Architecture of the Cortez Hills breccia body

Cortez Hills Breccia Zone (CHBZ) is a breccia-related Carlin-type ore deposit located
in northeastern Nevada. While most breccias associated with Carlin-type mineralization
can be genetically tied to tectonic, sedimentary, or dissolution processes
via their geometry or textural relationships, the breccia body that hosts the bulk of
CHBZmineralization is not so easily categorized. This breccia body is conical in shape
with an elliptical cross section and crosscuts stratigraphy. It has gradational margins
with the surrounding country rock, and large (>10 m) blocks of country rock are present
within the breccia body itself. Zonation within the breccia body consists of a higher
energy polymictic portion in the center of the pipe grading outward to rotated breccia
and a peripheral shell of crackle breccia. Alteration occurred pre-, syn-, and
post-brecciation, including extensive deep post-breccia oxidation. High grade gold
mineralization is spatially associated with the central polymictic portion of the breccia,
and gold grade drops in the surrounding rotated and crackle breccias. This paper
describes the breccia body and its apparent spatial relationship to mineralization and
temporal relationship to alteration, and outlines how breccia architecture was integrated
into logging and underground face mapping in the production environment.