Ore Microscopy Research Articles

Petrographic Study of Sedimentary Iron Ore in Shendi-Atbara Basin,River Nile State, Sudan

This paper presents the results of petrographic study of sedimentary iron ore from surface strata of the Shendi-Atbara Basin, River Nile State, Sudan. The aims of this study are to investigate the geological behavior and geological conditions affecting precipitation of sedimentary iron ore. The methodologies have been used to realize the objectives of this study include field work, office work and laboratory work including thin sections and polished sections analysis. According to field observation sedimentary iron ore can broadly be considered as occurring in three major classes:Ferribands iron, ferricrete iron and oolitic iron ores. The modes of occurrence of iron ore were described at the outcrops and vertical sedimentary profiles revealed that the iron occurred in the study area at different types in stratigraphic sequence such as cap, bedded and interbedded conformable with Shendi Formation. Petrographic study of iron ore in collected samples using polarized microscope and ore microscope includes study of the textures and structures of ores to obtain ore history. The main types of textures and structures in studied samples are oolitic, granular, lamellar and bands.According to these results the origin of iron ore is formed by chemical precipitation during chemical weathering of surrounding areas in continental lacustrine environment. The iron ore in study area is potential for future mining works and steel industry

Characteristic of gold mineralization associated with granites at Hamash old gold mine, South Eastern Desert, Egypt

Well-known controversy over the genesis of orogenic gold mineralization in granites has been a subject of research worldwide. Hamash gold mine is considered one of the pharaohs mines in the South Eastern Desert of Egypt, where gold mineralization is hosted by granites. In this study, we utilized field, ore microscopy, and geochemical data to determine the genesis of granites and the associated gold deposits. We found that the granites, intruded into island-arc metavolcanics and metavolcanoclastic assemblages, are characterized by variable major and trace elements, calc-alkaline, and I-type granitoids that reflect a fractional crystallization. Their trace and rare earth elements reflect magma that is related to subduction tectonic setting. The gold mineralization is confined to quartz veins that cut through granitic rocks, extend in NW-SE and N-S directions, and are formed during shear-extensional tectonics. The gold is found with sulfides in quartz veins and wallrock alteration. Silicification and sericitization are the most hydrothermal alteration zones associated the ore formation, comprise an inner quartz-sericite-carbonate-chlorite-sulfide assemblage. The results of chemical analysis reveal an increase of SiO2, Fe2O3, S, and L.O.I. concentrations and moderate depletion in K2O, Na2O, and LILE suggesting that they were affected by mineral replacement reactions and sulfidation in the altered wallrocks close to Au-quartz veins. The gold is represented by tiny inclusions, with minor chalcopyrite, galena, and arsenopyrite that mainly fill the microfracture in quartz and pyrite grains. Furthermore, a general model of gold mineralization suggests that the gold was contemporaneously formed during syn-orogenic stage, transpressional deformation assigned to D2 deformation, and subduction-related thermal processes followed by gold-bearing fluids that fill the fractures, forming veins.

Quantifying Mineral Liberation – A Conventional and New Automatic Sophisticated Techniques Approach

The characterization of textural properties of minerals is closely related to the process of their respective liberation. Measurements ofmineral liberation, related to grinded ore, can be performed using optical ore microscope, by conventional, classical methods – pointcounting, linear intercepts method or planimetric measurements method (2D). Modern automatic devices and sophisticated measurement techniques (QEMSCAN/MLA) imply recording free surfaces area of mineral grains on polished sections samples in orderto determine mineral degree of liberation. Value of mineral liberation obtained over free surfaces area can be of interest to flotationconcentration, although not for gravity separation or, for example, magnetic separation. The prediction accuracy for behavior of onefeed ore during the concentration process depends on the method of measuring/recording mineral liberation. Considering raw materials with complex textural characteristics it is crucial which method will be applied for determination of mineral liberation respectingwhether for concentration process is crucial physical or chemical method.

