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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

December 7, 2016

Geosoft introduces IP and resistivity inversion in VOXI Earth Modelling

Geosoft has added induced polarization and resistivity data inversion to its VOXI Earth Modelling 3D inversion software service. Geoscientists are now able to create detailed 3D models of conductivity and chargeability from IP and resistivity survey data with VOXI. The resulting models can assist in interpreting and targeting regions for mineral and environmental applications...

December 5, 2016

Mexico's Deepwater Round Exceeds Expectations

Some of the world's biggest oil companies showed up Dec. 5 and agreed to invest on the Mexican side of the Gulf of Mexico, proving that deepwater exploration still has a pulse despite challenging market conditions...

November 30, 2016

Magnetic inversion results for Ngamiland available for download

A regional-scale geophysical inversion of magnetic field data in the Ngamiland region of northwestern Botswana is now available for download from the Botswana Geoscience Portal, a partnership initiative of the Botswana Geoscience Institute, industry sponsors and Geosoft...

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...

Rapid Reversal in the Earth’s Magnetic Field

Geoscientists uncover an example of rapid transitional field change (RTFC)
in Nevada’s Sheep Creek Range

Figure 1. Equal-area plot showing site-mean remanence directions (and 95% confidence limits) from flows near the top of the Sheep Creek transition zone. Open (closed) symbols correspond to upward (downward) pointing directions. Flow 20 is bracketed by Flow 19 (below, with E-down paleomagnetic direction) and Flow 21 (above, with Ndown direction).

[Click to enlarge]

Figure 2. Stepwise demagnetization of samples from a vertical profile through Flow 20. (a)Vector endpoint diagrams (horizontal component only) for thermal demagnetization on samples 1.2 m, 1.7m, 2.7m, and 2.9 m above flow base. Labels identify remanence components in the E-down direction of Flow 19 and N-down direction of Flow 21. Above 175°, heating steps range from 25°C to 10°C. Highest temperature steps are all 585°C. Plots are scaled so that north components of NRMs are equal. (b) Vector endpoint diagrams like those in (a) for AF and thermal demagnetization of companion specimens from 0.6 m above flow base. (c) Tub distributions for the N-down (black) and E-down (light gray) components of samples from 1.2m ,1.7m, 2.4m, and 2.7m above base of Flow 20 (overlapping Tub ranges shown in dark grey.) Height of bars is proportional to rate (per °C) of moment loss, with maximum rate at each level normalized to 1. Bars extend from lower to upper Tub of remanence component unblocked. Arrows indicate picks for baking temperature derived from these plots.

Figure 3. Initial susceptibility versus temperature (in argon) for sample 1.4 m above base of Flow 20. Sample was cycled to target temperatures of 150°C, 250°C, 300°C and 350°C before final heating to 625C. Arrows identify heating and cooling segments of curves. Curve for heating cycle to 250°C obscured by lower temperature portion of the 350°C curve. No progressive increase of Curie temperature during the heating cycles (diagnostic of low-temperature oxidized titanomagnetite) is displayed by the sample.

[Click to enlarge]

Figure 4. Results from conductive cooling model. (a) Time evolution of temperature profile in 3.9 m thick flow cooled to 150°C then capped by 8.2 m thick flow at 1100°C. (b) Inferred maximum baking temperatures in 3.9 m thick flow baked by 8.2 m flow. Curve with dash-dot pattern (1) shows temperature profile immediately before emplacement of upper flow. Solid curves show maximum baking temperatures if lower flow is fully cooled (2) or conductively cooled to maximum temperature of (3) 125°C, (4) 150°C, and (5) 200°C before upper flow is emplaced. Squares show maximum baking temperatures (corrected for cooling rate) inferred from the paleomagnetic data from Flow 20. Error bars show range of sample estimates. (c) Time evolution of temperature 1 m above the base of 3.9 m flow baked by 8.2 m flow. Remanence acquisition in E-down direction occurs between times I and II and all or part of the interval between II and III. Between III and IV, remanence previously acquired between II and III is unblocked. Remanence acquisition resumes (in N-down direction) starting at IV. Change in field direction occurred between II and IV. (d) Overall constraint on duration of rapid field change. Shaded area corresponds to the interval between times II and IV on (c).

