Ore Field Research Articles

Norilsk ore field: the new metamorphic-hydrothermal mineral association — pure zvyagintsevite and silver, hibbingite, Mn-hibbingite, siderite, sphalerite and phosgenite in the magmatogenic putoranite ores

The unique magmatogenic putoranite ores are developed within deep horizons (>1750 m) of the northeastern flank of the October deposit in the Norilsk ore field. Th ese are coarse-grained putoranite aggregates with lamellaes of moihoekite and isolated pentlfndite disproportionation. The composition of putoranite is: [(Fe17.6–17.9Ni0.4–1.1Co0–0.1)18–19Cu15.8–17.0]35S32; the composition of moihoekite is: [(Fe17.8–18.0Ni0.2–0.3Co0–0.1)18.2– 18.3Cu17.7–17.8]36S32; pentlandite contains 1,75 wt% of Co, its composition is: (Ni4.41Fe4.36Co0.23)9S8. Ores hold pneumatolytic stannopalladinite Pd5CuSn2, polyarite Pd(Bi,Pb), plumbopolyarite Pd(Pb,Bi), tetraferroplatinum Pt2Fe(Fe,Cu,Ni), tulameenite Pt2Fe(Cu,Fe,Ni) and kustelite (Ag,Au). Bornite is widespread in tectonized ores, as well as late hibbingite and Mn hibbingite (Fe2+,Mn2+)2(OH)3Cl, siderite and Mn siderite (Fe2+,Mn2+)[CO3] aggregates, replaced magnetite and Cu-Fe-Ni sulphides. Pure zvyagintsevite Pd3Pb and native silver compose syngenetic inclusions in hibbingite and siderite aggregates. Similar zvyagintsevite replaces pneumatolytic polyarite and plumbopolyarite. Metamorphogenic-hydrothermal zvyagintsevite probably arose from their material. Th is zvyagintsevite is sharply diff erent from pneumatolytic zvyagintsevite by the absence of Pt, Sn, Bi, Sb and Hg in its composition. The first detected hypogenic phosgenite Pb2[Cl2/CO3] forms pseudomorphoses aft er galena, sometimes with hibbingite. Th e described low-temperature metamorphogenic-hydrothermal mineral association arose involving carbon dioxidechloride solutions in reducing conditions. Later metamorphogenic-hydrothermal hisingerite, bornite and barite, partially replacing hibbingite, siderite and Cu-Fe-Ni sulfides, arose with an increased fugacity O2.

Using apatite to differentiate metallogenic potential and environment of granitic rocks: A case study from the Tongshanling W-Sn-Cu-Pb-Zn ore field, Nanling Range (South China)

The Tongshanling ore field is one of the most representative W–Sn–Cu–Pb–Zn polymetallic deposits in the central-western Nanling Ore Belt, which developed multiple mineralization types, including Cu–Pb–Zn (Tongshanling), W–Sn (Weijia), Pb–Zn (Jiangyong), and Mo (Yulong) deposits. Here, we analyzed apatite from the Tongshanling granodiorite and the Weijia granite porphyry, integrating major and trace elements, U–Pb dating, and Nd isotopic analyses to compare the difference in geochronology, magma source, redox environment, and evolution between the Tongshanling and Weijia deposit. The U–Pb dating of the Tongshanling and Weijia apatite samples yield a lower intercept age of 166.2 ± 11.3 Ma (1σ, MSWD = 0.22) and 160.87 ± 8.92 Ma (1σ, MSWD = 0.44) on Tera-Wasserburg diagrams, respectively. The 147Sm/144Nd and 143Nd/144Nd ratios of the Tongshanling apatite samples are 0.136769–0.182878 and 0.512159–0.512246, respectively, with corresponding εNd (t = 166 Ma) ranging from −8.32 to −6.60, suggesting that the Tongshanling granodiorite was produced by partial melting of metaigneous rocks in the deep crust. The Tongshanling apatite shows a right-inclined REE pattern, while the Weijia apatite displays a “V” type REE pattern. The Tongshanling apatite shows higher Eu/Eu* values, and lower Mn and Ce/Ce* values than the Weijia apatite, indicating that the former formed in higher magmatic oxidation state while the latter formed in more reduced conditions. The granodiorite in the Tongshanling deposit is characterized by a lower degree of fractionation than the granite porphyry in the Weijia deposit, of which the Weijia apatite has lower Sr, Mg contents, and higher Y contents. Furthermore, apatite from Cu-bearing granites exhibits lower F/Cl ratios compared to those from W-bearing granites in the South China Block. In the Tongshanling area, apatite from the Tongshanling granodiorite has higher Cl contents than the Weijia apatite, indicating that the crustal basement of the Tongshanling area was affected by the high Cl fluid derived from the Proterozoic oceanic subduction and remelted to form granite in the Mesozoic, while the Weijia granite porphyry formed from remelting of a sedimentary source. The Tongshanling granodiorite and Weijia granite porphyry with different degrees of fractionation, magma source, and halogens contents can be effectively distinguished by the geochemistry of apatite. The difference in trace elements (Sr, Y, Mg, and REE) and isotopes of apatite can be applied to the identification of different types of ore-bearing granites in the Nanling Range.

