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.
Orebodies in the Xiadian gold deposit in the Jiaodong Peninsula, China are mainly hosted in the Mesozoic granitoids, controlled structurally by the Zhaoyuan–Pingdu Fault Zone, and occur as disseminated and cataclastic altered type. Four mineralization stages were identified as follows: quartz–pyrite stage (I), gold‐bearing fine‐grained pyrite–quartz stage (II), polymetallic sulfide–quartz stage (III), and quartz–carbonate stage (IV). Quartz was classified as including quartz granules with dentation boundaries (I), cataclastic quartz grain assemblages (II and III), and rod‐like quartz grains (IV). Petrography, laser Raman analysis, and microthermometry of fluid inclusions in these stages (in both tunnel and borehole samples) reveal (a) CO 2 –H 2 O fluid inclusions (C–H type), (b) CO 2 –H 2 O ± CH 4 fluid inclusions (C–H–CH 4 type), and (c) aqueous fluid inclusions (H type). Fluid immiscibility caused by fluid mixing caused rapid precipitation of gold. The ore‐forming fluid of the Xiadian gold deposit evolves from an H 2 O–CO 2 –NaCl ± CH 4 system with medium temperature and salinity to an H 2 O–NaCl system with low temperature and salinity, from CO 2 ‐rich to CO 2 ‐poor in composition and from a mixture of magmatic water with increasing meteoric water as δ 18 O H2O values. Sulphur isotope compositions suggest a mixed source of ore metal, and the Jiaodong Group may be a major source for sulphur. Fluid parameters of borehole samples indicate that there is the same fluid system for Au precipitation at different depths and fault gouge with poor permeability may play a crucial role in forming a relatively closed semi‐open space for Au precipitation. Integrating the data obtained from the studies including regional geology, ore geology, and fluid inclusions and stable isotope geochemistry, the Xiadian gold deposit is concluded as an orogenic‐type gold deposit formed in the tectonic transition from compression to extension.
The Shanzhuang banded iron formation (BIF) occurs in the Shancaoyu Formation, Taishan Group, in the western Shandong Province (WSP), eastern North China Craton (NCC). We constrained the Shanzhuang BIF depositional age of ∼2.50 Ga based on the zircon U-Pb dating of the leptynite interlayers and the cross-cutting metagranitoid. After deposition, the Shanzhuang BIF was subsequently metamorphosed into amphibolite facies at 2.50–2.45 Ga. According to different mineral assemblages, the Fe ores can be divided into three types: magnetite + quartz ± hornblende (type-1 ore), magnetite + quartz + hornblende + garnet ± hematite (type-2 ore), and quartz + hematite ± magnetite ± hornblende (type-3 ore). In the Post-Archean Australian Shale (PAAS)-normalized rare earth element and yttrium (REY) patterns, the three ore types show consistent flat REY curves. All ore types have moderate ƩREY concentrations (27.24–143 ppm), (La/Yb)N values of 0.29–2.31, significant positive Eu anomalies (1.05–3.47), slightly negative or positive Ce anomalies (0.87–1.26), slightly positive Y anomalies (1.16–1.48), and no apparent fractionation between light REEs (LREEs) and heavy REEs (HREEs), indicating mixing of hydrothermal fluid and seawater. The similar REY patterns and heavy Fe isotopes (0.47–1.02‰) of the three ore types suggest a certain amount of continental detritus was incorporated during the precipitation of the Fe phases in the Neoarchean-Paleoproterozoic oceans. The post-depositional metamorphism did not significantly affect the original REY geochemical signature of the BIF. The Shanzhuang BIF ores are not highly pure chemical sediments, but the type-1 ore is relatively pure and more representative of the original sedimentary composition. By contrast, the type-3 ore tends to have higher δ56Fe ratios (0.74–1.02‰) but lower δEu (1.27–1.97‰), implying substantial post-depositional hydrothermal alteration. The Shanzhuang Fe deposit is an Algoma-type BIF, and the surrounding rock consists of pyroclastic materials. Our model indicates that the Shanzhuang BIF was probably deposited in a redox stratified paleo-ocean environment.
The Sanshandao Au deposit is located in the famous Sanshandao metallogenic belt, Jiaodong area. To date, accumulative Au resources of 1000 t have been identified from the belt. Sanshandao is a world‐class gold deposit with Au mineralization hosted in Early Cretaceous Guojialing‐type granites. Thus, studies on the genesis and ore‐forming element sources of the Sanshandao Au deposit are crucial. He and Ar isotopic analyses of fluid inclusions from pyrite (the carrier of Au) indicate that the fluid inclusions have 3 He/ 4 He=0.043–0.21 Ra with an average of 0.096 Ra and 40 Ar/ 36 Ar=488–664 with an average of 570.8. These values represent the initial He and Ar isotopic compositions of ore‐forming fluids for trapped fluid inclusions. The comparison of H–O isotopic characteristics combined with deposit geology and wall rock alteration reveals that the ore‐forming fluids of the Sanshandao Au deposit show mixed crust–mantle origin characteristics, and they mainly comprise crust‐derived fluid mixed with minor mantle‐derived fluid and meteoric water during the uprising process. The ore‐forming elements were generally sourced from pre‐Cambrian meta‐basement rocks formed by Mesozoic reactivation and mixed with minor shallow crustal and mantle components.
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