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Gejiu is geographically located near Gejiu city, SW China. It is one of the largest tin-polymetallic districts in the world and contains approximately 3 million tons (Mt) of Sn and smaller quantities of Cu, Pb, and Zn. The deposit primarily yields three different types of ore: skarn-hosted ore, basalt-hosted stratiform ore, and carbonate-hosted stratiform ore. Kafang is one of the primary ore deposits in the Gejiu district and is an unusual occurrence hosted in basaltic rocks. Genetic models of the Kafang deposit suggest that it is related either to Anisian (Lower stage of Middle Triassic) Gejiu basalts or to Cretaceous Gejiu granite. In this study, we performed zircon SIMS U–Pb dating, major and trace element analyses, and Sr–Nd–Pb isotopic analyses for the Gejiu basalts and S isotopic analyses for stratiform Cu ore. Our results and previous studies are used to interpret the petrogenesis of the Gejiu basalts and the origin of the basalt-hosted stratiform Cu deposit. The SIMS zircon U–Pb analyses of the Gejiu basalts yield an age of 244.4 Ma. The trace element ratios of the Gejiu basalts are similar to those of ocean island basalt and have positive εNd(t) values (ranging from 0.6 to 2.5) and uniform (87Sr/86Sr)i values (ranging from 0.70424 to 0.70488). These ratios are close to those of the Permian Emeishan flood basalt. Thus, the Gejiu basalts may represent coeval volcanisms within the plate involving remelting of the Emeishan plume head through a stress relaxation process after the main plume event. The Pb and S isotopic compositions of the Gejiu basalts and the stratiform Cu ores indicate that the source of Cu and S is primarily derived from the Gejiu basalts. However, the age of sulfide mineralization (84.2–79.6 Ma) and the age of hydrothermal alteration (85.5–81.9 Ma) are temporally consistent with the age of the Cretaceous granite emplacement (85.5–83.3 Ma). From a petrological and geochemical study, we determine that the Gejiu basalts may have been subjected to pervasive granite-related hydrothermal alteration during the emplacement of granite. These processes increase the K and Mg contents of basalt and probably caused the formation of the Cu ores. Thus, the Kafang stratiform Cu deposit can be considered as a granite-related hydrothermal deposit. 相似文献
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<正> 地质概况 娘娘山碱性火山杂岩体位于下扬子火山岩带宁芜断陷盆地中段的西翼,临近北北东向和北西向基底断裂的交汇处。杂岩体由含有假白榴石、黝方石的熔岩、火山碎屑岩和火山一侵入岩所组成,出露面积约15平方公里。碱性火山喷发杂岩不整合于粗面安山质火山岩之上。碱性火山碎屑岩内含有粗面安山岩和安山岩的角砾,在某些地区还见到碱性次火山岩侵入于粗面安山岩。宁芜地区安山质火山岩同位素年龄为136—114×10~6年,而娘娘山碱性火山杂岩年龄为105.7—91×16~6年。这都证实碱性火山杂岩为安山质岩浆火山活动之后(属晚白垩世)的产物。 相似文献
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贵州遵义地区黄家湾镍钼多金属矿是寒武系底部的黑色页岩型矿床。黑色岩系中微量元素特征显示镍钼多金属矿层的Ni,Mo,Cd,V,Cu,Zn明显富集,而高场强元素Nb,Th,Hf,Zr,Ti亏损。稀土元素显示多金属矿层的艿（Eu）呈正异常,中稀土富集,重稀土亏损。结合镜下观察发现的有机质、红藻囊果与金属硫化物之间密切的共生关系和前人研究结果,分析了黑色岩系镍钼多金属矿的成因,认为镍、钼、铜、锌等金属元素的来源与热液有关,通过生物作用聚集并在缺氧的还原沉积环境下大量堆积,富集形成Ni—Mo金属硫化物矿床。 相似文献
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Kafang is one of the main ore deposits in the world-class Gejiu polymetallic tin district, SW China. There are three main mineralization types in the Kafang deposit, i.e., skarn Cu–Sn ores, stratiform Cu ores hosted by basalt and stratiform Cu–Sn ores hosted by carbonate. The skarn mainly consists of garnet and pyroxene, and retrograde altered rocks. These retrograde altered rocks are superimposed on the skarn and are composed of actinolite, chlorite, epidote and phlogopite. Major ore minerals are chalcopyrite, pyrrhotite, cassiterite, pyrite and scheelite. Sulfur and Pb isotopic components hint that the sources of different types of mineralization are distinctive, and indicate that the skarn ore mainly originated from granitic magma, whereas the basalt-hosted Cu ores mainly derived from basalt. Microthermometry results of fluid inclusions display a gradual change during the ore-forming process. The homogenization temperature of different types of inclusions continuously decreases from early to late mineralization stages. The salinities and freezing temperatures exhibit similar evolutionary tendencies with the T homogenization, while the densities of the different types keep constant, the majority being less than 1. Oxygen and hydrogen isotopic values (δ18O and δD) of the hydrothermal fluids fall within ranges of 3.1 to 7.7‰ with an average of 6.15‰, calculated at the corresponding homogenization temperature, and − 73 and − 98‰ with an average of − 86.5‰, respectively. Microthermometry data and H–O isotopes indicate that the ore-forming fluid of the Kafang deposit is mainly derived from magma in the early stage and a mixture of meteoric and magmatic water in late stage. Molybdenite Re–Os age of the skarn type mineralization is 83.4 ± 2.1 Ma, and the stratiform ores hosted by basalt is 84.2 ± 7.3 Ma, which are consistent with the LA-ICP-MS zircon age of the Xinshan granite intrusion (83.1 ± 0.4 Ma). The evidence listed above reflects the fact that different ore styles in the Kafang deposit belong to the same mineralization system. 相似文献
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