栖霞金矿矿物、流体和同位素特征及意义

MINERAL, ORE FORMING FLUID AND ISOTOPE CHARACTERISTICS OF THE QIXIA GOLD DEPOSIT AND THEIR IMPLICATIONS

栖霞金矿床伴生的黑钨矿是低温热液的产物。成矿流体的成分与典型的大气降水热液组分相类似，其δ１８Ｏ约为－３．６‰～４．５‰，δＤ约为－５６‰～－９５‰，变化范围较大，但这些氢、氧同位素值很好地反映了大气降水在不同温度和Ｗ／Ｒ比值条件下与胶东群变质岩交换后的分布特征，成矿作用以Ｗ／Ｒ比值较低为特点。金矿床的Ｒｂ－Ｓｒ等时线年龄为１２５．８×１０６ａ，与胶东群变质岩系和混合花岗岩的时差较大，矿化物质的Ｓｒ同位素初始比高达０．７１６８，大气降水深循环对流作用是形成栖霞金矿床的主要原因。

The Qixia gold deposit is one of the important quartz vein type deposits hosted in metamorphic rocks in eastern Shandong.Wolframite associated with gold mineralization of the deposit is rich in iron but poor in manganese,suggesting that the mineral is crystallized from hydrothermal solution at low temperatures. The main metallogenic stage of Qixia gold deposit has temperature of 160～270℃,and the gaseous phase in the fluid inclusions is dominated by H 2O and CO 2.Na +,Ca 2+ and Cl - are the major components of the liquid phase while K + and F - are present in relatively small amounts; the wt% NaCl equiv. values of fluids are between 4% and 8%. In addition, the fluid is characterized by either Ca 2+ >Na +>K + (in five samples) or Na +>Ca 2+ >K + (in two samples), quite similar to the composition of the ore forming fluid derived from meteoric water. Initial data of the hydrogen and oxygen isotopic compositions of ore forming fluid fall whithin a wide range: δ D H 2O = -56‰ ～-95‰ and δ 18 O H 2O =-3 6‰～4 5‰, relative to SMOW. These isotopic values fully reflect the distributive features of meteoric water exchanging with metamorphic rocks of Jiaodong Group under the conditions of different temperatures and W/R ratios, and the metallogenic process is charactered by low W/R ratios. The Rb Sr isochron age of the Qixia gold deposit is (125 8 ±1 7)×10 6 a, with ( 87 Sr / 86 Sr) i being 0 7168. The time interval between the gold deposit and its country rocks (granite or metamophic rocks)is very long. The formation of Qiaxia gold deposit is directly related to the evolution of geological history in eastern Shandong, and a genetic model in which the deep convective circulating meteoric water react with country rocks can be used to explain the metallogenic mechanism of the deposit.