Pétrographie et géochimie des matières organiques des séquences plombo-zincifères d'âge Carbonifère, Bassin Salmon River, Nouvelle-Écosse, Canada

• Published in: Organic geochemistry 1989, Vol.14 (3), p.253-268
• Main Authors: Héroux, Y., Michoux, D., Desjardins, M., Sangster, D.
• Format: Article
• Language: fre
• Subjects: alteration; carbon; Charbon; coal; lead; M.O; MEB; petrography; plomb; pétrographie; Roches sédimentaires; Sciences de la terre; Sciences exactes et technologie; SEM; Terre, ocean, espace; zinc
• ISSN: 0146-6380; 1873-5290
• DOI: 10.1016/0146-6380(89)90054-5

Les conditions oxydo-réductrices du milieu de dépôt des solutions métallifères régissent les transformations des matières organiques dansl le cyclothème grs̀o-charbonneux et plombo-zincifère de Yava, Nouvelle-Écosse. L'influence du soufre et des sulfures sur la pyrolyse des matières organiques semble annuler, tout comme la houillification, l'effet de l'oxygénation décelé en microscopie. Les modifications des matières organiques pouvant être associées aux zones métallifères sont: 1—la pétrification par les sulfures; 2—la perte de fluorescence des spores; 3—l'apparition d'anisotropie anormale et de textures végétales rehaussées; 4—la formation de fissures et de vacuoles; 5—la formation de bourrelets de réflectivité négative et positive; 6—une évolution anormale des gradients du pouvoir réflecteur et de l'indice d'altération thermique. This paper reports preliminary results from an investigation of organic matter (OM) from the Carboniferous coarse to fine grained clastic sequences of the Salmon River Basin, Nova Scotia, Canada. The study focuses on the lead-zinc bearing fluviatile sandstone of the Yava ore deposite and its purpose is to explore how the metalliferous fluids might have modified the OM for different lithologies near the ore body. Previous researches have shown that vitrinite reflectance ( R o-vi) of OM in sandstone increases both with depth and regionally toward the Yava area. This lead previous investigators to conclude that the R o-vi was due to thermal effects of mineralizing fluids. On the other hand, thermal alteration index (TAI), based on spores from interbedded shales, is quite homogenous throughout the area and with values too low to fit with the maturation rank based on R o-vi. In the latter case the present authors argue that oxidizing effects of the metalliferous fluids are responsible for higher and increasing R o-vi in the more porous and permeable sandstone. Organic matter petrography, reflectance, fluorescence, color estimation, pyrolysis, ultimate analysis and scanning electron microscopy techniques were used to study 159 samples from 69 boreholes and hand specimens. OM petrography proved to be the most conclusive technique while reflectance and color evaluation support their results. The bulk of OM occurs as dispersed coaly fragments and thinly bedded coal in sandstone units. Rather undeformed and well preserved tree parts from sandstone and finer clastic rock show distinct morphology. Rare fractures filled with solid bitumen o