… wake up in bed sweating and tossing. It’s a nightmare, but a familiar one.

 The incident that sparked this trauma took place over 50 years ago.

Five am, Saturday 6^th July 1968.

Thirty-six men quietly assemble at the government wharf, near the Provincial capital of Kieta on the southeast coast of Bougainville Island. Most are uniformed and steel-helmeted members of the Royal Papua Niugini Constabulary, all armed with wooden pickaxe handles. An unfit-looking Inspector from Melbourne and a grizzled old Sergeant from Mt Hagen, armed with pump-action shotguns and side arms, lead the uniformed force. In overall charge is a young Australian civilian Patrol Officer, known in Papua Niugini as a “Kiap”. Tied to the wharf behind the group, with its strange profile becoming clearer as the tropical dawn creeps in, is the MV Craestar, a 25 m long exploration ship owned by Conzinc Rio Tinto of Australia[1] Exploration (CRAE). From the ship, three company geologists – armed with geology hammers – join the group. They are Warren Atkinson (the Senior Geologist), Geoff Scott and I. Once assembled, we board open-topped trucks or light four-wheel-drive vehicles and set off along the rutted coast road. We face two hours driving on ever smaller tracks followed by a two-hour march on jungle paths before we arrive at our destination – a village deep in the interior, about 10 km to the SE of the porphyry copper-gold prospect of Panguna, then at advanced feasibility stage.

As you have probably guessed, we were expecting trouble.

 The MV Craestar tied to the Government wharf near Kieta on Bougainville Island, June 1968. The ship was a 30m Japanese tuna fishing vessel converted by CRA Exploration into a mobile exploration base by the addition of an assay lab in the hold and a helicopter pad and extra cabins at the stern. We liked to think of it as the world’s smallest aircraft carrier. From my 1968 sketchbook.

The Back Story

 That trouble had been brewing for a couple of years. The Panguna deposit was found by CRA in 1964 near the crest of the Crown Prince Range which forms the central spine of Bougainville Island. By 1968, through a massive drilling campaign, CRA had defined a giant open-pitable porphyry copper-gold deposit. The company needed to acquire land for mine, roads, port, and townships. The Australian colonial administration oversaw the land purchases, restricting prices so as not to upset existing stakeholders in the coastal copra industry. Subsistence farmers in and around Panguna thus saw land worth billions of dollars in contained metal value being taken from them and compensation offered based on its value in growing coconuts, the whole issue being exacerbated by long-held political resentment in Bougainville Island to rule from Port Moresby on the PNG mainland.

Underemployed and unsophisticated young men muttered about Bougainville independence and play-trained in the forest with mock wooden rifles.  I was told that only a few months before I arrived, a Kiap had been ambushed in a remote jungle area and hacked to death with machetes [2]. Before the 1968 field season, the Australian colonial administration held meetings with village leaders to explain the CRAE stream-sediment sampling program that was planned for that year throughout the island. Most islanders welcomed the incoming exploration team from the Craestar – they wanted a mine to be found in their district that would bring infrastructure and jobs. Throughout Bougainville, this friendliness was our usual experience. Many times, our helicopter could barely take off from the ground by the weight of baskets of local produce (pineapple, citrus, banana, melon, sweet potato, corn) tied to our skids, which we were unable to refuse without giving offence. But in an area of 10-15 km radius around Panguna, many locals resolved that they would repel any incursions by CRA explorers. In the event, we geologists, using a helicopter to leapfrog each other up and down the drainage to collect stream sediment samples, managed to pass through the country so quickly that we were usually gone by the time local villagers were able to organise, or even be aware of our presence on the ground. That is, until…

Friday 5^th of July, 1968

On this day, Warren, Geoff, and I landed in some overgrown native gardens near a large village located about 10 km SW of Panguna. Anticipating potential trouble, Warren and Geoff headed off to wet sieve a -80-mesh silt sample from the bank of a small river which flowed past the village. I undertook the safer task – as we thought – of sampling a small tributary stream that flowed in from the jungle. This involved following a forest track that ran along the bank of the stream to collect a sample upstream from its confluence. The track was faint and overgrown, constantly looping away from the stream to bypass fallen trees, thickets of thorn or overgrown gutters. I had to travel at least a kilometer before I found a suitable sample site. As I was kneeling in the stream bed, angry shouts suddenly broke out behind me. Three men stood on the bank, brandishing machetes. Their rapid Pidgin English was beyond my limited command of the language, but their message was very clear, and Anglo-Saxon swear words are a universal language.

 No kissim sample long dis pela ples!

 Itambu! [3]

 Fuck off long Australia!

It was clear they were not happy. I made an exaggerated pantomime of dumping my sample back into the stream, waved my hands in what I hoped were apologetic and deprecatory gestures, and hurried back the way I had come. The men followed close behind, continuing to harangue and swear at me, flicking branches onto the back of my head and shoulders to hurry me along. I thought of the Kiap, hacked to death just a few months before in circumstances very much like my own. If attacked, my geology pick would be a poor defensive weapon. As unobtrusively as I could, I slipped my hand into my shoulder bag and hooked a finger into the ring-pull ignition of a rocket-propelled parachute flare. We always carried a couple of these flares as part of our emergency equipment to signal to the helicopter from the ground: fired vertically, the device ignited and released a rocket that, with impressive noise, smoke, and showers of sparks, shot 100-150 m into the air before releasing a bright magnesium flare to slowly descend on a parachute. I hoped that, fired horizontally, it would create enough confusion and noise for me to escape. A smoke flare would have been better – we usually carried them too, but I had none with me that day. I was not optimistic: fired too early it might escalate a threatened attack into a genuine deadly one; but waiting for a deadly attack would probably be too late. In any case, there was no guarantee that my one-shot horizontal missile, even if I was given the chance to fire it, would have worked as I hoped. Thankfully, although the aggression continued at the same level, I did not have to make that choice. After twenty minutes of pure terror, I made it safely back to the clearing by the main river.