Superimposed mineralization in the Tongbai composite orogen, central China: Revealed from geological and geochronological data of the Yindongpo gold deposit

Multi-period mineralizations commonly form superimposed deposits in the orogenic belt, resulting in some disputes about the ore geneses and metallogenic background. Here, we present a comprehensive geological and geochronological study on the Yindongpo super-large gold deposit in the Tongbai composite orogen, central China, to reveal the ages of multi-period gold mineralizations and their links to the complex tectonic evolution framework of the Tongbai orogen. The Yindongpo gold deposit is located in the Weishancheng ore field in the northern segment of the Tongbai orogen and is mainly hosted in the carbonaceous schist of the Waitoushan Formation. Zircon U-Pb dating of leptynite (445 ± 3 Ma) from the Waitoushan Formation shows that it was deposited in the Ordovician, in an island arc or back-arc basin setting during the accretionary orogeny. Orebodies at Yindongpo are strictly controlled by the Zhuzhuang anticline and related fault systems, and are mainly distributed in the turning end, the collapsed part of the dipping end, and the conjugate thrust shear zone of the limbs. Based on field and petrographic observations, two periods of mineralization and four paragenetic stages (stage I to IV) are recognized: the early period consists of the laminated quartz-molybdenite-pyrite stage (I) and laminated-disseminated pyrite stage (II), whereas the late period consists of the quartz-pyrite vein stage (III) and the quartz-polymetallic sulfide vein stage (IV). Molybdenite from stage I has a Re-Os model age of 409 ± 6 Ma, which broadly matches the U-Pb age of intergrown rutile grains (396 ± 4 Ma). These two ages, in combination with the mineralization characteristics, indicate that the early-period gold mineralization was generated by the metamorphism of the accreted terranes during the Early Devonian northward subduction of the oceanic plate. The timing of the late-period mineralization is constrained by the U-Pb age of monazite (127 ± 2 Ma) intergrown with gold-bearing pyrite from stage III and the 40Ar/39Ar ages of ore-related sericite (131 ± 1 Ma) from stage IV and altered sericite (133 ± 1 Ma) from the carbonaceous schist. Combined with the extensive development of coeval granitoids and porphyry Mo deposits in the region, the late-period gold mineralization at Yindongpo belongs to a unified large-scale metallogenic event related to the Early Cretaceous intensive granitic magmatism in an extensional tectonic setting. The results presented here thus reveal two discrete mineralization processes at Yindongpo related to the Tongbai composite orogeny: the early mineralization of Devonian accretionary orogeny and the later mineralization of Cretaceous intracontinental orogeny. Our study contributes to the knowledge of superimposed metallogenesis in composite orogen, and also highlights the decisive role of multi-mineral isotopic dating in revealing the metallogenic epoch of superimposed deposits.

Geochemistry of fluorine in halo waters of ore fields of the southeastern part of the Dnipro-Donetsk avlakogen

The geochemical features of fluorine and its possible sources in the waters of the hydrothermal ore fields of the Dnipro-Donetsk avlakogen (DDA) are considered. It was established that the formation of anomalies occurs due to the interaction of infiltration waters of the zone of free water exchange and waters of deep formation, which are unloaded along the zones of deep faults. It is substantiated that the water migration of fluorine is determined by the geochemical type of groundwater, the degree of its mineralization, acid-base (pH) and oxidation-reduction (Eh) potentials, the presence of complex-forming elements with which fluorine forms mobile complex compounds, etc. Formulation of the problem. Fluorine is a typomorphic chemical element that is widely present in groundwater. It forms large-scale, contrasting hydrogeochemical anomalies in various types of hydrothermal ore fields, which are controlled by zones of deep faults - fluorite, mercury, polymetallic, and others. Presenting main material. Anomalies of the element are also formed in those fault zones, where the processes of modern heat and mass transfer are observed, manifested in the upward discharge of endogenous fluids against the background of increased intensity of the geothermal field. This indicates the probable arrival of fluorine in endogenous fluid flows, which are mixed with formation waters during their upward migration. The most contrasting aureoles of fluorine scattering are established in the zone of hypergenic weathering of fluorite of the Pokrovo-Kyreevsky deposit and in the aureole waters of the Mykytiv mercury ore field, in the rocks of which fluorite mineralization is absent. In them, fluorine, together with other trace elements, forms multicomponent anomalies and is part of the hydrogeochemical association of elements-indicators of hidden mercury mineralization - Hg, As, B, F, (Sb). Conclusions. 1. Geochemical features of fluorine in the processes of hydrothermal mineralization are caused by both hypogenic and hypergenic factors of its migration and concentration in the hydrolithosphere of the Dnipro-Donetsk avlakogen. 2. The high migration activity of fluorine in fluid systems and, in particular, in groundwater, is determined by numerous mobile forms of the element that exist under different geochemical conditions - in the form of gas, simple anions, complex compounds with metals, silicon, manganese, boron and other chemical elements Fluorine migrates best in alkaline sodium bicarbonate and sodium chloride waters, in which Сl–, Na+ and ОН– ions not only act as a complexing agent, but also provide high ionic strength of aqueous solutions. 3. The high content of fluorine in the waters of the Pokrovo-Kyreivsky fluorite deposit is provided by two different geochemical processes: a) hypergenic physicochemical destruction of CaF2 by gravitational infiltration waters of the zone of free water exchange; b) the influx of fluorine into deep formation waters together with endogenous fluids that are discharged along fault structures at the post-hydrothermal stage of their tectonic activation. 4. Abnormally high concentrations of fluorine in the hydrothermal mercury ore fields of the Mykytivskyi and Druzhkivsko-Kostiantynivskyi deposits, in the rocks of which there is practically no fluorite mineralization, are due to the influx of the element into the mineralization zones from deep fluid flows and underground waters of deep horizons. 5. The main natural sources of fluorine in the waters of hydrothermal deposits of the region are: a) products of hypergenic weathering of hydrothermal mineralization of fluorite; b) flows of endogenous postheterothermal fluids; c) pore solutions of sedimentary rocks of marine origin.

