Geochemical and mineralogical evidence for a coal-hosted uranium deposit in the Yili Basin,Xinjiang, northwestern China

The petrological, geochemical, and mineralogical compositions of the coal-hosted Jurassic uranium ore deposit in the Yili Basin of Xinjiang province, northwestern China, were investigated using optical microscopy and field emission-scanning electron microscopy in conjunction with an energy-dispersive X-ray spectrometer, as well as X-ray powder diffraction, X-ray fluorescence, and inductively coupled plasma mass spectrometry. The Yili coal is of high volatile C/B bituminous rank (0.51–0.59% vitrinite reflectance) and has a medium sulfur content (1.32% on average). Fusinite and semifusinite generally dominate the maceral assemblage, which exhibits forms suggesting fire-driven formation of those macerals together with forms suggesting degradation of wood followed by burning. The Yili coals are characterized by high concentrations of U (up to 7207 μg/g), Se (up to 253 μg/g), Mo (1248 μg/g), and Re (up to 34 μg/g), as well as As (up to 234 μg/g) and Hg (up to 3858 ng/g). Relative to the upper continental crust, the rare earth elements (REEs) in the coals are characterized by heavy or/and medium REE enrichment. The minerals in the Yili coals are mainly quartz, kaolinite, illite and illite/smectite, as well as, to a lesser extent, K-feldspar, chlorite, pyrite, and trace amounts of calcite, dolomite, amphibole, millerite, chalcopyrite, cattierite, siegenite, ferroselite, krutaite, eskebornite, pitchblende, coffinite, silicorhabdophane, and zircon. The enrichment and modes of occurrence of the trace elements, and also of the minerals in the coal, are attributed to derivation from a sediment source region of felsic and intermediate petrological composition, and to two different later-stage solutions (a U–Se–Mo–Re rich infiltrational and a Hg–As-rich exfiltrational volcanogenic solution). The main elements with high enrichment factors, U, Se, As, and Hg, overall exhibit a mixed organic–inorganic affinity. The uranium minerals, pitchblende and coffinite, occur as cavity-fillings in structured inertinite macerals. Selenium, As, and Hg in high-pyrite samples mainly show a sulfide affinity.     

Enrichment of U-Re-V-Cr-Se and rare earth elements in the Late Permian coals of the Moxinpo Coalfield,Chongqing, China: Genetic implications from geochemical and mineralogical data

Rare metals in coal deposits have attracted much attention in recent years because of their potential economic significance. This paper reports the abundance and enrichment origin of rare metals in the Late Permian coals (K1 and K2 Coals) of the Moxinpo Coalfield, Chongqing, southwestern China. The K1 Coal is characterized by highly-elevated concentrations of U-Re-V-Cr-Se and Nb(Ta)-Zr(Hf)-REE assemblages; the latter assemblage is also enriched in the K2 Coal. The high temperature ash (815 °C) of the K1 Coal is enriched in V, Cr, Se, Re, U and REE; the ash of the K2 Coal, and also the floor strata of each seam, are enriched in REE, potentially making all of the units economically viable sources for these elements.The minerals in the K1 Coal are mainly represented by kaolinite, illite and mixed-layer illite/smectite, and pyrite, while the minerals in the K2 Coal consist mainly of kaolinite and tobelite [(NH₄,K)Al₂(AlSi₃O₁₀)(OH)₂]. Authigenic roscoelite [K(V^3 +,Al)₂(AlSi₃O₁₀)(OH)₂] is commonly observed in the K1 Coal under the SEM, and was probably formed by interaction of kaolinite with V derived from permeating U-Re-V-Cr-Se-rich solutions during early diagenesis. The tobelite enriched in the K2 Coal was formed by reaction between kaolinite already present in the coal and NH^4 + derived from decomposition of the organic matter during hydrothermal alteration at a relatively high temperature.The mafic tuffs directly underlying the K1 Coal and containing limestone residual breccias not only served as the substrate for coal accumulation but also as the source of sediment from the uplifted areas around the coal basin. The latter is indicated by low Al₂O₃/TiO₂ ratios (from 10.09 to 14.24), positive Eu anomalies enrichment of medium rare earths (relative to upper continental crust), and detrital calcite of terrigenous origin. The highly-elevated concentrations of U-Re-V-Cr-Se assemblages in the coal were derived from exfiltrational hydrothermal solutions and were then deposited in a euxinic environment. The terrigenous materials in the K2 Coal, however, were derived from felsic-intermediate rocks at the top of the Kangdian Upland, although the elevated concentrations of Nb(Ta)-Zr(Hf)-REE assemblages are attributed to the input of hydrothermal solutions.     

