Ore-bearing Rocks Research Articles

Importance of hydrogeological conditions during formation of the karstic bauxite deposits, Central Guizhou Province, Southwest China: A case study at Lindai deposit

Karstic bauxite deposits are widespread in Central Guizhou Province, SW China, and high-grade ores are frequently sandwiched with overlying coal and underlying iron-rich layers and form a special “coal–bauxite–iron” structure. The Lindai deposit, which is one of the most representative karstic bauxite deposits in Central Guizhou Province, was selected as a case study. Based on textural features and iron abundances, bauxite ores in the Lindai deposit are divided into three types of ores, i.e., clastic, compact, and high-iron. The bauxite ores primarily comprise diaspore, boehmite, kaolinite, illite, and hematite with minor quartz, smectite, pyrite, zircon, rutile, anatase, and feldspar. The Al2O3 (53–76.8wt.%) is the main chemical contents of the bauxite ore samples in the Lindai district, followed by SiO2, Fe2O3, TiO2, CaO, MgO, S, and P etc. Our geological data on the Lindai deposit indicated that the ore-bearing rock series and its underlying stratum have similar rare earth elements distribution pattern and similar Y/Ho, Zr/Hf, and Eu/Eu∗ values; additionally, all ore-bearing rock samples are rich in MgO (range from 0.16wt.% to 0.68wt.%), and the plots of the dolomites and laterites lie almost on or close to the weathering line fit by the Al-bearing rocks in Zr vs. Hf and Nb vs. Ta diagrams; suggesting that the underlying Middle Cambrian Shilengshui Formation dolomite is the parent rock of bauxite resources in the Lindai district.Simulated weathering experiments on the modern laterite from the Shilengshui Formation dolomite in the Lindai bauxite deposit show that hydrogeological conditions are important for karstic bauxite formation: Si is most likely to migrate, its migration rate is several magnitudes higher than those of Al and Fe under natural conditions; the reducing inorganic acid condition is the most conducive to Al enrichment and Si removal; Fe does not migrate easily in groundwater, Al enrichment and Fe removal can occur only in acidic and reducing conditions with the presence of organic matter.The geological and experimental studies show that “coal–bauxite–iron” structure in Lindai deposit is formed under certain hydrogeological conditions, i.e., since lateritic bauxite or Al-rich laterite deposited upon the semi-closed karst depressions, Si can be continuously removed out under neutral/acidic groundwater conditions; the coal/carbonaceous rock overlying the bauxitic materials were easily oxidized to produce acidic (H2S, H2SO4, etc.) and reductant groundwater with organic materials that percolated downward, resulting in enrichment of Al in underlying bauxite; it also reduced Fe3+ to its easily migrating form Fe2+, moving downward to near the basal carbonate culminated in precipitating of ferruginous (FeS2, FeCO3, etc.) strata of the “coal–bauxite–iron” structure. Thus, the bauxitic materials experienced Al enrichment and Si and Fe removal under above certain hydrogeological conditions forming the high-quality bauxite.