Hibbingite and Its Manganoan Variety from Metamorphosed Pentlandite–Putoranite Ores at Deep Levels of the Oktyabrskoe Deposit, Norilsk Ore Field

Hibbingite and Its Manganoan Variety from Metamorphosed Pentlandite–Putoranite Ores at Deep Levels of the Oktyabrskoe Deposit, Norilsk Ore Field

Genesis and metallogenic characteristic of Dongnan Cu–Mo deposit associated granitoids: LA-ICP-MS zircon U–Pb dating and isotope constraint from Zijinshan ore field in southeastern China

Genesis and metallogenic characteristic of Dongnan Cu–Mo deposit associated granitoids: LA-ICP-MS zircon U–Pb dating and isotope constraint from Zijinshan ore field in southeastern China

Geochemistry and textural evolution of As-Tl-Sb-Hg-rich pyrite from a sediment-hosted As-Sb-Tl-Pb ± Hg ± Au mineralization in Janjevo, Kosovo

The sediment-hosted As-Sb-Tl-Pb ± Hg ± Au Janjevo occurrence is located in the southern part of the Kizhnica-Hajvalia-Badovc ore field, in the Trepça (Trepča) Mineral Belt (TMB) in Kosovo. The As-Sb-Tl-Pb ± Hg ± Au mineralization is hosted by Upper Triassic marbles and occurs in the form of quartz-stibnite veins and dolomitized irregular pockets associated with jasperoid rocks. The main sulfide most widespread in the mineralization studied is pyrite which is the main carrier of thallium. A wide range of techniques was used to characterize the geochemistry and textural evolution of pyrite/marcasite from Janjevo: polarized reflected-light microscopy, electron microprobe (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray powder diffraction (XRPD), Mössbauer spectroscopy, and isotopic studies. The study of 42 thin and polished sections resulted in the identification of 4 generations of pyrite/marcasite. The first generation of pyrite related to the pre-ore stage occurs as framboidal pyrite with different degrees of evolution (Py1a), as well as recrystallized pyrite/marcasite (Py1b). Au-enriched pyrite (Py2) occurs as elongated fibrous aggregates and is genetically associated with the formation of stibnite veins (Sb stage). As-Tl-Sb-Hg pyrite (Py3) forms irregular colloform aggregates which fill the stylolites and also overgrow older generations of pyrite. The youngest generation is represented by marcasite (Py4), which forms euhedral crystals. Co/Ni ratio < 1 in all pyrite/marcasite generations implies a sedimentary fingerprint. On the other hand, δ34S isotopic studies confirm a magmatic sulfur source for As-Tl-Sb-Hg pyrite (Py3), as well as co-occurring stibnite and realgar. The most important minor and trace elements in pyrite/marcasite are As (up to 14.1 %), Tl (up to 3.94 %), Sb (up to 3.73 %), and Hg (up to 0.55 %), which are mainly hosted by Py3. In addition to arsenic, thallium, antimony, and mercury, other generations of pyrite show enrichment in Ni, Co, and Cu (framboidal pyrite Py1), Au, and Se (Au-enriched pyrite Py2), and Se (marcasite Py4). The highest gold content of up to 6.08 ppm was recorded at Py2. Studies on Py3 geochemistry confirm the presence of 2Fe2+ ↔ Tl+ + Sb3+ heterovalent substitution in pyrite. As-Tl-Sb-Hg pyrite (Py3) is the main thallium host mineral in the mineralization studied, with significantly less thallium present in the Pb-Sb ± Tl ± As sulfosalts. In addition, the high arsenic content of Py3 is due to the presence of arsenic in the form of As1− and As0 related to amorphous arsenic-rich nanoparticles. The reported Py3 is the best phenomenon of the crystallization of colloform As-Tl-Sb-Hg-rich pyrite under hydrothermal conditions. Pyrite-rich sediment-hosted As-Sb-Tl-Pb ± Hg ± Au mineralization from Janjevo is associated with the distal manifestation of a concealed porphyry system.

Specific features of gold ore formation&#x0D; in the southeastern Baikal-Patom metallogenic province (Dzhalagun ore field)

In the course of geological prospecting fulfilled with participation of the FGBI TsNIGRI within the Chayangro ore cluster of the Dodykhta-Uryakh ore region in the southeastern Baikal-Patom metallogenic province, the Dzhalagun lode gold prospect within the ore field of the same name was studied and its economic significance has been proved. It has been substantiated that the Dzhalagun gold prospect is closely similar to the typical gold ore deposits of the Bodaibo ore region in sense of the ore formation phasing, the character of the hydrothermal metasomatic processes, and the structure of the mineralized vein-veinlet zones. At the same time, a series of specific geological features of the Dzhalagun ore field and the prospect have been determined as to the structure and composition of the ore-hosting rocks, the intrusive magmatism, the hydrothermal metasomatic processes, and the mineral composition of the veinveinlet mineralization.