Mineral and geochemical compositions,regularities of distribution,and specific formation of ore mineralization of the Rogovik gold-silver deposit (northeastern Russia)

New data on the mineral composition and the first data on the geochemical composition of ores of the Rogovik gold-silver deposit (Omsukchan ore district, northeastern Russia) have been obtained. Study of the regularities of the spatial distribution of ore mineralization shows that the deposit ores formed in two stages. Epithermal Au-Ag ores of typical poor mineral and elemental compositions were generated at the early volcanic stage. The major minerals are low-fineness native gold, electrum, acanthite, silver sulfosalts, kustelite, and pyrite. The typomorphic elemental composition of ores is as follows: Au, Ag, Sb, As, Se, and Hg. The content of S is low, mostly < 1%. Silver ores of more complex mineral and elemental compositions were produced under the impact of granitoid intrusion at the late volcanoplutonic stage. The major minerals are high-Hg kustelite and native silver, silver sulfosalts and selenides, fahlore, pyrite, chalcopyrite, galena, and sphalerite. The typomorphic elemental composition of ores is as follows: Ag, As, Sb, Se, Hg, Pb, Zn, Cu, and B. The content of S is much higher than 1%. The ores also have elevated contents of Mo, Ge, F, and LREE (La, Ce, and Nd). At the volcanoplutonic stage, polychronous Au-Ag ores formed at the sites of the coexistence of silver and epithermal gold-silver mineralization. Their specific feature is a multicomponent composition and a strong variability in chemical composition (both qualitative and quantitative). Along with the above minerals, the ores contain high-Hg gold, hessite, argyrodite, canfieldite, orthite, fluorapatite, and arsenopyrite. At the sites with strongly rejuvenated rocks, the ores are strongly enriched in Au, Ag, Hg, Cu, Pb, Zn, Ge, Se, La, Ce, Nd, S, and F and also contain Te and Bi. The hypothesis is put forward that the late silver ores belong to the Ag-complex-metal association widespread in the Omsukchan ore district. A close relationship between the ores of different types and their zonal spatial distribution have been established. In the central part of the Rogovik deposit, epithermal Au-Ag ores are widespread in the upper horizons, Ag ores are localized in the middle horizons, and rejuvenated polyassociation Au-Ag ores occur at the sites (mostly deep-seated) with ore-bearing structures of different ages.     

Marbles and carbonate rocks from central Morocco: a petrographic,mineralogical and geochemical study

Petrographic, mineralogical, and stable isotopes (δ¹³C, δ¹⁸O values) compositions were used to characterise marbles and sedimentary carbonate rocks from central Morocco, which are considered to be a likely source of ornamental and building material from Roman time to the present day. This new data set was used in the frame of an archaeometric provenance study on Roman artefacts from the town of Thamusida (Kenitra, north Morocco), to assess the potential employment of these rocks for the manufacture of the archaeological materials. A representative set of samples from marbles and other carbonate rocks (limestone, dolostone) were collected in several quarries and outcrops in the Moroccan Meseta, in a region extending from the Meknes–Khenifra alignment to the Atlantic Ocean. All the samples were studied using a petrographic, mineralogical and geochemical methods. The petrographic and minerological investigations (optical microscopy, electron microscopy, X-ray diffraction) allowed to group the carbonate rocks in limestones, foliated limestone, diagenetic breccias and dolostone. The limestones could be further grouped as mudstones, wackestones–packstones, crinoid grainstones, oolitic grainstone and floatstones. Textural differences allowed to define marbles varieties. The stable carbon and oxygen isotope composition proved to be quite useful in the discrimination of marble sources, with apparently less discriminatory potential for carbonate rocks.     

