Abstract:

 Jinla Pb-Zn-Ag polymetallic ore field across China and Myanma, is tectonically located in the south segment of the Mengtong-Gengma-Ximeng passive continental margin of Proterozoic eraPalaeozoic era，and the eastern margin of the Baoshan.Shantai Massif. The granitoids related to mineralization within the ore field include Laochang amphibole admellite, Menglinshan biotite admellite and Nanla K-feldspar granite-porphyry. This paper systematically presents the characteristics of the major elements, REE and trace elements (including ore-forming elements) of the granites and their isotopic ages determined by zircon SHRIMP dating. The intrinsic connection and genesis of the granites, and the relationships between granites and Pb-Zn-Ag mineralization are discussed. It comes to the conclusions as follows：(1) Among three types of granites, Laochang amphibole admellite and Menglinshan biotite admellite have the same age of (45±1) Ma and likely emplaced in a deeper setting at the earlier stage of tectonomagmatic evolution; Nanla Kfeldspar graniteporphyry has an age of (43.41±0.78) Ma and emplaced in a shallower setting at the later stage of tectonomagmatic evolution.（2）Studies on both major elements and trace elements of the granites, combined with their zircon U-Pb age, such as REE and Zr/Hf，Nb/Ta，Rb/Sr，Rb/Ba，K/Rb，(Rb/Yb)N，Sr*，K* and Zr* show that these granites emplaced in an extension tectonic environment at the age of 43~45 Ma during the later stage of syncollision of the Himalayan orogenic episode, which are the products of crystallization and differentiation from their mother granite magma at different stage of tectonomagmatic evolution. (3) It has been shown in the Al(Na+K+Ca/2) diagram that the Jinla granitoids are all plotted within the area of “S” type of granites, but the samples from Laochang amphibole admellite, Menglinshan biotite admellite and Nanla K-feldspar graniteporphyry are scattered gradually far away from the boundary between “I” and “S” types of granites, implying that the components from the upper mantle gradually decreasing from the Laochang amphibole admellite to the Menglinshan biotite admellite and then to the Nanla K-feldspar granite porphyry. (4) In contrast to granites in China, Nanla K-feldspar graniteporphyry are strongly richer in oreforming elements such as W, Cu, Bi, Sb, Mo, Sn, Ag, Pb, and Au as well as volatile elements F, B, and As than the other two types of granites. In addition to that, the Pb-Zn-Ag ore deposits are spatially associated with K-feldspar granite-porphyry veins in depth within this ore field, which implies that the Kfeldspar granite-porphyry may be closely related to the Pb-Zn-Ag mineralization and may be regarded as visible marks for finding new ore deposits.

Key words:

Jinla granitoids; zircon U-Pb dating; element geochemistry; Pb-Zn-Ag mineralization; across China and Myanmar