Magmatic sulfide copper-nickel deposits related to basic-ultrabasic rocks in the world are mainly produced in Late Archean-Proterozoic and Mesozoic. Jinchuan deposit, which occupies the second largest copper-nickel deposit in the world, is a special case: the ore-forming rock mass was formed in the early Mesoproterozoic Great Wall, and the ore bodies are concentrated in a single rock mass dominated by lherzolite, so the enrichment and enrichment of nickel metal elements must be the result of extraordinary geological processes. According to the layered characteristics of earth elements and the enrichment degree of nickel in iron-nickel cores, the different depths of mantle material sources determine the number of enrichment sources of mantle-derived metal elements, while the magnesium ultramafic rocks in ocean crust, which generally represent the source of upper mantle materials, are difficult to enrich nickel on a large scale. Modern marine surveys have confirmed this inference. The magma that formed Jinchuan ore-forming rock mass may have come from the deep, and the recent interpretation of seismic tomography in the deep earth also supports the existence of low-speed anomalies of mantle plume originating from the core-mantle boundary (28,965,438+0 km) (Xu Zhiqin et al., 2003). Therefore, the author speculates that Jinchuan ore-bearing ultramafic rocks may have formed in the continental rift environment induced by mantle plume. Qilian Mountain is probably the "hot spot" of ancient mantle plume in early Mesoproterozoic, and Jinchuan deposit is the product of hot spot. It is precisely because the early Paleozoic tectonic facies occupied the main body of Qilian Mountain, and the ore-bearing geological bodies formed in Mesoproterozoic moved to the flank of Qilian Mountain, which led people not to regard Jinchuan deposit as Qilian Mountain deposit in the past. In fact, it represents the most important metallogenic event in the early geological evolution of Qilian Mountain.
It is speculated that Jinchuan deposit was formed in a "hot spot" environment, which is helpful to understand the extraordinary enrichment of the deposit and further understand the future prospecting work. Mantle plume provides an abnormal source of metal, but large-scale mineralization also needs enough sulfur and its solubility in magma system to drop sharply, otherwise nickel metal elements mainly combine with silicified rocks to enter rock-forming minerals. The general loss of chromium spinel nickel in Jinchuan rock mass (Tang Zhongli et al., 1998) shows that the sudden change of physical and chemical conditions before diagenesis reduces the solubility of sulfur and enough sulfur, which leads to the immiscibility of silicate magma and nickel-containing sulfide liquid phase, and finally leads to large-scale mineralization. The most direct reason for the sudden change of physical and chemical conditions of magma system should be the mixing of different end-member magma (Barnes et al., 1985), and Jinchuan rock mass has signs of mixing of different end-member magma (Li, 1996). Therefore, the prospecting work around Jinchuan should pay attention to the transformation of the basement of the early Mesoproterozoic hot spot rift in Qilian Mountain, and also pay attention to the investigation of magma mixing evidence. In terms of further prospecting for Jinchuan-type deposits in Qilian Mountains, mafic-ultramafic intrusions in the basement of Hualong Group in Lajishan area of southern Qilian Mountains should be an important investigation and study area, and deposits and occurrences such as Lashuixia are important indicators.