Abstracts
Abstract
Field, petrographlcal and geochemical evidence collected from three case study areas within the peraluminous granites of the Meguma Zone Indicates that airborne gamma-ray Bpectrometrlc data can be a valuable aid In bedrock mapping and mineral exploration. The three case study areas include the Hew Ross Pluton and Big Indian Polyphase Intrusive suite which underlie a portion of the central and eastern region of the 10.000 km South Mountain Bathollth, and the Sangster Lake and Larrya River plutons from the eastern end of the Heguma Zone.
Utilizing predominately the eO/eTh ratio, it is shown that these data can delineate the various granitic units which comprise large plutons and bethollths. A direct correlation la observed between areas of highest ratio response and the presence of small two-mica leucogranltic intrusive bodies. Conversely, areas underlain by biotite-tich nonzo-granltic units possess the lowest ratio response. The concentration of trace elements such as D. Th. Rb, Sr, Zr and Tl within the various unite confirm these observations and indicate that the variation in eU/eTh may be attributed to the degree of magmatic differentiation.
The case studies presented In this paper also Indicate that factors other than bedrock composition can influence the airborne radioelement response of a given area. For example, parameters such as type and style of mineralization, type and degree of fluid interaction, and also the provenance and thickness of till deposits may all play an important cumulative role In the determination of the airborne spectrometrlc signature over an area. Accordingly, any geological investigation or mineral exploration venture utilizing such data must be prepared to address these variables.
RESUME
La collecte de donnees de terrain, petrographiquea et geochlmlques en trois sites repreeentatifs au sein de granites peralumlneux de la Zone de Heguma indlque que la spectrometrie aeroportee a rayons gamma pent s'averer un outll fort utile a la cartographic du socle et A 1'exploration minerale. Parmi ces Bites, on retrouve le Pluton de New Ross et la suite Intrusive Polyphasee~de Big Indian, sous-jacents A une portion des regions central* et orientale du Batholite de South {fountain (10,000 km ), ainsi que les plutons de Sangster Lake et de Larrys River A l'extremite orientale de la Zone de Heguma.
A 1'alde surtout du rapport eUVeTH, on montre comment ces donnees peuvent clrconscrire les diverses unites granltlques englobant ces gros plutons et batholltes. Les sites montrant le rapport signal: bruit le plus Aleve se correlent dlrectement avec la presence de petits intrueifs leucogranitiques A deux micas. A 1'oppose, le rapport le plus bas s'observe dans les regions formees d'unites monzogranltiquea riches en blotite. La concentration des elements en traces, tels D, Th, Rb. Sr, Zr et Tl. au sein de ces diverses unites confirme cee observations et indlque que la variation en etJ/eTh pourrait resulter du degre de differenciation magmatlque.
Lee cas repreeentatifs decrits dans cet article nontrent auasl que des facteurs autres que la composition du substratum peuvent Influencer le relevA radiometrique aeroporte d'une region donnee. Par exemple. certains parametres tels que le type et le style de la mineralisation, le type et le degre d'Interaction dee fluldes ainsi que la provenance et l'epaisseur des depots de till peuvent ausal Jouer un rSle cumulatlf majeur dans la determination de la signature speetroroetrique aeroportee au-dessus d'une region. Par consequent, on doit tenlr compte de ces variables lors de toute investigation geologique ou campagne d'exploration.
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