A review of Te and Se systematics in hydrothermal pyrite from precious metal deposits: Insights into ore-forming processes

Manuel Keith,Daniel J Smith,Gawen R.T Jenkin,David A Holwell,Matthew D Dye

doi:10.1016/j.oregeorev.2017.07.023

Manuel Keith, Daniel J Smith + Show 3 more

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https://doi.org/10.1016/j.oregeorev.2017.07.023

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Abstract

Pyrite is one of the most common minerals in many precious and base metal hydrothermal ore deposits and is an important host to a range of trace elements including Au and Co and the semi-metals As, Se, Sb, Te and Bi. As such, in many hydrothermal ore deposits, where pyrite is the dominant sulphide phase, it can represent a major repository for these elements. Furthermore, the concentrations and ratios of Au, As and Co in pyrite have been used to infer key ore-forming processes. However, the mechanisms controlling the distribution of Te and Se in pyrite are less well understood. Here we compare the Te and Se contents of pyrite from a global dataset of Carlin-type, orogenic Au, and porphyry-epithermal deposits to investigate: (1) the potential of pyrite to be a major repository for these elements; and (2) whether Te and Se provide insights into key ore-forming processes. Pyrite from Carlin-type, low-sulphidation and alkaline igneous rock-hosted epithermal systems is enriched in Te (and Se) compared to pyrite from high-sulphidation epithermal and porphyry Cu deposits. Orogenic Au pyrite is characterised by intermediate Te and Se contents. There is an upper solubility limit for Te as a function of As in pyrite, similar to that established for Au by Reich et al. (2005); and this can be used to identify Te present as telluride inclusions, which are common in some epithermal-porphyry and orogenic Au deposits. Physicochemical fluid parameters, such as pH, redox and temperature, as well as crystal-chemistry control the incorporation and concentration of Se and Te in pyrite. Neutral to alkaline fluids have the ability to effectively mobilise and transport Te. Fluid boiling in porphyry-epithermal systems, as well as wall rock sulphidation and oxidation in Carlin-type (and orogenic Au) deposits can effectively precipitate Te in association with pyrite and Au. In contrast, Se concentrations in pyrite apparently vary systematically in response to changes in fluid temperature, irrespective of pH and fO2. Hence, we propose that the Se contents of pyrite may be used asa new geo-thermometer for hydrothermal ore deposits. Furthermore, the comparison of bulk ore and pyrite chemistry indicates that pyrite represents the major host for Te and Se in Carlin-type and some epithermal systems, and thus pyrite can be considered to be of economic interest asa potential source for these elements.

Highlights

Pyrite is the most abundant sulphide mineral in the Earth’s upper crust and represents a major mineral in most hydrothermal ore deposits (Rickard and Luther, 2007; Cook et al, 2009a; Deditius et al, 2014; Keith et al, 2016a)
Pyrite is stable under various physicochemical fluid conditions and its refractory behaviour to post-depositional metamorphism compared to other sulphides (Craig and Vokes, 1993; Fleet et al, 1993; Craig et al, 1998; Agangi et al, 2013) and its near-ubiquity makes it suitable for micro-analytical studies to reconstruct ore-forming processes through space and time (Agangi et al, 2013; Reich et al, 2013; Wohlgemuth-Ueberwasser et al, 2015; Keith et al, 2016b)
The new application of the Au solubility line in the Te-a log (Se)-log (As) system presents a method to distinguish between Te solid solution and an inclusion related appearance in pyrite

Summary

Introduction

Pyrite is the most abundant sulphide mineral in the Earth’s upper crust and represents a major mineral in most hydrothermal ore deposits (Rickard and Luther, 2007; Cook et al, 2009a; Deditius et al, 2014; Keith et al, 2016a). Previous investigations have highlighted that pyrite represents an important sink for many trace metals including Co, Ni, Cu, As, Se, Mo, Ag, Sb, Te, Pb, Bi, Au and PGE (e.g., Large et al, 2009; Maslennikov et al, 2009; King et al, 2014; Smith et al, 2014; Tanner et al, 2016) Most of these studies have focused on As and associated trace metals, such Ag, Sb, Au and Pb (e.g., Reich et al, 2005, 2013; Large et al, 2009; Deditius et al, 2009a, 2014; Keith et al, 2016a), but far very few investigations have included Te and Se (Huston et al, 1995; Wohlgemuth-Ueberwasser et al, 2015; Keith et al, 2016b). Much less is known about the processes that control the incorporation of Te and Se into pyrite – adjacent group 16 elements that might be expected to show some similarities in geochemical behaviour..

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