Petrogeochemical assessment of rock units and identification of alteration/mineralization indicators using portable X-ray fluorescence measurements: Applications to the Fire Tower Zone (W-Mo-Bi) and the North Zone (Sn-Zn-In), Mount Pleasant deposit, New Brunswick, Canada

Abstract

The Mount Pleasant polymetallic deposits are located along the southwestern margin of the Late Devonian Mount Pleasant Caldera Complex in southwestern New Brunswick, Canada. The Fire Tower Zone (W-Mo-Bi) and the North Zone (Sn-Zn-In) comprise the main mineralized zones within the Mount Pleasant deposit. The rock units examined at surface in both zones are highly altered and are surface weathered to some extent. In order to classify these rock units with confidence, the Olympus X-5000 portable X-ray Fluorescence (pXRF) spectrometer was used in this study to rapidly obtain the geochemical composition of these rocks, identify lithologic discriminants, and find alteration/mineralization indicators in these areas. The immobile elements Ti, Zr, Nb, Y, and Th were selected to discriminate among various rock types. The Little Mount Pleasant Formation has the highest Ti and Zr and the Mount Pleasant Granitic Suite (MPGS, GI and GII) contains the highest Y, Nb, and Th. The McDougall Brook Granitic Suite (MBGS) has an intermediate composition between them. The element ratios of Zr/Ti, Nb/Ti, Y/Ti, and Th/Ti effectively discriminate these rock units and increase from the Little Mount Pleasant Formation, to the MBGS, and then to the MPGS. Greisen and propylitic alteration are reflected by strong depletion of K and Rb in some samples. The Fe and Mn typically are leached out of the mineralization system during the greisen alteration. Principal component analysis (PCA) was performed on the pXRF datasets. The first principal component (PC1) of the pXRF data from both the Fire Tower Zone and the North Zone mainly extracts information on Ti, Zr, Ce, Cr, V, Nb, Y, U, and Th, and thus represents different rock units. The PC2 is characterized by high-positive loadings of K, Rb, Fe, and Mn and negative loading of As and Mo. It is interpreted as the W-Mo mineralization indicator showing by the enrichment in Mo and depletion of K, Rb, Fe, and Mn associated with quartz+topaz+sericite+fluorite alteration. The PC3 consists of positive loadings of Sn, Zn, Cu,

A review of pXRF (field portable X-ray fluorescence) applications for applied geochemistry

“…Clever combinations of elements allowed Brand and Brand (2016) to use pXRF for Li exploration, despite this light element being out of reach of pXRF. A similar approach was used by Zhang et al (2017) at the Mount Pleasant deposit (Fire Tower Zone, W-Mo-Bi, and North Zone, Sn-Zn-In). They deduced mineralisation signatures (As and Mo, along with K, Rb, Fe, and Mn depletion, interpreted as the W-Mo mineralisation; and Sn, Zn, Cu, and S with slightly depleted Sr and Ba, representing Sn-Zn mineralisation) from principal component analysis (PCA) of the multi-element pXRF data.…”

Portable X-Ray Fluorescence Spectrometry: Principles and Applications for Analysis of Mineralogical and Environmental Materials

“…To simplify the collected pXRF dataset, the authors used a chemometrics technique called Principal Component Analysis (PCA). The authors found that an enrichment in Mo and As, and depletion of Fe, Mn, K and Rb indicating mineralization of W and Mo in Mount Pleasant area [23].…”

“…Wei Zhang [23] and coworkers used pXRF to obtain the geochemical composition, identify lithologic discriminants, and find alteration/mineralization indicators in rocks located in Mount Pleasant polymetallic deposits in southwestern New Brunswick, Canada. Two main regions inside Mount Pleasant Complex were analyzed: The Fire Tower Zone and the North Zone.…”

Portable XRF applied to regional bedrock mapping in Quebec, Canada

“…When purchasing and commissioning a new pXRF analyzer, producing quantitative data is not a "point-and-shoot" exercise. First, there must be a QA/QC program that includes blanks and reference materials (e.g., Fisher et al, 2014;Le Vaillant et al, 2014;Zhang et al, 2017;Lemière, 2018). Then, before quantitative analyses can be made, the user must determine the optimal measurement time and number of spots per sample, and establish a matrix-matched secondary calibration (Hall et al, 2013(Hall et al, , 2014Le Vaillant et al, 2014;Ross et al, 2014aRoss et al, , 2014bBourke and Ross, 2016;McNulty et al, 2018;Martin and Carr, 2020;Adams et al, 2021).…”