Graphite mineralization in migmatites of the Central Ceará Domain, Borborema Province, NE Brazil: the role of anatexis
- 1Geological Survey of Brazil
Abstract
This study investigates the role of anatexis in the distribution of graphite in migmatites and S-type granites of the Central Ceará Domain, Borborema Province, by the integration of field data, petrography, mineral chemistry, and total carbon analyses. The results demonstrate that the degree of partial melting exerts a fundamental control on both the structural framework and the concentration of graphite in the mineralized domains. In migmatites with low melt fractions, graphite occurs predominantly as disseminated flakes and in lenses within residual domains, preserving regional structures. In these lithotypes, graphite flakes are mainly associated with biotite, muscovite, and locally garnet, reflecting their origin through progressive metamorphism of organic-rich protoliths. Graphite mineralization in metatexites is related to the extraction of silicic melt from the residue and its predominantly mechanical migration toward fold hinge zones. The most significant graphite mineralization occurs in rocks with high melt fractions (diatexites and S-type granites) characterized by massive aggregates of graphite flakes within nebulitic structures in diatexites and schlieren in granites. These rocks contain the largest graphite flake sizes (up to 10 mm) and high carbon contents (up to 64%). Such occurrences are preferentially concentrated at the contact zones between diatexites and S-type granites and are spatially associated with regional fold hinge zones, where melt segregation and fluid circulation were intensified, ultimately leading to the development of the Itapiúna Suite. Petrographic and microstructural evidence indicates that, although graphite is not significantly dissolved in silicic melts, its redistribution within leucosomes occurs through physical processes and possibly through recrystallization and/or precipitation from carbon-bearing fluids during syn- to post-anatectic stages. Rutile thermometry indicates peak metamorphic temperatures of ~790–840 °C, consistent with high-grade conditions, while mineral chemistry reveals clear differentiation between leucosome and residue, with more sodic plagioclase compositions in the melt. These results support a hybrid genetic model in which graphite formation is linked to regional metamorphism of organic matter, whereas its concentration and textural evolution are primarily controlled by partial melting, with a possible contribution of fluids to flake growth and carbon enrichment. Partial melting accounts for the coexistence of disseminated, lenticular, and massive graphite mineralization in the study area. Accordingly, lithological and structural controls must be considered in conjunction with anatexis, particularly in high melt-fraction domains, which represent the most prospective targets for effective mineral exploration.
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BibTeX
@article{lopes2026graphite,
title = {{Graphite mineralization in migmatites of the Central Ceará Domain, Borborema Province, NE Brazil: the role of anatexis}},
author = {Angela Lopes and Debora Freire and Vidyã Almeida and Iaponira Gomes},
journal = {Journal of the Geological Survey of Brazil},
year = {2026},
month = nov,
doi = {10.29396/jgsb.2026.v9.n3.3},
url = {https://doi.org/10.29396/jgsb.2026.v9.n3.3},
note = {CC BY},
}
RIS
TY - JOUR
TI - Graphite mineralization in migmatites of the Central Ceará Domain, Borborema Province, NE Brazil: the role of anatexis
AU - Angela Lopes
AU - Debora Freire
AU - Vidyã Almeida
AU - Iaponira Gomes
PY - 2026
DA - 2026/11/05
JO - Journal of the Geological Survey of Brazil
DO - 10.29396/jgsb.2026.v9.n3.3
UR - https://doi.org/10.29396/jgsb.2026.v9.n3.3
AB - This study investigates the role of anatexis in the distribution of graphite in migmatites and S-type granites of the Central Ceará Domain, Borborema Province, by the integration of field data, petrography, mineral chemistry, and total carbon analyses. The results demonstrate that the degree of partial melting exerts a fundamental control on both the structural framework and the concentration of graphite in the mineralized domains. In migmatites with low melt fractions, graphite occurs predominantly as disseminated flakes and in lenses within residual domains, preserving regional structures. In these lithotypes, graphite flakes are mainly associated with biotite, muscovite, and locally garnet, reflecting their origin through progressive metamorphism of organic-rich protoliths. Graphite mineralization in metatexites is related to the extraction of silicic melt from the residue and its predominantly mechanical migration toward fold hinge zones. The most significant graphite mineralization occurs in rocks with high melt fractions (diatexites and S-type granites) characterized by massive aggregates of graphite flakes within nebulitic structures in diatexites and schlieren in granites. These rocks contain the largest graphite flake sizes (up to 10 mm) and high carbon contents (up to 64%). Such occurrences are preferentially concentrated at the contact zones between diatexites and S-type granites and are spatially associated with regional fold hinge zones, where melt segregation and fluid circulation were intensified, ultimately leading to the development of the Itapiúna Suite. Petrographic and microstructural evidence indicates that, although graphite is not significantly dissolved in silicic melts, its redistribution within leucosomes occurs through physical processes and possibly through recrystallization and/or precipitation from carbon-bearing fluids during syn- to post-anatectic stages. Rutile thermometry indicates peak metamorphic temperatures of ~790–840 °C, consistent with high-grade conditions, while mineral chemistry reveals clear differentiation between leucosome and residue, with more sodic plagioclase compositions in the melt. These results support a hybrid genetic model in which graphite formation is linked to regional metamorphism of organic matter, whereas its concentration and textural evolution are primarily controlled by partial melting, with a possible contribution of fluids to flake growth and carbon enrichment. Partial melting accounts for the coexistence of disseminated, lenticular, and massive graphite mineralization in the study area. Accordingly, lithological and structural controls must be considered in conjunction with anatexis, particularly in high melt-fraction domains, which represent the most prospective targets for effective mineral exploration.
SN - 2595-1939
ER -