Modes of occurrence of minerals in the Carboniferous coals from the Wuda Coalfield,northern China: with an emphasis on apatite formation

The mineralogical compositions of the Nos. 9 and 13 coals, which are medium-volatile bituminous coals in rank, from the Wuda Coalfield at the northwestern margin of the Ordos Basin in northern China, were investigated by optical microscopy, field emission-scanning electron microscopy in conjunction with energy-dispersive X-ray spectrometry (SEM-EDX), and X-ray powder diffraction techniques. The minerals in the Wuda coals are mainly represented by quartz, kaolinite, illite, pyrite, marcasite, apatite, dolomite, and ankerite, with trace amounts of anatase, calcite, boehmite, jarosite, gibbsite, anhydrite, and bassanite in some samples. The rod-like pyritized bacteria have been identified with SEM-EDX in Wuda coals. Moreover, the slightly reducing and alkaline environment in the original peat swamp favored bacterial action and propagation. The average concentrations of P₂O₅ in the Nos. 9 and 13 coals are 0.47 and 0.18 %, respectively. Phosphorus is not uniformly distributed within the Wuda coal seam. The maximum content of apatite in Wuda coals in certain horizon can reach up to 91.4 % (on an organic matter-free basis), corresponding to the fluorine and P₂O₅ concentrations of 2803 μg/g and 5.96 %. The high proportion of fluorine and P₂O₅ in the Wuda coals is mainly due to the authigenic apatite. The phosphorus in Wuda coals was probably derived mainly from phospho-proteins in the organic matter of the original peat deposits.     

Authigenic carbonate precipitates from the NE Black Sea: a mineralogical,geochemical, and lipid biomarker study

Carbonate precipitates recovered from 2,000 m water depth at the Dolgovskoy Mound (Shatsky Ridge, north eastern Black Sea) were studied using mineralogical, geochemical and lipid biomarker analyses. The carbonates differ in shape from simple pavements to cavernous structures with thick microbial mats attached to their lower side and within cavities. Low δ¹³C values measured on carbonates (−41 to −32‰ V-PDB) and extracted lipid biomarkers indicate that anaerobic oxidation of methane (AOM) played a crucial role in precipitating these carbonates. The internal structure of the carbonates is dominated by finely laminated coccolith ooze and homogeneous clay layers, both cemented by micritic high-magnesium calcite (HMC), and pure, botryoidal, yellowish low-magnesium calcite (LMC) grown in direct contact to microbial mats. δ¹⁸O measurements suggest that the authigenic HMC precipitated in equilibrium with the Black Sea bottom water while the yellowish LMC rims have been growing in slightly ¹⁸O-depleted interstitial water. Although precipitated under significantly different environmental conditions, especially with respect to methane availability, all analysed carbonate samples show lipid patterns that are typical for ANME-1 dominated AOM consortia, in the case of the HMC samples with significant contributions of allochthonous components of marine and terrestrial origin, reflecting the hemipelagic nature of the primary sediment.     

Neotectonic stage in the formation of the Khokhlovskoe uranium deposit, eastern Transural region: Structural, hydrochemical, mineralogical, and geochemical formation conditions

The structural, hydrochemical, mineralogical, and geochemical features of the Khokhlovskoe uranium deposit related to neotectonic processes are considered. The structural feature is expressed in neotectonic dislocations in the form of overall intense fragmentation of host rocks and widespread low-amplitude strike-slip faulting. The hydrochemical specificity is determined by the appearance of thermal carbonated formation water in ore-bearing aquifers. This water is similar in chemical and gas composition to hydrothermal solutions in fluid inclusions and mineral waters abundant in this district. The mineralogical and geochemical features comprise the occurrence of newly formed ferroan carbonates and late iron hydroxides in altered (bleached) pelitic rocks; the formation of silicic opal segregations in ore-bearing sand and sandstone; late sulfides, arsenides, and selenides of iron and other metals; and multiphase gel-pitchblende enriched in Zr especially typical of high-grade uranium ore. The age of high-grade ore determined by a precision uranium-ionium method coincides with the time when thermal carbonated water appeared in the host rocks. This time was estimated from a mathematical model of heat transfer and regional dynamics of underground water. This coincidence clearly indicates that the aforementioned processes are related to the late Quaternary neotectonic reactivation of the eastern Transural region.     

