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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 ...

Expanding Norway’s mineral potential

by Graham Chandler on March 27, 2014 applied

Inversion of Airborne Gravity Gradient data helped to enhance earth models and interpretation of Norway’s Karasjok Greenstone Belt shown above.

In the early 1980s, the Geological Survey of Norway (NGU) conducted an exploration program in the northern county of Finnmark, a highly prospective greenfield area which encompasses the Karasjok Greenstone Belt. It was the first aeromagnetic and gravity survey of the area and served to establish a preliminary description of its lithology, stratigraphy and mineralizations.

In the ensuing decades, however, it became necessary to revise the data as it was no longer providing adequate mineralization information. For example, many of the original gravity points were acquired on the ground using snowmobile transportation.

“The original gravity anomaly is dominated by a regional field and so it was difficult to link local anomalies to the local geology,” explains Dr. Jörg Ebbing of the NGU. He adds that those efforts were accompanied by petrophysical sampling even though large parts of the areas are covered by overburden. The sampling showed that the amphibolites and komatiites of the greenstone belt have a higher density and magnetization than the surrounding gneiss and migmatite complexes.

The Karasjok greenstone belt is a continuation/part of the Central Lapland greenstone belts. In Finland, high-resolution gravity data and seismic are available, and the results of their interpretation by the Geological Survey of Finland (GTK) showed the need to improve the geophysical data base in Norway on the way to increasing the geological understanding of the whole northern Fennoscandian Shield.

Better coverage needed

Improved datasets were thus in order. “In recent years, Store Norsk Gull [a Norwegian exploration company] has identified Finnmark as the most prospective greenfield area in Norway,” says Ebbing, adding that the company’s efforts were focused on the Karasjok Greenstone Belt. Further geochemical and geological mapping, combined with fixed-wing aeromagnetics and drilling, confirmed the existence of copper and gold mineralization. Apart from these limited efforts, no systematic remapping of the area was done; nor was anything done specifically to test the greenstone belt’s extension at depth. Says Ebbing: “Depth extents to mid-crustal or even lower-crustal level are suggested for other greenstone belts, [such as] the Barberton in South Africa, the Pilbara Craton in Australia, and the Kuhmo greenstone belt of Finland.”

Karasjok Greenstone Belt data program

[Click to enlarge]

Regional field sources. At left: Residual IGRF corrected RTP, upward continued 1km. At right: Gzz Bouguer, upward continued 1km with >0 RTP contours.

[Click to enlarge]

Unconstrained AGG density model (left) compared with the IRI focused AGG density model (right), sliced to northern portion of the survey area. Notice improved amplitude recovery and sharpening of thrust fault contact. Colour legend density contrast range for both models.

[Click to enlarge]

Comparison of magnetization source depth. Looking due East. Top is unconstrained: highly magnetized sources >0.1 normalized units, source depths reach <2km. Bottom is constrained by high density contrasts: highly magnetized sources >0.1 normalized units, source depths reach <4km.

So in 2011, NGU launched a program called Mapping of Mineral Resources in Northern Norway (MINN). The program collects and assembles geophysical, geological and geochemical background data so that mineral resources could be mapped and studied. (See the data on

As part of this program, aeromagnetic and gravity gradient data were collected in the area of the Karasjok Greenstone Belt. These efforts, Ebbing notes, were co-funded by Store Norske Gull AS. Fugro Airborne Surveys (now CGG) flew the program, and the gradient data were measured using the FALCON Airborne Gravity Gradiometer (AGG). A combined total of 3,291 line-kilometres of data were flown with an average drape height of 160 metres with 200 metre in-line and 5 km tie-line spacing.

The particular combination of data types – magnetic and AGG -- was significant. “The combined acquisition of gravity gradient and magnetic data has become increasingly popular for industrial applications,” says Ebbing, adding that both data sets are highly sensitive to near-surface structures. “The greenstone belt of the Karasjok area was of interest for acquiring this novel type of data set as mineral deposits often are found in connection with them.”

