Page 85 - Sumatra Geology, Resources and Tectonic Evolution

72 CHAPTER 6

Table 6.6. Metavolcanics and meta-ultrabasic rocks in the Riau-Billiton Accretionary Complex in the Tin Islands Archipelagos
Island Litbological description Reference
Batam Grey and violet sericite-schist, quartz-sericite-talc phyllite and silicified, sericitized, kaolinised metavolcanics Van der Bold & Van der Sluis (I 942)
with altered former plagioclase phenocrysts
Sugi Radiolarian cherts and metavolcanics are recorded from the NW corner ?in situ Van Wessem (1942)
Pait Talc schist is present on Pait between Sugi and Combol lslands
Bangka Narrow zone of talc schists and mica-chlorite schists south of the Klabat Batholith on both sides of Klabat Bay Westerveld ( 1937); Katili (1967)
Serpentinites exposed in Belinyu No. 17 pit; 100 m of serpentinite encountered in a borehole at the Pulunggono & Cameron (1984);
Permali Mine Suryono & Clarke (1981)
Skarns at Pemali mine: idocrase-actinolite-diopside-epidote; diopside-wollastonite-calcite-quartz; Schwartz & Surjono (1991)
hornblende-quartz-muscovite; diopside-quartz-chlorite-plagioclase; hornblende-muscovite-quartz-
epidote-plagioclase
Permali Group: Volcanic Chert Facies with sills or stratified basic to intermediate volcanics, tufts, cherts & shales Ko (1986)
Billiton Lenticular masses of ?original fayalite in the Seloemar lode See Adam (1960, Fig. 26)
Nam Salu lithologies: metasandstone, metasiltstone, radiolarian chert, metavolcaniclastics and skarns Schwartz and Surjono (1990b)
The Schachtader lode (currently inacessible) a 2-3 m skarn composed of green amphibole (?actinolite), See Adam (1960, Fig. 24)
pyroxene, andradite, ilvaite, iron sulphides and cassiterite overlain by + 10 m of radiolarite beneath shales.
Manganese-facies ironstone is reported in boreholes
Siantu Formation: Metabasalts, agglomerates and breccias at Cape Siantu Bahruddin & Sidarto (1995)

Malay Peninsula through the Tin Islands and beneath the Triassic Gigantopteris plant fossils (van Overeem 1960; Hosking et al.
graben on Bangka, rather than a discrete line as illustrated by 1977) and the occurrence of fusulinids (De Roever 1951;
Pulonggono & Cameron (1984) (see Fig. 14.2). Strimple & Yancey 1976).
The accretionary complex is well known in Malaya where it Early geological studies in the Riau and Lingga archipelagos
consists of severely deformed sediments, volcanics and slivers are summarized by van Bemmelen (1949) and the scattered
of ultrabasic rocks ranging in age between Devonian and occurrences of metavolcanics, ultrabasic rocks and their metamor-
Upper Permian (Metcalfe 2000). In the Tin Islands, where phosed derivatives are compiled in Table 6.6 and the localities are
fossils are scarce, Bothe (1925a,b) distinguished Pre-Triassic shown in Figure 6.8.
(?Carboniferous-Permian) volcanics and sediments, from Ko (1986) identified poorly exposed pre-Triassic rocks
similar, but also deformed, Triassic volcanics and sediments, on (Fig. 6.9) on Bangka Island as facies of the Pemali Group. The
the basis of their more intense deformation and metamorphism, Pebbly Mudstone Facies in the Toboali area in the south of the
their basic and ultrabasic (as opposed to acidic) composition, island is correlated with the glaciogenic Late Carboniferous-
and the absence of associated granitic plutons. One fossil locality Early Permian Bohorok Formation of Sumatra and is included in
on Bangka yielded Permian fossils, and on Billiton, fossils span- the Sibumasu Block (Barber & Crow 2003). The other Pemali
ning the Sakmarian to Kungurian stages have been identified Group facies of Volcanic-Chert, Bedded Chert, Laminated
(Fontaine & Gafoer 1989). The Permian rocks in the Tin Islands Mudstone and Pyritic black shale-limestone are considered to
are considered to have a Cathaysian affinity (Indochina Block) be components of the accrelionary complex and include Early-
on the basis of the identification by Jongmans of poorly preserved Mid-Permian rocks (Fontaine & Gafoer 1989).

105 ~ V~I h ,I. i I
.~,~,~a, _ ~ lo6 ~ 107 ~
TRIASSIC ~ Tempilang
Cape LOWER- Sandstone
Penjabung MIDDLE ~ Oceanic Facies
PERMIAN
PERMIAN ~'~ Undifferentiated

CARBONIFEROUS-EARLY PERMIAN
iii:iiii:iii ii:iii Pebbly mudstone
Facies

Bebulu Batholith
:::::::::::::::::::(
""~ Thrusts ~ t
GRANITE PROVINCE~_q ~
}]q:FF~ Main Range (S type) / i
~
Main Range (Stype)
@
9 ""'"''"'"'"'""'"'"'"'"'"" :'1 Fig. 6.9. Simplified geological map of
Eastern Province (I-type)
P. Bangka. Geology compiled from Ko
- 3~ 0 50km 3 ~ _ (1986), Katili (1967), Osberger (1968) and
, 106 ~ j TOBOALI 107 ~ Verbeek (1897). Granite typology after
Cobbing et al. (1992).