Hydrothermal Alteration of High Sulfidation Epithermal Deposits in Secang Area, Tulungagung, East Java, Indonesia

This research aims to determine geological condition and alteration in an epithermal high sulfidation mineralization as an initial guide for further exploration stages. Detailed geological mapping with scale of 1:12,500 is conducted to identify geological aspects and distribution of alteration zones. Selected rocks samples were prepared for laboratory analysis which are petrography, XRD (X-Ray Diffraction), and FA-AAS (Fire Assay-Atomic Absorption Spectrometry) analyse. Geological condition of the study area consists of six rock units including andesite lava, andesite breccia, diorite intrusion, polymict breccia, limestone, and alluvial deposit. Geological structures found are left strike-slip fault with right strike-slip fault as accompany. Result of XRD analysis shows the presence of clay minerals group: smectite, kaolinite, illite, diaspore, alunite, and pyrophillite. The alteration zones of study area are propylitic, argillic, advance argillic, and silisification zones. The further exploration stage is recommended to focus at the southwest and northeast of study area

Geology and Alteration of East Pinolosian Area, Bolaang Mongondow, North Sulawesi Province

Bolaang Mongondow is located on the Eastern North arm of Sulawesi. This area is a Neogene-aged magmatic arc composed of plutonic and volcanic rocks that indicate mineralization-bearing host rocks. The study aimed to determine the geological setting and alteration based on geological observations and geochemical analysis. The method used is geological mapping, followed by laboratory and studio data analysis. The lithology of this area is composed of andesite, diorite, and pyroclastic breccia units. Two main faults are the Northwest-Southeast trending dextral fault and the Northeast-Southwest trending sinistral fault, which causes hydrothermal mineral alteration. Mineral alteration in the study area is divided into several zones, including the Silicification Zone (massive silica + vuggy silica), Advance Argillic Zone (illite + alunite + dickite + halloysite + kaolinite), Argillic Zone (illite + montmorillonite + pyrophyllite), Prophyllitic Zone (chlorite + montmorillonite). The presence of mineral assemblages and alteration zones shows the characteristics of High Sulfide Epithermal deposits with the highest level of 0.47/ppm in the Advance Argillic Zone

Geologia e geoquímica da zona inferior do corpo de minério Ingá, distrito aurífero de Crixás, Goiás, Brasil : implicações genéticas e exploratórias

O corpo de minério Ingá foi descoberto em 2012 e é localizado na Unidade Serra Grande da AngloGold Ashanti, depósito de classe mundial no Distrito Aurífero de Crixás, Brasil central. Localizado nas rochas supracrustais, o corpo Ingá é dividido em Zona Superior e Zona Inferior. A Zona Superior contém lentes de sulfeto maciço hospedadas em dolomitos. A Zona Inferior foi sistematicamente estudada por DRX, FRX, ICP-MS, microssonda eletrônica e LA-ICP-MS. É controlada por uma falha de empurrão de baixo ângulo principal (Estrutura III) e suas litologias incluem, do topo para a base: dolomitos, filito carbonoso (GXN), veio de quartzo massivo (VQZ), quartzo-clorita-sericita-granada xisto e metagrauvaca com dois raros tipos de dique cortando a estratigrafia. Halos de alteração hidrotermal desenvolveram-se a partir da Estrutura III: silicificação, potássico, fílico e carbonático. A mineralização ocorre em três diferentes estágios. Três tipos de arsenopirita foram identificados: Aspy1 (cedo hidrotermal), Aspy2 (tardi hidrotermal, possivelmente rica em ouro invisível) e Aspy3 (tardi hidrotermal, rica em ouro visível como inclusões, preenchendo fraturas ou ao longo de suas margens). Ouro visível também ocorre como cristais livres nos níveis basais do VQZ e na matriz do GXN. Possível remobilização de ouro invisível inferido em Aspy2 para formar ouro visível em Aspy3 ao longo de fraturas tardias e alteração seletiva em direção às margens dos cristais, ocorreu como consequência do dobramento F2, aumentando a quantidade de ouro passível de extração no corpo de minério. Os gráficos de Bi ppm x Se ppm e S % x Bi ppm e consideráveis ganhos de As, Ni e Co na zona de silicificação sobre GXN rico em arsenopirita, podem ser usados para identificar zonas potencialmente ricas em ouro. Quatro parâmetros prospectivos foram estabelecidos: VQZ, Aspy2 e Aspy3, falhas de acomodação e zona de silicificação.The Ingá orebody was discovered in 2012 and is located in the world-class AngloGold Ashanti – Serra Grande Unit of the Crixás Gold District, Central Brazil. Located in the supracrustal rocks, Ingá is divided into Upper and Lower Zones. The Upper Zone contains massive sulfide lenses hosted in dolomites. The Lower Zone was systematically studied by XRD, XRF, ICP-MS, EMP and LA-ICP-MS. It is controlled by a major low angle thrust fault (Structure III) and lithologies include, from top to bottom: dolomites, carbonaceous phyllite (GXN), major quartz vein (VQZ), quartz-chlorite-sericite-garnet schist, and metagraywacke with two types of rare cross-cutting dikes. Hydrothermal alteration haloes developed outwards from Structure III: silicification, potassic, phyllic and carbonatic. Mineralization occurs in three different stages. Three types of arsenopyrite were identified: Aspy1 (early hydrothermal), Aspy2 (late hydrothermal, possibly invisible gold-rich) and Aspy3 (later hydrothermal, visible gold-rich as inclusions, filling fractures or along its margins). Visible gold also occurs as free crystals in the VQZ basal levels and in the GXN matrix. Possible remobilization of inferred invisible gold in Aspy2 to form visible gold in Aspy3 along late crystal fractures and selective alteration towards the margins occurred as consequence of F2 folding, increasing the orebody gold budget. The Bi ppm x Se ppm and S percent x Bi ppm plots and major gains in As, Ni and Co in the arsenopyrite rich GXN silicification zone could be used to identify potentially gold rich zones. Four prospective parameters were established: VQZ, Aspy2 and Aspy3, accommodation faults, and silicification zone

