胶东夏甸金矿床地球化学特征及其地质意义
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本文为国家自然基金项目山东招远- 平度断裂带夏甸金矿深部成矿特征研究(编号41572068)、国家重点研发计划项目胶西北地区深部构造格架研究- 依托于深部反射地震(编号2016YFC0600107- 5)、国家公益性专项胶东招平断裂带深部特征与金矿成矿过程研究(编号201511029)、招平断裂带中段深部金矿成矿理论找矿方法与成矿预测(编号2017CXGC1605)和山东省泰山学者建设工程专项联合资助的成果。


Geochemical characteristics and geological significance of the Xiadian gold deposit, Jiaodong area
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    摘要:

    为探讨夏甸金矿床不同元素的地球化学成矿行为,本次以夏甸金矿床外围花岗岩、构造碎裂岩和金矿石的主微量和稀土元素地球化学资料为依据,研究其化学成分、微量元素和稀土元素在不同岩矿石中丰减富集变化及成矿过程。在化学成分方面,招平断裂带碎裂岩中具有较高的SiO 2、K 2O值,Fe 2O 3、Na 2O、CaO降幅较多,反映了成矿阶段存在有普遍的硅化现象和钾化现象和铁质流失现象进入到热液成矿中;矿石化学成分中SiO 2、Al 2O 3和Fe 2O 3具有较大幅度的增升和降低的双重变化特点,尤其是铁、钾、钙增加比例较高,指示与成矿过程中普遍发育的黄铁矿化相一致,矿石中K 2O含量比玲珑花岗岩平均含量高30%,则代表钾化的岩石更有利于金矿的沉淀。夏甸金矿区的围岩中Au元素含量普遍低于正常的玲珑花岗岩,但Ag、W等元素含量则普遍较高,是平均值的3~10倍,断裂带碎裂岩中亲硫(亲铜)元素Ag、Cu、Pb、Zn明显增高,尤其是Ag和Zn分别是玲珑花岗岩的2. 79倍和2. 09倍,说明亲硫(亲铜)元素与金矿成矿作用关系密切;亲铁元素Cr、Co、Ni、Mo、Au、Sn、W整体上呈递增状况,大离子亲石元素Li、Be、Rb、Zr、Nb、W、Sr、Ba、As大多呈亏损状态。矿石中Au、Ag、W、Cu等具有强烈的富集,其中Au富集了381. 40倍,W富集了3961. 23倍,Ag富集了254. 16倍,Cu富集了116. 19倍,而Bi、Mo、As、Pb、Zn等富集度相对稍低,在3~20倍之间。在围岩、破碎蚀变带和金矿石中,皆出现了非常高的W元素富集,展示了招平断裂带具有独特的成矿地球化学行为。夏甸矿区围岩、构造蚀变碎裂岩和金矿石中的ΣREE总量分别为78. 82×10 -6、27. 15×10 -6和102. 43×10 -6,LREE/HREE比值分别为19. 3、8. 46和12. 66,金矿石中具有相对较高的ΣREE、LREE和HREE,说明在成矿过程中外来物质的加入改变了稀土元素的含量和比值,也是区分矿与非矿的重要地球化学标志。矿区围岩、构造蚀变碎裂岩和金矿石的δEu分别为1. 88、1. 49和0. 83,Eu/Sm值分别为1. 57、2. 05和0. 69,Ce/Yb值分别为25. 15、5. 33和12. 86,轻重稀土内部分馏均较小,成矿环境为弱氧化环境,说明夏甸金矿在成矿过程中,稀土元素更多地是反映从流体体系中带入到成矿的过程,使矿石中稀土元素含量相对增加。结合光片鉴定结果,在金成矿过程中,先期形成的黄铁矿多呈碎粒状,裂纹十分发育,黄铜矿呈他形粒状充填于黄铁矿裂纹中与金共生,说明自然金是与黄铜矿是同期形成的,而晚于黄铁矿的形成时间。

    Abstract:

