The Otago Schist is being subdivided on a regional scale
into structurally, metamorphically and lithologically distinct blocks. Differences between
blocks are subtle, and difficult to map in the field. Boundaries are
late-metamorphic or immediately post-metamorphic in origin, and are different
from later brittle faults which disrupt the schist. Mapping of
late-post-metamorphic structural discontinuities has direct application for
basic grassroots exploration in the Otago Schist. The mineralised (and currently
mined) Hyde-Macraes Shear Zone forms a regional scale boundary between a block
dominated by politic schist and a block with massive psammitic schist, pelitic
schist, and minor greenschist and chert. The HMSZ forms a metamorphic
discontinuity, with garnet and biotite in the underlying schist, and neither
index minerals apparent in the overlying schist. The HMSZ is also a structural
boundary between domains with differing lineation orientations. The HMSZ can not
yet be traced along strike to the northwest to the Rock and Pillar Range, where the only major
discontinuities recognised are the Caples-Torlesse boundary and a normal fault
separating low grade from high grade schist. Structural and lithological
discontinuities in the Dunstan Range break the range up into distinct
structural blocks, two of which are separated by the gold-mineralised Rise and
Shine Shear Zone.