Tourmaline, scheelite, and magnetite compositions from orogenic gold deposits and glacial sediments of the Val-d'Or district (Québec, Canada): Applications to mineral exploration

Abstract

Tourmaline, scheelite, and magnetite from orogenic gold deposits (n = 22) and glacial sediments (n = 5) of the Val-d'Or mining district (Québec, Canada) were investigated by Electron Probe Micro-Analyzer (EPMA) and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) in order to determine their chemical signature and to assess their potential as indicator minerals for gold exploration. Three types of tourmaline are recognized. Type I tourmaline from deposits hosted in felsic and intermediate-composition calc-alkaline rocks has low contents of V, Cr, Mn, Fe, Co, Ni, Zn, and Sn and a high content of Mg compared to Type II tourmaline from deposits hosted in mafic tholeiitic rocks. Type III tourmaline from deposits located at the contact between mafic metavolcanic and metasedimentary rocks shows a chemistry similar to Type I tourmaline with slightly higher Li, Mn, and Pb contents. Tourmaline from orogenic gold deposits is characterized by lower contents of Zn, Cu, Sn, and Pb compared to data from tourmaline associated with Cu-Zn, Pb-Zn-Cu, and Sn mineralization. Till tourmaline carries the chemical signature of that from orogenic gold deposits with a majority having the signature of Type I tourmaline. Orogenic gold deposits scheelite from the Val-d'Or district hosted in calc-alkaline intrusions of intermediate composition displays high Na, REE, and Y contents compared to scheelite from sediment- and mafic-hosted gold deposits. Till scheelite carries the chemical signature of that from orogenic gold deposits. Although rare in orogenic gold deposits of the Val-d'Or district, hydrothermal magnetite in the gold veins is characterized by higher Cr, Zn, Mn, K, Ca, Ti, and Al than magmatic magnetite found in dioritic and gabbroic host rocks. Magnetite associated with gold mineralization forms fine, disseminated grains, suggesting that the coarse-grained magnetite recovered in till does not originate from the gold veins. Till tourmaline and scheelite carry the signature of the orogenic gold deposits and can thus be used for exploration in overburden sediments.