 I had been away for over an hour. At the helicopter, Warren, Geoff, and the pilot had been waiting with increasing anxiety for my return. They themselves had not got far, having almost immediately been chased back to the landing site by a large crowd of village men who were now surrounding the helicopter. My three aggressors joined this crowd and added their voices to the cacophony of angry shouts and calls.

We quickly flew off, glad to get away so easily and, in my case, to be still alive.

Once safely landed on the ship at the government wharf, Warren hurried off to Kieta to inform the District Commissioner of what had happened. It was determined that we must go back to the village – this time with police protection. The Commissioner had over 50 riot police housed in nearby barracks at his disposal. They had been flown in at the beginning of the season from New Britain and the PNG mainland for just such an eventuality. Government authority had to be maintained: CRAE had to be seen to take a sample at the site where Warren and Geoff had been repulsed that day. Thankfully, my own sample did not need to be retaken because, although I had made a show of emptying it back into the stream, there was enough fine silt still adhering to the paper sample packet to allow a full suite of assays to be made.

A confrontation near the Panguna Copper prospect between Bougainville villagers and geologists from the MV Craestar. It took place a few days before the incident described in this story. The spokesman in the white T-shirt, probably an agitator from outside the area, spoke good English and is making forceful points about land rights and expropriation. In this instance, we were eventually given grudging permission to collect our samples. The dark skin colour and fine physique are typical of the inhabitants of Bougainville. Photo by author.

The Following day, Saturday 6^th July

 A long file of armed men climbs steadily into the mountains along a narrow foot track. The Kiap leads, followed by Warren, Geoff, and I, then the Sergeant at the head of his 30 men, many of whom are soon limping due to a recent issue of new boots. The Inspector from Melbourne brings up the rear. As we pass each village, crowds of locals appear: men, women and children, the numbers swelling until at least 200 people are advancing through the jungle and into the hills. Raucous obscenities are shouted, but no one tries to impede our passage – most are obviously just along for the fun: some even cheering us on. After about two hours of steady climbing, the head of our group, consisting of the Kiap, we three geologists, the Sergeant and four of his men (the rest of the police party nowhere to be seen) reach the overgrown gardens beside the river from which we had been evicted the previous day. By this time most of the spectators who had followed us from the coast have melted away, but around two dozen locals, now ominously all men, are waiting for us. Most carry machetes.

 “Okay guys” says the Kiap “take your sample now, then we can all go home.” 

Warren and Geoff wade into the stream with their sieves and scoop up some silt from its bed. The crowd presses forward, shouting with rage. The Sergeant and his four men try to hold them back, swinging and thrusting with their pickaxe handles. But several men evade the weak cordon, plunge into the stream, and start to wrestle with Warren and Geoff for control of their sieves. The police are badly outnumbered, the Sergeant unslings his shotgun and bloody mayhem threatens. But just at that moment another half dozen police arrive at the top of the ridge overlooking the little valley, and seeing the developing battle below, charge down the hill yelling and swinging their clubs in the manner no doubt instilled in them at the Port Moresby Police Academy. This unexpected flank attack wins the day, and the angry crowd pulls back. All except one – a skinny, white-haired old man – who continues to grapple with Warren for possession of his sieve (he is the one in the white lap-lap on the right of the photo below). The Sergeant promptly arrests and handcuffs him. By the time the remainder of the police contingent – the Inspector from Melbourne still bringing up the rear – trickle in by ones and twos over the next half hour, everything is quiet, and the ex-belligerents and the few remaining spectators are gone. The return march to the coast with our prisoner is uneventful.

 Villagers near Panguna copper deposit in Bougainville Island try to stop CRAE geologists Geoff Scott (left) and Warren Atkinson (second from right) from collecting a stream-sediment sample. The guy in the hat is the Kiap. The old man in the white lap-lap (extreme right) is struggling with Warren for control of his sampling sieve. Photo by author.

What Happened Next

 The little old man, I was told, was found guilty of civil affray, and sentenced by the magistrate to a week in the Kieta jail.

CRAE successfully completed their geochemical sampling program across the Island. No significant new copper or gold mineralisation was found.

The MV Craestar departed Bougainville and sailed on to conduct similar geochemical exploration programs in the Solomon and Trobriand islands, New Britain, and the north coast of Papua Niugini.

There were more riots and violent protests in 1968 and 1969 before the Australian administration managed to secure a deal with the locals that enabled CRA to proceed with mine construction.

Seven years later (September 1975), Papua New Guinea gained independence from Australia as a separate sovereign nation.

The Panguna mine, through CRA subsidiary Bougainville Copper Limited, operated successfully through the 1970s and 1980s and became a major contributor to the coffers of both the company and the new government of Papua Niugini.

But disquiet over returns to Bougainville from the super profits of the mine and continuing political unrest over Bougainville independence had not gone away. In 1989, the outbreak of the Bougainville Civil War forced Bougainville Copper to precipitously walk away from the mine. Rio Tinto has had no access to the mine site since, which today lies abandoned to the tropical rains.

