摘要
胶东作为中国最重要的金矿集区,区内大型-超大型金矿床集中产出,已探明金矿资源量占全国近1/3。其中,破碎带蚀变岩型金矿床是最重要的金矿床类型,占胶东已探明金矿资源量的90%以上,焦家金矿床是著名的＂焦家式＂破碎带蚀变岩型金矿的命名地,内发育大规模的绢英岩化蚀变带（宽20~200m）和钾化蚀变带（50~300m）,蚀变岩型金矿体主要发育在焦家断裂带下盘的绢英岩化蚀变带中。本文通过详细的野外地质观测,查清了焦家金矿床蚀变类型及矿物组合特征,系统采集了不同蚀变类型的岩石样品,进行了岩石元素地球化学分析,运用质量平衡方法讨论了热液蚀变过程中元素迁移规律,初步探讨了焦家金矿床热液蚀变机理。其中,钾化蚀变是成矿前蚀变,钾化花岗岩常以团块状或角砾状残留于黄铁绢英岩和绢英岩内;黄铁绢英岩化和绢英岩化蚀变受焦家断裂及其下盘的次级断裂控制,其规模大小受断裂的规模控制;其中焦家主断裂下盘的绢英岩化蚀变带规模最大,一般宽10~200m;而次级断裂控制的绢英岩化蚀变带规模相对较小,一般以0.1~1m宽的脉状发育在钾化花岗岩内,指示绢英岩化蚀变晚于钾化蚀变。相对于黑云母花岗岩,不同蚀变带岩石普遍表现出高K2O、低Al2O3、CaO和Na2O,而不同蚀变岩石Si、Fe、Mg等元素各表现出不同特征。钾化带岩石表现为K2O的富集,而绢英岩带和黄铁绢英岩带岩石表现为MgO、Fe2O3增加的趋势。黑云母花岗岩发生钾化蚀变过程中,SiO2、K2O表现为明显的带入,指示在钾长石化过程中,流体为富硅的碱性氧化流体。在钾化花岗岩→黄铁绢英岩过程中,Fe2O3表现为明显的带入,可能是由于黑云母等暗色矿物的分解造成的;此外,亲硫元素（Au、Ag、As、Pb、Zn）均表现为带入,特别是成矿元素Au表现为明显的带入。结合本区金的来源可能部分为玲珑黑云母花岗岩,本研究认为钾化过程中的富硅碱性氧化流体通过交代蚀变反应使金从围岩中释放、成为高价态离子活化进入成矿流体,即分散还原态的金（Au0）被活化为氧化态（Au＋、Au3＋）以AuH3SiO4形式随热液迁移。在绢英岩化过程中,热液中的SiO2等组分损失,引起热液中的AuH3SiO4稳定性降低,造成AuH3SiO4分解,Fe2＋、Fe3＋被消耗形成黄铁矿,导致金大量沉淀和聚集沉淀,此时完成了金由活化→迁移→沉淀富集成矿。
Jiaodong Peninsula, the most important gold province in China, is an area with concentration occurrence of large- superlarge gold deposits, the proved reserves in Jiaodong Peninsula account for nearly 1/3 of the country＇ s. Fracture zone altered type gold deposit is the most important deposit type which accounts for more than 90% of the proved gold reserves in Jiaodong Peninsula. Jiaojia gold deposit is named after ＂Jiaojia-type＂ fracture zone altered rock type gold deposit, large-scale serieite-quartz alteration zone （with the width of 20 ~ 200m） and potassic alteration zone （with the width of 50 -300m） occur in the gold deposit. Altered rock type gold orebody mainly develops in the serieite-quartz alteration zone which is in the footwall of Jiaojia fault zone. Based on the detailed geologic observations in the field, this paper found out the alteration type and mineral assemblage of the Jiaojia gold deposit, collected different types of alteration rock samples scientifically, and conducted rock geochemistry element analysis which uses the method of the mass balance to discuss the regularity of elements migration in the hydrothermal alteration process and mechanism. Thereinto, potassic alteration occurs in the premineralization, potassic granite is usually as lumpy and breccia residual in the pyrite-serieite-quartz and serieite-quartz altered rock which is controlled by the secondary faults in the footwall of the Jiaojia fault, and the scale is controlled by the faults. The scale of serieite-quartz altered rock is the largest in the footwall of the Jiaojia fault with the width of 10 ~ 200m, serieite- quartz altered zone controlled by secondary faults is relatively small, usually presenting as wide O. 1 - 1 m veins in the potassic granite, which indicates sericite-quartz alteration is later than potassie alteration. Compared with biotite granite, rocks from various alteration zones show high contents of I（20 and low contents of A1e O3 , CaO and Na~ O, but elements like Si, Fe, and Mg have different characteristics. Potassic granite are rich in K20, while both sericite-quartz altered rock and pyrite-sericite-quartz altered rock are characterized with increasements of MgO and FezO3. During the process of potassic alteration, SiO2 and K20 were added, indicating that the forming fluid is silicon-rich, alkaline and oxidation. In the process of alteration from potassie granite to pyrite-sericite-quartz altered rock, the Fez O3 increased obviously, which may be caused by the decomposement of biotite and other melanoeratic minerals. Furthermore, sulfophilie elements like Au, Ag, As, Pb and Zn also increased significantly. Part of the gold may he derived from Linglong biotite granite. In the process of potassie alteration, the metasomatism between the wall rock and silicon-rich, alkaline and oxidation fluids, extracted gold in the form of high valence ion from wall rocks. To be specific, dispersed reduced gold （Au~ ） was activated to be oxidized （ Au ~ , Au3 ＋ ） , and migrated with the fluids in the form of AuH3 SiO4. In the process of sericite-quartz alteration, the descent of the content of SiO2 induced the deeomposement of AuH3SiO4. Fez＋ and Fe3. were consumed to form the pyrites, which induced the deposition and enrichment of gold. Gold activate, migrate and deposit run through all these process.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2014年第9期2533-2545,共13页
Acta Petrologica Sinica
基金
国家自然科学基金重点项目(41230311)
国家科技支撑计划课题(2011BAB04B09)
地质过程与矿产资源国家重点实验室开放课题(GPMR201307)联合资助
关键词
热液蚀变
质量平衡
焦家金矿床
胶东
Hydrothermal alteration
Mass balance
Jiaojia gold deposit
Jiaodong