The application of radar chart in geoscience and its significance

The radar chart method is a very common method among all the multi-statistic charts that can project the status of each index to the two-dimensional plane, and it gets its name for its similarity with the images shown on radar navigation screens. Now, although the radar chart method has already been broadly used in evaluating company performance, financial situations, human resources, risk and so on, it is seldom applied in the geosciences, especially petrology, minerology, geochemistry, structural geology, and geophysics. Compared with traditional basalt discrimination diagrams, the radar chart has advantages in comprehensive analyses, for each of its axes can represent not only data information but also geological phenomena and geological background information. Radar charts can combine all kinds of different indicators, which means they share a same thinking mode with the prevalent analytical method called Big Data analytics. Radar charts can represent not only data information but also other scientific factors, such as observations and geological records, which give it more advantages in composite analyses. The scope of the application of radar charts is scalable, meaning they can be used to analyze global statistical information or just evaluate the data of a particular region. The number of factors of every radar chart varies but usually ranges from three to ten or more. The practical uses of radar charts cannot be fully illustrated, thus, only a few geological examples are presented in this paper in an effort to explain their priority in classification. The research shows that radar charts can simplify the usage of different diagrams in the geosciences by considering the most typical indicators of different problems. For example, when discriminating the tectonic settings of the basalts, a five-dimensional radar chart containing the factors of LaN/YbN, Th/Ta, YbN, SrN/NdN, and PbN/CeN can clearly discriminate the tectonic settings of the basalts into MORB, OIB, IAB, CRB and CFB. A radar chart containing the factors of FeO*/MgO, 10000Ga/Al, Zr+Nb+Ce+Y, Na2O+K2O/CaO, Sr, and Yb can also easily distinguish A-type granites from other types, and a radar chart containing the typical ore-forming elements can separate ore-bearing rocks from normal rocks. Meanwhile, the superiority of radar charts is also shown in their ability to simplify the discriminative process of the tectonic settings of clastic rocks and hot-water deposition characteristics according to their different features (i.e., major elements, trace elements, and their ratios), They can also be used to trace the mineral sources of ore-deposit and fluvial sediments, make comparisons between trace elements of the south Yellow Sea, contrast the differences in the mineral assemblages of shales, and identify ophiolites based on their trace elements and mineral assemblage features. However, all the factors used in the radar charts are picked based on the knowledge that has already been accepted by experts in geological field. Overall, radar charts have no fixed limitations, and they can be used flexibly. One of the significant features of radar charts is that they allow for boundless imagination and creativity, which means different researchers can design their unique radar charts based on different scientific issues. The radar chart method is just a simple method aimed at simplifying complicated scientific issues and making it easy to observe and solve problems. Although radar charts also have drawbacks (e.g., the data materials should be normalized to a certain scale and the user should possess comprehensive knowledge about the specific field), they still have promising prospects in the geosciences field and are worth being popularized.

Multiple-stage mineralization in the Sawayaerdun orogenic gold deposit, western Tianshan, Xinjiang: Constraints from paragenesis, EMPA analyses, Re–Os dating of pyrite (arsenopyrite) and U–Pb dating of zircon from the host rocks

The Sawayaerdun deposit, located in the southern Tianshan orogenic belt in Xinjiang, NW China, is one of many orogenic gold deposits in the Central Asian Orogenic Belt (CAOB). The deposit is controlled by reverse faults and hosted in highly deformed carbonaceous turbidites that have undergone pyritic, arsenopyritic, silicification, carbonate and sericitic alteration. Gold occurs mainly in the form of electrum and native gold, and is also present in pyrite and arsenopyrite as “invisible gold”. Three generations of auriferous pyrite have been recognized through detailed petrographic studies and EMPA analyses. The pyrite with framboidal texture (Py0) is disseminated in the host rock, and is locally enriched in gold. The anhedral pyrite (Py1), associated with silicification and quartz veins that experienced strong deformation, has an average Au content of 0.021wt.%. The euhedral–subhedral pyrite (Py2), showing octahedron cube and pyritohedron habits, is associated with least deformed quartz veins that are best developed in the main orebodies, and has an average Au content of 0.023wt.%. The Py0 is interpreted to have formed contemporaneously with the ore-bearing rocks, with a maximum depositional age of 355±7.3Ma based on U–Pb dating of detrital zircons. Re–Os isotopic analyses of four Py1 samples yielded an isochron age of 324±4.8Ma, and those of five Py2 samples yielded an isochron age of 282±12Ma. Py1 is interpreted to have formed in the syn-tectonic stage, during the collision between the Tarim craton and the Central Tianshan terrane in Late Carboniferous, whereas Py2 was formed in a later mineralization event, during the late- to post-tectonic stage in Early Permian. These study results suggest that multiple stages of gold mineralization have developed in the Sawayaerdun deposit, and similar mineralization processes may have taken place in other parts of the Western Tianshan Orogen.

THE USE OF THERMAL ANALYSIS IN THE EVALUATION OF PROBABLE RESOURCES OF GOLD IN CARBONACEOUS DEPOSITS OF THE BELORETSK METAMORPHIC COMPLEX (SOUTHERN URALS)

