半干旱—干旱地区以钙积层为采样介质的隐伏金矿地球化学勘查

Calcrete as a new sampling medium for geochemical exploration of concealed gold deposits in semi-arid and arid areas

在隐伏金矿的地球化学勘查中,常用的采样介质包括岩石、水系沉积物、土壤、植物和地气等。近几十年,澳大利亚在半干旱—干旱地区以钙积层作为隐伏金矿床地球化学勘查的采样介质,并取得了成功。本文对以钙积层作为隐伏金矿地球化学勘查采样介质的理论和勘查进展进行总结,其勘查理论基础是土壤剖面中金-钙高度相关性,其成因机理较合理地解释为:原生金矿或金矿化通过风化作用形成金的各种络合物、纳米金以及其胶体等,这些金受蒸发蒸腾、植物根系、电化学、地气、地震泵等作用由深部迁移至浅表,浅层土壤中的这部分金早期与钙质相关性弱;在湿润期,在微生物分解有机质过程中,金可以形成金-氨基酸络合物或者胶体金呈溶解态,在干旱期由于金络合物和胶体失稳而与碳酸钙等一起沉淀;最终,在植物、微生物、气候综合作用下形成钙积层金异常。然而,我国的相关研究表明,钙积层中金异常的形成会受到黏土矿物以及石膏含量的影响,金-钙并非呈正相关关系,黏土矿物会使金发生富集,石膏或碳酸钙大量存在会使金发生贫化,且地形也会对钙质层中金异常的形成产生影响。因此,该方法能否应用于澳大利亚以外地区仍需做进一步的研究和尝试。

Commonly sampling media in gold geochemical exploration include rock, stream sediment, soil, plant, and gas. In recent decades, calcrete has been successfully used as a sampling medium in geochemical exploration of concealed gold deposits in semi-arid and arid areas in Australia. In this paper, the theory and advances in the use of calcrete as the sampling medium in geochemical exploration of concealed gold deposits are summarized. This method is based on the high correlation of gold with calcium in the soil profile. A probable explanation for the genetic mechanism is as follows: the weathering of primary gold deposits or mineralization forms various gold complexes, nano gold, and its colloids. Then, the dissolved gold and nano gold can be migrated from deep to shallow horizon by evaporation and transpiration, plant roots, electrochemistry, earth gas, seismic pumping, and other functions. In a wet sub-period, gold could form gold amino acid complex or gold colloid with the help of microbial breakdown of plant organic material. There is no correlation between gold and calcium in soils at early time;in drying sub-periods, the destabilization of gold amino acid complex or gold colloid gold results in co-deposition of gold and calcium. Finally, combined plant-microorganism-climate effect leads to form gold anomaly in calcrete. Notably, the research in China suggested that the contents of gold and calcium are not positively correlated since the presence of clay would promote gold enrichment, and the presence of plaster and calcium carbonate would prompt gold depletion;in addition, topography will also affect the formation of gold anomaly in calcrete. Therefore, it still needs to be tested if the method could be applied outside Australia.