研究生知识库

川滇黔多金属成矿省位于扬子板块西南缘，是华南大面积低温成矿域的重要组成部分，发育铅锌矿床及小型矿化点400余个、产出铅锌矿石200余百万吨。区域内的绝大多数铅锌矿床都产于震旦系至二叠系的碳酸盐岩建造中，其中上震旦统灯影组白云岩是川滇黔地区最重要的赋矿地层，赋存了区域内超过75%的铅锌矿化。虽然前人已经开展了大量的研究工作，但该地区的成矿物质来源，尤其是成矿金属的来源，仍然存在很大争议。乌斯河和茂租铅锌矿床是川滇黔区域内赋存在灯影组地层中的两个大型-超大型代表性铅锌矿床，故选择这两个铅锌矿床作为研究对象。此次研究工作从乌斯河和茂租铅锌矿床的成矿物质来源出发，结合前人的研究成果对整个川滇黔地区的成矿物质来源进行探讨。在系统调研了乌斯河和茂租铅锌矿床闪锌矿锌-硫同位素组成、赋矿围岩和褶皱基底地层锌同位素组成的基础上，结合前人的研究工作，此次研究主要取得了以下成果和认识：(1)乌斯河铅锌矿床闪锌矿的锌、硫同位素组成具有明显时空变化的特点，从层状矿体的底部到顶部有系统性增加的趋势，结合铁、镉含量的变化，发现这种时空相关的变化不是受同位素的瑞利分馏控制的，而是受同位素组成有差异的流体混合控制的。来自基底的流体具有较轻的锌、硫同位素组成(δ66Zn=~0.3‰，δ34S=~5‰)，而来自围岩的流体具有较重的锌、硫同位素组成(δ66Zn=~0.6‰，δ34S=~15‰)。(2)茂租铅锌矿床闪锌矿的锌、硫同位素组成变化非常有限，也没有明显的空间演化趋势。整体偏轻的锌同位素组成(?0.06‰~0.23‰)反映了矿床中的锌主要来自基底地层，而成矿的硫主要来自围岩中的含硫蒸发岩。基底起源的富锌热变质流体与盖层起源的富硫冷流体的混合可能导致了成矿流体的温度骤降，进而限制了茂租铅锌矿床闪锌矿的锌同位素分馏。(3)结合前人的研究成果，中元古代褶皱基底地层可能是区域成矿元素锌的主要来源，但也有少数铅锌矿床的锌会有围岩及峨眉山玄武岩的贡献。赋存在古生代赋矿围岩中的含硫蒸发岩可能是区域成矿元素硫的主要来源，但也有少数铅锌矿床的硫有基底地层及峨眉山玄武岩的贡献。(4)根据川滇黔区域已经开展锌同位素研究工作矿床的整体锌同位素组成，茂租铅锌矿床具有整体最轻的锌同位素组成(茂租矿床平均值为0.08‰，其他矿床平 均值为~0.4‰)。根据流体迁移过程中的锌同位素组成变化规律，结合这些矿床在区域内的地理分布位置，我们推测茂租矿床很可能是或更靠近川滇黔区域成矿流体的中心位置。但此结论还需要更多的研究工作加以证实。(5)共变的锌、硫同位素组成可能反映了锌、硫同位素组成存在差异的流体混合成矿，即混合流体中锌、硫是共同运移的。而解耦的锌、硫同位素组成可能反映了成矿过程没有发生流体混合，但也可能是含锌流体和含硫流体的混合成矿，即混合流体中锌、硫是分别运移的。

The Sichuan-Yunnan-Guizhou (SYG) polymetallic metallogenic province in the southwestern Yangtze Block is an important component of the giant South China low-temperature metallogenic domain. More than 400 Pb-Zn deposits or spots occur in the SYG, yielding total Pb-Zn metals of more than 200 million tonnes. Most of these deposits are hosted in Sinian to Permian carbonate rocks, and the Upper Sinian Dengying Formation is the most important ore-hosting strata with more than 75% of the regional Pb-Zn ores. Despite of many studies that have been conducted, the ore-forming components, especially the ore-forming metals, for the regional Pb-Zn mineralization remains controversial. In the SYG area, the Wusihe and Maozu Pb-Zn deposit are two representative large-scale Pb-Zn deposits hosting in the Dengying Formation dolostone, and thus choosing these two ore deposits for cases study. Through the studies of the sources of ore-forming components in the Wusihe and Maozu Pb-Zn deposits, combined with previous studies, we attempt to constrain the regional sources of ore-forming components in the SYG. After the examination of Zn and S isotope composition of the sphalerite in the Wusihe and Maozu Pb-Zn deposits, and Zn isotope composition of host rocks and basement rocks, combining with previous work, this work has made the following achievements and understandings:(1) In the Wusihe ore deposit, the Zn and S isotope compositions of sphalerite yield temporal and spatial variation. There are systematically increasing Zn and S isotope compositions of sphalerite from the bottom to the top of the layered ore-bodies. Combined with the change of the Fe and Cd contents in sphalerite, the temporally and spatially dependent variation of the Zn and S isotope composition of the sphalerite could be ascribed to the mixing of multi-source fluids, instead of Rayleigh fractionation. The fluid from the basement is characterized by lighter Zn and S isotope composition(δ66Zn=~0.3‰, δ34S=~5‰), while the fluid from the hosting rocks is of heavier Zn and S isotope composition(δ66Zn=~0.6‰, δ34S=~15‰).(2) In the Maozu ore deposit, the variation of Zn and S isotope composition of sphalerite is very limited with no obvious spatial evolution. The integrally light Zn isotope composition of sphalerite reflects that the ore-forming Zn is mainly derived from the basement rocks, while the ore-forming S could predominantly source from the sulfur-bearing evaporates in the hosting rocks through thermochemical reduction. The mixing of Zn-rich metamorphic fluid from the basements and S-rich fluid from the host rocks could induce the sharp decrease in temperature of the ore-forming fluids, thus diminishing the Zn isotope fractionation of sphalerite in the deposit.(3) Combined with previous studies, the Mesoproterozoic folded basements could be the main source of the regional ore-forming Zn in the SYG, despite that a few ore deposit could have the contribution of Zn from host rocks or Emeishan basalts. The sulfur-bearing evaporates occurring in the Paleozoic host rocks may be the main source of regional ore-forming S, despite that a few ore deposit could have the contribution of S from basement rocks or Emeishan basalts.(4) Based on the integral Zn isotope composition of the deposit with Zn isotopic research in the SYG, the Maozu ore deposit has the lightest Zn isotope composition(0.08‰ for the Maozu deposit and ~0.4‰ for the other deposits). Based on the variation of Zn isotope composition in the fluid during regional fluid migration, with the geographical distribution of these deposits in the region, we infer that the Maozu deposit is probably the center of the regional ore-forming fluid in the SYG. However, this inference needs more research work to prove it.(5) The covariant isotope compositions of Zn and S may reflect the ore-forming mechanism of mixing fluids with different Zn and S isotope compositions, and the Zn and S in the mixed fluid are transported together. However, the decoupled isotopic compositions of Zn and S could indicate there is no fluid mixing during ore-forming processes, but it could also reflect the ore-forming mechanism of mixing containing Zn fluid with containing S fluid, in which the Zn and S are transported separately.