Identification of Alteration Zones Based on Resistivity and Induced Polarization Geoelectric Survey

Air Putih, Lebong Regency's geothermal field, is near gold mining. The relationship between the two can be illustrated in the type of rock alteration. The study aims to identify the rock alteration zone caused by the Air Putih, Lebong Regency geothermal system. It was described by the correlation of rocks' resistivity and chargebility values based on geoelectric measurement. Two tracks spread along the Air Putih tour, with a track length of 240 meters, were used to see variations in resistivity and chargeability values and the depth of geothermal potential due to deeper current penetration to determine the alteration zone in the study area. The results of field measurements are in the form of 2D models processed with Res2DinvX64 software. According to analysis, the subsurface rock lithology in the research area is relatively the same because the location of the two measurement lines is still close together; namely, there are wet valley rocks and alterated rock layers. Pores cause rock layers found in conductive areas in the rock filled with fluid or water at high temperatures. It is evidenced by the detection of manifestations on the surface in the form of warm soil, warm rocks, steamy soil, and small holes containing water grains. The higher the temperature and pressure, the lower the value of rock-specific resistance. At the Air Putih tourist area of Lebong Regency, it is found that it is a zone of prophylitic alteration containing several minerals of andesite lava, breccia, tuff, and soil

Occurrences and Characteristics of Gold Mineralization in Rampi Block Prospect, North Luwu Regency, South Sulawesi Province, Indonesia

This study is aimed to identify the occurences, characterisatics and genetic type of gold mineralization, and to elucidate the preliminary gold potential in the study area. Research method includes field observation of prospect geology, hydrothermal alteration and ore mineralization. Laboratory analysis consists of petrography, ore microscopy and ore chemistry. Geologically, quartz ± gold veins were found in Rampi block prospect, which are mainly hosted by metamorphic and metasediment rocks. The quartz veins has structurally segmented with massive, brecciated and laminated textures. Orientation and distribution of veins is controlled by NW–SE and NE–SW trending structures. Sulfides are present with minor abundance (9 ppm) commonly show laminated and brecciated texture and has been undergone a supergene enrichment. According to several characteristics above, gold deposit in Rampi block prospect tends to meet the criteria of orogenic/mesothermal gold type (cf. Groves et al., 2003). The deposit shares similarities with Awak Mas prospect, which is already confirmed to be a mesothermal type in Luwu district (cf. Querubin and Walters, 2011). Therefore, discoveries of economic mesothermal gold deposits are still open in the metamorphic terrains, and thus, it requires a systematic exploration based on the genetic model of the deposit

Geologi dan Studi Alterasi – Mineralisasi Endapan Timah Primer Daerah Ridingpanjang dan Sekitarnya Kecamatan Belinyu, Kabupaten Bangka Utara Kepulauan Bangka Belitung

