Mineral Zones Research Articles

Features of structural tectonics and geochemistry of Tomulakh metamorphism zone

The methods of geological and geochemical modeling for prospecting of mineralization in areas associated with the deposits of the Talnakh ore-forming system are considered. The geological and geochemical model is based on the geological and structural analysis of the spatial relationships of geochemical anomalies, which allows us to quantify the geochemical types of halos caused by both the multi-stage formation of deposits and the presence of different types of mineralization, which contributes to solving the forecasting problems. The subject of the study is the anomalous Tomulakh metamorphism zone (TMZ), the tectonic conditions of its formation, the material composition of metamorphic and metasomatic formations and facies, and their geochemical expression. The TMZ, located in the north of the ore-bearing Kharaelakh intrusive of the Talnakh ore-magmatic system, is traced along the Axial-Dyangin fault. The high density of faulting and the composition of the tectonic breccias in the upper exocontact zone ensure propagation of metamorphosing fluids over a considerable distance in the vertical and lateral directions. Within the TMZ, which is the flank part of the fluid-magmatic system, fluids evolve in space and time from alkaline to acidic. Alkaline and acidic near-fracture metasomatites developing along tectonic breccias are marked by the geochemical associations Y-Mo-Zr and Be-Mo-Zr. Ore mineralization in the form of rare scattered inclusions of pyrite, chalcopyrite, pyrrhotite, and sphalerite is mapped by the Zn-Cu-Ni-Co specialization. The development of ore mineralization in the contact-metamorphosed rocks of the upper Devonian TMZ is considered as a continuation of the contact halo of the Ni-Cu-Co specialization of the Kharaelakh intrusive. Calciteanhydrite metasomatites (americophile) and anhydrite marble in the top exocontact TMZ occur in the zone of dispersed mineralization and Sr anomalies traceable along the Axial-Dyingin fault and being the extension of the contact envelope of the Kharaelakh intrusion. It is assumed that the TMZ is formed under the influence of the fluid-magmatic Talnakh ore-forming system.

REE-Th mineralization in the Se-Chahun magnetite-apatite ore deposit, central Iran: Interplay of magmatic and metasomatic processes

The Se-Chahun Fe-P ore deposit is located in the Bafq mining district in the Central Iranian tectono-magmatic zone and contains REE and Th mineralization. The ore deposit consists of a magnetite-apatite massive ore that is significantly modified by late-stage metasomatic fluids that finally formed brecciated rocks within and at the margin of the ore deposit. Geochemical data from the rhyolitic rocks, Fe-P ore body and breccia as well as isotopic data from the breccia within the Se-Chahun Fe-P ore bodies, have been used to deduce the magmatic origin of the Fe-P ore zone and to assess the significance of post-magmatic processes with late-stage metasomatic fluids and the effects of these processes on remobilization of magmatic originated REE and concentration and deposition of Th. The chondrite-normalized REE patterns of the mineralized rocks in both the Fe-P ore and the Th mineralization zone demonstrate LREE enrichment and strongly negative Eu anomalies (Eu/Eu* = 0.25–0.91 for Th mineralization). δD and δ18O for actinolite paragenetic to Th-bearing silicates are estimated to be between −73.29 to −42.04 and 6.65 to 7.71, respectively, which lie within the both fields of magmatic and metamorphic fluids. Na-Ca metasomatism (which is evidenced by brecciation) has been a continuous process affecting the host rock, and the Fe-P ore body. Apatite, monazite, and Ti-La-Ce-Y-Nd-oxides are the main REE-bearing phases in the Fe-P ore body (REE≫Th) that are precipitated during magnetite crystallization whereas Th silicates (huttonite and thorite) occur within the breccia (Th ≫ REE) and were deposited from a late Th- and carbonate-rich fluid. Th mineralization occurred with late sodic-calcic fluids and Th-bearing minerals are paragenetic to actinolite, red albite, magnetite, titanite, calcite, and pyrite. Paragenetic association of Th minerals and actinolite, titanite, and calcite in carbonate veins and veinlets point to transportation of Th by carbonate complexes. The pH, fluid/rock ratio, Ca/Na ratio, and higher capability of Th (with respect to REE) in formation of carbonate complexes and lower concentration of Th (with respect to REE) in the source region are the most important geochemical parameters that triggered Th (Th ≫ REE) mineralization at the end of alkali metasomatism.

