广东怀集地区矽卡岩型铁多金属矿床同位素地球化学特征及其地质意义

Isotope Geochemical Characteristics and Geological Significance of Skarn Type Iron Polymetallic Deposit in Huaiji Area,Guangdong Province

怀集地区位于广东省南岭成矿带中段,成矿地质条件优越,区内已发现铁、铅、锌和银等大量矿床(点),但这些矿床与花岗岩的成因关系尚未得到深入研究。为确定该区成矿物质来源,开展了花岗岩体和典型矿床S、Pb、H和O同位素地球化学研究工作。研究结果表明:矿石δ^(34)S_(CDT)值为-0.12‰~6.58‰,平均值为3.23‰,峰值出现在3‰~5‰之间,呈现明显的塔式分布,由于矿石中没有硫酸盐,成矿流体中硫绝大多数为H_(2)S,处于低氧逸度f(O_(2))和低pH值环境,且黄铁矿的δ^(34)S值近似等于流体的δ^(34)S∑S值,说明其硫源主要来自深源,少部分来自地层海相碳酸盐岩中的硫酸盐物质;绝大多数矿石Pb同位素组成与晚白垩世花岗岩钾长石Pb同位素组成相似,但矿石的^(207)Pb/^(204)Pb值总体略低,说明成矿物质可能主要来源于花岗岩,在成矿时有少量幔源物质的加入;将研究区与晚白垩世花岗岩有关的代表性矿床石英流体H、O同位素测试结果投到流体H、O同位素组成图解中,除将军头铁多金属矿床之外,全落入岩浆水范围,表明成矿热液主要来源于岩浆水。同位素地球化学分析结果表明:研究区与~100 Ma花岗岩有关的矽卡岩型和矽卡岩—热液脉型矿床的成矿物质主要来源于晚白垩世花岗岩。

The Huaiji area belongs to the middle section of the Nanling metallogenic belt in Guangdong Province.The metallogenic geological conditions of the Huaiji area are superior.A large number of deposits(points)such as iron,lead,zinc and silver have been found in the area,but their genetic relationship with granite has not been studied in depth.In order to determine the source of minerals,S,Pb,H and O isotope geochemistry studies were carried out to explore the source of metallogenic minerals.On the basis of the background analysis of ore-forming elements,the Pb and S isotope analysis of sulfide in the ore,and the O,H,C isotope analysis of the quartz and carbonate in the altered rock and ore were carried out to trace the mineralization and the source of ore-forming fluids reveals the coupling relationship between magmatic activity and mineralization.The results show that:δ^(34)SCDT(‰)is-0.12‰~6.58‰,the mean value is 3.23‰,the peak is in the 3‰~5‰,there is a clear tower-like distribution.Since there is no sulfate in the ore,most of the S in the ore-forming fluid is H_(2)S,which is in a low f(O_(2))and low pH environment.Theδ^(34)S value of pyrite is approximately equal to theδ^(34)S∑S value of the fluid.Therefore,its sulfur source mainly comes from deep sources,and a small part comes from sulfate materials in stratigraphic marine carbonate rocks.The Pb isotopic composition of most ores is similar to that of Late Cretaceous granite potash feldspar,but the^(207)Pb/^(204)Pb value of the ores is generally slightly lower.The ore-forming material may mainly come from granite,but there is a small amount of mantle-derived material during the mineralization.The test results of the H and O isotopes of the representative quartz fluids related to the Late Cretaceous granites in the survey area are input into the fluid hydrogen and oxygen isotope composition diagram.Except for the Jiangjuntou deposit,all fall into the range of magmatic water,indicating the main source of ore-forming hydrothermal fluids in magma water.Through the study,it is further confirmed that the ore-forming materials and ore-forming fluids of the skarn type and skarnhydrothermal vein type deposits in Huaiji area are mainly derived from the late Cretaceous granite.