The article briefly describes the geological structure of the zonal Beloretsk metamorphic complex; listed suites, which includes carbonaceous deposits, is given all available data sampling of carbonaceous deposits of gold. Based on the thermal method of studying the carbonaceous shales of zigazin-komarov suite established that the exothermic effect in them occurs in the temperature range 630-730 °C, which corresponds to the greenschist and epidote-amphibolite facies of metamorphism. Mapping the temperature distribution within the Beloretsk metamorphic complex, as well as the analysis of patterns of gold-ore objects within it, allowed to bind gold mineralization to a specific temperature interval. This gave the possibility with minimal cost to assess the prospects for carbonaceous deposits of the Beloretsk metamorphic complex on the gold and select a specific area on it prospecting. It is shown that the largest gold mineralizations are confined to tectonically intensively destructed, silicified and sulfidation rocks of black-shale formation, located in an external high-temperature zone of the greenschist facies of metamorphism. The established regularity is very important search value in the further prospecting work on the periphery of the Beloretsk metamorphic dome and confirms correctness of the model of metamorphic-hydrothermal gold mineralization in black-shale strata. In such geological setting was discovered Otnurok gold mineralization in which by test of carbonaceous deposits was identified a layer of ore-bearing rocks with the thickness of six meters. This gold bearing zone is traced in a north-easterly direction for several kilometres along strike in a series of high-grade metal contents, which allowed to calculate probable resources of gold on P 2 categories.

Stable isotope geochemistry of sulfides from intrusion in Monchegorsk, northern part of Baltic Shield

The sulfide minerals from old mafic intrusion rocks from the Kola Peninsula were analyzed on stable sulfur isotopes. These samples were already dated by the Sm-Nd method. These sulfide samples were evaluated upon a geochemical composition by ICP-MS. The sulfide mineral samples were selected from the main ore-bearing rocks of the Monchetundra layered intrusion. The analyzed sulfides formed several generations of mineralization associated with primary and hydrothermal stage of formation of the deposits. Isotopic studies confirm a few consecutive stages of mineralization. These data were compared with the results of Sm-Nd dating of sulfide mineralization. The results of geochemical and geochronological studies indicate a complementarity in the context of determining the mineralization stages.

Genesis and crystallization of ultramafic alkaline carbonatite magmas of Siberia: ore potential, mantle sources, and relationship with plume activity

This paper discusses the genesis of large Siberian alkaline massifs hosting major ore deposits. These reference massifs are grouped based on the predominance of alkalies (K or Na) and their agpaitic index (miaskitic and agpaitic). We proposed new emplacement schemes for the Tomtor, Murun, Burpala, Synnyr, and Bilibino massifs supported by petrochemical and geochemical data, as well as new age estimates. Types of their ore potential and genesis of rare-metal mineralization are discussed. The formational types of carbonatites as the main ore-bearing rocks are given. The depth of magma generation and types of mantle sources are determined using isotopic data from previous studies. A model of plume-related generation of ultramafic alkaline magmas is proposed.

Geological setting for porphyry copper deposits in calc-alkaline rocks: Wadi Rofaiyed area, Sinai, Egypt

The close association of copper mineralization with porphyritic quartz diorite and intermediate volcanic rocks, the presence of hydrothermal alteration zones, the disseminated nature of sulfide minerals, and extremely absence of massive lenses and the volcanic arc (orogenic) tectonic situation of ore-bearing rocks are the main geological conditions associated with diorite-type porphyry copper system at Wadi Rofaiyed area, Sinai, Egypt. Chalcopyrite and pyrite are the main sulfide minerals in quartz diorite, whereas chalcopyrite, pyrite, galena, and sphalerite are the main sulfide minerals in Rutig volcanics. Secondary sulfide minerals include chalcocite and covellite. Quartz diorite and Rutig volcanics (intermediate composition) are calc-alkaline, enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs). The incompatible trace element patterns favor fractional crystallization of plagioclase and Fe-Ti oxides. Rutig volcanics developed in orogenic arc-type and anorogenic within plate, indicating an eruption in a transitional post-collisional tectonic setting. Two hydrothermal events are thought to take place, which are characterized by zonal pattern composed of a central potassic zone and a peripheral propylitic zone. Both zones are centered over porphyritic intrusive rocks that might be considered the source of hydrothermal solutions. A close relationship of mineralization to pre-Katerina ring dike structures, namely, joints and faults, was revealed. Generally, the gentle dips of bandings in Rutig volcanics and the presence of post-eruption faulting indicate a significant deformation by translational and rotational movement. The average thickness of Rutig volcanics is about 1.4 km, which along with the big masses of intrusive country rocks constitute a considerable volume of mineralized stock. Meanwhile, subsidence of Rutig volcanics which served as capping rocks played, to some extent, an effective role in preserving the mineralization in the underlying country rocks. Multi-scale structural investigations revealed the role of interstitial spaces and fracture network in localizing mineralization. Where two styles of mineralization are recognized, the first is dissemination and the second is fracture filling. The mineralization was formed during a large-scale extensional tectonic event that followed the collisional period.

