Vein Textures Research Articles

Petrological and mineralogical characteristics of “red material layer” in Patuha geothermal field, Bandung, West Java

Abstract Patuha Geothermal Field is located in Ciwidey, Bandung, West Java Province, with a total resource potential of approximately 400 Mwe (Megawatt electric). With such potential, seven power plants have been developed in Unit-1, capable of producing 60 MWe of electricity, and are currently being developed in stages for Unit-2. In the development of the Unit-2 power plant, there was a problem where collapse occurred around the drill hole area, especially since the color of the material that came out during drilling was red. We call this material the red material layer (a layer composed of red material). This problem also occurs in Unit-1. This research aims to characterize the type of red material layer to see why this problem occurs in this layer. We studied the petrological and mineralogical characteristics of the red material layer by cutting rock samples from six drill holes in Unit-1. The analytical methods used were megascopic observation, petrography, and XRD (X-ray diffraction) to determine the mineral content texture and identify the material’s origin, including clay minerals, alteration, and oxidation mineral aggregates. The petrological and mineralogical analysis found that the red-colored material is dominated by hematite, with some samples containing magnetite. We found four characteristic types of red layer material and four types of textures that appeared in iron oxide minerals: rim, vein, matrix replacements, and fragment replacements. We conclude from the visible vein texture that oxidation occurs due to oxygen penetration through gaps of a fault/fracture/joint. This oxidizes the area around the vein and then undergoes hydrothermal change. Meanwhile, those that do not have a vein texture are considered material resulting from an oxidation process on the surface, which is then deposited and undergoes hydrothermal change to contain oxide minerals such as hematite and magnetite. Apart from that, XRD observations also found high amounts of clay minerals such as chlorite, smectite, kaolinite, illite-smectite mixed layers, and chlorite-smectite mixed layers. The presence of these clay minerals is thought to cause a collapse in the area around the drill hole because its swelling and exfoliation properties are reactive to fluids, especially drilling fluids.

Geology and Ore Mineralization Characteristics of the Selodong Prospect, Lombok Island, Indonesia

Abstract The Selodong prospect is located in the southwest sector of Lombok Island which tectonically lies within the W-E trending Sunda-Banda magmatic arc, which hosts various gold-base metal mineralizations including porphyry and epithermal deposits. Lombok Island, particularly southwestern portion of the island is known to hosts gold, silver and copper prospects, including Selodong prospect. The Selodong prospect is divided into several sub-prospect areas which include the Blongas, Montong Botek, Kekalik and Belikat. However, this study only focuses on the Blongas sub-prospect. The study is aimed to discusses the geology, characteristics of alteration and mineralization of the sub-prospect. To achieve the objective, some methods such as mapping and numerous laboratory works were conducted. Petrography to identify alteration minerals, ore microscopy to identify type of ore minerals, and fluid inclusion microthermometry to characterize ore fluid were performed. The geological conditions of the study area are composed of andesite lava, andesite breccia, diorite intrusion and alluvial deposit. Typical porphyry alteration type i.e., potassic is present. Argillic, silicic, advanced argillic, propylitic and phyllic alterations are also identified. The distribution of potassic and some argillic alteration is controlled by lithology, while silicic alteration, advanced argillic, propylitic and some argillic alterations are controlled by geological structures with an NW-SE and NE-SW trending patterns. Propylitic alteration is characterized by chlorite + epidote + calcite ± clay. Argillic alteration is marked by the presence of clay minerals such as clay + quartz. Advanced argillic alteration is typified by quartz + alunite + pyrolusite ± paragonite. Phyllic alteration is typified by sericite + quartz ± clay. Potassic alteration is marked by secondary biotite + quartz ± clay. Silicic alteration is marked by quartz + pyrolusite + epidote. Ore mineralization in the study area is associated with massive and stockwork vein textures. Ore and metalliferous minerals are found as magnetite, chalcopyrite, pyrite, hematite, goethite, jarosite, sphalerite, pyrrhotite, chalcocite and native gold. Generally, homogenization temperatures in the research area range from 543 - >600 °C, with salinity of 26.3 - 73.95 wt.% NaCl eq associated with potassic alteration, whereas homogenization temperatures range from 251 to 349 °C, with salinity of 5.46 - 8.38 wt.% NaCl eq. associated with silicic alteration. Based on those characteristics, the prospect in the study area indicates a porphyry deposit type, which is transition to high sulfidation epithermal.