The now largely forgotten ten-year-long War of Independence that started in Bougainville in 1989 and resulted in around 20,000 deaths (Wikipedia) was much more violent than anything experienced by me more than 50 years ago.

The issue of Bougainville independence is still unresolved.

This article is modified and expanded from a post first published ten years ago in this blog.

The post An Incident in Bougainville appeared first on Roger Marjoribanks.

A moment of fierce joy

In a near 60-year career this experience has only happened to me three times. Two of these discovery outcrops eventually led to operating mines, the third, after years of exploration and drill testing, failed to make the cut (I still think it will be a mine someday, so I will say no more on that one)).  I take only modest credit for these discoveries. I was first on the ground and got the naming rights for the prospect and subsequent mines, but was part of a team, and a large element of luck was involved. All this happened 30-50 years ago when not all the low-hanging fruit had been plucked. Prospecting discovery of significant outcropping mineralisation  happens increasingly less these days. Maybe in a remote and under-prospected third world country? If there are any such left in this globalised world.

The Greenfields (1) gold deposit near Coolgardie in Western Australia, which I identified in the course of 1:5000 scale geological mapping, was named for the field below which it lay – full of Spring grass and wildflowers and big eucalypt trees when I first came upon it in 1984. I hoped that the name would preserve the memory of this pleasant little valley long after the bulldozers had moved in. Greenfields open cut mine is long exhausted, but the Greenfields Mill still operates today as a Toll facility for other gold mines in the district.

The Magellan Pb deposit near Wiluna in Western Australia was an entirely serendipitous discovery of high-grade (2) outcropping mineralisation which I made in in 1991 in the course of checking old gold claims in nearby rocks. That day was the first time that I had used a GPS unit in the field. This was a hand-held instrument made by a company called Magellan and the size and weight of a house brick, but a revelation and a boon. I thought it a cool name so gave it to my discovery. Magellan was the first discovery in a new and unique lead province. Later prospects in the area followed the same theme and named for 15th Century Spanish and Portuguese explorers. The Magellan lead mine is still in operation today although environmental restrictions have severely restricted its operations.

Discovery of outcropping mineralisation is invariably followed by collecting rock samples for assay.  The different types of rock chip sampling and how to collect them are detailed in an earlier blog post here.

 (1) The name I gave was actually Greenfield, but the company later added the final “s”, probably because they wanted investors to think they had more than one.

 (2) The first suite of rock chip samples from Magellan, collected from over 5km of strike, came back 5%-35% Pb. Near pure cerussite.

The post The Discovery Outcrop appeared first on Roger Marjoribanks.

In my previous post I described my encounter in 1984 with claim salting (or at least, alleged salting). These were early days, the late 20^th Century gold boom was still young, and claim salting considered a rather amusing but small-scale misdemeanor practiced by dishonest small-time prospectors – easily spotted by the sophisticated explorer.

KARPA SPRINGS

Two major multimillion-dollar scandals, in 1990 at Karpa Springs in Western Australia and in 1997 at Busang in Indonesia, ended this age of innocence. Although well known, the stories are worth re-telling, and as I had some peripheral first-hand knowledge of both scandals, I might be able to add some additional insights.

Here is the Karpa Springs story, as I understand it from information given to the press at the time and from talking to people involved. It begins with three wheat farmers (Clark Easterhay and the brothers Len and Dean Ireland), filling in time before the harvest, who pegged a Lease on the nearest available ground to Mount Gibson in the West Australian Yilgarn.  Mount Gibson was then a hot “address” following nearby well-publicized gold discoveries.  The ground acquired by the three wannabe prospectors was available for pegging because it was underlain by granite. Granite terranes in the West Australian goldfields have historically produced only insignificant amounts of gold compared to the adjacent, basalt-dominated, greenstone belts – hence usually ignored by experienced prospectors.   Having acquired a RC[1] drill rig, the trio then proceeded to drill a number (around 9, from memory) of random, 60m deep, vertical holes along the line of an old track that traversed the sandy soil and thick scrub of the property.  As an exploration strategy this was hardly sophisticated, but the trio’s next step showed more cunning: they added fine gold grains – acquired from somewhere else – to the drill cuttings.  On assay, all holes were mineralised, one of them yielding an intersection of 38m at 34 g/t Au. The fraudsters then contacted a mining consultancy group called the Aracus Syndicate that included entrepreneur Mike Novotny and geologist Laurie Whitehouse[2].  Whitehouse travelled to the site and supervised the prospectors while they drilled a duplicate set of holes on each of the original sites. He then sampled the cuttings and was able to replicate the earlier assays.  Convinced they had a major new discovery, the Syndicate then promoted the property around  Mining Companies in Western Australia, one of which was my then employer Renison Goldfields Corp. (RGC). My colleague Keith Watkins visited the site and panned RC cuttings from the holes which were lying on the ground. Keith told me he recovered gold that was clearly alluvial and not consistent with the granite bedrocks being drilled: on Keith’s recommendation and suspecting fraud, RGC declined to become involved. However, an Australian Junior company called Perilya, along with their Canadian partner Noranda (a major player with deep pockets), were less discriminating: Perilya optioned the property and made a first payment of Aus$6.5 million to the fraudsters (reports at the time said the Aracus Syndicate were to receive a 5% Royalty on the profits from any subsequent mine). But in the absence of the merry farmers (they were in Perth, cashing their cheque) and their magic drill rig, all Perilya’s subsequent test holes were duds. To cut a long story short: Perilya stopped payment on the cheque and the police were informed.  The West Australian Department of Mines then got involved and, under police supervision, drilled a fresh set of holes on all the earlier sites. No gold was found. At this stage there were now four closely grouped holes on each of the nine original sites. The first of each set were those drilled and sampled by the prospectors. The second were drilled by the prospectors under the supervision of, and sampled by, the Aracus Syndicate. The third drilled by Perilya using their own contract drilling team.  The fourth by the Mines Department in the process of collecting evidence for criminal prosecution. Clearly, the prospectors had salted the second round of holes in full view of Laurie Whitehouse, but this was probably not too difficult for them – in these innocent days he would not have been expecting fraud, and it is easy to be wise after the event. Eventually, the prospectors were charged, found guilty of fraud and served 13 months in jail. But see footnote [3].