GEOLOGY, PETROGEOCHEMISTRY OF AKHMEROVSKY GRANITE MASSIF AND ORE MINERALIZATION IN ITS FRAME

The article considers the geological structure, composition and geochemical features of Akhmerovsky granite massif, which is an integral and central part of zonal beloretsk metamorphic complex. It is shown that the massif consists mainly of granite and diorite, which in mineral composition meet the standard granites. The source rocks for beloretsk complex are sandy-clayey and carbonate rocks with thick interlayers of carbonaceous formations. On the characteristic geochemical diagrams granites of Akhmerovsky massif form a compact field in the area of intraplate granitoids. They are comagmatic the mashak volcanic rocks and their paleotectonic regime corresponds to stable consolidated structures of platform type. The formation of the main phase granites of Akhmerovsky massif belongs to the early phase of the middle Riphean and corresponds to the time of formation of Berdyaushsky, Ryabinovsky and Kusinsko-Kopansky intrusions. It is studied the carbonaceous deposits within the beloretsk metamorphic complex on the gold. It is shown that the largest manifestations of gold are confined to tectonically intensively deformed, silicified and sulfidation rocks of black-shale formation, located in an external high-temperature zone of the greenschist facies of metamorphism, which is an important exploration indicator for carrying out further work on the periphery of the beloretsk metamorphic dome. In such geological setting was revealed the gold manifestation of Otnurok, where was tested the carbonaceous formations which allowed us to identify a member of ore-bearing rocks. This zone of gold-bearing mineralization was traced in a north-easterly direction for several kilometres along strike, but not delineated, that allow us to continue research work in this direction.

Application of strain analysis to estimate pressure solution processes in regional shear zones

This paper considers the basic principles of the strain analysis method based on the analysis of antitaxial regeneration fibrous fringes around linear rigid inclusions in a low-viscosity rock matrix. This method has been developed for pressure shadows composed of fibrous minerals, whose orientation is controlled by the major elongation direction rather than the orientation of rigid inclusions. This approach is applicable only for rocks exposed to uniform coaxial straining. The strain ellipse is calculated in two ways: for three variably oriented strain markers, it is calculated using Mohr’s circles, and for numerous strain markers by average body ellipse. The strain ellipsoid is calculated using the parameters of a few strain ellipses calculated with three and more non-parallel planes. This paper provides the data on the method testing in reference sites of Dora–Pil’ ore field in the Upper Indigirka district and Vangash area in the Yenisei Range. Regeneration fibrous fringes around fragments of fern fossils and linear rutile metacrystals were used as markers. The results of strain analysis obtained for the reference sites in the Upper Indigirka district made it possible to describe the signs of variable strain stages of developing strike-slip zones making up the Adycha–Taryn Fault Zone. Sublatitudinal ore-bearing strike-slip zones are characterized by a subvertical orientation of the elongation axes X of elongated strain ellipsoids, which are subperpendicular to quartz–carbonate veins and slope kink zones. NW-trending strike-slip zones are characterized by subhorizontal orientation of the Z shortening axes of flattened strain ellipsoids, which are subparallel to the normals of quartz–carbonate veins and veinlets. The results of strain analysis obtained for reference sites in the Vangash area made it possible to describe the thrust strain environment following the metamorphism stage and to reveal specific features in the formation of the strain textures of ore-bearing rocks based on their rheological properties.