Mineralogy and Hydrothermal Fluids Characteristics of the Mekarbakti Low Sulfidation Epithermal Gold Prospect at Garut Regency, West Java, Indonesia

Abstract Mekarbakti prospect is situated in the western sector of Java Island which tectonically lies within the W-E trending Sunda-Banda magmatic arc. This arc hosts numerous prospects for ore mineralization with various types of mineral deposits, one of which is epithermal that found in the study area. The Mekarbakti prospect is located close to the Arinem prospect, about 8 km to the east, which is confirmed as a low sulfidation epithermal deposit type. Arinem is proven to be economical to mine, thus it becomes interesting to conduct study on the Mekarbakti prospect, to elucidate its mineralization model. This paper is dealing with the characteristics of hydrothermal alteration using petrographic and X-Ray Diffraction (XRD) to identify the alteration minerals, using ore microscopy analysis to identify the type of ore minerals, and fluid inclusion to reveal the hydrothermal fluid characteristics. The geological condition of the study area is composed of andesite lava, andesite breccia, tuff, lapilli, and andesite intrusion. The distribution of silicification alteration is controlled by geological structures with an NW-SE pattern, while argillic and propylitic alterations tend to have a gradient trend towards silicification alteration. Propylitic alteration is characterized by chlorite+illite+smectite±epidote. Argilic alteration is marked by the presence of clay minerals such as kaolinite+illite+smectite+quartz. Silicification alteration typified by quartz+kaolinite+diaspore+illite. Ore mineralization in the study area is associated with massive, brecciated, comb, cockade and, stockwork vein textures. Ore and metalliferous minerals are found as pyrite, hematite, goethite, chalcopyrite, sphalerite, galena, pyrrhotite, covellite, chalcocite, acanthite, native gold, and native silver. Generally, the mean homogenization temperature in the research area ranged from 248.05 – 266.12 °C, with salinity ranged from 1.01 – 1.68 wt.% NaCl eq. The epithermal deposit in the study area is classified as deep low sulfidation epithermal deposit specifically in transition between base metal and precious metal interval.

Genetic implications of vein texture and mineralogy at the Au-bearing El Morado mining district, Sierras Pampeanas, San Juan, Argentina

El Morado mining district is located in Sierra de La Huerta, in the Sierras Pampeanas of San Juan province, Argentina. It comprises numerous Au-bearing quartz veins hosted by intensely deformed igneous-metamorphic units of lower Paleozoic age. In the El Morado mining district, Maira mine is the only deposit producing gold at the present time. Quartz veins in this mine and surroundings, occur in concordance with their host rocks foliation and show numerous evidences of brittle-ductile deformation, mainly represented by a pinch-and-swell structure and extended development of breccia bodies.The application of scanning electron microscopy cathodoluminiscence in quartz samples lead to the recognition of homogeneous texture, which is evidence of recrystallization, commonly observed in orogenic gold quartz veins. Intracrystalline deformation is ubiquitous and represented by undulose and patchy extinction in relicts of large old grains where bulging and sub-grain rotation recrystallization microstructures are well represented. These dynamic quartz deformation processes indicate temperatures going up to ∼350 °C. Fluid inclusion post-entrapment modifications were recognized in quartz veins as numerous collapsed, small-sized fluid inclusions.Ore mineralization at Maira mine occurred after quartz veins emplacement and deformation in the upper crustal brittle-ductile transition zone. Galena, chalcopyrite and lesser pyrite and bornite, together with gold and tetrahedrite were identified infilling fractures in quartz veins. Gold grains were also identified closely related to malachite, cuprite, goethite and lepidocrocite in oxidizing horizons.

Leaves and Twigs Image Recognition Based on Deep Learning and Combined Classifier Algorithms

In recent years, the automatic recognition of tree species based on images taken by digital cameras has been widely applied. However, many problems still exist, such as insufficient tree species image acquisition, uneven distribution of image categories, and low recognition accuracy. Tree leaves can be used to differentiate and classify tree species due to their cognitive signatures in color, vein texture, shape contour, and edge serration. Moreover, the way the leaves are arranged on the twigs has strong characteristics. In this study, we first built an image dataset of 21 tree species based on the features of the twigs and leaves. The tree species feature dataset was divided into the training set and test set, with a ratio of 8:2. Feature extraction was performed after training the convolutional neural network (CNN) using the k-fold cross-validation (K-Fold–CV) method, and tree species classification was performed with classifiers. To improve the accuracy of tree species identification, we combined three improved CNN models with three classifiers. Evaluation indicators show that the overall accuracy of the designed composite model was 1.76% to 9.57% higher than other CNN models. Furthermore, in the MixNet XL CNN model, combined with the K-nearest neighbors (KNN) classifier, the highest overall accuracy rate was obtained at 99.86%. In the experiment, the Grad-CAM heatmap was used to analyze the distribution of feature regions that play a key role in classification decisions. Observation of the Grad-CAM heatmap illustrated that the main observation area of SE-ResNet50 was the most accurately positioned, and was mainly concentrated in the interior of small twigs and leaflets. Our research showed that modifying the training method and classification module of the CNN model and combining it with traditional classifiers to form a composite model can effectively improve the accuracy of tree species recognition.

