The people, science and technology behind discovery

Subscribe to the Magazine

Get new articles sent directly to
your mailbox.


Join the network

Twitter Updates Group Forum

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...

Airborne EM methods: be wary of relying on the tried and true

by Virginia Heffernan on MaRCH 8, 2013 expertise

[Click to enlarge]

Mineral Deposits of Canada: Overview Of Geophysical Signatures Associated With Canadian Ore Deposits, Geological Survey of Canada; K. Ford , P. Keating and  M.D. Thomas , 2007.

Matching an exploration target with a geophysical technique can be tricky for an explorer, partly because there are so many options available and partly because there can be significant differences in rock properties even among the same deposit types.

Even airborne electromagnetics (EM), which has contributed to a diverse array of major Canadian discoveries over the past half-century, including the Thompson nickel camp in Manitoba, the Athabasca uranium complex in Saskatchewan, the Lac de Gras diamond deposits of The Northwest Territories and more recently, the Ring of Fire base metal discoveries in northern Ontario, is ineffective in some environments.

Most gold deposits, for instance, are poor conductors. Diamond-bearing kimberlite deposits such as the Ekati and Diavik pipes at Lac de Gras can also elude EM instruments because they range from relatively conductive to resistive depending on the pipe geology and host rock.

At the Diavik mine, for instance, half of the diamondiferous kimberlite pipes are detectable using EM while the other half respond better to magnetics because of the differences in pipe geology. And about a decade after the initial discoveries, a gravity gradiometry survey overthe Ekati property picked up a diamondiferous pipe that had been previously undetected by either EM or magnetics.

“It is very important to be able to optimize the EM system for the target and environment, from the high frequency, high resolution of DIGHEM to the high-powered, deep detection of HELITEM or MEGATEM,” says Greg Hodges, Chief Geophysicist for Fugro Airborne Systems, which offers a diversity of geophysical solutions.  “And sometimes magnetic, radiometric, and/or gravity techniques will be better able to directly detect the deposit.”

Another classic example of how a deposit can confound geophysical assumptions is the Kidd Creek copper-zinc mine in northern Ontario, one of the world’s largest VMS deposits. When the deposit was discovered in 1963, most explorers assumed all sulphide deposits carried magnetic signatures. But because Kidd Creek has little to no pyrrhotite, it proved to be a significant exception to the rule that forever changed the way explorers looked for VMS deposits.

Hodges urges explorers to cast aside assumptions such as this and instead consider the geology of the target area on a case-by-case basis before deciding which system to use.

“It always grieves me when I see companies, without thought, use the same survey system they’ve always used for a new deposit, or automatically use whatever is most popular at the time.”

He says a common complaint in gold exploration, for instance, is that the magnetic highs do not correspond with the gold mineralization. But by considering the process of alteration around a gold deposit and how that alteration would have reduced the magnetite in the host rock, it becomes clear that magnetic lows are more likely to indicate gold mineralization in most cases.

“You know there is a certain geological change, so you have to predict the geophysical change and then pick the best system to use and the best way to interpret the data, ” says Hodges, who teaches a short course on geophysics for geologists and wishes more educators taught geophysics from a geological perspective.

As economic targets become deeper and/or subtler and therefore harder to find, the way geophysics is used to find mineralization is changing. Often it makes more sense to use a mapping system that, rather than trying to find the needle in the haystack, maps subtle changes indicating alteration zones as a means of narrowing in on the target.

“It is very important to be able to optimize the EM system for the target and environment, from the high frequency, high resolution of DIGHEM to the high-powered, deep detection of HELITEM or MEGATEM,” says Hodges. “And sometimes magnetic, radiometric, and/or gravity techniques will be better able to directly detect the deposit.”

In those cases, fixed-wing systems that survey large areas relatively quickly and cheaply might be a better choice than a helicopter system that provides higher sensitivity and resolution but at a higher cost.

“The more rock properties you can measure, including conductivity, magnetic susceptibility, density, and radio-element concentration, the better chance you have of mapping changes in geology and alteration zones,” says Hodges.“The low altitude of helicopter surveys adds resolution to all the rock properties measured, but the big fixed-wing aircraft like Gryphon can measure more properties over big areas faster.”

Hodges describes Fugro’s new Gryphon system as a flying laboratory. The aircraft can carry an array of geophysical tools including the huge MEGATEM EM system, a magnetometer, radiometric crystals, and the Falcon gravity gradiometer. The resulting information helps narrow down targets over large claim blocks by recording several different physical properties at once.

Gryphon is currently making its debut over a land package in South America. The details of the survey and its target remain confidential, but for the epithermal or porphyry-related gold systems commonly found in that area of the world, a combined geophysical package will allow explorers to pick up on the subtleties of geology and alteration that might otherwise be missed.

“There is no single airborne geophysical system that is the answer to all exploration needs,” says Hodges. “Explorers need to analyze the target and host to choose the best geophysical method, then select the optimum system for that method.


View all articles »