By Leonard Chan

Since the 16th century, we have known that the Earth is a giant magnet with a dipolar magnetic field. In the 1920s, we learned that the magnetic field undergoes reversals, exchanging its North and South poles at numerous times throughout our planet's history. The quest to understand the cause of these geomagnetic reversals is ongoing, as geoscientists scour the Earth for evidence of past field reversals, recorded in ferromagnetic minerals of solidified sedimentary deposits or volcanic flows cooled on land.

Towering 9,733 feet over the barren playa of the Alvord desert, the east face of the Steens Mountain is a journey back through time. Composed of basalts stacked one atop the other, each lava flow offers a snapshot of the earth's magnetic field. In that stack is recorded a 16.7 million year old polarity transition. When, in 1995, geoscientists examined one lava flow in particular, a 4 meter thick flow erupted during the transition, they found that the top and base, the parts that cool quickest, were magnetized in directions different from its interior, a pattern possible only if the geomagnetic field changed 6°/day. This is astonishingly high and orders of magnitude greater than typically-observed rates of secular variation.

The timeline for geomagnetic field reversals is on the order of a few thousand to a few tens of thousands of years with the magnetic direction believed to reorient slowly over this time frame.

These previously-held beliefs are now being challenged by a new hypothesis called "rapid transitional field change" (RTFC). Developed by Scott Bogue of Occidental College and Jonathan Glen of the United States Geological Survey (USGS), this controversial hypothesis suggests that transitions can be punctuated by rapid directional field changes many orders of magnitude greater than the steady changes observed in historical times or those typically observed during reversals.

The RTFC hypothesis has been debated, with some geoscientists arguing that the Earth's liquid core is incapable of generating the magnetic fields required to induce such rapid change, and others who contend that the electrical conductivity of the lower mantle would block such high-frequency electromagnetic signals from being observable at the Earth's surface.

And perhaps more importantly, up until now, the only evidence to support the hypothesis was from Steens Mountain.

But Bogue and Glen believe they have uncovered a second example of this phenomenon.

Nestled in the Sheep Creek Range in Lander County, Nevada, is a wellspring of paleomagnetic data: an exposed 150-meter thick section of basaltic and basaltic andesite lava flows. The radiometric age of these lava flows is 15.58 million years, approximately 1 million years younger than the flows at Steens Mountain.

One flow in particular caught the scientists' attention. Dubbed Flow 20, this 3.9m thick lava flow was sandwiched between two other flows, appropriately named Flow 19 (below) and Flow 21 (above). Using a portable gas-powered drill (essentially a converted chainsaw) armed with a diamond-studded bit, 1"-diameter cylindrical cores were extracted from the flows and cut into 1”-long specimens for analysis.

All the lava flows in the Sheep Creek Range acquired their magnetization, otherwise known as remanence, during the later stages of a reverse-to-normal polarity transition. Each of the flows had a primary remanence, acquired when the rock was formed and generally indicative of the direction and strength of the earth's geomagnetic field at the time, and a secondary remanence, which can be the result of more localized effects, such as lightning strikes or influences from the present-day field. In order to isolate the useful primary remanence, the secondary remanence was stripped away using techniques such as stepwise alternating-field (AF) or thermal demagnetization.

"Thermal was nice in this case because it essentially mimics, but in reverse, the acquisition process. When we heat the sample up, we do so in a stepwise fashion to incrementally demagnetize the sample. The remanence lost in a given temperature range is equivalent to what was gained at those temperatures. Those grains that are the least stable, whose magnetization is easily lost, do so at low temperatures. The more stable magnetizations are only removed at the higher temperatures. By doing this, we can watch how it changes, and determine precisely the different components," explains Glen.

After each demagnetization cycle, the samples were analyzed with a cryogenic magnetometer, revealing an unusual acquisition history.

