The potential for massive-scale mining operations is attracting exploration in emerging IOCG districts.
Iron-oxide-copper–gold (IOCG) deposits rank alongside porphyry deposits as some of the world’s largest deposits and most consistent in grade, making for highly profitable mines and therefore attractive targets for major mining companies.
Found in various types of host-rock around the globe, this relatively new deposit type is still considered a rare find; however, new IOCG districts are emerging in regions hitherto not commonly associated with the deposit type. Canada’s mining-friendly jurisdictions of Ontario and Yukon present two examples.
IOCG deposits are typically large and polymetallic
IOCG deposits represent a broad range of polymetallic orebodies and contain some of the world’s most critically important commodities. As the name suggests, these deposits can contain significant resources of iron, copper and gold; however, some IOCG deposits are also known to contain considerable amounts of uranium, cobalt and rare earth elements. Other elements that may be present in these mineralized systems include molybdenum, silver and nickel. The deposits have no specific host rock control, with individual deposits hosted in metamorphic domains from near-granulite facies to greenschist or sub-greenschist facies. They can be hosted in greenstones or other volcanic rocks, at greenstone-sedimentary rock interfaces, in volcano-sedimentary rock sequences or in granitic intrusions.
Alongside their polymetallic nature, IOCG deposits are also well known for their massive scale, often exceeding 100 million metric tons. The world’s largest, and some have argued most valuable, single ore body is an IOCG deposit. BHP’s (ASX:BHP,NYSE:BHP,LSE:BLT) Olympic Dam, located along the eastern margin of the Gawler Craton in South Australia, is best recognized for being the world’s largest uranium resource, but it is also third in the world for gold resources and fifth in the world for copper resources.
Global IOCG districts
The Gawler Craton is considered a global hotspot for IOCG deposits and is also home to OZ Minerals’ (ASX:OZL,OTC Pink:OZMLF) Prominent Hill copper-gold mine and the Carrapateena deposit. The world’s other significant IOCG regions include the Carajas district in Brazil and the Coastal Cordillera of the Andes in Chile. Vale’s (NYSE:VALE) low-cost IOCG Salobo and Sossego deposits are two of the biggest copper-producing deposits in Brazil. Chile’s prolific Atacama IOCG Belt hosts such notable deposits as Lundin Mining’s (TSX:LUN,OTC Pink:LUNMF) low-cost Candelaria open-pit mine, which has been in operation since 1993. Lundin paid Freeport-McMoRan (NYSE:FCX) US$1.8 billion for its 80 percent interest in Candelaria in 2014. The company has made a significant investment in exploration at Candelaria, extending the mine life from 14 years to over 20 years.
“IOCG systems can form large polymetallic mineral deposits with long mine life that are becoming the backbone of significant mining camps around the world. Canada is lagging behind in mineral exploration for IOCG deposits, but this is not because of a lack of exploration potential,” Dr. Jean-François Montreuil, an expert on IOCG exploration modeling and Chief Geologist of MacDonald Mines Exploration (TSXV:BMK), told INN. “Advancement of knowledge and ongoing mineral exploration are demonstrating that IOCG systems can form gold-rich polymetallic deposits that could become considerable polymetallic gold mines in the future with variable cobalt, copper, uranium and silver as potential by-products.” MacDonald Mines has identified the potential for gold-rich IOCG-style mineralization on its wholly owned SPJ project in the Wanapitei Lake area of Ontario, Canada, which is part of the Southern Province geology in the Canadian Shield. The SPJ project hosts the past-producing Scadding mine, which between 1984 and 1990 reportedly produced 914 kilograms of gold grading 7.43 grams per metric ton.
Emerging IOCG districts in Ontario and Yukon
IOCG deposits are increasingly being identified in previously unrecognized settings around the world, including Canada. While Canada has no currently producing IOCG style mines, new geological research studies and exploration results are pointing to the potential for IOCG districts in Ontario and Yukon.
In 2007 the Geological Survey of Canada identified the Wanapitei Lake area of the Southern Province as a promising district for the discovery of IOCG mineralized systems. Key IOCG indicators found in the region include the localized formation of iron oxide mineralization, corridors of sodic alteration associated with polymetallic mineralization and the presence of gold and copper in mineralized zones.
Historical data on MacDonald Mines’ SPJ property includes grab samples with anomalous cobalt, copper, nickel and gold indicating a possible extension 3.5 kilometers northeast of Scadding Deposit as well as a uranium anomaly of up to 9 kilometers.
Outside of gold, the Wanapitei area has also been found to host elevated concentrations of copper, iron, cobalt and nickel. In fact, the Scadding deposit is one of the region’s many polymetallic gold deposits with variable copper and cobalt showings and occurrences. “Historic drilling indicates that sizeable gold zones with high-grade mineralization, open along strike and depth, exists in the deposit but that the challenging and complex geology classically associated with IOCG deposits hindered previous exploration,” said Quentin Yarie, P.Geo., President and CEO of MacDonald Mines. During the company’s 2019 drill program, multiple high-grade gold structures at the Scadding deposit were identified, including 50 grams per metric ton gold over 12 meters as well as multi-element mineralization indicative of an IOCG deposit.
In Yukon, the Wernecke Breccia belt offers another case example of an IOCG geological setting in Canada, with a similar style and age as Carrapateena and Olympic Dam. Go Metals (CSE:GOCO) has recently identified multiple large untested IOCG drill targets on its Monster project, which covers 63.5 square kilometers of the Wernecke Breccia system in the Yukon Dawson district. The IOCG signature for the Monster project — including widespread mineralization at surface — was confirmed by geophysics, alteration mapping and chemistry. Go Metals has completed new high-resolution detailed ground gravity and 3D inversion modeling for the property with exploration work focused on the Bloom and Beast targets. There are elevated copper, cobalt, gold and silver showings with high-tonnage potential.
IOCG mineralization systems carry significant potential for large-scale deposits. Due to the massive scope and polymetallic nature of these deposits, IOCG systems are frequently pursued by explorations companies in search of their next big project.
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