Finger Vein Recognition Based on a Histogram of Competitive Gabor Directional Binary Statistics

Traditional methods of extracting finger vein texture changes and orientation features are susceptible to illumination, translation, noise, and rotation, and the process has difficulty directly extracting structural features through the original image. In this paper, the histogram of competitive Gabor directional binary statistics (HCGDBS) is proposed to extract discriminative structural features. First, the index of the largest filter value is obtained based on the multidirectional Gabor filter as the dominant direction, thereby obtaining the rotation-invariance feature. Second, according to the filter response size of each pixel in different directions, the order difference relationship between the adjacent three directions is compared, and a highly discriminative competitive Gabor direction binary pattern (CGDBP) is constructed. Finally, the CGDBP features are extracted in blocks, and the HCGDBS is constructed to overcome image translation. Experimental results show that it improves the recognition performance and overcomes illumination, translation, noise, and rotation.

Finger Vein Image Deblurring Using Neighbors-Based Binary-GAN (NB-GAN)

Vein contraction and venous compression typically caused by low temperature and excessive placement pressure can blur the captured finger vein images and severely impair the quality of extracted features. To improve the quality of captured finger vein image, this paper proposes a 26-layer generator network constrained by Neighbors-based Binary Patterns (NBP) texture loss to recover the clear image (guessing the original clear image). Firstly, by analyzing various types and degrees of blurred finger vein images captured in real application scenarios, a method to mathematically model the local and global blurriness using a pair of defocused and mean blur kernels is proposed. By iteratively and alternatively convoluting clear images with both kernels in a multi-scale window, a polymorphic blur training set is constructed for network training. Then, NBP texture loss is used for training the generator to enhance the deblurring ability of the network on images. Lastly, a novel network structure is proposed to retain more vein texture feature information, and two residual connections are added on both sides of the residual module of the 26-layer generator network to prevent degradation and overfitting. Theoretical analysis and simulation results show that the proposed neighbors-based binary-GAN (NB-GAN) can achieve better deblurring performance than the the-state-of-the-art approaches.

Geology, geochemistry, fluid inclusion data, stable isotope characteristics, and ore genesis of the Barout Aghaji gold deposit, NW Zanjan, Iran

The Barout Aghaji gold deposit is located ∼90 km northwest of Zanjan, within the Takab-Takht-e-Soleyman subzone of the Sanandaj-Sirjan metamorphosed-deformed zone. Ore-bearing quartz veins are hosted by Neoproterozoic amphibolite and Eocene to Oligocene granitic gneisses. Oligo-Miocene Upper Red Formation unconformably overlies the amphibolite and granitic gneisses. Field observations and petrographic studies show that two deformation stages occurred in this area. The first deformation stage was ductile, producing mylonitic and proto-mylonitic microstructures, but the second one was brittle, represented by sheeted quartz veins and veinlets. In the first stage, barren milky quartz veins occurred containing minor sulfide minerals, but dark to light gray ore-bearing quartz veins and veinlets are formed in the latter stage. The mineralized veins appear as massive microcrystalline quartz cut by sheeted quartz veins with comb, druse, and crustiform textures. The gold-bearing quartz veins contain as much as 3% sulfide minerals. Pyrite is the main sulfide mineral and is associated with minor chalcopyrite. Sulfides are commonly altered to hematite, goethite, and rarely malachite. Hydrothermal alteration around the quartz veins consists of silicification, pyritization, and sericitization. The whole-rock geochemistry of the collected samples from the granitic gneisses and quartz veins shows that Au is enriched in the quartz veins (average of 114 ppb) relative to host rocks (average of 22.5 ppb). Au shows strong positive correlations with As, Ba, Mo, Pb, Sc, Tl, Ag, and negative correlations with Cu, Bi, Se, and Te in the granitic gneisses. It also shows strong positive correlations with S, Hg, Th, Co, Bi, Pb, and Ag and negative correlations with P, V, Te, W, Sc, Zn in quartz veins. Four types of primary fluid inclusions were identified, including type I, two-phase aqueous-rich fluid inclusions (liquid > vapor; LV); type II, two-phase vapor-rich fluid inclusions (gas > liquid; VL); type III, three-phase fluid inclusions containing CO2 with clathrate formation (L1L2V); and type IV three-phase fluid inclusions (aqueous, vapor, and solid; LVS). The homogenization temperatures of fluid inclusions in auriferous quartz veins range from 199 −446 with a mode of 270–300 °C. Salinities range from 0.8 to 49.02 wt% NaCl Equiv. with two distinct populations at 0.8–8.5 and 31.1–49.02 wt% NaCl Equiv. The large variations in the homogenization temperatures and salinities can be attributed to the cooling and isothermal mixing of fluids. The δ34S values for four pyrites separated from auriferous quartz veins range from +2.9 to +7.1‰, with an average of 4.5‰. δ34S values of fluids in equilibrium with pyrite were calculated from +3.5 to +7.3‰, with an average of 5.4‰, indicating a metamorphic source for the sulfur using temperatures estimated from the fluid inclusion study. The Field observations, vein textures, mineralogy, ore geochemistry, fluid inclusion studies, and sulfur isotope data indicate that gold mineralization in the Barout Aghaji area has many similarities to orogenic and intrusion-related gold deposits, such that low salinity fluids derived from metamorphic rocks are mixed with high salinity fluid inclusions possibly derived from granitic gneisses during syn to post tectonic magmatism.

