Application of Vein
Abundance
Studies in Exploration in the Ertsberg
Porphyry
Deposit, West Papua, Indonesia
Friehauf, K., Titley,
S.*, and Gibbins, S.*, Dept. of Physical
Sciences, Kutztown Univ,
Quantitative vein abundance measurements of drill
core can
delineate exploration vectors in the diorite of the Ertsberg
porphyry deposit and are most useful in bodies of rock that have
marginally
anomalous copper and gold assays. Within the Ertsberg
porphyry deposit, copper and gold grades correlated with the abundance
of: 1) bornite-anhydrite veins with biotite
alteration, and 2) bornite-quartz ±
chalcopyrite
veins with green sericite alteration, but
do not
correlate with 3) pyrite ± chalcopyrite veins with white sericite
alteration, 4) magnetite-actinolite veins
with propylitic alteration, or 5)
sulfide-poor quartz veins
associated with biotite-K-feldspar
alteration.
Although copper and gold grades had erratic spatial distribution
outside the
ore zone, overall total vein abundance (n) and the abundances of vein
types 1
and 5 and total vein abundance decrease systematically laterally away
from the
ore zone. Vein abundance is highest both within the ore zone and in
low-grade
rocks underlying the ore zone, making vein
abundance
values a measure of proximity to the center of mineralization,
irrespective of
grade. The region with high vein abundance also contains the most
intensely biotite-altered rock and the
most dikes of magmatic biotite-rich diorite in
the study area. Very high vein abundance values in low-grade rocks
beneath the
ore zone are due primarily to the presence of barren quartz and
K-feldspar
veins. High vein abundances laterally adjacent to the ore zone are due
to the
presence of barren hairline biotite veins.
Late stage
veins (types 2 and 3) characterized by sericitic
alteration styles have a more erratic distribution due to clustering of
such
veins. Late stage veins occur both within and peripheral to the ore
zone.
Clustering of sericitic veins, however,
makes vein
abundance data for late-stage veins a weaker indicator of exploration
vectors.
Regions cut by swarms of late-stage veins, however, may suggest
mineralization
at depth. Changes in the nature and distribution of veins through time
have
important implications on the way porphyry systems cool, the extents of
fluid
flow paths, and the distribution and redistribution of metals.
2003
Session No. 164
Economic Geology II: Porphyry, Gold, and Other
Deposits
1:30 PM-5:30 PM, Tuesday, November 4, 2003
Geological
Society
of