Organic Mineralization of Lead-Zinc Deposits in Devonian System, Xicheng Ore Field
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摘要: 西成矿田是秦岭多金属成矿带最重要的铅锌矿田之一.从有机地球化学特征、有机质和有机分子与金属元素的关系、矿石、围岩及与矿石共生的炭沥青的元素分析及有机流体萃取金属元素的模拟实验方面出发, 探讨了有机质在西成铅锌矿田形成过程中的作用.结果表明: (1) 与矿化有关的岩石(硅质岩和灰岩), 主峰碳数均为nC18, 中间支链烷烃、伽玛蜡烷、胡萝卜烷系列含量比非矿化岩石高; (2) 与矿化有关岩石(硅质岩和大理岩) 的生物母源以菌藻类低等生物为主, 并有陆源母质混入, 矿床形成于还原环境, 矿床中存在来源相同或相似的异源有机质; (3) Pb、Zn元素与芳烃、氯芳沥青“A”、非烃+沥青呈显著的负相关; 与非烃、有机硫、有机硫/(有机碳× 1.22) 比值呈正相关关系; Pb、Zn元素与正构烷烃、甾萜烷、胡萝卜烷等有机分子丰度具正相关关系, 而与w(∑C22-)/w(∑C22+)、w(三环萜烷)/w(四环萜烷)、w(C20+C21)/w(C23+C24)及w(萜烷)/w(甾烷) 等有机分子比值具负相关关系; (4) 炭沥青与围岩、矿石中子活化分析结果表明, 在后期改造成矿作用中, 炭沥青与矿石有紧密联系, 有机质和成矿元素一起在改造成矿期抵达成矿部位并参与了成矿; (5) 模拟实验表明, 在热水流体中, 有机水的加入增大了对Pb、Zn元素的溶解能力, 增加了岩样释放成矿元素的能力, 有机质在热水流体运移过程中确实对成矿元素发生了作用.在此基础上, 提出生物有机质在西成地区铅锌矿床的形成过程中发挥了重要作用.Abstract: One of the most important ore fields in Qinling multi-metallic ore-forming belt is Xicheng Pb-Zn deposit which is controlled strictly in the Middle Devonian series. Viewing from organic geochemistry, the correlation between ore-forming elements and organic matter, organic molecules, the analysis of neutron activation for asphalt, ore, wall rock and the experiment simulation, this paper probes into the role of organic matter in the forming process of Xicheng Pb-Zn ore field. The analysis results for organic geochemistry of fresh rock and ore samples selected systematically show that the content of chloroform bitumen "A" from the cherts and the silicified limestones involved in mineralization is lower than that from the unmineralized rocks. While GC-MS-MS analysis of rocks and ores suggests that the dominant carbon is almost nC18 in all mineralization rocks (siliceous rocks and limestone rocks). Organic molecules of the rocks relevant to mineralization and limestones are mainly pentacyclic triterpene. Studies on the correlation analysis between organic matter and ore-forming elements show that the contents of Pb and Zn have striking negative correlations with aromatic hydrocarbon and chloroform asphalt "A" and positive correlation with non-hydrocarbon and organic sulfur/(organic carbon×1.22). The contents of Pb and Zn have positive correlations with the abundances of some organic molecules, whereas they have negative correlations with the ratios of some organic molecules. The analysis results of neutron activation for asphalt, ore, wall rock reveal that the asphalt has a close relationship with ores, and that the organic matter comes to the ore-forming site together with ore-forming elements at the reformed mineralization stage. The dissolution ability of Pb-Zn, the ability of the rock samples of releasing ore-forming elements have been increased because of the adding of organic water in hot water fluid. Therefore, it can be inferred that the organic matter played an important role in the formation of lead-zinc deposits in Xicheng ore field.
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Key words:
- organic mineralization /
- lead-zinc deposit /
- Devonian /
- Xicheng ore field
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图 2 金属元素含量与有机分子丰度的正相关关系(数据见表 2)
Fig. 2. Positive correlation between metallic elements content and abundance of organic molecule
图 3 金属元素与有机分子比值的负相关关系(数据见表 2)
Fig. 3. Negative correlation between metallic elements content and organic molecules ratios
表 1 西成矿田岩(矿) 石氯芳沥青族组成及有机碳、有机硫含量
Table 1. Content of chloroform asphalt components, organic matter and organic sulfur in rocks/ores of Xicheng ore field
表 2 西成矿田有机分子丰度及Pb、Zn元素含量
Table 2. Organic molecular abundances and Pb-Zn elements content in Xicheng ore field
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