Geology of the Golenkie Gorki gold occurrence (Siratur ore field, the Southern Urals)

В статье рассмотрено золотое рудопроявление Голенькие Горки, входящее в Сиратурское рудное поле. Оно расположено в северной части южноуральского сегмента Главного Уральского разлома, в зоне сочленения Башкирского мегантиклинория с северным замыканием Магнитогорской мегазоны.&#x0D; Углеродистые и углеродисто-хлорит-кварцевые сланцы имеют площадное распространение, образуют самостоятельные пачки и имеют преимущественно гранобластовую структуру и массивную, реже, пятнистую текстуру. Результаты термического анализа показывают температуру начала экзотермического эффекта углерода в интервале 500–640°С, что соответствует высокотемпературной субфации зеленосланцевой фации регионального метаморфизма. Среднее содержание Сорг составляет около 2.4%, что позволяет относить данные породы к углеродистому типу.&#x0D; Показано, что золоторудная минерализация приурочена к зоне контакта довольно мощной толщи углеродистых сланцев поляковской толщи с серпентинитами Нуралинского габбро-гипербазитового массива. В пределах контакта установлена зона лиственитов длиной 1400 м и шириной до 30 м. Опробование всех разновидностей пород на золото выявило его повышенные содержания в ожелезненных и окварцованных углеродисто-хлорит-кварцевых сланцах и жильном кварце, а также околорудные значения в окварцованных лиственитах.&#x0D; Анализ золотин позволил отнести их к низкопробному типу. Значительные примеси серебра указывают на золото-сульфидный тип оруденения. По периферии зерен отмечено очищение золотин от элементов-примесей в зоне гипергенеза.&#x0D; The article considers the Golenkie Gorki gold ore occurrence, which is part of the Siratur ore field. It is located in the northern part of the South Ural segment of the Main Ural Fault, in the junction zone of the Bashkir meganticlinorium with the northern closure of the Magnitogorsk megazone.&#x0D; Carbonaceous and carbonaceous-chlorite-quartz shales have areal distribution, form independent packs and have a predominantly granoblastic structure and a massive, rarely spotted texture. The results of thermal analysis show the temperature of the onset of the exothermic effect of carbon in the range of 500–640°С, which corresponds to the high-temperature subfacies of the greenschist facies of regional metamorphism. The average content of Corg is about 2.4%, which makes it possible to attribute these rocks to the carbonaceous type.&#x0D; It is shown that gold ore mineralization is confined to the contact zone of a rather thick sequence of carbonaceous shales of the Polyakovka Formation with serpentinites of the Nurali gabbro-ultramafic massif. A zone of listwanites 1400 m long and up to 30 m wide was established within the contact. Testing of all types of rocks for gold revealed its increased content in ferruginous and silicified carbonaceous-chlorite-quartz schists and veined quartz, as well as near-ore values in silicified listwanites.&#x0D; The analysis of gold grains made it possible to refer them to the low-quality type. Significant silver impurities indicate the gold-sulfide type of mineralization. Along the periphery of the grains, the purification of gold grains from impurity elements in the hypergenesis zone was noted.

Assessment of Berezkinskoye ore field prospectivity using Micromine software

The use of modern computer aided methods, in particular the use of the Micromine software, is an important part of the integrated research for the determination of deposit prospects for various ores. The paper is devoted to the analysis of prospects and estimation of reserves for open-pit and underground mining in the Berezkinskoye ore field. For this purpose, silver reserves were determined as the principal valuable component. The deposit balance reserves were estimated separately for all types of ores in the optimal open pit envelope adopted in the final mining feasibility study (FS of permanent exploration conditions for ore extraction). To vectorize and verify the geological information entered into the database, graphical materials in the form of cross-sections and plans with the corresponding borehole database were georeferenced using the Micromine software. The final inspection was carried out to ensure that the sample depth information entered was consistent with the excavation depth. The database contains information on the location of boreholes and trenches, the design of boreholes, the spatial positioning of the boreholes/trenches axes, the data of sample assays for silver and copper. For underground mining, the delineation of ore bodies was carried out based on the cross-sections identified in the boreholes at a cut-off grade of 10.7 g/t, taking into account the orientation of geological structures. Reliability of the ore bodies delineation was verified in a Micromine three-dimensional model. For open-pit mining, the position of small ore bodies may be clarified by operational exploration with possible subsequent upgrading their reserve categories. The wireframe model of ore zones and bodies was constructed using the outlines obtained by the developed methodology. A wireframe model of faults was based on the Berezkinsky area plans and cross-sections. The construction of the fault wireframe model was performed in several steps. Application of modern geoinformation system (GIS) technologies makes it possible to qualitatively assess the prospects and estimate the reserves at the deposits. The Berezkinskoye deposit ore material composition, metallurgical properties, hydrogeological and geotechnical features were investigated.

Material Source and Genesis of the Daocaowan Sb Deposit in the Xikuangshan Ore Field: LA-ICP-MS Trace Elements and Sulfur Isotope Evidence from Stibnite

