australia’s Northern Territory, “less than 1 per cent of the landscape has rocks exposed above ground, and these have revealed some of the largest gold deposits in Australia”, says Steve Hill at the University of Adelaide. “The same rocks extend underneath, and so far there have been extremely few discoveries from this 99 per cent of the landscape.” So compelling is this figure that the Australian government has created a programme to address it: the Cooperative Research Centre for Landscape Environments and Mineral Exploration, or CRC LEME, headed by Lisa Worrall of Geoscience Australia. Worrall says CRC LEME, which includes Hill’s team, aims to study the regolith as a whole – lock, stock and termites – to substantially improve the success of mineral exploration.
Regurgitated mud To find out whether termite mounds could reliably reflect the minerals below, Hill and his two graduate students, Anna Petts and Nathan Reid, sampled mounds near the Coyote gold mine in the western Tanami, where the underlying geology is well mapped. At each mound Petts uses GPS to pinpoint the location, then she digs in with her rock hammer and pulls out a fistful. “The inside of the mounds is a type of mud-regurgitated cement, and probably also faeces,” says Petts. “Many species of termites chew up organic material and fine regolith material, then regurgitate it back up to make the walls.” The termites seem to take the geologists’ intrusions in their stride. “The mounds start being repaired by the termites while we are sampling,” Hill says. “Typically within a few minutes the mounds are resealed, and by the next day we generally see no sign that the mound had been sampled at all.” Petts bags the samples and sends them off for analysis, scanning for a range of signature” elements that indicate gold might be present, including chromium, titanium and arsenic. These elements may be bound with gold, or occur in rock that also contains gold; pure gold sometimes comes up, too. The project’s aim is to add scientific rigour to the process, using meticulous sampling
BILL BACHMAN/WILDLIGHT
“Termites can get their mandibles into gold because it is soft”
methods to reduce cross-contamination with other surface materials. In addition to looking for gold, they also track where the termites have been, and what they ate. For example, chewed samples of spinifex grass, a plant that is dotted all over the Tanami desert, often turns up in little piles in termite nurseries. The team has been amazed at the results. The mounds reflect the underlying geology surprisingly well. “We are getting great signatures of buried mineralisation up to 30 metres from the surface” says Hill. “I suspect that almost any part of the landscape has its chemical story to tell. It’s just a matter of learning how to read that story.” What’s more, geologist Michael Milner, a private consultant based in Toronto, Canada, who has worked extensively on African termite colonies, reckons that some termites even seek out gold preferentially. “They can get their mandibles into it because it’s soft,” he says. He and Timothy Myles of the University of Toronto have published electron micrographs of gold freshly peeled by termites, and incorporated in the mound. Their tiny jaws can give a nasty bite, too. Petts claims she has mostly escaped that, partly by working during the heat of the day when the termites retreat underground. She has apparently fared better than North, who www.newscientist.com
:?==?D=:;;F J^[ckZWdZmWj[hj^Wjj[hc_j[iWdZif_d_\[n]hWiiXh_d]kf \hecj[die\c[jh[iX[bemj^[Z[i[hjYedjW_dY^[c_YWb i_]dWjkh[ie\j^[X[ZheYa"feii_Xbo_dYbkZ_d]jhWY[ie\fh[Y_eki c_d[hWbi$J^_iYekbZX[YhkY_Wb_d\ehcWj_ed\ehfheif[Yjehi 7meha[hj[hc_j[_i`kij'Yc bed]"XkjYWdjkdd[b)&&&j_c[i _jiXeZob[d]j^_di[WhY^e\ ckZ\eh_jicekdZ$JecWjY^ j^_i\[Wj"W^kcWdmekbZ^Wl[ jeZ_]ceh[j^Wd+acZemd" ed[#j^_hZZ[[f[hj^Wdj^[ mehbZÊiZ[[f[ijc_d[ +c[jh[i Jeikhl_l[_dj^[Z[i[hj" if_d_\[n]hemiheejih_]^j Zemdjej^[mWj[hjWXb[ &
+
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www.newscientist.com
Mineral prospectors in the Tanami desert need look no further than the termite mounds and Spinifex plants
and together provide a more complete geochemical picture than either one alone. The strength of the results has caught the attention of mining companies around the world and should lead to new discoveries in both Australia and Africa. “These techniques are becoming valid for routine use, rather than exotic, experimental or complementary,” says Trevor Ireland of Australasia Gold. “Hill’s team seems to have produced more consistent and reproducible results than earlier efforts.” “A whole bunch of companies who once said, ‘I didn’t think that worked’ are now starting to take a second look,” says David Giles, director of the University of Adelaide’s Centre for Mineral Exploration Under Cover. To Petts, using termite mounds to peek underground makes sense. The method is low impact compared to drilling, and for very little outlay and effort you might just find something. “Why not take advantage of all the hard work that nature’s little drillers have done to prepare a sample for you?” she says. ● Beth Geiger is a freelance science writer based in Seattle