Vectors to ore in replacive volcanogenic massive sulfide (VMS) deposits of the northern Iberian Pyrite Belt: mineral zoning, whole rock geochemistry, and application of portable X-ray fluorescence

Abstract. In this work we have performed a detailed study of vectors to ore to a representative volcanic-rock-hosted replacive volcanogenic massive sulfide (VMS) deposit located in the northern Iberian Pyrite Belt (Spain), the Aguas Teñidas deposit. The investigated vectors include the following: (1) mineralogical zoning, (2) host sequence characterization and mineralized unit identification based on whole rock geochemistry discrimination diagrams, (3) study of the characteristics and behaviour of whole rock geochemical anomalies around the ore (e.g. alteration-related compositional changes, characteristics and extent of geochemical halos of indicative elements such as Cu, Zn, Pb, Sb, Tl, and Ba around the deposit), and (4) application of portable X-ray fluorescence (p-XRF) analysis to the detection of the previous vectors. In the footwall, a concentric cone-shaped hydrothermal alteration zone bearing the stockwork passes laterally, from core to edge, from quartz (only local) to chlorite–quartz, sericite–chlorite–quartz, and sericite–quartz alteration zones. The hydrothermal alteration is also found in the hanging wall despite being tectonically allochthonous to the orebody: a proximal sericite alteration zone is followed by a more distal albite-rich one. Whole rock major elements show an increase in alteration indexes (e.g. AI, CCPI) towards the mineralization, a general SiO2 enrichment, and FeO enrichment as well as K2O and Na2O depletion towards the centre of the hydrothermal system, with MgO showing a less systematic behaviour. K2O and Na2O leached from the centre of the system are transported and deposited in more external areas. Copper, Pb, and Zn produce proximal anomalies around mineralized areas, with the more mobile Sb, Tl, and Ba generating wider halos. Whereas Sb and Tl halos form around all mineralized areas, Ba anomalies are restricted to areas around the massive sulfide body. Our results show that proposed vectors, or adaptations designed to overcome p-XRF limitations, can be confidently used by analysing unprepared hand specimens, including the external rough curved surface of drill cores. The data presented in this work are not only applicable to VMS exploration in the Iberian Pyrite Belt, but on a broader scale they will also contribute to improving our general understanding of vectors to ore in replacive-type VMS deposits.

Hydrothermal troctolite alteration at 300 and 400 °C: Insights from flexible Au-reaction cell batch experimental investigations

Abstract Troctolites are increasingly recognized as a common rock found in association with oceanic core complexes. They are similar to komatiite in composition, and hence troctolite alteration may provide insight into H2 production on Early Earth. We investigated the hydrothermal alteration of olivine-rich troctolites in two batch experiments (300 °C, and 400 °C – 40 MPa) by reacting forsteritic olivine and anorthite-rich plagioclase with salt solutions. The alteration process was evaluated based on concomitant fluid samples and solids retrieved upon the termination of the experiments. In both experiments, the initial rock powder was turned into a hard, compact mass through cementation by secondary phases. The heterogeneity of this mass was documented using µ-computed tomography and electron microscopy. Thermodynamic computations were conducted to determine the equilibrium phase assemblages and fluid compositions with increasing reaction turnover. Mineral zonation developed between the fast-reacting, fluid-dominated top portion of the solids and the more isolated portions at the bottom of the reaction cell. At 300 °C, the total reaction turnover after 1800 h was 77.5%. Serpentinization of olivine controlled the fluid composition after plagioclase had reacted away in the top layers. In contrast, a Ca- and Al-enriched assemblage of xonotlite and chlorite developed alongside unreacted plagioclase at the bottom. The porosity is very low in the top layers but high (around 15%) in the bottom part of the cemented mass. At 400 °C, the reaction turnover was only 51% as olivine was stable after plagioclase had reacted away. Clinopyroxene and andradite ± chlorite had formed in the top layers, whereas xonotlite, grossular, and chlorite had formed at the bottom. The permeability is more uniform and the mineral zonation less pronounced at 400 °C. These mineral zonations developed as a consequence of increased mobility of Ca, Al, Mg, and to a lesser extent of Fe in the experiment, which may be facilitated in the highly permeable granular materials when compared to a compact rock. Steady-state hydrogen concentrations were at least 20 mmol L−1 at 300 °C and <1 mmol L−1 at 400 °C. A lack of magnetite formation at the higher temperature is responsible for the low-H2 yields.