Bogue and Glen hypothesize that Flow 20's initial direction was acquired when it first erupted over top of Flow 19. However, Flow 21 erupted shortly afterwards, reheating the underlying Flow 20. The uppermost part of Flow 20 was reheated to such a degree that it effectively erased the memory of its original remanence, and acquired a different magnetic direction as it cooled for a second time.

The difference between the two magnetic directions recorded by Flow 20 was estimated to be 53°, indicating a significant change in the Earth's geomagnetic field from Flow 20's initial eruption to its final cooling.

While they knew the change was substantial, what they did not know was the period of time over which it occurred. Using an open source programming language, they coded a one-dimensional model of the cooling history of a 3.9m thick lava flow that was capped by an 8.2m thick lava flow at 1,100°C.

Their results indicated that the remagnetization could only be accounted for if Flow 21 erupted while Flow 20 was still cooling. They estimated that the observed geomagnetic changes happened over the period of a year, translating to a little over 1°/week. While not as high as those recorded at Steens Mountain, this rate of field change is still 2-3 orders of magnitude greater than that of typical secular variation.

Glen says that there is still much to learn about reversals and admits the possibility that the RTFC phenomenon may be localized. "The reversal process is more complex than these rapid directional changes. This is one place in the world where we've observed this. The other is Steens Mountain. We don't know how extensive these kinds of fluctuations are around the globe. There may be localized eddies. Smaller currents produce fields only locally, which you might not see on the other side of the globe. During a transition, these local features might dominate."

Regardless of the mechanism behind RTFC, the paleomagnetic evidence from Flow 20 certainly strengthens the case that they are happening, not only by representing a second observation of the phenomenon, but one with a remanence acquisition history distinct from the Steens Mountain example.

This latest evidence should re-open the debate about the characteristics of flow in the Earth's outer core and the electrical conductivity of the lower mantle.

"If these kinds of signals are making their way out of the core," Glen posits, "then that tells us something about conductivity in the mantle. Perhaps there are large heterogeneities that give us windows through to the core from which flux lines can make their way out quickly and unperturbed."

The last reversal on record is the Brunhes-Matuyama reversal, named after Bernard Brunhes and Motonori Matuyama. It occurred approximately 780,000 years ago. At present, the overall geomagnetic field has been steadily weakening (declining 10-15% in the last 150 years) since it was first measured, leading to speculation that the Earth is headed for yet another reversal. What would happen during a field reversal is anybody’s guess since humanity has not yet experienced one in the age of modern instrumentation.

Speculating on the effects of rapid field reversal on the Earth's biosphere, Glen says, "There are lots of animals who use the magnetic field for navigation. The majority are bacteria who use it to navigate to find food. They could be significantly affected. They have relatively short life-cycles and occur in large numbers so they can adjust rapidly compared to higher organisms. On the other hand, it appears that many higher organisms have other tools at their disposal to find their way around and are not solely dependent on the magnetic field to navigate."

When asked about the possible effects on Homo sapiens, he says, "If we were to undergo a polarity reversal and experience this today, it would certainly have profound effects on the way we do things. It would significantly affect space weather, which would affect satellites, and communications and power systems. But we have really good records of when these events have occurred in the past, and for the most part, they don't correlate with mass extinctions."

For the most part?

Glen laughs, and then explains, "It's difficult to do the correlation to assess whether there are more subtle effects on life because rarely do you find good magnetic records in the same stratigraphic sections as good biologic records. The largest mass extinction, the Permian-Triassic, as far as the resolution and magnetic record and dating can tell us, coincided with a polarity reversal. Although the likelihood of two very large and rare events like this coinciding is rare, this type of coincidence can, and given enough time, will occur".

Possible apocalypse aside, Glen and his colleague will continue work in Sheep Creek, gathering more data, and furthering understanding within this relatively young branch of geoscientific study.

"As with any research, you never know where it will end up leading," Glen says. "But my main drive, and I suspect why Scott does this too, is sheer awe and curiosity. Here's this really important earth process that we know very little about. The fact that we know so little about it; it's something you can actually contribute to."