The Bikkulovskoe manganese deposit (South Urals): Geological setting,composition of metalliferous rocks,and formation model

The results of investigation of the Bikkulovskoe manganese deposit confined to volcanosedimentary piles of the Magnitogorsk paleovolcanic belt are presented. The paper characterizes the geological setting of the deposit and mineral-chemical compositions of ores and enclosing rocks (volcanomictic sandstones; ferruginous, manganiferous, and ferruginous-siliceous tuffites; and jasperites). Analysis of the data obtained made it possible to identify four sequential stages of deposit formation: (1) accumulation and diagenesis of ore-bearing sequences (D_2–3); (2) burial and low-grade (T = 200–250°C, P = 2 to 3 kbar) regional metamorphism of rocks (D_2–3-C₁); (3) tectonic deformations of volcanosedimentary piles (C₂-P); and (4) hypergenesis and partial denudation of rocks (MZ-CZ). According to the model proposed for the accumulation of ore-bearing rocks, the productive member was formed in a zone of hydrothermal solution outflow to the seafloor surface. Discharge of solutions and precipitation of Fe and Si began below the seafloor surface (rather than above the surface) in the near-bottom sequence of volcanomictic sediments. Upon reaching the seafloor, the impoverished solutions mixed with seawater and gave up metals completely: Fe and Mn were transferred to sediments to make up the ore-bearing bed. Thus, zonal sediments with ferruginous tuffites at the base and manganese ores at the top were formed.     

The Pokrovskoe gold-silver deposit (Amur Region): Geological settings, formation factors, and ore mineralogy

The Pokrovskoe gold-silver deposit is explored by drill holes. Its gently dipping orebodies (lodes) revealed by core sampling are quarry mined. It is considered that they also consist of gently dipping quartz veins and vein-stringer zones. The performed investigation of the terraces in the exploited quarries made it possible to correct the available present-day concepts. It is shown that their structure is dominated by steeply dipping veins and vein-stringer zones. They are characterized by the northeastern strike in the central part of the deposit and its western flank and the mostly northwestern one in its eastern part. An important role in the formation and distribution of the orebodies belongs to various geological screens poorly permeable for fluids. The main factors responsible for the ore localization in screened hydrogeological systems are revealed with the assessment of the thermal impact of a dacite sill on the formation of the ore-hosting cavities and ore deposition. The electron microscope investigation of the ores substantially widened the spectrum of ore minerals previously unknown in this deposit, including gold-bearing varieties (copper gold and its complex intermetallic compounds). Based on the dominant micrometer sizes of all the ore minerals and their dispersion within the quartz matrix, it is inferred that the deposition of productive ores occurred in nonequilibrium environments.     

Palladium and gold minerals from the Baronskoe-Kluevsky ore deposit (Volkovsky complex, Central Urals, Russia)

Summary Drill cores from the newly discovered Baronskoe-Kluevsky Pd–Au deposit (Volkovsky massif, Central Urals) have been investigated by reflected-light and electron microscopy, and the ore minerals were analyzed by electron microprobe. The most abundant Platinum-group mineral (PGM) is vysotskite, ideally PdS, characterized by an unusual Pt,Ni-poor composition. Palladium also occurs in kotulskite (PdTe), stillwaterite (Pd₈As₃), and unknown Pd–As–Te compounds with vincentite-type Pd₃(As,Te), stillwaterite-type Pd₈(As,Te)₃, and Pd₇(As,Te)₂ stoichiometries. The main carrier of Au is Pd-rich electrum, approaching the composition Au₇₅Ag₁₅Pd₁₀, with minor Fe, Cu, Ni and Pt. The precious minerals are closely associated with minute blebs of chalcopyrite+magnetite disseminated throughout serpentinized olivine-apatite host rock. Paragenetic relationships among the ore minerals define a succession of crystallization events in the order: 1) Cu–Pd sulfides+electrum, 2) replacement by Pd–Te–As and late Pd–As PGM, 3) final replacement by magnetite. The paragenesis is tentatively related with cooling of a fluid phase in the late- to post-magmatic stage.     