Metamorphic Evolution of Calc-silicate Rocks at Akarui Point, Lützow-Holm Complex, East Antarctica

We report on the petrology and metamorphic history of boudined bodies of zoned calc-silicate rock, up to 1 m in width, which are enclosed in gneisses, transitional between upper amphibolite to granulite facies, at Akarui Point, Lützow-Holm Complex, East Antarctica. Zircons extracted from a closely related body of Mn-exhalative derived calc-silicates indicate that the metamorphism occurred in two separate events, at 546.6 ± 0.6 and 524.3 ± 0.6 Ma, during the Pan African Orogeny. Based on the meionite content of scapolite from different mineral zones in the calc-silicates, we derive a metamorphic history that involved a peak temperature of a minimum 810 – 820 °C, followed by a fall to 760-800 °C and then to 690-765 °C during uplift and decompression to 5.5 – 7 kbar. GAP geothermo-barometry indicates that the enclosing gneiss partially re-equilibrated during retrogression at 500-580 °C.

Re‐Os Isotopic Age of Molybdenite of the Jingren Deposit and its Mineralogical Significance of Magnetite, Pyrite and Chalcopyrite

AbstractThe Jingren deposit is part of the Qimantage metallogenic belt within the eastern Kunlun orogenic belt, the largest metallogenic belt in Qinghai Province, northwestern China. Exploration data show that the metal resources of the Jingren deposit are greater than 93000 t in a mining area of 76.15 km2, which indicates significant exploration potential in the near future. Three W–E‐trending faults, F1‐3, dominate the extension of the mineralization zone, which consists of chalcopyrite, pyrite, magnetite, galena, sphalerite, and molybdenite as well as bismuth‐bearing minerals. The deposit contains a large amount of late Triassic intrusive rocks, however, previous research did not reach a consensus on the timing or the origin of the mineralization owing to a lack of geochronological data and poor exposure conditions. In the present study, Re‐Os isotopic dating from six molybdenite samples collected from a borehole of the granodiorite in the Jingren deposit using negative thermal ionization mass spectrometry (NTIMS) showed 187Re and 187Os concentrations of 0.26–4.40 ppm and 1.03–16.46 ppb, respectively, with an initial 187Os/188Os value of 0.06 ± 0.19. This proves that the Jingren deposit has a metallogenic age of (225 ± 4) Ma and is the product of united mineralization of the Qimantage metallogenic belt and that the Jingren deposit might actually be an Indosinian metallogeny. In addition, the Re content of these samples, at 0.42 ppm to 7.00 ppm shows that the mineralization was derived mainly from a crustal source. Furthermore, electron probe microanalysis (EPMA) conducted on chalcopyrite obtained from 22 metallic mineral samples revealed (Fe + Cu)/S ratios of 1.801–1.947 with an average of 1.852, which is lower than the ideal value (1.875). Besides, the main ore body formed in a relatively higher temperature environment than the surrounding rocks in the Jingren deposit. These data indicate that the Jingren deposit formed in a metallogenic environment at lower temperature. Moreover, according to the TiO2‐Al2O3‐(MgO + MnO) and TiO2‐Al2O3‐MgO genetic classification diagram for magnetite, the Jingren deposit most likely belongs to the skarn family. In addition, the Co‐Ni‐As genetic classification diagram of the pyrite indicates sedimentary and skarn genetic characteristics.

Delineation of the porphyry-skarn mineralized zones (NW Turkey) using concentration–volume fractal model

This study is carried out for delineation of the Tepeoba porphyry-skarn Cu-Mo ± Au mineralized zones at the Biga peninsula (NW Turkey) using the concentration–volume (C–V) fractal model. The power-law C–V relationships of Cu, Mo, and Au reveal five mineralized zones of Cu, three zones of Mo, and five zones for gold in the Tepeoba deposit. The main phase of the mineralization has average ore grades of 0.257% Cu, 0.357% Mo and 5.3083 ppm Au. Cu–Mo sulfide-rich hypogene ore zone overlain by mineralized oxidation zone are encompassed by three main alteration types, which are represented by biotite ± muscovite-K-feldspar, actinolite-albite and outer chlorite-epidote-calcite mineral associations occurring within the porphyritic microgranite and hornfels in the mine area. The delineated mineralization trend, based on the C–V fractal model, suggested that Cu and Mo enrichment zones were controlled by the same geochemical processes in the deposit due to their similar trends with the C–V log-log plot. Cu and Mo occurred mainly within the breccia zones along with stockwork veining at the contact between the hornfels and the biotite (±muscovite)-K-feldspar-altered Eybek microgranite. The main mineralization zone of Au developed in the oxidation zone due to of supergene enrichment processes.

