地球化学调查数据在地质背景、成矿条件分析中的应用:以中国西北干旱荒漠区为例

Application of Geochemical Data in Analysis of Geological Background and Metallogenic Conditions:A Case Study of Northwest China

1∶5万矿产地质调查中通常会优先部署地球化学调查工作,采样密度一般大于8点/km2,并分析多达38项地球化学指标,其主要目的是发现"矿致异常",指导矿产勘查工作.而研究表明,区域地球化学数据是地表物质化学组成的直接反映,所以不仅包含了与成矿有关的异常信息,更包含了丰富的地质信息.在本次工作中应用中国西北干旱荒漠景观区1∶5万地球化学调查数据成功识别了工作区地质体单元的分布.相比1∶20万地质底图,通过clr-PCA分析提取出的1∶5万地球化学数据信息展现了更多的细节:(1)地质体单元可以更为细致地划分为多个次级单元;(2)侵入体单元可以进行期次或岩相划分;(3)可为地质体单元的归属提供依据.本项研究结果成功指导了后续开展的1∶5万地质调查工作,并对最终的1∶5万地质图进行了验证,此外还提供了多处有利找矿线索.

In most 1∶50000 geological and mineral surveys,geochemical surveys are conducted first and sampling density is higher than 8 samples/km^2,with up to 38 geochemical indices being analyzed,because the main purpose is to identify"ore causing anomalies"and to facilitate mineral exploration.However,it has been found in previous studies that regional geochemical data directly reflect the chemical composition of surface materials,which contain more extensive geological information than mere anomalies related to mineralization.Based on 1∶50000 geochemical surveys of arid desert landscapes in Northwest China.Geological units in the working area and their geochemical characteristics were studied and identified in this study.Compared to 1∶200000 geological maps,the results of the PC analysis performed on clr-transformed 1∶50000 geochemical data show more details:(1)some geological units could be further divided into multiple sub-units;(2)some intrusive rocks could be divided by phases or lithofacies characteristics;(3)could provide clues for the classification of geological units.The results of this study have been successfully used in the follow-up 1∶50000 geological mapping and verification of the final 1∶50000 geological map.Furthermore,the division of geological units and the identification of geochemical characteristics could provide information for excluding the geochemical anomalies which are irrelevant to mineralization.