Postorogenic carbonatites at Eden Lake, Trans-Hudson Orogen (northern Manitoba, Canada): Geological setting, mineralogy and geochemistry

The Eden Lake pluton in the Trans-Hudson Orogen is the first known occurrence of carbonatites in Manitoba. The pluton is largely made up of modally and geochemically diverse syenitic rocks derived from postorogenic magma(s) of shoshonitic affinity. Their diversity can be accounted for by a combination of crystal fractionation and fluid release in the final evolutionary stage (crystallization of quartz alkali-feldspar syenite). At Eden Lake, carbonatites, represented predominantly by coarse-grained massive to foliated sövite, occur as branching veins and lenticular bodies up to 4 m in thickness showing crosscutting relations with respect to all of the syenitic units. The host rocks are intensely fenitized at the contact, and there is also abundant mineralogical and textural evidence for assimilation of silicate material by carbonatitic magma through wallrock reaction and xenolith fragmentation and digestion. The bulk of the carbonatites are composed of (in order of crystallization): Sr–REE-rich fluorapatite, aegirine–augite, and coarse calcite crystals surrounded by fine-grained calcite (on average,  90 vol.% of the rock). Noteworthy accessory constituents are celestine, bastnäsite-(Ce) (both as primary inclusions in calcite), Nb–Zr–rich titanite, low-Hf zircon, allanite-(Ce) and andradite. The calcite is chemically uniform (Sr-rich, Mg–Mn–Fe-poor and low in ¹³C), but shows clear evidence of ductile deformation and syndeformational cataclasis. Geochemically, the carbonatites are enriched in Sr, Ba, light rare-earth elements, Th and U, but depleted in high-field-strength elements (particularly, Ti, Nb and Ta). The stable-isotope composition of coarse- and fine-grained calcite from the carbonatites and interstitial calcite from syenites is remarkably uniform: ca. − 8.16 ± 0.27‰ δ¹³C (PDB) and + 8.04 ± 0.19‰ δ¹⁸O (SMOW). The available textural and geochemical evidence indicates that the Eden Lake carbonatites are not consanguineous with the associated syenites and may have been derived from a Nb–Ti-retentive and ¹³C-depleted source such as the subducted crustal material underlying the Eden Lake deformation corridor.     

Geological setting, mineralogy, geochemistry and genesis of the Middle Archaean Kalyadi copper deposit, western Dharwar craton, southern India

The Kalyadi polymetallic copper deposit occurs within the Middle Archaean (≥3.0 Ga), medium-grade Kalyadi schist belt which consists predominantly of ultramafic-mafic schists interbedded with chemogenic chert, detrital high Al-Mg schists and siliceous schists. This sedimentary exhalative type (SEDEX type) ore-body is the only copper deposit hosted in cherts in the western Dharwar craton. The Kalyadi supracrustal rocks are intruded by tonalite-trondhjemitic gneisses (ca. 3.0 Ga) and granite (ca. 2.6 Ga). The Kalyadi copper deposit is polygenetic in nature. The primary ores represented by disseminations of pyrite ± linneite and chalcopyrite ± magnetite essentially along the bedding lamination of the metachert are referred to as the metamorphosed chert-sulphide rhythmites of a primary stratiform type. The ore is of low-grade and records imprints of at least two events of deformation. Pyrite is characterised by high-Co values (262–4524 ppm) and high–Co/Ni ratios (3.0–19.7). Rare earth element patterns of the primary ores and the host metacherts are identical, characterised by La enrichment, absence of Eu anomalies and flat to depleted HREE patterns with δ ³⁴ S = −0.8‰. The secondary (remobilised) ores are structurally controlled occurring as veins and stringers discordant to the bedding lamination or schistosity. The constituent ores are chalcopyrite-pyrite-pyrrhotite with minor pentlandite. These sulphides with low-Co/Ni ratios (0.87–1.80), have either a strong positive or negative Eu anomaly and show slight HREE enrichment. The δ ³⁴ S value ranges from +2.64 to −4.29‰. It is interpreted that the primary stratiform ores and the cherts were derived from volcanogenic hydrothermal fluids as syngenetic/chemical deposits in a deep sea environment. The secondary epigenetic mineralisation is related to subsequent migmatisation, deformational events and granitic activity. Received: 8 September 1995 / Accepted: 18 November 1996     

Lake Boga Granite,northwestern Victoria: mineralogy,geochemistry and geochronology