Quantitative chemical mapping of plagioclase as a tool for the interpretation of volcanic stratigraphy: an example from Saint Kitts, Lesser Antilles

Establishing a quantitative link between magmatic processes occurring at depth and volcanic eruption dynamics is essential to forecast the future behaviour of volcanoes, and to correctly interpret monitoring signals at active centres. Chemical zoning in minerals, which captures successive events or states within a magmatic system, can be exploited for such a purpose. However, to develop a quantitative understanding of magmatic systems requires an unbiased, reproducible method for characterising zoned crystals. We use image segmentation on thin section scale chemical maps to segment textural zones in plagioclase phenocrysts. These zones are then correlated throughout a stratigraphic sequence from Saint Kitts (Lesser Antilles), composed of a basal pyroclastic flow deposit and a series of fall deposits. Both segmented phenocrysts and unsegmented matrix plagioclase are chemically decoupled from whole rock geochemical trends, with the latter showing a systematic temporal progression towards less chemically evolved magma (more anorthitic plagioclase). By working on a stratigraphic sequence, it is possible to track the chemical and textural complexity of segmented plagioclase in time, in this case on the order of millennia. In doing so, we find a relationship between the number of crystal populations, deposit thickness and time. Thicker deposits contain a larger number of crystal populations, alongside an overall reduction in this number towards the top of the deposit. Our approach provides quantitative textural parameters for volcanic and plutonic rocks, including the ability to measure the amount of crystal fracturing. In combination with mineral chemistry, these parameters can strengthen the link between petrology and volcanology, paving the way towards a deeper understanding of the magmatic processes controlling eruptive dynamics.

The Teena Zn-Pb Deposit (McArthur Basin, Australia). Part I: Syndiagenetic Base Metal Sulfide Mineralization Related to Dynamic Subbasin Evolution

Abstract Divergent genetic models have been proposed for clastic dominant (CD-type) massive sulfide Zn-Pb mineralization in the Proterozoic Carpentaria Zn Province. Due to varying degrees of tectonic overprint, it has been difficult to accurately constrain structural and paragenetic timing aspects of the CD-type genetic model, and the most basic timing constraints (syngenetic vs. epigenetic, synextension vs. syninversion) remain debated. The recently discovered Teena Zn-Pb deposit is hosted by an exceptionally well preserved subbasin that permits relative timing relationships to be well defined. Using a combination of geophysical, structural, sedimentological, and petrographic datasets, a new model for subbasin development and syndiagenetic hydrothermal replacement mineralization is developed for the Teena mineral system. At Teena, sulfide mineralization was deposited from lateral fluid flow beneath an impermeable seal several hundred meters below the paleosurface and maximum flood surface, after formation of fine-grained diagenetic pyrite (py1) and dolomite nodules. Sulfide mineralization resulted from syndiagenetic carbonate replacement and pore space cementation where thermochemical sulfate reduction took place. The sulfide mineralization is therefore partly cospatial but not cogenetic with its thick pyritic hanging wall, and its lateral alteration footprint is much smaller than predicted by sedimentary exhalative (SEDEX) models. An additional zone of low-grade Zn-Pb mineralization in the footwall W-Fold Shale Member represents a different style of mineralization not previously reported for Carpentaria CD-type Zn deposits: it is associated with strata-bound lenses of hydrothermal dolomite (HTD) that formed by both replacement and carbonate dissolution and infill, which yielded diverse cavity-infill textures that include coarse-bladed dolomite fans cemented by interstitial sphalerite, dolomite, and quartz. Volumetrically minor Zn mineralization is also present in a fault conduit hydrothermal breccia and in hanging-wall synorogenic vein sets derived by hydrothermal leaching and remobilization of Zn from the underlying mineralized zones. Whereas both the Teena and nearby McArthur River Zn-Pb deposits are located along the northern margin of the 3rd-order Hot Spring-Emu subbasin, they formed in separate 4th-order subbasins in association with local extensional growth faults. Growth fault movement in the Teena subbasin was initiated during deposition of the W-Fold Shale Member and persisted episodically until a weak structural disconformity associated with sedimentary facies regression developed in the Upper HYC unit. Shifting patterns in depocenter location, sedimentary facies development, mineralization, and alteration zonation are attributed to progressive growth and linkage of segments of a regionally anomalous ENE-trending, synsedimentary fault zone. Similar patterns of extensional subbasin development were repeated in other Zn-mineralized subbasins throughout the River supersequence across the northern Carpentaria Zn Province, and formed in response to a short-lived episode of north-northwest–south-southeast regional extension around ca 1640 ± 5 Ma, triggered by far-field subduction events.