Determination of the copper-nickel ores formation sequence of the Kun-Manye deposit (Amur region)

The purpose of the article is to determine the sequence of mineral formation of copper-nickel ores of Kun-Manie deposit, which is located in Zeya district of Amur region. Three ore chutes take part in the structure of the deposit. Ore-bearing formations are sheet and sheetlike bodies of ultra-basic composition of the Kun-Manien complex, lying among rocks of crystal foundation of the Early Archean. Among the rocks, hornblende differences of gabbro-pyroxenites and pyroxenites predominate. In addition to nickel, the ores contain a wide range of associated components. The ores oxidation zone within the deposit and the entire ore field is not developed. The relevance of the work is due to the fact that detailed studies of ore minerals have not previously been carried out. The study presented in the work was conducted by polarizing ore microscope on polished ore samples characterizing different zones of the ore body. The result of the study was the establishment of mineral paragenesis and the sequence of mineral formation. It has been determined that the main ore minerals are pyrrhotine, pentlandite, also found - pyrite, chalcopyrite, less often - ilmenite, magnetite, sphalerite, platinum group elements. Ore mineralization formed in two stages. The magmatic stage is an early and main mineral formation phases including pyrite-magnetite, polymetallic and pentlandite associations. The hydrothermal stage is a late phase involving a pyrite association.

Comparative study on mineralogy and beneficiation potential of western Crete iron ores

ABSTRACT This study aims to investigate and compare the mineralogical characteristics of the western Crete iron ores in the Kakopetros and Arolithi areas. In addition, conventional beneficiation techniques, namely, magnetic and heavy liquid separation, were examined in order to potentially upgrade these ores. The ores were characterized through X-ray diffraction, X-ray fluorescence, Scanning electron microscopy and ore microscopy. Kakopetros iron ore consists mainly of compact goethite masses, while cryptomelane in the form of concentric shells was observed in several samples. Arolithi ore consists of several compact masses of goethite and fine-grained graphite and pyrite which are dispersed in the groundmass. Conventional beneficiation of specific fractions indicated that the heavy liquid treatment of the 0.063-0.250 mm size fraction of the Kakopetros ore resulting in a significant increase in upgrading. Overall, the results showed that fine-grained gangue minerals are locked in the iron-rich masses, making the separation techniques of ores ineffective.

Characteristics of chromitite mineralization in Sebuku Island based on thin section, polished section, and geochemical data

Sebuku Island is located in Kotabaru Regency, South Kalimantan and is known as one of the main sources of laterite iron in Indonesia. Based on its tectonic setting, Sebuku Island is located within the suture zone that connects Southwest Borneo Block (SWB) and East Java West Sulawesi Block (EJWB). Due to its tectonic setting, Sebuku Island is composed of various rocks associated with suture zone, such as ophiolite rocks. The ophiolite rocks could host mineralization that occurred in Sebuku Island. The aim of this study is to determine the characteristics of lithology and mineralization as determinants of geological processes that influence the formation of rocks and mineral deposits in Sebuku Island. This study was carried out through petrological, petrographic, ore microscopy analysis, and geochemical analysis (x-ray fluorescence). 22 rock samples from Sebuku Island were collected and the result of this research shows that the chromite host rocks are composed of serpentinized dunite and serpentinite. Chromite minerals (FeCr2O4) were found in massive forms with cataclastic, brecciated texture and disseminated with pull-apart texture. Based on observation of the polished sections, it is known that the associated mineral of chromite is magnetite which is an alteration of chromite minerals. Chromitite chemical data shows the chromite composition is Al-rich (Cr# = 0.6) and classified as podiform chromitite formed by fractional crystallization. There are two magma series of igneous rock in the study area i.e. tholeiitic series consists of ultramafic-mafic rocks and calc-alkaline consists of micro-diorite. The abundance of Al2O3 and TiO2 in chromitite shows that Al-rich chromitite has formed in Supra Subduction Zone (SSZ) and has occurred near or above the Moho-transition zone.

