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通过对甘肃大桥金矿硅质岩野外及岩石学特征、主元素、微量元素及稀土元素等地球化学分析,研究了该矿区硅质岩的成因特征,并探讨了其地质意义。结果表明,硅质岩化学成分中SiO_2含量为75.59%~93.00%,Al/(Al+Fe+Mn)平均值为0.82;大部分微量元素与克拉克值相比处于亏损状态,而Au、Ag、As、Sb、Hg等微量元素富集;稀土元素SREE平均值为88.68μg/g,经北美页岩标准化后其δCe值为0.68~1.21,δEu值为0.77~1.32,LREE/HREE值为2.76~23.32,平均值为14.54,轻稀土元素富集明显,(La/Ce)N平均值为1.22,(La/Yb)N平均值为2.33。地球化学数据在反映大桥金矿硅质岩成因上具有不一致性,但是通过与国内金矿床硅质岩的稀土元素地球化学特征对比,并结合区域地层对比,可以初步判定大桥金矿硅质岩沉积环境靠近大陆边缘,使得该套硅质岩既受到了海底热液作用,同时又受到了陆源沉积作用的影响,属于热水沉积与正常沉积的过渡类型。然而硅质岩对于该矿床中金在矿源层形成阶段的初步富集所起的作用还需进一步研究。
The geochemical characteristics of the cherts in the Daqiao gold deposit, Gansu Province, and the geochemical characteristics of the main elements, trace elements and rare earth elements were studied. The results show that the contents of SiO_2 in chert are from 75.59% to 93.00% and the average values of Al / (Al + Fe + Mn) are 0.82. Most trace elements are in a depletion state compared with the Clarke value, while the contents of Au, Ag, As, Sb, Hg and other trace elements are enriched. The average SREE of REE is 88.68μg / g, and the δCe value is 0.68-1.21, the δEu value is 0.77-1.32 and the LREE / HREE value is 2.76 ~ 23.32, with an average of 14.54. The light rare earth elements are abundantly enriched, the average value of (La / Ce) N is 1.22, and the average value of (La / Yb) N is 2.33. The geochemical data are inconsistent in reflecting the origin of the cherts in the Daqiao gold deposit. However, comparing with the REE geochemical characteristics of the cherts in the gold deposits in the country and the comparison of regional strata, the sediments of the chert The environment is close to the continental margin, making the siliceous rocks not only affected by seafloor hydrothermal fluids but also influenced by terrigenous sediments, belonging to the transitional type of hydrothermal sedimentation and normal sedimentation. However, the role of cherts for the initial enrichment of gold in the formation phase of the source rock needs further study.