Nanhuan manganese deposits within restricted basins of the southeastern Yangtze Platform, China: Constraints from geological and geochemical evidence

The Nanhuan manganese deposits in the southeastern Yangtze Platform occur in the black shale series in the lower part of the Datangpo Formation. In order to constrain the genesis of the deposits, a detailed study was undertaken that involved field observations, major and trace element analyses, organic carbon analyses, and isotope analyses (C, O, S). The major findings are as follows. (1) The ore-bearing rock series, morphology of the ore bodies, and characteristics of ores in several deposits are similar. The ore minerals are rhodochrosite and manganocalcite. The gangue minerals are mainly quartz, feldspar, dolomite, and illite. Minor apatite and bastnaesite occur in the manganese ores. (2) The ores are enriched in Ca and Mg, whereas they are depleted in Si, Al, K, and Ti compared to wall rocks. The ores normalized to average Post-Archean Australian shale (PAAS) are enriched in Co, Mo, and Sr. The chondrite-normalized rare earth element (REE) patterns for ores and wall rocks are between those of typical hydrogenous and hydrothermal type manganese deposits. Additionally, the ores have positive Ce anomalies with an average Ce/Ce* of 1.23 and positive Eu anomalies with an average Eu/Eu* of 1.18 (normalized to PAAS). (3) The average content of organic carbon is 2.21% in the samples, and the average organic carbon isotopic value (δ13CV-PDB) is −33.44‰. The average inorganic carbon isotopic value (δ13CV-PDB) of carbonates in Gucheng is −3.07‰, while the values are similar in the other deposits with an average of −8.36‰. The oxygen isotopic compositions (δ18OV-PDB) are similar in different deposits with an average of −7.72‰. (4) The sulfur isotopic values (δ34SV-CDT) of pyrite are very high and range from +37.9‰ to +62.6‰ (average of 52.7‰), which suggests that the pyrite was formed in restricted basins where sulfate replenishment was limited. The sulfate concentrations in the restricted basins were extremely low and enriched in δ34S, which resulted in the very high δ34S values for the pyrite that formed in the manganese deposits. Therefore, a terrigenous weathering origin for manganese can be excluded; otherwise, the sulfate would have been introduced into the basins together with terrigenous manganese, which would have decreased the δ34S values of pyrites. The manganese, which originated from hydrothermal processes, was enriched in the restricted and anoxic basins, and then, it was oxidized to manganese oxyhydroxide in the overlying oxic waters whereby the products precipitated into the sediments. The manganese oxyhydroxide in the sediment was then reduced to Mn2+ and released to the pore waters during the process of diagenesis. Some organic carbon was oxidized to CO32−, which made the depletion of 13C in manganese carbonates. Therefore, we suggest that the Nanhuan manganese deposits are hydrothermal–sedimentary/diagenetic type deposits.

The Luanchuan Mo–W–Pb–Zn–Ag magmatic–hydrothermal system in the East Qinling metallogenic belt, China: Constrains on metallogenesis from C–H–O–S–Pb isotope compositions and Rb–Sr isochron ages

The Luanchuan Mo–W–Pb–Zn–Ag polymetallic ore district is located in the East Qinling metallogenic belt on the southern margin of the North China Craton. Two ore fields (Nannihu and Yuku) are recognized in the district, and three types of deposits are identified from the two ore fields as follows: (1) the 6 proximal porphyry–skarn type Mo–W deposits occurring at the inner contact zone of the granite porphyries, (2) the 3 middle skarn–hydrothermal type Zn deposits, and (3) the 8 distal hydrothermal type Pb–Zn–Ag deposits at the periphery of the porphyry. We present C–H–O isotope compositions of hydrothermal quartz and calcite, S–Pb isotope compositions of sulfide minerals, and sphalerite Rb–Sr isochron ages from the 17 deposits. The geochemical and geochronological data from the two ore fields all show systematic temporal and spatial variation, and primarily lead to the following inferences. (1) The temperatures and salinities of the ore-forming fluids decreased during mineralization. The ore-forming fluids gradually evolved from magmatic water to mixed magmatic–meteoric water. (2) The metallogenic components were primarily derived from igneous rocks, with increasing proportions of the materials from the ore-bearing rocks. (3) The mineralization ages of these deposits are close (147–136Ma), which correspond to the emplacement of the granite intrusions. (4) The three types of deposits and the ore-related late Mesozoic intrusives constitute a unified magmatic–hydrothermal–mineralization system. Finally, we also suggest exploration strategies for the Luanchuan ore district.

