利用地震反射剖面研究辽东青城子矿集区浅层地壳结构

Studying the shallow crustal structure of the Qingchengzi ore filed in Liaodong by using seismic reflection profile

青城子矿集区位于辽东地区中部,发育大量的金及铅锌矿床.尽管前人对矿集区内的矿床进行了大量的地质研究,但仍存在矿集区控矿构造延深情况不清、浅层地质格架不明的问题,制约了对矿集区成矿作用的认识及下一步的找矿工作.本文基于青城子矿集区布设的二维反射地震测线,通过偏移成像获得了矿集区9 km以浅地质构造特征,结果表明:(1)青城子矿集区的上地壳呈现“双层”结构特征,即古元古代变沉积岩系辽河群覆于太古代基底之上,同时还反映出该地区辽河群可分为上、中、下三个地层层序,其界面及展布形态等较为清楚,总体厚度5000~6700 m;(2)矿集区构造格架是以尖山子深大断裂为根带的一个逆冲推覆体系,为分析白云、小佟家堡子金成矿构造样式及成矿提供了可靠的依据;北西向尖山子断裂为青城子矿集区内一级控矿断裂,可能是区内的导矿构造,控制着青城子东部地区金矿床的空间展布;(3)在小佟家堡子断裂下盘大石桥组地层内部解译出一个隐伏岩体,推测其可能是与金成矿有成因关系的印支-燕山期岩体,暗示青城子矿集区深部具有较好金成矿潜力;并在此基础上建立了该区金成矿模式,为确定深部找矿远景区指明了方向.

The Qingchengzi ore field is located in the central part of Liaodong region, and contains a large number of gold and Pb-Zn deposits. Although many studies of geology and mineral deposits of the ore field have been conducted, the ore-controlling structures and the shallow geological framework have been unclear yet, which hampers our understanding of the mineralization process and the future ore exploration. Based on the two-dimensional seismic profiles in the Qingchengzi ore field, this article conducts tomographic imaging research to obtain shallow geological structural characteristics of the crust above 9km depth beneath the ore field. Our imaging results show that: (1) the general upper crustal structure beneath the Qingchengzi ore field is characterized by a "double-layer" framework, meaning that the Paleoproterozoic metamorphic sedimentary rock series, the Liaohe Group, overlies the Archean basement, and that the Liaohe Group in the area can be divided into three stratigraphic sequences: upper, middle, and lower, with evident interfaces and a total thickness of 5000~6700 m;(2) the structural framework of the ore field is a thrust system rooted from the Jianshanzi reverse deep fault, which provides a reliable basis for analyzing the structural styles and mineralization of the Baiyun and Xiaotongjiapuzi gold deposits;the NW-trending Jianshanzi fault is a first-order fault in the Qingchengzi ore field, which likely acted as the conduit for the ore-forming fluids in the area, controlling the distribution of gold deposits in the eastern part of Qingchengzi;(3) a hidden intrusion was identified within the Dashiqiao Formation on the footwall of the Xiaotongjiapuzi fault, and it is speculated to form during the Indosinian-Yanshanian period and to be genetically related to the gold mineralization, suggesting that the deep part of the ore field has a high potential for gold mineralization. Based on these new results, a gold mineralization model was established for the area, which is helpful for determining the ore-looking for and exploration directions.