Episodic ferricretization of the Deccan Laterites (India): Inferences from ore microscopy, mineral magnetic and XRD spectroscopic studies

Studies based on sampling a ~40 m thick profile comprising the basalt protolith, saprolitic horizon and various levels of ferricretization in the Deccan upland lateritic sequence of the western Maharashtra (India), indicated episodic nature of lateritization. Mineral magnetism precisely demarcated the ferrimagnetic to anti-ferromagnetic (fm/afm) boundary at the base followed by various stages of lateritic developments in the upper horizons. The fm/afm boundary can be traced in field using magnetic susceptibility and therefore provide a datum for laterite base-level mapping. Ore microscopy details the inter-association and paragenesis of amorphous and crystalline varieties of iron oxide minerals (hematite, limonite, goethite) that are further modified by allochthonous inputs and changes in porosity. The lowermost horizons show silcretization, while the XRD studies record sporadic kaolinitic occurrence throughout the profile with gibbsite appearing in the upper part of the profile. Combination of mineral magnetic and ore microscopic observations depict frequent lateral inputs possibly during periods of heavy precipitation arresting and further reclaiming the process of lateritization to produce large composite thicknesses of the Deccan lateritic sequence without matured lateritization.

Halamishite, Ni5P4, a new terrestrial phosphide in the Ni–P system

Halamishite, Ni5P4, is a new natural phosphide discovered in pyrometamorphic assemblages of the Hatrurim Formation (Mottled Zone), Southern Levant. The mineral occurs as minute grains up to 20 μm in size intimately intergrown with zuktamrurite, FeP2, and transjordanite, (Ni,Fe)2P, which are disseminated in fine-grained diopside microbreccia. Chemical composition of the holotype material (electron microprobe, wt%): Ni 69.23, Fe 1.80, P 29.59, total 100.62, was recalculated to (Ni4.90Fe0.13)5.03P3.97 on the basis of nine atoms per formula unit. The ideal formula of halamishite is Ni5P4. In reflected light, the mineral is white with beige tint, non-pleochroic. It is moderately anisotropic and bireflectant (ΔR589 = 7.2%). Reflectance values for the four wavelengths recommended by the IMA Commission on Ore Microscopy are [Rmax/Rmin (%), λ (nm)]: 44.3/36.6, 470; 49.2/42.1, 546; 51.3/44.1, 589; 53.3/46.1, 650. Crystal structure of halamishite was solved and refined to R1 = 0.031 based on 425 unique observed [I ≥ 2σ(I)] reflections. The mineral is hexagonal, space group P63mc, a 6.8184(4), c 11.0288(8) A, V 444.04(6) A3, Z = 4. Dx calculated for an empirical formula is 6.249(1) g cm−3. Halamishite is named for its type locality, the Halamish wadi in the Hatrurim basin, Negev Desert, Israel. It is a naturally occurring analogue of synthetic Ni5P4, the compound widely used in electro- and photocatalytic applications. Due to chemical proximity to the Ni5P4 end-member, halamishite can be used as a geothermometer indicating that formation of phosphide assemblages had occurred at a temperature below 870 °C.

New Occurrence of Gold Mineralization at the Eastern Part of Wadi El Gemal, South Eastern Desert, Egypt

The basement rock units of the study area are represented by metasediments-metavolcanics association, diorite rocks, granodiorites and syenogranites. The whole sequence is cut by basic dykes, pegmatites and different quartz (jasper) veins. Metasediments-metavolcanics association is represented by hornblende schist and metadacite respectively. There is visible sulfides mineralization in hornblende schist, metadacite and diorite rocks at their contacts at the wadi level. So, polished sections were prepared to study opaque minerals under the ore microscope, which reveals the presence of gold, pyrite and goethite. The radioactivity of this area is weak, where the average eU contents in metasediments-metavolcanics association, diorites, granodiorites, syenogranites, pegmatites and jasper veins are 2.8 ppm, 1.9 ppm, 3.26 ppm, 4.91 ppm, 4.32 ppm and 6.7 ppm respectively. The intrusion of granodiorite rocks may act as a source for hydrothermal solutions ascending along fractures of all older rocks. During this stage, a chemical reaction of hydrothermal fluids with metasediments-metavolcanics association and diorite rocks lead to forming sericite and enrichment of silica content. The enrichment of silica content led to the formation of quartz-diorite. Also, iron derived from the host rocks and sulfur from the hydrothermal fluids could have formed pyrite while the gold was precipitated at the contact between metasediments-metavolcanics association and diorite rocks.

