Mineralium Deposita

, Volume 42, Issue 6, pp 627–637 | Cite as

Three mechanisms of ore re-mobilisation during amphibolite facies metamorphism at the Montauban Zn–Pb–Au–Ag deposit

  • Andrew G. TomkinsEmail author


The relative importance of mechanical re-mobilisation, hydrothermal dissolution and re-precipitation, and sulphide melting in controlling redistribution of metals during concurrent metamorphism and deformation is evaluated at the middle amphibolite facies Montauban deposit in Canada. As at many other deposits, ductile deformation was important in driving mechanical re-mobilisation of massive sulphides from limb regions into hinge regions of large-scale folds and is thus the most important for controlling the economics of Pb and Zn distribution. Two possible stages of hydrothermally driven re-mobilisation are discussed, each of which produces characteristically different alteration assemblages. Prograde hydrothermal re-mobilisation is driven by pyrite de-sulphidation and concurrent chlorite dehydration and is thus an internally driven process. At Montauban, the H2S-rich fluid generated through this process allowed re-mobilisation of gold into the wall rock, where it was deposited in response to sulphidation of Fe Mg silicates. Retrograde hydrothermal re-mobilisation is an externally driven process, whereby large volumes of fluids from outside the deposit may dissolve and re-precipitate metals, and cause hydration of silicate minerals. This second hydrothermally driven process is not recognised at Montauban. Sulphide melting occurred as temperatures neared the peak metamorphic conditions. Melting initiated in the massive sulphides through arsenopyrite breakdown, and a small volume of melt was subsequently re-mobilised into the wall rock. Trace element partitioning and fractional crystallisation of this melt generated a precious metal-rich fractionate, which remained mobile until well after peak metamorphism. Thus, prograde hydrothermal re-mobilisation and sulphide melting were the most important mechanisms for controlling the distribution of Au and Ag.


Mechanical re-mobilisation Hydrothermal re-mobilisation Ore metamorphism Sulphide melt Grenville province 



I would like to particularly thank David Pattison at the University of Calgary for both the opportunity to do a post-doctoral fellowship and the many enjoyable discussions. Brian Marshall and Michel Gauthier are thanked for their reviews and Associate Editor Pat Williams is thanked for his comments, which helped to improve this paper. Jean Bernard was very helpful in giving a tour of the Montauban deposit and assisting with selecting drill core samples. Funding for this project was provided by an Alberta Ingenuity Fellowship and a Monash University Fellowship to the author.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Department of Geology and GeophysicsUniversity of CalgaryCalgaryCanada
  2. 2.School of GeosciencesMonash UniversityMelbourneAustralia

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