The Sierra Blanca Laccolith (“SBLC”) Complex is situated in a structurally complex zone within the western alkali-calcic belt of the Trans-Pecos magmatic province of West Texas. The only laccolith dated, the Sierra Blanca laccolith, has a biotite potassium-argon age of 36.2±0.6 Ma. The similar geochemical values, mineral content, and stratigraphic position suggest all five laccoliths within the complex were emplaced contemporaneously.
Mineralizing events within the SBLC occurred in multiple stages that include 1) rare earth element and other elements of interest associated with the Eocene emplacement of the rhyolite laccolith intrusion, and 2) post-emplacement fluid interaction that mobilized and concentrated rare earth elements within chemical brecciation zones between 6.2 Ma and 1.7 Ma.
The SBLC rhyolite has significantly-higher heavy rare earth elements in comparison to other felsic intrusions in the Trans-Pecos Texas magmatic region (i.e., North Quitman stock and Quitman Mountains), which rules out any crystal fractionation magmatic links between the intrusive groups. The heavy rare earth element nature of the laccoliths (including the Little Blanca and Sierra Blanca laccoliths) is petrographically supported by the identification of yttrocerite, yttrofluorite, and bastnäsite. Other rare earth element minerals, or rare earth element fingerprinting minerals, include fluorine, lithium-rich mica, columbite, tantalite, cassiterite, thorite, and niobium-rich rutile. These minerals define the rare earth element mineralization within the laccolith rhyolite with substantial enrichment of heavy rare earth elements. The mineralizing environment includes the potential for incompatible trace element co-product value (e.g., beryllium, fluorine, lithium, gallium, rubidium, yttrium, and niobium).
As a result, the laccoliths have remarkably consistent mineralization that outcrops at surface with no to minimal overburden.