Zhu J.,Chinese Academy of science |
Zhu J.,University of Chinese Academy of Sciences |
Hu R.,Chinese Academy of science |
Bi X.,Chinese Academy of science |
And 5 more authors.
Acta Petrologica Sinica | Year: 2011
The Yangla copper deposit is located in the middle zone of Jinshajiang suture zone. The Beiwu, Linong and Lunong granitoids exhibit a linear distribution from north to south in the ore district. The three granitoids have similar compositions of major, trace elements and Sr-Nd isotopes, indicating that they have a common magma source. They do not contain muscovita, and have high concentrations of SiO2(64% ∼73% ), K2O (2. 15% ∼4. 05% ) and low P2O3 (0. 04% ∼ 0. 11% ) content. In addition, they have low δ((K2O+Na2O) 2/(SiO2-43); 1.4 ∼ 2.4) and A/CNK (molecular Al 2 O3/(CaO + Na2O+K2O) ; 0.92-1, 11). The granitoids display significantly negative anomalies of Nb, Ta, Ti and P, obvious enrichment of LREE and Rb, Th, U and Pb. The 10000Ga/Al ratios ( 1. 7 ∼ 2. 1 ) of those rocks are lower than typical A-type granites. Moreover, considering the slightly negative Eu anomalies, it is suggested that the three granitoids belong to high-K calc-alkaline, metaluminous-slightly peraluminous I-type granites. Compared with the continental crust (i. e. , the Lincang granite and the Shaba granulite) , the granites have lower ( 87Sr/ Sr86)¡ (0. 7078 ∼0. 7105) and higher εNd(t) (-5. 1∼ -6. 7), with ancient Nd two-stage model age (tDM2 = 1. 5Ga). And there occur a number of coeval mafic microgranular enclaves (MMEs) in these granitoids, suggesting that mantle-drived magmas were involved in the source region (see in a separate article ). By combining with comparative analyses of the tectonic settings, we propose a model in which the Beiwu, Linong and Lunong granitoids were generated under a late collisional or post-collisional setting. Decompression induced those mantle-derived magmas underplated and provided the heat for the anatexis of the crust The hybrid melts ( i. e. , mantle-derived and the lower crustal magmas ) and subsequent fractional crystallization could be responsible for the formation of the Beiwu, Linong and Lunong granitoids.
Zhou D.,Wuhan University |
Zhang Z.-F.,Wuhan University |
Long F.,Mining Development Co. |
Luo C.,Mining Development Co.
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences | Year: 2013
In mountainous areas with eluvium overburden thickness, moisture and vegetation of the overburden layer may be locally increased where faults are developed in the bedrock. At such localities thermal inertia of the near-surface materials is larger than that in the surrounding areas and relatively low surface temperature due to slower diurnal heating rate may be observed in the daytime. Therefore, the temperature-vegetation-dryness index (TVDI), a combination of surface temperature and vegetation, may be used to retrieve buried faults. Using Landsat7 ETM+ data, we have identified buried faults in this study with TVDI in Yangla copper mining district, Yunnan which is about 26 km2 in area and is covered by residual deposits for the most part. A distribution map of faults of the district is obtained with linear lows of TVDI as indicators of buried faults combined with visible image interpretation and field investigation. While essential for mining practice in Yangla, our results show a remarkable potential of thermal infrared remote sensing in ore-field geological studies in poorly outcropped regions.