The Daocaowan antimony (Sb) deposit is a newly discovered Sb deposit located outside the northeast Xikuangshan ore field. In the absence of geochemical data, the metallogenic mechanism of the Daocaowan Sb deposit and its relationship with the Xikuangshan ore field remains unclear. Using high-resolution LA-ICP-MS technique, this study quantitatively determined the in-situ S isotope values and trace element composition of stibnite from the Daocaowan Sb deposit in South China to investigate the source of ore-forming materials and genesis of this deposit. The trace element compositions of stibnite from the Daocaowan Sb deposit revealed the form of occurrence and substitution mechanism of trace elements in stibnite, providing new constraints for explaining the genesis of Sb deposits. The relatively smooth LA-ICP-MS profiles indicate that As, Cu, Hg, and Pb primarily occur as solid solutions in stibnite. Therefore, we speculate that the substitution 3Sb3+↔As3+ + 2Cu+ + Hg2+ + Pb2+ may be the reason for the enrichment of As, Cu, Hg, and Pb in stibnite. A comparison with the Xikuangshan Sb deposit reveals the metallogenic mechanism of the Daocaowan Sb deposit, and the relationship between the two. With the exception of higher content of Fe in Stibnite from the Daocaowan deposit as compared to the Xikuangshan deposit, other trace elements are similar between the two deposits. The results show that the Daocaowan and Xikuangshan Sb deposits may have the same source of ore-forming fluids. We propose that the ore-forming fluid flowed through the Xikuangshan Sb deposit along the F75 fault and dissolved pyrite in the wall rock. Subsequently this fluid containing a high concentration of Fe precipitated and mineralized at Daocaowan. Meanwhile, the S isotope value of the Daocaowan Sb deposit (+6.65 to +9.29‰) is consistent with that of the Xikuangshan, proving that the ore-forming materials of the two deposits are from the same source, probably the basement strata. We propose that the Daocaowan Sb deposit is part of the Xikuangshan ore field, indicating a great prospecting potential in the northeast of the Xikuangshan ore field.

Trace Elements in Chromite as Indicators of the Origin of the Giant Podiform Chromite Deposit at Kempirsai, Kazakhstan

Abstract This study presents a complete trace element data set of chromite from the world’s largest podiform chromite deposit at Kempirsai, Kazakhstan, together with platinum group element (PGE) and Re-Os isotope compositions, to explore the potential of trace elements in the study of podiform chromite deposits. Chromite orebodies in the Karaagash area of the Kempirsai Main ore field are hosted by dunites in the mantle sequence of the ophiolite. Dunites slightly distal to the orebodies are composed of olivine (forsterite content = 91.5–93.4) and minor euhedral chromite with variable Cr# (0.73–0.83). These dunites have primitive mantle-normalized Pt-Pd–poor PGE patterns and subchondritic 187Os/188Os ratios (0.12174–0.12220). Negative correlations between Cr# and incompatible trace elements (Sc and Ti) of the chromite are consistent with melt-rock reaction, whereas positive correlations between Cr# and compatible trace elements (V and Ga) reflect the role of fractional crystallization. It is therefore proposed that chromite in the distal dunites was crystallized from magmas after reaction with mantle peridotites. In comparison, chromite grains in the ores and adjacent dunites exhibit relatively uniform Cr# numbers (0.81–0.86) and higher 187Os/188Os values (0.12319–0.12414). Both compatible and incompatible trace elements of chromite exhibit negative correlations with Cr#, which are best explained by mixing between the modified magma after melt-rock reaction and a later injected magma from a more depleted source. After the ore formation, subsolidus reequilibration between olivine and chromite reduced Mg# and modified divalent trace elements of chromite in the order of Zn &amp;gt; Co = Mn &amp;gt; Ni but did not affect distribution of nondivalent trace elements, except V and Fe3+. The decoupling of redox-sensitive and redox-insensitive trace elements suggests that the redox states have been modified during subsolidus reequilibration. The existing iron equilibrium between olivine and chromite records high fO2 values (quartz-fayalite-magnetite buffer [∆QFM] 0.8–2.4), whereas correction of subsolidus reequilibration results in a decrease of the fO2 values toward the QFM buffer (∆QFM 0.1–0.6), indicating that increase in fO2 was not a critical factor in the ore formation. Principal component analysis and factor analysis were further carried out to identify differences in trace elements between high-Cr and high-Al podiform chromite deposits worldwide. High-Cr chromite deposits have variable divalent trace element compositions and show complex distributions of nondivalent trace elements. The former reflects longer and slower cooling histories of the high-Cr chromite deposits with respect to the high-Al chromite deposits, whereas the latter indicates more variable magma compositions and complex processes during the formation of the high-Cr chromite deposits.

Žune Ba-F epithermal deposit Part 1: Mineralogical and geochemical characteristics

The Žune Ba-F epithermal deposit is situated in the Ljubija ore field (NW Bosnia and Herzegovina), within Upper Palaeozoic dolostone. A typical ESE-WNW Variscan vergency fault zone separates the dolostone from Lower Triassic schists and sandstones. External and internal pseudo-bedding, with massive, homogenous structure and partial limonitization characterizes the dolostone. Its geochemical composition exhibits low SiO2 (1.33 – 2.06 mass. %), Al2O3 (0.27 –0.38 mass. %), BaO (0.02 – 0.83 mass. %), ƩREE (5.7 – 9.4 ppm), Sr (61.7 – 120.4 ppm), Sm (0.3 – 2.2 ppm) and Eu (0.1 – 0.6 ppm), while having high CaO (30.24 – 32.38 mass. %), MgO (16.47 – 17.35 mass. %) and LOI (44.6 – 45.58 mass. %). The dolostone-mineralization contact zone consists of metasomatically recrystallised host dolostone with quartz and pyrite, where the presence of accessory tremolite, magnesiochloritoid and pyknite indicates peak formation conditions in the pre-mineralization phase with temperatures above 300°C. Two ore types are described: (i) Ba-F vein-type mineralization composed of barite – fluorite ± quartz, and (ii) hydrothermal breccia composed of coarse-grained fluorite and barite, surrounding fragments of dolostone, and occupying ≈20 % of the deposit. Mineralized samples show slightly elevated SiO2 (2.20 – 5.53 mass. %) and Al2O3 (0.24 – 0.74 mass. %), low MgO (below 0.02 mass. %) and LOI (0.3 – 3.1 %), with high BaO (up to 50.74 mass. %), CaO (up to 66.03 mass. %), ƩREE (20 – 166 ppm), Sr (exceeding 1 mass. %), Sm (up to 118 ppm) and Eu (up to 44 ppm). Elevated Sr can be correlated to other barite epigenetic hydrothermal deposits in the Dinarides, interpreted as BaSr substitution in the barite crystal lattice. Fluorite-rich samples are characterized by Y (0.6 –49.2 ppm) and HREE enrichment, accompanied by depletion of LREE. The Ba-F deposit Žune, having variable REE concentration and a negative cerium and ytterbium anomaly corresponds geochemically to world-class fluorite deposits associated with carbonate sedimentary rocks.

