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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 ...

Corvettes in a cave: applying geophysics to a classic car tragedy

by Kylie Williams on July 25, 2016 applied

Video footage from the National Corvette Museum security cameras showing the sinkhole collapse in the Skydome.

Brian Ham (CG-5 operator) and Jason Kuykendall (blocking wind) collecting microgravity measurements at night along a traverse on the south side of the Skydome.  

Wreckage of the recovered 1992 1-Millionth Corvette (white) and 1993 ZR-1 Spyder Corvette (black with red).

The collapse prior to preliminary stabilization and Corvette recovery, including the 2009 ZR-1 Blue Devil, 1993 40th Anniversary Corvette (red), and 1962 Corvette (black).

Dr. Jason Polk (Western Kentucky University) drafting the cave map with the collapse entrance and Skydome in the background.

[Click to enlarge]

Microgravity survey results plotted in 3-dimensional graph.

[Click to enlarge]

Plan view of microgravity survey results and interpreted anomalies.

[Click to enlarge]

Scintrex Autograv CG-5 meter and the recovered 1992 1-Millionth Corvette.

February 12, 2014, was a tragic day for Corvette lovers around the world. Shortly after 5:30am, surveillance cameras inside the National Corvette Museum (NCM) in Bowling Green, Kentucky, USA, captured stunning footage of a sinkhole opening up and swallowing eight classic Corvette cars.

Although sometimes heartbreaking and rarely recorded on video, sinkhole collapses are not uncommon in this part of south-central Kentucky. The area is known for its karst topography, characterised by sinkholes and caves formed when limestone is eroded by groundwater dissolution.The world's longest known cave system, Mammoth Cave, is just a short drive away from the museum.

Within hours of the disaster occurring, a team of museum staff, general contractors, geotechnical and civil engineers, karst scientists, and Corvette enthusiasts had assembled onsite to survey the damage and guide the recovery.The priority was to ensure the structural integrity and safety of the NCM Skydome, the distinctive, yellow, rocket-shaped building where the collapse occurred. First, water hammer drilling was used to install micropiles for structural stabilization.

Next, environmental engineering company EnSafe was engaged to design and conduct a geophysical survey to map the extent of the collapse.  EnSafe had worked with the NCM previously, providing environmental site assessments during development of the nearby Motorsports Park and racetrack, and were familiar with the geology of the area.

“News of the collapse created quite a buzz at EnSafe’s offices and as more information came in, we were already laying the groundwork for assessment strategies and potential methods for subsurface investigation,” said Nashville-based EnSafe geologist, Brian Ham, who first heard about the collapse from his colleagues in Bowling Green. Caves are both a profession and a passion for Ham who works as a professional geologist, specializing in hydrogeology and geophysics, during the week, and maps caves on the weekends.

Ham and the EnSafe team discussed the pros and cons of various geophysical methods for the job. Electrical Resistivity (ER) surveys are often used to survey karst environments. However, in this case, contiguous cable placement was impossible because of the void and buildings along the traverses, and the ER data may have been compromised by conducive metal pipes and buried wires near the surface. Seismic and ground penetrating radar, used successfully elsewhere in karst environments, were also considered but not employed. A seismic traverse directly over the void was not possible and may not have defined the voids accurately, and the high clay content in this region limits penetration of the ground penetrating radar signal to only 2-3 meters.

A microgravity survey was chosen because of the unique conditions at NCM and the method’s established success at industrial and commercial sites. However, Ham describes designing and conducting the survey on the populated and busy site as “challenging”. 

“The areas near the collapse edges were inaccessible and the team had to take into consideration areas with unique cultural features, such as the HVAC supply trunk running under portions of the Skydome,” said Ham.

Microgravity measurements were collected at 10-foot intervals along 25 west-east traverses between 10-14 March, 2014,using a Scintrex CG-5 Autograv Microgravity Meter. The team managed little sleep during the survey. The microgravity meter is extremely sensitive to vibrations, so, because drilling and micropile installation was being conducted during the day, data collection had to be conducted at night. 

Base station readings were collected before and after each traverse, along with latitude, longitude, and elevation at each station.  The data were processed and corrected for instrument drift, relative changes in latitude, elevation, and slab mass using Geosoft Oasis montaj software with the Gravity and Terrain Correction extension, which Ham has been familiar with since his research days at Western Kentucky University’s (WKU) Center for Cave and Karst Studies. 

“The Geosoft software enabled an efficient data processing work flow which helped us to evaluate data in real time and make field decisions regarding the need for additional data collection,” said Ham.  The microgravity data were used to prepare a map showing the general shape of the void, the concentric pile of debris directly below the collapse, and the cave passages north and south of the collapse which had intact bedrock ceilings.

Almost one month later, on April 5, 2014, Ham joined an experienced team of cave surveyors from WKU-Dr. Jason Polk, Dr. Pat Kambesis and Kegan McClanahan - to survey the collapse and associated cave passages from within. Safety was a major consideration and by this time the Skydome was stabilized and the debris and all but one of the Corvettes had been recovered from the collapse; a 2001 Mallett Hammer Corvette Z06 - still lay covered in rock and soil.

Descending carefully into the cave, the survey team found two ‘rooms’, each about 12 meters wide by 18 meters long with a maximum height of 6 meters. Reduced to crawling on their bellies at times through narrow passages and scrambling over piles of rubble, the team mapped the cave and established survey stations at micropiles visible in the cave for georeferencing purposes.

“It was a great opportunity to inspect the geology up close and we noted a lithologic marker bed, the Corydon Ball Chert, which also helped us calibrate our geologic model, establishing elevations for the contact between the St. Louis and St. Genevieve Limestones which influences karst development in the Bowling Green area,” explains Ham.

The 2D microgravity map was combined with the high-resolution cave survey, drilling information and geologic data to create a detailed model of the collapse that was used in the geotechnical remediation of the site. There was excellent correlation between the anomalies identified via the microgravity survey and the map prepared by the cave survey team.  The void below the Skydome was backfilled with aggregate supported by steel plates and micropiles with monitors installed to detect any future movement at the site.

Today, visitors to the NCM can peer into a manhole installed during the recovery and explore a new exhibit which opened two years after the initial collapse, on February 12, 2016. The exhibit tells the story of the collapse, which cars were affected, how they were recovered, what karst landscapes and caves are, how the building was fixed, and includes a map of the EnSafe microgravity results.

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