Abstract
The Sisson Brook deposit is a low-grade, large-tonnage W-Mo deposit with notable Cu located in west-central New Brunswick, Canada, and is one of several W-Mo deposits in New Brunswick associated with fluids sourced from granitic plutons emplaced during the Devonian Acadian Orogeny. The younger Devonian-aged stockwork and replacement scheelite-wolframite-molybdenite (and chalcopyrite) mineralization straddles the faulted boundary between Cambro-Ordovician metasedimentary rocks with Ordovician felsic volcaniclastic rocks and the Middle Silurian Howard Peak Granodiorite, with dioritic and gabbroic phases. U-Pb dating of magmatic titanite in the host dioritic phase of the Howard Peak Granodiorite using LA ICP-MS resulted in a 204Pb-corrected concordant age of 432.1 ± 1.9 Ma. Petrologic examination of selected mineralization combined with elemental mapping of vein selvages using micro-XRF and metasomatic titanite and ilmenite grains using LA ICP-MS indicates that saturation of titaniferous phases influenced the distribution of scheelite versus wolframite mineralization by altering the aFe/aCa ratio in mineralizing fluids. Ilmenite saturation in Ti-rich host rocks lowered the relative aFe/aCa and led to the formation of scheelite over wolframite. Altered magmatic titanite and hydrothermal titanite also show increased W and Mo concentrations due to interaction with and/or saturation from mineralizing fluids.
Highlights
Characterizing the interactions among mineral phases and ore-forming fluids is critical to understanding the mineral assemblages and mineralizing process occurring in a given deposit.The careful examination of petrographic relationships among minerals can assist in determining conditions required for their formation
This study aims to characterize the influence of titaniferous phases, i.e., titanite and ilmenite, on Fe and Ca in the mineralizing system and aFe/aCa effects on the distribution and degree of scheelite and wolframite mineralization
Magmatic titanite grains examined show inhomogeneous enrichment of both W and Mo with the highest enrichments occurring on the veinward side of the grain, and metasomatic titanites record both mineralized and non-mineralized fluids
Summary
Characterizing the interactions among mineral phases and ore-forming fluids is critical to understanding the mineral assemblages and mineralizing process occurring in a given deposit.The careful examination of petrographic relationships among minerals can assist in determining conditions required for their formation. The geochemistry of titaniferous minerals, such titanite (CaTiSiO5 ), rutile (TiO2 ), and ilmenite (FeTiO3 ), can be indicative of W-Mo mineralization as these minerals can substitute W and Mo into their Ti site due to similar ionic radii [1]. Titanite can accommodate REE, Y, U, Th, Pb, and Mn substitutions in its Ca site [1,2,3]; the examination of these substitutions can provide additional insight into the nature of fluid(s) responsible for the formation of a deposit (e.g., [1,3,4,5]). Titanite has been used extensively in the study of skarn deposits due to its abundance in calcium-rich host rocks, and it has been used as an indicator of fertility of source plutons for W-Mo mineralization [5] and for the identification of fluid sources [2]. Titanite is a common accessory mineral in intermediate metaluminous rocks [6], such as those hosting portions
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