An occurence of metasomatic aujminosilicates related to high alumina hydrothermal alteration within the South Mountain Batholith, Nova Scotia
DOI:
https://doi.org/10.4138/1642Abstract
A zone of high alumina hydrothermal alteration (HAHA) is documented within granitoid rocks of the Big Indian Polyphase Intrusive suite (BIPI suite), which forms part of the Late Devonian-Early Carboniferous South Mountain Batholith (SHB). The alteration, which la confined to a NE-trending shear zone, is characterized by the quartz-deficient mineral assemblage andalusite-sillimanlte-spinel-oiuscovite-cordierite-apatite-pyrite. The HAHA zone represents the first reported occurrence of this alteration type within the South Mountain Batholith. Field observations indicate that the HAHA zone is only one of a series of successive and superimposed metasoraatic-hydrothermal events which, together with U-Cu-Ho + U-Cu mineralization, exhibit a transition in style from early pervasive to late fracture-controlled. This change in style within the BIPI suite is considered to reflect a progressive Increase in fluid pressure. Petrography and mineral chemistry suggest that the HAHA zone formed in response to the interaction of the leuco-monzogranlte host with a Na(+Al)-rich, siliea-undersaturated fluid. Although speculative, alumina may have been a mobile element transported as an alkali-complex via the fluid. High temperature mineral assemblages (gndalusite-aillimanite; andalusite-spinel) Indicate that the initial temperature of the aqueous fluid phase was ≥620oC for 2 kb pressure. It la proposed that the fluid phase represents a residual magmatic-fluid which was accessed by deep-seated fracturing. RÉSUMÉ On documenté une zone d'altération hydrothermale hautement alumlneuse (AHHA) à l'intérieur des granitoides de la suite intrusive Polyphasée de Big Indian (suite IPBI) qui fait partie du Batholite de South Mountain (BSM) d'âge tardidévonien à éocarbonifère. Confinée à une zone de cisaillement A tendance NE, l'altération est caractérisée par un assemblage de minéraux, deficient en quartz, à andalousite-sillimanite-spinelie-museovite-cordierite-apatite-pyrite. La zone AHHA représente la première mention de ce type d'altération à l'intérieur du BSM. D'après les observations sur le terrain, cette zone AHHA n'est qu'un d'une serie d'evenements métasomatiques et hydrothermaux successifs et superposes qui. ainsl qu'une minéralisation en W-Cu-Mo+U-Cu. exbibent un style d'abord pénétrant et enfin filonlen. On consideré que ce changement de style A l'intérieur de la suite IPBI représente un accroissement progressif de la pression des fluides. La pétrographie et le chimisme des minéraux tendent à montrer que la zone AHHA e'est établie en reponse à l'intersction de l'encaissant leucomonzogranitique avec un fluide sous-sature en silice et riche en Na±Al. Bien que cela reste speculatif, l'alumine pourrait avoir été un élément mobile transports par le fluide à l’état de complexe alcalln. D'après les assemblages de minéraux A haute température (andalousite-sillimanite; andalousite-spinelie), la température inltiale de la phase aqueuse fluide était ≥620oC pour une pression de 2 kb. On propose que la phase fluide représente un fluide magmatique residuel extrait par une fracturation en profondeur. [Traduit par le journal]Downloads
Published
1988-04-01
How to Cite
Corey, M. C. (1988). An occurence of metasomatic aujminosilicates related to high alumina hydrothermal alteration within the South Mountain Batholith, Nova Scotia. Atlantic Geoscience, 24(1). https://doi.org/10.4138/1642
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