川东北普光地区新型杂卤石钾盐矿的物源:Sr、S同位素证据

新型杂卤石钾盐矿是近年来发现于四川盆地东北部早—中三叠世的一种可溶性海相固体钾盐,因其可利用性及低成本可开采特征,及其对海相找钾实现突破性进展提供的指示意义,引起了工业界及学术界的广泛关注。但当前以新型杂卤石钾盐矿为载体的海相成钾理论研究尚处于探索阶段,本文聚焦川东北普光地区中下三叠统新型杂卤石钾盐矿,将锶、硫同位素研究方法应用于杂卤石碎屑、石膏及"绿豆岩"等样品,以探讨新型杂卤石钾盐矿中不同组分的物源特征。分析结果显示,杂卤石碎屑和矿层底部硬石膏样品具有相似的δ³⁴S和⁸⁷Sr/⁸⁶Sr同位素特征,δ³⁴S分布在27.9‰～28.9‰之间,⁸⁷Sr/⁸⁶Sr介于0.70826～0.70829之间。该研究结果与同时期全球海相硫酸盐的δ³⁴S和全球海水的⁸⁷Sr/⁸⁶Sr的可对比性表明上述组分的主要物源应为同时期海水。该研究结果为进一步新型杂卤石钾盐矿成矿模型的建立及海相成钾理论的补充和完善提...     

The morphology and chemistry of K-feldspar megacrysts from Ikizdere Pluton: evidence for acid and basic magma interactions in granitoid rocks, NE-Turkey

Ikizdere Pluton consists of granite, granodiorite, tonalite, monzonite, quartz monzonite containing pinkish colored K-feldspar megacrysts (KFMs). The crystal sizes of the KFMs range from 1 to 4 cm. The lath-shaped megacrysts are uniformly (i.e., randomly) distributed in the host plutonic rocks and have mafic and felsic inclusions whose crystal sizes are smaller than 1 mm. The crystal inclusions are biotite, slightly annitic in composition with X_Mg[=Fe_tot/(Fe_tot+Mg)]=0.50-0.58, amphibole (magnesio-hornblende, X_Mg[=Mg/(Mg+Fe_tot)]=0.70-0.79), iron-titanium oxide (low titanium magnetit and ilmenite), plagioclase (Ab₇₅₋₂₅An₆₅₋₃₅) and as minor quartz. The compositions of the KFMs range from Or₉₅Ab₅An₀ to Or₈₂Ab₁₇An₁. BaO contents of the megacrysts increase from core to rim. The mafic and felsic inclusions are compositionally similar those of the host rocks.The chemical and textural features of K-feldspar are typical for megacrysts that grew as phenocrysts in dynamic granitoidic magma systems. The overgrowth of KFMs and mafic magma injections (magma mixing) may be related to temperature, pressure and compositional fluctuations in the magma chamber. Remnant of earlier formed K-feldspar crystals remain in the felsic magma system, while the mafic injection can decompose some earlier precipitated KFMs. The remnant of K-feldspar remaining after mafic injection are overgrown by rapid diffusion of Ba, K and Na elements in liquid phase, during the later stages of crystallization of the host magma.     

贵州铜仁塘边铅锌矿床成矿时代和成矿物质来源——来自Rb-Sr同位素测年和S-Pb同位素的证据

对贵州铜仁塘边铅锌矿床开展闪锌矿Rb-Sr测年和黄铁矿、方铅矿、闪锌矿S、Pb同位素分析,以获得矿区的成矿年龄,探讨其成矿物质来源。塘边铅锌矿床闪锌矿Rb-Sr等时线年龄为477±5Ma(MSWD=1.2),与前人获得的卜口场矿区闪锌矿Rb-Sr等时线年龄486±6Ma在误差范围内一致,表明矿床形成于加里东早期。黄铁矿、方铅矿、闪锌矿S同位素变化于+25.2‰~+36.1‰之间,与湘西—黔东主要铅锌矿床相似,明显富集重硫,认为S可能来源于寒武系海水碳酸盐和/或下伏地层。方铅矿、闪锌矿Pb同位素~(208)Pb/~(204)Pb值为38.389~38.584,~(207)Pb/~(204)Pb值为15.737~15.790,206Pb/~(204)Pb值为18.181~18.217,μ值为9.75~9.86,显示铅主要来源于上地壳。     

The long-lived partial melting of the Greater Himalayas in southern Tibet,constraints from the Miocene Gyirong anatectic pegmatite and its prospecting potential for rare element minerals

