Halogen Chemistry of Hydrothermal Micas: a Possible Geochemical Tool in Vectoring to Ore for Porphyry Copper-Gold Deposit

Porphyry copper-gold deposit commonly exhibits an extensive alteration zone of hydrothermal micas particularly biotite and sericite. This study is aimed to analyze and utilize the chemistry of halogen fluorine and chlorine of biotite and sericite to be a possible tool in vectoring to ore for copper porphyry deposits. To achieve the objectives, several selected altered rock samples were taken crossing the Batu Hijau copper-gold mine from inner to outer of the deposit, and hydrothermal micas contained by the rocks were analyzed petrographically and chemically. Mineral chemistry was detected by electron microprobe analyzer, whilst biotite is petrographically classified as either magmatic or hydrothermal types. Sericite replacing plagioclase occurred as fine-grained mineral and predominantly associated with argillic-related alteration types. Biotites in the Batu Hijau deposit are classified as phlogopite with a relatively low mole fraction magnesium (XMg) (~0.75) compared to the “typical” copper porphyry deposit (~0.82). The relationship between the XMg and halogen contents are generally consistent with “Fe-F and Mg-Cl avoidance rules”.  F content in biotite and sericite decrease systematically from inner part of the deposit which is represented by early biotite (potassic) zone where the main copper-gold hosted, to the outer part of the deposit. However, chlorine in both biotite and sericite from each of the alteration zones shows a relative similar concentration, which suggests that it is not suitable to be used in identification of the alteration zones associated with strong copper-gold mineralization. H2O content of the biotite and sericite also exhibits a systematic increase outward which may also provide a possible geochemical vector to ore for the copper porphyry deposits. This is well correlated with fluorine content of biotite in rocks and bulk concentration of copper from the corresponding rocks

P.T Conditions and Oxygen Fugacity of The Intrusion Emplacement at The Batu Hijau Porphyry Copper Gold Deposit, Sumbawa Island:A Constraint From Geothermobarometric Data

Among the southeast Asian countries, Indonesia, nowadays, has a biggest resources and production of copper and gold. The majority of copper and gold resources and production is derived from porphyry copper-gold deposits, such as Grasberg in Irian Jaya and Batu Hijau in Sumbawa Island. To enhance an understanding on the genesis and characteristics of the porphyry deposits, it is crucial to estimate the physicochemical conditions, including temperature, pressure (depth) and oxygen fugacity (f02) of the ore-bearing intrusions during their emplacement and crystallisation. There are many ways to estimate the physicochemical conditions, such as isotope geochemistry, microthermometric analysis of fluid inclusion and geothermobarometric analysis. In this paper, the physicochemical conditions of the causative tonalite intrusions in the Batu Hijau deposit will be constrained from the geothermobarometric data, by applying the hornblende-plagioclase and magnetite-ilmenite thermometers and the Al-in-hornblende barometer. The thermobarometers indicate that the tonalite porphyries emplace at 764 ± 22°C and 1.5 ± 0.3 kbar and completely crystallised at â540°C. If the pressure is assumed to be lithostatic, it is interpreted that the hornblende and plagioclase phenocrysts crystallised at depths of about 5.5 km. Log f02 of the magma crystallisation ranges from -20 to -12 (between NNO and HEM-MAG buffers)

Petrography and Mineral Chemistry of Magmatic and Hydrothermal Biotite in Porphyry Copper-Gold Deposits: a Tool for Understanding Mineralizing Fluid Compositional Changes During Alteration Processes

DOI: 10.17014/ijog.5.1.47-64This study aims to understand the petrography and chemistry of both magmatic and hydrothermal biotites in porphyry copper-gold deposits, and to evaluate the fluid compositional changes during alteration processes. A total of 206 biotite grains from selected rock samples taken from the Batu Hijau porphyry Cu-Au deposit was analyzed. Detailed petrography and biotite chemistry analysis were performed on thin sections and polished thin sections, respectively, representing various rocks and alteration types. A JEOL JXA-8900R electron microprobe analyzer (EMPA) was used for the chemistry analysis. The biotite is texturally divided into magmatic and hydrothermal types. Ti, Fe, and F contents can be used to distinguish the two biotite types chemically. Some oxide and halogen contents of biotite from various rocks and alteration types demonstrate a systematic variation in chemical composition. Biotite halogen chemistry shows a systematic increase in log (XCl/XOH) and decrease in log (XF/XOH) values from biotite (potassic) through chlorite-sericite (intermediate argillic) to actinolite (inner propylitic) zones. The y-intercepts on the log (XCl/XOH) vs. XMg and log (XF/XOH) vs. XFe plotted for biotite from potassic and intermediate argillic zones are similar or slightly different. In contrast, the y-intercepts on the log (XCl/XOH) vs. XMg and log (XF/XOH) vs. XFe plotted for biotite from inner propylitic zone display different values in comparison to the two alteration zones. Halogen (F,Cl) fugacity ratios in biotite show a similar pattern: in the potassic and intermediate argillic zones they show little variation, whereas in the inner propylitic zone they are distinctly different. These features suggest the hydrothermal fluid composition remained fairly constant in the inner part of the deposit during the potassic and intermediate argillic alteration events, but changed significantly towards the outer part affected by inner propylitic alteration. High halogen content, particularly Cl, in hydrothermal biotite may portray that copper and gold were transported in mineralizing fluids in the form of chloride complexes CuCl2- and AuCl2-, respectively