Automated ore microscopy based on multispectral measurements of specular reflectance. I – A comparative study of some supervised classification techniques

Automated mineralogy, including quantitative compositional and textural information, is a requirement for an efficient ore processing, and is comprised as an important input for geometallurgical planning. Classical ore microscopy is seen by many potential users as an outdated, time consuming, tool. Thus, SEM-based systems are often the choice for those who can afford them, in spite of their evident limitations for some minerals (e.g. for iron oxide ores). However, automated and quantitative mineral characterisation of metallic ores is also possible with optical (reflected light) microscopes, attaining similar performance at a much lower price than SEM systems, as shown by the AMCO (Automated Microscopic Characterisation of Ores) prototype. This system relies on the measurement of multispectral specular reflectance, R, on polished ore sections, to achieve automated identification of the ore species (reflectance is computed from grey levels of digital images acquired by automated scanning of the sample). The performance of this approach, supported by a multispectral reflectance database covering the VNIR range (370–1000 nm) built with the AMCO System, is analysed in this paper, comparing the reliability of different classification methods to achieve ore identification.The work outlined in this article focuses on checking the actual behaviour of four classification techniques, based respectively on spectral angle mapper, euclidean distance, Mahalanobis distance and linear discriminant analysis. The tests carried out reveal that the last two techniques are powerful tools to determine to which mineral corresponds a pixel based on its reflectance spectrum.The obtained results prove that automated multispectral optical microscopy is a reliable tool for mineral characterisation of common/industrial ores, with few exceptions (distinction of cassiterite and chromite, or sphalerite and wolframite). For optimisation of its performance, the multispectral information may be complemented with some additional criteria, such as paragenesis or type of deposit (e.g. to differentiate cassiterite from chromite). The reflectance database can also be enriched with measures of local ores, to account for existing reflectance variations due to local conditions or to learn new ores. The performance is particularly good for iron oxide ores (hematite, magnetite, goethite), a very important commodity. In the tests carried out, they are successfully identified in more than 99% of the cases.

Hydrothermal Alteration Associated with Vein-Type Sulphide Mineralization at Lappadata Prospect, South Sulawesi, Indonesia: A Preliminary Study

In Lappadata area, Bone Regency, South Sulawesi Province, Indonesia, indication of vein-type sulphide mineralization is occurred. This paper describes a recent study of the prospect which focused on hydrothermal alteration associated with the mineralization. In this study, alteration and mineralization samples have been collected selectively and representatively from the field and then analyzed in laboratory using petrography, ore microscopy, and X-ray diffraction methods. The study resulted that host rocks of the mineralization are porphyritic basalt and limestone members of the Early Eocene to Late Oligocene Salo Kalupang Formation. Hydrothermal alteration mineral assemblages include quartz, chlorite, muscovite, sericite, calcite, actinolite, epidote, illite, kaolinite, and pyrite, which generally zoned from distal-propylitic mainly characterized by chlorite, calcite and epidote to proximal-argillic characterized by sericite and illite. The mineralization occurred in quartz vein and disseminated with identified hypogene ores of sphalerite, chalcopyrite, galena, and pyrite as well as supergene ores of covellite, chalcocite, and malachite. Study of the hydrothermal alteration stability temperatures suggested that the mineralization was formed in temperature range of about 200 to 300°C, from a near-neutral pH hydrothermal fluid. The whole characteristics of hydrothermal alteration, ore and gangue minerals, mineralization types, as well as range of formation temperature and composition of the responsible hydrothermal fluid indicated that the mineralization in Lappadata prospect is an epithermal type.