The Kalguty complex deposit, the Gorny Altai: Mineralogical and geochemical characteristics and fluid regime of ore formation

The results of detailed mineralogical, geochemical, and thermobarogeochemical studies of the Kalguty complex greisen deposit are presented. The chemical compositions of ore veins, greisens, and other geological bodies have been determined. A wide range of chemical elements from Li to U (48 elements, including noble metals and REE) has been determined in ore minerals. Graphite in association with quartz and sulfides was identified in ore veins for the first time. Graphite is enriched in a light carbon isotope. The δ¹³C value varies from ?26.3 ± 0.4 to ?26.6 ± 0.3‰. High Au, Ag, Hg, Te, Sb, Bi, Cu, Pb, Zn, Fe, and S contents were detected in graphite grains with a microprobe. The graphite content increases regularly with depth; the spatial correlation of graphite with W, Mo, Cu, Au, Pt, Pd, and other metals is established. The highest Au, Ag, Pt, Pd, and Os contents are characteristic of minor intrusions of albitized granite porphyry (γπ₂J₁vk), intramineral dikes of hydrothermally altered kalgutite (γπ₃J₁vk), ore veins, their greisen selvages, and autonomous ore-bearing greisen bodies of the Mo stock type. Gold occurs in native form, while silver is contained largely in sulfides and sulfosalts. High PGE contents are characteristic of pyrite, wolframite, and molybdenite. The major components of fluid inclusions in quartz (H₂O, CO₂, CO, and H₂) have been studied, as well as hydrocarbons (CH₄, C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₆H₁₄, C₂H₂, and C₂H₄) contained therein. Two-phase fluid inclusions are predominant, while single-and three-phase inclusions are less abundant. The homogenization temperatures of primary and secondary inclusions are 290–340 and 140–160°C, respectively. The concentration of dissolved salts (NaCl and KCl) in two-phase inclusions amounts to 11.6–14.0%. The H₂O and CO₂ contents decrease with depth, whereas the CO, H₂, and HC concentrations increase in the same direction. Graphite is regarded as a product of reactions with participation of fluid (gas) components. The ore mineralization was formed under contrasting conditions related to the oxidation of a primary reduced deep metalliferous fluid.     

A comparative mineralogical and geochemical study of sulfide mine tailings at two sites in New Mexico, USA

A comparative study of sulfide mine tailings from two sites near Silver City in southwest New Mexico has shown the need for environmental monitoring in a geological context. The Cyprus-Piños Altos and Cleveland deposits consist of Cu and Zn skarn mineralization in the Piños Altos Mountains of New Mexico. Primary ore minerals in both deposits include chalcopyrite, sphalerite, and galena. The Cyprus-Piños Altos Mine ceased operation in 1995 and the Cleveland Mill closed in 1950. The deposits have similar mineralogical characteristics; however, the tailings are different in terms of age, degree of oxidation and method of disposal. The Cyprus-Piños Altos tailings (CPAT) are stored in a lined, bermed impoundment. They are dominantly water-saturated and exhibit no secondary-phase formation. The grains are not cemented and show no evidence of primary-mineral dissolution. The geochemical data show a predominantly primary signature. The tailings pond water is neutral to slightly alkaline (pH?from 7 to 8.3), partly as a result of processing methods. The Cleveland mill tailings (CMT) were deposited in a valley at the headwaters of an ephemeral stream. They are highly oxidized and differentially cemented. They have undergone numerous wet/dry cycles resulting in extensive oxidation. Secondary minerals predominate, and consist mainly of jarosite, goethite, hematite, and Fe-oxyhydroxides and -oxyhydroxysulfates. The pH of the stream draining the CMT is as high as 2.15. Maximum metal contents in the stream immediately downstream from the tailings are 5305?ppm Zn, 454?ppm Cu, 1.16?ppm Pb, 17.5?ppm Cd, 1.4?ppm As, and 0.01?ppm Hg.     