Altered mineral mapping based on ground-airborne hyperspectral data and wavelet spectral angle mapper tri-training model: Case studies from Dehua-Youxi-Yongtai Ore District, Central Fujian, China

Mineral mapping is an important procedure for the utilization of mineral resources, and it is also significant to the analysis of mineralization zone especially for altered minerals. The emergence of remote sensing, especially hyperspectral data has become a new approach for mineral mapping on a wide scale. In addition, spectral angle mapping (SAM) is a commonly used classifier to distinguish the minerals, but the discrimination ability is weak on a mapping scale, and the identification accuracy is poor for a series of minerals with similar spectral curves when a single classifier is applied. In this work, altered minerals are identified at Dehua-Youxi-Yongtai Ore District uniting ground and airborne hyperspectral data, and wavelet SAM (WSAM) tri-training model is constructed to discriminate the category of 9 altered minerals. Experimental results demonstrate that the proposed technique provides the identification accuracy of 82% and 70% for virtual and XRD verifications, and the mapping result is believable compared with measured sampling.

Integration of Landsat 8, gravity, and field data for exploration of gold mineralization in Gamba District, Northern Cameroon

Remote sensing is a robust and useful tool for providing high‐resolution image data and enabling reliable geological mapping during the initial stage of mineral exploration. One of its main applications is the extraction of lineaments and to locate alteration areas to target gold exploration. It has been long used in the Pan‐African belt of Cameroon to identify a hydrothermal alteration and a great number of lineaments associated with mineralizations. The study area located in the Pan‐African belt hosts numerous alluvial gold deposits where the primary mineralization was still largely poorly unknown until now, due to deep weathering. Therefore, remote sensing combined with field data is useful for targeting potential zones of primary gold resources involved in the hydrothermal and lineament systems. In this study, remote sensing data from Landsat 8 imagery were selected to map the distribution of hydrothermal minerals, and gravity data were interpreted for highlighting structural patterns related to the control of high‐potential zone for gold mineralization, generating a mineral prospect map. The lineaments network shows directions ranging from ENE‐WSW to E‐W, with main direction N45° and a secondary striking N275°. Image enhancement/processing techniques included the application of band ratio and principal component analysis that were helpful to demarcate potential alteration zones marked by iron oxide/hydroxides in which haematite and pyrite are used as proximal alterations and hydroxyl‐bearing minerals in which sericite (muscovite) is used as a marker of proximal alteration, while chlorite, epidote, biotite, quartz, and calcite are used as distal alteration zone, as described by field and petrographic data. The identified alteration zones display a high consistency with the known locations of gold occurrences (mining sites) and closely concordant with large‐scale gold mineralization in the study area. This study presents an integrated approach of Landsat 8 imagery with gravity data and field data for discovering primary mineral resources in a deep weathering area.

Gold-and silver-bearing assemblages in the Ann-Mason copper porphyry deposit, Yerington, Nevada

Porphyry deposits are an important source of copper and their value may be upgraded by minor contents of precious metals, if they are extractable. The mechanisms for enrichment of precious and base metals in these systems are not well understood. This study investigates the deportment of trace metals in the Ann-Mason porphyry deposit, including gold, silver, palladium, mercury, lead and bismuth. Petrographic and geochemical data are integrated to characterise the size and habit of minerals, the host mineral assemblages, and their association with alteration assemblages. Ann-Mason is one of several ore deposits hosted by the Yerington batholith in Nevada, and is being assessed for copper extraction from bornite and chalcopyrite ore assemblages, associated with potassic alteration. Mineralisation assemblages at Ann-Mason have been categorised as chalcopyrite-bornite, chalcopyrite-pyrite and pyrite > chalcopyrite zones. Limited two-metre assay data indicates that gold is most closely associated with bornite, although it is found in all three mineralisation zones. Analysis by SEM-EDS shows that trace elements are mostly present as microparticles hosted by sulfide minerals. Of the 438 grains measured, 89% are hosted by a sulfide mineral, with 68% hosted by bornite. Silver is most commonly present as hessite and gold as electrum, hosted by bornite and associated with potassic alteration. Palladium, mercury and bismuth are most commonly observed as telluride and selenide minerals. Palladium minerals are associated with potassic alteration, while mercury and bismuth minerals are mostly found with sericitic alteration. High fineness native gold is observed as three round blebs hosted by pyrite or silicates. Observations suggest that the trace metals in the chalcopyrite-bornite zone may have been incorporated by bornite and chalcopyrite, and exsolved upon cooling. In the chalcopyrite-pyrite and pyrite > chalcopyrite zones, the trace metals may have been deposited directly from a mineralising hydrothermal fluid and incorporated into the growing sulphide minerals. These findings have implications for the paragenesis of porphyry deposits, as well as for the milling processes that would be needed to extract precious metals at the Ann-Mason porphyry deposit.

