胶西北金矿控矿断裂深部特征及对找矿的启示——来自地球物理探测的证据

Deep characteristics of ore−controlling faults in Jiaoxibei gold deposits and its implications for prospecting:Evidence from geophysical surveys

[研究目的]胶东是全球著名的金成矿区,金矿床主要受断裂构造控制,该区尚有很多断裂是无矿的,以往对断裂的深部形态及赋矿断裂与无矿断裂的区别特征缺乏深入研究。[研究方法]本文通过在胶东西北部实施重、磁、电长剖面和穿越主要金矿集区的广域电磁剖面、反射地震剖面,揭示了断裂深部特征,为赋矿断裂和无矿断裂的识别提供了重要证据。[研究结果]地球物理探测表明,胶西北地区的断裂构造有陡倾角的深断裂、缓倾角的铲式断裂和陡倾角的小断裂,其中控矿的三山岛、焦家和招平断裂均是铲式断裂。结合对金矿床的研究发现,矿床主要赋存于缓倾角断裂中,矿体呈阶梯分布特征,陡倾角的深断裂中未见明显的金矿化蚀变,现今金矿床赋存的最大深度在5 km左右。[结论]综合分析认为,低角度拆离断层和连续性不好的高角度小断层有较好的物理圈闭条件,有利于矿化富集;而产状平直、陡倾的深断裂不具备物理圈闭的条件,不利于成矿。胶东型金矿的找矿方向应集中于缓倾角的铲式断裂及其派生、伴生的陡倾角小断裂附近。

[Objective]Jiaodong Peninsula is a famous gold metallogenic area in the world.The gold deposits are mainly controlled by fracture.Certainly,there are still many fractures in this area without ore.In the past,the deep form of the fracture and the distinction between the ore−bearing faults and the ore−free faults have not been thoroughly studied.[Methods]In this paper,the gravity,magnetic and electric length profiles,wide area electromagnetic profiles and reflection seismic profiles that traverse the main gold deposits areas in Jiaoxibei area are used to reveal the deep characteristics of the fractures,providing important evidence for the identification of ore−bearing faults and ore free faults.[Results]The geophysical detection shows that there are deep faults with steep dip angle,shovel faults with gentle dip angle and small faults with steep dip angle in Jiaoxibei area,among which the ore−controlling Sanshandao,Jiaojia and Zhaoping faults are shovel faults.Combined with the study on the gold deposits,it is found that the deposits mainly occur in the gentle dip faults,the ore bodies present the step−like mineralization pattern,while no obvious gold mineralization alteration has been found in the deep faults,and the maximum depth of the present gold deposits are about 5 km.[Conclusions]Comprehensive analysis shows that the low−angle detachment faults and the large−angle small faults have better physical trap conditions,which are conducive to mineralization enrichment.However,the deep faults with flat and steep dip do not have the condition of physical trap,which are not conducive to mineralization.The prospecting direction of Jiaodong type gold deposits should be concentrated in the vicinity of the gentle dip shovel faults and its derived and associated small steep dip faults.