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Earth Explorer is an online source of news, expertise and applied knowledge for resource explorers and earth scientists. Sponsored by Geosoft.


News & Views

News Archive

August 17, 2016

New IGS Xplore prospectivity maps for Botswana

International Geoscience Services have released a series of base metal prospectivity maps for the Ngamiland District of northwestern Botswana using free geodata available on the recently-launched Botswana Geoscience Portal, hosted by Geosoft. The maps identify favorable areas for copper, zinc and lead mineralization using geological, geochemical and geophysical datasets downloaded directly from the portal.

August 11, 2016

NexGen Makes New High Grade Discovery

NexGen Energy reported the discovery of a new high grade zone of mineralization 4.7 km northeast of the Arrow Deposit as part of an on-going summer drilling program on its 100% owned, Rook I property, Athabasca Basin, Saskatchewan...

August 10, 2016

Rampion UXO Disposal to Take Place This Week

E.ON has confirmed that the two unexploded devices, detected along the Rampion offshore cable route will be safely disposed this week following the consultation with the Marine Management Organisation...

August 9, 2016

Diamonds In The Rough: E&Ps Find New Reserves In Mature Basins

The oil industry’s history demonstrates clearly that new plays and prospects have long been found in mature basins that were thought to be well on the way to being squeezed dry. Through the acquisition of new data, developing new concepts and coming up with fresh interpretations, long-producing basins around the world from the North Sea to Malaysia have continued to reveal new riches...

August 8, 2016

Northern Shield Identifies High Quality VTEM Targets at Séquoi

Northern Shield Resources announced the results of the interpretation and modelling of the VTEM survey from the Séquoi Property in the Labrador Trough of Quebec . Séquoi is owned 100% by Northern Shield and is being explored for Noril'sk style Ni-Cu-PGE massive sulphides. After geophysical modelling and interpretation of the VTEM data from Séquoi, six VTEM anomalies of significant interest have been identified...

August 3, 2016

Rio Tinto tailors big data drive to copper

Rio Tinto will put the weight of an exploration big data push and its newly-formed Growth and Innovation group behind its desire to identify a "tier 1" copper asset. Speaking at the annual Diggers & Dealers conference in Kalgoorlie, Growth and Innovation group executive Stephen McIntosh said Australia was "overdue for a tier 1" mineral discovery of any type...

August 1, 2016

Tetra Tech Awarded $200 Million Navy CLEAN Contract

Tetra Tech announced that it has been awarded a $200 million, single-award contract by Naval Facilities Engineering Command (NAVFAC) Atlantic. Through the Comprehensive Long-term Environmental Action Navy (CLEAN) contract, Tetra Tech will provide environmental engineering support services to installations within the NAVFAC Atlantic Area of Responsibility...

May 3, 2016

NATO Science for Peace and Security (SPS), MODUM Partners announce "Young Scientist Summer School on Sea Dumped Chemical Weapons"

This international project cooperates closely with CHEMSEA (Search and Assessment of Chemical Weapons) Project for and sharing and knowledge transfer...

April 12, 2016

Monday mad rush for gold stocks

Renewed optimism about the outlook for gold saw investors pile back into gold stocks, pushing many stock to 52-week highs in heavy volumes...

April 11, 2016

Medgold Resources: Continues to Expand the Boticas Gold Project, Portugal; Proposes $200,000 Private Placement

Medgold Resources is pleased to announce new assay results from contiguous rock-chip sampling from the Limarinho South zone at its Boticas gold project in Portugal, which include a highlight of 6.0m @ 5.7 g/t Au...

April 8, 2016

De-carbonizing our energy sector

Nuclear energy currently provides around 11 percent of the world's electricity. China, the European Union, the United States, India, Russia, South Korea, and other nations’ have major existing fleets...

April 1, 2016

Follow-Up Drilling Results Indicate Wide Gold Zones at Hendricks Gold Discovery

Gascoyne Resources Limited announced that it has received the final assay results from the 10,000 metre aircore exploration drilling programme...

