| The Haoyaoerhudong gold deposit, which is discovered as an important part of "Central Asian belt" with the gold resource reserves of 147 t, has became one of the biggest breakthrough in Inner Mongolia for gold exploration in recent years.The Haoyaoerhudong gold deposit with low grade large-scale features is the largest open-pit gold mine, and the wall rock is Bayan Obo Group epimetamorphic rock in the western section of the northern margin of North China Craton. Haoyaoerhudong gold deposit(147t~0.62g/t),Muruntau gold deposit(5264t~2-3g/t) at West Tianshan zone and Sukhoi Log gold deposit(1100t~2.8g/t)in the south edge of Siberia plate have a similar metallogenic environment, but there is a big difference between resource reserves and average grade. In recent years, there is a huge disagreement about the genetic model of the deposit during the process of exploration. The main difference is focused on which factors that strata or magma play a dominant role in controlling mineralization. In fact, these argument result from the lack of clear understanding of the enrichment process of Au element.With the continuous operation of mining industry, gold quality has been declined gradually, and open pit excavation of low grade ore body has been unable to meet the economic requirements, which means there is a urgent desire to find a high grade ore body in the periphery or deep areas.In this paper, the research object is gold-bearing mineral in Haoyaoerhudong gold deposit.Based on the previous work, a detailed field geological survey was carried out. We analyzed samples for the characteristics of sulfur compounds and geochemical characteristics in different geological processes, completed a total of 60 electron microprobe points points, 100 LA-ICP-MS points, the following conclusions have been made:1.There are two kinds of ore types in the mining area, the mixed type ore and quartz vein type ore. There are three main types of metal sulfides: The first is the formation of a fine-grained disseminated, vein and bedding fine metal sulfide film-like, widely distributed in the mining area, mainly pyrite; The second is a clear stretching lineation sulfide mineral types are pyrite, pyrrhotite, mainly distributed in the mining area within the strongly foliated with the site; The third is related to hydrothermal veins, veinlets distribution of quartz sulfide, concentrated in the south east part of belt, quartz-sulfide veinlets within the near surface to deep underground 500 m range, mineral assemblage of quartz-pyrite-based, with width of 0.5-5cm ranging and intrusive relationship formation was bedding. Below the 500 m depth, the mineral assemblage are dominated by quartz-pyrrhotite-chalcopyrite,and the width of ore vein is more than 10 cm.2.Combined withthe previous research results and the morphological characteristics of the mineral samples, the mineralization period is divided into sedimentary diagenetic stage, tectonic deformation stage, hydrothermal stage and hydrothermal solution. By electron microprobe analysis, the contents of Fe、S element in pyrite were(46.04 ± 0.44)% and(53.26 ± 0.50)%, slightly less than the theoretical value. With the ongoing process of mineralization, S element content was decreasing, the deep impurity related to sulfur fugacity reduced accordingly. The contents of Fe、S element in Pyrrhotite were(59.76 ± 0.32)% and(39.13 ± 0.40)%,respectively, Fe atomic percent content(46.60 ± 0.31)%, it is categorized as monoclinic pyrrhotite.3.The results of LA-ICP-MS analysis of sulfide showed that:(1)The average content of Au elements in the sedimentary diagenetic pyrite was 0.098 ppm. During the tectonic deformation and hydrothermal period, the Au elements in pyrite are mostly lower than the detection limit. The hydrothermal transformation period, the average content of Au in pyrite was 0.12 ppm. In combination with the average content of Au element in the sedimentary diagenetic period, it is found out that hydrothermal alteration of the relative deposition diagenetic enrichment of Au element takes only 22.4 percent;(2)The total content of five kinds of ore-forming elements(Au, Ag, Cu, Pb, Zn) in pyrite, In the sedimentary diagenetic stage, tectonic deformation stage, hydrothermal stage and hydrothermal transformation period are 103.10 ppm, 59.16 ppm, 22.47 ppm, 51.60 ppm, respectively, The sedimentary diagenesis plays an important role in the whole process of mineralization;(3) The contents of Co,Ni in sedimentary diagenetic pyrite was(0.038ppm-34.88ppm),(0.6096-122.1ppm), the contents of Co,Ni in hydrothermal stage pyrite(243.5ppm-408.6ppm),(734.1ppm-1535ppm),there is significant differences between them; the ratio of the elements of Co and Ni content only rarely become larger than 1, most of the rest were less than 1.4.Through the investigation of sulfide geochemical characteristics in different geological process. It can be concluded that the gold element enrichment of Haoyaoerhudong gold deposit mainly occurred in the sedimentary diagenetic stage, Subsequent brittle ductile shear and hydrothermal fluid activity did not lead to the conclusion that gold elements enriched again. This is why there is a large differences on gold grade scale between the Haoyaoerhudong gold deposit and Sukhoi Log gold deposit, which are located at same metallogenic belt of the Muruntau gold deposit and Sukhoi Log gold deposit. |
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