CHARACTERIZATION OF HYDROTHERMAL ALTERATION ZONES IN PANTI GEOTHERMAL FIELD, PASAMAN DISTRICT, WEST SUMATERA PROVINCE

Abstract

anti geothermal area is located in Pasaman Regency, West Sumatra Province. The survey area
is about 200 km away from the city of Padang and about 30 km away from the capital city of
Pasaman Regency, Lubuk Sikaping. The purpose of this research activity was to determine the
characteristics of hydrothermal alteration in an observed well. The method used was petrological
analysis on PNT-1 well core data from the depth of 41.5 m until 533.5 m, petrography analysis of
17 rock samples, and Specterra analysis based on secondary data. The alteration minerals that
appeared in the observed well were calcite, sericite, chlorite, secondary quartz, anhydrite,
opaque minerals, iron oxide, clay, and epidote minerals; with alteration types in the form of
replacement and direct depositional. Two zones were sorted based on the presence of minerals
and determination of alteration zones, namely the Smectite-Chlorite zone, and the illit-smectitechlorite
and sericite zone. The smectite-chlorite zone was located at the
depth
of
±
41-
±
454
m

and
was
characterized
by
the
presence
of
smectite,
ilite-smectite,
calcite,
and
chlorite
alteration

minerals;
which
were
more
dominant
than
other
alteration
minerals.
This
zone
according
to
the

alteration

zone division comprised of argillic zone with a temperature of 140° C - 220° C. The
ilite-smectite-chlorite and sericite zone was located at the depth of ± 454- ± 533 m
characterized by the presence of illit-smectite, chlorite, sericite, calcite and quartz minerals. This
zone, according to the alteration zone division, was comprised of argillic zone with a temperature
of 200° C - 250° C. It was concluded that the alteration rocks in PNT-1 well were estimated to
serve as caprock zone of the Geothermal Panti system which formed due to the interaction
between rocks and acidic to neutral fluid in temperatures between 140° C - 250° C.