Petrology of Granites of the Tommot Rare-Earth Ore Field (Verkhoyansk–Kolyma Orogenic Belt)

The article presents the results of studying the aegirine–arfvedsonite granites of the Somnitelnyi massif within the Tommot ore field located in the Verkhoyansk–Kolyma orogenic belt (NE Asia). Along with the crustal signatures, the rocks display features of mantle contamination at their origin. Their affinity for A-type granites characteristic of continental rifts and hot spots is shown. The associated Tommot REE deposit is the only one discovered in NE Russia. New data are presented for the previously studied Tommot massif within the same ore field, with a wide compositional range from alkaline-ultrabasic rocks to alkaline syenites. It is established that despite a common geochemical enrichment of both massifs’ rocks with REEs, the Somnitelnyi massif granites cannot be interpreted as the final phase of the Tommot massif emplacement. Specific REE mineralization and high crystallization temperatures (up to 1045 °C) of the Somnitelnyi granites may be explained by the existence within the study area of an undepleted mantle source (“hot spot”), whose maximum activity occurred during the granitic melt generation. The ore bodies of the Tommot deposit consist of fenitized albitites, granite gneisses, and, more rarely, the cross-cutting pegmatite veins. They are confined mostly to exocontacts of the Somnitelnyi massif, are less often in its endocontacts, and are not found in the host rocks and in the inner part of the massif away from the contacts. Principal ore minerals are chevkinite, yttrialite, gadolinite, and fergusonite. Based on the data obtained, the deposit is classified as a metasomatic complex Ce–Y–Nb–Zr deposit associated with the alkaline granites.

Geochronological and geochemical constraints on magmatic evolution and mineralization of the northeast Ke’eryin pluton and the newly discovered Jiada pegmatite-type lithium deposit, Western China

The Ke’eryin ore field in the Songpan-Garze Fold Belt (SGFB), western China, is an important area of pegmatite-type lithium accumulation. However, the petrogenesis of the pegmatites and their genetic relationships with the neighboring granitic pluton are still a topic of debate. In this work, LA-MC-ICP-MS zircon and columbite-tantalite U-Pb dating, whole-rock and mica geochemical analysis, and lithium isotopic analysis of the Ke’eryin pluton and pegmatites in the newly discovered Jiada deposit were performed. Zircon U-Pb dating of biotite K-feldspar granite (BG), fine-grained two-mica monzogranite (FTG), and medium-grained two-mica monzogranite (MTG) of the Ke’eryin composite pluton yielded crystallization ages of 219.5 ± 0.7 Ma, 212.8 ± 1.1 Ma, and 209.1 ± 0.7 Ma, respectively. Columbite-tantalite U-Pb dating of albite-spodumene type pegmatite (ASP) from the Jiada deposit yielded crystallization ages of 204.7 ± 1.0 Ma. The results show that the lithium mineralization in the Jiada deposit was temporally closest to the MTG emplacement. Combined with the regional magmatic evolution sequence, it is suggested that the Ke’eryin composite pluton and the Jiada deposit were emplaced during the period of transition from tectonic compression to extension under the effect of lithospheric delamination during post-collision. Geochemically, the compositional variation in the major elements of mica minerals indicate that BG, FTG, and MTG of the Ke’eryin composite pluton and the AP (albite type pegmatite) and ASP in the Jiada deposit were formed via the same continuous magmatic evolution process. The increasing Li, Rb, Cs, Nb, Ta concentrations and decreasing K/Rb, K/Cs, Nb/Ta ratios in mica minerals show that the degree of magmatic differentiation increased in the order BG-FTG-MTG-AP-ASP, indicating that MTG could be the parent rock of the Jiada pegmatites. The increase in the δ7Li values in muscovites from MTG through AP to ASP provides new evidence to support the fact that the fractional crystallization played a significant role in the formation of pegmatites in the Jiada deposit. Alkali metal elements (e.g., K, Rb, Cs) in the muscovites of MTG, AP, and ASP followed the Rayleigh fractionation law, indicating that a Rayleigh-type fractionation process occurred. Rayleigh fractional crystallization modelling of these alkali metal elements showed that the MTG could produce a magma melt of ASP through extreme fractional crystallization (∼98–99 % fractionation). Taken together with associated geological evidence, the aforementioned features indicate that the favorable tectonic setting and the prolonged and extreme fractional crystallization of the granitic melt jointly contributed to the formation of the Jiada pegmatite-type lithium deposit.