Pyrite as a Microtextural and Geochemical Tracer of Ore-Forming Processes, Central Zone Orogenic Gold Deposit, Gabgaba District, Sudan

Abstract Gold deposition in structurally controlled deposits is triggered by changes in the mineralizing fluid conditions. Recent research has demonstrated that in deposits with a well-established paragenesis, the processes that control the ore-forming fluid conditions, and thus the gold timing and deposition, can be inferred from the study of both textural and chemical characteristics of ore-bearing minerals such as sulfides, which are ubiquitous in almost every gold deposit type. In this contribution, we carried out a coupled investigation of (1) microscopic-scale expression of regional deformation, (2) textures of mineralized veins and pyrite generations, and (3) laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) trace element concentrations in pyrite from the Neoproterozoic Central Zone gold deposit, located in the poorly studied Gabgaba gold district, central Keraf suture, Sudanese Nubian shield. The Central Zone gold mineralization is associated with late-collisional Keraf strike-slip shearing. It is expressed by visible gold-bearing quartz-ankerite-(albite) conjugate veins hosted by metagranitoids surrounded by metasediments. Some structurally lattice-bound gold occurs in proximal As-Au-Ni–enriched pyrite associated with sericite-albite-ankerite alteration. Vein textures and proximal pyrite oscillatory zoning and geochemical signatures indicate that vein infilling occurred as a response to sudden pressure drops and boiling of the mineralizing fluid. We therefore interpret the Central Zone deposit as a typical orogenic gold deposit, with microtextural evidence and geochemical data supporting the existence of earthquake-induced fault-valve processes.

Multiphase deformation, fluid flow and mineralization in epithermal systems: Inferences from structures, vein textures and breccias of the Kestanelik epithermal Au-Ag deposit, NW Turkey

We investigate the multiphase deformation, fluid flow, and mineralization processes in epithermal systems by presenting a detailed study of vein textures and breccias of the Kestanelik epithermal Au-Ag deposit, NW Turkey. The mineralization in the deposit is associated with several quartz veins. Fault-hosted veins and mode I veins share many textural and breccia characteristics owing to (i) overprinting of tectonic breccias formed during coseismic rupturing by subsequent coseismic hydrothermal brecciation and (ii) reworking of earlier vein breccia phases by repeated rupturing and hydraulic fracturing events. The spatial distribution of breccias at fault-hosted veins proposes that power of coseismic hydrothermal brecciation is controlled by the distance to the level of boiling within a vein. The brecciation affects the entire vein proximal to the level of boiling; however, it is limited to the footwall contact of the vein more distally at the upper levels of a vein. Varying number of mineralization events for the veins suggests that any individual earthquake event reopened only one or more sealed vein, but not all at once. Fewer mineralization events in fault-hosted veins compared to the mode I veins is either linked to (i) focusing of high fluid flux into the conduits of mode I veins that accommodate more dilation or (ii) reopening of mode I veins owing to the driven of extensional failure under low differential stress. Although fault-hosted veins record fewer mineralization events, they have higher average Au grade (4.106 g/t) compared to that of mode I veins (2.736 g/t). On the other hand, fewer mineralization events in wall rock structures compared to the adjacent faults is attributed to (i) absence or poor development of the damage zone structures in earlier seismic events or (ii) deactivation of them after clogging due to the rotation of the optimum stress field or (iii) their formation as hydraulic extension fractures. This study emphasizes the importance of detailed studies of vein infill for understanding the internal structural evolution of the veins in epithermal deposits that is interest to the geologists within both industry and academic fields.