The Cenozoic Himalayan leucogranite-pegmatite belt has been a hotspot for rare metal exploration in recent years. To determine the genesis of the pegmatite in the Himalayan region and its relationship with the Greater Himalayan Crystalline Complex (GHC), the Gyirong pegmatite in southern Tibet was chosen for geochronological and geochemical studies. The dating analyses indicate that the U-Th-Pb ages of zircon, monazite, and xenotime exhibit large variations (38.6–16.1 Ma), with the weighted average value of the four youngest points is 16.5 ± 0.3 Ma, which indicates that the final stage of crystallization of the melt occurred in the Miocene. The age of the muscovite Ar-Ar inverse isochron is 15.2 ± 0.4 Ma, which is slightly later than the intrusion age, showing that a cooling process associated with rapid denudation occurred at 16–15 Ma. The ε_Hf(t) values of the Cenozoic anatectic zircons cluster between −12 and −9 with an average of −11.4. The Gyirong pegmatite shows high contents of Si, Al, and K, a high Al saturation index, and low contents of Na, Ca, Fe, Mn, P, Mg, and Ti. Overall, the Gyirong pegmatite is enriched in Rb, Cs, U, K, Th and Pb and depleted in Nb, Ta, Zr, Ti, Eu, Sr, and Ba. The samples show a high ⁸⁷Sr/⁸⁶Sr_{(16 Ma)} ratio of ca. 0.762 and a low ε_{Nd(16 Ma)} value of −16.0. The calculated average initial values of ²⁰⁸Pb/²⁰⁴Pb_{(16 Ma)}, ²⁰⁷Pb/²⁰⁴Pb_{(16 Ma)} and ²⁰⁶Pb/²⁰⁴Pb_{(16 Ma)} of the whole rock are 39.72, 15.79 and 19.56, respectively. The Sr-Nd-Pb-Hf isotopic characteristics of the Gyirong pegmatite are consistent with those of the GHC. This study concludes that the Gyirong pegmatite represents a typical crustal–derived anatectic pegmatite with low metallogenic potential for rare metals. The Gyirong pegmatite records the long–term metamorphism and partial melting process of the GHC, and reflects the crustal thickening caused by thrust compression at 39–29 Ma and the crustal thinning induced by extensional decompression during 28–15 Ma.©2023 China Geology Editorial Office.     

The ore genesis of the Jebel Mecella and Sidi Taya FBa (ZnPb) Mississippi Valley-type deposits,Fluorite Zaghouan Province,NE Tunisia,in relation to Alpine orogeny: Constraints from geological,sulfur, and lead isotope studies

Jebel Mecella and Sidi Taya F–(BaPbZn) deposits are located within the Fluorite Zaghouan Province (NE Tunisia). The mineralization occurs along the unconformity surface between the Jurassic limestones and Upper Cretaceous rocks. The mineralization consists mainly of fluorite, barite, sphalerite, and galena. The δ³⁴S values of barite at Jebel Mecella (14.8–15.4‰) and at Sidi Taya (21.6–22.2‰) closely match those of the Triassic evaporites and Messinian seawater, respectively. The range of δ³⁴S values of galena and sphalerite in both deposits (?6.9 to +2.4‰) suggests the involvement of thermochemical sulfate reduction and possibly organically-bound sulfur in the generation of sulfur. Lead isotope data with ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.893–18.903, 15.684–15.699, and 38.850–38.880, respectively suggests a single homogeneous source reservoir of Paleozoic age and/or the homogenization of the Paleozoic–Cretaceous multireservoir-derived fluids along their long migration paths to the loci of deposition during the Alpine orogeny.     

东昆仑夏日哈木镍铜硫化物矿床成矿岩浆条件:流体挥发份化学组成与碳同位素组成制约

夏日哈木镍铜硫化物矿床是我国东昆仑造山带新发现的全球岛弧环境最大的岩浆镍铜硫化物矿床。早泥盆世镁铁-超镁铁质成矿岩体中不同类型岩石的辉石中流体挥发份化学组成和碳同位素组成表明,流体挥发份总量较低,平均含量为888mm~3.STP/g(STP:标准温度和大气压)。流体挥发份组成以H_2O为主(48mol%),其次为H_2(26%)、CO_2(15%)和CO(5%)。H_2S含量从二辉橄榄岩(10mm~3/g)、橄榄辉石岩(18mm~3/g)到二辉辉石岩(28mm~3/g)逐渐增加,表明岩浆就位结晶演化过程中含硫组分的加入。CO_2的δ~(13)C值(-23.5‰~-5.0‰)位于地壳和地幔值范围之间。CH_4同系物碳同位素组成随碳数具有总体正序、局部反序的分布特征,显示大洋沉积有机质热裂解成因特征。夏日哈木成矿镁铁-超镁铁质岩体流体组分中较低的H2_O含量和较高的H_2含量表明,岩浆演化处于还原性挥发份条件,地幔岩浆源区存在俯冲洋壳沉积有机质,岩浆房围岩的混染和富S流体的加入可能是夏日哈木岩浆镍铜硫化物矿床硫饱和的主要机制。     

The Late Pleistocene Afton Lodge Clay Formation,Ayrshire, Scotland: evidence for Early to Middle Devensian climatic changes and Late Devensian onshore ice flow and rafting from the Firth of Clyde

An investigation into the late Pleistocene sediments exposed at Afton Lodge has helped to clarify the glacial history of western central Scotland. The sequence includes several allochthonous bodies of ‘shelly clay’ (Afton Lodge Clay Formation) associated with Late Devensian (Weichselian) age diamict. The shelly clay contains abundant marine macro- and microfauna, as well as palynomorphs consistent with its deposition within a shallow marine to estuarine environment. Faunal changes within the main body of marine clay record at least one, millennial-scale cycle of Arctic-Boreal, to Boreal, and back to Arctic-Boreal climatic conditions. A radiocarbon date of over 41 ka ¹⁴C BP obtained from the foraminifera indicates that the marine clays are older than the surrounding till. Afton Lodge is thus one of a suite of ‘high-level’ shelly clay occurrences around the Scottish coasts that are now considered to be glacially transported. Together with closely associated ‘shelly tills’, the rafts were emplaced during an early phase of the last glaciation by ice flowing from the western Grampian Highlands of Scotland through the topographically-confined Firth of Clyde basin. The blocks of marine sediment were detached subglacially, unfrozen, and carried at least 10 km by ice that splayed out onshore against reversed slopes favouring raft emplacement and the creation of closely associated ribbed moraine. Transport of the rafts was facilitated by water-lubricated décollement surfaces and their accretion was accompanied by dewatering. The shelly tills were formed mainly by the attenuation and crushing of rafts of shelly clay during their transport within the subglacial deforming bed.