Genesis and formation conditions of deposits in the unique Strel’tsovka Molybdenum-Uranium ore field: New mineralogical,geochemical, and physicochemical evidence

The ambiguity of genetic interpretations of uranium ore formation at Mo-U deposits of the Strel’tsovka ore field led us to perform additional geochemical, mineralogical, and thermobarogeochemical studies. As a result, it has been established that closely related U and F were progressively gained in the Late Mesozoic volcanic rocks from the older basic volcanics (170 Ma) to the younger silicic igneous rocks (140 Ma). The Early Cretaceous postmagmatic hydrothermal epoch (140–125 Ma) is subdivided into preore, uranium ore, and first and second postore stages. The primary brannerite-pitchblende ore was formed in association with fluorite. At the first postore stage, this assemblage was replaced by a U-Si metagel, which was previously identified as coffinite. The metagel shows a wide compositional variation; its fine structure has been studied. The preore metasomatic alteration and related veined mineralization were formed under the effect of sodium (bicarbonate)-chloride solution at a temperature of 250–200°C. The uranium ore formation began with albitization and hematitization of rocks affected by supercritical fluid at 530–500°C; brannerite and pitchblende precipitated at 350–300°C. The chondrite-normalized REE patterns of pitchblende hosted in trachybasalt, trachydacite, and granite demonstrate a pronounced Sm-Nd discontinuity and a statistically significant tetrad effect of W type. These attributes were not established in REE patterns of rhyolites derived from the upper crustal magma chamber. This circumstance and a chronological gap of 5 Ma between silicic volcanism and ore formation do not allow us to suggest that uranium was derived from this magma chamber. According to the proposed model, the evolved silicic Li-F magma was a source of uranium. U⁴⁺, together with REE, was fractionated into the fluid phase as complex fluoride compounds. The uranium mineralization was deposited at a temperature barrier. It is suggested that hydromica alteration and the formation of molybdenum mineralization were genetically unrelated to the uranium ore formation.     

Chemical compositions of sulfides in the porphyry Cu ores,Yangla Cu deposit,Yunnan, China: implication for ore genesis

Acta Geochimica - The Yangla Cu deposit is the largest ore deposit in the Jinshajiang polymetallic metallogenic belt, northwest Yunnan, China. There is no consensus on the genesis of the ore...     

东南亚红土镍矿床地质地球化学特征及成因探讨——以印尼苏拉威西岛Kolonodale矿床为例

Kolonodale矿床是东南亚红土镍矿带上一处典型矿床,位于印度尼西亚苏拉威西岛东部。矿床产自富镁超基性岩红土风化壳,矿化剖面自上而下出现红土层→腐岩层→基岩层垂向分带。红土镍矿石产在红土剖面上部,载镍矿物是铁质氧化物。硅镁镍矿石产在红土剖面中下部,载镍矿物为镍蛇纹石、镍滑石等含水层状硅酸盐矿物。地球化学分析显示,沿矿化剖面元素地球化学分异非常显著,Ni次生富集效应明显。超基性岩红土化过程的元素地球化学行为具有多样性,Fe、Al、Ti、Cr属残留富集组分,Si、Mg属淋滤缺失组分,Mn、Ca、Co、Ni属次生富集组分。通过典型矿床对比,Kolonodale矿床属原地自生硅酸盐型红土镍矿床,其发育受地质背景和地表环境条件的综合制约。富镁超基性岩、良好的构造组合、稳定的大地构造环境、湿热热带雨林气候、有利地形地貌等均是成矿有利条件。综合分析认为,Kolonodale矿床的成矿过程可划分为腐岩化、红土化和次生富集3个成矿阶段。     