Low sulfidation epithermal gold mineralization at Tambang Sawah, Lebong, Bengkulu Province, Indonesia

The Tambang Sawah area, Lebong, Bengkulu Province, is geologically located in the Barisan mountain range and the Sumatran fault zone and is composed of igneous rocks of the Sunda – Banda magmatic arc. This study is aimed to elucidate geological framework and characteristics of the low sulfidation epithermal gold at Tambang Sawah. Gold mineralization is hosted by the lithology of granite and andesitic breccia rocks, and controlled by faults, especially the Ketahun fault which forms a fracture and extensional zone. Hydrothermal fluid filled the structure found to form gold-bearing quartz veins. Hydrothermal alteration recognized at the study area is a typical type of alteration found in epithermal gold deposits, namely, argillic, silicified and propylitic. The characteristic sulfide minerals are low sulfidation epithermal gold deposits in the Sawah Mine area which are found, pyrite, chalcopyrite, covelite, sphalerite and galena with vein textures of colloform banded, cockade-crustiform, moss, and brecciated texture. Gold is interpreted to be coevally deposited with sulfides within quartz veins. Gold grade in rocks and veins varies from 0.07 ppm to 21.3 ppm.

GEOLOGY AND ORE CHARACTERISTICS OF LOW SULFIDATION EPITHERMAL GOLD MINERALIZATION AT TAMBANG SAWAH, LEBONG, BENGKULU PROVINCE

Abstract –– Tambang Sawah Area, Lebong Regency, Bengkulu Province, is geologically located in the Barisan mountains and Sumatra fault zone. The prospect of Tambang Sawah area lies in the physiography of the central Sumatran mountains ranges composed by the igneous rocks of the Sunda – Banda magmatic arc. This study is aimed to understand the deposit geology and ore characteristics of the gold deposit at the study area. Quartz vein mineralization of Tambang Sawah occurred in granite rock intruded into andesitic breccia rocks, with the geological structure of mineralization control in the form of joint, breccia, dike, and fault, namely the Ketahun fault that forms extentional fracture zones which were filled by hydrothermal fluid in form of quartz veins. Hydrothermal alterations that appear at the study site are typical types of alterations found in epithermal gold deposits, namely, argillic, silicified and propylitic. Sulfide minerals markers of low sulfidation epithermal type gold deposits found, namely, pyrite, calcopyrite, covelite, sphalerite and galena with colloform vein texture, cockade-crustiform, moss, and brecciated texture. Gold is interpreted to be derived from the deposition of sulfide minerals and the deposition of quartz veins, the level of gold in rocks and veins varies greatly with an average 4,8 ppm. Based on the results of ore geochemical analysis of positively correlated gold with elements Ag, Cu, Pb and Zn.
 Keywords: Mineralization, low sulfidation epithermal gold, Tambang Sawah, Lebong, Bengkulu.

A Novel System and Experimental Study for 3D Finger Multibiometrics

Fingers contain various discriminative biometric traits, such as fingerprint, finger vein, finger knuckle, finger shape, and so on, which are complementary in identity information. However, only one or a few traits are used in most current research and practical applications, while others are ignored, resulting in degraded recognition performance and vulnerability to forgery. In this paper, we make the first attempt to collect and study all biometric traits on the finger. Firstly, a novel multi-view, multi-spectral 3D finger imaging system is proposed. To the best of our knowledge, it is the first biometric imaging system capable of capturing almost all finger-based traits. We scanned numerous fingers with this 3D finger imaging system, obtaining external skin images and internal vein images from 6 different views. The proposed 3D finger reconstruction and texture mapping algorithms are then used to generate 3D finger models with skin and vein textures. Second, we establish a benchmark dataset, namely the Large-scale Finger Multi-Biometric database and benchmark for 3D Finger Biometrics (LFMB-3DFB). The LFMB-3DFB contains 695 fingers, and each finger is acquired 10 times, yielding 6 finger skin images and 6 finger vein images for a total of 83,400 images and 6,950 3D finger models. Finally, we design a more scientific and comprehensive evaluation protocol to conduct extensive experimental research and analysis on this database for both subject-independent verification and subject-independent close-set identification tasks. Comprehensive and rigorous experiments for 2D finger traits recognition, multi-view finger traits recognition, 3D finger traits recognition, and score-level fusion on LFMB-3DFB are carried out, and excellent results are achieved. The LFMB-3DFB database will be released at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/SCUT-BIP-Lab/LFMB-3DFB</uri> to promote 3D finger multi-biometric research using cutting-edge imaging techniques.

