Cerro Matoso is the only open-pit nickel mine in Colombia and the largest in the American continent; it is a nickel laterite ore deposit, where approximately 40,000 tonnes of ferronickel are mined monthly.
Nickel and nickel alloys with iron, copper, chromium, and zinc are used to manufacture coins, jewelry, or hydraulic valves among others, however, the greatest part is used for fabricating stainless steel.
Geologists, Sciences-Geology M.Sc. and Universidad Nacional de Colombia (UNal) PhD. candidate Andrés Castrillón Peña collected tubular structures which could be related to marine fossils and given its source, there is the possibility of being rocks originating from the ocean floor.
“With the fossils, I also discovered evidence of fossilized shells and tubular worms that could lead to thinking these rocks, which formerly were thought of having a supergene origin, may come from other origins,” said the researcher.
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“On the contrary, they would have come from the ocean floor and when formed on the mid-ocean ridge, organisms such as bivalves and ocean worms (extremophiles) made this profound and hydrothermal environment their home,” he added.
The collected evidence was his support for his doctoral thesis. In it, he analyzed the stable carbon and oxygen isotopes present in rock carbonates which could help determine the source footprint of the methane formed in hydrothermal springs. The isotopes showed temperatures between 50 o and 70o C (122 o and 158o F), an impossible range, where temperatures vary between 40 o and 50o C (104 o and 122o F).
According to Castrillón, all the materials were clayey, therefore it was important to analyze them, as clay is considered a paleoclimatic indicator: “I carried out X-ray diffractometry analysis and discovered clay types that indicated a high-temperature environment, specifically of a greenalite type which showed a correlation between isotopes and the fossils, providing the proof that this was indeed a hydrothermal environment of the late Jurassic period, or 140 to 160 million years ago.”
The findings of this research project can not only help to better understand the geology of this deposit but also to mining companies toward new exploration activities to find similar deposits.
Hydrothermal activity is a phenomenon present in different parts of the planet and its as if great sea volcanoes erupted with fluids from the Earth’s mantle and crust. Manifestations of the processes are known as black or white fumaroles seen on the ocean floor.
Submarine hydrothermal systems host living communities such as bacteria, mollusks, brachiopods, and annelids, as seen on the Galapagos mid-ocean ridge, the first hydrothermal deepwater system discovered.
Hydrothermal vents were discovered in 1977 thanks to small manned or remotely manned submarines which explored the mid-ocean ridges. They produce specific pH and temperature levels among other factors that favor the formation or precipitation of clayey and carbonate minerals, which are geochemical anoxic-reductor environment characteristic indicators, that reflect changes in the concentrations of sulfur in the geological environment.
According to reports of other research projects, these environments have abundant organisms and microorganisms which base their sustenance on the symbiosis with sulfur-oxidizing or methanotrophic bacteria (using methane as their source of carbon and energy.)
This biological activity could have favored mineral precipitation processes which led to the formation of sediments that stand out in the peridotites (ultramafic igneous rocks generally formed by olivine) of Cerro Matoso and the mid-ocean ridges of the Pacific and Atlantic oceans.
“One of the marvels of the research project is being able to preserve these types of rocks that traveled through the ocean crust for millions of years and that were finally exposed without losing its features, thanks to fossilization of this hydrothermal environment of Cerro Matoso,” said Castrillón.
For Castrillón, getting to these discoveries earlier would have helped mining exploration, as they would have had a better understanding of the origin of the rocks. Thanks to the former hydrothermal activity of Cerro Matoso, this area is rich in nickel.
Nickel laterite ore deposits and ultramafic rocks that formed them are also present in countries such as Cuba and Venezuela. Generally, these deposits have a high nickel content of about 4%, while in Cerro Matoso these levels surpass 10%, which had not been explained before.
“This hydrothermal influence explains that this hydro-thermalism produced additional nickel, producing these great world-class deposits,” he added.
According to Castrillón, his research contributes to future geology analysis for this type of deposit, which encourages going further and think that thanks to this type of influence there is the possibility of having additional different nickel deposits in the country.
He also says that from the environmental and economic development perspective, it would be valuable to identify the fossil fauna discovered and have details that are lost during the mining process. “Much of what I saw when I worked in the area was mined but it would be interesting that Colombia could preserve this information in geology museums, as much of this will probably be lost,” finally said Castrillón.
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