Gold contents of sulfide minerals in granitoids from southwestern New Brunswick, Canada

Xue Ming Yang, David R. Lentz, Paul J. Sylvester

Research output: Contribution to journalArticle

29 Scopus citations

Abstract

The abundance of gold and selected trace elements in magmatic sulfide and rock-forming minerals from Silurian-Devonian granitoids in southwestern New Brunswick were quantitatively analyzed by laser-ablation inductively coupled plasma mass-spectrometry. Gold is mainly hosted in sulfide minerals (i.e., chalcopyrite, pyrrhotite, and pyrite), in some cases perhaps as submicron inclusions (nanonuggets). Gold is below detection (<0.02 ppm) in major rock-forming minerals (i.e., plagioclase, K-feldspar, biotite, hornblende, and muscovite) and oxides (i.e., magnetite, and ilmenite). Gold distribution coefficients between sulfide and granitoid melt are calculated empirically as: DAucpy/melt = 948 ± 269, DAupo/melt = 150 ± 83, and DAupy/melt = 362 ± 96. This result suggests that gold behavior in the granitoid systems is controlled by the conditions of sulfur saturation during magmatic evolution; the threshold of physiochemical conditions for sulfur saturation in the melts is a key factor affecting gold activity. Gold behaves incompatibly prior to the formation of sulfide liquids or minerals, but it becomes compatible at their appearance. Gold would be enriched in sulfur-undersaturated granitoid magmas during fractionation, partitioning into evolved magmatic fluids and favoring the formation of intrusion-related gold deposits. However, gold becomes depleted in residual melts if these melts become sulfur-saturated during differentiation, leading to gold precipitation in the early sulfide phases of a granitoid suite. Late-stage Cl-bearing magmatic-hydrothermal fluids with low pH and relatively high oxidation state derived from either progressively cooling magmas at depth or convective circulation of meteoric water buffered by reduced carbon-bearing sediments, may scavenge gold from early sulfide minerals. If a significant amount of gold produced in this manner is concentrated in a suitable geological environment (e.g., shear zones or fracture systems), intrusion-related gold deposits may also be generated. Exploration for intrusion-related gold systems should focus on the areas around evolved phases of granitoid suites that remained sulfur-undersaturated. For sulfur-saturated granitoid suites, the less differentiated phase and associated structures are the most prospective targets.

Original languageEnglish
Pages (from-to)369-386
Number of pages18
JournalMineralium Deposita
Volume41
Issue number4
DOIs
StatePublished - Jul 2006

Keywords

  • Appalachians
  • Gold abundance
  • Gold partitioning
  • Granitoids
  • Intrusion-related gold systems
  • LA-ICPMS
  • New Brunswick
  • Sulfide minerals

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