The Devonian Lake Boga Granite in northern Victoria, while almost entirely under thin Murray Basin cover, is one of the largest plutons in the western Lachlan Fold Belt. Its only exposure is a quarry penetrating the Cenozoic sediments. In the quarry, prominent pod pegmatites and miarolitic cavities suggest a high level of emplacement. The granite, a non-magnetic, fractionated S-type, contains a large range of accessory minerals, including primary uranium- and REE-bearing phosphates and oxides, and primary copper sulfides. Monazite-series minerals show an exceptionally wide range of compositions, from normal monazite-(Ce) through cheralite (Ca – Th-rich) to rare huttonitic monazite (Th-rich) and brabantite; U contents in monazite also vary widely (0 – 7.9 wt%). Primary low-Ca uraninites are well preserved and are unusual in having low Th/U and LREE. Late-stage cavity fluorapatite crystals up to several centimetres across show intricate elemental zoning patterns with extreme U gradients (<10 – 6900 ppm) in some crystals. New ⁴⁰Ar – ³⁹Ar ages for magmatic biotite, muscovite and K-rich feldspar average 365 ± 3 Ma, which approximates the emplacement age of the granite. This is supported by a 377 ± 12 Ma U – Th – Pb (CHIME) age for primary uraninite. New whole-rock geochemical data support earlier observations: the granite is strongly fractionated (SiO₂ 70.7 – 76.0 wt%; 4.2 – 0.6 wt% FeO_t) and peraluminous (ASI = 1.23 – 1.45), and has slightly elevated Na₂O and P₂O₅ (0.30 wt%) contents compared with other fractionated S-type granites from the Lachlan Fold Belt. Trace-element abundances are typical of fractionated granites, although U and Cu concentrations vary strongly and reach >60 and ≈1400 ppm, respectively. REE patterns also vary strongly, from LREE-enriched with moderate Eu depletion, to flat with strong Eu depletion. The flattest of the REE patterns, in samples with FeO_total < 1%, are characterised by M-type tetrad effects. These and other samples also show low (subcrustal average) and variable Zr/Hf (35 – 16) and Nb/Ta (8 – 4) ratios; these and other unusual elemental fractionations are related to changes in elemental partitioning during the late magmatic stage, when felsic peraluminous magma and high-temperature magmatic fluid coexisted.     

Manganese deposits in northeastern European Russia and the Urals: Isotope geochemistry,genesis, and evolution of ore formation

Based on new data on the lithology, mineralogy, chemistry, and isotopic composition of manganese carbonate ores and rocks at the deposits and occurrences in the Novaya Zemlya Archipelago, the Pai-Khoi, and the Urals, as well as using data from the literature, the main Phanerozoic basins of manganese deposition have been established in the geological history of Laurasia, Pangea, and Siberian paleocontinents. The formation conditions of manganese ore gradually changed from hydrothermal-sedimentary in the Middle Paleozoic to sedimentary-diagenetic in Mesozoic and Cenozoic. The ore was also formed under catagenetic conditions. Carbon of oxidized organic matter plays a substantial role in the formation of manganese carbonates.     

Economic minerals of the Kovdor baddeleyite-apatite-magnetite deposit,Russia: mineralogy,spatial distribution and ore processing optimization

The comprehensive petrographical, petrochemical and mineralogical study of the Kovdor magnetite-apatite-baddeleyite deposit in the phoscorite–carbonatite complex (Murmansk Region, Russia) revealed a spatial distribution of grain size and chemical composition of three economically extractable minerals — magnetite, apatite, and baddeleyite, showing that zonal distribution of mineral properties mimics both concentric and vertical zonation of the carbonatite-phoscorite pipe.The marginal zone of the pipe consists of (apatite)-forsterite phoscorite carrying fine grains of Ti–Mn–Si–rich magnetite with ilmenite exsolution lamellae, fine grains of Fe–Mg-rich apatite and finest grains of baddeleyite, enriched in Mg, Fe, Si and Mn. The intermediate zone accommodates carbonate-free magnetite-rich phoscorites that carry medium to coarse grains of Mg–Al-rich magnetite with exsolution inclusions of spinel, medium-grained pure apatite and baddeleyite. The axial zone hosts carbonate-rich phoscorites and phoscorite-related carbonatites bearing medium-grained Ti–V–Ca-rich magnetite with exsolution inclusions of geikielite–ilmenite, fine grains of Ba–Sr–Ln-rich apatite and comparatively large grains of baddeleyite, enriched in Hf, Ta, Nb and Sc. The collected data enable us to predict such important mineralogical characteristics of the multicomponent ore as chemical composition and grain size of economic and associated minerals, presence of contaminating inclusions, etc. We have identified potential areas of maximum concentration of such by-products as scandium, niobium and hafnium in baddeleyite and REEs in apatite.     

