In the (1) era, the main copper mineralization was later than the residual asphalt of organic fluid, and basalt was interspersed in the asphalt and crystal caves were filled in the veins. Isotopic dating of Zhu Bingquan and others also shows that mineralization is later than basalt 15 ~ 90 Ma (Figure 9- 1).
(2) Regionally, basalts are developed in several synclines adjacent to Zhaotong area in northeast Yunnan. There is no difference in the thickness of the fourth lithologic member of basalt in these synclines, and there is no obvious difference in the thickness and eruption cycle of ore-bearing strata (the lower submember of the fourth lithologic member), but their ore-bearing properties are quite different. Maolin syncline and Xiaozhai syncline have good ore-bearing properties, while other synclines have poor ore-bearing properties (Table 9-65438
(3) On the profile, the Cu content in the second and third lithologic sections of Emeishan basalt is stable, while the Cu content in the fourth lithologic section changes greatly, and the background content and high value points are affected by the mineralization and alteration of supergene hydrothermal solution. From bottom to top, from the second lithologic member to the fourth lithologic member, there is no obvious enrichment trend of Cu background content (Figure 2-2). Further research shows that the existing copper content in the fourth lithologic member is as high as 4532× 652. There are also almond basalt, massive basalt and tuff, with the Cu content as low as 54 ~ 198× 10-6, and the Cu content in the fourth lithologic member tends to decrease from bottom to top (Table 3- 1 and Figure 3-2), which also shows that copper mineralization has nothing to do with volcanic magma evolution. Therefore, the basalt copper deposit in this area is not a syngenetic volcanic hydrothermal mineralization, but an epigenetic hydrothermal mineralization.
Table 9- 1 Basalt thickness, eruption cycle and ore-bearing property of syncline ore-bearing beds in northeastern Yunnan
According to the measured geological profile summary.
Figure 9- 1 copper mineralization age of basalt type (according to Zhu Bingquan et al., 2005)
The obvious stratabound characteristics of copper mineralization are controlled by the special rock formation at the top of basalt flow-basalt breccia and carbonaceous sedimentary rock interlayer. Quenched basaltic breccia is rich in pores, which is not only a favorable storage place for organic fluids, but also a favorable storage space for ore-forming fluids. The organic matter of organic fluid and carbon in carbonaceous sedimentary rocks provide favorable reduction conditions for copper precipitation in the form of native copper in ore-forming fluid. Therefore, the combination of hardened basaltic breccia and carbonaceous sedimentary rocks formed in the shallow water environment of land-sea transition constitutes two main types of rocks for copper mineralization.