Distribution, Characteristics And Genesis Of Mississippi Valley-type Lead-zinc Deposits In The Triangle Area Of Sichuan-Yunnan-Guizhou Provinces

The triangle area of Sichuan-Yunnan-Guizhou Provinces located on the southwestern margin of the Yangtze platform,which is the most important Mississippi Valley-type (MVT) Zn-Pb metallogenic belt in China. Regional sedimentary (metamorphic) formation, magmatite,tectonic evolution, and regional geochemistry condition have been analysised in order to expound the metallogenic Geological Condition about the Sichuan-Yunnan-Guizhou triangle Region brilliantly in this paper. In this belt, there are more than four southands ore deposits, and the main exposed strata are Paleozoic and Mesozoic fine-grained clastic rocks and >10,000 m thick carbonate rocks (containing a few layers of volcanic rocks in some places). There occurred plentiful fault activities in the region, but magmatism was lacking. The characteristics of the tectonic evolution and timing of metallic mineralization are described. Many deposits are apparently controlled by faults and distributed along deep faults, especially at the intersection of the faults. They also show regular distribution in space and time and are controlled mainly by strata, lithology, rock facies and structures in particular, showing the characteristics of control by multi-order structures. Recently, the authors have found a new method for accurate dating of the Mississippi Valley-type Zn–Pb deposits. During geological surveys of the Huize Zn-Pb deposit, Yunnan, the authors found a high-K altered clay mineral and used this new K-Ar dating method to obtain a mineralization age of 176.50±2.54 Ma. This mineralization age is notably younger than the age (251–262 Ma) of eruption of the Emeishan basalt. This dating method will afford a new approach to solving the problem of the mineralization age of MVT Zn–Pb deposits. After detail field inspecting,combined with the deep indoor research result,the author regarded that those deposits,which districted in This area(such as Huize, Tianbaoshan, Daliangzi, Lehong and so on) are belong to Mississippi Valley-type Lead-Zinc deposits. Based on all of these, the metallogenic model of these Mississippi valley type lead-zinc deposits have been built up.