Rare Earth Deposit Types
Information only, not investment advice. This guide explains how the rare earth industry works; it does not recommend any company or security.
A rare earth deposit type is the kind of geology that gathered the rare earths into one place. There are four main types: carbonatites, alkaline igneous rocks, ionic clays and mineral sand placers. The type decides which minerals hold the rare earths, how many of the valuable heavy ones are present, and how hard they are to get out.
Read a rare earth company's news and you'll see words like carbonatite, peralkaline or ionic clay in the first paragraph. Those words tell you more about a project's likely costs than the headline grade does.
What are the main types of rare earth deposit?
The main types are carbonatites, alkaline igneous rocks, ion-adsorption clays and placers rich in monazite and xenotime, according to a US Geological Survey fact sheet. A longer USGS list adds a few rarer settings, such as iron oxide deposits, but almost all production comes from these four.
| Type | Main rare earth minerals | Typical grade | Known for | Examples |
|---|---|---|---|---|
| Carbonatite | Bastnaesite | High; several percent rare earth oxide at the biggest mines | Almost all light rare earths | Mountain Pass (US), Bayan Obo (China), Mount Weld (Australia) |
| Alkaline igneous | Eudialyte, loparite and others | About 0.3% to 2.6% rare earth oxide | Yttrium and heavy rare earths | Strange Lake and Nechalacho (Canada), Norra Kärr (Sweden), Lovozero (Russia) |
| Ionic clay | Rare earths held on clay surfaces | About 0.04% to 0.25% rare earth oxide | Heavy rare earths; cheap to leach | Southern China |
| Placer (mineral sands) | Monazite, some xenotime | Varies by deposit | Monazite, which carries thorium | Beach and river sands worldwide |
Grades from USGS Fact Sheet 2014-3078 and Professional Paper 1802-O.
Which minerals hold the rare earths?
Three minerals hold most of the world's rare earth resources: bastnaesite, monazite and xenotime, says the British Geological Survey. Bastnaesite is usually the main ore mineral in carbonatites. Monazite is the main one in placer sands, with smaller amounts of xenotime.
Alkaline rocks are less tidy. They host minerals such as eudialyte and loparite, which carry zirconium, niobium and other metals as well. Loparite concentrate contains 30% to 35% rare earth oxide, the USGS reports.
What are carbonatite deposits?
A carbonatite is an unusual igneous rock made mostly of carbonate minerals, and it hosts the world's biggest rare earth mines. Carbonatites have been the main source of light rare earths since the 1960s, according to USGS Professional Paper 1802. Their rare earths are almost entirely the light ones, the BGS notes, so they're rich in neodymium and praseodymium but poor in dysprosium and terbium.
Grades can be high. Bayan Obo in Inner Mongolia, the world's largest rare earth deposit, held about 800 million tonnes of ore at roughly 6% rare earth oxide, the USGS says. Mountain Pass in California reported reserves grading about 8% in figures the USGS compiled in 2017. Mount Weld in Australia is mined from a weathered layer sitting on top of a carbonatite.
What are alkaline igneous deposits?
Alkaline, or peralkaline, deposits form in igneous rocks unusually rich in sodium and potassium. They're often lower grade than carbonatites but richer in yttrium and the heavy rare earths, which is why so many heavy rare earth projects outside China are this type.
The catch is processing. The USGS says routine methods for treating these ores don't exist, so each deposit needs its own process worked out. That adds time and testing before a company can show its rare earths can be recovered at a profit.
Canada has several well-known examples. The USGS lists Strange Lake on the Quebec and Labrador border, Nechalacho (Thor Lake) in the Northwest Territories and Kipawa in Quebec. Norra Kärr in Sweden is another.
What are ionic clay deposits?
An ionic clay deposit is a thick layer of soil where rare earths leached out of granite have stuck loosely to clay minerals such as kaolinite. Grades are very low, about 0.04% to 0.25% rare earth oxide. Even so, clays in southern China are the world's main source of heavy rare earths.
The USGS gives three reasons they pay. Weak acids can wash the rare earths out, the clays are often rich in high-value heavy rare earths, and labour costs have been low. The BGS adds that no drilling, blasting or milling is needed. The USGS also notes a localized lack of environmental protection at some Chinese operations.
Outside China, ionic clays are only starting to produce. A mine in Brazil made mixed concentrates from ionic clays with elevated terbium and dysprosium in 2025, according to the USGS heavy rare earths summary.
