陕西略阳煎茶岭金矿床成矿作用探讨

摘要

煎茶岭金矿床位于勉略宁三角区东北缘,矿体产于环绕超基性岩体分布的含金蚀变带中,属蚀变岩型矿床.由于对其成矿作用认识分歧较大,严重影响了后续的找矿勘探工作.从矿床地质特征入手,通过矿区岩矿石常量元素、微量元素、稀土元素以及硫、氢、氧同位素的测试分析,探讨其控矿因素和成矿机理.结果表明,矿床受叠加于接触带部位的韧脆性剪切带控制,成矿不仅与超基性岩有关,而且与花岗斑岩关系密切.花岗斑岩的侵入引起超基性岩的彻底蚀变,同时导致原岩中的金等成矿物质被释放出来.矿石、蚀变超基性岩、白云岩中黄铁矿的硫同位素组成与花岗斑岩中黄铁矿的硫同位素组成具有较好的一致性,并表现出一定的规律性,说明花岗斑岩提供了成矿所需的硫；矿石氢、氧同位素组成介于岩浆水与大气降水之间,且多数样品聚集在雨水线附近,暗示花岗斑岩提供了初始热液,随着成矿作用的进行,大气降水不断加入,从而形成复合热液.鉴于矿床与花岗斑岩的密切关系以及铬云母化的产出特点,根据同位素年龄,认为矿床形成于印支中期—燕山中期.%Jianchaling gold ore deposit, located in the northeast edge of Mianxian-Liieyang-Ningqiang triangle area, is associated with ultrabasic rock and the ore bodies occur in the gold-bearing altering belt round the ultra-basic rock. Since the contentious understanding of mineralization, the subsequent exploration was influenced. Beginning with the geologic characteristics, ore-controlling factors and mineralization mechanism are discussed by measurement of major, trace and rare earth elements as well as S, H and 0 isotopic composition. The result shows that the deposit is controlled by ductile-brittle shear zone developed in the contact belt of ultrabasic rock and Sinian dolomite, and the mineralization is not only related with the ultrabasic rock, but also tightly with the granophyres. The emplacement of granophyres results in thorough alteration of the ultrabasic rock and the metal-logenic elements to be released. Since δ34 S of pyrites in the ore, ultrabasic rock and dolomite is approximate to that in the granophyres, and shows definite regularity spatially, it is believed that sulfur in the ores is derived from the granophyres. Hydrogen and oxygen isotope composition of the ores lies between magmatic and meteoric water, and most of them gather together near the meteoric water line, which suggests that the hydrothermal solution originated from the granophyres and gradually turned into mixed water with the meteoric water added succes-sively in. In view of the close relation between the deposit and granophyres and the appearance of fuchsite, it is considered that the deposit is formed between intermediate Indosinian and intermediate Yanshanian according to the isotopic ages.