Geochemical characteristics of the Kal-e Kafi Cu-Mo-Au porphyry deposit, Central Iran

The Kal-e Kafi intrusive suite, located about 65 km northeast of Anarak Village in Central Iran is host to the significant un-tapped (virgin) Mo-bearing porphyry deposit. Trend-lines, fitted by linear regression, are plotted for values of vertical zonation coefficient (Kz) vs. elevation for the porphyry Cu-Mo deposits of Kal-e Kafi, Sungun (Iran), Aktogay (Kazakhstan), and Tekhut (Armenia). The slope of the trend-line at Kal-e Kafi deposit is much closer to horizontal, compared to the other deposits, signifying that the ore-body is preserved at subsurface. Geochemical anomalies, based on 121 samples, have been delineated and plotted over the 1:50,000 scale geological map of the study area. Contoured geochemical anomalies exceed 10,000 ppm for Pb, 2500 ppm for Zn, 20,000 ppm for Cu and 500 ppm for Mo. Previous work carried out by Technoexport used the “Cu-Mo Ore-Mineralization Vertical Zonation Coefficient” and the “Cu-Mo Ore-Mineralization Vertical Intensity Coefficient” to define fertile ore-bearing host rocks. The anomalies for Pb, Zn, Cu, and Mo, besides those determined by the abovementioned coefficients calculated by Soviet geologists, coincide with ore deposits used in this study. Grade-depth log interpretation of drill hole reveals that, at shallower depths, there are patterns of supergene sulfide enrichment, while at deeper intervals, primary sulfide stockwork mineralization occurs. Elevated Au/Ag values at same-depth intervals could be characteristic of the abovementioned mineralization types. Therefore, from a geochemical perspective, they could be considered as Pb-Zn-Cu±Au supergene sulfide enrichment and Cu-Mo±Au primary sulfide stockwork mineralization zones.

Oxygen and hydrogen isotopic composition of the fluid during formation of anthophyllite metaultramafic rocks in the Sysert metamorphic complex, central Urals

The oxygen (δ18O) and hydrogen (δD) isotopic composition of H2O-bearing minerals was studied for the ore-bearing amphibole metaultramafic rocks, which are the products of the early regional (435 ± 44 Ma) and late local (260 ± 6 Ma) silicic metasomatose in the Sysert metamorphic complex. The gold-sulfide mineralization of the Karas’evogorskoe deposit and anthophyllite-asbestos bodies of the Tersut deposit are related to the regional and local metasomatose combined with plagiogranitization and potassium granitization, respectively. The H2O-bearing minerals of metasomatites (anthophyllite, tremolite, talc) of the Karas’evogorskoe and Tersut deposits are characterized by heavier δ18O (9.8 to 12.2 and 7.6 to 9.4‰, respectively) and lighter ·D (87 to −91 and −56 to −67‰, respectively) values. The calculated isotopic composition of the fluid in equilibrium with these minerals indicates a heterogeneous source of water for the fluids related to the formation of metasomatites and the metamorphic origin of fluids. During the regional metasomatose, this fluid was a result of equilibrium of the deep fluid with volcanosedimentary rocks enriched in the heavy oxygen isotope. At the local metasomatose, the metamorphic fluid was formed by interaction of magmatic water produced by potassium granitization with ultramafic rocks.

Mineralogical characteristics of the karstic bauxite deposits in the Xiuwen ore belt, Central Guizhou Province, Southwest China

The karstic bauxite deposits in the Xiuwen ore belt of Central Guizhou Province are hosted by the Lower Carboniferous Jiujialu Formation and show parallel unconformity with the overlying and underlying strata. The ore-bearing rock series that exhibits a typical “coal–bauxite–iron” structure is divided into three segments from the bottom upward, namely, an iron layer, a bauxite layer, and a coal layer. Based on the textural features and iron abundances, the bauxite ores occurring in the middle segments are divided into three types of ores—clastic, compact, and high-iron. The bauxite ores primarily comprise diaspore, boehmite, kaolinite, illite, and hematite with minor zircon, pyrite, rutile, and feldspar. The existence of rutile within diaspore lumps, which were inherited from laterization, suggests that diaspore was transformed from gibbsite and that karstic bauxite was transformed from laterite bauxite. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe X-ray microanalyses (EPMA) suggest that diaspore and boehmite differ with regard to appearance and element abundance: diaspore (2–10μm) displays short prismatic or platy shapes and contains low SiO2 abundances (ranges from 0.2 to 0.51wt.%), whereas boehmite (0.2–5μm) exhibits granular or irregular shapes and contains high contents of SiO2 that vary between 2.71 and 10.4wt.%. The Fe–Cu–Pb–Zn–Ba sulfide and sulfate mineral assemblages associated with cryptocrystalline kaolinites are discovered in the Xiaoshanba deposit from the Xiuwen ore belt. Mineralogical and geochemical studies reveal that the genesis of these assemblages is controlled by the decomposition processes of organic matter and the activities of microorganisms within the ore-bearing rock series. Geochemical data suggest that elements rich in high-organic cryptocrystalline kaolinite are produced from the adsorption effect of organic matter, whereas the low concentration of these elements in pure kaolinite can be attributed to the scavenging effect during kaolinite crystallization. In addition, coexisting organic matter, cryptocrystalline kaolinite, and sulfide and sulfate minerals (see sample XSB-14) indicate that the forming environment of the bauxite was hot, humid tropical or subtropical climates.