Porphyry Cu mineralization processes of Xinqiao deposit, Tongling ore district: Constraints from the geochronology and geochemistry of zircon, apatite, and rutile

Xinqiao is a large ore deposit that is well known for its stratabound massive sulfide and skarn ores. Recently, deep drilling has shown that Xinqiao also has typical porphyry mineralization and alteration features. The Cu grade is 0.3–0.6% and occurs as quartz-pyrite-chalcopyrite in potassic and phyllic alteration zones. The characteristics and genetic processes of the porphyry mineralization at Xinqiao have not previously been reported.Three intrusion types are recognized; pyroxene diorite, quartz diorite and quartz monzodiorite porphyry; Cu mineralization is associated with the quartz diorite and quartz monzodiorite porphyry. Zircon U-Pb dating shows that the three intrusions were all emplaced at about 140 Ma. Zircons from the quartz diorite and quartz monzodiorite porphyry show higher Ce4+/Ce3+ and Eu/Eu* (>0.5), 10,000(Eu/Eu*)/Y (>5), and (Ce/Nd)/Y (>0.01), than the pyroxene diorite, and apatites from the mineralized intrusions have slightly higher SO3 (average 0.40) contents than ones from the pyroxene diorite (average 0.33). These results indicate that the fertile magmas were more oxidized, hydrous, and S-rich than the barren pyroxene diorite, consistent with their association with porphyry Cu mineralization. U-Pb dating of hydrothermal rutile from the porphyry mineralization and garnet from the skarn ore both yield ages of about 140 Ma, suggesting that the porphyry and skarn mineralization belong to same system. The geochemistry of hydrothermal rutile and apatite in the porphyry mineralization zone also indicates that Xinqiao ores were produced from a S-rich magmatic-hydrothermal fluid system. Our results highlight huge porphyry Cu mineralization potential beneath stratabound and skarn deposits in the Middle-Lower Yangtze River metallogenic belt.

Diagenetic Controls on the Formation of the Anarraaq Clastic-Dominated Zn-Pb-Ag Deposit, Red Dog District, Alaska

AbstractThe Anarraaq clastic-dominated (CD) Zn-Pb-Ag deposit (Red Dog district, Alaska, USA) has an inferred mineral resource of 19.4 Mt at 14.4% Zn, 4.2% Pb, and 73 g/t Ag and is spatially associated with a separate ~1 Gt barite body. This study presents new cross sections and petrographic evidence from the Anarraaq area. The barite body, previously shown to have formed in a shallow subsurface environment akin to a methane cold seep, contains multiple generations of barite with locally abundant calcite masses, which are discordant to sedimentary laminae, and is underlain by an interval of massive pyrite containing abundant framboids and radiolarians. Calcite and pyrite are interpreted to have formed by methane-driven diagenetic alteration of host sediment at the sulfate-methane transition (SMT). The sulfide deposit contains two zones of Zn-Pb mineralization bounded by faults of unknown displacement. The dominant hydrothermal minerals are marcasite, pyrite, sphalerite, quartz, and galena. The presence of hydrothermal pseudomorphs after barite, early pyrite resembling diagenetic pyrite associated with the barite body, and hydrothermal quartz and sphalerite filling voids formed by dissolution of carbonate all suggest that host sediment composition and origin was similar to that of the barite body prior to hydrothermal mineralization. Rhenium-osmium isochron ages of Ikalukrok mudstone (339.1 ± 8.3 Ma), diagenetic pyrite (333.0 ± 7.4 Ma), and hydrothermal pyrite (334.4 ± 5.3 Ma) at Anarraaq are all within uncertainty of one another and of an existing isochron age (~338 Ma) for the Main deposit in the Red Dog district. This indicates that the Anarraaq deposit formed soon after sedimentation and that hydrothermal activity was approximately synchronous in the district. The initial Os composition of the Anarraaq isochrons (0.375 ± 0.019–0.432 ± 0.025) is consistent with contemporaneous seawater, indicating that a mantle source was not involved in the hydrothermal system. This study highlights the underappreciated but important role of early, methane-driven diagenetic processes in the paragenesis of some CD deposits and has important implications for mineral exploration.

