Abstract

The Mobrun Zn-Cu-Au-Ag orebodies show metal zonation typical of volcanic-associated massive sulfide deposits, although some metamorphic remobilization of metals has occurred. The nature and distribution of primary facies are the result of synvolcanic deposition and reworking of sulfides by hydrothermal fluids. Secondary facies resulting from metamorphism and deformation locally overprint primary facies and include transgressive veins which contain remobilized Au as electrum. The distribution of secondary facies was controlled by the mechanical properties of the mineralization as well as of the surrounding rocks; the mechanical response of different facies to deformation influenced the development and distribution of zones containing easily recoverable gold. Preservation of primary textures is best in the Main and Satellite lenses. The 1100 lens also shows significant preservation of primary facies; however, development of secondary facies is pronounced. Textural, structural, and chemical evidence indicates that the 1100 lens was subjected to more extreme metamorphic recrystallization and deformation than the other lenses. Metamorphic remobilization was important in releasing refractory Au from sulfides and locally concentrating it in a recoverable form (electrum).

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