The Emeishan basalt has a high Cu background value (170×10-6 on average), and thus provides a ore-forming material source for copper ores. The collected samples were exposed in basalt lavas of the third segment of the Emeishan basalt eruptive cycle. By using a set of automatically cycling glass apparatuses, weathering-leaching experiments by three kinds of rainwater on the collected samples were carried out in the open system (at normal temperature and normal pressure). The analysis results showed that the most intensive export of Cu occurred under acidic rainwater-induced weathering-leaching conditions, almost 2-3 orders of magnitude the export of Cu by mod-ern air rainwater, and 1-2 orders of magnitude higher than the export of Cu by CO2 rainwater. In addition, the total amount of Zn, Cu, U, Ni and Sr exported by acidic rainwater are greater than 1%. All this indicates that copper in the Emeishan basalt provided the copper source for Cu mineralization at the contact between the basalt and the Maokou Formation limestone at the bottom.
Adsorption experiments were made at room temperature and neutral pH value on different types of min-erals associated with the Lower Cambrian black shale series polymetallic layers in Hunan and Guizhou provinces on nanometer-sized Pt colloids and PtCl42--bearing ionic solutions with an attempt to constrain the relationship between the different types of minerals in the polymetallic layers and the enrichment of platinum group elements (PGEs). Experimental results showed that the different types of minerals show strong selectivity to the adsorption of nano-meter-sized Pt colloids and PtCl42--bearing ionic solutions. Metallic sulfides, organic matter and clay minerals are the strong adsorbents of PGEs, while quartz, albite, muscovite and other silicate minerals show a week adsorbility to both of them. This phenomenon is well consistent with the geological fact that metallic sulfides, organic matter and clay minerals in the polymetallic layers of the black shale series are the major carrier minerals of PGEs, giving a thorough explanation to the mechanism of enrichment of previous metal elements. Adsorption may be a principal mechanism of enrichment of precious metal elements under lower temperature conditions. The presence of the aforementioned strong adsorbents is the good geochemical barriers for the enrichment of PGEs.
Ore minerals in the sedimentary-type Cu deposits in the Xuanwei Formation overlying the Emeishan basalt are dominated by copper sulfides and native copper. As the ores mostly exhibit concretionary structure, previous researchers named them the "Madouzi-type Copper Deposit". Here the authors carried out mineralogical and isotopic studies on copper nodules in this ore deposit. The mineralogical study shows that copper nodules are composed of copper sulfides that have been cemented by ferruginous amorphous minerals, clay, and carbonaceous fragments in the modes of metasomatism and sedimentation. The nodules are preliminarily present as aggregates of gelatinous material. The isotopic analysis shows that the δ 13CPDB values of an- thraxolite are within the range of-24.8‰--23.9‰, indicating that the anthraxolite is the product of sedimentary metamorphism of in-situ plants. The δ 34SV-CDT values of chalcocite are within the range of 7.6‰-13.1‰, close to those (about 11‰) of Permian seawater. The δ 34SV-CDT values of bornite and chalcopyrite are 21.6‰-22.2‰, similar to the sulfur isotopic composition (20‰) of marine sulfate, indicative of different sources of sulfur. The above characteristics indicate that the copper nodules were formed in such a process that Cu-bearing basalt underwent weathering-leaching and copper-bearing material was transported into waters (e.g., rivers, lakes, and swamps) and then adsorbed on clay and ferruginous amorphous mineral fragments. Then, the copper-bearing material was suspended and transported in the form of gelinite. In lake or swamp environment, it was co-deposited with sediments to form copper nodules. At later stages there occurred metasomatism and hydrothermal su- perimposition, followed by the replacement of chalcocite by bornite and the superimposition of chalcopyrite over bornite, finally resulting in the formation of the "Madouzi-type" nodular copper deposit.
Tailings produced in a concentration plant are the discharge of solid wastes after grinding ore into size and selecting useful components in the specific economic and technological condition. According to statistics, for the mining of metal ore, non-metallic ore, coal, clay, etc, the production of tailings of the world is up to 100 million tons per year. The number of existing tailing piles is 12718 in China, of which the construction ones are 1526, accounting for 12% of the total, and the closed tailing piles are 1024, accounting for 8%. As of 2007, the national total tailings accumulation is 8.046 billion tons. The non-ferrous metal mining is one of the largest discharge of solid wastes industries because of its low comprehensive recovery rate. For example, the beneficiation and recovery rate of non-ferrous metal mine is from 50% to 60% in China, which is lower 10% to 15% than developed countries, and the associated non-ferrous metal recovery rate is 40%, which is lower 20% than developed countries. On the utilization of duns, Poland is 90% to 100%, United States, Australia, France, Canada, Belgium and other countries followed, while China is only about 20%. The utilization of fly ash is to 100% in Japan and Denmark, France is 65%, UK is 55%, and China is just 45%. Quantities of waste rock, waste slag, and waste water have occupied land, destructed vegetation, deteriorated the soil and water quality, and caused land subsidence, landslides, mud-flow and other geological disasters. Therefore, the comprehensive utilization of resources is the right choice of mining sustainable development, environment protection, resource conservation, economic and social development.
WANG FudongZHU XiaoqingWANG ZhonggangHAN TaoLI ZengshengSUN XiaohuiLING Kunyao
