PETROGENESIS OF QUARTZ IN SOME POTENTIAL HIGH PURITY QUARTZ DEPOSITS IN MAIN ISLAND OF SUMATRA, BANGKA AND BELITUNG ISLANDS AND RIAU ARCHIPELAGO
A.S. Subandrio (a), M.I. Agadinata (b), V. Susanto (a) and I.A. Kurniawan (a)

(a) Prodi Teknik Geologi - FITB - ITB
(b) Independent Geologist

Abstract

High Purity Quartz (HPQ) is one of the most abundant minerals in the Earth^s crust and the most important silica mineral, occurring in large amounts in igneous, metamorphic and sedimentary rocks. The demand for the raw material quartz is increasing worldwide, in particular, the demand for high-purity quartz. Therefore, high purity quartz has become one of today^s key strategic raw materials for the high-tech industry. It can be used either for high added value applications such as silicon-metal wafers , optical glass or solar cells of PV panels. HPQ for advanced high-tech applications is currently sourced from just a few locations around the world. Such is the expected growth in demand that more sources are required to be found. For successful raw HPQ resources identification detailed analysis and appropriate process technology selection is essential. This paper reviews general aspects of HPQ deposits, exploration requirements, quality evaluation of raw quartz, and provides basic insight into the different specifications and market developments of the hightech end-user industries reliant on very high purity refined quartz products. Intensive exploration work in area of main island of Sumatra, islands of Bangka and Belitung as well as Riau Archipelago resulted in the identification of medium to high purity quartz vein and sand of beach and river deposits. This research examines the origin of quartz-rich sands, documents the range of environments in which they are found and suggests a model for their genesis in islands of Sumatra, Bangka and Riau Archipelago. Cretaceous quartz arenites are a very common geological feature on the southeastern part of Riau Archipelago. Provenance analysis and study of weathering effects was done for Cretaceous sandstone from south-eastern Riau Archipelago, including Singkep island. In this study we distinguish different quartz types by XRF analyses combined with standard optical petrography on the on vein, sandstone and quartz sand. This is done on a suite of samples collected from beach sand and sinclinal basin of the Sebangka island. Our results show that the quartz sand were derived from local Cretaceous sandstone source rocks, whereas quartz sand of Sibolga area may have been derived from local source of Triassic plutone of Sibolga Granitoid Complex. This study also highlights the importance of understanding alteration processes of acid plutonic rocks that affecting the deposits from source to sink, and to be careful to describe quartz-rich rocks as simply recycled deposits. The mineralogical characterization of Sibolga beach sand suggested that the powder quartz deposit was formed by long-term weathering of feldspathic or felsic rocks, possible of pegmatitic origin associated with Triassic Sibolga granitoid rocks. The main chemical impurities of Pasaman quartz vein are Al (30-1400ppm), K(100-3000 ppm), Fe (100-1100 ppm), Na (200-600 ppm), Ca (20-600 ppm), and Ti (15- 110 ppm). All the samples from deposits under this study meet the requirements of the HPQ definition and they are thus high purity quartz deposits. The petrologic analyses of 13 thin sections from two location in Sebangka and Sirai islands allowed the identification of primary composition and diagenetic patterns of Semarung Formation. The original detrital compositions included arenite, and lithic sandstones. The discovery of some potential HPQ deposit in Sumatra, Bangka and Riau Archipelago, together with a better knowledge of the processes leading to the formation of HPQ in pegmatitic veins and arenitic sandstone, could lead to the recognition of a Indonesian type of HPQ resourcse applicable for industrial use. Beneficiation study on these deposits is recommended to establish possible industrial applications that may be feasible.

Keywords: High purity quartz, Sumatra, Bangka, Riau archipelago, national

Topic: Interdisciplinary Geosciences