International Geologiical Congress - Oslo 2008

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MAG-04 Scales, scaling, non-linearity and complexity in the geosciences

 

The digital characteristics of the granitoid and its implications for Pb-Zn-Ag mineralization in the Jinla poly-metallic ore field across China and Myanmar

 

Yongqing Chen, China University of Geosciences (China)
Jingning Huang, China University of Geosciences (China)
Hongguang Liu, China Library of Geosciences (China)
Pengda Zhao, China University of Geosciences (China)
 

 

The granitoid associated with Pb-Zn-Ag mineralization in Jinla poly-metallic ore field across China and Myanmar, located at the Eastern Tethyan Ore-forming Domain, includes the Laochang amphibole admellite, the Menglinshan biotite admellite and the Nanla K- feldspar granite. In this paper, the digital characteristics such as the major elements and micro-elements including rock-forming elements, ore-forming elements and REE of the granites are systematically studied and established their ages using the zircon SHRIMP. The intrinsic connection, genesis and evolution of the granitoid, and the relationship between the granitoid and Pb-Zn-Ag mineralization are explored from the viewpoint of tectonic-magmatic evolution. The conclusions are as follows. (a) The granitoid were emplaced in extension tectonic environment at the age of 43-45±1Ma at the end of syn-collision stage of the Himalayan orogenic episode. (b) the samples of the granites scatter within the S-Type granites area in the(Na+K+Ca/2)-Al chart, and that of the Laochang amphibole admellite near the I-Type granites area, that of the Nanla K- feldspar granite away from the I-Type granites area, and that of the Menglinshan biotite admellite between the two granites, which show that the magma forming the granitoid may mainly originates from partial melting of the crust and mix with the components from the upper mantle at a certain extend, and that the components from the upper mantle gradually reduce from the Laochang amphibole admellite to the Menglinshan biotite admellite and to the Nanla K-feldspar granite. (c) The chondrite-normalized pattern of the granites REE are all steep right-leaning with weak negative Eu anomalies, and the contents of REE from the Laochang admellite(320.82ppm-466.83ppm) to the Menglinshan biotite admellite (217.01ppm-286.21ppm) and to the Nanla K- feldspar granite(93.14ppm-174.78ppm) gradually decrease, which imply that they may be the crystallization differentiation products of different stage of the same magma process.(d) In contrast to the average contents of some ore-forming elements of the granitoid in China, the concentrated order of the corresponding elements of the Laochang admellite are Sb(5.69, concentrated coefficient)F(3)Mo(2.83)As(2.67)W(2.56)U(1.78)Pb(1.6)Zn(1.2), the Menglinshan biotite admellite Sb(3.00)Pb(1.90)As(1.83)B(1.55)U(1.44)Bi(1.33)Zn(1.2), and the Nanla K- feldspar granite As(49.61)W(42.84)Cu(40.00)Bi(26.13)Sb(7.85)B(3.14)Ag(4.50)Sn(3.00)U(1.83)Pb(1.42). In conclusion, both in the enrichment variety and the enrichment degree of the ore-forming elements, the Nanla K-feldspar granite are all greater than that of the two former granites, which says that Nanla K- feldspar granite may be of the most potential to Pb-Zn-Ag mineralization among the three types of granites in the study area.

 

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