Abstract The application of whole-rock compositions to trace magma evolution or crystal-melt equilibrium may be called into question when foreign crystals are incorporated into host magmas. To address this challenge, establishing the origins (orthocrysts, antecrysts, xenocrysts, etc.) of minerals with variable textures in magmatic plumbing systems is necessary. In this paper, we describe complex oscillatory zoning patterns of clinopyroxenes (Cpx) from the Miocene Majuangou (MJG) alkali basalts from West Qinling, China. Our detailed petrographic, mineralogical, and geochemical analyses unravel the origins of various Cpx crystals with distinct textural patterns, thereby providing information about magma storage, recharging and/or mixing, and transportation, as well as the reactions between crystals and melts/fluids. Based on textural patterns, Cpx may be divided into four types: normal (Type-1 Cpx), simple oscillatory (Type-2 Cpx), complex oscillatory (Type-3 Cpx), and grains that lack zoning (Type-4 Cpx, suggested to be orthocrysts). Through the textural characterization of Cpx, the comparison between different types of Cpx, and the relationships between Cpx major compositions from different lithologies, we concluded that Type-1–3 Cpx cores are antecrysts or xenocrysts with diverse origins: primitive magma (Type-1 Cpx cores), magma mush (Type-2 Cpx cores), and crustal granulite (Type-3 Cpx cores). The zoning patterns and the compositions of these Cpx crystals indicate at least three batches of magmatic activity, i.e., the Batch-1 low-Mg# magma (Mg#: 47.4–53.3), the Batch-2 primitive magma (Mg#: 57.2–64.5), and the Batch-3 low-Mg# host alkali magma (Mg#: 47.2–54.6). Cpx-melt thermobarometry demonstrates that at least two crustal magma reservoirs existed in the magma plumbing system at depths of 30.1 and 40.9 km. The antecrystic/xenocrystic Cpx cores were captured by, continued to grow in, and subsequently reacted with ascending K-rich melt/fluid. The spongy textures in Cpx cores/mantles are attributed to this reaction, which may be expressed as: Melt 1 (primitive or evolved) + K-rich melts/fluids + Cpx (CaMgSi2O6) = K-feldspar (KAlSi3O8) + ilmenite (FeTiO3) + Melt 2 (derivative). The products of this reaction (K-feldspar and ilmenite) filled the sieves in the spongy zones of Type-1–3 Cpx. This detailed investigation of compositional and textural features of Cpx antecrysts/xenocrysts suggests that the interactions between various interconnected magma reservoirs are widespread beneath the magmatic plumbing system. Our study emphasizes the importance of the incorporation of foreign crystals and the Cpx-melt/fluid reaction in magmatic plumbing system, which can significantly modify the whole-rock compositions and lead to the formation of spongy textures without the need for fractures and cracks in minerals.
胶东地区金矿巨量金质来源一直是学界争论的焦点,很难找到有说服力的直接证据。在没有其它更有效的直接证明巨量金质来源的情况下,本文通过胶北隆起主要地质体新鲜岩石大量微量元素地球化学数据的变化规律,间接得出中生代壳幔岩浆的混合反应是巨量金质来源的关键,即郭家岭和伟德山两期壳幔岩浆的混合反应和演化可能是巨量金质来源的主要形成机制,同时更是热量供给源,而玲珑花岗岩可能是少量金质的提供者和主要赋矿地质体。胶东地区金矿主要成矿时间(130~105Ma)与郭家岭(130~125Ma)和伟德山(126~108Ma)两期花岗岩浆演化结晶时间完全吻合,说明其关系密切,岩浆混合反应和冷凝期,岩浆热液上升运移沉淀成矿。该区中生代地质体对早前寒武纪的地球化学环境有一定的继承性,中生代地壳混合了大量地幔物质,Au丰度偏高,平均为1.31×10-9,为地球化学高背景场。;The huge material source of gold deposits in Jiaodong area has always been the focus of academic debate, and it is difficult to find convincing evidence. In the absence of other more effective direct proof of the source of huge gold, this paper indirectly draws the conclusion that the huge gold comes from the mixing reaction of Mesozoic crust-mantle magmas based on the variation law of large amounts of trace elements geochemical data from fresh rocks of main geological bodies in Jiaobei area. The mixing reaction and evolution of the Guojialing and Weideshan crust-mantle magmatism may be the main mechanism for the formation of huge gold source, and it is also the source of heat supply. Linglong granite may be a small amount of gold supplier and the main ore-hosting geological body. The main metallogenic time of gold deposits in Jiaodong area (130~105Ma) is the same as the evolution and crystallization time of granite magma of Guojialing (130~125Ma) and Weideshan (126~108Ma) granites, which means they are closely related. During magma mixing reaction and condensation period, magmatic hydrothermal fluids ascending, migration, and precipitation mineralization. The Mesozoic geological bodies inherited geochemical environment of Early Precambrian in this area. The Mesozoic crust was mixed with a large amount of mantle materials, and the Au abundance was high, averaging 1.31×10-9, which was a geochemical high background.
