辽宁省海城市小孤山铅锌多金属矿集区成矿地质特征及成因分析

Metallogenic Geological Characteristics and Analysis of the Xiaogushan Polymetallic Mineralization Area in Haicheng City,Liaoning Province

勘查结果表明,小孤山矿集区的成矿作用受印支期花岗岩体、脉岩、断裂和地层的多重控制。康家岭铅锌矿区含矿围岩与正常大理岩碳同位δ13C存在明显差异,分别为+0.186和-6.055。说明矿集区的成矿作用在成岩作用之后,这种差异是成矿过程中热液蚀变造成的。铅同位素模式年龄均为负值,具明显异常铅特征,表明本区铅锌矿体的成矿物质具多源性。根据矿集区内唐望山印支期花岗岩体的化学成分及特征值判断,岩体为S型花岗岩。其Pb、Zn、Au、Ag的丰度均低于辽河群地层。岩体在早期侵入过程中,同化围岩并在岩体边部发生分异作用,使围岩中成矿元素在岩体边部及脉岩内富集,随着岩体及脉岩的进一步分异形成含矿热液,与脉岩在共同的断裂系统内运移,并在有利的岩性组合和断裂内充填成矿;岩体在侵入的晚期,随着温度和压力的下降,同化围岩及富集成矿元素的能力都相应减弱,并在与围岩接触部形成大规模的碎裂岩带,从而形成大规模的硅化带和地球化学异常。

Exploration results show that the mineralization of the Xiaogushan deposit is controlled by granite mass and vein rocks, faults and strata. The carbon and oxygen isotopes exhibit a distinct difference between marble surrounding orebody and normal marble,which are ＋0.186 and-6. 055, respectively. It implies that mineralization was after lithogenesis in this mineralized ditriet and caused by hydrothermal alteration in the mineralizaton process. The lead-isotope ages are all negative, indicative of conspicuous lead anomalies. Meanwhile, it shows that ore-forming material came from many sources. According to the chemical content of Indo-China epoch granite mass in Tangwangshan of this area,the characteristic parameters are calculated,which show that the Tangwangshan granite mass is of S-type granite, of which the abundances of metallogenetic elements, such as Pb, Zn, Au and Ag, are all lower than the formation of the Liaohe group. So,we can conclude that when the granite intruded in the early stage of Indo-China epoch,it captured and assimilated the surrounding rocks. Meanwhile ,the differentiation happened on the fringe of the granite mass, and lots of veins formed in this process. Besides, in this process,lots of metallogenetic elements of the surrounding rocks were captured and concentrated, and these ore-forming materials were sent to the faults in the surrounding rocks and forming orebodies, or forming large-scale geochemical anomalies. In the later stage of the intrussion of the granite mass, the capa- bility of it to assimilate the surrounding rocks reduced, and the capability to concentrate metallogenetic elements correspondingly declined. Meanwhile, a large-scale cataclastic rock belt formed in the contact zone between the granite mass and surrounding rocks, which is an open system for hydrothermal fluid migration. In this stage, the main way to exchange contents between granite mass and surrounding rocks is silication, so a large-scale silication belt and geochemical anomaly belt formed. Because of shortage of metallogenetic material, only small orebodies and mineralization were produced in this stage.