March 26, 2016

The Oil Market Is Finally Hitting Its Breaking Point

After a significant reduction in investments over the past two years, oil companies can no longer overcome the production declines from legacy wells...

March 15, 2016

N-Sea Expands into the French Offshore Wind Industry

Subsea IMR provider, N-Sea, has signed a letter of intent with CERES Recherches & Expertise Sous-Marine and TechSub Industrie Environement, to provide subsea survey, installation and remediation services to the French offshore wind industry...

March 9, 2016

PDAC 2016 Convention Exceeds 22,000 Attendees

Optimism and opportunity abounded at the PDAC 2016 Convention of The Prospectors & Developers Association of Canada in spite of recent industry challenges...

March 3, 2016

6 Alpha Launches EOD Contracting Division

6 Alpha Associates, a specialist risk consultancy practice, with expertise in the assessment and management of unexploded ordnance, has launched a dedicated explosive ordnance disposal division...

February 10, 2016

Cameco's new uranium discovery revealed

Canada's top uranium producer has a significant new discovery nearby to one of its largest existing mines...

February 9, 2016

NexGen Drills Most Intense Mineralization to Date at Arrow

NexGen announces further results from its on-going six rig 30,000 m winter 2016 drill program on its 100% owned Rook I Property in the Athabasca Basin, Saskatchewan...

February 9, 2016

Rio Tinto scales up its big data ambitions

Rio Tinto is opening its "vast troves" of exploration data to junior explorers in the hopes they will help sift for opportunities and supply ideas and labour...

February 8, 2016

Online portal improves access to geoscience data from Africa

The Botswana Geoscience Institute is launching a Geoscience Portal...

February 8, 2016

5 Best Minerals & Fossils To Buy With Your IRS Tax Refund

You just got your IRS tax refund and now you're presented with some cash to go out and buy one of a kind minerals and fossils from your local...

February 5, 2016

World's largest offshore windfarm to be built off Yorkshire coast

Dong Energy makes final investment decision on 1.2-gigawatt project that will power more than a million UK homes...

February 2, 2016

World's top 10 rookie gold mines

These high-grade mines will soon start competing with gold mining's industry leaders ...

January 25, 2016

Exxon Mobil Corp's defiant outlook predicts Canadian and Venezuelan oilsands output will 'quadruple' over next 24 years

In sharp contrast to the grim medium-term prognosis for the Canadian oilsands, Exxon Mobil Corp. is predicting sunnier times for bitumen in the decades ahead...

January 23, 2016

Magnetic Survey Keeps Cost Down

At a contaminated furniture factory site in North Carolina, a reconnaissance magnetic survey was conducted toward the end of a Phase 2 investigation ...

Hunting for a lost ship

Archaeologists use geophysics to focus their search for a historically important Dutch slave ship wrecked off the Cape in 1766

By Graham Chandler

At the southern tip of the African continent about 175 kilometres southeast of Cape Town lies a wetland estuary system which has been of considerable interest to BirdLife International for preserving the breeding grounds of the endangered Damara Tern. But this complex system, the southernmost estuary in Africa, is also of considerable interest to archaeologists and historians, especially near the mouth of its main river, the Heuningnes.

Two hundred and forty-three years ago, in March 1766, the 450-ton Dutch slave ship Meermin (“Mermaid”) ran aground off Cape Agulhas near here after her cargo of 140 Madagascan slaves revolted in a valiant bid for freedom. A series of events culminating in an unsuccessful attempt to man the Dutch East India Company (VOC) vessel resulted in her drifting with no anchor and hitting a sandbank. Authorities recaptured most of the slaves, but the master shipwright sent from Cape Town to inspect the wreck declared the Meermin a write-off, citing extensive structural damage. Already the shifting sands had begun to build a sandbank on the vessel’s stern side. Any useful goods were removed, much of them auctioned right on the beach and she was left to the whims of the capricious shifting sands.