In this paper, 219 concordant detrital zircons from the main stem and tributary rivers of the Central Qilian Block (CQB) have been analyzed using excimer laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to determine their U-Pb ages and Lu-Hf isotopic compositions. The detrital zircons from three samples show four major age groups: 246–509 Ma, 899–1176 Ma, 1620–2089 Ma, and 2131–2610 Ma. These age populations indicate that prominent magmatic events occurred at 0.5 Ga, 0.9 Ga, 1.8 Ga, and 2.5 Ga. Archean basement components are rare in these river sands and likely derived from Paleoproterozoic metamorphic complexes. The crustal model ages from Hf isotopic analyses show age peaks at ~2.5 and 1.8 Ga. The crustal accretion of material derived from the depleted mantle of the CQB occurred in two stages at 3.2–1.8 Ga and 1.8–0.6 Ga. The crustal accretion curve based on the Hf model ages indicates that approximately 10% of the present crustal volume of the CQB formed at 3.2 Ga, while ~60% formed at 1.8 Ga. Few crustal components have accreted from the depleted mantle since 0.6 Ga in the CQB. The reworking rate calculation shows that continental crustal accretion also occurred at 2.5 Ga in the CQB; the most intensive crustal reworking occurred at 0.8 Ga. Comparisons of Precambrian continental growth patterns of the African continent and CQB indicate that the zircon Hf isotopic compositions can be used to accurately constrain the growth patterns of continental crust and that a microcontinent can serve as window into the crustal growth of supercontinents during certain periods.
“Trapiche-like” texture is distinct from “trapiche” texture as typically observed in emeralds, amethysts, and aquamarines. It is also occasionally encountered in sapphires from Changle, eastern North China Craton. The advent of the trapiche-like texture has enhanced the ornamental value of sapphire, although its origin is still unclear. In this study, techniques, such as Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV-Vis) spectroscopy, Raman spectroscopy, electron probe microanalysis (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), have been applied to test the spectroscopic data of the cores, arms, and blue sectors of trapiche-like sapphires from Changle and explore the mineralogical characteristics of different domains. The main component of the core, arms, and blue sectors of trapiche-like sapphire is corundum (Al2O3), with trace elements including Fe, Ti, Mg, Cr, V, Ga, etc. From arms to cores to sectors, trace elements show a trend of increasing and then decreasing. Nb and Ta elements are more enriched in the arms than in the sectors, indicating the existence of rutile. With changes in physicochemical conditions during magma evolution, rutile melted, and related voids were filled with glassy inclusions, which formed the arms of trapiche-like sapphires. Field observations of primary deposits, as well as petrological and geochemical analyses, reveal that the trapiche-like sapphire of Changle belongs to magmatic sapphire.