The Quartz Veins, Hydrothermal Alteration and Ore Mineralization of Orogenic Gold Deposit at Mendoke Mountains, Southeast Sulawesi, Indonesia

The research at Mendoke Mountains, Southeast Sulawesi Province, particularly for the study of gold deposits, becomes a new challenge because there is no previous detailed study. This study aims to analyze the characteristics of orogenic gold deposits, which include the type and texture of quartz veins, alteration and hydrothermal mineralization with hosted metamorphic rocks. The research methods used include fieldwork and laboratory analysis. The type and texture of quartz veins were identified based on the field observations. The hydrothermal alteration was analyzed using X-ray diffraction analysis, and hydrothermal mineralization which analyzed by ore microscopy. The results showed that there are three types of quartz veins parallel and crosscut to the direction of foliation, and laminated quartz veins. The quartz veins’ texture is deformed, segmented, brittle, sheared, laminated, sheeted, irregular veins, brecciated, massive and sigmoidal. The hydrothermal alteration consists of sericitization, argillic, propylitic and carbonization alterations. The hydrothermal mineralization consists of native gold, chalcopyrite, pyrite, stibnite, covellite, cinnabar, galena, arsenopyrite, chrysocolla, magnetite, hematite and goethite. The host rock of gold mineralization in the study area is classified into the greenschist facies. Based on these characteristics, it shows that gold deposits in the Mendoke Mountains are orogenic gold deposits.

Intermediate‐sulfidation epithermal mineralization at Monterado goldfield in Western Borneo (Indonesia): Geological, mineralogical, and fluid inclusion microthermometric perspectives

Gold mining in Western Borneo can be traced back over a century in the Dutch era. Many of these gold deposits are hosted in auriferous quartz veins, yet their geology and alteration/mineralization features have never been well documented. In this study, we present the first detailed account on gold mineralization in Western Borneo, using the Monterado goldfield as an example. Our results reveal that the auriferous quartz veining occurred in both intrusions (Mensibau granodiorite and Sintang Suite diorite porphyry) and volcanic‐sedimentary sequences (Raya Volcanics and Hamisan Formation), and wallrock alterations are well developed. Distributions of the veins are controlled largely by N‐S‐trending (tensional veins, e.g., Nek Rimban and Muisan) and NW‐SE (en‐échelon tensional gash veins, e.g., Mertua, Lipan, and Sekar) structures. Vein textures include mainly massive, breccia, comb, drusy, and stockwork. Advanced Mineral Identification and Characterization System mineral mapping on the ore veins and mineralized wallrocks show the presence of electrum, acanthite, pyrite, chalcopyrite, bornite, sphalerite, galena, and supergene products such as malachite, covellite, cuprite, chalcocite and rosasite. Polymetallic sulfide mineralization is spatially associated with adularia within auriferous quartz veins and silicic alteration. Ore chemistry on 285 vein ore samples yielded on average 1.46 g/t Au and 6.58 g/t Ag. Fluid inclusion microthermometry indicates that the homogenization temperature ranges from 273 to 362°C (avg. 338°C), with salinities of 1.1–8.7 wt% NaCl eq. (avg. 4.4 wt% NaCl eq.). Accordingly, the Monterado Au–Ag quartz vein‐type mineralization is best classified as intermediate‐sulfidation epithermal style.

Karakteristik Mineralisasi Endapan Emas Epitermal Sulfidasi Rendah di Daerah Mekarbakti, Kecamatan Bungbulang, Kabupaten Garut, Provinsi Jawa Barat

The southern mountains of western Java have been known to have large gold deposit potential. The Mekarbakti area, located in Garut regency, is known to have gold-bearing quartz veins, but the distribution and characteristics of these veins are not well recorded. The purpose of this study is to determine the geological conditions of the deposits and the characteristics of the epithermal deposits in the study area, in term of alteration, ore mineralization, vein texture, and ore geochemistry. Field work includes random sampling of veins from surface outcrops and cores. Laboratory analysis includes mineragraphic, geochemical analysis by means of Fire Assay Atomic Absorption Spectrophotometry (FA-AAS) and Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) . The lithology of the Mekarbakti area is composed of volcanic rocks including andesite lava, andesite intrusion and pyroclastic rocks such as breccia and tuff. The mapping results show that the hydrothermal alteration that developed is divided into three zones of alteration type, namely the silicification zone (silica + - clay), the argillic zone (kaolinite + - smectite - illite) and the propylitic zone (chlorite - smectite - epidote - illite). Quartz texture is generally dominated by brecciated, colloform, comb, lattice bladed and cockade textures. The texture interpretation of the veins shows a crystalline quartz zone, which is enriched in base metals such as galena, sphalerite and chalcopyrite and a crustiform – colloform zone which usually contains gold and silver. Veins in the study area contain the elevated grades of 3.21 ppm Au and 75.5 ppm Ag.