BUSANG

Karpa Springs was serious fraud – an attempt to steal $6.5 million – but it was very small beer compared to what happened a few years later (1995-98) in Central Kalimantan on the island of Borneo. A group of Filipino contract geologists, working for a Canadian Junior Mining Company called Bre-X, salted diamond drill cuttings from a genuine (albeit, as much later established, sub-economic) epithermal hard-rock gold prospect known as Busang. The resulting assay results, consistent over almost 300 diamond drill holes, caused the penny-stock Bre-X to soar to over Can$285 on the Toronto Stock Exchange, valuing the company at over $6 billion. The site geologists, and Bre-X Vice-President of Exploration John Felderhof, reportedly sold their stock at the inflated values: Felderhof reputedly making over $80 million, and in 1997 awarded the title “Prospector of the Year” by PDAC – the Prospectors and Developers Association of Canada (4).

Over a period of several years, the conspirators had operated a secret jungle laboratory where carefully calculated and measured amounts fine gold were added to literally thousands of drill samples from hundreds of holes. An astonishing, sustained, industrial-scale operation. The doctored samples were then dispatched to an outside laboratory for assay. Such was the scale of the deception it is estimated that well over $30,000 worth of alluvial gold must have been used in the deception. External ore reserve geologists (working from data provided by Bre-X in their reports to the Toronto Stock Exchange) estimated an 80 million oz. gold resource (well over $160 billion at today’s prices).  No outside experts were allowed in to visit the property. However, international investors and stockbrokers (money men, who would not know an epithermal from an epitaph) were given site tours and produced uncritical, glowing reports. With hindsight these were all warning signs, but at the time no one seriously considered fraud. Where that thought occurred, the sheer scale, technical difficulty and effrontery of the effort that would have been required led to the idea being dismissed.

But in 1998 the Bre-X bubble was to burst, as all bubbles do. The events took place rapidly, and I am not clear on all the details (perhaps no one is) but here is my understanding..

In 1997, at the height of the stock market bubble, major North American gold mining companies, including Barrick, Placer and Freeport, became involved in a bidding war for the Busang property.  Each sought advantage by signing up various members of President Suharto’s family or his close confidants. Freeport won this war, but before committing to a large up-front cash payment (which would have been in excess of $100 million), sent a team of geologists to the Busang site in Kalimantan to conduct a forensic examination of the drilling, sampling and assay methodologies employed by Bre-X, and re-drilling and sampling a number of check holes. This was standard due diligence: the Freeport geologists were not expecting fraud. The Filipino site team, and especially Chief Project geologist Michael de Gusman, must have realised that the game was up. While this was going on, there was a dramatic development: Michael de Guzman, returning to site from the Toronto PDAC meeting, had fallen from a helicopter (or did he jump, or was he pushed?) and his body (or at any rate, someone’s body) found in the jungle four days later, partially eaten by pigs. A few weeks later, Freeport announced their conclusion that the core they had drilled at Busang contained only insignificant amounts of gold, and that the core previously drilled from the same sites by De Gusman’s team had been doctored with added alluvial gold. The Bre-X stock price collapsed, the company was de-listed and went bankrupt. Vice-President of Exploration John Felderhof (who after his triumph at the Toronto PDAC meeting had retired to his new villa on the Cayman Islands: David Walsh had retired to his in the Bahamas) was put on trial in Toronto for insider trading. That was the best the Canadians could do as the physical crime of salting drill core had taken place in a foreign jurisdiction. Felderhof’s defense was that he too had been duped and all his actions were made in good faith. Felderhof’s trial lasted for years and, although he was ultimately acquitted, he was reportedly bankrupted by his legal fees. He was still in litigation in 2011. Only the (now conveniently dead) De Guzman is known to have been certainly involved in the fraud. Other participants (and there must have been many) in the biggest mining fraud in history simply disappeared into the barrios of Manila, never named or charged.

The crime took place in the jurisdiction of the Indonesian Government, but in view of the involvement of the President Suharto’s family (and the mysterious Indonesian Air Force helicopter pilot that featured in early press reports, then mentioned no more), it is perhaps not surprising that their investigation was cursory and inconclusive. The de-helicopterisation of de-Gusman remains a mystery.

