USEFUL GUIDES IN THE PRELIMINARY
APPRAISAL OF PORPHYRY COPPER PROSPECTS
DOMINGO G. MALICDEM
Geologist, Lepanto Consolidated & Mining
"Guides" to potentially economic
porphyry copper deposits are essential
in their preliminary appraisal.
Secondary biotite in dioritic host rocks
and significant amounts of copper in
stream sediments are the most
significant in the early assessment of
It is generally being recognized that
zones with strong secondary biotite is
generally coincident with oreógrade
porphyry copper mineralization.
Secondary biotite is one of the
diagnostic minerals of the innermost
zone, the zone of potassic alteration.
Case A, B and C show the close
association between areas of intense
secondary biotite alteration and strong
Although stream sediment sampling.
particularly for cold extractable
copper, is fairly established as an
efficient and economical tool for
prospecting for porphyry copper
deposits, there is still need for more
geochemical data particularly those
pertaining to hot extractable copper and
total copper in stream sediments in and
around mineralized areas. Case B and C
indicate that HxCu and total copper in
stream sediments over mineralized zones
is generally greater than 1000 ppm.
Copper in sediments outside of
mineralized areas is generally less than
The presence of these features over a
wide area suggests deposits with
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