Geology – the bedrock of the operation
1.9 billion years. That is the approximate age of the bedrock and our deposits. That makes the bedrock particularly interesting from a geological perspective. It holds many unsolved mysteries, undiscovered treasures and the keys to understanding its history.
“Our work is mostly investigative. We have to find out why it looks this way,” says field geologist Jo Miles, who is studying the Per Geijer deposit.
Quite simply, geology is the study of the origin, constitution and changes in the Earth’s crust, the bedrock, rock types and soil types. Normally, in geology, it is not enough to study Earth’s crust over millennia. Instead, we must consider it over millions of years. However, in the case of Scandinavia, geologists talk in terms of billions of years.
But changes can happen quickly, literally from one day to the next, which means that the playing field is suddenly redrawn. This happens most often during volcanic eruptions. It also happens with minerals and rock types. We see this when we study mineral deposits and how they formed.
“Much of our work is about learning why things are as they are,” says Jo Miles. She is a field geologist studying the Per Geijer deposit.
“We look for the reasons underneath and how everything fits together,” she says. “This helps us understand the origins and the processes of the deposit.”
Analysis of the bedrock
LKAB holds an exploration permit for the Per Geijer deposit, which gives us the opportunity to survey the properties of the bedrock. This is always done initially, long before there is a mine, in order to determine the conditions and extent of the orebody, and whether it’s mineable.
This is done through several methods, including test drilling. Drill core samples help geologists better understand the deposit over time. Each drill core contains an important piece of information that is decisive for the entire picture. In other words, each core sample is a clue to understanding both the past and the future.
“Since this is ancient geology, we may never know the deposit’s origin for sure. For example, it relates to the position of the Earth’s tectonic plates from the beginning, and they are no longer there for us to study,” explains Jo Miles.
Studying bedrock properties involves mapping rock types and their extent and distribution. It also includes mineral composition, age, and possible structures. In some way, it is the first chapter of a new story about Per Geijer, about old processes and events. And as with all memorable stories, it offers excitement, drama and plot twists.
“When we study an orebody, we often find the answers in the surrounding rock mass. Reddish stone, for example, gives an indication that we are approaching the ore,” says Johan Hilmo, a field geologist and member of the exploration team for Per Geijer.
In geology, there is seldom a single answer or a simple explanation for why things are as they are. Discoveries often have to be mulled over, considered and reconsidered. “It’s a continuous learning process, and we need a team of geologists to discuss the appearance and composition of the drill cores,” says Johan Hilmo.
Analysis of drill core samples
Being a geologist is not just about using inherited knowledge and tools. It also involves the senses: sight, hearing and touch. How a core sample feels when touched with a magnetic pen, a telescopic magnetic tool, matters. Its colour also matters. These factors affect the data later entered into the system. “I have more faith in my colleagues’ judgement, experience and knowledge than any system that makes estimates,” says Laura Lauri, section manager for the field exploration team.
That is why discussion and dialogue among colleagues is necessary; to help assure information quality when studying core samples. In geology, this type of study is called geological mapping, which is done using a set procedure. Each core sample undergoes the same type of basic visual inspection.
“We use a few tools; a magnifying glass, different types of hard scrapers and water,” says Jo Miles.
Water brings out the colours, making it easier to study the core sample. However, this isn’t true for iron ore, especially magnetite. Magnetite is very dark and turns black when water is applied.
“Core samples are sent to two different laboratories, were they are crushed, so the material can be studied in more detail. The laboratory results give us a accurate and reliable body of data,” says Jo Miles.
A deposit is born
What drives an exploration geologist has little to do with how a deposit can be mined. Instead, the driving reason is often a desire to understand the origin and why things are the way they are.
“We began work in 2020 and have since drilled about 100 holes – including some 100 kilometres of drill cores.” Laura says they are getting a clearer picture of the geology. “Working from the ground up, we can see that we have similar mineralisations in Svappavaara and Malmberget, with similar rock types.”
