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The role of carbon in the genesis of Carlin-type gold deposits Greg B. Arehart

Summary: The role of carbon in the genesis of Carlin-type gold deposits
Greg B. Arehart
University of Nevada, Reno
Whether carbon has played an active or a passive role in the genesis of Carlin-type gold deposits
has been debated since the discovery of these deposits in the 1960s. Recent experimental data
suggest that activated carbon, both synthetic and natural, absorbs gold from a bisulfide solution at
temperatures from 25C to 75C. Comparison of thermodynamic data for gold and other metals
suggests that gold should also be absorbed frombisulfide solutions by active carbon at hydrothermal
temperatures. Given the likely presence of active carbon at the time of mineralization in what are
now ore zones, it is suggested that carbon did remove gold from solution and acted as a temporary
storage location before the gold was incorporated into arsenian pyrite.
It is suggested that gold was sorbed onto the margins of active carbon where the carbon structure
was "frayed," thus providing more surface area. This is borne out in part by stable isotope studies
of active and non-active carbon in the Carlin trend. Preg-robbing carbon typically has a low
crystallinity and low 13
C values, typical of many preg-robbing carbons in other ore deposits. In the
Carlin trend, the intrusion of the Goldstrike stock matured this organic carbon, resulting in higher
crystallinity and higher 13
C values. However, in zones of weathering, previously-matured carbon
(as measured by the 13


Source: Arehart, Greg B. - Department of Geological Sciences, Mackay School of Mines, University of Nevada, Reno


Collections: Geosciences