南秦岭山阳—柞水矿集区夏家店金矿床微量-铂族元素地球化学特征及其对矿床成因的指示

夏家店金矿床位于南秦岭造山带内，是一个受构造和地层控制的大型金矿床，矿石类型为角砾岩型、碎裂岩型和石英脉型3种类型，赋矿围岩主要为寒武系水沟口组的炭泥质板岩、炭硅质板岩、硅质岩及白云岩，次为泥盆系西岔河组的角砾岩。本文对夏家店金矿床中矿石（角砾状炭硅质板岩、碎裂硅化白云岩、碎裂炭泥质板岩和石英脉状矿化的硅质岩）和围岩（硅质岩、硅化白云岩和硅质板岩）的微量元素、铂族元素（PGE）质量分数进行测试，进而探讨成矿物质来源以及矿床成因。结果表明：不同类型的矿石与其各自的围岩具有高度的相似性，均富集Sr、Ga、Zr等元素；不同类型的矿石稀土总量均高于各类围岩，但是两者具有相似的稀土配分模式，轻稀土富集，重稀土亏损，均表现出负Eu异常（δEu值为0.51~0.63）；不同类型的矿石PGE总量（7.71×10^-9~38.30×10^-9，平均值23.00×10^-9）均明显大于各类围岩PGE总量（1.28×10^-9~2.44×10^-9，平均值1.86×10^-9），相比上地壳，不同类型的矿石均明显富集Os、Ir、Pt和Pd，亏损Ru、Rh，而各类围岩均富集Os，亏损Pt、Ru、Rh、Pd，但两者的铂族元素配分曲线具有高度相似性，呈Ru亏损的V型，为地壳的（Os）-Pt-Pd型配分模式。以上特征表明不同类型的矿石和围岩具有明显的微量、稀土元素和PGE地球化学继承性，暗示夏家店下寒武统有可能是重要的矿源层之一。同时，所有矿石和围岩的Au/Ir值（分别为4 821~299 666）和406~8 050）及Pd/Ir值（分别为16.9~588.0和15.2~47.5）变化范围均较大，两者Au/Ir值远高于炭质球粒陨石和原始地幔值、Pd/Ir值远高于岩浆成因矿石值，且夏家店金矿床矿石和围岩的PGE配分曲线与典型热液成因矿床一致。这些特征显示夏家店金矿床具有明显的热液成因，是构造-热液流体成矿作用的产物。

Geochemistry of Trace and Platinum Group Elements of Xiajiadian Gold Deposit in Shanyang-Zhashui Ore Concentration Area in South Qinling:Implications of Ore Genesis

The Xiajiadian gold deposit, located in the South Qinling orogenic belt, is a large-scale gold deposit controlled by structure and strata. The ore is divided into three types: Breccia type, cataclastic type,and quartz vein type. The host rocks are mainly carbonaceous argillaceous slate, carbonaceous siliceous slate, siliceous rock and dolomite of the Cambrian Shuigoukou Formation, followed by breccia of the Devonian Xichahe Formation. In this paper, the content of trace elements and platinum group elements (PGE) of ores (brecciated carbonaceous siliceous slate, cataclastic silicified dolomite, cataclastic carbonaceous argillaceous slate,and quartz vein mineralized siliceous rock) and surrounding rocks (siliceous rock, silicified dolomite, and siliceous slate) in Xiajiadian gold deposit are determined, and then the source of ore-forming materials and the genesis of the deposit are discussed. The results show that: 1) Different types of ores and their surrounding rocks are highly similar, and they are rich in Sr, Ga, Zr and other elements; 2) The total amount of rare earth elements (REE) in different types of ores is higher than that in various types of surrounding rocks, but they have similar REE distribution patterns with light rare earth enrichment, heavy rare earth depletion, and negative δEu anomaly (0.51-0.63); 3) The total amount of PGE in different types of ores (7.71×10^-9-38.30×10^-9, average 23.00×10^-9) is significantly higher than that in various types of surrounding rocks (1.28×10^-9-2.44×10^-9, average 1.86×10^-9). Compared with the upper crust, the ores are obviously rich in Os, Ir, Pt, and Pd, and depleted of Ru and Rh; The surrounding rocks are rich in Os and depleted in Pt, Ru, Rh, and Pd, but PGE distribution curves of the two are highly similar, showing the V-type Ru deficiency, which is the (Os)-Pt-Pd type distribution model of the crust. The above characteristics indicate that different types of ores and surrounding rocks have obvious trace, REE and PGE geochemical inheritance, suggesting that the Lower Cambrian strata in Xiajiadian may be one of the important ore source strata. The Au/Ir ratio (4 821-299 666 and 406-8 050, respectively) and Pd/Ir ratio (16.9-588.0 and 15.2-47.5, respectively) of all ores and surrounding rocks vary widely, the Au/Ir ratios of both ores and surrounding rocks are much higher than those of carbonaceous chondrites and primitive mantle, the Pd/Ir ratios are much higher than those of magmatic ores, and the PGE distribution curves of ores and surrounding rocks of Xiajiadian gold deposit are consistent with those of the typical hydrothermal deposits, which show that Xiajiadian gold deposit has obvious hydrothermal genesis and is the product of tectonic hydrothermal fluid mineralization.