Geological and geochemical studies of the Shujiadian porphyry Cu deposit, Anhui Province, Eastern China: Implications for ore genesis

Most porphyry deposits in the world occur in magmatic arc settings and are related to subduction of oceanic plates. A small proportion of porphyry deposits occur in intracontinental settings, however they are still poorly understood. Shujiadian, a newly-discovered porphyry Cu deposit, is located in the Middle–Lower Yangtze River Valley metallogenic belt and belongs to the intracontinental class. The deposit has classic alteration zones defined by a core of potassic alteration and local Ca-silicate alteration, which is overprinted by a feldspar-destructive alteration zone and cut by veins containing epidote and chlorite. Wallrocks of the deposit are unreactive quartz-rich sedimentary rocks.Three main paragenetic stages have been recognized based on petrographic observations; silicate stage, quartz-sulfide stage, and sulfide-carbonate stage. Quartz+pyrite+chalcopyrite±molybdenite veins, and quartz+chalcopyrite+pyrite veins of the quartz-sulfide stage contribute most of the copper, and chalcopyrite+chlorite±pyrite±pyrrhotite±quartz±illite veins of the sulfide-carbonate stage also contribute part of the copper; all the mineralized veins are associated with feldspar-destructive alteration. Investigations on the fluid inclusions in Shujiadian indicate that the ore-forming fluids had four evolutionary episodes: immiscibility and overpressure in the silicate stage, boiling in the quartz-sulfide stage and mixing with meteoric water in the sulfide-carbonate stage. Sulfur and strontium isotope studies suggest that ore metals were mainly derived from magmatic–hydrothermal fluids, and combined with our study of fluid inclusions, we infer that decompression, changes in oxygen fugacity and sulfur content were the main factors that caused Cu precipitation. Compared with porphyry deposits in magmatic arc settings, there are some differences in the ore-bearing rock, alteration, and the composition of ore-forming fluids.

The Lac Des Iles Palladium Deposit, Ontario, Canada. Part II. Halogen variations in apatite

Analysis of apatite from the Mine Block Intrusion (MBI) of the Lac des Iles Igneous Complex shows two pronounced trends in the halogens. Apatite from relatively fresh norite and melanorites from the Pd-sulfide zone contain up to 57 mol% chlorapatite endmember with significant hydroxyapatite component. In contrast, in altered rock (amphibolite and greenschist assemblages) the chlorapatite component is typically less than 10 mol% with wide variation in the F- and OH-endmember components. The latter trend is attributed to Cl loss to degassing and alteration, whereas the former is attributed to Cl enrichment in the ore-bearing rocks. It is suggested that the relatively H2O-rich and intermediate Cl content of the early igneous fluids degassed from the deeper levels of the MBI can explain the high Pd/Pt and Pd/Ir ratios of the deposit. A model is presented in which disseminated Pd-rich sulfides are initially introduced by a high-temperature magmatic fluid that also influenced crystallization to produce the gross modal variations of the igneous host rock. This high-temperature mineralization event was subsequently modified by the influx of late igneous and country fluids at amphibolite to greenschist conditions.

Extraction of Prospecting Information for Sedimentary-Metamorphic Type Iron Deposit Based on Ziyuan-3 Satellite Data — Taking Xinjiang Taxkorgan Area as an Example

In this study, the significance and content of prospecting information of sedimentary-metamorphic type iron deposit are expounded. Ziyuan-3 high spatial resolution satellite data are used to extract the prospecting information of sedimentary-metamorphic type iron deposit in taxkorgan area in Xinjiang. By using the pertinent methods of image processing, the information of ore-bearing bed, ore-control structures have been extracted, and based on the ferric altered mineral spectrum characteristics, the ratio method also has been used to extract iron mineral anomalies in study area. Based on the ore-control structure, ore-bearing rocks and ferric anomalies information, 2 remote sensing prospecting targets have been circled. Our research have laid foundation for the evaluation of mineral resources in this region, and also broadened the thinking for domestic high resolution image scale application in geology and mineral resources.

