摘要
锡铁山大型铅锌矿床发育有完好的喷流沉积系统,赋矿地层产状倒转。与成矿关系密切的大理岩延长约2km,延深约1km,往深部厚度增大,至代表管道相的网脉状蚀变岩,厚度迅速减薄、尖灭。角砾状非层状铅锌矿体赋存于紧邻网脉状蚀变岩的厚层状大理岩中,条带状层状矿体赋存于外侧条带状大理岩的下盘。对锡铁山矿床两条典型剖面系统的地质地球化学研究表明,近喷口相大理岩与远离喷口相大理岩相比,具有相似的变化规律。以反映远端沉积的剖面为例,自下往上,条带状矿体条带状大理岩块状大理岩,Al2O3、Fe2O3、Sr、B、Tl以及MgO/(CaO+MgO)、Na2O/(Na2O+K2O)比值等逐渐降低,Sr/Rb、Sr/Ba比值等迅速降低,REE总量降低,分异增强,Eu异常减弱,Ce负异常更加明显;δ18OSMOW=10.1‰～12.5‰,向上增高,δ13CV-PDB=-0.9‰～0.2‰;大理岩87Sr/86Sr=0.7113～0.7148,低于矿石方解石的0.7146～0.7147,高于同时期的正常海相灰岩。综合这些地质地球化学特征,锡铁山矿床的容矿大理岩明显不同于正常海相沉积碳酸盐岩,而是介于喷流卤水与海水特征之间,上部的大理岩中有更多的海水参与。以Sr同位素数据计算出本区大理岩来自海水的组分约占1/3,来自卤水的组分约占2/3,大理岩总体上仍主要分布于喷口附近,更多地受到卤水的影响。通过大理岩的地质地球化学研究揭示出,矿床中发育有两条同生断层,一条沿以网脉状蚀变带代表的管道相分布,另一条分布于25线附近,共同制约着大理岩与成矿物质的堆积。锡铁山矿床可能存在着规模巨大的层状矿体,其分布范围可能超越一直作为重要找矿评价标志的大理岩。
Xitieshan lead-zinc deposit is located in north margin of the Qaidam basin, Qinghai Province, tained about 50 million tones of ore with a grade of 8% Zn, 10% Pb. It formed in a rift basin at the originally con- Ordovician pcriod. The marble distributes about 2km of length in NW--SE and lkm of depth. The orebody can be divided into two main types： unbedded and bedded ores. The unbedded ore-body occurred discordantly in thick marble that formed in exhalation sedimentation, which contributes more than 3/4 of known lead-zinc reserves, and consists dominantly of massive, coarse galena, sphalerite, pyrite and ganuge minerals, and abundant hydrothermal eruption and vent breccias. The bedded ore-body occurred near concordant banded marble. An exhalation-sediment system has been found in the deposit, including feeder channel-stockwork altered rock, vent-proximal-unbedded ore-body, thick marble and vent-distal face-banded bedded ore-body with banded marble. The two sections reflecting vent- proximal and distal are studied. From base of the marble upward, the contents of A1203, Fe203, Sr, B, T1 and MgO/（CaO ＋ MgO）, Na20/（Na20 ＋ K20） determined by ICP-MS analysis decrease slightly, Sr/Rb and Sr/Ba ratio increases significantly. REE contents, 8Eu and 8Ce of marble decrease in the upper part of the section. 81SOsMow = 10. 1%o - 12. 5%o, δ^13CpDB = - 0. 9%o - 0. 2%o and ^87Sr/^86Sr = 0. 7113 - 0. 7148, and all three at the both sections lie between that for Ordovician marine sedimentary carbonate and that of hydrothermal fluid estimated from calcite of ore, ^87Sr/^86Sr = 0. 7146 - 0. 7147. The studies of geology and geochemistry suggest that the marble of the deposit is a result of the interaction of exhalation hydrothermal （brain） fluid with seawater, more seawater takes part in the reaction in the upper part of the section, and more brine in the lower part. The calculations or the ratio of seawater（Ordovician） and hydrothermal fluid in the forming of carbonate gangue, based on the Sr-isotope of the marb
出处
《地质论评》
CAS
CSCD
北大核心
2007年第1期52-64,共13页
Geological Review
基金
国家科技部科技攻关项目(编号2003BA612A-07)
国家自然科学基金资助项目(批准号40672061)的成果
