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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...

Constrained inversion models identify new resources at Ivanhoe's Platreef deposit

by Kylie Williams on December 8, 2016 applied

Dr Nick Williams, Global Geophysicist for High Power Exploration, presented on the use of advanced gravity and magnetic inversion methods in the Platreef at the 25th International Geophysical Conference and Exhibition.

[Click to enlarge]

Figure 1: Ivanhoe's flagship Platreef Project is located in the Bushveld Igneous Complex, 280 kilometres northeast of Johannesburg in South Africa.

[Click to enlarge]

Figure 2: A 'focused' Geosoft VOXI Magnetization Vector Inversion (MVI) model for Platreef, solves for the 3D magnetization vector in each 50 X 50 X 25m cell by accounting for induced, remanent, and demagnetization effects.

[Click to enlarge]

Figure 3: Subset of a predictive geologically-constrained gravity inversion model for Platreef area built using surface mapping and drilling observations to support the gravity data, measuring 4 square km and showing schematic platinum assays.

Certain minerals, such as magnetite, are valued for their role as magnetic time capsules, locking-in the direction and intensity of the Earth’s magnetism at the time they were formed. This magnetic memory, called remanence, is a useful tool for dating rocks and rock sequences, but can be misleading for geophysicists modelling magnetic and gravity data.
In 2010, Ivanhoe Mines requested the expertise of Barry de Wet and Nick Williams, both geophysicists with Ivanhoe Australia at the time, to help overcome this remanence problem at their flagship Platreef Project in the Bushveld Igneous Complex (BIC), 280 kilometres northeast of Johannesburg in South Africa.

The Platreef, a high-grade reef of platinum group element (PGE), nickel, copper, and gold mineralization, occurs just below a regional contact within the BIC that can be traced more than 30 kilometres along strike. Ivanhoe geologists correlate the reef with the famous Merensky and UG2 PGE reefs which account for 60% of the world’s annual PGE production.

Ivanhoe Mines had been exploring the down-dip extent of its original Platreef discovery, now known as the Flatreef Deposit, since 2007. They provided aeromagnetic data, a database of downhole physical property measurements from several hundred drill holes, and regional mapping information to de Wet and Williams, who, together with the Ivanhoe team, set out to see if the significant density and magnetic anomalism associated with the contact could be used to predict the depth of westerly extensions of the Flatreef.

“The mineralized zone, as they had defined it at that time, had flattened out at about 800 meters below the surface,” says Dr Nick Williams, Global Geophysicist for High Power Exploration (HPX), who presented this work for the first time in a keynote address to the 25th International Geophysical Conference and Exhibition in Adelaide, South Australia.

“The resolution of any potential field method, gravity or magnetics, is weak at those depths, and only capable of imaging really large, thick bodies,” says Williams, “It was critical to find ways to maximize the resolution given the weak signals that would be involved.”

A paleomagnetic solution

The solution to removing this remnant magnetization overprint and modelling the intrinsic magnetic variability of the rocks was to be found in published paleomagnetic studies that characterised the magnetic properties of the rocks in the BIC.
One of these papers was published by de Wet himself, who graduated from Pretoria University in 1972 and has been interested in finding a magnetic interpretation solution to the complexity of the Bushveld Complex magnetic signature for much of his career. In 1995, de Wet and Pretoria University’s Professor Hattingh published a study detailing how magnetic reversals were prevalent in some of the intrusive rocks in the Bushveld.

“Any predictive interpretation or modelling had to take these effects into account, but acquiring the palaeomagnetic data for all rock units in the Complex would be practically impossible,” says de Wet, who retired from his role as Chief Geophysicist at HPX in June 2016, “The only solution was to eliminate all vector magnetic effects from the magnetic data and to use those vector data to help discriminate the lithology.”

To extract the true magnetic structure of the geological units at depth, and create predictive models for exploration, they needed to integrate the standard aeromagnetic data collected over the area in 2004 with other physical property data from drill logs and the literature, such as density, velocity, conductivity and chargeability.

“Geosoft VOXI MVI was the only inversion software algorithm that we could use to do the modelling, to accommodate the high remnant magnetization we were seeing in the rocks,” says Williams.

Ivanhoe Australia and Geosoft collaborated to develop the Geosoft VOXI Magnetization Vector Inversion (MVI) software. Unlike other inversion software packages that assume rock magnetization is parallel to the Earth's inducing field, VOXI solves for magnetization along any direction without a priori knowledge of remanence, allowing it to account for the recorded magnetic field reversals and thermochemical variations within the magnetic minerals.

Drilling success

The true anomalies were identified by integrating all available datasets. The first models generated predicted a deep extension of the regional contact and Flatreef host rocks over an area of about four square kilometers, approximately 1.5 km west of the prior drilling. The target was drilled in 2011 and hit the contact and reef within 200 meters of the predicted 1300-meter depth. “Such a large step-out drill program just couldn’t be supported without robust geophysical modelling,” says Williams.

New drilling information and a FALCON airborne gravity gradiometer survey flown in 2012 were used to update the inversion models and refined the geometry of the flat-lying reef. de Wet and Williams moved from Ivanhoe Australia to HPX in 2012 and continued the Platreef work, generating three major iterations of models using Geosoft VOXI over a five-year period. Inversion models incorporating the FALCON survey identified a southerly extension to the Flatreef at relatively shallow depths, which was drilled in 2013.

“Ivanhoe Mines drilled about six holes and intersected the contact and reef within approximately 50 m of predicted depth. All of the holes intersected mineralization,” says Williams.

Ivanhoe Mines Executive VP Exploration, Dr. David Broughton, commented on the value of an integrated approach to deep exploration at Platreef: “Without the robust geophysical modeling developed by Barry and Nick, we would not have been able to predict and drill with confidence for deep extensions to the reef.”

After being awarded a Mining Right in November 2014, and submitting a positive pre-feasibility study in January 2015, construction of the No. 1 Shaft at the Platreef Project is currently underway.

Next generation geophysics

The two biggest challenges faced on the Platreef Project were relating the fine-scale physical rock property measurements to the large volumes of rock involved, and the limited resolution of the gravity and magnetic data sets at depth.

“The next generation of geophysics will be based around routine physical property logging down each and every hole just like they have been doing in the petroleum industry for decades,” says Williams. Physical property measurements, he says, are an invaluable tool for defining geophysical problems and deciding which data sets will provide the best targeting results.

Williams and de Wet are also proponents of using 3D seismic and other more powerful methods as an early exploration stage tool for better resolution at depth. Seismic and electrical methods are complementary, providing more intrinsic 3D information than gravity and magnetic data, but are more expensive and respond to different physical property variations. The geometries identified by modelling those datasets can be used to support revised gravity and magnetic modelling, which can then be used to find new targets.

“True integration requires all physical properties and drilling data on a single platform and this can only be achieved when the structure of the physical properties can be accurately modelled using appropriate geological constraints. The process becomes manageable with VOXI MVI and the Geosoft integration platform” says de Wet.


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