Ore geochemistry,zircon mineralogy,and genesis of the Sakharjok Y-Zr deposit,Kola Peninsula,Russia

The Sakharjok Y-Zr deposit in Kola Peninsula is related to the fissure alkaline intrusion of the same name. The intrusion ∼7 km in extent and 4–5 km² in area of its exposed part is composed of Neoarchean (2.68–2.61 Ma) alkali and nepheline syenites, which cut through the Archean alkali granite and gneissic granodiorite. Mineralization is localized in the nepheline syenite body as linear zones 200–1350 m in extent and 3–30 m in thickness, which strike conformably to primary magmatic banding and trachytoid texture of nepheline syenite. The ore is similar to the host rocks in petrography and chemistry and only differs from them in enrichment in zircon, britholite-(Y), and pyrochlore. Judging from geochemical attributes (high HSFE and some incompatible element contents (1000–5000 ppm Zr, 200–600 ppm Nb, 100–500 ppm Y, 0.1–0.3 wt % REE, 400–900 ppm Rb), REE pattern, Th/U, Y/Nb, and Yb/Ta ratios), nepheline syenite was derived from an enriched mantle source similar to that of contemporary OIB and was formed as an evolved product of long-term fractional crystallization of primary alkali basaltic melt. The ore concentrations are caused by unique composition of nepheline syenite magma (high Zr, Y, REE, Nb contents), which underwent subsequent intrachamber fractionation. Mineralogical features of zircon-the main ore mineral—demonstrate its long multistage crystallization. The inner zones of prismatic crystals with high ZrO₂/HfO₂ ratio (90, on average) grew during early magmatic stage at a temperature of 900–850°C. The inner zones of dipyramidal crystals with average ZrO₂/HfO₂ = 63 formed during late magmatic stage at a temperature of ∼500°C. The zircon pertaining to the postmagmatic hydrothermal stage is distinguished by the lowest ZrO₂/HfO₂ ratio (29, on average), porous fabric, abundant inclusions, and crystallization temperature below 500°C. The progressive decrease in ZrO₂/HfO₂ ratio was caused by evolution of melt and postmagmatic solution. The metamorphic zircon rims relics of earlier crystals and occurs as individual rhythmically zoned grains with an averaged ZrO₂/HfO₂ ratio (45, on average) similar to that of the bulk ore composition. The metamorphic zircon is depleted in uranium in comparison with magmatic zircon, owing to selective removal of U by aqueous metamorphic solutions. Zircon from the Sakharjok deposit is characterized by low concentrations of detrimental impurities, in particular, contains only 10–90 ppm U and 10–80 ppm Th, and thus can be used in various fields of application.     

The Gagarka gold deposit in the central Urals, Russia

The Gagarka gold deposit was formed in two stages. The gold-telluride ore of the main early stage was formed ～260 Ma ago synchronously with Permian collision, which was accompanied by retrograde metamorphism with mobilization of Au and Te from geochemically similar massive sulfide lodes in the rift zone. The Au-bearing argillic metasomatic rocks of the late stage presumably Mesozoic in age are distinguished by specific geochemistry and locally superposed on the ore related to the early stage. The upper part of the metasomatic column consists of quartz-kaolinite rock, which is confused in many cases with products of Mesozoic-Cenozoic weathering and because of this is not perceived as a guide for hidden Au-bearing argillic alteration, whose resource potential remains underestimated in the Urals.     

