Portable x-ray fluorescence spectrometry investigation of till in the McDougall lake area, southwestern New Brunswick
University of New Brunswick
Basal till samples were collected at 274 locations across the eastern half of the McDougall Lake area (NTS: 21 G/07) and geochemically analyzed at a commercial laboratory by 59-element Sodium Peroxide Fusion Inductively Coupled Plasma-Mass Spectrometry and Optical Emission Spectrometry, and at the University of New Brunswick by a relatively new method, 40-element Portable X-Ray Fluorescence Spectrometry. With respect to accuracy, precision, element suite, and limits of detection, commercial laboratory geochemistry is a superior method, although it is relatively slower and more expensive. Testing suggests that the methods can produce results of similar quality for the purposes of mineral exploration; excellent agreement in accuracy and precision were demonstrated for As, Th, Zr, and others. Portable X-Ray Fluorescence Spectrometry data were also empirically calibrated to compensate for systematic error, which greatly improved data quality for Ba, Ca, U, and others. This study recognizes two till populations: “granite-rich” and “reddish”. Within the McDougall Lake area, the occurrence of granite-rich till is widespread and common, while reddish till is generally limited to the Scoullar and Clarendon Hills, east of the Magaguadavic Highlands. Granite-rich till is often sandy, loose, and yellowish brown, while reddish till is often loamy, firm, and dark red. Geochemically, the granite-rich till population has a relatively variable concentration range for incompatible elements, which reflects the diverse plutonic bedrock composition of the McDougall Lake area. This study emphasizes that in the McDougall Lake area, variable bedrock geochemistry and the presence of two tills should be considered as important interplaying factors which can control till geochemistry.