GLACIAL STRATIGRAPHY AND TILL GEOCHEMICAL CONTROLS ASSOCIATED WITH THE BRAZIL LAKE PEGMATITES, YARMOUTH COUNTY, NOVA SCOTIA

An occurrence of albite-spodumene pegmatite at Brazil Lake, Yarmouth County, is currently being explored for its rare-metal potential (e.g. Ta, Li, Be, Cs, Rb, Nb and Sn). The pegmatite dykes are not easily delineated because of their small size, the pervasive till cover that limits outcrop exposure, and the complex ice flow history of the region. Specialized investigative methods were employed to trace the diluted yet anomalous dispersion zones in the till back up-ice to their bedrock sources.

Till stratigraphy in the study region is highly variable with complexity decreasing inland. Three distinct ice flow directions have been recognized from coastal exposures. Two tills (lodgement till and overlying ablation till) are present at the Brazil Lake area and fabric data indicates a westward and southeastward ice flow direction, respectively. Conventional surveys target samples from the “A1” organic humus horizon and/or the unweathered till layer (taken from approximately 1 m depth). Traditional methods of sample collection were not suitable for this study area because of the complex glacial stratigraphy. At many sites, 1 m deep sample pits did not penetrate into the lodgement till and initial analysis of the ablation till indicated that it was not necessarily representative of dispersion processes. Additional lodgement till samples were collected at 2 to 4 m depths along a 3 km traverse, perpendicular to the pegmatite trend. The high proportions of local lithologies and clast angularity in the pebble data, reflects the lack of clastic dispersion in the area.

An important part of this study was the identification and refinement of the appropriate sampling, analytical, and interpretation strategies that are employed in till geochemistry surveys. Preliminary results indicated that the - 0.063mm and - 2 +1 mm size fractions provided the most reliable indications of rare element mineralization. Consequently, these size fractions were analyzed in additional samples collected during the detailed survey. Initial geochemical data shows enriched zones of limited areal extent southeast (“down-ice”) and northwest (“up-ice”) of known pegmatite occurrences. The northeastern zones could possibly represent another pegmatite occurrence.