贵州水银洞金矿床载金黄铁矿的矿物学特征及Nano-SIMS原位硫同位素示踪

发布时间：2018-04-27 16:45

  本文选题：水银洞金矿 + 载金黄铁矿　； 参考：《成都理工大学》2017年硕士论文

【摘要】：卡林型金矿是于上个世纪六十年代在美国内华达州卡林镇被首次发现而命名的一种金矿类型。它的特点是金以“不可见金”形式赋存于载金硫化物之中。世界范围内的卡林型金矿集中分布在美国内华达州和犹他州以及我国滇黔桂、陕甘川“金三角”中。目前,我国卡林型金矿探明金储量已超过1000吨。贵州贞丰水银洞金矿是滇黔桂“金三角”中最具代表性的超大型卡林型金矿床,具有极其重要的经济价值和科学研究价值。以往的研究已经对矿床的基础地质特征、金的赋存状态、流体特征等内容进行过详细的探讨。但由于载金矿物——黄铁矿颗粒细小,且黄铁矿单矿物颗粒普遍发育环带结构,这对传统的分析测试技术提出了挑战。本文在对贵州贞丰水银洞金矿野外踏勘的基础上,通过对矿石的显微镜下观察和电子探针背散射电子图像(BSE)分析,发现矿石中存在草莓状黄铁矿、自形黄铁矿以及半自形-它形黄铁矿。其中后两者普遍发育环带结构,即围绕成矿前形成的黄铁矿核部生长一到两期次热液环带,表明水银洞金矿床中黄铁矿的形成是多期次地质事件的产物。Au富集在黄铁矿的富砷环带之中。Nano-SIMS元素面扫描分析(Mapping)显示黄铁矿环带相对富集Au、As、Cu元素,而Se元素则相对富集在核部,表明成矿流体具有富Au-As-Cu、贫Se的特征。Au在核部含量极低,暗示成矿前并未发生金的预富集作用。同时,即使在同一个增生环带中微量元素也并非完全均匀分布,环带之中有次一级环带发育,表明热液流体活动具有阶段性和“脉冲式”特征。电子探针成分分析表明,黄铁矿中As含量在0~10.884wt%,平均值为2.814wt%,属砷黄铁矿。黄铁矿中除了含有Fe、S、As、Au元素之外,还含有Co(0.046~0.447wt%)、Cu(0~0.252wt%)、Cr(0~0.312wt%)等微量元素。元素相关性证实As-S呈负相关关系,证明As类质同象置换了黄铁矿中的S。在lgAu-lgAs图上绝大多数测点落于金溶解度曲线之下,表明金主要以晶格金(Au+)的形式赋存于载金黄铁矿之中。黄铁矿的Co/Ni普遍大于1,暗示了成矿流体可能来源于岩浆热液。原位微区硫同位素测试结果显示黄铁矿核部的δ34S值变化范围为1.3‰~6.5‰,而富金环带的δ34S值为-3.5‰~7.4‰。这些硫同位素特征显示了岩浆硫特征,暗示了载金黄铁矿的硫主要来源于深源岩浆硫,但不排除有部分沉积硫混入的可能。对比研究发现,水银洞金矿载金黄铁矿的硫同位素特征与美国内华达州典型的卡林型金矿硫同位素类似。综合以上研究成果,本文提出水银洞金矿的成矿模式,即受燕山期地壳伸展作用的影响,深源中酸性岩浆分泌的含Au-As-Cu-Si-S流体沿深大断裂上升至地壳浅部,并沿构造薄弱带(区域不整合面和灰家堡背斜轴部)侧向运移、充填、交代富Fe碳酸盐围岩成矿。在这个过程中,大气降水的下渗和淋滤也在一定程度上有利于金矿化。
[Abstract]:Carlin gold deposit was first discovered in Carlin, Nevada in the 1960s. It is characterized by the presence of gold in gold sulphides in the form of invisible gold. Carlin gold deposits in the world are concentrated in Nevada and Utah in the United States, and in the "Golden Triangle" of Yunnan, Guizhou and Guangxi in China. At present, the proven gold reserves of Carlin gold deposits in China have exceeded 1000 tons. Zhenfeng Shuiyindong gold deposit in Guizhou is the most representative super large Carlin gold deposit in the "Golden Triangle" of Yunnan, Guizhou Province, which has extremely important economic value and scientific research value. Previous studies have discussed in detail the basic geological characteristics of the deposit, the occurrence state of gold and the fluid characteristics. However, due to the small particle size of pyrite, a gold bearing mineral, and the general zonal structure of pyrite single mineral particles, it is a challenge to the traditional analytical and testing techniques. On the basis of field exploration of Shuiyindong gold deposit in Zhenfeng, Guizhou province, through microscopic observation and BSEanalysis of electron probe backscattering electron image, it is found that strawberry pyrite exists in the ore. Self-shaped pyrite and semi-automorphic-it-shaped pyrite. The latter two generally developed zonal structure, that is, one or two stages of secondary hydrothermal ring formed around the pyrite core before mineralization. It is suggested that the formation of pyrite in the Shuiyindong gold deposit is the product of multiple geological events. Au is enriched in the arsenic-rich ring zone of pyrite. Nano-Sims elemental surface scanning analysis shows that the pyrite ring zone is relatively enriched in Au-As-Cu element, while the se element is relatively enriched in the nucleus. The results show that the ore-forming fluid is rich in Au-As-Cuand, and the content of au in the nucleus is very low, indicating that there is no pre-enrichment of gold before mineralization. At the same time, even in the same proliferative zone, trace elements are not uniformly distributed, and there is a secondary ring in the belt, indicating that the hydrothermal fluid activity has the characteristics of stage and "pulse". The electron probe analysis shows that the content of as in pyrite is 10.884wtand the average value is 2.814wt.The pyrite belongs to arsenopyrite. The pyrite contains not only the element of Fe ~ (2 +) S ~ (2 +) As-Au, but also some trace elements, such as: Co-0.046 ~ 0.447 wt ~ (4) ~ 0.252 wt ~ (2) ~ (2) ~ (2) ~ (2) ~ (2) ~ (2) ~ (2) ~ (2) ~ (2) ~ (2). The element correlation confirmed the negative correlation of As-S, which proved that the isomorphism of as replaced the S in pyrite. Most of the measured points on the lgAu-lgAs diagram fall below the gold solubility curve, indicating that gold mainly exists in gold-bearing pyrite in the form of lattice gold (au). The Co/Ni of pyrite is generally greater than 1, suggesting that the ore-forming fluid may originate from magmatic hydrothermal solution. The results of in situ sulfur isotope measurements show that the 未 34S values of the pyrite core vary from 1.3 鈥，

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