Significant, too, was NGU’s choice of 3D inversion techniques in Geosoft VOXI Earth Modelling to interpret the data. “The VOXI inversion tools offer a straightforward inversion for gravity gradients, which is not yet a standard in other software packages,” Ebbing says. “Greenstone belts in general are an ideal target for gravity and/or magnetic studies as they often feature higher density and magnetization than the surrounding bedrock.” “From petrophysical studies in Finnmark we could expect that the komatiite components of the belt are to be characterized by positive density contrasts [greater than 50-250 kg/m3] and higher magnetization than the surrounding bedrock,” he says, adding that an advantage of gravity gradients is that their characteristics are comparable with magnetic field behaviour. “Gravity gradients, in contrast to conventional gravity anomalies, are more sensitive to the upper crustal structures.”

This application of VOXI Earth Modelling was done with enhancements: for the first time, improvements in the prismatic approximation of surfaces and Iterative Reweighting Inversion (IRI) methods for reverse-modelling of gravity gradient data were used. This was followed by a co-modelling exercise using the combined AGG and aeromagnetic data to interpret the greenstone belt in terms of its petrophysical properties.

Ebbing endorses the approach: “While it is challenging to estimate the depth from gravity and magnetic data alone, the inversion can give a minimum/maximum bound of depth extension within the parameter range provided. Furthermore, the sequential inversion of the density and magnetization allowed us to identify areas with different characteristics. As an example, we expected the dominant high magnetization regions to coincide with the dense mafic units to be identified as the greenstone belt. From the two high-density regions identified in the upper to mid-crust, one shows such a characteristic.” He adds that the western branch is identified by a slightly lower density contrast, “but with a significantly lower contrast in magnetization (lower susceptibility contrasts), which indicates a more granitic, felsic domain within the belt.”

The results were revealing. The tilt derivative of the gravity gradients shows a structure that extends from northwest to southeast and then swings into a northeast-southwest trend. “This anomaly,” Ebbing notes, “most likely reflects the greenstone belt, which underlies the geology observed at the surface and cannot as easily be identified from the gravity anomaly, not even from the magnetic anomaly map.”

Utility of new inversion methods

Ebbing believes the project was a vast improvement over older methods of inversion. The main improvement is that the measured AGG data can be directly used for the inversion. Other software packages still require that the vertical gravity component be used, which requires calculation of the conformed gravity field.

The second improvement is that the AGG-derived density structure can be used as an input into the magnetic vector inversion and as a constraint during the IRI.  This helps to force some of the magnetization to greater source depths than those created by running an inversion on the magnetics alone.

The depth aspect was significant, Ebbing says. “The unconstrained inversion of magnetic data would lead to near-surface distribution of the magnetic sources with a maximum source depth of less than two kilometres. The use of the AGG-derived density structure as input led to a distribution to four kilometres depth and within a reasonable range for magnetic susceptibility.”

The inversion has helped to outline the Karasjok Greenstone Belt and the NGU is prepared to evaluate different concepts as to its structure and evolution. The next step is to link the inversion results with a geological model in 3D.

Says Ebbing: “This will allow us to redefine the geological map and link the small-scale features like zones of mineralization to the semi-regional subsurface model. The Karasjok Greenstone Belt can serve as a case example for the use of geological and geophysical techniques both for mineral exploration and geology in 3D. For this next step, the integration of all available information through GIS and within the 3D model is vital.”

Efforts are also underway  to  make the MINN project data more accessible to explorers. All the geophysical data from NGU, including the MINN project, will be published and distributed through a Geosoft DAP Server from early 2014.  

Our current database system is outdated and is limited to display of existing data but does not provide any download facilities,” says Ebbing. “The new web solution, powered by DAP, will be modern and more easily accessible, enabling all clients to download the data of interest for a specific area.”

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