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 in!"elt# his belt e$tends from the western part of the %ala& %ala& penins peninsula ula (with (with the %ain %ain 'ange) 'ange) ia the Lingg Lingga a Archip Archipela elago go with with Singk Singkep, ep, to "angka dan "illiton# hese islands belong to a mountain range which had largerl& been beseleeled and which was partl& abraded# t has been dissected into a great number of islands owing to a rise of the sea in late quaternar& time# he& represent a drowned topograph&#
Singkep, bangka, and "illiton are surrounded b& an aureole of submerged rier alle&s, contai containin ning g allui alluial al tin!or tin!ores es## "angk "angka a and "illito "illiton n are the most most import important ant tin produc producing ing islands# "angka has an area of 11,*+ 11,*+ sq km, being being the 1-th island in si.e si.e of the whole ndian Archipelago# he %aras %ts in /orth bangka attain a height of 0-2 m aboe sealeel and the ading %ts in the southern part of the island are 0+ m high# "illiton measures +,- sq km and the two summits in its centre (ad3em Laki and ad3em "ini) both attain an altitude of 1 m#
he granites of "angka and "illiton belong to the 3urrasic intrusions of the mala&an tin! belt# belt# he e$pose e$posed d batho batholits lits are probab probabl& l& emine eminenci ncies es of an e$tens e$tensie ie granit granitic ic bod& bod& underl&ing the whole area# According to 4estereld the tin!granites are proph&ric biotite grantes with phenocr&sts of orthoclase of !0 cm length (up to 8 cm), microcline, perthite, acid, plagioclase, biotite, quart.# 5ircone, apatite, titanite, flourite, black turmaline and probabl& also cassiterite are locall& primar& constituents of these tin granites# Locall& also amphibole is present# According to the quantitatie spectrograpical determinations b& 6an ongeren (1-8*) relatie accumulations of 7,La,e, and /d are present#
A basic border facies is formed b& amphibole 9 quart.diorites# he pneumatol&tic! h&drothermal .one oerl&ing the .one of granitic and composition (in casu the granitic basement with its batholithic protuberances) has a thickness of 1, !2, km in "angka and of , 9 1, km in "illiton#
he emplacement of these tin!granites ma& hae occured b& means of grani.ation# A t&pical agmatite granite ariet& from and3ong "inga (/4!"illiton) has been describe b& the author (1-+ c)# his granites contains numerous angular inclusions of dark rock with sugar& te$ture# hese inclusions hae a composition of kersantite, spessartite, malchite, microdiorite, minette and the like (with ar&ing content of biotite, diopsidic augite, amphibole, plagioclase, some $enomorphic orthoclase, little or no quart.: accessor& titanite, ilmenite, apatite)# he granite itself has a granos&netic composition (biotite, diopsidic augite, amphibole, microperthitic orthoclase, albiteoligoclase and some qurt.)#
he second largest tin!island, "illiton, has an analogous geological structure as "angka# he oldest formation consists of a series of pelitic and psammitic sediments# he diabases of ape Siantu can be compared with the doleritic dikes and sills of en3abung in "angka# A hori.on of radiolarian cherts e$tends parallel to the ;lappa kampit ein, being comparable with the radiolarian bearing sili ceous shales of "angka#
According to 'oggeeen (1-*2), the strike of sediments in the klappa kampit mine is / 8 ! 12< = with a dip of 0< ! -<# he main ein in primar& tin!ore is intercalted conformabl& in the sediment series# t is cut b& two or three s&stems of faults, the most important of which strikes / 0< =# A fault with a / 1*< = direction runs along the north foot of the ;lappa ;ampit >ill# °
he faults show hori.ontal striations: the& are t&pical transerse faults, causing crustal stretching in the direction of the general strike of the sediments# he isoclinal folding of the sediment series in a /!S direstion was accompanied b& a sideward slipping and stretching b& transerse faults# After this folding and faulting, the intrusion of the granites and the minerali.ation of this area took place#
n the >olocene, after a long period of denudation and peneplanation, during which secondari tin!ores were formed, the relatie rise of the sealeel caused the transgression of the sea oer grearter part of the Sunda land# Also the tin!bearing alle& deposits partl& submerged: these sea!tin deposits are mined b& means of large sea!going dredges around bangka and "illiton#
A mollusc!bearing la&er in the &oung alluial coastal strip of %anggar (the species of which were determined br ;# %artin) has beesn considered as an aargument for a subrecent lowering of the sea!leel# his la&er was also e$posed b& alluial (land) mining (e#g# in "angkuwang SS4 of %anggar): it appears that it has also anland a position at oer or een below seleel# ts land!inward e$tension is onl& due to coastal accretion, and it does not indicate a relatie subrecent lowering of the sealeel#
FIGURE 1 ?
@eological Sketch %ap of "angka and "iliton
FIGURE 2 ?
Sketch %ap of he =ast ndies