Delineating the process of hydrothermal alteration is crucial for effectively enhancing exploration strategies and better understanding the gold mineralization process. Rutile, with its capacity to accommodate a wide range of trace elements including high-field-strength elements and base metals, serves as a reliable fluid tracer in ore systems. As one of the most significant gold ore concentrations globally, Jiaodong boasts a gold reserve exceeding 5500 t. The Xincheng gold deposit is a world-class high-grade mine, boasting a proven gold reserve exceeding 200 t, and stands as one of the largest altered-type gold deposits in the vast gold province of the Jiaodong Peninsula, Eastern China. In this study, rutile (Rt1,2,3) was identified in the K-feldspar alteration, sericitization, and pyrite–sericite–quartz alteration stages of the Xincheng gold deposit in Jiaodong based on petrographic characteristics. Rt1 coexists with hydrothermal K-feldspar and quartz, while Rt2 coexists with minerals such as sericite, quartz, muscovite, and pyrite. Rt3 is widely distributed in hydrothermal veins and is primarily associated with minerals including quartz, pyrite, chalcopyrite, and sericite. Raman spectroscopy, EPMA, and LA-ICP-MS analysis were conducted to investigate the characteristics and evolution of altered hydrothermal fluids. This study indicates that the Zr vs. W and Nb/V vs. W diagrams suggest that Rt1 is of magmatic–hydrothermal origin, while Rt2 and Rt3 are of metamorphic–hydrothermal origin. Notably, the W content in Rt2 and Rt3 is significantly higher than in Rt1 (<100 ppm), suggesting a close relationship between the W content in rutile and mineralization. The three types of rutile exhibit significantly different concentrations of trace elements such as W, V, Nb, Zr, Sn, and Fe, displaying distinct bright spots and elemental zoning characteristics in backscattered electron images and surface scans. These features arise from the isomorphic substitution of Ti4+. While Rt1 exhibits no significant element exchange with the hydrothermal fluids, Rt2 and Rt3 show a stronger substitution of W, Nb, V, and Fe, indicating a gradual enrichment of F and Cl in the fluids. This process activates and transports these elements into the fluids, leading to their continuous accumulation within the system. From Rt1 to Rt3, the increasing concentrations of Fe and W, along with the negative Eu anomaly, suggest a decrease in fluid temperature and oxygen fugacity during the alteration and mineralization process. The gradual increase in the contents of REEs and high-field-strength elements such as W, V, Nb, and Sn indicates that the hydrothermal fluids are enriched in F and Cl, exhibiting weak acidity. The nature of the fluids during hydrothermal alteration is closely related to the composition of rutile, making it a promising tool for studying hydrothermal alteration and related mineralization processes.
Abstract The newly discovered Shanzhuang BIF is hosted in the Shancaoyu Formation of the Taishan Group within the Eastern Block, southeastern margin of the North China Craton. The ores can be subdivided into three types in terms of mineral assemblages, corresponding to three types (I, II, III). The element concentration of the type I magnetite is similar to that of the type II magnetite, while the type III magnetite is similar to that of the schist. In general, magnetite and hematite grains from the ores show high concentrations of Mn (1317, 1162 ppm), Co (787, 1023 ppm), Al (2224, 2435 ppm) and Ti (540, 300 ppm), Whereas magnetite is depleted in Si (420 ppm) and hematite enriched in Si (1690 ppm). Detailed petrographic and mineral chemical analysis of magnetite, hematite, amphibole/hornblende and pyroxene, reveals that almost all the minerals occur as subhedral‐anhedral grains with pits and fractures, and the BIF is recrystallized to metamorphic assemblages of high amphibolite facies. Hornblende is highly enriched in Fe, Mg and Ca, but depleted in K and Na, mostly belonging to magnesiohornblende. In addition, the ratios of Mg/(Mg+Fe 2+ ), Fe 3+ /(Fe 3+ +Fe 2+ ), Si/(Si+Ti+Al) and Al/Si are 0.48–0.64, 0.17–0.36, 0.79–0.88 and 0.14–0.27, respectively. It is suggested that hornblende is neither a typical magmatic origin nor a typical metamorphic. Pyroxene has the characteristics of high Ca and Fe, but low Ti and Al, with end‐member components En, Wo and Fs in the ranges of 25.22–28.64 wt%, 43.71–46.40 wt% and 24.51–27.62 wt%, respectively, belonging to clinopyroxene, and mostly diopside, might be formed during the prograde metamorphism in the absence of H 2 O. The carbonate such as dolomite‐ankerite series is probably a precursor mineral of the BIF deposit. Mass mineral chemical and structural characteristics indicate that the Shanzhuang iron deposit has been subjected to varying degrees of oxidized hydrothermal superimposed reformation, metamorphism, and supergenesis after mineralization, during which some elements have been migrated in some degree.
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