Bahan Galian Uranium Dan Prospek Pengembangannya Sebagai Salah Satu Sumber Energi Alternatif Dimasa Mendatang

Kata kunci: Uranium, energi alternati

Geology, Hydrothermal Alteration Characteristics and Ore Mineralization in Purnama Martabe Pit, Tapanuli Selatan District, North Sumatra Province

High demands of metal such as gold, silver, and copper, also their limited occurances causing an understanding of geological conditions, alteration and ore mineralization characteristics are needed for a sustainable exploration. This study aims to elucidate geological conditions, characteristics and the distribution of alteration zones and ores mineralization in Purnama Martabe Pit based on geological mapping, drill cores logging and sampling. Selected samples were analysed by XRF (X-Ray Fluorescenes), ASD (Analytical Spectral Devices), petrography, and mineragraphy analysis. Lithological units at the study area consist of andesite lava unit, diorite intrusion dome and polymictic phreatomagmatic breccia units. Based on ASD analysis, alteration zones in the study area are vuggy-massive silica, silica+dickite±alunite, illite+smectite, and smectite+chlorite. Based on mineragraphy and XRF, the mineralization occurred at the study area is composed of pyrite, enargite, hematite, goethite, and jarosite. Zonation and distribution of alteration and mineralization is predominantly controlled by the north east – south west structure in the form of quartz veins, north west – south east structure, and various porosities of the lithological units.Tingginya angka kebutuhan logam berupa emas, perak, dan tembaga serta keterdapatannya yang terbatas menyebabkan pemahaman mengenai kondisi geologi, karakteristik alterasi, dan mineralisasi bijih diperlukan dalam proses eksplorasi yang berkelanjutan. Penelitian ini bertujuan untuk mengetahui kondisi geologi, karakteristik dan persebaran alterasi serta mineralisasi bijih di Pit Purnama Martabe berdasarkan hasil pemetaan, deskripsi intibor dan pengambilan sampel yang kemudian dianalisis dengan XRF (X-Ray Fluorescenes), ASD (Analytical Spectral Device), petrografi, dan mikroskopi bijih. Litologi di daerah penelitian tersusun satuan lava andesit, satuan kubah intrusi diorit, dan satuan breksi freatomagmatik polimiktik. Berdasarkan analisis ASD, zona alterasi yang berkembang terdiri atas alterasi silika vuggy-masif, zona alterasi silika+dikit±alunit, ilit+smektit, dan smektit+klorit. Berdasarkan analisis mineragrafi dan ditunjang oleh data XRF, dapat diketahui bahwa mineralisasi di daerah penelitian berupa pirit, enargit, hematit, goetit, dan jarosit. Kondisi geologi yang mengontrol persebaran alterasi dan mineralisasi yang terjadi adalah adanya struktur berarah timur laut – barat daya berupa urat kuarsa dan barat laut – tenggara, serta litologi yang memiliki porositas bervariasi

Characteristics and Potential of Placer Gold Deposit in Lakan Bilem Block, West Kutai District, East Kalimantan, Indonesia

Kalimantan is recognized as one of Indonesian islands with huge prospect of minerals particularly gold both primary and secondary deposit styles. However, the publication of the gold resources is still restricted to be described in regional/district scale maps or exploration company internal reports, hence, a detailed study on deposit scale remains limited. This study is aimed to document the characteristics and the estimation of potential or resources of the secondary (placer) gold deposit in Lakan Bilem block, West Kutai district, East Kalimantan province, Indonesia. The study was done by field observation followed by microscopic analysis and simple resources estimation of the gold. Gold in the study area occur in the semi-consolidated paleo alluvial deposit as trace mineral. The gold morphologies show platy to angular form with coarse surface which indicates the process of gold deposition is predominantly controlled by hydrodynamic transportation at a relatively moderate regime. Estimation of the indicated resources of gold results a total of 4.96 tonnes of gold potentially occurred in the study area. Exploration drilling with 100 spacing grid is suggested to delineate lateral and vertical distribution of the gold deposit. The drilling also will upgrade confidence level of the resources from indicated to measured resources

The Metamorphic Rocks-Hosted Gold Mineralization At Rumbia Mountains Prospect Area In The Southeastern Arm of Sulawesi Island, Indonesia

Recently, in Indonesia gold exploration activities  are not only focused along volcanic-magmatic belts, but also starting to shift along metamorphic and sedimentary terrains. The study area is located in Rumbia mountains, Bombana Regency, Southeast Sulawesi Province. This paper is aimed to describe characteristics of alteration and ore mineralization associated  with metamorphic rock-related gold deposits.  The study area is found the placer and  primary gold hosted by metamorphic rocks. The gold is evidently derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC). These quartz veins are currently recognized in metamorphic rocks at Rumbia Mountains. The quartz veins are mostly sheared/deformed, brecciated, irregular vein, segmented and  relatively massive and crystalline texture with thickness from 1 cm to 15.7 cm. The wallrock are generally weakly altered. Hydrothermal alteration types include sericitization, argillic, inner propylitic, propylitic, carbonization and carbonatization. There some precious metal identified consist of native gold and ore mineralization including pyrite (FeS2), chalcopyrite (CuFeS2), hematite (Fe2O3), cinnabar (HgS), stibnite (Sb2S3) and goethite (FeHO2). The veins contain erratic gold in various grades from below detection limit <0.0002 ppm to 18.4 ppm. Based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposit type. The orogenic gold deposit is one of the new targets for exploration in Indonesi