| Summary: | Hargosari area is situated in the southern part of Java Island, Southern Mountain
range, where is known as the most prospective area for mineral deposits. Many
occurrences of mineral deposits have already been reported from some locations
along the Southern Mountain rang but Hargosari area, that why this current research
is conducted in this area.
The aims of the research are to elucidate the control of geological aspect to the ore
mineralization, to identify the alteration type, mineral composition, and map out the
hydrothermal alteration zone, to characterize the geochemistry of host rock, and to
elucidate the style of mineralization as well as the deposit type. In order to
accomplish these objectives, geological field mapping and laboratory analysis
including petrography, ore microscopy, XRD, XRF, and AAS were carried out
carefully for this research.
As the results, the ore mineralization in Hargosari area is possibly controlled by two
main strike slip faults (NW-SE and NE-SW), reverse fault (230
o
/75
o
/NE), and other
permeable features such as columnar joint which allow the hydrothermal fluids
bearing ore minerals to migrate and precipitate as veins and disseminate the mineral
contents in the country rocks or react with and replace receptive country rocks.
Propylitic and argillic alterations were found in Hargosari area. Propylitic alteration
consists of the variable amount of chlorite + epidote + quartz ± pyrite ± magnetite.
This kind of alteration is widespread in the study area. Argillic alteration is various
from white to yellowish which composed of illite + smectite ± chlorite. Rock
geochemistry shows that the lithology in Hargosari area is dominantly controlled by
hydrothermal alteration/mineralization which involves the chemical change in the
host rocks. K
2O and SiO2
generally increase in altered rocks. Whereas CaO, MgO,
Fe2O3
, TiO2
, and Cr
2O3
decrease. The mineralization commonly associates with
propylitic and argillic alteration which the grade of gold � 0.02 ppm, silver � 0.05
ppm, copper � 173 ppm, lead � 7 ppm , and zinc � 91 ppm. The style of
mineralization is more likely to be low sulphidation epithermal deposit and the age of
mineralization is possibly in Miocene.
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