The Round Top Mountain near Sierra Blanca, in Hudspeth County, Texas, holds one of the biggest deposits of heavy rare-earth elements (REE) in the US. It also contains a variety of critical industrial minerals and technology metals including lithium, uranium, thorium, beryllium, gallium, hafnium and zirconium.

The Round Top REE and critical minerals deposit is located on state property owned by the Texas General Land Office (GLO), and the Texas government has recommended it as a high priority infrastructure project soliciting federal support and approval.

Texas Mineral Resources (formerly Standard Silver) holds 950 acres of lease encompassing the 380m-tall and 1.6km-diametre Round Top hill, apart from prospecting permits on 9,345 acres in adjacent areas.

Texas Mineral Resources (TMRC) has teamed up with the US and Australian-based privately held investment group USA Rare Earth to jointly develop the project, which is estimated to be of £1.2bn ($1.56bn) net present value (NPV).

A revised preliminary economic assessment (PEA) for the project was completed in August 2019. It predicts a 16-months payback period for £269m ($350m) initial capital investment on a 7.3 million tonnes per annum (Mtpa) open-pit mining and processing operation that can produce 2,212(t) of rare earth oxide (REO) as well as 8,956t of lithium carbonate annually over a mine life of minimum 20 years.

Round Top REE project development

TMRC initiated a PEA for the Round Top REE project in November 2011 and completed it in November 2013.

The PEA was based on extensive exploration drilling and a number of geological and metallurgical studies carried out for the Round Top prospect during 2011 and 2013.

The updated PEA of 2019 expanded the Round Top resource base and called for a low-cost, open-pit heap leach operation to produce critical minerals such as lithium, uranium, beryllium, gallium, hafnium, and zirconium, apart from producing a range of rare earth elements.

TMRC entered into a development and funding agreement with USA Rare Earth for the Round Top project in November 2018.

USA Rare Earth is entitled to acquire a 70% interest in the project by spending £7.7m ($10m) for the finalisation of processing technology and the completion of a bankable feasibility study (BFS). It also has an option to acquire an additional 10% interest through £2.3m ($3m) cash payment to TMRC.

Navajo Transitional Energy (NTEC), the owner and operator of the Navajo Mine that supplies coal to the Four Corners power plant in New Mexico, purchased more than 5.1 million TMRC shares for a total of approximately $1.84m in August 2019. NTEC also agreed to purchase an additional five million shares to ultimately become a 20% shareholder of TMRC.

Pilot processing plant for the Round Top mine

TMRC and USA Rare Earth announced the launch of a rare earth and critical minerals pilot processing facility in Wheat Ridge, Colorado in December 2019.

Expected to be operational in the first quarter of 2020, the Colorado-based pilot facility will utilise continuous ion exchange/continuous ion chromatography (CIX/CIC) processing technology to demonstrate the production of fully separated REEs, lithium, as well as other technology metals and industrial minerals from the polymetallic ore of the Round Top deposit.

USA Rare Earth also entered into a strategic relationship with Australia-based Arafura Resources to process heavy rare earth concentrates from Arfura’s 100% owned Nolans Bore Neodymium-Praseodymium (NdPr) deposit in Australia’s Northern Territory, at the Colorado pilot plant, in December 2019.

The Colorado pilot plant is claimed to be the first processing facility outside of China which will be capable of separating the full range of rare earths.

After a successful demonstration, the pilot plant is planned to be moved to Texas and scaled up for commercial operation.

The strategic importance of the Round Top project

Round Top is being pursued as a strategically important project for the US national security as the country is implicated in a trade war with China that continues to dominate the global supply of rare earths.

According to the US Geological Survey (USGS), the US is the world’s second-biggest rare earth producer. It produced 26,000t of rare-earth oxide (REO) equivalent in 2019, following the world’s biggest REE producer China that produced more than five times (132,000t) in the same year.

The US was dependent on China for approximately 80% of its total rare-earth compounds and metals imports during 2015-2018.

