Summary:
Deposit Type
The Red Mountain pluton (RMP) of the Halleck Creek Rare Earths Project is an example of a magmatic allanite hosted REE deposit composed of rocks ranging from monzonitic to syenitic.
A-type granites are formed by partially melting mantle rock within stable continental blocks or rift zones. Mantle magma ascends through the crust and changes chemically in response to various factors, including temperature, pressure, and chemistry of wall rock. The term alkaline infers that the parent magma has a primary enrichment of Na2O and K2O and, as such, contains abundant Na- and Kbearing minerals such as feldspathoids, alkali pyroxenes, and alkali amphiboles. These magmas are not only enriched in REEs but are typically enriched in zirconium, niobium, strontium, barium, and lithium (Balaram, 2019). Primary alkaline deposits are commonly associated with elevated levels of uranium and thorium. The RMP deposit, however, is unusually depleted of radioactive elements.
It is also common for primary magmatic mineralization to be overprinted by late magmatic and/or hydrothermal fluids (Balaram, 2019). Hydrothermal alteration at the RMP deposit is minimal and has not affected REE mineralization.
REE mineralization in deposits such as observed at Halleck Creek is directly attributed to fractional crystallization in the late stages of magma body evolution.
Primary rare earth bearing rock types within the RMP consist of clinopyroxene quartz monzonite (CQM), and biotite-hornblende quartz syenite (BHS). Allanite is the primary rare earth element (REE) host mineral at the Halleck Creek Project. Allanite is a sorosilicate within the epidote group which contains a significant number of REEs in its primary mineral structure. Allanite usually occurs in association with clinopyroxene, hornblende, olivine and zircon agglomerated as “mafic clots” within CQM.
Deposit Dimensions
The Halleck Creek REE project currently contains two primary resource areas: the Red Mountain area and the Overton Mountain area. Resources also extend into the Cowboy State Mine area and the Bluegrass resource area.
Like the Red Mountain drilling, RC samples at Overton Mountain contained TREO assay values exceeding 3,500 ppm to depths of 150m in 18 holes. One, 302m diamond core hole additionally exhibited grades exceeding 2,000 ppm to the bottom of the hole. Therefore, ARR considers the Overton Mountain resource area to be open at depth.
Mineralization
Rare earth element mineralization within the pluton is hosted within allanite [Ce,Ca,Y,La)2(Al,Fe3)3(SiO4)3(OH)], a sorosilicate of the epidote group, and zircon. Mineralization occurred due to fractional crystallization of the RMP bodies over time.
Commodity Production
Samarium (Sm), Europium (Eu), Gadolinium (Gd) mixed oxide concentrate also referred to as “SEG” concentrate.
| Commodity | Product | Units | Avg. Annual | LOM |
|
Lanthanum
|
Carbonate
|
t
| | 36,200 * |
|
NdPr
|
Oxide
|
t
| 1,833 * | 38,500 * |
|
SEG
|
Oxide
|
t
| 488 * | 10,300 * |
|
Terbium
|
Oxide
|
t
| 24 * | 500 * |
|
Dysprosium
|
Oxide
|
t
| 98 * | 2,100 * |
|
NdPr Equivalent
|
Oxide
|
t
| | 87,500 * |
|
Total Rare Earth Oxides
|
|
t
| 4,169 * | |
* According to 2025 study.