CONCLUSIONS

During the 1990s, I knew John Felderhof, Mike Novotny and Laurie Whitehouse. They were part of an informal syndicate or network of geologists, assay chemists and general “fixers” who offered services to mining/exploration companies in the fields of target generation, land acquisition, government liaison and ready-made contract geological teams (5). They had long experience in Australia and Indonesia and provided useful services for incoming players to these countries. Novotny- no scientist – was an old Indonesia Hand who spoke fluent Bahasa and knew how to navigate the Byzantine Jakarta bureaucracy. I thought Felderhof and Whitehouse were able, honest and hard-working geologists. After the events at Busang, I have come to believe that gold fever and desire for riches and fame led Felderhof at Busang to suspend oversight and critical judgement and become a dupe for an unscrupulous group of technically clever on-site Filipino fraudsters. But I might be wrong.

Would I have been any smarter had I ever been in a similar situation? I like to think that I would. You may judge that is just my conceit, and there, but for the grace of God…..

MORAL

If something is too good to be true, it most likely is.

Caveat Emptor

The post How to salt a gold claim – Part 2, Karpa Springs and Busang appeared first on Roger Marjoribanks.

Looking through a box of my old field notebooks the other day I came across one which contained a cartoon sketch I had made of an old Queensland prospector and remembered the story behind it.

In 1984, as an employee of a multinational mining company, I was seeking properties with significant potential for gold discovery (wasn’t everybody?). On a 250,000 scale Queensland Government geology map there was a small black dot with the magic symbol Au printed beside it in small letters – an isolated occurrence, far from any known Camp. No further data was recorded. The location was about 200 kilometres inland from the coast, near the base of a Permian sandstone unit. I thought it might be a palaeoplacer[1], and this this excited me because the biggest gold camp in the world (Witwatersrand in South Africa) is a palaeoplacer.

I drove inland to check it out. The area was a rolling open landscape with dry creek beds, isolated stands of eucalypt and dusty unmetalled roads – cattle country, very like that pictured below. First stop was the local station[2] homestead: some ranchers object to strangers driving over their land and can get nasty if you don’t seek their permission first. Their isolation can make them misanthropic, or perhaps the cause and effect is the other way around. As it turned out, this particular cattleman was friendly and glad to see a new face. He invited me in for a welcome cup of tea and a slice of his wife’s home-baked cake.

We talked about the endless drought, the floods of five years before and the price of beef. By the second cup he told me about Scotty Morten[3]. Scotty was his nearest neighbour. It seemed he was the prospector who had discovered the gold many years before and still held a small Mining Lease over it and lived onsite. Scotty had initially exploited the gold himself through a small underground mine before Joint Venturing the Lease to a succession of Exploration companies.  “But” said my new friend, “you gotta watch that old bastard[4], he ran rings round them companies”.

Scotty was a master at claim salting, I was warned. He had several techniques: he would offer to pan a sample from his mine, and never failed to get a strong tail of gold in his dish, but the gold would have dropped from the ash of his roll-your-own cigarette, or fallen from the band of his battered Akubra[5] when he took it off to wipe a sweaty brow. Scotty could even salt a whole rock face with gold: it seems he filled shotgun shells with sand and gold dust and blasted the face, which he would then point out to a geologist as a good place to collect a sample.  One company, I was told, used explosives to expose a new face in his mine to collect a bulk sample for testing, but made the mistake of using fracture provided by Scotty. Easy to add a few pinches of gold dust to a bag of anfo[6].

I camped that night in a nearby dry river bed and looked forward to meeting Scotty the next morning.

He was a short, lean and sinewy, bird-like man of about 70 years, dressed in a faded blue singlet and jeans, an ancient sweat-stained Akubra⁴ on his head. His face, burnt and battered by long outdoor exposure, featured large ears, a nicotine-stained moustache and a pair of surprisingly large and innocent-looking eyes. An ill-rolled cigarette was permanently affixed to his lower lip. A shotgun and rifle leant against the wall in a corner of his shack. Scotty spoke in a slow Queensland drawl. He had a natural courtesy, but was a man of few words, giving the constant impression that he knew more than he said[7].  

I introduced myself and explained my interest. Scotty politely offered to show me around. I could tell that I wasn’t the first company geologist to have driven up to the door of his shack and asked for a tour.

An adit[8] had been driven into the base of a low (50m high) mesa. About 100 meters in, two largish chambers had been hollowed out – a few hundred tonnes of rock having been removed. The rocks were flat-lying, pebbly sandstone and conglomerate, well weathered and oxidised – easily mined with pick and shovel with perhaps a bit of blasting now and then. Piles of “ore” were heaped outside the mine entrance, beside an old rusting crusher and some wooden sluices.  On top of the mesa were signs of previous big-company exploration: several large vertical drill holes with roundels of 30cm diameter diamond drill core scattered on the ground. The biggest core I had ever seen.

I collected six  approximate 10kg samples from underground: some were from places that my host indicated as “high grade”, some from places I selected myself. The rock was friable and easily broken with a pick.  Scotty helped me carry the samples outside where I panned half of each sample in a water trough that my host had set up for this purpose. Four of my six samples yielded a few colours of gold. Scotty looked on, silently contemptuous of my efforts and of my dark-green plastic hi-tech panning dish bought the week before from Prospectors Supplies in Sydney. “Let me have a go there” he said “there’s a technique to panning a good tail of gold, son”. Hat on head, and cigarette in mouth, he produced his own panning dish – a dented and rusty pressed-tin affair – and proceeded to pan each of my sample splits. A good tail of gold appeared in every dish.

