广东河台金矿硫化物地球化学特征及地质意义
投稿时间:2024-01-01  修订日期:2024-03-25  点此下载全文
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焦骞骞* 昆明理工大学 650017
中文摘要:河台金矿是广东省最大的金矿,被认为是典型的剪切带型金矿。尽管矿床产于云开群变质岩中,但是在产出时间和空间展布上又与云楼岗和伍村岩体有密切关系,再加上成矿的多阶段性,导致对成矿流体及物质来源一直存在争议。河台金矿的金主要以自然金形式产出,与黄铁矿、黄铜矿、磁黄铁矿等矿石矿物紧密共生。本文对河台金矿田热液成矿期金-硫化物阶段的黄铁矿、磁黄铁矿进行了微量元素和Sr-Nd同位素分析,以进一步示踪成矿流体及物质来源。两种硫化物Co/Ni比值为0.36~3.33,显示主要为热液成因。Hf/Sm、Nb/La、Th/La值<1,暗示成矿热液是以富Cl-的流体为主;Y/Ho比值为12.0~33.0,与糜棱岩有明显区别;(87Sr/86Sr)i值为0.707078~0.713545,εNd(t)为-19.36~ -15.12,位于华夏板块元古代基底和EM1富集地幔之间。这些特征暗示成矿流体的多源性。黄铁矿∑LREE/∑HREE值介于5.53~15.4,在球粒陨石标准化图中呈明显右倾,δEu值介于0.48~0.75,具有明显的Eu负异常,与糜棱岩特征相似,暗示成矿物质主要来自围岩。结合前人年代学研究结果,推测印支期在混合岩化和韧性剪切作用下,变质流体将云开群中的成矿物质运移到剪切带中,使Au初步富集;燕山期地壳深部华夏板块中-古元古基底重熔产生的岩浆流体混入少量地幔流体,为剪切带中成矿物质发生活化迁移提供载体和动力,并在局部再次富集形成工业矿体。
中文关键词:黄铁矿  微量元素  Sr-Nd同位素  成矿物质及流体来源  广东河台金矿
 
Geochemical characteristics and geological implications of sulfides in the Hetai goldfield, Guangdong Province, south China
Abstract:Hetai goldfield, the largest gold concentration district in Guangdong Province, was considered as a typical example of gold mineralization related to ductile-shear deformation. The deposits in the goldfield occurred at the Yunkai metamorphic series, however, the close spatial and temporal association with the Yunlougang and Wucun granitoids, and the multi-stage mineralization resulted in long- term controversy about the source of ore-forming fluids and metals. The Au mineralization in the goldfield predominantly occurs as native gold intimate intergrowth with ore minerals that include pyrite, chalcopyrite, and pyrrhotite. We analysis of the trace elements and Sr-Nd isotopes of pyrite and pyrrhotite that present at the gold-sulfide substage of hydrothermal mineralization stage to further constrain the origin of the ore-forming fluids and metals. Two types of sulfides have Co/Ni ratio in range of 0.36 to 3.33, indicating a mainly hydrothermal genesis. The ratios of Hf/Sm, Nb/La, and Th/La of the sulfides are less than 1, suggesting the ore-forming fluids is enriched in Cl-; Y/Ho ratio varying from 12.0 to 33.0, significantly differ from that of mylonite; and (87Sr/86Sr)i and εNd(t) values in range of 0.707078 to 0.713545 and -19.36 to -15.12, is between the HuaXia Plate basement and EM-1 enriched mantle. The above results suggest the multi- origin for the ore-forming fluids. The pyrite with ∑LREE/∑HREE values ranging from 5.53 to 15.4 and obviously negative Eu anomaly with δEu values from 0.48 to 0.75, have remarkable similarity to the mylonite in the chondrite-normalized diagram with right incline pattern, suggesting the ore-forming metals mainly derived from the surrounding metamorphic series. Combined with previous geochronological result, we proposed that in the Indosinian period, the metamorphic fluids that derived from the migmatization and ductile shearing drove the ore-forming metals from the Yunkai Group to initially concentrate in the shear zones; in the Yanshanian period, magmatic fluids that derived from the remelting of Paleo-Proterozoic HuaXia Plate basement mixed with some mantle-derived fluids, playing a role as the carrier and driving force for the activation and migration of ore-forming metals, resulted in the formation of economic orebodies at the favorable place within the shear zones.
keywords:Pyrite  Trace elements  Sr-Nd isotopes  Sources of ore-forming fluids and metals  Hetai goldfield in Guangdong Province
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