Lokasi daerah penelitian yang berada di Daerah Ridingpanjang, Kecamatan Belinyu, Bangka Utara, dengan luas lokasi penelitian 28,98 km (6,3 x 4,6 km) dan berada pada koordinat UTM WGS 84 588000-594200 mE dan 9811000-9815700 mN. Daerah penelitian merupakan salah satu daerah yang memiliki prospek timah sehingga penulis menjadikan lokasi tersebut sebagai bahan kajian dalam menyelesaikan laporan tugas akhir. Metodologi pada penelitian yang dilakukan antara lain dimulai dengan persiapan awal, pengambilan data lapangan hingga pengolahan dan analisis data. Daerah penelitian tersusun atas 4 satuan litologi yaitu Satuan Schist, Satuan Coarse Grained Granite, Satuan Fine Grained Granite, dan Satuan Endapan Fluvial. Berdasarkan hasil analisis petrografi, analisis ASD (Analytical Spectral Device), dan analisa XRF (X-ray fluorescence), tipe alterasi yang berkembang pada daerah penelitian antara lain: zona alterasi pada daerah penelitian yaitu zona ± Kaolinit ± Halloysite ± Kuarsa ± K-Illite disetarakan dengan zona kaolinisasi, zona ± Kaolinit ± Alunit ± Kuarsa ± Pirit disetarakan dengan zona silisifikasi. Mineralisasi yang berkembang pada daerah penelitian menunjukkan tipe sistem endapan greisen dengan mineralisasi berupa kasiterit pada urat dengan asosiasi mineral pembawa berupa turmalin-kuarsa yang berkembang pada zona sesar berarah baratlaut-tenggara sebagai periode struktur pertama di daerah penelitian

Comparison of Different Multispectral Images to Map Hydrothermal Alteration Zones in Kokap, Kulon Progo

Using remote sensing data for hydrothermal alteration mapping beside saving time and reducing  cost leads to increased accuracy. In this study, the result of multispectral remote sensing tehcniques has been compare for manifesting hydrothermal alteration in Kokap, Kulon Progo. Three multispectral images, including ASTER, Landsat 8, and Sentinel-2, were compared in order to find the highest overall accuracy using principle component analysis (PCA) and directed component analysis (DPC). Several subsets band combinations were used as PCA and DPC input to targeting the key mineral of alteration. Multispectral classification with the maximum likelihood algorithm was performed to map the alteration types based on training and testing data and followed by accuracy evaluation. Two alteration zones were succeeded to be mapped: argillic zone and propylitic zone. Results of these image classification techniques were compared with known alteration zones from previous study. DPC combination of band ratio images of 5:2 and 6:7 of Landsat 8 imagery yielded a classification accuracy of 56.4%, which was 5.05% and 10.13% higher than those of the ASTER and Sentinel-2 imagery. The used of DEM together with multispectral images was increase the accuracy of hydrothermal alteration mapping in the study area

Geologi dan Studi Alterasi – Mineralisasi Endapan Timah Primer Daerah Temayang dan Sekitarnya Kecamatan Toboali, Kabupaten Bangka Selatan Kepulauan Bangka Belitung

Bangka Selatan merupakan salah satu penghasil timah terbesar di Indonesia. Casiterit Pulau Bangka Selatan telah mengalami pengayaan sekunder oleh proses erosi yang berlangsung selama jutaan tahun, menghasilkan endapan-endapan aluvial yang terkayakan akan timah. Seiring berjalannya penambangan letakan (aluvial) cadangan timah sekunder yang ada pun semakin menipis. Hal ini membuat eksplorasi endapan timah primer kembali dilakukan. Salah satunya yaitu didaerah Bangka Selatan yang sampai saat ini masih dilakukan eksplorasi dengan cara pengeboran. Penelitian dilakukan untuk mengetahui kondisi geologi, alteraimineralisasi dan arah sebaran urat. Metode yang digunakan adalah sampling litologi, analisis petrografi, analisis mineralgrafi yang dilakukan pada urat, analisis ASD dan XRD untuk mengetahui zonasi alterasi dan analisis XRF untuk mengetahui kandungan Timah (Sn). Morfologi daerah penelitian dibagi menjadi dua yaitu Satuan Dataran Intrusi Denudasional dan Satuan Fluvial. Zona alterasi daerah penelitian terbagi menjadi dua zona yaitu Zona Argilik Dalam dan Zona Argilik Luar, dibagi berdasarkan temperatur dan Ph pembentukanya, mineralisasi daerah penelitian berupa Kasiterit, Sphalerit, Kalkopirit dan Mineral Oksidasi, yang didapat dari hasil analisis urat. Dimana arah persebaran urat daerah penelitian dominan arah NW-SE. Zonasi alterasi greisen daerah penelitian diawali dari adanya pengkayaan Zona Greisen (kuarsa+muscivit), Zona Silicification, Zona Albitisation II dan Zona Microclinisation II, Zonasi tersebut terbentuk pada saat Post-Magmatic