Mapping lithological units, structural lineaments and alteration zones in the Southern Kibi-Winneba belt of Ghana using integrated geophysical and remote sensing datasets

Geophysical and remote sensing datasets were employed to delineate potential zones of gold mineralization within the southern Kibi-Winneba belt of Ghana. The study area, which is characterized by the Birimian metavolcanic and metasedimentary rocks with prevalence of intrusive granitoids hosts several scientifically unguided operational activities by artisanal miners locally referred to as Galamsey. In this study, various enhancement techniques were employed on geophysical datasets encompassing magnetic, gravity and radiometric to delineate various lithological units, which corroborated with the Birimian formation and its related granitoid intrusives within the study area. The Center for Exploration Targeting grid analysis and Line Module Algorithm techniques were employed respectively on the magnetic and Sentinel 2A datasets to delineate various structural lineaments within the study area. Approximately 72% and 67% structural lineaments delineated respectively from the magnetic and Sentinel 2A datasets trended in the NE-SW and N-S direction, which control gold mineralization within the Birimian system. The prinicpal component analysis based on the Crosta technique was employed on the Sentinel 2A bands to highlight alteration zones within the study area. A potential map of gold mineralization zones within the study area was generated by integrating exploration layers comprising magnetic, gravity, structural density, radiometric and alteration zones delineated by Crosta technique. This mineral potential map categorized the belt into low, moderately low, moderately high and highly prospective regions with area coverage of 600.4 km2, 681.27 km2, 635.95 km2 and 295.20 km2 respectively. The mineralization potential map obtained was validated with available gold geochemical data and locations of artisanal mining operations (Galamsey), which corroborated with the highly potential mineralization zones of gold deposits delineated within the study area.

Application of geostatistical hierarchical clustering for geochemical population identification in Bondar Hanza copper porphyry deposit

Several machine learning approaches have been developed for the identification of geochemical populations. In these approaches, the geochemical elements are usually the sole quantitative variables used as inputs for geochemical population recognition. This means that the presence of other qualitative variables, such as geological information, is overlooked in the analysis. Hierarchical clustering, as an unsupervised machine learning method, is a common approach for dimensional reduction in the analysis of geochemical data. In this study, an alternative to this technique, known as geostatistical hierarchical clustering (GHC), is applied to identify geochemical populations in 3D in the Bondar Hanza copper porphyry deposit, Iran. In this paradigm, the qualitative geological variables can also be incorporated for geochemical population identification, in addition to qualitative geochemical elements. In this study, an innovative solution is presented to tune the weighting parameters of each variable in GHC, based on the associations that the clusters (i.e., geochemical populations) should have with the geological information. The results are compared with k-means and number–size fractal/multifractal (N–S) methods. As a result, GHC showed better agreement with alterations, rock types, and mineralization zones in this deposit. Finally, some important instructions are provided for further mineral exploration.

Isotope-hydrogeochemical features of the Belokurikha field radon waters

The purpose of the work is to carry out integrated isotope-geochemical studies of the mineral waters of the Belokurikha deposit. The methods of titrimetry, ion chromatography, inductively coupled plasma mass spectrometry (ICPMS) have been used in the laboratory investigation of the chemical composition of waters. The isotope composition of oxygen, hydrogen and carbon in dissolved carbon dioxide has been studied with the help of the Isotope Ratio Mass Spectrometer FinniganTM MAT 253 equipped with the attachments for sample preparation H/Device (to analyze the δD ratio) and GasBench II (to analyze δ18O and δ13СDIC ratios). There are two aquifers at the deposit. The first nonartesian aquifer comprises loose sediments of the Quaternary age. The second artesian aquifer includes the granites of the upper Paleozoic age with the different fracture degree: from monolith to loosened. Three groups of waters are distinguished on the basis of geochemical coefficients: fracture-vein waters bedded in weathered granites; groundwaters of the zone of rare earth mineralization and background composition; surface waters of the Belokurikha river. The isotope data on oxygen and hydrogen provide evidence that the production aquifers of the Belokurikha field are fed through the infiltration of meteoric waters, with the feeding shift to winter precipitation. The paper provides the first data of the integrated isotope-hydrogeochemical studies of nitric-siliceous low-radon thermal waters of the Belokurikha deposit. The composition of these waters is HCO3-SO4 Na and SO4-HCO3 Na with the total dissolved salts value ranging from 198 to 257 mg/dm3. The waters are characterized by alkaline pH of 8.6–9.6, silicon content ranging from 19.8 to 24.6 mg/dm3, and they are referred to the fracture-vein waters of the Upper Paleozoic granites. 222Rn activity is up to 359 Bq/dm3. The ratios of δD (from -126.9 to -102.7 ‰) and δ18O (from -17.5 to -14.2 ‰) in the studied waters indicate their atmospheric origin. The values of δ13СDIC vary from -9.7 to -25.6 ‰ and point to the biogenic origin of carbon.