焦家式蚀变岩型金矿床热液蚀变成因: 磷灰石矿物学、年代学和地球化学约束

胶东是我国最大的金矿集中区, 累计探明金资源量5000余吨, 焦家式蚀变岩型金矿床提供了80%以上的金资源量, 钾长石化和黄铁绢英岩化蚀变是该类矿床的重要找矿标志, 但对其成因与形成时限缺乏有效约束。为探究两类蚀变的成因并限定其形成年龄, 本文对典型蚀变岩型金矿床中钾长石化花岗岩与黄铁绢英岩化碎裂岩进行锆石和磷灰石LA-ICP-MS U-Pb地质年代学、磷灰石微区原位微量元素地球化学测试。结果表明, 钾长石化玲珑花岗岩的锆石U-Pb年龄为155.0±1.1Ma~155.8±1.3Ma, 代表了其岩浆侵位年龄; 钾长石化玲珑花岗岩蚀变弱的A1型磷灰石没能得到有效年龄, 而蚀变较强的A2型磷灰石U-Pb年龄为146±7Ma~147±6Ma, 代表了钾长石化蚀变作用发生的时间; 黄铁绢英岩化碎裂岩蚀变较弱的B1型磷灰石数量较少未形成协和年龄, 强蚀变B2型磷灰石U-Pb年龄为125±6Ma, 代表了黄铁绢英岩化蚀变作用发生的时间。A1型磷灰石的稀土配分曲线与未蚀变玲珑花岗岩较为一致, A2型磷灰石显示更高的轻稀土含量和更明显的Eu负异常, 随着钾长石化蚀变程度增强, La/Yb比值逐渐增大, Sr含量和Sr/Y比值同步降低, 暗示蚀变流体相对富轻稀土, 蚀变过程磷灰石的Sr被活化迁移; B1型磷灰石的稀土配分曲线与未蚀变玲珑花岗岩相似, B2型磷灰石和未蚀变郭家岭花岗岩较为一致, 轻重稀土分异明显, 且Eu异常不明显, 在黄铁绢英岩化蚀变过程中Sr含量、Sr/Y比值和La/Yb比值显著增高。本文认为与焦家式蚀变岩型金矿成矿相关的蚀变作用与区域岩浆作用有关, 晚侏罗世玲珑花岗岩的自交代作用形成了钾长石化蚀变, 早白垩世郭家岭花岗岩分异的热液沿区域性断裂迁移, 导致断裂带内发生黄铁绢英岩化。

     

Mineralogy and metamorphism conditions of manganese ore at the South Faizulino deposit, the southern Urals, Russia

The mineralogy of slightly metamorphosed manganese ore at the South Faizulino hydrothermalsedimentary deposit in the southern Urals has been studied; 32 minerals were identified. Quartz, hausmannite, rhodochrosite, tephroite, ribbeite, pyroxmangite, and caryopilite are major minerals; calcite, kutnahorite, alleghanyite, spessartine, rhodonite, clinochlore, and parsettensite are second in abundance. This mineralic composition was formed in the process of gradual burial of ore beneath the sequence of Middle Devonian-Lower Carboniferous rocks. The highest parameters of metamorphism are T ≈ 250°C and P ≈ 2.5 kbar. The relationships between minerals and their assemblages made it possible to reconstruct the succession of ore transformation with gradually increasing temperature and pressure. Manganese accumulated in the initial sediments as oxides and a gel-like Mn-Si phase. Rhodochrosite and neotocite were formed at the diagenetic stage. In the course of a further increase in temperature and pressure, neotocite was replaced with caryopilite; ribbeite, tephroite, pyroxmangite, and other silicates crystallized afterwards. In addition to the PT parameters, the formation of various metamorphic mineral assemblages was controlled by the Mn/(Mn + Si) ratio in ore and X _CO2 in pore solution. The latter parameter was determined by the occurrence of organic matter in the ore-bearing rocks. Ore veinlets as products of local hydrothermal redistribution of Mn, Si, and CO₂ were formed during tectonic deformations in the Middle Carboniferous and Permian.     

The Talgan massive sulfide deposit, the southern Urals, Russia, as an example of subseafloor ore deposition from magmatic fluid

The sequence of orebody formation at the Talgan massive sulfide deposit; morphology of sulfide orebodies; mineralogy, texture, and structure of ore; chemical composition of minerals; and fluid inclusions and relationships between stable isotopes (S, C, O) in sulfides from ores and carbonate rocks are discussed. The deposit is localized in the Uzel’ga ore field of the northern Magnitogorsk Megazone. The sulfide ore is hosted in the upper felsic sequence of the Middle Devonian Karamalytash Formation, composed of basalt, basaltic andesite, and rhyodacite. Orebodies are irregular lenses lying conformably with host rocks. Pyrite, chalcopyrite, sphalerite, and fahlore are the major ore minerals; galena, bornite, and hematite are of subordinate abundance. Sulfide mineralization bears attributes of deposition under subseafloor conditions. The carbonate and rhyolite interlayers at the roofs of orebodies and the supraore limestone sequence served as screens. Zoning typical of massive sulfide deposits was not established. The study of fluid inclusions has shown that the temperature of the hydrothermal solution varied from 375 to 110°C. δ³⁴S‰ ranges from ?2.4 to +3.2‰ in pyrite, from ?1.2 to +2.8‰ in chalcopyrite, and from ?3.5 to +3.0‰ in sphalerite (CDT). These parameters correspond to an isotopic composition of magmatic sulfur without a notable percentage of sulfate sulfur. δ¹³C and δ¹⁸O of carbonates vary from ?18.1 to +5.9‰ (PDB) and from +13.7 to +27.8‰ (SMOW), respectively. The carbon and oxygen isotopic compositions of carbonates from ores and host rocks markedly deviate from the field of marine carbonates; a deep source of carbon is suggested. The results obtained show that the main mass of polysulfide ore at the Talgan deposit was formed beneath the floor of a paleoocean. The ore-forming system was short-lived and its functioning did not give rise to the formation of zonal orebodies. Magmatic fluid played the leading role in mineral formation.     