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has been termite bait in Africa many times. Simon Bolster, a geochemist with Newmont Mining Corporation, has far freakier tales from Africa. He once saw six snakes, including two cobras, inside a mound. “Since then I have always been very wary when sampling termite mounds,” he says. While Petts annoys the termites, Reid samples spinifex grass and other plants that survive in the arid Tanami. “Spinifex plants don’t waste effort growing above ground, only to get burned in fires or desiccated in the wind and sun,” Hill says. “They put their efforts into vertical roots that extend down tens of metres.” If a termite drilling to 30 metres seems impressive, spinifex can sends roots to 50 metres or more. No one had analysed this plant for its prospecting potential before, partly because its notoriously spiky leaves can make sampling a traumatic experience. Reid, though, decided it was worth a shot. Like termites, spinifex is after groundwater, so it also picks up traces of whatever chemicals are in the bedrock and accumulates them in its leaves and roots. “As far as I can tell, both spinifex and termites can tap into mineralisation and draw the signature to the surface,” says Reid. Spinifex and termites concentrate different metals,
>;?=>JE<B?D9EBDC;CEH?7B"M7I>?D=JED:9
'+
30 June 2007 | NewScientist | 37
that
BILL BACHMAN/WILDLIGHT
termite Want to find buried treasure? Nature’s little diggers will show you the way, says Beth Geiger
●
THE Kalahari desert in Botswana guards its geological secrets well. A layer of sand, soil and weathered rock tens of metres thick blankets all but a few outcrops of the underlying bedrock. Trying to find precious minerals embedded in the bedrock is a blind and very expensive grope. That’s why, when a geologist in the 1970s discovered a single fleck of a mineral called ilmenite on the surface, he paid attention. Ilmenite comes from a type of rock called kimberlite, and kimberlite hosts diamonds. That telltale fleck gave up an invaluable secret from the rock below: the richest diamond deposit in the world, now the Jwaneng diamond mine. But the minerals were 40 metres down, so how did a lone grain of ilmenite see the light of day? Termites hauled it. Desert termites dig deep. They need to. In hot, arid areas, termites build large mounds above ground to help air circulation and temperature control. If a mound is damaged, it must be repaired immediately to keep out predators and protect the colony. However dry the desert, termites always need wet mud for
www.newscientist.com
construction. To get it the insects tunnel 30 metres or more down to the water table, clamp bits of clay or wet rock in their jaws, then climb back home to build the mound, grain by damp grain. In doing this they not only bring up samples of the soil from that depth, but also traces of water that may have flowed through rocks containing precious ores. Termite mounds are packed with clues to what lies beneath. Now geologists and mining companies are waking up to the true potential of termite sampling. A team of Australian researchers is developing precise techniques that make the mounds, along with desert plants, reliable indicators of the rocks below. As well as scouring termite mounds for traces of gold, they are searching for chemical signatures of gold formation, brought up from the water table and concentrated in the mounds. Termites, they believe, are the ticket to new reserves of diamonds, gold and other buried treasure. Normally, to get a sample of bedrock from beneath all the accumulated sand, soil and stones, collectively known as regolith, 30 June 2007 | NewScientist | 35
STEVE HILL
geologists must drill an exploration hole. Termites do more or less the same thing for free, and the results are dotted all over the desert. “A termite mound is an inverted drill hole. It’s just what we want,” says Jon North of North Atlantic Resources in Toronto, Canada. Though some geologists, including North, have dabbled in termite mound sampling in parts of Africa, until recently many geologists and mining companies saw it as a “hobby” or complementary approach, rather than a reliable way to find gold. In Australia there was no need to try it out – most of Australia’s mineral wealth has come from the 30 per cent of the land where rocks are exposed, the geologic equivalent of low-hanging fruit. Now, though, the easy finds have run out and it’s time to explore the other two-thirds, where regolith masks the bedrock. But regolith is problematic. It can be tens or hundreds of metres thick. In Australia it is also very old and therefore has been churned and blown around for millions of years. That means it may have little geochemical connection to the rocks underneath. Still, there’s little doubt that it hides worthwhile targets. In the Tanami desert of
Samples Anna Petts of the University of Adelaide takes from termite mounds can show telltale signs of gold 36 | NewScientist | 30 June 2007
Australia’s Northern Territory, “less than 1 per cent of the landscape has rocks exposed above ground, and these have revealed some of the largest gold deposits in Australia”, says Steve Hill at the University of Adelaide. “The same rocks extend underneath, and so far there have been extremely few discoveries from this 99 per cent of the landscape.” So compelling is this figure that the Australian government has created a programme to address it: the Cooperative Research Centre for Landscape Environments and Mineral Exploration, or CRC LEME, headed by Lisa Worrall of Geoscience Australia. Worrall says CRC LEME, which includes Hill’s team, aims to study the regolith as a whole – lock, stock and termites – to substantially improve the success of mineral exploration.
