GEOLOGICAL REVIEW OF BROKEN LIMESTONE SURROUNDING THE CUAU GRASBERG OPEN PIT – Papua, Indonesia

“Broken Limestone” zones occur in the northeast and southwest areas of the Grasberg Pit. These
broken limestone zones are generally trending parallel to the regional fault structures. The broken
Limestone zones are controlled by regional and major fault structures, as well as pebble dike,
karst and dissolution breccia occurrences. In the northeast area the broken limestone zone is
complicated by the occurrence of a muskeg rich lake sediments.
Due to the brittle nature of the faults the RQD in the broken limestone zones is generally below
40%. The RQD of the dissolution breccia and karst is due to its nature also below 40%. However,
the RQD of the pebble dikes are generally 50-100%, with a mean of 68%. The spatial
coincidence of the dissolution breccias, karst and pebble dike features suggest a similar origin; at
least for the first two features.
The occurrence of these broken limestone zones will have an impact on the short- and long-term
mine plan design.

By:

Geoffrey de Jong, Sugeng Widodo, Bambang Antoro, Nur Wiwoho, Anton Perdana and Paul Q.
Warren; July 2008; PT Freeport Indonesia, Geo & Technical Services Division, Tembagapura
99930, Papua, Indonesia