Jc. Carlile et al., DISCOVERY AND EXPLORATION OF THE GOSOWONG EPITHERMAL GOLD DEPOSIT, HALMAHERA, INDONESIA, Journal of geochemical exploration, 60(3), 1998, pp. 207-227
The Gosowong epithermal gold deposit, on the island of Halmahera in ea
stern Indonesia, is located in an ar ea of primary tropical rain fores
t with no previous history of gold mining or record of gold mineralisa
tion. The deposit occurs in a newly recognised mineral district which
contains a number of epithermal vein systems and at least two centres
of low-grade porphyry style Cu-Au mineralisation. Several zones of arg
illic and advanced argillic alteration have been noted which may be re
lated to additional centres of mineralisation. Gosowong is classified
as a low-sulphidation epithermal quartz vein. Bonanza-grade gold-silve
r mineralisation is developed in shoots over a 400-m strike section of
the vein system. Three types of veining are recognized; quartz-adular
ia veins and breccias; quartz-chlorite-illite veins and breccias; and
crystalline or chalcedonic quartz vein stockworks. The area was target
ted using a simple geological concept and the deposit was discovered a
nd tested using basic exploration techniques commonly applied in the r
ugged tropical terrains of Indonesia. Sequential exploration methods c
omprised reconnaissance drainage sampling of stream sediment, BLEG and
float media, ridge and spur soil sampling, prospect scale grid soil s
ampling, hand trenching and diamond drilling. Lapse time from identifi
cation of the initial reconnaissance anomaly to an inferred resource e
stimate of almost 1 million ounces of gold was less than 3.5 years. Th
is case history illustrates that very detailed exploration is necessar
y to locate high-grade vein-type gold deposits in a tropical environme
nt, but demonstrates that such resources still remain to be discovered
in the relatively under-explored Neogene magmatic arcs of Indonesia.
(C) 1998 Elsevier Science B.V.