摘要
深穿透地球化学是针对寻找隐伏矿的需求而发展起来的一门新的勘查地球化学技术。本文通过对深穿透勘查地球化学元素垂向迁移机理理论以及金元素活动态测量技术的研究总结,选择金成矿背景较好,但常规地质和地球化学找矿方法难以奏效的甘南草甸覆盖区进行了方法有效性试验,并应用其开展了找矿实践。
研究区内以岷县—礼县—合作—夏河区域性断裂为界,北为秦岭北部褶皱带,南为西秦岭中部三叠系裂陷槽。该断裂普遍认为其高渗透的环境直达地壳深部,有利于深部矿液向上运移,并在其旁侧的次级断裂聚集、沉淀,对成矿十分有利。金资源普查评价工作在研究区已经发现了多处具有良好找矿前景的矿化线索。但由于研究区覆盖较厚,地势平缓,基岩露头少,水系不发育,区内表生条件不利于金在地表的侧向迁移,通过常规的地质及化探方法找矿效果不明显。
本文在深穿透勘查地球化学理论研究的基础上,首先在甘肃石青硐及忠曲金矿已知矿区隐伏矿体的上部,采用金属活动态测量进行了剖面测量试验。利用中科院廊坊物化探所提出的选择性提取5个相态金的技术提取到水提取态、有机态和游离自然金3个相态的金。3种方法都很好的在已知隐伏金矿体上方圈定了异常。
随后,根据研究区景观条件制定了针对草甸区金的深穿透测量方法。在将其那梁和枣子沟南两个地区采用1：20000大比例尺开展了面积性深穿透地球化学测量。采样布局参考200×200m基本网度,采集样品为利于活动态金富集的A层下部或B层土,采样深度30～40cm,利用选择性提取技术提取和分析了两个地区水提取态、有机结合态和自然游离态3种相态金的含量,制作了金的深穿透地球化学图,按3种方法均圈出了金的异常,3种方法圈出的异常有一定的吻合程度。
在甘南草甸区进行深穿透地球化学的方法试验与应用,以及对个别异常的验证,显示本方法在该区可以有效地圈定异常,为甘南草甸区开展深穿透化学找矿提供了依据,对此地区隐伏或半隐伏矿勘查评价有重要指导意义。
Deep-penetrating geochemistry is a kind of new geochemical technique for prospecting buried ore-body in overburden area. Through studying the theory of deep-penetrating geochemical migration mechanisms and summarizing the technology of leaching of mobile forms of gold, and after test of method effectiveness, this technology has been employed for prospecting the deposit buried under the grassy marshland in the South Gansu Province, where is the favorable area of gold formation, but the conventional geological and geochemical prospecting methods are ineffective to evaluate the effectiveness of this technology.
The study area was divided by the regional fault of Minxian-Lixian-Hezuo-Xiahe, Northern Qingling fold zone in the north, and middle section of Triassic rift geosynclines in Western Qingling in the south. It has been recognized widely that the high percolation environment of the regional fault of Minxian-Lixian-Hezuo-Xiahe was favorable for metallogenesis because the fault reached the deep crust, which caused deep ore solution moving up, accumulating and depositing in the flanking area of the fault. The investigation and evaluation of gold resources done in Xiahe-Hezuo Region has identified many good clues for potential exploration.
The surface conditions of study area impede the lateral movement of ultra-fine gold. Although some good clues have been identified in the periphery of rock-mass contact zone, the prospecting result through the conventional geological, geophysical and geochemical methods was not notable because the sections of key anomaly are the area with the thick overburden, the gentle terrain, the shortage of bedrock, and undeveloped drainage system.
On the basis of study of the theory, the leaching experiment of partial extraction of mobile gold in the soil and profiling survey on the known buried ore bodies in Shiqingdong Gold Mine and Zhongqu Gold Mine have been carried out. It has been employed the partial extraction technology provided by Institute of Geophysical and Geochemical Exploration in Langfang to leach 5 phases'gold of soil sample, among which 3 phases'gold including water extractive, organic and free natural phase gold were determined. All of 3 phase's gold shows the mobile gold anomalies on the top soil of buried gold body.
Subsequently, the method of deep-penetrating geochemical area survey for gold prospecting in the grassy marshland is designed according to the landscape condition, by which the area survey of scale 1:20000 has been completed at the basic grid of 200×200m. The soil samples were collected from the lowest part of soil A horizon or the upper part of B at the depth of 30-40cm. The contents of 3 phase's gold were analyzed, and the geochemical maps of 3 phase's gold were made. The anomalies of gold by the deferent indications show their consistency of a certain extent.
The experiment and application of deep-penetrating geochemical survey and verification of a few anomalies revealed that this method is effective for identifying the anomalies. It will be the evidences for the further study, and important for guiding exploration and evaluation of the buried or semi-buried deposit in this region.
引文
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