桂西南的两类大型断裂构造与金矿成矿──以凭祥地区为例

Two kinds of large-scale fault structures and gold ore mineralization—An example from Pingxiang region

桂西南发育两类大型断裂构造 :( 1 )逆冲推覆构造为前展式、叠瓦状构造 ,走向2 5°～ 4 0°,倾向SE ,倾角 2 0°～ 30°,逆冲方向 31 0°± ,分带明显 ;e =-33 3% ,εγ=66 7% ,s>560 0m ,为印支—燕山早期冲断 -推覆成因。 ( 2 )东门断裂为一长寿深断裂 ,走向 4 5°～ 80°,总体南倾 ,倾角 50°～ 80° ,海西期为拉张控相 ,印支期以后为右旋走滑 ,先后形成糜棱岩—碎裂岩 ,有限应变测量结果 :k =1 5,γ =3～ 4 ,X∶Z =1 0∶1～ 2 0∶1 ,古差异应力Δσ达 1 0 0～ 1 2 0MPa。金矿主要与东门深断裂有关 ,主断裂导矿 ,北侧NNE—NE向次级断裂容矿 ,原生金矿化常见于T1熔岩质蚀变碎裂岩中 ,表生氧化作用有利于次生富集。逆冲推覆构造中金 (w (Au) )的变化规律是 :锋带 1 0× 1 0 - 9,中带 1 94× 1 0 - 9,根带 2 1 8× 1 0 - 9,从锋带向根带递增 ,今后要适当注意根带附近的找矿工作。

There are two kinds of large-scale fault structures in the southwestern Guangxi, one is the onward outspreaded imbricate Pingxiang thrust-nappe tectonics,with strike between 25°～40°, dip to SE, dip angle between 20°～30°, thrust direction towards 310±. It has an obvious zoning system with e =-33 3%. ε γ=66 7%, S >5 600 m, and it was formed as a result of the fault-thrust movement of the Indo-Chinese-Yanshan epoch. The other is Pingxiang-Dongmen fault.It stikes at 45°～80°and dips generally southward with dip angles between 50°～80°, it was a tension fault during the Hercynian epoch, and was transformed into a dextral strike-slip one during the Indo-Chinese-Yanshan epoch with a mixed product of mylonite-cataclasite. The results of the finite strain measurements show that k =1 5, γ =3～4, X∶Z =10∶1～20∶1, paleostress Δ σ is between 100～120 MPa. Gold ore is related to the stike-slip faults, with main faults directing the ore-forming flow while the secondary NE faults control the ore bodies. Gold ore mineralization is usually existed in the altered lava cataclasite, and T 1 medium-acidic volcanic lava is an important layer to look for gold ore deposits. Supergene oxidation helps secondary ore enrichment.The gold enrichment variation in the thrust-nappe tectonics is as follows:front zone 1 0×10 -9 ,middle zone 1 94×10 -9 ,root zone 2 18×10 -9 ,the value increases from the front zone to the root zone,and this will have to be paid attention to in our geological exploration around the root zones.