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Mineralium Deposita

, Volume 45, Issue 7, pp 683–705 | Cite as

Lithogeochemical localisation of disseminated gold in the White River area, Yukon, Canada

  • Doug MacKenzie
  • Dave Craw
  • Mike Cooley
  • Adrian Fleming
Article

Abstract

Gold mineralisation in the White River area, 80 km south of the highly productive Klondike alluvial goldfield, is hosted in amphibolite facies gneisses in the same Permian metamorphic pile as the basement for the Klondike goldfield. Hydrothermal fluid which introduced the gold was controlled by fracture systems associated with middle Cretaceous to early Tertiary extensional faults. Gold deposition occurred where highly fractured and chemically reactive rocks allowed intense water–rock interaction and hydrothermal alteration, with only minor development of quartz veins. Felsic gneisses were sericitised with recrystallisation of hematite and minor arsenic mobility, and extensively pyritised zones contain gold and minor arsenic (ca 10 ppm). Graphitic quartzites (up to 5 wt.% carbon) caused chemical reduction of mineralising fluids, with associated recrystallisation of metamorphic minerals (graphite, pyrrhotite, pyrite, chalcopyrite) in host rocks and veins, and introduction of arsenic (up to 1 wt.%) to form arsenopyrite in veins and disseminated through host rock. Veins have little or no hydrothermal quartz, and up to 19 wt.% carbon as graphite. Late-stage oxidation of arsenopyrite in some graphitic veins has formed pharmacosiderite. Gold is closely associated with disseminated and vein sulphides in these two rock types, with grades of up to 3 ppm on the metre scale. Other rock types in the White River basement rocks, including biotite gneiss, hornblende gneiss, pyroxenite, and serpentinite, have not developed through-going fracture systems because of their individual mineralogical and rheological characteristics, and hence have been little hydrothermally altered themselves, have little hydrothermal gold, and have restricted flow of fluids through the rock mass. Some small post-metamorphic quartz veins (metre scale) have been intensely fractured and contain abundant gold on fractures (up to 40 ppm), but these are volumetrically minor. The style of gold mineralisation in the White River area is younger than, and distinctly different from, that of the Klondike area. Some of the mineralised zones in the White River area resemble, mineralogically and geochemically, nearby coeval igneous-hosted gold deposits, but this resemblance is superficial only. The White River mineralisation is an entirely new style of Yukon gold deposit, in which host rocks control the mineralogy and geochemistry of disseminated gold, without quartz veins.

Keywords

Gold Graphite Arsenopyrite Hematite Hydrothermal Alteration Klondike 

Notes

Acknowledgements

Funding for this research was provided by Underworld Resources Ltd, University of Otago, and NZ Foundation for Research Science and Technology. Discussions with Jim Mortensen, Howard Poulsen, Rob McLeod, Lamont Leatherman, Colin Brodie, Hanne-Kristen Paulsen, Jodie Gibson and Hamish Blakemore helped to clarify numerous geological issues. Technical assistance was ably provided by Kat Lilly, Brent Pooley, Damian Walls and Anna Craw. Katy Evans, and two anonymous referees provided incisive reviews that substantially improved the ms, and editorial comments by Pat Williams and Georges Beaudoin further improved the presentation.

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Doug MacKenzie
    • 1
  • Dave Craw
    • 1
  • Mike Cooley
    • 2
  • Adrian Fleming
    • 3
  1. 1.Geology DepartmentUniversity of OtagoDunedinNew Zealand
  2. 2.Structural Geology ConsultingKingstonCanadaK7M 1H5
  3. 3.VancouverCanada

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