甘肃北山古岛弧期后张裂带及海相火山岩金矿

甘肃北山地区古生代处于塔里木、哈萨克斯坦与西伯利亚三大板块聚合部位。晚古生代(D₂-D₂)形成岛弧带和弧后盆地,之后又处于板内构造演化时期,石炭纪-二叠纪有拉张-闭合构造运动,形成规模较大的火山喷发活动和岩浆侵入作用,对金矿的形成提供了有利条件。本区划分出4条张裂带,每条张裂带控制着金矿床(点)的分布。从金矿成矿构造环境,成矿机制及矿床地质特征分析,本区金矿床属于海相火山岩型金矿。

POST PALEO-ISLAND ARC EPOCH TENSION ZONES AND MARINE VOLCANIC ROCK GOLD DEPOSITS OF BEISHAN AREA, GANSU PROVINCE

1. Post paleo-island arc epoch tension zonesThe studied area was situated at the intersection of Tarim and Kazakhstan plates during early Paleozoic period. In late paleozoic (D2-D3), the south Mongolian ocean crust under-thrust form north to south, which resulted in the collision of the two plates with Siberian plate. The late Paleozoic area zone and back-arc-basins were formed, in the area, followed by a period of mid-plate tectonic activity. There were three extension-closure structure movements (O -S, C, and P), of which the third had the largest scale and strength, formed a large scale volcanic eruption and magmatic intrusion, and provided a favourite condition for gold mineralization. Four tension zones are recognized by study. They are; (a) Ganquan-Daqishan tension-depression trough ; (b)Jinwozi tension-depresion zone ; (c)Mazhuangshan - Nanjinshan tension-depression basin; (d) Baishan-langwashan rift zone.2. Characteristics of marine volcanic rock gold depositsThe gold deposits of this area belong to marine volcanic rock type. The mineralization system is submarine volcanic eruption hydrothermal circulation system. For a nother type of gold deposit related to granitoid,its mineralization system is postmagmatic hydrothermal sys tem. The acid -intermediate to acid volcanic rocks and related intrusive rocks were formed in about the same time and associated spacially. Their REE composition, REE pattern and microelement characteristics are similar. Therefore, it is believed that the acid to acid-intermediate volcanic rcks and acid-intermediate granitoid in this area share the same material source and mineralization geology environment.The marine volcanic rock gold deposits of this area occur in volcanic dome and volcanic sedimentray basin within the post island arc epoch tension zones. The ore-bearing stratum is lower Carboniferous Baishan formation. Hydrothermal alteration are mainly secondary quartzification sericitize and pyritization.