Epithermal deposits in South China: Geology,geochemistry, geochronology and tectonic setting

South China Block (SCB) is the broad area including the Yangtze Craton in the northwest and Huanan Orogen in the southeast. It is an important epithermal metallogenic province in China, containing at least 1 high-sulfidation (HS) and 42 low-sulfidation (LS) Au-Ag ± Cu ± Pb-Zn ± Sb epithermal deposits. Porphyry-type mineralization was recognized in four of the LS deposits, and thus they were regarded as LS–P type. These 43 deposits are mainly located in: (1) the Lower Yangtze River Belt and (2) the Northeastern Jiangnan Orogenic Belt in the Yangtze Craton, (3) the Wuyi-Yunkai Orogenic Belt and (4) the Southeast Coastal Volcanic Belt in the Huanan Orogen. They are mostly located in Mesozoic volcanic basins, especially where the regional faults and their subsidiaries occurred. The host rocks include Jurassic–Cretaceous volcanic-sedimentary rocks, coeval or slightly older subvolcanic, granitoids and breccias, and metamorphic basement rocks. The alteration of the HS epithermal deposit (Zijinshan Cu-Au) zoned from silicic (vuggy quartz), through alunite, to dickite and phyllic alteration zones, from the ore veins outwards. The alteration of the LS deposits is zoned from adularia-chalcedony-bladed calcite (or quartz pseudomorphs after bladed calcite) in ore veins to distal illite-sericite-chlorite-kaolinite assemblages. For those LS–P systems, besides the dominated LS alteration assemblages, phyllic and potassium silicate alteration related to porphyry mineralization were identified. Acid leaching textures and vein, stockwork and breccia structures are common in HS deposit, while the LS epithermal deposits are characterized by open-space filling, crustifications, colloform banding and comb structures. The ore-forming fluids are low-temperature, low-salinity meteoric water-dominated in most epithermal deposits in SCB, with variable input of magmatic water. The ore components were derived from both the deep magma and host rocks, and transported upwards or laterally and precipitated in the fracture systems by fluid boiling, mixing and cooling. Most of the epithermal deposits are formed at depth of < 1.5 km and < 300 °C, with few exceptions containing porphyry-type mineralization, such as the Zhilingtou, Yinshan and Longtoushan deposits. Deep drilling is suggested in these deposits as more epithermal and/or porphyry mineralization could be expected. The mineral systems were formed in Early Yanshanian (180–130 Ma) and Late Yanshanian (120–90 Ma) periods. The Early Yanshanian epithermal ore systems are mainly located in a series of E–W-trending metallogenic belts to the west of the Lishui–Haifeng Fault, which were formed in a syn- or post-collision tectonic setting by the collision between the SCB and its surrounding plates. The Late Yanshanian epithermal deposits are mainly located in Southeast Coastal Volcanic Belt, genetically related to the westward subduction of the paleo-Pacific plate.     

