Philipp Siebold, MSc

In this study, the lithium pegmatite dikes and their spatially related intrusives are investigated to better understand spatial geochemical gradients that may be useful for exploration targeting on the district- and deposit-scale. We obtained multi-element whole rock geochemical data derived from bore holes, surface composite chip samples and channel samples collected from multiple field campaigns. The geochemical data is screened for spatial trends using x-y element plots, GIS and 3D modelling software. Magmatic and hydrothermal muscovite related to Li pegmatites are currently being analyzed for Rb-Sr muscovite dating using LA-ICP-MS. Spodumene-bearing pegmatites at Yellowknife seem to be spatially related to locally enriched intrusive stocks within the large voluminous body of the parental batholiths. These intrusions are characterized by a high abundance of apatite and are strongly enriched in Li, Cs, Rb, Be and other incompatible elements. However, the background Li concentrations of intrusive in the area is generally high, which disqualifies Li for the use as a pathfinder element. Apparently, fertile intrusions are characterized by exceptionally high 1/(K/Rb), P and Cs/(Cs+Li+Be). Preliminary field and microscopic observations suggest that the Yellowknife pegmatite field shows a concentric zoning around locally anomalously highly fractionated intrusions. A spatial trend from proximal barren pegmatites to more distal spodumene-bearing dikes is recognized. The dikes do not exhibit strong intra-dike zoning but typically are composed of an aplitic border zone and a medium to coarse-grained internal zone. The border zone is composed of primarily quartz, muscovite and accessory phases such as tourmaline, garnet, Columbite-tantalite minerals and cassiterite, whereas the internal zone is primarily composed of quartz, albite, k-spar and spodumene (up to 20 vol.%).