The Hemlo gold deposit,Ontario: A geochemical and isotopic study

The Hemlo deposit, near Marathon, Ontario, is one of the largest gold deposits in North America. It is stratiform within Archean metamorphosed volcano-sedimentary rocks. The main ore zone is composed of pyritic, sericitic schist, and massive barite. This is the first report of stratiform barite in the Archean of North America, but other occurrences have since been found west of Hemlo. The mineralization is substantially enriched in Au, Mo, Sb, Hg, Tl and V and lacks carbonate. Because of metamorphism and deformation of the body its genesis is uncertain.${}^{87}\text{Sr}{}^{86}\text{Sr}$ of .7017 for barite from the deposit is similar to that of the sedimentary barite west of Hemlo and to initial ratios of contemporaneous volcanic rocks. At the base of the main ore zone, barite with δ^34S of +8 to +12%. was deposited with ~0%. pyrite. Upward, both barite and pyrite get isotopically lighter, with minimum values for pyrite, to ?17.5%, in non-baritic schist forming the upper part of the ore zone. In drill section, Au grades correlate with the isotopic composition of pyrite. This, and the association of fractionated sulphide with sulphate, suggests that Au, pyrite and barite were deposited contemporaneously. The linked, asymmetric distributions of S minerals and isotopic distributions, which are continuous from section to section, and the isotopic similarity of the Hemlo and western barites are consistent with a syngenetic depositional model.Two sources for the S minerals are considered. In the first, exogenous sulphate from a restricted basin were partially reduced in a geothermal system to form ³⁴S-depleted sulphide. In the second, the sulphate and sulphide are of magmatic-hydrothermal origin. Sulphate and fractionated sulphide are uncommon in Archean rocks, but one or both occur with unusual frequency in major Archean gold deposits. Hydrothermal fluids of moderately high , containing sulphate and permitting isotopic fractionation between oxidized and reduced S species, may have favoured the dissolution, transport and precipitation of Au.     

MVT矿床中与成矿有关热液方解石的地球化学判据——以青海多才玛超大型铅锌矿床为例

碳酸盐矿物是MVT型铅锌矿床最为常见的热液蚀变矿物,记录了成矿流体特征,其元素或同位素组成对示踪和定位矿体具有一定的指示意义,但由于该类矿床中碳酸盐矿物成因多样,单一的岩相学观察往往难以准确识别与成矿有关和无关的方解石,需要辅以地球化学手段来确定方解石成因。本文利用钻孔编录、岩相学观察、C-O-Sr同位素和原位微量与稀土元素组成分析等手段,探讨了青海多才玛超大型MVT铅锌矿床中与成矿有关和无关两期方解石的矿物化学特征。结果表明,多才玛矿床成矿前方解石(Cal1)空间上与矿体无相关关系,遍布于中二叠统九十道班组灰岩内,阴极发光呈暗棕色至棕黄色,无明显生长环带;成矿期方解石(Cal2)主要产于铅锌矿体内及其上盘围岩中,多呈砂糖粒状-皮壳状充填于围岩裂隙和溶孔内,阴极发光呈暗黄色至亮橙色,常发育生长环带。相对于Cal2, Cal1与围岩的C-O-Sr同位素组成更为接近,这表明水岩反应期间,Cal1组成受围岩影响更大,Cal2组成受影响更小;相比于Cal1,Cal2具有较高的Mn、Fe、Zn、Pb含量和U/Th、V/Cr值以及较低的LREE/HREE值、Mg、Sr含量和弱的Ce负异常,指示成矿...     

Nakhlak carbonate-hosted Pb(Ag) deposit,Isfahan province,Iran: a geological,mineralogical, geochemical,fluid inclusion,and sulfur isotope study

The Upper Cretaceous Nakhlak epigenetic vein-type Pb(Ag) deposit is located 55 km northeast of the town of Anarak in Isfahan Province, Iran. The deposit contains 7 Mt of galena-barite ore with an average grade of 8.33% Pb, 0.38% Zn, and 72 ppm Ag. The ore mineralization occurs as stratabound, epigenetic, steeply dipping, east-west–trending veins in faulted- or fracture-controlled Upper Cretaceous Sadar carbonates. Galena and barite are the primary minerals. Minor sphalerite, tennantite-tetrahedrite, pyrite, and chalcopyrite occur as inclusions in galena. Cerussite with minor amounts of anglesite and plattnerite formed in the oxidized supergene zone. The ore and ore-related minerals were deposited in the hydrothermally dolomitized carbonate host rock containing saddle-shaped dolomite. Geochemically, the dolomitized carbonate host rocks are enriched in MgO, Fe₂O₃, MnO, Pb, Zn, and Ba, but depleted in CaO. The galena concentrate contains high values of Ag (932 ppm), Sb (342 ppm), Cu (422 ppm), As (91 ppm), and Zn (296 ppm); the presence of these trace elements indicates a low-temperature type of galena mineralization. This interpretation is corroborated by fluid inclusions containing 12.98 wt.% NaCl equivalent salinity; the inclusions homogenize at the low temperature of about 152.1 °C. The similarity between δ³⁴S_(V-CDT) values in Nakhlak barite and Permian–Triassic δ³⁴S marine sulfate values indicates that the Nakhlak sulfur was probably provided from evaporates of Permian–Triassic age. The δ³⁴S_(V-CDT) values of galena and barite samples occupy the ranges of − 1.04‰ to + 8.62‰ and + 10.95‰ to + 13.71‰, respectively, and are similar to Mississippi Valley–type (MVT) deposits. The low-temperature basinal fluids, evaporate-originated sulfur, and fault- or fracture-controlled galena-rich veins in the Nakhlak deposit resemble the type of geological features documented in Pb-rich MVT deposits.     

