42 Cordilleran Mineral Systems: Interdisciplinary Perspectives on Critical Metal Ore Deposits

Explore the processes responsible for selective transport and accumulation of critical metals in the Earth’s crust: mineral systems science, economic geology, mineral exploration, geochemistry and isotopes, fluid inclusions, and mineral chemistry (bilingual session (English/Spanish)).

Friday, 24 April 2026
1:30 PM - 5:30 PM
LMH, Meeting Room

Rare metal mineralization associated with agpaitic syenites in the northern Eastern Mexican Alkaline Province

Paper number: 42-10
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

Alkaline magmatism in the Eastern Mexican Alkaline Province (EMAP) extends from the Gulf of Mexico to the Mexico-USA border, yet its northern sector remains poorly characterized in terms of rare-metal potential. This study documents the mineralogical and petrogenetic evolution of alkaline complexes in the Sierra Maderas del Carmen region, with particular emphasis on eudialyte-group-mineral (EGM)-rich syenites identified as the most prospective lithologies for Zr-Nb-REE mineralization. Magmatism defines an evolutionary sequence from alkali gabbros and intermediate intrusions to silica-saturated and silica-undersaturated syenites derived from enriched, OIB-like mantle melts emplaced in an intracontinental setting. EGM-rich syenites occur as narrow dikes, sills, and small plugs, locally associated with well-developed calc-silicate skarn haloes in carbonate host rocks. Five syenite types are recognized, ranging from fine-grained agpaitic to transitional agpaitic assemblages dominated by EGM, aegirine-augite, alkali feldspar, and sodalite ± analcime. The most metal-enriched syenites are characterized by early crystallization of EGM, feldspar, and aegirine-augite, followed by late-stage albite + calcite + gittinsite assemblages, reflecting extreme differentiation under dry, reducing conditions. These processes promoted increasing peralkalinity and the concentration of Zr, Nb, REE, Th, and Ti into late magmatic and magmatic-hydrothermal assemblages. Scanning electron microscopy reveals a diverse suite of rare-metal minerals, including eudialyte, britholite-(Ce), thorite, pyrochlore, ancylite-(Ce), gittinsite, and baddeleyite, occurring both within syenites and associated skarns. Regionally, emplacement ages (~48–28 Ma) coincide with slab detachment beneath northeastern Mexico, linking intraplate alkaline magmatism to rare-metal fertility. These results highlight the northern EMAP as an underexplored province for agpaitic-related Zr-Nb-REE mineralization in the North American Cordillera.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410793

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