Alteration and Ore Mineralogy Of Metamorphic Rocks Hosted Hydrothermal Gold Deposit At Rumbia Mountains, Bombana Regency, Southeast Sulawesi, Indonesia

In Indonesia, gold is commonly mined from porphyry, epithermal and skarn type deposits that are commonly found in volcanic/magmatic belts. However, were recently numerous gold prospects discovered in association with metamorphic rocks. This paper is intended to describe an alteration and ore mineralogy hosted by metamorphic rocks at Rumbia mountains, Bombana regency, Southeast Sulawesi province, Indonesia. The study area is found the placer and primary gold hosted by metamorphic rocks. The placer gold is evidently derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC). This study is conducted in three stages, three stages including desk study, field work and laboratory analysis. Desk study mainly covers literature reviews. Field work includes mapping of surface geology, alteration and ore mineralization as well as sampling of representative rocks types, altered rocks and gold-bearing veins. Laboratory analysis includes the petrologic observation of handspecimen samples, petro graphic analysis of the thin section and ore microscopy for polished section and XRD (X-ray diffraction) analysis. From petrographic observation, the type of alteration found in the study area can be divided into six types including sericitization, argillic, inner propylitic, propylitic, carbonization and carbonatization alterations. These quartz veins are currently recognized in metamorphic rocks at Rumbia mountains. Mineralogically, gold is closely related to chalcopyrite, pyrite, hematite, cinnabar, stibnite and possibly minor goethite. Based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposits type. The orogenic gold deposit is one of the new targets for exploration in Indonesia.

The effect of degree of liberation on copper recovery from copper-pyrite ore by flotation

ABSTRACT Flotation of grinding products with 55, 60, 65, 70, and 75% of grain size <74 μm, was conducted at the pulp’s pH values of 10 and 12. Higher copper recovery was obtained in concentrates at pH 10, but with lower copper grades, approximately 2%. Copper recovery in concentrates at pH 12 was slightly less, but copper grades were much higher. The effect of grinding was higher at pH 12, especially in terms of copper grades in concentrates, which declined with the increase of grinding time. Ore microscopy tests were done on the concentrates with 55 and 75% of grain size <74 μm at pH 10 and 12. All particles of copper minerals were divided by grain size fractions and by the degree of liberation. Analysis have shown that degree of liberation was higher in finer grinding products.

LA-ICP-MS trace element analysis of arsenopyrite from the Samgwang gold deposit, South Korea, and its genetic implications

The Samgwang deposit, previously classified as an orogenic gold deposit, consists of several structurally controlled auriferous quartz veins hosted by metasedimentary rocks of the Precambrian Gyeonggi massif, South Korea. The gold at Samgwang occurs as electrum commonly associated with arsenopyrite. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), coupled with ore microscopy, was conducted on Au and trace elements distributed in arsenopyrite grains contained in quartz vein and wall rock samples. Resulting profiles for Au, Co, Ni, and Sb were relatively flat and showed little variability, indicating that the elements were relatively homogeneously distributed and exchanged via substitution in arsenopyrite, while variability and noisy depth profiles inferred that Pb was present as tiny inclusions or discrete particles. Furthermore, measured gold concentrations were typically higher in arsenopyrite grains from laminated quartz veins (avg. 2.07 ppm) than in grains from massive quartz veins (avg. 0.26 ppm) and wall rock samples (avg. 0.33 ppm). In the case of wall rock and massive quartz vein samples, arsenopyrite grains of euhedral shape illustrate an element distribution pattern whereby Au concentrations tend to decrease towards the rims of the analyzed grains. In contrast, the rims of arsenopyrite grains in laminated quartz vein samples recorded much higher Au concentrations of up to 20.1 ppm, with increasing Pb, Bi, and Ag, particularly within domains of fractured or recrystallized arsenopyrite grains. The newly acquired LA-ICP-MS data, along with textural evidence, may be interpreted in terms of the release and remobilization of invisible gold that was originally locked up in the arsenopyrite. This release is linked to late deformation and hydrothermal event during which the remobilized invisible gold was redeposited as electrum. In addition, there is evidence for the introduction of additional gold and other precious and base metals by the late-stage hydrothermal fluids. Based on the above and in contrast to previous genetic models, we propose a more complex metallogenic concept for Samgwang in which the economically important gold enrichment process was genetically related to intrusive activity during the waning stages of Jurassic to Early Cretaceous Daebo orogenesis.