西藏多龙矿集区铜元素遥感地球化学模型

遥感在一定程度上可以反映地物元素含量的特征,利用遥感反演元素特征在地质工作程度低地区或者国外地质资料难以获取地区可以提供一个参数。本文根据元素含量与光谱关系,建立了波段相关斜率、波段的斜率指数、波段相关吸收深度指数、波段的相关多项式指数这4个遥感地球化学反演模型的指标,以西藏多龙矿集区为研究区,通过回归算法反演了铜元素遥感地球化学,并经过F检验证实反演可信,比较预测值与实际值吻合较好,最后把实测铜元素地球化学、蚀变遥感异常与遥感反演铜元素地球化学进行了对比,证实遥感铜元素地球化学反演结果较好,且可以作为一个独立的遥感参数。     

Petrogenesis of Dongguashan skarn-porphyry Cu-Au deposit related intrusion in the Tongling district,eastern China: Geochronological,mineralogical, geochemical and Hf isotopic evidence

The Dongguashan skarn-porphyry Cu-Au deposit, located in the Tongling district of the Middle-Lower Yangtze River Valley metallogenic belt (MLYB), consists of skarn ore bodies in the upper part and porphyry ore bodies in the lower part, both of which are hosted in quartz diorite and quartz monzodiorite. Zircon U-Pb age and geochemical studies show that the quartz diorite of the Dongguashan intrusion formed at 140.3 ± 2.0 Ma (MSWD = 0.19) and belongs to the high potassium calc-alkaline series. It is enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), depleted in high field-strength elements (HFSE) and heavy rare earth elements (HREE), and has a slightly negative Eu anomaly. ¹⁷⁶Hf/¹⁷⁷Hf values of the rims of zircons show a variable range (0.282087–0.282391), corresponding with calculated ε_Hf(t) values of − 10.72 to − 21.46. Plagioclases in the quartz diorite have unbalanced structure characterized by bright andesine and labradorite (An = 37.0–65.5) cores with higher contents of Fe and Sr and are corroded by dark oligoclase (An = 13.8–27.6) rim. Major elements, trace elements, Hf isotope, and the composition of plagioclases indicate that the parental magma of the Dongguashan intrusion was produced by the mixing of underplating mafic magma and felsic magma formed by remelting of Paleoproterozoic and Neoarchean crustal rocks, Neoproterozoic crust may also provide some material to the felsic magma. Mafic magma played a key role and made the parental magma rich in water, sulfur, metals (Cu, Au) and gave it a high oxygen fugacity. During its magmatic evolution, the parental magma underwent fractional crystallization of hornblende, apatite, sphene and other mafic minerals. Some quartz diorite and quartz monzodiorite samples that show adakitic signatures, may result from injection of mafic magma. Some inherited zircons of the quartz diorite in the Dongguashan intrusion gave ages of 2.40–2.50 Ga, 1.95–2.05 Ga and 0.74–0.81 Ga, coming from ultramafic, mafic and andesitic igneous rocks, and this indicates that there may have been three periods (2.4, 2.0, and 0.8 Ga) of magmatic activity in the Tongling district.     

