北祁连白银厂铜多金属矿田若干问题探讨

针对白银厂铜多金属矿田各矿床之间的关系、成矿元素分带机理和细碧角斑岩的判别等问题,通过野外实地调研并结合研究前人资料,认为火焰山矿床处于背斜构造的南翼,为正常翼;折腰山矿床处于背斜构造的北翼,矿体已发生倒转。该矿田中各矿床处于喷流成矿系统的不同位置,折腰山、火焰山等铜(锌)矿床为近热液喷口型矿床,分布于火山穹窿中心破火山口位置;四方山、四个圈、小铁山等锌铅铜矿床为远热液喷口型矿床,分布于火山穹窿斜坡洼地;在更远处的海底洼地形成黄崖口等铅锌矿点。白银厂铜多金属矿田形成过程中,由于海水在较高温度下的渗滤参与,正常火山岩常发生细碧角斑岩化,Na2O含量大多3.5%,可利用Na2O-SiO_2图解判别火山岩是否已发生细碧角斑岩化,并作为一种重要找矿标志。如果火山岩细碧角斑岩化强烈,说明成矿条件有利;反之,如果火山岩没有细碧角斑岩化,则说明成矿条件不利。

Discussion on Some Problems about Baiyinchang Copper Polymetallic Orefield in North Qilian

This paper concentrate discussions on the relationship among the deposits in Baiyinchang copper polymetallic orefield, metallogenic element zoning mechanism and identification of spilite keratophyre. Based on the field investigation and previous research results, the authors consider that Huoyanshan and Zheyaoshan deposits were under the control of the same antiform, the former was situated in the south limb, the latter was located in the north limb, and its orebodies have been inverted. The deposits in Baiyinchang copper polymetallic orefield were situated in different locations of the effusive mineralization system. Zheyaoshan and Huoyanshan deposits are near hydrothermal vent type deposit, and distributed in the caldera of the volcano dome center. Sifangshan, Sigequan and Xiaotieshan zinc lead copper deposits are far hydrothermal vent type deposit, and distributed in the slope depression of the volcano dome. Huangyakou lead zinc mineral occurrence distributed in the submarine depression, where is far away from the hydrothermal vent. During the process that Baiyinchang copper polymetallic orefield was forming, seawater participated in percolation under high temperature conditions, so the normal volcanic rock turn into the spilite keratophyre, usually its Na2O content greater than 3.5 percent. The spilite keratophyre is an important prospecting criteria, we can use the Na2O-SiO2 diagram to distinguish the spilite keratophyre from the normal volcanic rock. The more spilite keratophyre, the better condition of mineralization. On the contrary, the less spilite keratophyre, the more unfavorable condition of mineralization.