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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

November 30, 2016

LIGO Resumes Search for Gravitational Waves

After a series of upgrades, the twin detectors of LIGO, the Laser Interferometer Gravitational-wave Observatory, have turned back on and resumed their search for ripples in the fabric of space and time known as gravitational waves. LIGO transitioned from their engineering test runs to full science observations at 8 a.m. Pacific Standard Time on November 30...

November 9, 2016

International Volcano Scientists Unite

For the first time, the United States will host the international Volcano Observatory Best Practices workshop, previously held only in Italy. The workshop will take place this month in Vancouver, Washington. It is designed specifically for volcano observatories around the world and their staff to exchange ideas and best practices with each other...

October 4, 2016

USGS Assesses Mineral Potential for Sagebrush Habitats in Six Western States

USGS has completed a comprehensive assessment and inventory of potential mineral resources covering approximately 10 million acres of Federal and adjacent lands in Idaho, Montana, Nevada, Oregon, Utah and Wyoming...

October 3, 2016

Uganda Targets Up to U.S.$100 Million for Mineral Exploration

Uganda is well endowed with mineral resources and, like many naturally-gifted African countries, is becoming keen on ensuring that these resources play a transformative role in its long-term structural transformation dream - the Vision 2040...

September 9, 2016

Small-Scale Fishers Get A Big Boost With First-Of-Its Kind Impact Investment Fund

Conservation organization Rare announces the Meloy Fund for Small-Scale Fisheries at Our Ocean Conference. The Global Environment Facility, one of the largest funders of conservation worldwide, will be investing $6 million into the fund...

September 1, 2016

Scientists take to the skies to track West African pollution

Scientists operating research aircraft over West Africa have detected organic materials in the atmosphere over a number of urban areas, contributing to concerns of the rise in pollution across the region...

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...

Inversion of magnetic field data provides fresh insights from the Andes to the Arctic

by Virginia Heffernan on February 18, 2015 applied

Magnetization Vector Inversion (MVI) is a modern technique which is gaining acceptance as an effective tool for subsurface exploration in areas where magnetization does not necessarily run parallel to the earth’s magnetic field, a more common scenario than geoscientists have traditionally appreciated.

Magnetization Vector Inversion has provided fresh insights on three blind greenfield exploration projects in Finland, South Australia and northern Chile. Shown above field work in Finland.

The global applicability of the technique to target delineation was demonstrated by Michael Webb, principal of Perth-based Blue Sky Geoscience at a recent ASEG Geophysical Inversion workshop, where he, in collaboration with Rob Ellis, Principal Earth Modelling Scientist with Geosoft, presented inversion results from magnetic surveys on three blind greenfield exploration projects operated by Anglo American: a Cu-Ni-PGE project in Finland; IOCG and mafic intrusive Ni-Cu targets near Cooper Pedy in South Australia; and a copper porphyry project in northern Chile.

MVI, a feature of Geosoft’s VOXI Earth Modelling, provided useful insights for target delineation on all three projects. Unlike susceptibility inversion, the technique allows for magnetization effects that are not related to induced magnetism. These include magnetic remanence, self demagnetization and magnetic anisotropy resulting from geological processes such as local tectonics and alteration. As a result, MVI often provides a more reliable picture of subsurface geology.

MORE: Choosing the right magnetic field inversion method for your geological situation

Magnetic ignimbrite cover in Chile

The copper porphyry project lies under cover along the Domeyco fault system in northern Chile, home to some of the largest copper porphyry deposits in the world, including Escondida and Collahausi. This low magnetic latitude project has a relatively flat magnetic field but the prospective rocks are covered by a weakly magnetic ignimbrite. To complicate matters further, gullies (quebradas) dissect the ignimbrite and correlate with the linear magnetic highs outlined by the draped helimag survey flown over the area.

Video of magnetic susceptibility and magnetization vector inversions, conducted on a copper porphyry project in northern Chile.

In fact, the quebrada response dominates the TMI image making interpretation challenging. One approach in this situation is to compute the response from the quebradas using VOXI with its Cartesian Cut Cell method which provides a highly accurate TMI terrain response.  Following this approach, Webb found that the short wavelength magnetic anomalies associated with the topography could be explained using a dissected surface layer of constant susceptibility. Webb then subtracted the results of the forward model from the observed data to generate residual data for both MVI and susceptibility inversions.  The two methods gave very different outcomes.

“There was very little overlap,” says Webb “If you were to drill a hole into the susceptibility anomaly, you could be drilling a kilometre away from the MVI anomaly.” The company can now decide to either do more modelling or test the inversion results.

Magnetic Remanence in South Australia

Cooper Pedy in southern Australia is best known for its opal deposits, but Anglo American was interested in the area’s potential for both IOCG and mafic intrusive nickel deposits.

[Click to enlarge]

Drillhole AD 001 magnetic properties: data from CSIRO report by D Clarke

The company drilled a large negative magnetic anomaly under 200m of barren cover, hoping to intersect mafic rocks. Instead, what was pulled from 300 metres downhole was a gneissic rock with strong magnetic remanence (testing by CSIRO returned an average Koenigsberger ratio of 600). The main remanence carrier was titaniferous hematite. Because of the strong magnetic remanence, susceptibility inversion provided a completely nonsensical model. "The MVI, on the other hand, provided a realistic result", says Webb.

Remanence in Northern Finland?

The Cu-Ni-PGE project is located north of the Arctic Circle in Finland. Although the area was devoid of outcrop, the application of a combination of traditional exploration techniques (i.e. base of till sampling and VTEM) and in house geophysical technology (SQUID EM) successfully identified subsurface anomalies.  Subsequent drilling outlined Cu-Ni-PGE sulphide mineralization hosted predominantly by a serpentinized ultramafic olivine cumulate rock.

When Webb ran unconstrained models using both magnetic susceptibility inversion and MVI, the two methods produced different interpretations of the plunge and extent of the mineralization. When he took the modelling a bit further by constraining the MVI using magnetic susceptibility measurements from the core, the MVI fitted the exploration model, but the amplitude component implied that the magnetic intrusive was more extensive than currently defined.

Video of magnetization vector inversion constrained by drillhole susceptibility measurements, conducted on a Cu-Ni-PGE project in Finland.

Webb concluded that if MVI had been used for modelling in the early stages of exploration, the drilling priorities may have been somewhat different. He has recommended measuring the magnetic remanence of the core to determine if it could account for the difference.

Overall, Webb finds VOXI to be a flexible software service that can be used for both forward modelling as well as unconstrained and constrained inversion.

“The MVI approach in areas with obvious magnetic remanence and at low magnetic latitudes is a great tool that is producing geologically reasonable targets that can be tested by further modelling or drilling” he says. “And the software’s ease of use is a bonus.”



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