西沙海槽研究区天然气水合物地球化学勘探及成藏模式研究

依据ODP204航次1250C站位钻井样品酸解烃数据结果,以及作者在南海西沙海槽研究区天然气水合物地球化学现场勘查中得到的多种烃类指标数据、异常点上微量甲烷碳同位素数值等资料,对海洋水合物地球化学勘探的依据和研究区气态烃异常特征、气体成因、天然气水合物成藏模式等相关问题进行了研究探讨。结果表明:气态烃指标地球化学异常主要分布在工区北部斜坡地带,并与BSR等地震标志及深部断裂关系密切;西沙海槽研究区海底沉积物气态烃甲烷以热解成因为主,但也有混合成因;推测该区天然气水合物为断层渗滤综合成藏模式。研究成果比较合理地解释了BSR分布和海底沉积物甲烷局部异常并非完全一致的原因;评价预测了该区天然气水合物有利勘探目标。成果为该区天然气水合物勘探、天然气水合物成因机制研究和天然气水合物远景预测,提供了地球化学方面的证据。     

Genesis of the Zhengguang gold deposit in the Duobaoshan ore field,Heilongjiang Province,NE China: Constraints from geology,geochronology and S-Pb isotopic compositions

The Zhengguang gold deposit in the Duobaoshan ore field, hosted in volcanic rocks of the Middle Ordovician Duobaoshan Formation, is one of the largest gold deposits in the Northeastern Great Xing’an Range of the Central Asian Orogenic Belt (CAOB). The deposit comprises the No. I, II and III ore zones with a total resource exceeding 35 tonnes of Au, 100,000 tonnes of Zn and 100 tonnes of Ag. A genetic relationship between gold mineralization and concealed tonalite porphyry is inferred based on the characteristics of cryptoexplosive breccia and hydrothermal alteration indicative of porphyry-type and epithermal mineralization. Zircon LA-ICPMS U-Pb dating reveals that the tonalite porphyry was emplaced at 462.1 ± 1.8 Ma (Middle Ordovician). The δ³⁴S_V-CDT values of sulfide minerals range from −3.0‰ to −1.7‰ with an average of −2.33‰, indicating that sulfur was mainly derived from a magmatic source. The Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb ranging from 17.572 to 17.629, ²⁰⁷Pb/²⁰⁴Pb from 15.424 to 15.486, and ²⁰⁸Pb/²⁰⁴Pb from 37.206 to 37.418) suggest a major mantle component for Pb and, by inference, for other ore metals. Therefore, we suggest that the ore-forming elements in the Zhengguang gold deposit may be related to the mantle-sourced tonalite porphyry. On the basis of the geological characteristics and geochemical signatures documented in this study, we conclude that the Zhengguang gold deposit was formed in a porphyry to epithermal transitional environment associated with the concealed tonalite porphyry, as part of the Duobaoshan porphyry-epithermal ore system that is related to the subduction of the Paleo-Asian Ocean during the Ordovician.     

云南某硫化铜矿选矿试验

为确定云南某硫化铜矿矿石性质,制定合适的选矿方案.采用化学多元素分析、X射线衍射分析仪(XRD)、物相分析、矿物解离分析(MLA)和扫描电镜等分析测试技术,研究了矿石的矿物组成、连生体矿物共生特性及铜、硫的嵌布状态等.结果 表明,原矿含铜0.141％、硫9.80％,铜主要以硫化铜形式存在,硫的赋存形式以硫化物(黄铁矿)为主.黄铜矿多呈它形粒状,主要与黄铁矿、磁黄铁矿、褐铁矿、菱铁矿、石英、绿泥石共生;黄铁矿多呈它形粒状,主要与磁黄铁矿、菱铁矿、石英、钙铁榴石共生.脉石矿物主要为石英和钙铁榴石.针对矿石性质,采用"混合浮选—铜硫分离"的选铜工艺流程,根据最佳条件参数进行铜硫分离闭路试验,得到了铜品位、回收率分别为15.34％、58.75％的铜精矿;硫品位、回收率分别为30.44％、55.04％,含铁39.13％的硫精矿.相较现场生产指标,铜精矿品位提高了5％,回收率提高了近20％.铜硫分离效果显著,为低品位硫化铜矿铜的回收提供了借鉴.