胶东蓬莱金成矿区的S-Pb同位素地球化学和Rb-Sr同位素年代学研究

S-Pb isotope geochemistry and Rb-Sr geochronology of the Penglai gold field in the eastern Shangdong province.

蓬莱金矿区位于胶东三大金矿带中的栖霞-蓬莱金矿带内。本文系统研究了该金矿化集中区内的黑岚沟、大柳行和河西金矿的 S、Pb、Rb-Sr 同位素地球化学特征,并与招远-掖县成矿带中的玲珑金矿化集中区内的大型-超大型金矿床进行了对比研究。蓬莱金矿区δ^(34)S 值总体变化为6.3‰～9.5‰,平均值为7.5‰。其中河西金矿δ^(34)S 值为7.4‰～8.5‰,黑岚沟金矿δ^(34)S 值为6.3‰～9.5‰,大柳行金矿δ^(34)S 值为6.4‰～8.2‰。不同矿床的硫同位素组成差异十分小,并与玲珑金矿区的硫同位素组成相近(δ^(34)S=6.4‰～8.6‰,平均值为7.6‰)。蓬莱金矿区的铅同位素组成变化小,其中河西金矿^(206)Pb/^(204)Pb 为17.3086～17.4799,^(207)Pb/^(204)Pb 为15.5264～15.5543,^(208)pb/^(204)Pb 为38.0642～38.3698;大柳行金矿^(206)Pb/^(204)Pb 为17.3653～ 17.5037.^(207)Pb/^(204)Pb 为15.5142～15.5355,^(208)Pb/^(204)Pb 为38.1249～38.31 36:黑岚沟金矿^(206)Pb/^(204)Pb 为17.3558～17.5958,^(207)Ph/^(204)Pb 为15.5105～15.5746,^(208)Pb/^(204)Pb为38.0749～38.4361。投影到 Zartman and Doe(1981)铅构造模式图上,成分点落在造山带演化线附近。蓬莱金矿区与玲珑金矿区的铅同位素组成基本一致,部分数据与矿区内煌斑岩的铅同位素组成相近,而与赋矿围岩郭家岭花岗岩相差甚远,表明矿体中的铅可能与煌癍岩有相同的源区。矿石铅呈线性趋势分布,它正好位于煌斑岩与一个极具放射成因铅的胶东群地层的铅同位素组成之间,很可能说明矿石铅是壳幔混合的产物。对蓬莱金矿区黄铁矿的 Rb-Sr 同位素分析结果表明,河西金矿的成矿年龄为122.3±3.1Ma(MSWD=1.7),初始^(87)Sr/^(86)Sr 比值为0.71208;黑岚沟和大柳行金矿的成矿年龄为117.8±6.5Ma(MSWD=17),初始^(87)Sr/^(86)Sr 比值为0.71085。说明蓬莱金矿区具有与玲珑金矿区相近的成矿时代,两者均为120Ma 左右。锶同位素初始比值也说明成矿物质具有壳慢混合的特征。从蓬莱金矿区具有与玲珑金矿区一致的地质、地球化学和年代学特征可知,蓬莱金矿区具有产出大型一超大型金矿的巨大远景。

Penglai gold field is located in the Qixia-Penglai gold belt, one of the three large gold belts in the eastearn Shangdong province （Jiaodong）. In this study, we report S, Pb and Rb-Sr isotope data of the Heilangou, Daliuhang, and Hexi gold deposits from the Penglai gold field, and compare them with those large and super-large gold deposits from the Linglong gold field. The sulfur isotopes in the Penglai gold field show an overall range from 6. 3‰ to 9.5‰, average 7.5‰. The δ^34S values are 7.4‰ to 8.5‰ in the Hexi deposit; 6. 3‰ to 9.5‰ in the Heilangou deposit; and 6. 4‰ to 8.2‰ in the Daliuhang deposit. These sulfur isotope data are similar to those of the Linglong gold field （δ^34 S = 6.4‰ - 8.6‰, average7. 6‰）. The lead isotope variations are small in the Penglai gold field. The ^206Pb/^204 Pb, ^207Pb/^204 Pb, and ^208 Pb/^204 Pb ratios in the Hexi deposit are 38. 0642 - 38. 3698, 17. 3086 - 17.4-799, and 15. 5264 - 15. 5543, respectively. Those ratios in the Daliuhang deposit are 17. 3653 - 17. 5037, 15. 5142-15. 5355, and 38. 1249 -38. 3136, respectively, whereas in the Heilangou deposits, these ratios are 17. 3558 - 17. 5958, 15. 5105 - 15. 5746, and 38. 0749 - 38. 4361, respectively. These data are plotted near the orogen curve of the Zartman and Doe （ 1981 ） Plumbotectonic model. The lead isotope data in the Penglai gold field are similar to those in the Linglong gold field, and both are close to the data for mafic dikes in the area, but totally different from the host granites, suggesting that the ore lead shares similar origin with the mantlederived mafic rocks. The linear array of the ore lead isotope suggests a mixing of mantle-derived and crust-derived sources. The Rb-Sr isotope dating of pyrites from the Penglai gold field yields an isochron age of 122. 3 ± 3. 1Ma （ MSWD = 1.7 ） with initial ^87Sr/^86 Sr ratio of 0.71208 for the Hexi deposit, and an isochron age of 117.8 ±6.5Ma （ MSWD = 17） with initial ^87Sr/^86Sr ratio of 0. 71085 for the Heilangou and Daliuhang deposits. These data suggest a similar mineralization age for the Penglai and Linglong gold field, with ore materials derived from mixing of mantle and crust-derived sources. On the basis of similar geologic, geochemical features and ore formation ages in the Penglai and Linglong gold fields, we suggest a great potential for occurrence of large and super-large gold deposits in the Penglai gold field.