塔里木盆地西北缘志留系砂岩型铜矿床地质特征及地球化学意义

Geological characteristics and geochemical significance of Silurian sandstone-type copper deposit in the northwestern margin of Tarim Basin

塔里木盆地西北缘是我国重要的砂砾岩型矿床的成矿带,该地区首次在志留系地层中发现砂岩型莫洛克斯铜矿,矿区圈出铜矿体3条,铜平均品位为0.57%~2.5%,矿体厚度为1.33~4.76 m,走向延伸为110~520 m。地球化学特征上,铜在围岩-蚀变砂岩-含矿砂岩逐渐富集;稀土元素对球粒陨石标准化后δEu、δCe为负异常,蚀变砂岩稀土总量相对于围岩的明显降低,含矿砂岩相对于蚀变砂岩又有稀土元素的带入;微量元素特征上,矿区砂岩均具有沉积岩物源区特征,沉积构造背景为被动大陆边缘。总结矿床地质特征与地球化学特征,认为区域上及矿区内稳定产出的灰绿色岩层及其中的铜矿化为原始沉积形成,矿区内蚀变砂岩及铜矿体则是由还原性富Cu盆地流体沿构造运移在氧化还原界面发生沉淀形成。

The northwestern margin of Tarim Basin is an important sandstone-type mineralization zone in our country.A sandstone-type copper deposit is newly discovered at the Silurian strata in Morlocs mining area.Three copper orebodies are circled out in the Morlocs mining area.The average grade of copper is between 0.57%and 2.5%,the thickness is from 1.33 to 4.76 meters,and the striking extension is 110 to 520 meters for the three orebodies.In terms of geochemical characteristics,copper element is gradually enriched in wall rock-altered sandstone-orebearing sandstone.δEu andδCe are negative anomalies after chondrite standardization of rare earth elements.Compared with the surrounding rock,the total amount of REE of altered sandstone is significantly reduced.Compared with altered sandstone,ore-bearing sandstone has enriched for rare earth elements.For the geochemical characteristics of trace elements,the sandstone in the mining area has the characteristics of sedimentary source area,and the sedimentary structure background belongs to a passive continental margin.For the summary of the geological and geochemical characteristics of this deposit,it is believed that the gray-green rock layers and the stable copper mineralization strata in the region are formed by the primitive sedimentary process,and the altered sandstone and copper orebodies in the mining area are developed along the structure for Cu-rich reductive basin fluids is migrating to precipitate at the redox interface.