Had Scotty contaminated my samples with a few added pinches of alluvial gold? Well, perhaps he had:  although, forewarned, I was watching him closely and could not be sure. On the other hand, I have no doubt that he was a much more accomplished gold panner than I, and his neighbour the cattleman could have been telling an exaggerated story to a (presumed) naïve stranger. And there was another consideration: the hand lens showed the millimetre-sized gold grains had fine leaf-like shapes and a light colour indicating a primary origin and high silver content . Alluvial gold is typically a deep dull butter-yellow (i.e. a high fineness) with smooth rounded shapes. Scotty had told me that he had an alluvial claim down south which he worked in the winter months and I would have expected him to use this material if he had wanted to salt the samples. But then again, perhaps wise to the tricks of geologists (as I thought I was wise to his) he knew enough to salt the mine with gold hard-won from the actual mine?

But, ultimately, it did not really matter. Panning a few samples hacked from a rock face is an indicative test only. At the very least, I considered that my efforts showed the property contained some gold. 

I did not think the deposit was a palaeoplacer, but an epigenetic[9] deposit. That was indicated by the physical nature of the gold as described above, and the presence of pyrite (oxidised) throughout the rock and porphyry intrusions nearby. Not that that affected its economic potential. The host rocks were gold bearing and would have been worth a more detailed look, but I felt that previous explorers had probably done enough to test the potential for a company-sized operation. That is the sort of decision you have to make, using limited knowledge and balancing probabilities – always aware that you might be wrong.

So, I did not try to option the property but learned something of the tricks of the gold salting trade. And I rather liked the old bastard.

CAVEAT EMPTOR.

The post How to salt a gold claim: Part 1, Queensland interlude appeared first on Roger Marjoribanks.

 Let’s explore that idea. 

In prospective areas where outcrop is poor, or that have been subject to intense mineral search over a long period of time (generally known as “mature” exploration areas), the explorationist increasingly has to make use of geophysical and geochemical methods in order to extend the search into areas of shallow cover inaccessible to more traditional prospecting. Some of these geophysical and geochemical methods also allow for rapid regional appraisal of areas where ground access may be difficult ‑ for example rain‑forest terrain or Third World countries with poor infrastructure. 

Geophysical and geochemical techniques typically measure objective characteristics that are possessed by all rocks to some degree and result in the collection of large amounts of geographically referenced digital data. Explorationists undertake two different kinds of survey: those that are aimed at defining regional geology and those that aim to directly locate ore. In some cases there is an overlap between these two types.

 The second type of geophysical/geochemical survey is aimed at measuring unusual or atypical features of rocks that directly reflect, and have close spatial relationships to, economic mineralization. Since ore bodies are in most cases small relative to the earth’s crust, such surveys have to be based on detailed, close-spaced measurements and are generally expensive. Ore targeting surveys would normally be undertaken after a prospect, or at least a prospective belt of limited area, has been defined. The critical step in analysing the results of ore-targeting surveys is to select those measurements that can be considered as “anomalous”. The selected anomalies are then analysed to determine the probable nature, size, position and shape of the causative body as a prelude to a follow-up detailed exploration programme, usually drilling.

 But just what constitutes an “anomalous” value? How do we define an anomaly and how do we recognise it?

 Defining “anomalous” is never easy. If, for example, a level of 20 ppb (parts per billion) gold in a geochemical soil survey is selected as a cut-off number to define anomalism, it would be hard to argue that there is some significant difference between that assay and one of 19 ppb which falls outside the cut-off line. And if 19 is anomalous, then what about 18? And so on. How can one apply cut-off points in what is a continuously graduated series? The same problem applies in the analysis of all numerical data sets of this type.

 Here is another problem. Is the size of the anomaly (the size of the number in a measurement) a measure of its prospectivity?  Bigger is not necessarily better (whether of chemical concentration, magnetism, conductivity, chargeability or whatever). Just consider this: a small number may reflect the effect of a very large source which is a long way from the point at which the measurement was taken. A large number may have come from a relatively small source which just happens to be close to the sample point. And nearness to the sample point is only one of many factors that might enhance or detract from the value of a particular measurement. For example, in geochemical surveys, assay values from samples collected at surface, while they may show the effects of primary bedrock distribution can also be expected to reflect the superimposed effects of surface weathering which can cause enhancement or depletion of critical elements by both chemical and physical processes. In geophysical surveys, measurements of magnetic, electrical or gravity fields are collected remotely. The relationship of fields measured at the instrument head to causative bedrock features is dependent upon interpretation which, however expert, is almost always subjective, qualified and non-unique.

 Real data sets that provide an adequate sampling of the environment seldom possess sharp natural cut-offs: they typically have a continuous or “fuzzy”’ distribution. The science of fuzzy logic describes such systems ‑ everything is true to a degree and black and white are merely special cases in a continuous scale of grey. Fuzzy logic is the way human brains work, but is incompatible with the either/or bivalent logic of the computer. For this reason, present-day computers cannot be programmed to select all significant anomalous numbers from a data set: only a human expert can attempt that with any hope of success. The role of computer processing of geochemical and geophysical data is to present it in such a way as facilitates the human judgement process.

 This problem of defining anomalous values can often be partly overcome by looking for natural groupings and patterns within the data set and making the reasonable assumption that such groupings reflect the operation of fundamental geological factors, including mineralization processes. Sometimes the natural breaks like this are apparent by simply eyeballing a print‑out of the raw data. More subtle cut‑offs in the data or breaks in their trends are often definable by graphical means or by statistical analysis. Many commercially available software programs are available which can highlight these features. These programs are powerful and useful tools that nowadays form an essential part of most analyses of geophysical and geochemical surveys. However, in my experience, if the basic signals cannot be found by eyeballing the data (once basic presentation as maps, sections or tables is carried out), then it is usually a vain hope to expect that statistical processing will make things much clearer.