The Meermin has captured the attention of historians. She was a hoeker, a type of ship with 14th century roots. The name is derived from the ships’ design function: using baited hooks on lines to catch cod and haddock. The first hoekers had just one or two masts, but in the 17th century the VOC built several as cargo carriers with three masts—the Meermin was one of these rare models.

Popular with the VOC for a short period from about 1665 to 1670, the hoekers’ construction allowed it to withstand the warping effects of the eastern waters better than the ‘fluits’ – the ship type of choice until then. “The VOC stopped using hoekers towards the end of the 17th century,” explains Jaco Boshoff, maritime archaeologist at Iziko Museums of Cape Town. “But they constructed some periodically mainly for use at their colonies as multi-purpose vessels.” He says four hoekers were constructed in the second half of the 18th century for the Cape service. “One needs to add that vessels stationed at the Cape were used for multiple tasks like transport of timber from Table Bay to False Bay, the provisioning of the various company outposts and then of course for obtaining slaves especially from Madagascar,” he says. “In fact the request for a new vessel from the government at the Cape in 1759 to their masters in Holland mentions the slave trade with Madagascar as one of the main functions for the new vessel.” 

Boshoff says the historical significance of the Meermin grounding event and what it means for a South Africa in transition had not been recognized or received any attention until recently. So about five years ago, the Meermin Project was launched by Iziko Museums of Cape Town. “The project is important in the context of a changing South Africa and what meaning it should have for maritime archaeology for the country,” he says.

He has his work cut out for him. “The area where the wreck of the Meermin is most likely to be found is in the mouth of the Heuningnes estuary as it is the only river mouth in the bay,” he says. The problem he faces is that the estuary has changed massively since the time of the grounding, including some due to relatively recent man-made changes. “In 1939 the then Department of Forestry started with a dune reclamation project in the Heuningnes estuary area,” he explains. “It was at the behest of the local farmers as the river mouth used to close up periodically, flooding the hinterland and destroying crops and grazing areas.” The region had already been known for its dynamic sand movement patterns, but with the reclamation project the river mouth became restricted to one location in order to prevent it from silting up. “It’s a different environment from the one of 1766,” he says.

This creates several problems for archaeologists searching for the wreck. Complicating the search is the fact that there have been several wrecks historically recorded in the area and none has an accurately described location. Moreover, the river mouth has closed up several times in the past and reopened at different locations. “Its historical position varied from two kilometres to the west to 1.6 kilometres to the east of its current position,” says Boshoff. “Nowadays it is restricted to an area of about 500 metres.”

A marine magnetometer survey to locate the wrecks was first attempted but proved of limited value: very shallow waters near the coast preclude small watercraft from approaching within 200 metres of shore. An airborne magnetometer survey became the tool of choice. Flying on board a Cessna navigated by SATLOC GPS, with a Geometrics 823 Cesium vapour magnetometer having an instrument resolution of 0.001 nT and a total noise envelope on collected airborne data not exceeding 0.5 nT sampled at ten times a second, data were collected. “A SATLOC real-time differential GPS recording once a second to an accuracy of less than three metres in X and Y and five metres in Z was utilized,” explains Boshoff. Flying at 130 knots at a height of 30 metres above ground, lines were spaced 40 metres apart while data were digitally recorded. He says a base station for differential correction wasn’t needed. “It records its position relative to the WGS84 [World Geodetic System 1984] Spheroid. This can be converted, if required, to other popular co-ordinate systems.” At the start and end of each flight, the pilot flew over a known point to verify the GPS position, which was plotted out after each day’s flying.

The airborne survey delivered 22 potential targets, most of them on the beach. As the data at first were provided on contour maps only, “I contacted Anglo American Corporation South Africa and they analyzed the data with Geosoft Oasis montaj,” says Boshoff. “What I liked about it was firstly the fact that I could download a viewer without purchasing the program, enabling me to read the processed data. As an archaeologist and not a geophysicist it was a learning curve made easier by montaj magnetic intensity maps.” Through the analysis done in Geosoft they were able to eliminate several of the targets as unlikely or of natural magnetism. 