The country has only one operational rare-earths mine, the Mountain Pass mine in San Bernardino County, California, which is owned and operated by Molycorp.

The Mountain Pass mine commenced production in 1952 but was discontinued from 2002 to 2011 and again from 2015 to 2018 because of low rare-earth prices. Production restarted at the Mountain Pass mine in the first quarter of 2018.

The Round Top deposit hosts 15 of the 17 rare earth elements as well as other high-value minerals including lithium that are increasingly in demand for energy, industrial, and military technology applications in the US.

It is being regarded as a high-potential project to reduce dependence on Chinese imports as it offers a secured and long-term domestic supply of critical materials required for advanced technology manufacturing capabilities in key sectors including defense and energy.

Location, geology, and mineralisation

The Round Top project is located approximately 12.8km north-west of Sierra Blanca in Hudspeth County, Texas.

The REE and critical minerals deposit is located in the Trans-Pecos region in far-west Texas that forms part of the Chihuahuan Desert, the biggest desert in North America.

The geology of the project area is characterised by rhyolites containing both heavy and light REEs in a concentrated manner and at a relatively consistent grade, as well as pegmatites containing a host of critical minerals including lithium, uranium, and thorium.

Heavy rare-earths are estimated to account for approximately 70% of the total REEs contained in the deposit. REE mineralisation at Round Top occurs in vugs and crystal coatings and is mainly found hosted in disseminated microcrystals of varieties of fluorite.

Early exploration activities

Early mineral exploration at Round Top is traced back to the fluorite exploration activities that continued from 1969 through the late 1970s.

Although the fluorite project didn’t take off due to weak market conditions, early exploration works led to the discovery of beryllium mineralisation in the area.

Cabot Corporation continued beryllium exploration at the deposit during the 1980s and formed a joint venture with Cyprus Metals in 1987 to complete a feasibility study for the Sierra Blanca beryllium project in 1988.

The beryllium project, however, could not be developed with Cyprus Metals subsequently leaving the joint venture to focus on copper mining.

Mineral resource estimates

The Round Top deposit was estimated to hold 364,000t of measured and indicated resources and 735,000t of inferred resources containing REEs, technology metals and industrial minerals as of August 2019.

Mining and ore processing

The Round Top is expected to be a 20,000 tonnes per day (tpd) conventional open-pit mine involving drill-blast-load-haul operations.

Mining will proceed in 20ft benches form the uppermost part of the Round Top Mountain, while the pit slopes are designed at 45° inter-ramp wall angle. The mining fleet will comprise 12m3 wheel loaders and 90t haul trucks, while the haul roads are designed to be 100ft-wide.

The extracted ore will be conveyed to a crushing plant near the leach pads adjacent to the processing facility. The ore will undergo three-stage crushing to be reduced to 0.5in size.

The crushed ore will be conveyed and stacked on the heap pads with the use of conveyors, grasshoppers, and radial stackers. Heap leaching will be done with the use of sulphuric acid.

REEs and other minerals from the resultant pregnant leach solution (PLS) are planned to be extracted using continuous ion exchange (CIX) and continuous ion chromatography (CIC) processes.

Infrastructure facilities

The Round Top project site is accessible from the Interstate 10 highway a series of paved and unimproved dirt roads. The nearest major airport is located in El Paso, approximately 142km north-west of the project site, while the nearest railroad line is located approximately 4.8km away from the project area.

Power supply to the site will be provided by El Paso Electric Company which has approximately 1.6GW of generating capacity, while water supply is expected to be sourced from an existing well-field located approximately 4km east of the proposed processing plant site.

Consultants involved with the Round Top project

Gustavson Associates, an international mining consulting firm based in Colorado, US, provided mineral resource estimates as well as prepared both the original and updated PEAs for the Round Top project.

Inventure Renewables, Fenix NZ, Resource Development (RDI) and Pro Solv Consulting were engaged for the design of the Colorado-based pilot processing plant for the Round Top REE and critical minerals project.