Get new articles sent directly to
Earth Explorer is an online source of news, expertise and applied knowledge for resource explorers and earth scientists. Sponsored by Geosoft.
February 25, 2015
NexGen Energy Ltd. announced ongoing results from their winter 2015 drilling program at their our 100% owned Rook I property, Athabasca Basin, Saskatchewan...
February 24, 2015
Kootenay Silver Inc. announced that camp upgrades are complete and Phase II drilling has now commenced on its La Negra Silver discovery, contained within the Promontorio Mineral Belt in Sonora, Mexico...
February 23, 2015
Geosoft's Explorer Speaker Series at the PDAC 2015 includes presentations on Peregrine's Chidliak Project and Cameco's initiatives to increase efficiency and 'harvest time' through data organizationâ€¦...
February 18, 2015
The effects of dam removal are better known as a result of several new studies released this week by government, tribal and university researchers...
February 18, 2015
Exeter Resource Corporation has announced further positive results from the expanded water exploration drilling program for its Caspiche gold-copper project in northern Chile...
February 17, 2015
In response to the rapidly increasing demand for high quality geodata of the Arctic Ocean, Earthstar Geographics LLC has compiled a detailed satellite imagery mosaic of the entire region and released it in map projections optimized for visualizing the northern polar areas...
February 11, 2015
Geosoft's program for the ASEG-PESA, February 15-18 in Perth, includes a workshop on practical geophysical workflows for resolving common problems in minerals targeting...
February 9, 2015
Pilot Gold announced the final 2014 results from its third gold rich porphyry discovery at TV Tower, located 6.5 kilometres north of the Valley and Hilltop porphyries...
February 5, 2015
Coastal Gold has defined a high grade resource at its 100%-owned Hope Brook gold deposit in Newfoundland by developing a 3D model that has tighter constraints and focuses on higher grade drill results.
February 4, 2015
Finding Petroleum is hosting a half-day event on the role of non-seismic geophysical techniques. Are they coming of age? Reserve your space for this free event, being held in London, February 19.
January 27, 2015
Rig counts are a highly imperfect guide to future oil production but they are one of the few readily available statistics on oilfield activity so it is unwise to dismiss their importance entirely...
January 23, 2015
Steve Todoruk, a broker with Sprott Global Resource Investments, explained in Sprott’s Thoughts recently why ‘juniors’ should look for new discoveries by drilling into the unexplored depths near existing mines...
January 20, 2015
Italian oil and gas group Eni said on Tuesday it had won two exploration licenses in the Barents sea and in the North Sea in Norway...
January 9, 2015
A collaboration between the U.S. Geological Service and West Virginia University has resulted in a better understanding of the chemicals that spilled into the Elk River in 2014, affecting the drinking water of 300,000 Charleston-area residents...
January 7, 2015
Precipitate Gold Corp announced results from its recently completed Phase 2 induced polarization ("IP") geophysical survey at the Ginger Ridge Zone within the Company's Juan de Herrera project in the Dominican Republic...
December 18, 2014
Integrated Geophysics Corporation (IGC) announced today the successful completion their Eastern Seaboard regional integrated interpretation package. Designed for oil and gas companies needing a First Pass Look at the regional tectonics and structural trends for this new frontier...
December 10, 2014
Integrated within Geosoft’s GM-SYS 3D Modelling software program, VALEM is an improved, interactive solution for sub-salt interpretation that resolves the base of salt from gravity data bound by the constraints of seismic modelling...
December 03, 2014
Petrobras reported the discovery of a natural gas accumulation with the Orca-1 exploratory well drilled on the Tayrona block in the deepwater Caribbean Sea, 40 km offshore La Guajira, Colombia...
by Virginia Heffernan on June 24, 2013 Applied
Panoramic view of the El Roble project site in Columbia. Atico Mining’s exploration program for El Roble is focused on discovering several million tonnes of high grade copper – gold ore.
