云南茂租铅锌矿床成矿流体的 C、O同位素约束

The ore-forming fluid of Maozu lead-zinc deposit in Yunnan Province: Constraints from C and O isotope

中文关键词: C-O同位素  成矿流体  云南  茂租铅锌矿床

英文关键词: carbon and oxygen isotopic geochemistry  ore-forming fluids  Yunnan Province  Maozu Pb-Zn de-posit

中文摘要:

      云南茂租大型铅锌矿床规模大、品位高，伴生有用元素多，找矿潜力大，但在成矿物质来源和成矿流体性质等方面还存在分歧。本文系统分析了该矿床与铅锌矿共生的蚀变白云岩、方解石和近矿围岩上震旦统灯影组白云岩的 C、O同位素组成，结果表明，蚀变白云岩和热液方解石的 C、O同位素组成相对均一，除裂隙矿外，不同类型矿体的 C、O同位素组成不具明显差别，近矿围岩灯影组白云岩的 δ13CV-PCD=-7.38‰~ -1.40‰(均值 -4.23‰)、δ18OV-SMOW=20.18‰~23.87‰(均值 21.93‰)，蚀变白云岩的 δ13CV-PCD=-1.30‰~3.50‰(均值 1.13‰)、δ18OV-SMOW=17.90‰~18.50‰(均值 18.27‰)，热液方解石的 δ13CV-PCD=-6.80‰~-1.95‰(均值-3.25‰)、δ18OV-SMOW=13.80‰~17.50‰(均值 15.26‰)。在 δ13CV-PCD -δ18OV-SMOW图上，近矿围岩灯影组白云岩的 C、O同位素值多数落入正常沉积的海相碳酸盐岩范围及其附近，层矿状中蚀变白云岩和热液方解石的 C、O同位素值落入岩浆碳酸岩与海相碳酸盐岩之间狭小范围内，裂隙矿中热液方解石的 C、O同位素值反映沉积有机物氧化特征。结合矿床球化学研究成果表明:茂租铅锌矿床的成矿流体为壳-幔“多来源混合”流体，其中壳源组分可能主要由矿区(或区域)碳酸盐岩地层提供，幔源组分可能与峨眉山玄武岩浆活动的去气作用有关。

英文摘要:

      The Maozu large Pb-Zn deposit is characterized by its big scale, high contents of Pb+Zn and mul-tiple concomitant elements, which shows that its has great potential for mineral exploration. This paper analyzes thecarbon and oxygen isotopic compositions of eroded dolomite, hydrothermal calcite occurring as gangue mineral inores and in carbonate strata that host the ores. The results show that the carbon and oxygen isotopic compositions ofthe eroded dolomite and hydrothermal calcite are relatively homogeneous, and the carbon and oxygen isotopic com-positions of the calcite that appear in different ore bodies, have different occurrences and the same ore body withvaried occurrences are not obviously different from one another except for fractured ores. The values of δ13CV-PCD and δ18OV-SMOW of Dengying formation dolomite range respectively from -7.38‰--1.40‰ (the average value is -4.23‰)and 20.18‰-23.87‰ (the average value is 21.93‰), the eroded dolomite range respectively from -1.30‰-3.50‰(the average value is 1.13‰) and 17.90‰-18.50‰ (the average value is 18.27‰), the calcite range respectivelyfrom -6.80‰--1.95‰ (the average value is -3.25‰) and 13.80‰-17.50‰ (the average value is 15.26‰). In theδ13CV-PCD -δ18OV-SMOW diagram, the samples of host rocks mostly fall within the range of normal sedimentary marine car-bonate rocks and their vicinity, the eroded dolomite, hydrothermal calcite are plotted in a small field between car-bonatite and marine carbonate. Based on the research results of ore deposit geochemistry, it is shown that the ore-forming fluids are of the crustal-mantle“multi source mixing”type, with the crustal compositions being mainlyoriginated from the carbonate strata in the orefield, and the mantle compositions being related to the degassing pro-cess of the Emeishan basalt magmatism.