Structure and texture of ores from the Pravourmiisky deposit in the Khabarovsk region of Russia as evidence for its formation conditions

The structure and texture of the ores and ore-bearing metasomatic rocks at the Pravourmiisky tin-tungsten deposit are discussed. The zonal distribution of various genetic and morphological types of structure and texture has been revealed in vertical sections of the ore zone. The most diversity with a prevalence of cataclastic texture is characteristic of the middle (in section) ore zone segment, where the main economic greisen-type tin mineralization is hosted. Upsection, this mineralization gives way to the quartz-tourmaline Cu ore with widespread exsolution microtextures indicating high-temperature ore deposition. The structural and textural diversity of the ore is caused by the long-term geological history of the deposit under conditions of low-amplitude strike-slip and thrust faulting when compression was repeatedly followed by periods of relative quiescence or weak extension.

Kizilcaören ore-bearing complex with carbonatites (northwestern Anatolia, Turkey): Formation time and mineralogy of rocks

The results of isotope-geochronological and mineralogical studies of the rocks making up the Kizilcaoren fluorite-barite-REE deposit, northwestern Anatolia, Turkey are discussed in the paper. The ore is a constituent of the subvolcanic complex localized in a large fault zone. The complex combines (from earlier to later rocks): (1) phonolite and trachyte stocks, (2) carbonatite and carbonate-silicate dikelike bodies; and (3) fluorite-barite-bastnaesite ore in the form of thick homogeneous veins and cement in breccia. The K-Ar dating of silicate igneous rocks and carbonatites shows that they were formed in the Chattian Age of the Oligocene 25–24 Ma ago. Mineralogical observations show that the ore is the youngest constituent in the rock complex. Supergene alteration deeply transformed ore-bearing rocks, in particular, resulting in leaching of primary minerals, presumably Ca-Mn-Fe carbonates, and in cementation of the residual bastnaesitefluorite framework by Fe and Mn hydroxides. Most of the studied rocks contain pyrochlore, LREE fluorocarbonates, Nb-bearing rutile, Fe-Mg micas, and K-feldspar. The genetic features of the deposit have been considered. In general, the ore-bearing rock complex is compared in the set of rocks and their mineralogy and geochemistry with deposits of the Gallinas Mountains in the United States, the Arshan and Khalyuta deposits in the western Transbaikalia region, and Mushugai-Khuduk deposit in Mongolia. The Kizilcaoren deposit represents a variant of postmagmatic mineralization closely related to carbonatite magmatism associated with alkaline and subalkaline intermediate rocks.

Genesis of garnet-bearing rocks at the Berezitovoe deposit, Upper Amur Region, Russia

The geological position, composition of mineral assemblages, and typomorphism of major minerals from garnet-bearing rocks at the Berezitovoe gold-base-metal deposit in the Upper Amur Region have been studied in detail. These are ore-bearing metasomatic rocks and metamorphosed porphyritic dikes. The garnet-bearing metasomatic rocks reveal zoning, which is caused by various degrees of metasomatic transformation of the Paleozoic porphyritic granodiorite that hosts the ore zone. The metasomatic replacement of granodiorite was accompanied by loss of Na, Ca, Ba, Sr and gain of K, Mn, and Rb. Garnet-bearing metamorphosed intermediate dikes occur within the metasomatic zone. The PT conditions of metamorphism and metasomatism are similar and estimated at 3.9 kbar and 500°C from various mineral equilibria. The results of physicochemical simulation of garnet-bearing mineral assemblages carried out by minimizing the Gibbs free energy and the geological data show that garnet-bearing mineral assemblages arose at the Berezitovoe deposit as a result of local high-temperature thermal metamorphism of previously formed low-temperature metasomatic rocks close in composition to classic beresite. In this connection, we propose considering garnet-bearing metasomatic rocks as high-temperature metamorphosed beresites.