Dizhi lixue xuebao (Aug 2021)
On relationship between the superimposed mineralization systems and the zoning patterns of vertical tectonic lithofacies in the Gejiu concentration area of Sn-Cu-W and three rare metals in Yunnan
Abstract
Based on the zoning pattern and the deformation sieving of tectonic lithofacies, as well as the macroscopic and microscopic studies of tectonic lithofacies, the superimposed mineralization systems and the Gejiu ore-concentrated area in Yunnan has been studied. The relationship among the enrichment mechanism of strategic key minerals, the superimposed mineralization, and the pattern of tectonic lithofacies has been uncovered. It was believed that the Triassic arc-back rift basin at the pre-magmatic intrusive stage, the tectonic system of magmatic intrusion at the syn-magmatic intrusive stage, and the karstic tectonic system at the post-magmatic intrusive stage, all of them are of syn-space superimposing lithofacies and mineralizations within different time domains and syn-time lithofacies differentiation. All of them had different controls on the Gejiu superimposed mineral system and Sn-Cu-W-Co-Cs-Rb mineralization. There are 9 vertical tectonic lithofacies zones (VTZs) in different patterns of VTZs around the Gejiu superimposed mineralization system. Firstly, the light-colored granite (VTZ8) and crystal-nucleus lithofacies of magmatic pneumatolytic hydrotherm (VTZ9), being the tectonic lithofacies of syn-magmatic intrusive stage for the biotite granite (γK2a-b-c), was formed at the top and on the edges of the granite intrusion. Secondly, skarn alteration lithofacies to skarn lithofacies (VTZ7) in the magma-contact metasomatic tectonic lithofacies zone is the tectonic lithofacies zone for coupling reaction by the strata and the magmatic system at the syn-magmatic intrusion.Thirdly, on the one hand, cryptoexplosive brecciation of magmatic pneumatolytic hydrotherm enriching in residual magma was forced into the Middle Triassic Gejiu Group, resulted in the magmatic hydrothermal plume and lithofacies zones of tourmaline-hydrothermal cryptoexplosive breccias (VTZ6). On the other hand, the upper part of the fault-fold-type carbonate layer (VTZ4), the marble lithofacies with cataclastic facies and the cataclastic tourmaline-marble lithofacies (VTZ5), and stratiform-like Sn-bearing dolomite with cataclastic facies (VTZ3) in the farthermost-end part, were formed by tectonic hydrothermal coupling derived in the syn-magmatic intrusive stage from the underlying magmatic hydrothermal plume. Fourthly, the alkaline picritic rocks and alkaline volcanicrocks, and their volcanic erupting structure in the Triassic arc-back rift basin were the tectonic lithofacies at the pre-magmatic intrusive stage. Fifthly, the erosion-level in the Yungui plateau (VTZ1) and the supergene karstic tectonic system (VTZ2) were formed in the post-magmatic intrusive stage; however, they (VTZ1, VTZ2) were superimposed on the tectonic system of the syn-magmatic intrusion (VTZ3, VTZ4, VTZ5, VTZ6, VTZ7, VTZ8, VTZ9). The above achievements are foundations of innovated theory for the deep-probe and the modeling prediction for the buried tectonic lithofacies in the area.
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