 In spite of such naturally occurring patterns, if a data set represents an adequate sampling of an area, then any realistic first stage analysis will almost always divide it into three basic groups.

 In the first group – almost invariably the largest one ‑ are those measurements that are definitely not anomalous. These are known as background values and they can be safely ignored, at least as far as the results of that survey are concerned. In the second group ‑ probably a rather small one, if it exists at all ‑ are those measurements that are so different from the background that they cannot be ignored and demand to be explained in some way. Such numbers are so outside the mean for that domain that they will generally be confidently labelled as anomalous. The third group is a widely defined category that can be given the distinctly “fuzzy” label of “possibles”. It comprises all the remaining measurements that do not fit into the first two categories. They are those numbers that are slightly above, or at the upper limit of, background values but could be readily explained by non-mineralizing processes. They could, however, equally well be subtle expressions of ore. Since there will probably be insufficient time and money to exhaustively test all of the measurements of this third “possibles” group, a decision on which ones to follow up must be made based on knowledge gained from outside of that particular survey. This may be results from other types of geophysical or geochemical survey or knowledge of the geology and mineralization of the area. The input of an experienced explorationist is required at this point and no software program can make the decision for her.

If your geochemical anomaly is as distinctive as this one, then there is little problem.  Few anomalies are as distinct. Image of colour-contoured gold in soils (ppb)  Separator Fault, Carlin Trend Nevada. Image from Altan Nevada Minerals Ltd : www.altnav.com

 This is the main reason why no exploration technique should be conducted in isolation. The most powerful exploration programme is the one that combines data gathered from several different appropriate geological, geophysical and geochemical surveys. Ultimately, once all processing and presentation steps have been performed, the key to interpreting the results of geophysical and geochemical surveys is an understanding of the geology and ore forming processes of the area.  

This takes judgement and your judgement could be wrong. But having made your decision, go back and test your “anomalies” with all the further tests that time and money allow. If you can learn from each failure,  knowledge and understanding will increase.

The post What is an Anomaly and How do you Recognise It? appeared first on Roger Marjoribanks.

Explorationists seek to find new ore bodies. Ore bodies that reach or approach the surface are the easiest to find, but the world is big, ore bodies are small and “easiest” is a relative term: the really easy ones, we can be reasonably certain, were found a long time ago.  

But explorers are aided in their search by two factors:

• Although metallic ore bodies may be small, they are the result of large scale and long-continued earth processes (faulting, fluid movement, sedimentation etc..) that almost certainly have left their mark through a volume of rock that is larger than the associated metal concentration that is of interest to miners.
• Metals are mobile in the near surface environment as a result of mechanical and chemical weathering. These processes can distribute a halo of low metal concentration around or adjacent to the primary concentration.

Because of these two factors, ore bodies at or near surface typically have a large chemical “footprint” that can provide a pathway to ore discovery. The art of geochemistry is to take samples from the surface environment and assay them for the presence of elements that might reveal that footprint and, hopefully, a vector to the metal concentration. The range of media which geochemists can sample is wide and wonderful: from in-situ soils to alluvial silt; regoliths of all kinds; coarse pebble floaters to panned heavy mineral concentrate; calcrete and ferricrete; leaf litter and termite mounds. Orientation surveys are needed to decide the most suitable of these techniques.

But if there is fresh bedrock at surface – either as natural outcrop or exposed in artificial openings such as trenches, or mines – then sampling the actual rock itself is always the most direct route to ore.

Three main techniques are used to collect the sample: chip sampling, chip-channel sampling and sawn-channel sampling.

CHIP SAMPLING

This technique is used by the prospector who does not have much time to spend on the outcrop. He or she simply seeks to determine if there are any interesting metal values in the exposed rocks.  The sample is generally not intended to be representative of all the exposed rocks in the area. Rather the geologist attempts to high-grade her sample, deliberately biasing it by including only these chips that appear to have the best chance of containing the element sought. Thus if the target is gold, quartz fragments will figure prominently amongst the chips collected. If the target is base metal (or if gold is associated with base metal, as it often is) then the sample will be over-weighted with fragments showing evidence of sulphide content (i.e. gossanous).  The idea is to maximise the chance of finding something interesting, even although mineralised rocks might constitute a minor part of the exposure.  If the assays for the sample show elevated numbers – even if only in trace amounts – the geologist relies on returning to the outcrop to conduct a more detailed, representative sampling using one of the other sampling methods detailed below.

The chip sample consists of a number of small rock fragments collected over a limited area – perhaps 10 – 50 square meters.  Over this area, 20-30 small chips are broken off the outcrop with a geology hammer and composited into one sample weighing around 3kg. The sample is collected in a coarse cotton sample sack which can be sealed by tying at the top (see figure). A fabric bag is used because a plastic bag would likely be pierced by any sharp edges amongst the rock chips. The sample bag is labelled with an identifying number written onto the outside of the bag with a permanent marker pen.  That number corresponds to the number in a pre-printed sample book on which details of the sample (GPS coordinates, type of sample, rock description etc..) can be recorded. A numbered tear-off tag from the sample book is placed with the rock chips inside the sack. It is also good practice to mark on the ground the centre of the sampling site by means of plastic flagging tape and/or a metal tag nailed to a tree.  These ground markers should also bear the sample number.

