甘肃公婆泉铜矿田中—晚志留世浅海相火山喷发旋回及火山作用演化

The Middle and Late Silurian Marine Volcano Eruption Cycle and Volcano Action Evolution of Gongpoquan Copper Ore Field, Gangsu Province

根据甘肃公婆泉铜矿田内４条典型地层剖面，确立了甘肃公婆泉群中－上志留统浅海相火山喷发沉积岩系的标准层和层序，并将其划分为１４个韵律和５个旋回。火山喷发旋回由早→晚，火山岩岩性由安山质凝灰岩、安山岩→英安岩、钠流纹岩→石英粗面岩→安山岩，火山岩中铁族元素的丰度由高→低→最低（在石英粗面岩中）→高，形成一个较完整的演化周期。中晚期火山岩所表现出的岩性（出现碱性岩－石英粗面岩）和铁族元素丰度（出现最低值）的突变与区域北西走向断裂的深切活动有关，为铜、银等金属成矿提供主要的地球化学条件。铜、银等成矿元素主要富集在火山喷发旋回中期的英安岩中，表明火山活动中期是主要的成矿期，英安岩可作为重要的找矿标志。此外，早中期火山旋回主要发育于矿田的中西部，而晚期旋回则主要分布在矿田的东部，并且火山喷发的强度和频率增高，表明晚期火山活动中心已明显向东部迁移。

According to four typical layer sections of Gongpoquan copper ore field,Gangsu,we established the standard layer and sequence of S 2-3 marine volcano eruption sedimentary rock series of Gongpoquan group,Gangsu, and divided this series into five cycles and fourteen rhythms.From early to final cycle, the volcanic rock shows the following regular evolution of rock types: andesite tuff, andesite→dacite, Na rhyolith→quartz trachyte→andesite; element abundance (V, Cr, Mn, Co, Ni, Zr, Sr): high→low→lowest (in the quartz trachyte)→high.These regularities form a more perfect evolutionary cycle.The middle-late volcanic rock betrays a sudden change in rock component (appearing of alkali rock quartz trachyte) and the element abundance (V, Cr, Mn, etc.).This change was due to the deep cutting of north west trending fault acrossing Gongpoquan field, and offered a major geochemical condition for the mineralization of Cu, Ag etc..The mineral forming elements (Cu, Ag, etc.) concentrate mainly in dacite of the middle volcanic cycle.This fact shows that middle volcano action is the major mineralization period,and that the dacite is an important prospecting criterion. In addition,because the early and middle volcanic cycles mainly occur at the middle western field,while the late cycles mainly cover the eastern field with increasing intensity and frequency of volcanic eruption,it is obvious that the center of volcanic action had already moved to eastern field in the late period.Therefore,the eastern field has more prospective potentiality.