The gold occurrence in pyrite and Te–Bi mineralogy of the Fancha gold deposit, Xiaoqinling gold field, southern margin of the North China Craton: Implication for ore genesis

The Fancha lode gold deposit is hosted in the Neoarchean Taihua Group metamorphic rocks in the Xiaoqinling gold field, on the southern margin of the North China Craton. Pyrite, as the predominant sulphide mineral and Au‐hosting mineral, was investigated using a combination of ore microscopy and in‐situ laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). Three types of pyrite were identified during the ore‐forming process, that is, the coarse euhedral grains in milky quartz veins (Py1), the fine to medium, euhedral to subhedral grains in light grey quartz (Py2), and the fine grains intergrown with abundant sulphide minerals in light grey quartz (Py3). The trace elements exhibit systematic different concentrations among three types of pyrite, implying different crystallization processes. The Py1 grains have the lowest concentrations of Au and other accompanying elements such as Ag, Te, Bi, Cu, Pb, and Zn, and the trace elements of pyrite in wall rock are similar to those of Py1. The Py2 and Py3 grains show consistently high contents of Au, Ag, Te, Bi, Cu, Pb, and Zn. The uneven distribution of gold and positive correlation between Au, Ag, Te, and Bi within Py2 and Py3 grains, indicating that gold mainly occurs as submicroscopic inclusions of Au–Ag–Te–Bi assemblages in the pyrite. This interpretation is supported by the microscopic observation that large quantities of telluride and Bi‐sulfosalt minerals contact directly with gold. Observed Te–Bi minerals include petzite, sylvanite, hessite, calaverite, rucklidgeite, altaite, volynskite, tellurobismuthite, buckhornite, tetradymite, krupkaite, and bismuthinite, and native bismuth is also found. Bi (Te) melts, as an excellent gold scavenger, have played a certain role in governing gold distribution patterns and leading to high concentrations during the mineralization process in the Fancha gold deposit. The Te–Bi mineral assemblages also reveal that the gold was precipitated under variable redox conditions with logfTe2ranged from &lt;−11.0 to −6.4, and logfS2ranged from &lt;−11.8 to −8.6 at 300°C, vertically upward from the deep fluid source. Combined with available geochronological and geochemical data, enrichment of Te and Bi indicates that the ore‐forming fluids and metals might be stemed from a mantle‐derived magmatic system.

The physical-chemical regime of a sulfide-bearing semi-graphite mineral assemblage in metabasic rocks (SE Germany) – A multidisciplinary study of the missing link between impsonite and graphite

