Role of arsenian pyrite in hydrothermal ore deposits: A history and update

Arsenic-bearing pyrite, known as arsenian pyrite, is the most important and in
many cases the onlyAu-bearing mineral in Carlin-type and some epithermal deposits.
Because it incorporates Au from solutions that are undersaturated with respect to native
Au, precipitation of arsenian pyrite is the key to removal of Au from solution and
formation of an economic deposit. Recent micro-scale studies of arsenian pyrite from
awide range of deposits have provided new information on its role as a host forAu and
on the nature and significance of its growth zoning. Two types of arsenian pyrite have
been recognized so far:

1) As1–-pyrite, in which As1– substitutes for S; it is found in Carlin-type and
low-sulfidation epithermal deposits that formed in reduced hydrothermal systems.

2) As3+-pyrite, in which As3+ and possibly other forms of oxidized As substitute for
Fe; it is found in high-sulfidation epithermal deposits that formed in oxidized hydrothermal
systems.