image: Main types of iron ore in the Bakchar deposit. view more
Credit: Tomsk Polytechnic University
The world’s largest deposit of iron ore is the Bakchar deposit located in Western Siberia, Russia. Its proven reserves are over 28 billion tons. Scientists search for an answer to a global question: Where from and how was there the accumulation of a huge amount of iron. Researchers propose the origin of the Bakchar ironstone deposit by upward migration of a mixture of Fe-rich brine and hydrothermal fluid through marine sediments.
Scientists from Tomsk Polytechnic University together with colleagues from the Indian Institute of Technology Bombay refute a widespread theory that iron in such kind of deposits came into the sea from the eroded mountainous areas of the ancient continents. According to their last article published in the journal Marine and Petroleum Geology, the emissions of solutions containing iron, breaking through the seabed could be the source of iron.
95 million years ago, there was a shallow warm sea there. The Bakchar ironstone deposit is considered the most promising in the West Siberia iron ore basin which is in turn world's largest deposit.
However, to date, there is no ore mining at the deposit.
As.Prof. Maksim Rudmin from the TPU Geology Department, a co-author of the article says: 'This geological object is truly unique by scale. There is no precise answer yet where such great amount of iron came from. The oolit iron deposits were formed 90 to 56 million years ago within the ancient sea in quiet seashore conditions. The most common theory claims that iron was transported into the sea by the erosion of ancient mountainous areas by the river systems. A careful study of the geological situation and ore samples from the deposit allows us to disagree with it.'
The scientists argue that firstly, currently there are no traces of giant sources of iron in the regions which were eroded in the period when the deposit was formed. Secondly, no major intermediate deposits were found in the areas of ancient rivers that should have transported iron. Thirdly, the coastline of the ancient sea repeatedly shifted while the Bakchar deposit was formed at a certain location, though its borders also had to shift and stretch.
'These are just some counterarguments. If the source of iron is not in the ancient continent then where? We believe that a promising direction for search is the deep parts of the sediment basin. That is the source of iron can be under the deposit itself. Firstly, in the ore we found iron, lead, zinc, silver, copper sulphides, mineral forms of arsenic, mercury and barium sulphates, which are closely associated with iron-containing minerals. These minerals are not stable, river water could not bring them, and they would dissolve during such a travel. Secondly, we identified the features of distribution and relationship of a number of rare metals, for example, nickel, cobalt, lead, zinc, copper, molybdenum, arsenic, vanadium which are observed in other marine ferrous sediments on the planet, exposed to emissions of hydrothermal solutions through sea or ocean bed,'
Explains the scientist.
In addition, the researchers found the inclusion of methane bubbles in the ore. In their opinion, this could occur if in this area there were upward methane fluxes from the bottom through the sediments.
'It is possible that different elements, including iron, could have come together with methane and water. Thus, in the ore samples, we found mineral forms of metals that accompany ore accumulation, i.e. lead and zinc sulfides (galena and wurtzite), lead selenide (claustite), cobalt and nickel arsenide and others. Their origin is beyond doubt. They got in the ore via the emission of gas-liquid fluids from the underlying layers,' says Maksim Rudmin.
If further research of the West Siberian Iron Ore Basin confirms the theory of the TPU scientists, this will make it possible to take a fresh look at the exploration methods both for similar iron deposits and genetically related minerals. These include, for example, lead and zinc deposits that are significant for industry.
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Journal
Marine and Petroleum Geology