内蒙古喀喇沁旗安家营子金矿蚀变及其分布研究

Alteration and Distribution of Anjiayingzi Gold Deposit in Harqin Banner,Inner Mongolia

位于华北克拉通北缘的安家营子金矿是一赋存在花岗岩中的复合型金矿,既有石英脉型矿化,也有蚀变岩型矿化,矿区发育广泛的热液蚀变。本文在详细的矿床地质特征研究基础上,通过系统采样、镜下鉴定,详细研究了安家营子金矿蚀变岩的类型、矿物组合、空间分布以及地球化学特征,探讨了蚀变岩的分带性、成矿流体的演化等。结果表明,安家营子金矿主要受NNE向脆性断裂的控制,蚀变岩即分布在断裂的影响范围内。主要的蚀变类型有钠长石化、绢云母化、绿泥石化、硅化和黄铁绢英岩化等,其中钠长石化在整个矿区均有分布,其余蚀变则分散在不同的独立区域。热动力学数据表明,安家营子金矿早期成矿流体K^+含量不高,可能相对富Na^+,因此钠长石化大量出现;随着钠长石的大量形成,流体成分演化至绢云母和钾长石的稳定范围,并出现绢云母化,但钾长石保持稳定。随着流体进一步演化至绢云母的稳定范围,绢英岩化开始大量出现,并且斜长石和钾长石基本消失,形成矿区主要的蚀变岩型矿体。安家营子金矿形成于喀喇沁变质核杂岩快速隆升期,因此控矿的次级脆性断裂构造的性质在拉张和剪切之间波动,导致蚀变分带不明显,也使得脉状矿化和蚀变岩型矿化叠加在一起。

The Anjiayingzi gold deposit,located in the northern margin of the North China Craton,is a composite type of gold deposit hosted in granite containing both quartz vein type and altered rock type mineralization.Extensive hydrothermal alteration is developed at the mining area.Based on the detailed study of the geological characteristics,through systematic sampling and microscope identification,this work studied the types,mineral assemblages,spatial distribution and geochemical characteristics,and discussed the zonation of altered rocks and the evolution of ore-forming fluids in this deposit.The results show that the Anjiayingzi gold deposit is mainly controlled by NNE-trending brittle faults,and the altered rocks are distributed within the influence of the faults.The main alteration types include albitization,sericitization,chloritization,silicification and beresitization,with albitization distributed throughout the whole mining area and others scattered in different independent areas.Thermodynamic data suggest that the early ore-forming fluids of the deposit were poor in K^+and relatively rich in Na^+,hence albites occurred in large quantities.With massive formation of albites,the fluid composition evolved into the stable range of sericite and K-feldspar,and sericification occurred,but K-feldspar remained stable.As the fluid further evolved into the stable range of sericite,sericitization began to appear in abundance,and plagioclase and K-feldspar largely disappeared,forming the main ore body of altered rock type.The Anjiayingzi gold deposit formed during a period of rapid uplift of the Harqin metamorphic core complex,therefore the nature of the secondary brittle faults which controlled the ore body fluctuated between tensile and shear,resulting in obscure alteration zoning and the superimposition of vein type and alteration rock type mineralization.