宁芜北部脉状铜矿床地质与成矿流体特征研究

Geological and ore-forming fluid characteristics of vein type copper deposits in northern Ningwu area

提要：宁芜北部地区分布众多热液成因的脉状铜矿床.本文对区内的谷里铜矿和南门头铜矿进行了流体包裹体研究,结果表明,二者石英-金属硫化物期石英的流体包裹体均一温度分别为202.9～299.4℃、166.7～355.4℃;盐度分别为4.5 wt％ NaCl eqv.～11.1 wt％ NaCl eqv.、3.5 wt％ NaCl eqv.～12.0 wt％ NaCl eqv.；密度分别为0.75～1.01 g/cm3、0.80～0.89 g/cm3;估算二者的成矿压力和深度分别为18.2～30.4 MPa、0.69～1.15 km和12.8～35.1 MPa、0.48～1.32 km.谷里和南门头铜矿（体）成矿流体均具有中低盐度、低密度和浅成条件等共同点,但前者为中温流体,后者为中高-中低温流体.激光拉曼光谱分析显示二者的包裹体气相组成有明显区别,南门头的包裹体气相成分组合为H2O＋CO2±N2,而谷里铜矿包裹体气相组分仅见H2O.结合矿床地质特征,如矿物组合、赋矿围岩、矿化蚀变、成矿岩体等方面的差异,推测宁芜北部可能存在两期铜成矿,早期与大王山旋回的辉石闪长玢岩有关（以谷里铜矿为代表）；晚期与姑山—娘娘山旋回的花岗岩类有关（以南门头为代表）.

There exist many vein type copper deposits of hydrothermal origin in northern Ningwu area. The authors focused on ore-forming fluid inclusions of Guli and Nanmentou copper deposits in the study area. The results show that the homogenization temperatures of fluid inclusions in quartz of the quartz-metal-sulfide stage range from 202.9 to 299.4%2 for Guli, and from 166.7 to 355.4% for Nanmentou; the salinities range from 4.5 to 11.1 wt% NaC1 eqv. for Guli, and from 3.5 to 12.0 wt% NaC1 eqv. for Nanmentou; the densities range from 0.75 to 1.01 g/cm3 for Guli, and from 0.80 to 0.89 g/cm3 for Nanmentou; the ore-forming pressures and depths range from 18.2 to 30.4 MPa and from 0.69 to 1.15 km for Guli, and from 12.8 to 35.1 MPa and from 0.48 to 1.32 km for Nanmentou respectively. These analytical data combined with data available suggest that the ore- forming hydrothermal fluids of Guli and Nanmentou copper deposits have similar characteristics of middle-low salinity, low density and low depth, but the former is of middle temperature, whereas the latter is of middle-high to middle-low temperature. Raman spectra analysis of fluid inclusions show that there are obvious differences in the gas phase composition. The gas phase composition is mainly H20 ＋CO2---Y2 in the fluid inclusions of Nanmentou, but only H20 has been observed in the fluid inclusions of Guli. Combined with geological characteristics, such as the differences of mineral assemblages, the wall-rock mineralization alteration and ore- forming rock mass, the authors tentatively conclude that there might have existed two main copper metaUogenic periods in northern Ningwu area： one was related to early magmatic segregation of diorite porphyrite in Dawangshan cycle （ with the Guli copper deposit as the representative ） and the other was correlated with granite in late Gushan cycle （represented by Nanmentou）.