What are placer (mineral sand) deposits?
A placer is a deposit of heavy minerals sorted and concentrated by water, such as beach or river sand. In rare earth placers the main mineral is monazite, with minor xenotime. These sands were an important source of rare earths until the mid-1960s, when the Mountain Pass carbonatite was found.
Monazite's thorium content is the problem: Australia stopped recovering monazite from some operations to avoid concentrating radioactive material, the USGS says.
Why does deposit type affect cost and radioactivity?
Deposit type affects cost because each type needs a different process to free the rare earths, and some processes are far harder than others. The USGS calls the cost and complexity of processing one important part of developing a rare earth mine.
Radioactivity varies a lot by mineral. Monazite can contain up to 20% thorium oxide by weight, while bastnaesite holds less than 0.3%, according to the USGS. Ionic clays lack radioactivity altogether. A project that has to handle thorium faces extra permitting and waste costs. Our guide How Rare Earths Are Processed explains each step after mining.
What kinds of rare earth deposits does Canada have?
Canada has large rare earth resources, over 15.2 million tonnes of rare earth oxide in 2024 by Natural Resources Canada's estimate. That's a resource figure. Reserves, the part shown to be economic to mine, are far smaller.
Many of the best-known Canadian deposits are alkaline igneous rocks, including Strange Lake, Nechalacho and Kipawa. The BGS also names eastern Canada as a carbonatite region. Companies exploring these deposits appear on our rare earth stocks list.
How can you tell a project's deposit type?
A project's deposit type is usually stated in its technical report and in the geology section of its news releases. Look for the deposit word (carbonatite, peralkaline, ionic clay, mineral sands) and the ore mineral (bastnaesite, monazite, xenotime, eudialyte). The BGS puts it plainly: a deposit's economic potential is strongly influenced by its mineralogy and how it formed.
Once you know the type, you know what to check next. For a carbonatite, check whether there's a separation plan. For an alkaline deposit, check the metallurgical test work. For a clay project, check the leach recoveries, and for monazite, how the thorium will be handled. Our guide How to Read a Rare Earth Resource Estimate covers grades and resource categories, and What Are Rare Earth Elements? covers the basics.
Rare Earth Deposit Types: frequently asked questions
What are the main types of rare earth deposit?
The US Geological Survey names four main types: carbonatites, alkaline igneous rocks, ion-adsorption clays and mineral sand placers. Carbonatites have been the main source of light rare earths since the 1960s. Clays in southern China are the main source of heavy rare earths.
What is an ionic clay deposit?
An ionic clay deposit is a layer of weathered soil where rare earths washed out of granite have stuck loosely to clay minerals. Grades are very low, about 0.04% to 0.25% rare earth oxide. They still pay because weak acids can wash the rare earths out and the clays are often rich in heavy rare earths.
Why is monazite radioactive?
Monazite often contains thorium, a radioactive element. The USGS says monazite can hold up to 20% thorium oxide by weight, against less than 0.3% for bastnaesite. That thorium has to be managed during processing, and it is why Australia stopped recovering monazite from some mineral sands.
Does Canada have rare earth deposits?
Yes. Natural Resources Canada estimates Canada held over 15.2 million tonnes of rare earth oxide in resources in 2024. Many of the best-known Canadian deposits are alkaline igneous rocks, such as Strange Lake in Quebec and Labrador and Nechalacho in the Northwest Territories.
What is bastnaesite?
Bastnaesite is a rare earth carbonate mineral and the main ore mineral in carbonatite deposits. It is mined at Mountain Pass in California and at Bayan Obo in China. Along with monazite and xenotime, it hosts most of the world's rare earth resources.
Sources
- US Geological Survey, Professional Paper 1802-O: Rare-Earth Elements (2017)
- US Geological Survey, Fact Sheet 2014-3078: The Rare-Earth Elements, Vital to Modern Technologies and Lifestyles
- British Geological Survey, Rare Earth Elements mineral profile (2010)
- Natural Resources Canada, Rare earth elements facts
- US Geological Survey, Mineral Commodity Summaries 2026: Rare Earths (Heavy)
Related guides
- What Are Rare Earth Elements?Seventeen metals, most of them not rare at all. What they are and what they are used for.
- Rare Earth Magnets ExplainedHow NdFeB magnets are made, where they go, and why they drive rare earth demand.
- What Is NdPr Oxide?The neodymium-praseodymium product that sets most rare earth project economics.