Abstracts
Abstract
The results of a petrographic and lithogeochemical study of metasedimentary rocks (Lower Paleozoic Meguma Group) surrounding the northern part of the East Kemptville tin deposit, southwestern Nova Scotia are presented. The metasedimentary rocks, including interbedded psammites and pelites, are fine-grained and highly indurated. Pelitic horizons contain homfelsic textures (i.e., <5 mm cordierite grains) near the granite; sparse veining includes some cassiterite and sulphides. Hydrolhermal alteration is manifested by disseminated, fine-grained, secondary muscovite and/or muscovite and chlorite infilling and lining microfractures with bleached haloes and associated cassiterite, sulphides, tourmaline, fluorite and carbonate.
The major and trace element chemistry, including the rare-earth elements, of the metasedimentary rocks are compared to different data bases that comprise: (1) averages for pelites and psammitcs of Phanerozic age, (2) nonmineralized Meguma Group rocks, and (3) fields in discriminant binary clement diagrams. For most of the major and trace elements analyzed an apparently unaltered, normal chemistry is indicated, except for some LILE (e.g., Li, Rb, U) and ore-forming elements (e.g., Sn, Zn, Bi) where enrichment is considered to reflect infiltration of mineralizing fluids from the proximal granite/greisen of the main deposit area. The data indicate that infiltration of fluids was minimal and that, for the most part, the metasedimentary rocks acted as an impermeable cap to the ore-forming solutions.
RESUME
Les résultats d'une étudc pétrographiquc ct lithogSochimique des roches métas6dimentaires (Groupe dc Meguma du Paleozoique inferieur) entourant la partic nord du gisement d'étain de East Kemptville, dans le sud-oucst de la Nouvellc-écossc, sont presenter. Les roches mStasddimentaires, comprenant des gres et des pelites, sont a grain fin et fortement induces. Les horizons pelitiqucs montrent des textures dc corndennes (i.e., des grains de cordidrite <5 mm) pres du granite; des veines ^parses contiennent de la cassiterite et des sulfures. L'alteration hydrothermale se manifeste par de la muscovite secondaire a grain fin disscminde ou par dc la muscovite ct de la chlorite en remplissage et en tapis sage dc microfractures aux ^pontes lessivges et associccs a de la cassiterite, des sulfures, de la tourmaline, de la fluorite et des carbonates.
La composition en elements majeurs ct traces, incluant les terres rarcs, des roches métas6dimentaires sont companies a diverses bases de donnécs, incluant: (1) les composition moyennes des pelites et des gres d'age Phan6rozoi*que, (2) les roches non mineralisdes du Groupe dc Meguma et (3) les champs des diagrammes de discrimination binaires. Les teneurs de la plupart des elements majeurs et traces analyses indiqucnt une composition normale, apparamment inaltdr^e, a part pour certains elements a grand rayon ionique (e.g., Li, Rb, U) et certains elements 6conomiques (e.g., Sn, Zn, Bi) ou renrichissement estconsideVe" comme repnSsentant 1'inftitration de fluides min^ralisateurs provenant du greisen proximal de la region du gisement principal. Les donne'es indiqucnt que 1'infiltration des fluides Stait minimale et que les roches me^asddimentaircs ont agi principalcment comme une cnveloppe impermeable pour les solutions mineralisatrices.
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