甘肃白银厂铜多金属矿田折腰山矿床含铁硅质岩地球化学特征及其找矿意义
Geochemical characteristics of ferriferous silicalites in the Zheyaoshan deposit of the Baiyinchang copper polymetallic orefield in Gansu Province and their ore-prospecting significance
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摘要: 折腰山矿区含铁硅质岩赋存于含矿岩系与上部岩系间的沉积间断界面。含铁硅质岩矿物主要由细晶石英和赤铁矿组成，二者含量占90%以上，含少量的绢云母、钠长石、绿泥石等。该含铁硅质岩具有低的TiO2、A12O3和高的成矿元素（Fe、Cu、Pb、Zn）含量特征。Al/（Al＋Fe＋Mn）值具有热水沉积岩特征。在Fe-Mn-Al三角图解、Fe-Mn-（Cu+Co+Ni）×10三角图解和Zr-Cr图解中，该区含铁硅质岩均落在热水沉积岩区域中，含铁硅质岩的稀土元素总量很低，其北美页岩标准化配分模式为右倾曲线，具有弱的负Eu异常或正Eu异常和负Ce异常。部分样品MnO/TiO2值偏小，U/Th值偏大，Al2O3含量较高，出现负Eu异常，表明该矿区含铁硅质岩也有正常沉积硅质岩成分的加入。结合含铁硅质岩的地质产状、含矿岩系（石英角斑质凝灰岩）和含矿石英的稀土元素特征，认为含铁硅质岩的物源主要为石英角斑质凝灰岩，属于与火山作用有关的非生物成因类型，是该铜多金属矿田重要的找矿标志。Abstract: The ferriferous silicalites in the Zheyaoshan ore district occur in sedimentary discontinuity interface between the ore-bearing rock series (quartz keratophyre taff) and the upper rock system, and are composed mainly of fine-crystalline quartz and hematite, which account for more than 90%, with a small amount of silk mica, feldspar, sodium chlorite etc. The ferriferous silicalites are characterized by low TiO2 and A12O3 as well as high ore-forming elements (Fe, Cu, Pb, Zn). Through the calculation of Al/(Al+Fe+Mn) ratio, the characteristics of hydrothermal sedimentary rock were displayed. In the Fe-Mn-Al triangular diagram, Fe-Mn-(Cu+Co+Ni)×10 triangular diagram and Zr-Cr diagram, the ferriferous silicalites in this area are located in the hydrothermal sedimentary rock area, the total REE of ferriferous silicalites is very low, and the north American shale standardization distribution pattern is a right-oblique curve with weak negative Eu anomaly or positive Eu anomaly as well as weak negative Ce anomaly. The ω(MnO) /ω(TiO2) ratio of part of the samples is somewhat smaller, U/Th ratio is larger, Al2O3 content is higher, with a negative Eu anomaly, indicating that the addition of normal sedimentary silicalite ingredients. Combined with the geological background of ferriferous silicalites and rare earth elements of ore-bearing rock series (quartz keratophyre tuff) and mineralized quartz, the authors hold that the provenance of ferriferous silicalites was mainly derived from quartz keratophyre tuff and belonged to the abiogenic type related to volcanism, and this can be regarded as an important prospecting criterion in the orefield.
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