ZHAO Yun-chuan1, HU Jun2*, ZHOU Hong-bing1, HE Zhi-wei2,3

(1. Sichuan Institute of Metal Geologic Survey, Chengdu 611730, China; 

2. Contemporary Amperex Technology Co., Limited, Guiyang 550081, China; 

3. College of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China)

Abstract: The Nageng silver deposit is located in the eastern segment of the Eastern Kunlun orogenic belt. Many plagiogranite are exposed in the deposit. The genesis and tectonic background of these rocks can provide new evidences for revealing the tectonic evolution process of the region. Therefore, here, we have carried out detailed petrological, geochemical and zircon U-Pb geochronological analyses of the plagiogranite exposed in the central part of the deposit. The LA-ICP-MS zircon U-Pb age of the Nageng plagiogranite is (425.1±4.6) Ma, suggesting that it was formed in the middle Silurian. Petrogeochemical characteristics of the plagiogranite samples show that their SiO2 contents and K2O/Na2O ratios are 71.16%－71.32% and 0.29－0.35, respectively, with aluminum saturation indexes (A/CNK) ranging from 1.09 to 1.30, resembling to characteristics of typical peraluminous rocks. Their Ritmann indexs (δ) vary from 1.33 to 1.48, suggesting that the plagiogranite belongs to the calc-alkaline peraluminous I-type granite. The total REE contents (ΣREE) of the plagiogranite samples vary from 54.12 ppm to 55.90 ppm, with characteristics of the strong enrichment of LREE and the depletion of HREE. In addition, the plagiogranite samples have characteristics of relatively depleted high field strength elements. but relatively enriched large ion lithophile elements and incompatible elements (such as U) in their Primitive mantle-normalized trace element spidergrams. Combined with above petrogeochemical characteristics of the Nageng plagiogranite samples and previous research data on the tectonic evolution of the Eastern Kunlun, it is suggested that the Nageng plagiogranite could be formed by magma derived from the partial melting of the basaltic oceanic crust mixed with continental crustal materials in the northward subduction process of the Proto-Tethys Ocean. 

Keywords: plagiogranite; zircon U-Pb dating; geochemical characteristics; the Nageng silver deposit

ACTA MINERALOGICA SINICA Vol. 43, No. 5, 2023, Page 640