The Salts' Zoning Structure And Ore-forming Elements Distributing Pattern In Gobi Coverage

There is a excellent geological setting for mining in the expensive area in the Northwest China, thus it has a great potential for prospecting mines, especially for hidden ore bodies. Therefore, it is an imperative issue to trace the ore-forming information and search for the hidden ore bodies using geochemical exploration in Gobi hidden areas.Given the large areas of Gobi and desert in Jiuquan Gansu Province, we chose the coverage of Xiaoxigong gold mine and Tiaozishan-Jinwozi mine to analyze the chemical composition, for the aim of classification determination of secondary salts. Then we designed the experimental methodology of sequential separating extraction of the secondary salts, and measured the concentration of secondary salts and ore-forming metallic elements. Finally, we summarize the zoning structure of salt materials in the Gobi coverage and the distributing pattern of ore-forming elements.We used SEM to observe the samples'appearance and Energy Dispersive Spectrometer to determine their compositions. And we found there mainly were three kinds of secondary salts in Gobi coverage salts: dissolving salts, gypsum and calcite. And salt and Glauber's salt mainly constitute of dissolving salts.The underground water upward movement through evaporation in the Gobi coverage makes salts dissolving. And with the ascendant of water, the dissolved salt condensed and deposited in various layers of the coverage. As different phases of secondary salts conveyed different ore-forming elements, the zoning structure of the salts and the distributing pattern of ore-forming elements are essential fingerprint for prospecting hidden ore bodies.According to the different solubilities, we designed the experimental methodology of sequential separating extraction of the secondary salts. First, we extracted the dissolving phase, using deionizing water. Then we used 1mol/L NaCl to dissolve the residue to extract the gypsum phase, for 1mol/L NaCl can enhance the solubility of gypsum which could be fully extracted. Finally, we extracted the calcium carbonate with 6mol/L acetum because it can fully dissolve the secondary calcium carbonate without damage of the original ones.The analysis of the data implicits that SO₄^2- and Ca²⁺ concentration in the second step CO₃^2- and Ca²⁺ concentration corresponded well. This proved we did a successful separation and attained the goal to extract the gypsum in the second step and calcium carbonate in the third step.The data of salts and ore-forming elements indicated that the dissolving salts and gypsum mainly deposited at the bore skins and calcium laminations. the bore skins and the calcium laminations have significant enriched the underground ore-forming elements and the calcium carbonate in the coverage which tend to be hard dissolved have an extensively enrich of ore-forming elements. Several elements have a certain associations.