Contrasting Structural Styles of Orogenic Gold Deposits, Reefton Goldfield, New Zealand

摘要

This paper describes the structural setting of the Globe-Progress and Blackwater orogenic gold deposits, the only two +1-million ounce (Moz) deposits discovered to date within the Reefton goldfield of central New Zealand. Most of the Globe-Progress deposit is located along the Globe-Progress shear zone, a curviplanar, brittle-ductile, structure that juxtaposes tightly folded rocks in its footwall against largely unfolded rocks in its hanging wall. At its eastern end the Globe-Progress shear zone merges with the fold-parallel Oriental shear zone, with the Globe-Progress shear zone acting as a tear fault that transferred contractional deformation on the Oriental shear zone across the structural grain of the adjacent folded rocks, during or soon after the end of greenschist facies metamorphism. An early phase of mineralization at ca. 438 Ma (K-Ar, sericite) accompanied this contractional deformation, whereas a second phase of mineralization occurred during later brittle, oblique-normal, reactivation of the two shear zones at ca. 386 Ma (K-Ar, sericite). The resulting ore shoots plunge moderately towards the southwest, along intersections between (1) the two shear zones, (2) the Globe-Progress shear zone and minor normal faults in its hanging wall, and (3) the Globe-Progress shear zone and NV-dipping bedding in its hanging wall.