For the layman, Boshoff explains how magnetic anomalies can arise from wooden ships. “Iron fastenings were used extensively in wooden ships,” he says. “This combined with the possible presence of anchors and cannon give fairly good signatures.” He says even when objects like cannon and anchors are not present one can still pick up the fastenings that seemed to give a good signature as an assemblage rather than individual objects.

The data thus processed from the airborne survey revealed that 11 of the 22 targets—six on land and five underwater—had potential to be the Meermin. The six land targets were further investigated using a highly sensitive handheld magnetometer to get a more accurate picture of each wreck. “We used a Geometrics G-858 Walkmag with Trimble GPS and post processing of the positions to get it to differential,” says Boshoff. Line spacings depended on the size of the target but were typically two metres over each target. Again, Oasis montaj was used to process these data. “What the Geosoft gradient maps showed us was phenomenal,” he enthuses. “In one case we had a longitudinal anomaly that turned out to be a ship’s keel.” Signatures were incredibly accurate he says. They used the gradient maps to decide where to excavate, “which was no small matter as most of the wrecks were under three to four metres of sand.”

So the next step was to determine the depth of the sand deposit over the targets. This was done using a water probe system whereby seawater was pumped through a four metre long steel pipe. “The sand depth on most sites was found to be between three and four metres,” says Boshoff. “This presented a serious difficulty as shoring up an excavation is dangerous and not feasible in a wet sand environment. One has to keep in mind that these sites can only be accessed during spring low tide. Your window of operation is therefore limited to a maximum of three to four hours.” This was clearly not doable so a backhoe was brought in. There was little chance of damaging the wrecks. “As we knew how deep the deposit on any given site was, it was relatively easy to control the action of the backhoe,” explains Boshoff.

It’s a measure of the signature accuracy from Geosoft that, using the backhoe, all six targets revealed wreck assemblages. None was proved to be the Meermin but all were previously unknown wrecks, ranging in date from late 19th century to possibly late 18th century, judging from construction details.

How did they know none of the wrecks was the Meermin?“We are fortunate that a ship’s draft for the Meermin exists in the collection of the Netherlands Maritime Museum in Amsterdam,” says Boshoff. “This draft is one of the main tools for identifying the wreck of the Meermin as we can use the construction details and compare them with the wreckages found.” Another strategy they use is analyzing the wood, as they know what types of timber the Dutch used in their ship construction. For example, “most of the wrecks found so far have been mainly pine construction. This is evident in all the construction details sampled including outer hull planking, frames, knees and keelsons,” he says. “If a wreck is predominantly pine it rules that wreck out as being the Meermin. Only two wreck assemblages have any evidence of oak, but unfortunately so far, they do not measure up as the structures do not fit the measurements on the draft.”   

There’s still much work to be done on these new finds. “We have not quite established the identity of the wrecks, bar one that was indicated on an old chart,” says Boshoff. “One is potentially very significant as it could possibly be that of another slave ship that wrecked in the area in 1794.” He says further analysis such as DNA and dendrochronology [tree ring dating] might prove or disprove that assumption. However, as with most archaeological projects, more funding would be needed to complete these tests.

With six of the 11 promising targets excavated, there now remain the five underwater sites to investigate and narrow the search for the Meermin. For these, Boshoff says they’d like first to do an airborne gradiometer survey to help with more accurate positioning and higher target resolution. The finer resolution will be more important for the underwater sites than were the land sites, as they hope to use a diver operated magnetometer to run across them.

As the potential sites are ticked off, excitement grows. “We hope to do the gradiometer survey at the beginning of 2010 and a follow up field survey towards the end or middle of 2010 as funds, weather and other external factors allow,” says Boshoff.