In the high-stakes game of mineral exploration, companies that can test their model at an operating mine before venturing into the surrounding district are at a distinct advantage. It’s an approach that is paying off for Vancouver-based Atico Mining as the junior searches for volcanogenic massive sulphide (VMS) deposits near the El Roble copper-gold mine in Colombia.
“Having access to the mine workings helps us understand the geological and structural controls on mineralization,” says Atico CEO Fernando Ganoza, “and that in turn is helping us find additional resources.”
Atico uses the data collected from ongoing brownfields exploration combined with historical data to create 3D models using Geosoft’s Target and Geochemistry for ArcGIS. The models help guide exploration below the current workings and within the prospective host horizon that extends along strike from the mine.
“We input all of the geophysical and geochemical data into ArcGIS and then, based on the understanding of the geology, set parameters in the software,” explains Senior Exploration Manager Joseph Salas. “That’s how we generate targets.”
In early 2011, Atico signed a deal to earn a 90% interest in El Roble in return for paying its Colombian owners US$2.25 million in cash over two years plus a lump-sum payment of US$14 million due in January 2014. Over a production history of roughly 22 years, the underground mine has turned out 1.5 million tonnes grading an average of 2.5% copper and 2.5 grams gold per tonne.
Field geology discussion.
“Having access to the mine workings helps us understand the geological and structural controls on mineralization and that in turn is helping us find additional resources.”
- Fernando Ganoza
Although most of the historical resource, consisting of several VMS lenses, has been mined, Atico has found more ore at depth. These new targets were established by mapping the geology both at surface (1:5,000 and 1:10,000 scale) and underground (1:250 scale), following structural controls and mineral zoning patterns typical of VMS deposits.
Geophysics and Geochemistry Zero in on Targets
On of the most significant conclusions from the surface mapping program is that the mineralized contact between basaltic volcanic rocks and black and grey cherts extends for 10 km across the El Roble concessions. Follow-up prospecting has confirmed that resistivity lows and chargeability highs can be used as indicators of the favourable chert horizon.
However, additional geophysical tools were needed to distinguish between conductive graphite in the chert and VMS mineralization. So Atico launched a ground magnetic orientation survey around the mine and reprocessed about 40 line-km of ground magnetic data collected in the mid-1980s by Nittetsu Mining, a former joint-venture partner on the property. The reprocessed magnetic map shows a weak magnetic anomaly over the El Roble mine and four stronger magnetic anomalies to the north.
In the air, Atico ran a 500-km versatile time-domain electromagnetic survey to cover the trend with lines every 100 m and a spacing of 50 m between stations. (Time-domain EM surveys are often effective in pinpointing VMS mineralization above a depth of 200 m.) A follow-up ground gravity survey further refined drill targets by identifying several anomalies that could represent pockets of VMS mineralization.
El Roble – Geology Section 20 South.
Although drilling along the trend has yielded little of interest so far, underground drilling is showing that a gold-silver halo in the black chert is a significant geochemical indicator that can be used for both brownfield and greenfield exploration. Results from the northern end of the operating mine include 119 m of 6.9% copper and 6.3 grams gold per tonne.
The host rocks at El Roble are part of the Cretaceous Cañasgordas Group, which can be traced for more than 800 km along the western cordillera of Colombia. Locally, mafic volcanic rocks include pillow basalts, tuffs, hyaloclastites, and agglomerates, while pelagic sedimentary rocks consist of chert, siltstone, and minor limestone.
The VMS mineralization is dominantly pyrite and chalcopyrite, mostly fine-gained and showing little internal structure or banding. Underground drilling between the 2,000- and 1,980-metre levels has identified stockwork mineralization consisting of chalcopyrite with subordinate pyrite in massive veins and patches in a gangue of stockwork quartz and chlorite veins.
Since VMS deposits tend to occur in clusters and the mined-out zones at El Roble represent only about half of what an average VMS cluster would yield, there’s a good chance Atico will find more ore along the 10-km trend as it uses information from the mine to seek out economic mineralization.