四平山门Cu-Ni矿化辉长岩体锆石LA-ICP-MS年龄及其地质意义

LA-ICP-MS zircon U-Pb age of Longwang gabbro of Shanmen silver deposit in Siping City and its geological significance

吉林省四平市山门银矿受伊通-依兰深大断裂的控制,在矿区范围内除Ag-Au矿床外还发现有铜镍硫化物矿床。多年以来,人们忽视了对该小型Cu-Ni矿床的成因研究,至今未见到有关矿床精确同位素年龄的报道。文章在运用阴极发光技术对锆石晶体结构研究的基础上,利用LA-ICP-MS锆石原位定年方法,对含矿的龙王辉长岩体进行了年龄测定。结果显示,岩体形成于225.1Ma(MSWD=2.7),与吉林中部红旗岭含铜镍硫化物矿床的1号岩体年龄一致。2个受不同深断裂控制的红旗岭矿床和山门矿床成矿年代的一致性,一方面为敦化-密山断裂与依兰-伊通断裂同为郯庐断裂北延分支的观点提供了年代学依据,另一方面也揭示了区域Cu-Ni成矿作用和Au-Ag成矿作用是与郯庐断裂不同时期构造演化密切相关的规律。该成果对指导相似类型铜镍硫化物矿床和银金矿床的找寻具有重要意义。

In the mining area of the large-size Shanmen silver deposit in Siping of southern Jilin Province, Ni-Cu sul- fide mineralization was also found besides Ag-Au mineralization. However, no reliable isotopic dating result was available for the deposit. Based on the interior structure of zircons from the ore-bearing Longwang gabrro intru- sion and the results of CL analysis, the authors performed in-situ zircon U-Pb dating by means of LA-ICP-MS and, as a result, obtained reliable age data. The results show that the gabbro intrusion was formed at 225.1 Ma （MSWD = 2.7）, consistent with the age of the No. 1 intrusion in the Hongqiling Cu-Ni sulfide deposit of central Jilin Province. The comparability of the ages between the Shanmen silver deposit in southern Jilin and the Hongqiling Cu-Ni sulfide deposit in central Jilin provides the evidence for the previous argument that both Dun- hua-Mishan and Yilan-Yitong faults are northern extensions of the well-known Tanlu fault zone, and that the two types of mineralization belong to different stages of Tanlu fault evolution. It is concluded that the two types of mineralization probably have the same derivation, which could serve as an reliable guide to the exploration of these two types of mineralization in this area.