Along the western edge of the Bohemian Massif, SE Germany, graphitic carbon occurs in metabasic rocks plus calcsilicates, metabiolites, and paragneisses (graphite I), in pegmatites (graphite II) and in mineralized structure zones (semigraphite and impsonite) The current studies unveiled these graphitic carbon compounds are strikingly different with regard to their age and temperature of formation: Graphite I (≥324 Ma, 570 to 625 °C), graphite II (317 ± 3 Ma, >400 °C), semi-graphite (305 ± Ma, 225 to 400 °C), impsonite (<298 ± 4 Ma, 100 to 363 °C). Semi-graphite takes a special position among these graphitic carbon compounds because it links the different carbon modifications with regard to its age of formation, its structural position and its S- and C isotopes that point to a mantle and crustal influence on its formation in contrast to graphite (graphite I: crustal, graphite II: mantle) and impsonite (mantle). Semi-graphite precipitated in a fault zone which evolved from a zone of strong felsic mobilization in metabasic rocks spawning KNa feldspar-quartz pegmatoids/aploids. During conversion of a pre-existing zone of felsic mobilization into a brittle shearzone not only carbonaceous matter but also Ni-, Pb-, Cu-, Zn-, As-, Fe-, Hg- and Mo sulfides were concentrated. The semi-graphite-bearing mineralized zone is located near rare element pegmatites hosting graphite flakes. The C-bearing systems are useful pathfinders to locate structurebound mineral deposits hosting U or base metals in the Variscan orogen.The structurebound metalliferous semi-graphite mineralization in metabasic rocks can be taken as a reference type of dual-source hydrocarbon immigration into fault zones, syn- to postkinematically relative to the fault movement. The model can be applied to host rocks undergoing retrograde medium- to very-low-grade stage dynamo-metamorphic conditions.To elucidate the complex history of the various types of graphite and metamorphosed bitumen a multidisciplinary approach has been taken involving petrographic and geological field mapping combined with drill core examination, petrographic and ore microscopy supplemented by electron microprobe, X-ray diffraction and scanning electron microscopy with EDX, micro-Raman spectroscopy in addition to classical coal petrographic studies, and inorganic geochemistry of major and minor elements and isotope (carbon and sulfur) chemical analysis followed up by a statistical treatment of the various chemical datasets.

Geochemistry and origin of Mn deposits in the Bela ophiolite complex, Balochistan, Pakistan

We have studied geochemical characteristics, mineralogy and origin of the manganese deposits in Bela ophiolitic complex. Geochemical investigation was conducted in order to discuss the elemental correlations and to infer the probable origin of manganese deposits in Bela ophiolites. Ore microscopy was conducted to identify different manganese minerals and their paragenesis. Psilomelane and braunite were found to be the major ore minerals. Mineral paragenesis sequence as observed was braunite forming first. Psilomelane formed in later stages because it has been found that psilomelane is altering the braunite. Magnetite was observed as a secondary mineral as vein filling and cutting through both the braunite and psilomelane, therefore, younger than the psilomelane and braunite. The gangue minerals observed in the studied samples were quartz, cryptocrystalline silica and calcite. The correlations among different major and trace elements showed diversity of relations. MnO showed negative correlation with Fe2O3 (− 0.73), Si2O (− 0.27), positive correlation with Al2O3 (0.54), TiO2 (0.36), MgO (0.22), Pb (0.23), Ni (0.07), Cr (0.12), and no correlation was established with Zn, Cu, Co. Binary diagram of Si versus Al and ternary discrimination diagrams of Fe–(Ni + Co + Cu) × 10–Mn and Ni–Zn–Co showed hydrothermal-diagenetic-type deposits. Furthermore, the present study suggests that the enriched manganiferous fluid during its upward movement within the Tethys oceanic crust near spreading center started precipitating Mn along with Fe on the sea floor. Later on, these manganese minerals were obducted on land between Indian plate and Helmond block of Eurasian plate in existing position accompanying pillow basalt and pelagic sediments.

Alteration Alteration, Mineralization and Geochemistry of Metamorphic Rocks Hosted Hydrothermal Gold Deposit at Rumbia Mountains, Bombana Regency, Southeast Sulawesi, Indonesia