But this area is different, because the Per Geijer deposit formed in a volcano-sedimentary setting. This means the rock types formed through extension, sedimentation, and compression. Consequently, Per Geijer is a very complex deposit that formed over a long process – happening over millennia as tectonic plates shifted
“Each new drill hole reveals new truths and, together, we are seeing things that nobody has seen before. That’s exciting,” says Laura Lauri, continuing, “So, our different experiences as geologists matter when we discuss the deposit. My team are six different nationalities and, collectively, we share a broad range of different strengths and knowledge.”
Johan Hilmo and Jo Miles concur, emphasising the need for diversity in such a group. “Input from five or more individuals is much more valuable than a single person’s assessment,” says Jo Miles.
After just over three years, the team has made major progress in the exploration work, but it has not completely solved the mystery. Much work remains, but the team has started reaching the deposit’s outer edges. This gives them a clearer understanding of its extent.
“In exploration, every drill metre matters. When you start this kind of work, you begin big. Then you work down to the details,” explains Laura Lauri.
This means you space the first drill holes far apart, then place them in a denser pattern over time.
“We plan to drill another 40–50 kilometres next year,” adds Laura Lauri.
Magnetite and hematite
Iron ore mined in conventional mines normally occurs in two forms, hematite and magnetite. In many cases the orebody hosts both minerals, which is the case in all LKAB’s mines. But to complicate matters, LKAB’s mines and deposits also have mixed mineralisation with hematite and magnetite.
“Per Geijer contains both hematite and magnetite. The hematite occurs mainly near the surface, while the magnetite is deeper down in the mineralisation,” says Jo Miles.
The major difference between magnetite and hematite is that magnetite, unlike hematite, is magnetic. In addition, hematite often occurs near the surface. In some cases, this is because magnetite was exposed to oxygen and running water during formation. Sometimes, magnetite transforms into hematite, which is probably the case with Per Geijer.
“When we see more reddish core samples, it often means we are nearing magnetite ore,” says Johan Hilmo.
Unlike the Kiruna mine, which consists largely of pure magnetite, the composition of Per Geijer is much more complex. However, Per Geijer, just as the other deposits mined by LKAB, is a so-called apatite iron ore. This means that the ore has high phosphorus content; in the case of Per Geijer, a very high content.
“Apatite occurs in different forms in Per Geijer, in both hematite and magnetite. For example, apatite can occur as veins in the rock and often has a pink or light-grey tone,” explains Johan Hilmo.
As mentioned earlier, things are seldom obvious or self evident in geology. Undoubtedly, Socrates’ famous words, “The more I learn, the more I realise how much I don’t know,” feel most relevant in geology. The learning process and the continuous acquisition of knowledge are vital for improving our understanding. The occurence of apatite in Per Geijer is one example: how apatite presents itself and how the exploration team is becoming successively better at mapping it.
“Among other instruments, we use a so-called XRF scanner to detect apatite. We also use special lamps, since apatite shines in the dark. Over the years, we have learned much about the origin and appearance of the apatite,” adds Johan Hilmo.
Rock-solid foundation
The Kiruna mine and the so-called Kiruna ore are well known in the field of geology. Mainly due to the size of the orebody, the exceptionally high iron content, the presence apatite, but also because its geological history is still widely debated.
“Although Per Geijer’s hanging wall – the rock above the orebody – is unique, it shares many similarities with the rock type in Svappavaara,” says Johan Hilmo.
This is an indication that the two deposits are closely related and somehow linked. However, both the ore and the barren rock differ from that of the Kiruna mine.
“We know far from everything about Per Geijer. There is still a lot left to explore,” says Jo Miles.
Although the two deposits, Per Geijer and the Kiruna ore, formed at roughly the same time and lie close to each other, they have most probably formed in different ways.
“Even if the processes differ, there are signs that the rock types of the orefields formed through closely related processes and that, in some way, they fit together. There is reason to assume that Per Geijer and the Kiruna ore may be linked,” concludes Jo Miles.
