GEOLOGY REGIONAL OF BANGKA AND BILLITON ISLAND
he Lingga Archipelago (Singkep, Lingga, and surrounding islands,
with a total area of 2,188 sq km) belongs to the great Tin-Belt.
This belt extends from the western part of the Malay peninsula
(with the Main Range) via the Lingga Archipelago with Singkep, to
Bangka dan Billiton. These islands belong to a mountain range which
had largerly been beseleveled and which was partly abraded. It has
been dissected into a great number of islands owing to a rise of
the sea in late quaternary time. They represent a drowned
topography. Singkep, bangka, and Billiton are surrounded by an
aureole of submerged river valleys, containing alluvial tin-ores.
Bangka and Billiton are the most important tin producing islands.
Bangka has an area of 11,340 sq km, being the 19th island in size
of the whole Indian Archipelago. The Maras Mts in North bangka
attain a height of 692 m above sealevel and the Pading Mts in the
southern part of the island are 654 m high. Billiton measures 4,595
sq km and the two summits in its centre (Tadjem Laki and Tadjem
Bini) both attain an altitude of 510 m. The granites of Bangka and
Billiton belong to the jurrasic intrusions of the malayan tin-belt.
The exposed batholits are probably eminencies of an extensive
granitic body underlying the whole area. According to Westerveld
the tin-granites are prophyric biotite grantes with phenocrysts of
orthoclase of 5-6 cm length (up to 8 cm), microcline, perthite,
acid, plagioclase, biotite, quartz. Zircone, apatite, titanite,
flourite, black turmaline and probably also cassiterite are locally
primary constituents of these tin granites. Locally also amphibole
is present. According to the quantitative spectrograpical
determinations by Van Tongeren (1983) relative accumulations of
Y,La,Ce, and Nd are present. A basic border facies is formed by
amphibole quartzdiorites. The pneumatolytic-hydrothermal zone
overlying the zone of granitic and composition (in casu the
granitic basement with its batholithic protuberances) has a
thickness of 1,5 -2,5 km in Bangka and of 0,5 1,5 km in
Billiton.
he emplacement of these tin-granites may have occured by means
of granization. A typical agmatite granite variety from Tandjong
Binga (NW-Billiton) has been describe by the author (1940 c). This
granites contains numerous angular inclusions of dark rock with
sugary texture. These inclusions have a composition of kersantite,
spessartite, malchite, microdiorite, minette and the like (with
varying content of biotite, diopsidic augite, amphibole,
plagioclase, some xenomorphic orthoclase, little or no quartz;
accessory titanite, ilmenite, apatite). The granite itself has a
granosynetic composition (biotite, diopsidic augite, amphibole,
microperthitic orthoclase, albiteoligoclase and some qurtz). The
second largest tin-island, Billiton, has an analogous geological
structure as Bangka. The oldest formation consists of a series of
pelitic and psammitic sediments. The diabases of Cape Siantu can be
compared with the doleritic dikes and sills of Penjabung in Bangka.
A horizon of radiolarian cherts extends parallel to the Klappa
kampit vein, being comparable with the radiolarian bearing
siliceous shales of Bangka. According to Roggeveen (1932), the
strike of sediments in the klappa kampit mine is N 85 - 125 E with
a dip of 65 - 90. The main vein in primary tin-ore is intercalted
conformably in the sediment series. It is cut by two or three
systems of faults, the most important of which strikes N 65 E. A
fault with a N 130 E direction runs along the north foot of the
Klappa Kampit Hill. The faults show horizontal striations; they are
typical transverse faults, causing crustal stretching in the
direction of the general strike of the sediments. The isoclinal
folding of the sediment series in a N-S direstion was accompanied
by a sideward slipping and stretching by transverse faults. After
this folding and faulting, the intrusion of the granites and the
mineralization of this area took place.
n the Holocene, after a long period of denudation and
peneplanation, during which secondari tin-ores were formed, the
relative rise of the sealevel caused the transgression of the sea
over grearter part of the Sunda land. Also the tin-bearing valley
deposits partly submerged; these sea-tin deposits are mined by
means of large sea-going dredges around bangka and Billiton. A
mollusc-bearing layer in the young alluvial coastal strip of
Manggar (the species of which were determined br K. Martin) has
beesn considered as an aargument for a subrecent lowering of the
sea-level. This layer was also exposed by alluvial (land) mining
(e.g. in Bangkuwang SSW of Manggar); it appears that it has also
anland a position at over or even below selevel. Its land-inward
extension is only due to coastal accretion, and it does not
indicate a relative subrecent lowering of the sealevel.
FIGURE 1 : Geological Sketch Map of Bangka and Biliton
FIGURE 2 : Sketch Map of The East Indies
