铬铁矿地球物理勘探:回顾与展望

Geophysical exploration for chromite deposits:Review and prospects

铬铁矿是关键金属铬唯一可经济利用的自然资源,主要有层状铬铁矿和蛇绿岩中的豆荚状铬铁矿两种类型,其中豆荚状铬铁矿矿体规模小、发育不规律,是一个长期存在的勘探难题。由于铬铁矿特殊的经济战略地位,美国、欧洲、苏联和中国都非常重视铬铁矿地球物理勘探。铬铁矿地球物理探测技术发展始于20世纪30年代,至20世纪80年代,发展了以重力、磁法为主导的铬铁矿地球物理勘探技术,地震、电法也被应用。这一阶段在苏联乌拉尔肯皮尔赛等超大型蛇绿岩型隐伏铬铁矿勘探取得重大突破,在其他矿区取得一定的进展。自21世纪以来,高精度的便携式仪器和新兴地球物理技术逐渐运用到铬铁矿地球物理勘探,综合地球物理成为铬铁矿勘探的主流方法,在我国罗布莎等多个岩体隐伏铬铁矿勘探中取得突破,在印度、阿尔巴尼亚等国家也取得进展。本文回顾了铬铁矿地球物理勘探的发展历程,综述了铬铁矿岩石物理特征与测量方法、重磁勘探主要应用及存在问题、电磁法勘探的主要方法,并重点介绍了音频大地电磁测深在罗布莎铬铁矿的探测效果和电磁法勘探模式,展望了张量CSAMT技术、磁异常模量反演、高光谱遥感、高密度激电、无人机物探等有望在铬铁矿地球物理勘探中发挥重要作用的前沿技术。

Chromite is the only mineral that is a commercial natural source of chrome.Chromite deposits are subdivided into podiform and stratiform(layered)types based on the geometry of the ore bodies and their host rocks.The podiform chromite deposits are always developed in ophiolite complex.Geophysical exploration for podiform chromite deposits is difficult as these chromite deposits do not manifest significant geophysical anomalies.In addition,most of the podiform chromite ore bodies are small scale,they pinch out and then reappear in the host rocks.Geophysical studies for hunting the chromite deposits started around 1920s.A great number of exploration projects have been carried out between 1940s and 1980s.Geophysical approaches such as gravity,magnetic,and electromagnetic methods have been employed in chromite exploration in different survey scales.The largest podiform chromite deposit has been discovered in Kempirsai,Urals.Smaller concealed podiform chromite deposits have been found by geophysical exploration in Turkey,Greece,China and other countries as well.In the past two decades,high-precision miniaturized instruments and integrated geophysical prospecting have been widely used in chromite exploration.Comprehensive geophysical exploration using audio magnetotellurics,gravity and magnetic methods have been applied in Luobusa,southern of the Tibet Plateau,and discovered the largest and highest-grade chromite deposit in China till date.In this study,we reviewed the history and the state of the art of the chromite geophysical exploration.We summarize the rock-physical properties,geophysical approaches of chromite deposits explorations,the applications and challenges of gravity,magnetic and electromagnetic exploration for chromite deposits.Finally,we prospected the application of the emerging geophysics approaches such as the tensor CSAMT,magnetic amplitude inversion,hyper-spectral remote sensing,high-density IP and UAV used for the chromite deposits geophysical exploration.