Fluid inclusions,C-H-O-S-Pb isotope systematics,geochronology and geochemistry of the Budunhua Cu deposit,northeast China:Implications for ore genesis

The Budunhua Cu deposit is located in the Tuquan ore-concentrated area of the southern Great Xing'an Range,NE China.This deposit includes the southern Jinjiling and northern Kongqueshan ore blocks,separated by the Budunhua granitic pluton.Cu mineralization occurs mainly as stockworks or veins in the outer contact zone between tonalite porphyry and Permian metasandstone.The ore-forming process can be divided into four stages involving stage Ⅰ quartz-pyrite-arsenopyrite;stage Ⅱ quartz-pyrite-chalcopyrite-pyrrhotite;stage Ⅲ quartz--polynetallic sulfides;and stage IV quartz-calcite.Three types of fluid inclusions(FIs) can be distinguished in the Budunhua deposit:liquid-rich two-phase aqueous FIs(L-type),vapour-rich aqueous FIs(V-type),and daughter mineral-bearing multi-phase FIs(S-type).Quartz of stages Ⅰ-Ⅲ contains all types of FIs,whereas only L-type FIs are evident in stage Ⅳ veins.The coexisting V-and S-type FIs of stages Ⅰ-Ⅲ have similar homogenization temperatures but contrasting salinities,which indicates that fluid boiling occurred.The FIs of stages Ⅰ,Ⅱ,Ⅲ,and Ⅳyield homogenization temperatures of 265-396℃,245-350℃,200-300℃,and 90-228℃ with salinities of3.4-44.3 wt.%,2.9-40.2 wt.%,1.4-38.2 wt.%,and 0.9-9.2 wt.% NaCl eqv.,respectively.Ore-forming fluids of the Budunhua deposit are characterized by high temperatures,moderate salinities,and relatively oxidizing conditions typical of an H_2 O-NaCl fluid system.Mineralization in the Budunhua deposit occurred at a depth of0.3-1.5 km,with fluid boiling and mixing likely being responsible for ore precipitation.C-H-O-S-Pb isotope studies indicate a predominantly magmatic origin for the ore-forming fluids and materials.LA-ICP-MS zircon U-Pb analyses indicate that ore-forming tonalite porphyry and post-ore dioritic porphyrite were formed at 151.1±1.1 Ma and 129.9±1.9 Ma,respectively.Geochemical data imply that the primary magma of the tonalite porphyry formed through partial melting of Neoproterozoic lower crust.On the basis of available evidence,we suggest that the Budunhua deposit is a porphyry ore system that is spatially,temporally,and genetically associated with tonalite porphyry and formed in a post-collision extensional setting following closure of the Mongol-Okhotsk Ocean.     

华南地区三叠纪矿床地质特征、成矿规律和矿床模型

华南以中生代成矿大爆发为特征,燕山期矿床成矿规律的研究程度较高,近年来发现越来越多的三叠纪矿床,但三叠纪矿床的分布规律和矿床模型是值得关注的重要科学问题。本文基于最新研究成果,论述华南三叠纪矿床地质特征和矿床类型,提出成矿规律,初步地建立成矿动力学模型。华南地区三叠纪矿床分布较为广泛,目前确定的46个三叠纪矿床分布于5个区带,形成于晚三叠世 (230~200 Ma),被划分为花岗岩有关的钨锡多金属矿床、侵入岩有关的远端金锑矿床、卡林型金矿床和MVT型铅锌矿床4种主要类型。在空间上,华南三叠纪矿床存在成矿元素分带性,由西向东依次为MVT型铅锌矿床、卡林型金矿床、侵入岩有关的远端金锑矿床、花岗岩有关的钨锡多金属矿床。华南5个成矿区带普遍存在印支期和燕山期的叠加成矿作用,在南岭西段桂北苗儿山—越城岭和滇东南老君山地区还发育加里东和印支期的叠加成矿作用。     

俄罗斯叶尔果茹金多金属矿床地质特征及成因探讨

俄罗斯叶尔果茹金多金属矿床位于西伯利亚克拉通南缘隆起带的东萨彦—比留萨地垒中,含矿地层为古元古界阿尔哈德尔岩组第一岩段,金多金属矿体产于矽卡岩化带和多组韧性-脆性断裂破碎带内。矿区共分为7个矿段,现已圈出50余条矿体,主要产于1号—4号矿段和7号矿段,矿化分为产于矽卡岩化带中的缓倾斜似层状矿化和产于构造破碎蚀变岩中的陡倾斜脉状矿化,两种矿化在空间上多为交错关系,并在矿物组合、矿石构造等方面有明显区别;矿化元素主要为Au、Ag、Pb和Zn,伴生丰富的Cd、Cu、Co、Bi和S等元素可回收利用;叶尔果茹矿区的成矿作用受到地层层位和特定岩性、岩浆-火山作用、褶皱和韧-脆性断裂作用的共同控制,矿床属于与泥盆纪岩浆(火山)作用有关的中低温热液交代-充填型金多金属矿床。由于该矿区研究程度较低,勘查深度较浅,其深部及外围还有较大的找矿空间。     

