Western Yunnan Tengchong the Songpa tin Late Cretaceous A-type granite and its geological significance

Dasongpo tin deposit lies in the well-known West Yunnan Sn mineralization zone as well as in Tengchong-Lianghe Sn mineralization subzone. There are granites of three different ages including Early Yanshanian, Late Yanshanian and Early Himalayan. These granites have very close relationship with the metallogenesis of Sn-polymetallic deposits, though, the lithogeochemical characteristics and the connection between the intrusive and metallogenic need further research. In this paper, fine-grained biotite monzogranite and biotite granite of Guyong intrusive were selected in the area to make Ar-Ar age-dating. The K-feldspar of the finegrained biotite monzogranite gives a well-defined 40Ar/ 39Ar plateau age of 67. 84 ± 0. 60Ma (2σ) while the K-feldspar of biotite granite dating results give a well-defined 40Ar/ 39Ar plateau age of 65. 86 ±0. 42Ma (2σ), showing that the fine-grained biotite monzogranite formed slightly earlier than the biotite granite. Dasongpo granites from Guyong intrusive belong to high-K calc-alkaline to shoshonite series and peraluminous series based on lithogeochemical characteristics, and which have significant differentiation between HREE and LREE, no Ce anomalies but very significant negative Eu anomalies. In addition, they are depleted in Ba, Sr, P, Ti and enriched in U, Th, Ta, Rb, Pb. The range of 10000Ga/Al is from 3.53 to 5.52. These geochemical characteristics all indicate that they are typical A-type granites. From major element, trace element geochemical characteristics, and discrimination diagrams of tectonic environments we can determine that they are A2-type (post-collisional) granites, inferring Dasongpo granites from Guyong intrusive produced in the collision extensional tectonic environment. Greisen veins and Sn ores of Dasongpo Sn deposit have less REE and trace element than Dasongpo granites from Guyong intrusive, but their chondrite normalized REE distribution patterns and primitive mantle normalized multi-element spider diagrams are very similar to those of the Dasongpo Guyong granites, indicating that there is genetic connection between them. The Dasongpo greisen-type Sn veins were possibly formed by extracting metallogenic material from Dasongpo Guyong A-type granites while the hydrothermal transporting and then filling the fracture to mineralize. We infer that, combined with the Ar-Ar dating, Dasongpo Sn deposit is the metallogenetic response to magmatism of Guyong intrusive in Late Yanshanian to Early Himalayan in this area, and there is at least one Sn mineralization which is closely associated with the A-type granites of Guyong intrusive during 68 ∼65Ma.