The relationship between the hyde‐macraes shear zone, deformation episodes, and gold mineralisation potential in Eastern Otago, New Zealand

Abstract

The relationship between the mineralised Hyde‐Macraes Shear Zone (HMSZ), an extensive, low‐angle, semibrittle structure in the Otago Schist Belt within the Haast Schist, New Zealand, and folding events affecting metased‐iments is documented. The shear zone postdates F3 folds, although it is infparallel to S2, a shallow, north‐dipping penetrative cleavage. Evidence of the first shortening phase is only rarely preserved because initial fabrics are transposed. D2resulted in a strong mineral elongation (L2), a penetrative cleavage, and isoclinal folds. D3 produced generally asymmetrical northwest‐plunging folds in S2 at all scales but of variable intensity. In regions where intense D3 shortening has occurred, L2 is apparently rotated into parallelism with F3 axes. A fourth event resulted in micro‐ and mesofolding about a north‐plunging axis; after this, D5 produced a northeast‐trending micro‐crenulation. The HMSZ nucleated on the lower limb of an inclined macroscopic F3 fold, post‐F3 but pre‐D4 veins. The shear zone follows pre‐existing weaknesses but transects areas exhibiting variable intensity of D3 shortening. This is evident by different degrees of rotation of L2 towards F3 fold axes, resulting in changes in the shear direction and potential for mineralisation. Gold mineralised sites along the HMSZ are apparently localised adjacent to the lower limbs and near the hinges of upthrusted F3 folds and near the boundary of dominantly D2 and D3 folded areas, where pre‐existing weaknesses were reactivated. © 1991 Taylor & Francis Group, LLC.