冀东峪耳崖金矿床蚀变绢云母40Ar-39Ar年龄 及其地质意义

峪耳崖大型金矿床位于华北克拉通北缘燕山造山带东段,其主成矿阶段的时间尚待准确约束。本次工作开展了主成矿阶段矿石中蚀变绢云母40Ar-39Ar同位素定年研究,获得的坪年龄((169.4±1.1)Ma(MSWD=0.22)),与反等时线年龄((168.4±1.8)Ma(MSWD=5.5))一致,小于赋矿花岗岩的年龄(174～175 Ma)和辉钼矿的ReOs等时线年龄(172 Ma),限定了峪耳崖金矿主成矿过程自172 Ma持续至169 Ma。峪耳崖金矿与冀东地区其他金矿床显示相似的成岩成矿特征,均在中侏罗世蒙古-鄂霍次克洋闭合、两侧板块碰撞造山的远程影响下,冀东地区下地壳基底物质部分熔融形成的花岗质岩浆(可能伴有少量幔源物质混入)及其分异出的岩浆热液萃取基底成矿物质后,成矿流体在NE向构造有利空间发生沉淀富集,形成岩浆期后热液型金矿床。

40Ar-39Ar age of altered sericite from Yuerya Au deposit in eastern Hebei Province and its geological significance

Located in the east of Yanshan orogen in northern North China Craton, the Yuerya gold deposit is a mesothermal hydrothermal deposit concern. However, the age of the main Au mineralization stage has not been constrained accurately. In this paper, ⁴⁰Ar-³⁹Ar dating was carried out on the altered sericite from ores of the main mineralization stage, which yielded a plateau age of (169.4±1.1) Ma (MSWD=0.22), consistent to the inverse isochronal age of (168.4±1.8) Ma (MSWD=5.5). This Ar-Ar age is several million years later than that of the orebearing granite pluton (174~175 Ma) and initial time of mineralization (172 Ma) from molybdenite Re-Os dating, suggesting that the main Au mineralization process occurred in the range of 172~169 Ma, closely related to the magmatism. The Yuerya deposit shares similar characteristics of the ore-forming granite and mineralization with other gold deposits in eastern Hebei. The remote effect of the subduction and closure of the Mongolia-Okhotsk Ocean and the collision orogenesis gave rise to partial melting of the lower crust in eastern Hebei, with the mixture of minor depleted mantle-derived materials. The ore-forming materials like Au and S were leached to granitic magma and the exsolved hydrothermal fluid from the basement, and then precipitated in the NEtrending fractures, resulting in the formation of magmatic hydrothermal gold deposits like the Yuerya deposit in eastern Hebei.