Fluid Evolution at the Batu Hijau Porphyry Cu-Au Deposit, Indonesia: Hypogene Sulfide Precipitation from a Single-Phase Aqueous Magmatic Fluid During Chlorite–White-Mica Alteration

Abstract Mineralization at the Cu-Au porphyry deposit of Batu Hijau, Indonesia, was previously reported to be associated mainly within stockwork quartz veins accompanied by pervasive biotite-magnetite alteration. We use cathodoluminescence imaging of vein textures followed by microthermometry and laser ablation-inductively coupled plasma-mass spectrometry microanalysis of fluid inclusions to decipher the spatial-temporal evolution of the hydrothermal system. Our results indicate that sulfide precipitation largely postdated the main stockwork quartz veining. Chalcopyrite and bornite were found in three textural positions: (1) within conspicuous quartzpoor veinlets (“paint veins”) that postdate quartz stockwork veins and that also appear to account for the bulk of seemingly disseminated sulfides, (2) as centerlines in B-type veins, and (3) as interstitial grains in A-type veins. In all three textural positions, the sulfides occur together with a volumetrically minor, dull-luminescent quartz generation after local dissolution of the granular quartz dominating the stockwork veins. All three positions are associated with chlorite ± variable phengitic white mica with 3–6 wt % FeO + MgO. In the barren core of the deposit, quartz veins host, almost exclusively, fluid inclusions of intermediate density (~0.6 g/cm3) and near-constant salinity of ~3.7 wt % NaCl equiv, representing the input magmatic fluid. This fluid subsequently separated into a highly saline brine1 and low-density vapor during quartz vein formation in the mineralized parts of the deposit, but we found no textural or fluid-chemical evidence that brine + vapor already reached saturation in sulfides. Within the studied samples, Cu-Fe sulfides are invariably associated with the dull-luminescent quartz hosting only low-salinity (~2–8 wt % NaCl equiv) aqueous fluid inclusions with a density of ~0.8 g/cm3 and minimum formation temperatures of 300°–360°C, in agreement with Ti-inquartz and chlorite thermometry indicating trapping conditions only slightly above the boiling pressure of these liquids. On average, this mineralizing aqueous fluid is compositionally similar to the initial magmatic fluid, suggesting a common source, but some inclusion assemblages deviate to significantly lower or higher salinities (0.5–25 wt % NaCl equiv). We propose a formation model for the Batu Hijau porphyry Cu-Au deposit in which mostly barren quartz veins formed at high temperature (&amp;gt;400°C) in the central part of the system, while sulfide mineralization commences to form peripheral to this zone. The economic ore shell was growing inward and downward as a zone of active sulfide precipitation at 300°–360°C shifted in response to progressive retraction of isotherms, while barren quartz vein formation continued in the system’s core at higher temperature. The aqueous ore-forming liquid is interpreted to have formed by rehomogenization of magmatic brine and vapor that previously formed by phase separation and later became miscible again after cooling over a narrow temperature interval. Vapor condensation into the highly saline brine phase at low pressure and subcritical temperature led to partial dissolution of earlier formed quartz veins and created secondary porosity for subsequent sulfide deposition. We propose that Cu-Fe sulfide precipitation by the low-temperature aqueous fluid was driven by the rehomogenization of S-rich vapor with Cu-rich brine originating from the same input fluid. The selective dissolution of earlier quartz veins in an inward- and downward-growing ore shell explains the positive correlation of ore grades with the density of earlier quartz veining in the ore shell, even though copper mineralization postdates quartz vein formation at any location in the deposit. Late-stage sulfide deposition in paint veins has been noted at other porphyry Cu-(Au-Mo) deposits worldwide, indicating that the proposed fluid evolution model may be applicable to many other porphyry systems.

