Banca de DEFESA: Brunno Abílio Ciriaco Araujo

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Brunno Abílio Ciriaco Araujo
DATE: 21/12/2023
TIME: 14:00
LOCAL: Sala de Videoconferência do IG e Plataforma Teams
TITLE:

The Coqueiros Phosphate Deposit, Catalão II Alkaline-Carbonatite Complex: Significance of Magmatic Mechanisms in the Formation of Apatite Concentrations

KEY WORDS:

Bebedourites, Carbonatites, Igneous Phosphate Deposits.

PAGES: 225
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

The Catalão II complex is the northernmost alkaline-carbonatite complex of the Alto Paranaíba Igneous Province situated next to the homonymous city of Catalão (Goiás, Brazil). The complex is an NNE kidney-shaped body that comprises an area of 12 km2 dominantly consisting of bebedourites, phoscorites, and carbonatites, with subordinate alkali-feldspar syenites and ultramafic lamprophyres. Separate magmatic systems between the southern and northern portions of the complex are recognized based on differences in the mode of emplacement and predominant rock types. Catalão II South is predominantly composed of evolved phoscorites and calcite- to dolomite carbonatites in a complex system of cross-cutting dikes with subordinate small-scale intrusions. On the other hand, Catalão II North is composed of successive intrusions of bebedourites, calcite carbonatites, and late transgressive dikes that comprise phoscorites, calcite- to dolomite carbonatites, and alkali-feldspar syenite. Ultramafic lamprophyres are the last magmatic pulse and occur in all area as plugs, pipes, and dikes. Apatite-rich rocks host important phosphate resources in the northern portion. The area known as the Coqueiros deposit remains unexplored and the detailed lithological characterization was poorly constrained in previous works. Phosphate resources are estimated in the order of 45 Mt at a grade of 11. 0% P2O5 for residual apatite in the weathering profile, and 410 Mt at a grade of 9.0% P2O5 for fresh rock apatite. The major apatite-bearing lithologies are the bebedourites, apatitite, and associated calcite carbonatites. Although strictu sensu phoscorites contain an important apatite content, they are volumetrically limited and do not contribute substantially to the phosphate mineralization. Based on drill-core descriptions, petrographical characterization, mineral and hole-rock composition, at least three bebedourite stages can be recognized and two of them can be paired with a respective clinopyroxene-bearing calcite carbonatite. A tetraferriphlogopite-rich bebedourite composes an external ultramafic rim in the Coqueiros deposit. Marginal lens-shaped intrusions are composed of apatite bebedourite and diopside calcite carbonatite. The central core is predominantly composed of a tetraferriphlogopite apatitite. Late-stage titanite-rich bebedourites and an associated aegirine-augite calcite carbonatite occur as small-scale stocks and plugs. Petrographical and compositional data indicate a multistage emplacement of variably differentiated magma batches. The ultramaficcarbonatite association in Catalão II represents the result of a complex differentiation of a mixed silicatecarbonate parental magma probably similar to the coeval ultramafic lamprophyres in the complex. The first intrusion stage is represented by the tetraferriphlogopite bebedourite and the presence of basement xenoliths and distinct trace-element patterns are compatible with some contribution of crustal contamination. The second and third intrusion stages are represented by paired consanguineous bebedourites and carbonatites. In both cases, there is clear evidence from gradational contacts, mineral composition trends, and similar trace-element distribution, of an evolution mechanism via fractional crystallization. In that sense, hypogenic phosphate mineralization in the Coqueiros deposit is represented by apatite-enriched bebedourites formed due to an extensive fractionation of silicate minerals forming a sequence of bottom ultramafic cumulates, intermediate apatite-rich levels, and residual clinopyroxene calcite carbonatites.

COMMITTEE MEMBERS:
Externo à Instituição - ROGÉRIO GUITARRARI AZZONE - USP
Presidente - 418965 - CLAUDINEI GOUVEIA DE OLIVEIRA
Interno - ***.092.740-** - JOSE AFFONSO BROD - Durham
Interno - 6404885 - NILSON FRANCISQUINI BOTELHO