TSR Action and Genesis Mechanism of Antimony Deposit: Evidence from Aromatic Hydrocarbon Geochemistry of Bitumen from Paleo-Oil Reservoir in Qinglong Ore Field, Southwestern Guizhou Depression, China

In Qinglong ore field, the paleo-oil reservoir is found to be associated with antimony deposits, and they have a close genetic relationship. In this study, the aromatics geochemistry of paleo-oil reservoir bitumen was studied to further discuss the thermochemical sulfate reduction (TSR) reaction and the mechanism of antimony mineralization. A total of 124 aromatic compounds were identified by gas chromatography–mass spectrometry (GC–MS) analysis in bitumen samples, including abundant phenanthrene series, dibenzothiophene series, fluoranthene series, chrysene series, and a small number of fluorene series, naphthalene series, dibenzofuran series, biphenyl series, and triaromatic steroid series. Aromatic parameters such as trimethylnaphthalene index (TMNr), methylphenanthrene index (MPI), methylphenanthrene distribution fraction (MPDF, F1, and F2), methyldibenzothiophene parameter (MDR), C28TAS-20S/(20R + 20S), and benzofluoranthene/benzo[e]pyrene indicate that the Qinglong paleo-oil reservoir is in over maturity level. The abundance of phenanthrene and chrysene aromatic compounds and a small amount of naphthalene series, benzofluoranthene, fluoranthene, pyrene, anthracene, retene, perylene, and biphenyl suggest that the organic matter source of the paleo-oil reservoir was mainly low aquatic organisms, mixed with a small amount of higher plant. They detected a certain number of compounds, such as retene, triaromatic steroid series, and perylene, the ternary diagram of DBF–DBT–F and binary plot of Pr/Ph–DBT/P, DBT/(F + DBT)–DBF/(F + DBF), and Pr/Ph–DBT/DBF reveal that the source rock of the paleo-oil reservoir was formed in the marine environment of weak oxidation and weak reduction. The comprehensive analysis shows that the Qinglong paleo-oil reservoir originated from Devonian source rocks, just like other paleo-oil reservoirs and natural gas reservoirs in the Nanpanjiang basin. Abundant dibenzothiophene series were detected, indicating that the paleo-oil reservoir underwent a certain degree of TSR reaction. We believe that the gas reservoir formed by the evolution of the oil reservoir in the ore field participated in antimony mineralization; that is, hydrocarbon organic matter acted as a reducing agent and transformed SO42− in oilfield brine into H2S through TSR, providing reduced sulfur and creating environmental conditions for mineralization.

An evolving MVT hydrothermal system: Insights from the Niujiaotang Cd-Zn ore field, SW China

• The carbonate rocks acted as a key role during sulfide mineralization . • The change of alkaline-oxidized to acid-reduced resulted in sulfide precipitation. • The fluids evolved from the SW to the NE ore deposits . • The MVT deposits are the coupled mineralization product of fluid–structure-lithology. The metallogenic characteristics of Mississippi Valley-type (MVT) deposits have been widely concerned, but the evolution of MVT hydrothermal systems still needs to be further explored. The Niujiaotang Cd-Zn ore field (5,300 t Cd @ 0.04–1.43 wt% and 0.35 Mt of 5.85–24.48 wt% Zn) is located along the southeastern margin of the Yangtze Block, SW China, and consists of seven ore deposits, i.e. Dongchong, Mapo, Daliang, 768, Caiyuanhe, Shuanglongquan and Duniu. The ore bodies occur as stratiform or lenticular and are hosted by dolostone of the early Cambrian Qingxudong Formation, and are structurally controlled by the NE-trending Mandong fault. The hydrothermal dolomite has δ 13 C values of −3.03 ‰ to + 2.94 ‰, with lower contents of ΣREE (6.76–53.5 ppm), negative Eu and weakly positive Ce anomalies, all of which are similar to those of wall rocks. This suggests that the early Cambrian carbonate rocks involved in sulfide mineralization through water/rock (W/R) interaction and provided part of ore-forming materials. The δ 18 O values (+17.14 ‰-+22.79 ‰) are within the range of metamorphic fluids (δ 18 O=+16 ‰-+25 ‰), implying the hydrothermal fluids were derived from the Precambrian basement metamorphic rocks. The sulfides are characterized by scattered sulfur isotopes (δ 34 S=+10.03 ‰-+32.82 ‰), implicating that the reduced sulfur was derived from a mixed source of metamorphic fluids and thermo-chemical sulfate reduction (TSR). In situ Pb isotopes indicate that both Precambrian metamorphic rocks and early Cambrian sedimentary rocks provided metals for the hydrothermal fluids. In addition, the increased δ 34 S Σ values and Pb isotopes from Dongchong (SW part of the Niujiaotang ore field) to 768, and then to Duniu (NE part of the Niujiaotang ore field), indicating the hydrothermal fluids likely evolved from the SW to NE ore deposition sites along the Mandong fault, which is also confirmed by other evidence. Hence, we propose an evolving MVT hydrothermal system and a fluid-tectonic-lithology combination coupled metallogenic model for the Niujiaotang ore field. The determination of such metallogenic model of this ore field is conducive to the research and exploration of the similar MVT deposits nearby and worldwide.

