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...

Subsurface Geology Challenges Goiania's Metro

Planning study for Goiania's subway system characterizes what lies beneath the city on the proposed Metro route, and paves the way for construction.

By Graham Chandler

When Goiania, the modern capital city of the agricultural and cattle-raising state of Goias in central Brazil needed a subway system, they knew it wouldn't be an easy task. Beneath this beautiful city lurks a combination of differing lithologies including weak and brittle mica schist rocks mixed with softer soils. To top that off, it sits on a fertile plain crisscrossed by the river Meia Ponte and its tributaries, which means that some crossings will have to run below the city's very shallow water table.

Although the city is only 75 years old, its population has grown rapidly to 1.2 million. A planned city like the nation's capital Brasilia 209 kilometres to the northeast, 30 percent of its 740 square kilometres is devoted to green areas and wooded parks. Constructed following the demise of the area's gold mining, Goiania boomed with the creation of Brasilia in 1956 with new roads and agri-business that brought prosperity and a reputation for culture and the arts—the city's collection of Art Deco buildings is officially recognized as one of the finest in Brazil. It's known as the ‘spring capital' but the rapid growth has placed severe stress on its infrastructure such as health care and transport. Choked with cars—Goiania's one vehicle for every 1.7 residents is the highest in the country—some brand new public transport system was long overdue.

So in 2006 an extensive planning study to look at a Metro subway got underway which lasted two years.

Carlos Antonio Reis da Silva is senior geologist at the giant hydroelectric and thermoelectric generating and transmission firm FURNAS Centrais Eletricas SA headquartered in Rio de Janeiro and a holding of brazilian power plants (Eletrobras), of Brazil's Ministry of Mines and Energy. Reis, together with Está sediada em Botafogo , na cidade do Rio de Janeiro .geotechnical specialist Mauricio Sales Martinez and geologist Dionisio Uendro Carlos formed the project team for the planning study.

Special consideration was needed for one 15-kilometre stretch of subway. This was between Goiania's Civic Square and the bus station (Terminal Rodoviário). The geological makeup underneath it was so challenging it intrigued geologists and engineers—as such their study was presented last year in an academic paper at the 2008 international Seminar on Tropical Soils, entitled "Considerations about the profile of geotechnical-geological mapping of the subway in Goiania—stretch between the Civic Square and the Bus Station."

But it wasn't done just in the interests of academia. "The study was aimed at assisting the planning and development of the subway system," says Reis. His team first integrated several data sources: general geological and soil map data provided by mineral resource search company CPRM; local geological, soil, geomorphological, vegetal and hydrogeological maps from Goias state's mineral department (SGM); and topographical maps and population data obtained from IBGE, Brazil's statistics and geographic institute. Also into the mix went 3D topographic maps from the Shuttle Radar Topography Mission (SRTM). In total, it was a considerable volume of data and information to bring together.

Then, along with those sources, physical testing was needed—to learn the rock and soil structures and delineate the water table along the proposed underground route.

Standard penetration tests (SPT) were undertaken to profile the geological and geotechnical makeup of the rock. Because of the underground blending of fragile rock and varying soil types here, mixed drilling was conducted. "Mixed drilling is percussion and core drilling performed together," explains Reis. "We used percussion in soil layers and core drilling in the rock layers."

The SPT (Standard Penetration Test) data revealed an interesting combination of soils, the investigators found. Reis explains: "Excavation for the Metro route will be [entirely] under residual soils proceeding from mica schist rocks," he says, meaning basically that the natural geological process of rock weathering into soil is still underway beneath the surface of the city, so several transitional phases will be encountered, complicating construction.

Data were at first acquired in Excel format, but later specialized software from Geosoft was used for interpolation of the SPT data and drillhole mapping—the latter provided drillhole mapping capabilities. Reis says the geotechnical-geological profile was created in Geosoft's Target subsurface geology application using the SPT data contained in the drillhole database. "Interpolation of the SPT data was a challenge, especially in the deep areas, and it was easily managed with the Target software," says Reis.

Ascertaining the water table was particularly important, as Goiania's is very shallow. Rainfall here, which peaks at 270mm for the month of January, helps maintain those levels. "We used piezometers [a tubular instrument, installed into boreholes carried out along the route, for measuring water table level] and pluviometric data [measurements relating to rainfall]," recounts Reis. Here again, Geosoft Target subsurface geology software was used.

Initially seasonal variations in the water table were integrated with other data sets to develop profile drawings using AutoCad 2006, says Reis, which facilitated the understanding and visualization of the subsoil. Then with the help of Target he says "it was possible to organize and manage the geoprocessing database of the survey, and create a geological-geotechnical profile along the route of the subway, create plan maps, shape the images numerically and create a digital terrain model."

"The first product generated in the environment was a Target plan map showing the urban area of Goiania with an indication of the drilling carried out along the route," says Reis. He says it included points of interest and the districts that would directly benefit from the subway line. Which was a real bonus for the study: "With this product it was possible to see the neighborhoods around the subway with the highest potential for growth and property recovery," he says.

For the water table challenge, Target-generated 2D and 3D topographic maps "helped us to verify that the route of Metro Goiania is located for the most part on a water divider section," says Reis, which he explains as having to cross under two deep valleys of the river Meia Ponte's local tributaries. He says it's the main drainage area for the metropolitan area which crosses the entire city.

"This information will be of great interest for planning the subway construction," he says, "as it may indicate for example places of excavation that will require temporary lowering of the water table." This he says would probably only happen in the north part of the segment. But it's a significant problem to face. "Throughout the year, the water table will constantly be above the bottom of the excavation," he explains, which will present particular challenges to the construction engineers—not only will they have to lower the water table but maintain it below the excavation during the construction phase. "And it will involve design of an effective impermeable structure," adds Reis. 

In preparing for these construction challenges, data integration and planning was made easier through the use of Geosoft software. "The Target surface and drillhole mapping application provided essential tools for the development of the work," says Reis. For the entire process flow he says "Target was easily managed to generate digital terrain modeling with the interpolation of data to gain a better understanding of the geotechnical area." He says it is a useful tool for analyzing the geotechnical engineering needs of these types of urban work projects, and he particularly cited the generation of 2D and 3D map presentations.

It enabled the Goiania team to fully characterize what lies beneath the city on the proposed Metro route, and what engineering planners will be up against. "We found from our study that we'll need to take into consideration variations of lithology types—these rocks and soils have low mechanical resistance—as well as the depth of the water table," summarizes Reis. The construction planners now have their work cut out for them, but the study has paved the way for a Metro system that will help alleviate Goiania's congestion while preserving the city's beauty and heritage.