In Indonesia, gold is commonly mined from porphyry, epithermal and skarn type deposits that are commonly found in volcanic/magmatic belts. However, were recently numerous gold prospects discovered in association with metamorphic rocks. This paper is intended to describe an alteration and ore mineralogy hosted by metamorphic rocks at Rumbia mountains, Bombana regency, Southeast Sulawesi province, Indonesia. The study area is found the placer and primary gold hosted by metamorphic rocks. The placer gold is evidently derived from gold-bearing quartz veins hosted by Pompangeo Metamorphic Complex (PMC). This study is conducted in three stages, three stages including desk study, field work and laboratory analysis. Desk study mainly covers literature reviews. Field work includes mapping of surface geology, alteration and ore mineralization as well as sampling of representative rocks types, altered rocks and gold-bearing veins. Laboratory analysis includes the petrologic observation of handspecimen samples, petrographic analysis of the thin section and ore microscopy for polished section, XRD (X-ray diffraction), ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy), ICP-MS (Inductively Coupled Plasma Emission Mass Spectrometry and FA/AAS (Fire Assay/Atomic Absorbtion Spectophotometry) analysis. The results shows that the alteration characteristics of hydrothermal gold deposits in Mendoke and Rumbia mountain consist of 3 (three) alterations namely sericitic, argillic dan propylitic. Characteristics of mineralization hydrothermal gold deposits in the research area are generally p related to gold-bearing quartz veins/veinlets consist of chalcopyrite, pyrite, chrysocolla, covellite, cinnabar, magnetite, hematite and goetite in rocks categorized into greenschist facies. There are three generations of veins identified including the first is parallel to the foliations, the second crosscut the first generation of veins/foliations, and the third is of laminated deformed quartz+calcite veins at the late stage. The quartz veins commonly deformed, segmented, massive, laminated, irregular, brecciated, and occasionally sigmoidal. The veins contain erratic gold in various grades from below detection limit &lt;0.0002 ppm to 18,4000 at found in third generation veins which are laminated quartz±calcite in argillic alteration. ppm. The protoliths of metamorphic rocks in Rumbia Mountain, which comes from sedimentary rocks, spesifically pelitic rocks and graywacke. Based on those characteristics, it obviously indicates that the primary gold deposit present in the study area is of orogenic gold deposits type. The orogenic gold deposit is one of the new targets for exploration in Indonesia.

Petrography and ore mineral study at Beruang Kanan Site, Gunung Mas Regency, Central of Kalimantan Province

The methodology mainly includes four parts: pre-field studies, field investigations, laboratory analysis, and data analysis and interpretation. Laboratory analysis to be carried out is petrographic analysis and ore microscope. Research methods relating to petrography analysis studies and ore mineral that will be evaluated for genetic models and the origin of copper deposition mineralization. The rock units in the study area are differentiated based on the type of lithology, uniformity of rocks, the distribution of rocks and rock geometry found in one region and the stratigraphic position of the units below it or above it. In general, the stratigraphy of the research area is divided into 3 rock units that can be seen on the geological map, sequences from old to young, namely lithology of Sandstone Unit, Dense Tuf Unit, and Andesite Unit. ore mineralization generally occurs as a massive form, vein. Pyrite, enargite, luzonite, sphalerite, covellite, chalcopyrite, tennatite and tetrahedtrite are common sulfides and sulfosal minerals

LA-ICP-MS Trace-Element Analysis of Pyrite from the Huanxiangwa Gold Deposit, Xiong’ershan District, China: Implications for Ore Genesis

The Huanxiangwa deposit is a major gold deposit in the Xiong’ershan district, which is the third-largest gold-producing district in China. Pyrites from the Huanxiangwa deposit were investigated using ore microscopy and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Pyrite is the dominant Au-bearing mineral in the Huanxiangwa deposit and can be divided into two types: medium- to fine-grained subhedral-anhedral pyrite (Py1) disseminated in altered rocks and coarse-grained subhedral-euhedral pyrite (Py2) hosted in auriferous quartz veins. LA-ICP-MS time-resolved depth profiles show that invisible gold occurs primarily as solid solution or as homogeneously distributed nanoparticles of native gold, electrum, or Au-Ag-Te minerals in Py1, whereas it is present mainly as nano- to submicron-sized inclusions of complex Au-Ag-Cu-Pb-Zn domains in Py2. The presented data indicate that the Huanxiangwa deposit resulted from two episodes of hydrothermal mineralization associated with two distinct source reservoirs. The first episode of mineralization was linked to the dehydration of deep-seated mafic-ultramafic metamorphic rock during the Triassic collision of the North China Craton with the Yangtze Craton. The second episode of mineralization was related to hydrothermal activity resulting from Early Cretaceous I-type granitic magmatism.