老挝万象省爬立山(PHaLek)铁矿磁异常特征及找矿评价

Magnetic anomaly characteristics and prospecting evaluation of the PHaLek iron deposit in Laos

老挝万象省爬立山铁矿床位于长山褶皱带北西端,是长山成矿带内与岩浆作用有关的一个大型铁矿床.矿床类型以矽卡岩型为主,其次为热液型,成矿作用与花岗岩类侵入作用有关,矿区内发育致密块状磁铁矿、孔洞状赤铁矿、砂砾土状铁矿.该区地球物理工作研究程度较低,仅有部分航磁资料,难以准确控制矿化异常;老挝热带雨林气候植被覆盖严重,地表露头难寻,圈定矿体规模和划分地层界线难度较大.为了获得该区铁矿体地表规模及深部延展,笔者在该区开展了1∶10000地面高精度磁法测量,运用解析延拓、水平总梯度模、垂向导数、2.5D人机交互反演等方法有效克服了低纬度地区磁异常化极不稳定形成假异常的问题,解译了爬立山矿区磁异常特征,提高了磁异常的解译分辨率,更加准确的控制了爬立山铁矿区铁矿体的范围、深部延展.后期钻探验证结果表明,在老挝地质勘查程度低、覆盖严重的爬立山地区开展高精度磁法是控制该地区铁矿的有效地球物理方法.

PHaLek iron deposit of Vientiane,Laos is located in the northwest end of Trungson Fold Belt,which is a large iron deposit related to magmatism in Trungson Fold Belt.The deposit is mainly dominated by skarn type,followed by hydrothermal type.The mineralization is related to the intrusive effect of granitoid rocks,and there are dense massive magnetite,hole-like hematite and gravel soil-like iron ore in the mine area.Except aeromagnetic data,there is a lack of geophysical data for this area,so it is difficult to accurately control the mineralization anomaly.Due to the Laos'rainforest climate,the vegetation coverage is serious and the surface outcropping is hardly seen,and it is difficult to delineate the size of the orebody and divide the boundary line.In order to clarify the surface scale and deep extension of the iron deposit body in this area,the writers have conducted the 1∶10000 ground high precision magnetic measurement in this area,and has overcome the problem of false abnormity caused by the extreme instability of magnetic anomaly in a such low-latitude area by the methods of analytical continuation,horizontal total gradient model,vertical derivative,and 2.5D human-machine interaction inversion.The writers successfully interpreted the magnetic anomaly characteristics of PHaLek Iron deposit,improved interpretive resolution of magnetic anomaly,and controlled the range and deep extension of the iron orebody in PHaLek iron deposit,and provided the effective basis for the engineering verification in a later stage.The results show that high precision magnetic prospecting was a effective method to control the area of iron ore with low degree of geological exploration and serious coverage in Laos.