Regurgitated mud To find out whether termite mounds could reliably reflect the minerals below, Hill and his two graduate students, Anna Petts and Nathan Reid, sampled mounds near the Coyote gold mine in the western Tanami, where the underlying geology is well mapped. At each mound Petts uses GPS to pinpoint the location, then she digs in with her rock hammer and pulls out a fistful. “The inside of the mounds is a type of mud-regurgitated cement, and probably also faeces,” says Petts. “Many species of termites chew up organic material and fine regolith material, then regurgitate it back up to make the walls.” The termites seem to take the geologists’ intrusions in their stride. “The mounds start being repaired by the termites while we are sampling,” Hill says. “Typically within a few minutes the mounds are resealed, and by the next day we generally see no sign that the mound had been sampled at all.” Petts bags the samples and sends them off for analysis, scanning for a range of signature” elements that indicate gold might be present, including chromium, titanium and arsenic. These elements may be bound with gold, or occur in rock that also contains gold; pure gold sometimes comes up, too. The project’s aim is to add scientific rigour to the process, using meticulous sampling
BILL BACHMAN/WILDLIGHT
“Termites can get their mandibles into gold because it is soft”
methods to reduce cross-contamination with other surface materials. In addition to looking for gold, they also track where the termites have been, and what they ate. For example, chewed samples of spinifex grass, a plant that is dotted all over the Tanami desert, often turns up in little piles in termite nurseries. The team has been amazed at the results. The mounds reflect the underlying geology surprisingly well. “We are getting great signatures of buried mineralisation up to 30 metres from the surface” says Hill. “I suspect that almost any part of the landscape has its chemical story to tell. It’s just a matter of learning how to read that story.” What’s more, geologist Michael Milner, a private consultant based in Toronto, Canada, who has worked extensively on African termite colonies, reckons that some termites even seek out gold preferentially. “They can get their mandibles into it because it’s soft,” he says. He and Timothy Myles of the University of Toronto have published electron micrographs of gold freshly peeled by termites, and incorporated in the mound. Their tiny jaws can give a nasty bite, too. Petts claims she has mostly escaped that, partly by working during the heat of the day when the termites retreat underground. She has apparently fared better than North, who www.newscientist.com
:?==?D=:;;F J^[ckZWdZmWj[hj^Wjj[hc_j[iWdZif_d_\[n]hWiiXh_d]kf \hecj[die\c[jh[iX[bemj^[Z[i[hjYedjW_dY^[c_YWb i_]dWjkh[ie\j^[X[ZheYa"feii_Xbo_dYbkZ_d]jhWY[ie\fh[Y_eki c_d[hWbi$J^_iYekbZX[YhkY_Wb_d\ehcWj_ed\ehfheif[Yjehi 7meha[hj[hc_j[_i`kij'Yc bed]"XkjYWdjkdd[b)&&&j_c[i _jiXeZob[d]j^_di[WhY^e\ ckZ\eh_jicekdZ$JecWjY^ j^_i\[Wj"W^kcWdmekbZ^Wl[ jeZ_]ceh[j^Wd+acZemd" ed[#j^_hZZ[[f[hj^Wdj^[ mehbZÊiZ[[f[ijc_d[ +c[jh[i Jeikhl_l[_dj^[Z[i[hj" if_d_\[n]hemiheejih_]^j Zemdjej^[mWj[hjWXb[ &
+
'&
www.newscientist.com
Mineral prospectors in the Tanami desert need look no further than the termite mounds and Spinifex plants
and together provide a more complete geochemical picture than either one alone. The strength of the results has caught the attention of mining companies around the world and should lead to new discoveries in both Australia and Africa. “These techniques are becoming valid for routine use, rather than exotic, experimental or complementary,” says Trevor Ireland of Australasia Gold. “Hill’s team seems to have produced more consistent and reproducible results than earlier efforts.” “A whole bunch of companies who once said, ‘I didn’t think that worked’ are now starting to take a second look,” says David Giles, director of the University of Adelaide’s Centre for Mineral Exploration Under Cover. To Petts, using termite mounds to peek underground makes sense. The method is low impact compared to drilling, and for very little outlay and effort you might just find something. “Why not take advantage of all the hard work that nature’s little drillers have done to prepare a sample for you?” she says. ● Beth Geiger is a freelance science writer based in Seattle
(&
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)+
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has been termite bait in Africa many times. Simon Bolster, a geochemist with Newmont Mining Corporation, has far freakier tales from Africa. He once saw six snakes, including two cobras, inside a mound. “Since then I have always been very wary when sampling termite mounds,” he says. While Petts annoys the termites, Reid samples spinifex grass and other plants that survive in the arid Tanami. “Spinifex plants don’t waste effort growing above ground, only to get burned in fires or desiccated in the wind and sun,” Hill says. “They put their efforts into vertical roots that extend down tens of metres.” If a termite drilling to 30 metres seems impressive, spinifex can sends roots to 50 metres or more. No one had analysed this plant for its prospecting potential before, partly because its notoriously spiky leaves can make sampling a traumatic experience. Reid, though, decided it was worth a shot. Like termites, spinifex is after groundwater, so it also picks up traces of whatever chemicals are in the bedrock and accumulates them in its leaves and roots. “As far as I can tell, both spinifex and termites can tap into mineralisation and draw the signature to the surface,” says Reid. Spinifex and termites concentrate different metals,
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'+
30 June 2007 | NewScientist | 37