 Cloth sample bags with draw-string tops (top left diagram) are used to collect rock chip samples. A simple wire frame (top right) can be made to hold open the top of the sample bag so that it can be used one-handed as a catcher for chips hammered off the outcrop. A sample book (bottom right) with pre-printed numbers should be used to allocate the sample number and record details of the sample such as location coordinates, type of sample, lithology etc… A duplicate numbered tag can torn off and added to the sample in the bag. Sampling tools (bottom right) consist of a geologist’s hammer, chisel and eye protection.

Always wear safety goggles when breaking off rock samples with a hammer

A chip-channel sample is taken when a mineralised, or potentially-mineralised, zone can be identified in the exposed rock.  The sample attempts to define the approximate width and grade of the zone and the rocks immediately adjacent to it. Although the sample will be much more accurate and representative than the high-graded chip sample described above, it still provides only an approximate measure of the true width and grade of the zone. No one should ever use the assay results from a chip channel sample as the basis for a company announcement or prospectus (although this has been done – just Google “rock chip sample” for an egregious list of examples). No one should ever use a chip sample samples as the input to an ore reserve calculation (this has been done too).  But with these reservations, positive results from chip-channel sampling provide the confidence to proceed to the next exploration stage: drill testing.

The sample consists of a number of small contiguous rock chips broken from the rock along an approximate straight line[1], or channel, across the zone of interest. The chips are composited into one sample (3-5kg) representing the width of the mineralised zone.  However composited samples should not normally cover more than 1-2 meter of channel. If the zone is wider than that, a number of adjacent samples will be needed.  Extra channel samples should be taken for the country rock immediately adjacent both sides of the zone of interest. Where possible, the boundaries of individual channel samples should correspond to lithology contacts.

Rock chips are collected with a geologist’s hammer and chisel (warning, wear eye protection, see above!). For very hard rocks the use of a jack hammer has been found useful (see figure below). For field use, small electric jack hammers that can be powered by a portable generator are available. 

 All chips taken along the line of the channel should be approximately of the same size; over breaks need to be split separately so that only the required size portion goes into the sample bag.  Care needs to be taken that all rocks along the channel are sampled equally[2].  Care needs to be taken NOT to fill the sample bag with soft easily-broken material (all too easy to do) and NOT  to under-sample hard rocks[3] that are difficult to break free.

Normally a number of separate parallel channels across the mineralised zone are taken: the more the better depending on the extent of mineralisation and the time available. The chip-channels should be oriented at right angles to the boundaries of the zone of interest (assuming it is tabular). If the zone is flat-lying (a vein, or array of veins, for example) and exposed on a vertical face (the wall of a mine opening) the channel samples must be vertical. If the zone is steep dipping, then horizontal channels across it are indicated. 

The samples are bagged and labelled as described for the chip samples in the section above.

A field assistant is collecting a chip-channel sample from a trench wall. The sampler is using a small electric jack-hammer powered by a portable generator. The broken rock falls onto a tarpaulin laid along the trench floor. The same technique could be used for chip-channel sampling any hard rock exposure in the field or in a mine. ( Note the sampler wears goggles and gloves, but for even better safety, he would have been advised to wear more substantial clothing.)

Splitting a sample for assay from an even row of small rock fragments on the ground. The rock chips lie on a tarpaulin: a halved length of 100mm poly pipe is laid along the row and rocks and pipe are rolled together in the tarpaulin. Rock chips collected in the pipe constitute a split of the larger sample and can be easily slid into a sample bag.

SAWN-ROCK CHANNEL SAMPLING

This is the most accurate, objective and reliable way of determining the width and grade of outcropping mineralisation. It is also the slowest and physically hardest way to collect a rock sample. Such samples will normally be collected in a mine environment (or exploration trenches and costeans) were continuous exposure of fresh rock is exposed on accessible, approximately-flat, faces.  Results from carefully collected sawn-rock channel samples have the same status as assays obtained from diamond core drilling, and can be used as an input to ore reserve calculations or the basis for company public announcements.

As with chip-channel sampling, the sample is collected from a continuous channel across the width of the mineralised zone.  A rock saw (see figure below)[4] is used to cut the channel and free the sample which is then collected into a sample bag. Mineralisation widths over 1 meter will require several adjacent samples.  Once again, immediate wall rocks to the mineralisation will normally also be sampled to confirm the limits to ore.  In soft rocks such as sedimentary lithologies, a skilled operator can expect to cut a channel of up to 10m in one hour. In very hard rocks such as quartz an hour might only suffice for 1-2 meters.

An electric powered rock saw (this is a Hitachi model, sold as a “concrete saw”) with diamond impregnated blade capable of sawing at least 100mm into hard rock.

There are two methods of cutting the sample. In Method 1 (left-hand figure, below), two angled cuts are made which intersect in a “V” thus freeing a wedge-shaped sample (see figure). This method will yield a sample of around 5 kg for each meter of advance and is the quickest method. However, in practice, it is quite difficult to make cuts oriented at 45° to the operator’s body, and correctly angling two cuts so as to intersect is not always possible,  necessitating the frequent use of a chisel to free the sample. 

 A better method – Method 2 (right-hand figure, below) – is to make two parallel cuts about 100cm apart and then, in a separate operation,  use a chisel to break the sample free from between the cuts. This method will normally yield 8-10 kg of sample for each meter advance. 

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