Contrasting alteration textures and geochemistry of allanite from uranium-fertile and barren granites: Insights into granite-related U and ion-adsorption REE mineralization

AbstractAllanite is an important rare earth element (REE)-U-bearing mineral in granites, and it can act as a metal source for the formation of some hydrothermal uranium deposits and ion-adsorption REE deposits. To investigate the potential of allanite as a mineral probe of granite-related uranium mineralization processes and the formation of ion-adsorption REE deposits, we present textures, geochemistry, and in situ U-Pb isotope data for allanite from the fertile Changjiang granite associated with the Changjiang uranium ore field and barren Jiufeng granite in the Zhuguangshan batholith, South China. Alteration of allanite in the Changjiang granite is characterized by the altered domains with lower backscattered electron (BSE) intensities than the unaltered domains and replacement by other secondary minerals such as REE fluorocarbonates, calcite, fluorite, thorite, clay minerals, quartz, chlorite, and epidote. Crystals from the Jiufeng granite were partly replaced by the altered domains appearing darker in BSE images and minor REE fluorocarbonates. The darker domains of the Changjiang and Jiufeng allanite grains have higher Fe3+/(Fe3++Fe2+) ratios and U concentrations than those of the brighter domains, indicating that the alteration of allanite was probably related to more oxidized fluids. This study suggests that the Changjiang granite might have been subjected to the influx of F- and CO2-bearing fluids.The brighter domains of the Changjiang and Jiufeng allanite grains have weighted mean 207Pb-corrected 206Pb/238U ages of 156.7 ± 4.3 Ma and 161.6 ± 5.3 Ma, respectively, consistent with the corresponding zircon 206Pb/238U ages of 156.1 ± 1.4 Ma and 159.8 ± 1.8 Ma. The darker domains of the Changjiang allanite grains yield a weighted mean 206Pb/238U age of 141.4 ± 5.6 Ma, which overlaps within error the timing of a uranium mineralization event (~140 Ma) in the Changjiang uranium ore field and the age of a crustal extension event (140–135 Ma) in South China. The BSE images and elemental maps reveal that rare earth elements such as La and Ce have been released from the Changjiang allanites during alteration and were precipitated as REE-fluorocarbonates that are susceptible to chemical weathering, which sets the stage for the formation of an ion-adsorption REE deposit. Our study suggests that the regional crustal extension might have played an important role in the formation of both granite-related uranium and ion-adsorption REE deposits in South China, as it could have triggered alteration or breakdown of REE-U-bearing minerals in source rocks.

Crust–mantle interactions in Zijinshan ore field identified by zircon SIMS U–Pb age and zircon Hf–O isotopes

AbstractThis study presents zircon U–Pb geochronology and Hf and O isotope data for granitic rocks in the Zijinshan ore field, southwestern Fujian Province, China. The intrusive rocks comprise monzogranite, granite and granodiorite. The magmatic zircon U–Pb ages from these granitic rocks can be divided into four episodes: episodes 1 (157.9–159.9 Ma) and 2 (141 Ma) in the Late Jurassic and episodes 3 (108.1–103.2 Ma) and 4 (97.5–99.7 Ma) in the Middle and Late Cretaceous, respectively. Patterns of rare-earth elements (REE) show enrichment in light REE and obvious negative Eu anomalies. These rocks are also enriched in Rb, Th, U, La, Ce, Nd and Hf, and depleted in Ba, Nb, Sr, P and Ti. The increasing La/Yb ratio and decreasing heavy REE content with decreasing age may imply an increasing contribution of mantle-derived materials from the Late Jurassic to Cretaceous. The zircon ϵHf(t) and δ18O values, ranging from −37.7 to −2.8 and 12.0 ‰ to 6.3 ‰, respectively, indicate that the lower crust is an important source of granitic rocks. There was a significant increase in ϵHf(t) values and a decrease in δ18O values in the younger magmatic episodes (3 and 4), which ranged from −11.4 to −0.6 and 10.7 to 6.3 ‰, respectively. This suggests an increasing contribution of mantle-derived magma to the crustal melts from the Late Jurassic to late Early Cretaceous in response to the changing regional tectonic setting from compression to extension and an increasing interaction between the crust and mantle.

Contrasting U-Pb geochronology and geochemistry of uraninite from the Xianshi and Xiwang uranium deposits, South China: Implications for ore genesis

The Xiazhuang uranium ore field contains eighteen uranium deposits and is one of the most important granite-related uranium ore producers in South China. Silicified vein-type and intersection-type uranium deposits are the two main types of uranium deposits in this ore field. To constrain the mineralization ages and sources of uranium of these two types of uranium deposits, we present geochemistry and U-Pb isotopic data of uraninites from the representative Xianshi intersection-type and Xiwang silicified vein-type uranium deposits in the Xiazhuang ore field. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating on uraninite from the Xianshi deposit yielded the crystallization age of 89.9 ± 2.1 Ma, which is consistent with the emplacement age (∼90 Ma) of NNE-trending diabase porphyrite dykes in this area. Chondrite-normalized rare earth element (REE) patterns of uraninite from the Xianshi deposit are characterized by slight enrichment of light REE relative to heavy REE and weakly positive Eu anomalies. Our study suggests the involvement of mantle-derived metals in the formation of the Xianshi deposit. In situ LA-ICP-MS U-Pb dating on uraninite from the Xiwang deposit yielded a weighted mean age of 51.3 ± 0.8 Ma, which overlaps the timing of the 55–45 Ma crustal extension event in South China. Uraninite from the Xiwang deposit has much higher contents of W (5768–11305 ppm), Nb (294–1301 ppm), and Y (3013–6263 ppm) than those of uraninite from the Xianshi deposit (W = 291–371 ppm, Nb = 3–14 ppm, and Y = 1658–3149 ppm). Uraninite from the Xiwang deposit has “gull-winged” chondrite-normalized REE patterns with pronouncedly negative Eu anomalies, which resemble whole-rock REE patterns of the Maofeng and Xiazhuang granites. This study suggests that the Maofeng and Xiazhuang granites are probably the primary source of uranium for the Xiwang deposit.