新疆阿祖拜矿田伟晶岩型矿床遥感找矿综合信息研究

对利用ASTER、RapidEye、QuickBird及ASAR等多种类型遥感影像在伟晶岩型矿床遥感找矿中的综合应用进行了探讨。云英岩化和钠长石化是阿祖拜矿田两类主要的蚀变类型。在分析其光谱特征的基础上,确定了利用ASTER数据对这两类蚀变进行信息提取的方法。利用ASTER热红外数据进行了岩浆岩类型的划分,为不同岩性接触带的准确定位提供了依据。伟晶岩在可见光-近红外光谱段的高反射率是伟晶岩的自动识别及遥感解译重要的物理基础。以QuickBird的伟晶岩解译结果为检验标准,得到RapidEye的伟晶岩自动提取精度约86%。构造交汇部位、岩性接触带以及伟晶岩富集区与蚀变异常的叠加部分是该区成矿预测的重要依据。基于蚀变异常、伟晶岩富集区、地质构造等遥感找矿综合信息,圈定了4个远景成矿靶区,为进一步开展地质详查工作提供参考。关键词:伟晶岩;蚀变异常;遥感;信息提取;成矿预测

Remote Sensing Prospecting of Pegmatite Deposits in the Azubai Region, Xinjiang

Chinese Altay region is one of the important parts of Altay metallogenic belt of central Asia, and is a well-known mineralization area of non-ferrous metals, rare metals and precious metals. There are more than 100,000 pegmatite veins in Chinese Altay region, 90% of which occur in more than 30 pegmatite ore fields. In this paper, the Azubai pegmatite ore field in the central Altay, which is around 500 km2 with the centre coordinate of 88°48′E and 47°56′N, is studied. Remote sensing images of ASTER, RapidEye, QuickBird and ENVISAT-ASAR are used to extract prospecting information on pegmatite deposits in the Azubai region. Greisenization and albitization are the main alterations closely associated with mineralization. Based on the spectral characteristics, the method of Feature-orientated Principal Component Selection (FPCS) was used to optimize the ASTER band combination of 1-4-6-7 and 1-4-6-9 to extract greisenization and albitization respectively. ASTER thermal infrared data were used to estimate the surface content of SiO2, K2O and Na2O based on empirical formula, which provide effective technical support for the classification of magmatic rocks and effective basis for mapping and locating of the contact zones of different lithologies. It is the high reflectivity of pegmatite in the spectral range from visible to near infrared that provides the important physical basis for automatic identification and remote sensing interpretation of pegmatite. The pegmatite interpreted from QuickBird image with spatial resolution of 0.61 m was used to validate the automatic extraction of pegmatite from RapidEye image with 5m spatial resolution whose accuracy is about 86%. ASAR image is only used to do some preliminary experiment to identify pegmatite. Due to the lower spatial resolution, the extracted pegmatite from ASAR image was not used for metallogenic prediction. The conjunction parts of geological structures, contact zones of lithologies and superposed parts of pegmatite enrichment zones and alteration anomalies are the important basis for metallogenic prediction. According to above factors derived from remote sensing, four target areas were delineated, which will provide guidance for further prospecting.