Radiogenic geothermal systems of Bangka Island,Indonesia:Implications of high heat production and tectonic framework

The presence of geothermal manifestation in Bangka Island(Southeast Sumatra,Indonesia)with the absence of Quaternary volcanic activity and also relatively low seismicity events has raised intriguing questions on the control of the geothermal system in this area.As the regional tectonic setting of Indonesia volcanic geothermal systems has been known,that of non-volcanic geothermal systems such as radiogenic system become an issue to be investigated.This study reports the geochemistry and petrography analysis of Triassic granite related to radiogenic production at the vicinity of hot springs in Bangka Island.Surface temperatures of the Bangka hot springs range from 37 to 70.7 and pH values vary between 5.6 and 7.5.These hot springs are discharging either in close to massive granite bodies or occur in between two major NE-SW striking faults zones,i.e.,Pemali fault and Payung fault.Our results indicate the average radiogenic heat production of Late Triassic Klabat granite in the northern area ranges from 28.5 to 38.34μWm^(-3)and the southern area ranges from 28.3 to 49.5μWm^(-3).In comparison to similar granite belt located in Malaysia,heat production of granitoid in Bangka hot springs is four times higher,possibly due to their different granite origins.

Study on Epithermal Gold Mineralization System at Shwebontha Prospect,Monywa Copper-Gold Ore Field,Central Myanmar

The Shwebontha prospect area is situated in the Central Volcanic Belt,central Myanmar,where the well-known Sagaing Fault serves as its eastern boundary.This study aims to document key the mineralogy,host rock geochemistry and ore mineralizing fluids.The mineralization,hosted by Upper Oligocene to Middle Miocene rhyolites,displays a strong lithological control.Mineralization is characterized by gold-bearing silicified massive ore and chalcedonic quartz veins in which sulfides are clustered and disseminated not only in quartz gangue but also in rhyolite host rocks.The significant ore minerals in the mineralized veins include pyrite,sphalerite,galena,chalcopyrite,and gold.Common hydrothermal alterations such as silicic,argillic and propylitic alteration types are recognized.According to the fluid inclusion data and interpretation,ore mineralizing fluids in the research area are characterized by formation temperatures of 260-280℃ and salinity of 0.35-2.41%wt.NaCl eq.respectively.Mixing of hydrothermal fluids was generally considered to be an effective mechanism for ore transport and deposition.

Geochemical Behavior of Trace- and Rare-Earth Elements in the Hydrothermal Alteration Facies of the Cijulang Area, West Java, Indonesia

This study examines the behavior of trace- and rare-earth elements (REE) in different hydrothermal alteration facies (silicic, advanced argillic and argillic) of Cijulang high-sulfidation epithermal gold deposit, West Java, Indonesia. The results of the study indicate that remarkable differences in the behavior of trace elements and REE are observed in the studied alteration facies. All REE in the silicic facies are strongly depleted. In advanced argillic facies, Heavy rare-earth elements (HREE) are strongly depleted whereas light rare earth elements (LREE) are quite enriched. REE concentrations in the argillic facies show little or no variation with respect to fresh rock counterparts. A strong depletion of REE in the silicic facies is likely to be favored by the highly acidic nature of the hydrothermal fluids, the abundance of complexing ions such as Cl ˉ, F ˉ, and in the hydrothermal solutions and the absence of the secondary minerals that can fix the REE in their crystal structures. An apparent immobility of LREE in advanced argillic facies is possibly due to the presence of alunite. The immobility of REE in the argillic facies suggests the higher pH of the fluids, the lower water/rock ratios and the presence of the phyllosilicates minerals. -

Petrographic Characteristics and Geochemistry of Volcanic Rocks in the Kyaukmyet Prospect,Monywa District,Central Myanmar

The Kyaukmyet prospect lies approximately 5 km ENE of the high-sulfidation Kyisintaung copper-gold deposit,Monywa district,central Myanmar.Geologically,the research area is remarked by magmatic extrusion that occurred during the Late Oligocene to Middle Miocene of Magyigon Formation which led to the outcrops of volcanic rocks.Study detailed on petrographical and geochemical of the Kyaukmyet volcanic rocks has not been performed before the present work.The principal aim of this paper is to document the petrographical and geochemical characteristics of volcanic suite rocks exposed in the Kyaukmyet prospect.The results of this data have provided insight into the origin of the rocks and petrogenetic processes during evolution.Petrographically,all the studied volcanic rocks in the research area show that trachytic and porphyritic textures with phenocrysts of quartz,plagioclase,and K-feldspar which are embedded in a fine to medium grained groundmass.The accessory minerals of this rock consist of biotite,chlorite and opaque mineral.Geochemically,these volcanic rocks having calc-alkaline nature and classified as volcanic field(rhyolite)as well as volcanic arc setting.Based on the chondrite normalized spider diagram,LREE has enriched to HREE in this area which indicated negative Eu anomaly and subduction tectonic setting.