VEINS SYSTEM AND THEIR MINERALOGICAL AND MICROTHERMOMETRIC CHARACTERISTICS WITHIN THE HUMPA LEU EAST PORPHYRY COPPER-GOLD MINERALIZATION AT HU'U DISTRICT, SUMBAWA ISLAND, INDONESIA

The study area, i.e Humpa Leu East is a porphyry prospect located in Hu'u district, Sumbawa Island, Indonesia. This study is aimed to understand the characteristics of veins, the distribution of veins and mineralogy, microthermometric conditions of ore fluids, distribution of elements, and their implications for exploration and deposit model. The Hu'u district is a paleo-volcano member of the Miocene to Plio-pleistocene volcanic rocks. Hydrothermal alteration evolved to get out from the tonalitic body, consists of potassic, propyllitic and overprinted by phyllic and advanced argillic. The mineralization is dominated by chalcopyrite, associated with quartz±anhydrite veins, and hydrothermal breccia. Hydrothermal fluids temperature measured at the value of 109.9 °C - 525.3 °C and &gt; 550 ° C with an averaging range of Th is 296.5 -329.7 °C, and salinity of 10.9 wt% NaCl eq. Quartz veins occur as a package or series of porphyry type veins designated as EDM-M1-A1, A2-A3-Apsb-anh, A3-A2, M2-Apsb-A2-A3, M1-B-C, C-D-anhydrite, and epithermal veins. Hydrothermal fluids possibly have mixed by high-temperature hyper-saline fluids to medium temperature low saline fluids. The Humpa Leu East can be identified as a 'push-up porphyry system' that still remains more extensive system underneath or in the side area. These results can be used for understanding the texture of veins as a vectoring to ore, metal distribution in veins and rocks. Early type veins such as type A have more intensive metal content and are followed by type B, C and weaken until the latest stage.

Fluid boiling during high-grade gold deposition in an epithermal gold-telluride deposit, Guilaizhuang, China

Boiling is a well-established mechanism for precious metal mineralization in low-sulfidation epithermal veins, and is considered a key process in the formation of high-grade bonanza zones in those systems. In contrast, the potential role of fluid boiling in the formation of epithermal gold-telluride veins associated with alkalic porphyries has rarely been discussed. The Guilaizhuang gold-telluride deposit, Shandong Province, China, is an ideal location to investigate the possible role of fluid boiling because the deposit comprises several distinct styles of orebodies, ranging from finely-disseminated gold mineralization hosted in carbonate rocks at depth, through to very high-grade mineralized breccia zones at shallower levels. Here, we examine the relationships between ore-forming fluids and mineralization styles in this deposit, based on paragenesis, vein textures and fluid inclusions. In the deeper carbonate-replacement style orebodies, we found no evidence of fluid boiling and, as such, alternative mechanisms such as fluid mixing or fluid-rock reactions were likely occurring. In contrast, the shallower, high-grade breccias show clear evidence of fluid boiling, which we infer contributed to the formation of exceptional bonanza zones. Our results thus indicate that fluid boiling can play a key role in precious metal mineralization in gold-telluride deposits, analogous to the low-sulfidation epithermal deposits. Furthermore, our results illuminate how contrasting mechanisms of gold mineralization in these deposits (i.e., boiling versus non-boiling) can give rise to the diversity and distribution of gold grades and reserves within an epithermal gold-telluride system.

Texture and morphology of veins and their relationship to gold mineralization in the Penjom deposit, Malaysia

AbstractPenjom deposit is an orogenic gold deposit located in the Central Belt of Peninsular Malaysia. Gold mineralization is associated with various styles and textures of quartz‐carbonate veins hosted within the metasedimentary as the main host rock and felsic igneous rock including minor volcanic rock. Vein textural features and morphologies have been investigated based on macroscopic and microscopic characteristics to understand the process of veins formation, and the relationship with gold mineralization. At the hand specimen scale, veins show a variety of textures that are either primary or superimposed. Primary textures are comb, massive anhedral buck quartz veins, and laminae veins or vein septa representing early vein introduction without vein modification. Extension veins that are normally concordant to maximum compressive stress direction show either a common comb texture within these veins or buck texture inside thick veins. Secondary textures are ribbon, stylolites, breccias, and late spider veinlets that overprint early veins formed during repeated structural episodes. Later stage deformation events superimposed on the existing veins texture results in intensely deformed veins. The interrelationship of structure, vein‐type and texture, gold and sulfide mineralogy have been correlated to constrain the episodes of gold mineralization in the Penjom deposit. Characteristics of vein textures indicate physio‐environment under confining lithostatic pressure where fluids filled the space through crack and sealing mechanism. Vein systems and gold mineralization events that have been correlated with the D2D3 (fold‐fault) deformation events and inferred to be temporally related to the late‐stage regional orogenic event dated Late Triassic‐Early Jurassic that affected Peninsular Malaysia.