Heterotopic Ossifications of the Forearm: A Cause of Post-Traumatic Loss of Pronation-Supination

HO is defined by the development of ectopic mature bone within nonosseous tissues. It is a well-described phenomenon that complicates forearm fractures, especially when there is an open fracture, a significant soft tissue injury, and associated neural axis or thermal injury. HO mainly forms near metal hardware and may lead to the formation of radio-ulnar synostosis. CT is superior to plain radiographs, as it identifies the ectopic bone earlier, defines its exact localization, and helps planning the surgical intervention. Radiologic features are variable; in the early stage, CT shows a low-attenuation mass with indistinct surroundings. As the ossification process progresses, zones of mineralization are visible before leading to the formation of mature cortical bone at the periphery (Figure 1 and 2: arrows). Hastings classification describes 5 classes according to how HO affects the forearm range of motion.

Zonality of ore-forming chrome spinels of medium-chrome and aluminous chromitites of the Voikaro-Syninsky massif

Relevance of the work. The conditions for the formation of chromium ores in alpine-type ultramafites remain a topical subject of research. In recent years, scientific papers have focused on the issue of changing the chemical composition of ore-forming minerals and chromium ores under the influence of deformation and dynamic recrystallization processes accompanying metamorphism. The results of such studies make it possible to formulate a new model of the formation of chromium mineralization taking into account a significant amount of geological data indicating that alpine-type ultramafic rocks are “mantle tectonites”. In our work, we have studied zonal ore-forming spinels from chrome ores of the Polar Urals. The results of the study make it possible to associate the formation of chemical zoning in minerals and ore bodies with recrystallization under the influence of stress tension. Purpose of the work – study of the conditions for the formation of chemical zoning of chromium spinels from alumina and medium chromium ores of the Voikaro-Syninsky massif. Results. Zonal ore-forming spinels from medium-chromium and aluminous chromitites of the Voikaro-Syninsky massif (Polar Urals) have been studied. It was found that replacement rims are developed along the grains of oreforming spinels with an increased content of Cr2 O3 and an oxidation state of iron in relation to the core, as well as a reduced content of Al2 O3 . The oxidation state of iron in the rims of most grains does not exceed the values typical for unaltered ore-forming spinels. T–fO2 parameters of zoning formation in spinels were determined by oxythermobarometry. Comparison with zoned chrome spinels of the Golyamo Kamenyane massif (Bulgaria). Conclusion. Metamorphic transformations of alumina and medium-chromium chromitites of the Voikaro-Syninsky massif, occurring under subcrustal conditions under the action of directional stress at relatively constant T–fO2 parameters, lead to an increase in the chromium content of the ore mineral.

INTERPRETATION OF AEROMAGNETIC DATA AND LANDSAT IMAGERY OVER THE NIGERIAN YOUNGER GRANITES IN AND AROUND KAFANCHAN AREA, NORTH-CENTRAL NIGERIA

In this research the lineaments of the Kafanchan area in North-central Nigeria were investigated in order to explore the mineralization zones of the area. Aeromagnetic data over Kafanchan and environs within the Younger Granite Province, in the North-Central Nigeria were collated and analyzed. The aeromagnetic map of the area was interpreted both qualitatively and quantitatively so as to identify the nature of the magnetic sources and the trends direction in the study area. The trend of the Total Magnetic Intensity (TMI) map is predominantly in NE-SW. The First Vertical Derivative (FVD) Lineaments Map was also correlated with LADSAT lineaments map and both maps agreed in most areas. The study area is characterized by predominant magnetic lineament trend in NE-SW direction and subordinate E-W direction. The result also shows that the most significant structural trends affecting the distribution of these magnetic anomalies in the study area is in NE-SW direction. The TMI map indicates that there are three major mineralization zones in the study area. The high magnetization contrast in the NE and SE parts of the study area correlates with the migmatite-gneiss, biotite-granites, granites and basalts which are associated with high magnetic contrasts. Also, the high magnetization contrast in the NW part of the area correlates with basalt and the biotite-granite. However, the predominant low magnetization contrast observed in the western half does not correlate with the basic igneous rock