Critical Minerals Factbook
Deposit

Round Top

Round Top is a deposit with published resource estimates in Texas, recorded in the USGS USMIN rare earth element occurrence database (ver. 4.0, June 2019).

Facts on this page last re-verified Aug 12, 2026 — the oldest verification date among its current claims. How we verify.

Location: Texas, United States (31.272, -105.479 approx.)

Commodities: rare earth elements; beryllium; niobium; hafnium; tantalum; tin; uranium; thorium

Deposit model: peralkaline intrusion · unclassified

Tracked facility at this deposit: USA Rare Earth Round Top Mountain

Geology

“The Round Top rhyolite was divided into five different alteration phases based on the intensity of hematitic and hydrothermal alteration: gray rhyolite, pink rhyolite, red rhyolite tan rhyolite and brown rhyolite in the order of least to most altered. Hematitic alteration is a replacement of the magnetite by hematite and gives the rhyolite a red to pink color. Hydrothermal alteration was late and gives the rhyolite a tan to brown color. Mostly unaltered, gray rhyolite was also documented. Initial geochemical testwork, presented in Section 13, suggests that the gray and pink rhyolite units have the highest REE content, averaging between 554 and 615 parts per million (ppm) total REE + Yttrium (Y). Red and tan rhyolites, which may be strongly vapor-phase altered, contain about 8% lower abundance of REE and the brown rhyolite, which may be altered hydrothermally or by groundwater, contains about 23% less REE than the gray and pink varieties.” (Hulse and others (2014)) “Round Top rhyolite is enriched in Heavy Rare Earth Elements (HREEs). Statistical review of the current data shows that an estimated 70% of the total REE’s grade being HREEs. REE mineralization occurs primarily as disseminated microcrystals of varieties of fluorite (such as yttrium-rich yttrofluorite) where HREEs have substituted for calcium, and as other REE-bearing accessory minerals. REE minerals occur mainly in vugs and as crystal coatings, suggesting late-stage crystallization from an incompatible element-rich fluid. Other incompatible elements were concentrated in these late magmatic fluids. Uranium occurs as fine disseminated grains of uraninite and coffinite. Niobium-tantalum bearing columbite is relatively abundant. Zircon also is relatively abundant and is the mineral containing the zirconium and hafnium. Several unidentified tin minerals are present and thorium is contained in thorite and within zircon.” (Hulse and others (2014))

Published resource estimates

As compiled by USGS USMIN from the cited studies. Resource classes follow the source; "approximate" flags values USMIN reports as approximations. These are not current company reserve statements.

MaterialClassAmountGradeContainedAs ofReference
hafnium oxide (HfO2)Measured plus Indicated48,900 t—41,500 metric tons HfJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
hafnium oxide (HfO2)Inferred34,500 t—29,300 metric tons HfJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
tin dioxide (SnO2)Measured plus Indicated84,400 t—66,500 metric tons SnJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
niobium oxide (Nb2O5)Measured plus Indicated262,000 t—183,000 metric tons NbJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
thorium oxide (ThO2)Inferred68,500 t—60,200 metric tons ThJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
tin dioxide (SnO2)Inferred60,100 t—47,300 metric tons SnJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
niobium oxide (Nb2O5)Inferred184,000 t—129,000 metric tons NbJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
tantalum pentoxide (Ta2O5)Inferred27,700 t—22,700 metric tons TaJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
total rare-earth oxide (TREO)Inferred216,000 t—216,000 metric tons TREOJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
uranium oxide (U3O8)Inferred18,200 t—15,400 metric tons UJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
thorium oxide (ThO2)Measured plus Indicated97,500 t—85,700 metric tons ThJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
total rare-earth oxide (TREO)Measured plus Indicated304,000 t—304,000 metric tons TREOJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
tantalum pentoxide (Ta2O5)Measured plus Indicated39,400 t—32,200 metric tons TaJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.
uranium oxide (U3O8)Measured plus Indicated25,600 t—21,700 metric tons UJan 1, 2013Hulse and others (2014), Pages 90-91, Table 14-7 — Hulse, D. E. ,et al., 28-April-2014, NI 43-101 Amended Preliminary Economic Assessment Round Top Project Sierra Blanca, Texas: Prepared for Texas Rare Earth Resources: Gustavson Associates, 206p.

Exploration and site history

Record imported from USGS USMIN ver. 4.0 (June 2019). Developments after that date appear on facility records, not here; see the methodology.

Sources