Geology,geochronology, geochemistry and ore genesis of the Wangu gold deposit in northeastern Hunan Province,Jiangnan Orogen,South China

The Wangu gold deposit in northeastern Hunan, South China, is one of many structurally controlled gold deposits in the Jiangnan Orogen. The host rocks (slates of the Lengjiaxi Group) are of Neoproterozoic age, but the area is characterized by a number of Late Jurassic–Cretaceous granites and NE-trending faults. The timing of mineralization, tectonic setting and ore genesis of this deposit and many similar deposits in the Jiangnan Orogen are not well understood. The orebodies in the Wangu deposit include quartz veins and altered slates and breccias, and are controlled by WNW-trending faults. The principal ore minerals are arsenopyrite and pyrite, and the major gangue minerals are quartz and calcite. Alteration is developed around the auriferous veins, including silicification, pyritic, arsenopyritic and carbonate alterations. Field work and thin section observations indicate that the hydrothermal processes related to the Wangu gold mineralization can be divided into five stages: 1) quartz, 2) scheelite–quartz, 3) arsenopyrite–pyrite–quartz, 4) poly-sulfides–quartz, and, 5) quartz–calcite. The Lianyunshan S-type granite, which is in an emplacement contact with the NE-trending Changsha-Pingjiang fracture zone, has a zircon LA-ICPMS U–Pb age of 142 ± 2 Ma. The Dayan gold occurrence in the Changsha-Pingjiang fracture zone, which shares similar mineral assemblages with the Wangu deposit, is crosscut by a silicified rock that contains muscovite with a ca. 130 Ma ⁴⁰Ar–³⁹Ar age. The gold mineralization age of the Wangu deposit is thus confined between 142 Ma and 130 Ma. This age of mineralization suggests that the deposit was formed simultaneously with or subsequently to the development of NE-trending extensional faults, the emplacement of Late Jurassic–Cretaceous granites and the formation of Cretaceous basins filled with red-bed clastic rocks in northeastern Hunan, which forms part of the Basin and Range-like province in South China. EMPA analysis shows that the average As content in arsenopyrite is 28.7 atom %, and the mineralization temperature of the arsenopyrite–pyrite–quartz stage is estimated to be 245 ± 20 °C from arsenopyrite thermometry. The high but variable Au/As molar ratios (>0.02) of pyrite suggest that there are nanoparticles of native Au in the sulfides. An integration of S–Pb–H–O–He–Ar isotope systematics suggests that the ore fluids are mainly metamorphic fluids originated from host rocks, possibly driven by hydraulic potential gradient created by reactivation of the WNW-trending faults initially formed in Paleozoic, with possible involvement of magmatic and mantle components channeled through regional fault networks. The Wangu gold deposit shares many geological and geochemical similarities as well as differences with typical orogenic, epithermal and Carlin-type gold deposits, and may be better classified as an “intracontinental reactivation” type as proposed for many other gold deposits in the Jiangnan Orogen.     

Monzonitoid association of the Kavalerovo ore district (Primorye): geochronology and some genetic problems

This paper is dedicated to the isotope-geochronological study of the rocks that compose two large intrusions and a separate group of minor intrusions in the western part of the Kavalerovo ore district. In most publications, these rocks are considered as monzonitic or trachyandesite-monzonitic association. On the basis of the amphibole and biotite K-Ar ages and the Rb-Sr whole-rock and mineral datings, the studied association was formed within the interval of 113–98 Ma. A wider interval of 115–95 Ma was obtained with allowance for other isotope data, including those on the rocks of the volcanic facies. This is consistent with the concepts that the studied association belongs to a single magmatic complex. No significant and systematic age differences have been established between the compositionally similar rocks from the different massifs. In compliance with the scheme of the geodynamic evolution of the region, the chambers of latitic melts of the volcanic and most intrusive rocks of the complex were formed prior to the initiation of the Sikhote-Alin subduction volcanic belt. The initial stage of the formation of the latter is presumably constrained by the data on the biotite from the quartz diorites from the Uglovaya VTS (90 Ma), which is located in the central part of the region, and on the late amphibole from the monzonitoids of its western part (91–92 Ma). The geochemical differences between rocks from the different intrusive bodies could be caused by the specifics of the melt evolution in the intermediate or crystallization chambers.