    Jiaodong is located at the junction of Tethys, Paleo- Asian and Pacific Oceans. Their interaction and intracontinental process affect the magma- tectonic events and metallogenic dynamics in the Jiaodong area. The tectonic system transformation in the Mesozoic, the destruction and reconstruction of the craton, and the strong lithospheric thinning in eastern China are the main causes of the Mesozoic gold mineralization burst. The Sanshandao fault zone, the Jiaojia fault zone and the Zhaoping fault zone are the main ore control structures in the Jiaodong area. The amount of gold in these three structural zones has reached 3317t as proved by exploration. The Xiadian gold deposit is a large gold deposit located in the footwall of the Zhaoping fault zone and distributed along the contact zone between the Linglong granite and the basement rocks in Jiaodong. The ore bodies are mainly hosted in pyrite sericite cataclasite and pyrite sericite within 80 m of the footwall of the Zhaoping fault zone. They are vein like and layered, with slow wave- like changes along the strike and trend, with feature of branches, complex, expansion, sharp extinguish and reappearance. The metallogenic geological environment, deposit characteristics, inclusions and trace element geochemical characteristics of the Xiadian gold deposit have been studied by predecessors. Based on geochemical data of main elements, trace elements and rare earth elements of granite, structural cataclasite and gold ore in the periphery of the Xiadian gold deposit, this article studies the changes in chemical composition, trace elements and rare earth elements in different rocks and ores to obtain a preliminary understanding. In terms of main elements, SiO 2, Fe 2O 3, K 2O, Na 2O, CaO, MgO, MnO and P 2O 5 in the peripheral biotite monzogranite are lower than the average value of the Linglong granite, but the overall petrochemical characteristics are consistent; SiO 2 and K 2O in cataclastic rocks of the Zhaoping fault zone show a large increase, while Al 2O 3, Fe 2O 3, K 2O, Na 2O, CaO, MgO, MnO, TiO 2 and P 2O 5 are relatively lower, especially Fe 2O 3, Na 2O and CaO. The change in chemical composition reflects the occurrence of silicification and potassification in the ore- forming period. The chemical composition of ore is closely related to the original rock. The SiO 2 content is 42. 06%~81. 29%. SiO 2, Al 2O 3 and Fe 2O 3 have a double change characteristics of increasing and decreasing greatly, especially the increase in the proportion of iron, potassium, calcium and magnesium is relatively high, which indicates that the widely developed pyritization in ore leads to an increase in iron. The increase of K 2O content in the ore is 30% higher than the average content of the Linglong granite, indicating that large- scale potassium mineralization is a prelude to gold mineralization and provides material preparation for the formation of gold deposits. In terms of trace elements, the content of Au in the wall rock of the Xiadian gold deposit is generally lower than that of the Linglong granite. However, the content of Ag, W are generally higher, 3-10 times of the average value, and other elements are similar to the average value. The structural geochemical elements show that Au, Cu, Pb, Zn and Ag are the main enrichment elements. The sulfophilic elements Ag, Cu, Pb and Zn in the cataclastic rocks of the Zhaoping fault zone are obviously increased, especially Ag and Zn are 2. 79 times and 2. 09 times higher than those in the Linglong granite, showing a close relationship between the sulfophilic elements and the mineralization of gold deposits. The ferriophilic elements Cr, Co, Ni, Mo, Au, Sn and W are generally higher. The large ion lithophile elements Li, Be, Rb, Zr, Nb, W, Sr, Ba, As are mostly depleted, only Rb is enriched. In the ore, Au, Ag, W, Cu are highly enriched, while Bi, Mo, As, Pb, Zn are less enriched. Au is enriched 381. 40 times, W is enriched 3961. 23 times, Ag is enriched 254. 16 times, Cu is enriched 116. 19 times, while Bi, Mo, As, Pb, Zn are between 3-20 times lower. There is very high enrichment of W in both wall rock, fracture alteration zone and gold ore, which shows that the Zhaoping fault zone has a unique metallogenic geochemical premise. In terms of rare earth elements, the ΣREE of wall rock, structural alteration cataclasite and gold ore in the Xiadian gold deposit are 78. 82×10 -6, 27. 15×10 -6 and 102. 43×10 -6 respectively. LREE are 74. 92×10 -6, 4. 23×10 -6 and 94. 52×10 -6 respectively. HREE are 3. 88×10 -6, 2. 91×10 -6 and 7. 91×10 -6 respectively. LREE/HREE ratio is 19. 3, 8. 46 and 12. 66, and the ΣREE, LREE and HREE of gold ore is relatively high, but the LREE/HREE ratio is similar. The altered cataclasite in the Zhaoping fault zone has a lower ΣREE, while the gold ore has a relatively higher ΣREE, which indicates that the addition of foreign materials in the mineralization process changes the content and ratio of REEs. It is also an important geochemical indicator to identify ore from wall rock. The REE distribution pattern of ore in the Xiadian gold deposit is similar to that of the Linglong granite and altered rock in fracture zone. It is generally right dipping type with low ΣREE, characterized by enriched LREE and depleted HREE. The δEu of wall rock, structural alteration cataclasite and gold ore are 1. 88, 1. 49 and 0. 83; the Eu/Sm ratios are 1. 57, 2. 05 and 0. 69; the Ce/Yb ratios are 25. 15, 5. 33 and 12. 86 respectively. The internal fractionation of LREE and LREE is relatively small and the metallogenic environment is weakly oxidized. The increasing REE in ore is a reflection of fluid system carrying REE into the ore- forming process. According to the results of rock- mineral identification, the pyrites formed in early stage of gold mineralization process are generally fragmentary and cracks developed. The chalcopyrites are filled in the cracks of pyrites and coexists with gold, indicating that the native gold is formed in the same period with chalcopyrites, but later than pyrites.

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李逸凡,李洪奎,陈国栋,张玉波,陈莉,梁太涛.2021.胶东夏甸金矿床地球化学特征及其地质意义[J].地质学报,95(6):1822-1842.
Li Yifan, Li Hongkui, Chen Guodong, Zhang Yubo, Chen Li, Liang Taitao.2021. Geochemical characteristics and geological significance of the Xiadian gold deposit, Jiaodong area[J]. Acta Geologica Sinica,95(6):1822-1842.

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  • 收稿日期:2020-02-24
  • 最后修改日期:2020-08-17
  • 录用日期:2020-08-18
  • 在线发布日期: 2021-04-19