| 其他摘要 | The Altai orogen in China is a typical region of the Central Asian Orogenic Belt (CAOB), which is situated between the Siberia block and the Kazakhstan-Junggar block. According to previous statistics, there are nearly one hundred thousand pegmatite veins exposed in the Altay area. Among them, about one thousand pegmatite veins are rare metal mineralization pegmtite. Howere, it is quite deficient of the studies on pegmatite petrogenesis, formation age , provenance and geotectonic setting until now. The Halong granite is emplaced in early Paleozoic Halong-Qinghe hypozonal magmatic arc of mid-Altay tectonic units was encompassed by four pegmatitic fields, respectively, the Kelumute-Jideke pegmatite field and Alashan pegmatite field are located at the east side of halong granite, the Kaluan-Azubai pegmaite field and Qiongkuer pegmatite field are located at the west side of halong granite. There are more than ten thousands pegmatite veins in the four pegmatite pegmaite fields. Among them, including the Kaluan No. 806 and 807 pegmatites large-sized Li deposit, the Kukalagai No. 650 pegmatite large-sized Li deposit, the Kelumute No. 112 medium-sized Li-Nb-Ta deposit, the Jiamukai tourmaline deposit, and the Qiongkuer No. 1 medium-sized Nb-Ta deposit. In space, on the west side of Halong granite, westward by the granite and the Kulumuti group outer contact zones, the pegmatite mineralization presents zonality. In turn, it is appearing that no mineralized pegmatites, Be mineralized pegmatites, Li mineralized pegmaites and quartz veins. The pegmatites of Kaluan appear in Li mineralized zone. Because of lacking of system reliable chronology of pegmatite and granite, it is still inconclusive whether pegmaites of Kaluan mining area are genetically correlated with the Halong granite. The Kaluan minging area is a potential super-large deposit. The purpose of this paper is to reveal Kaluan mining pegmatites formation ages and stages, pegmatitic provenance, tectonic setting, petrogenetic relationship between pegmatites of Kaluan and the Halong granite, and tries to explore the gensis and geotectonic setting of the Halong granite. Zircon U-Pb dating and Hf isotopes of four pegmaites from the Kaluan-Azubai pegmatite mining area were carried out by LA-ICPMS and LA-MC-ICPMS, also the systematic studies on zincon U-Pb dating and geochemistry characters of the Halong granite were carry out in this paper, the following original understanding have been obtained: (1) The U-Pb data for the zircons from the pegmatite samples by LA-ICPMS shows, that the formation ages of pegmatites, numbered 805, 806 and 807 in the Kaluan mining area, were determined to be 216.0±2.6 Ma, 223.7±1.8 Ma and 221±15 Ma, respectively, as the products of Triassic magmatic activities. For the Kukalagai No. 650 pegmatite, that it mades up of two stages of pegmatites, that is, the early albite pegmatite (227.9±2.6 Ma) and the late spodumene-albite-lepidolite pegmatite (211.3±2.4 Ma). The intrusive age of Halong granite is in the range of 396.9~408.1 Ma, as the products of Devonian magmatic activities. (2) Researched pegmatites of Kaluan-Azubai pegmaite mining area formed in Triassic. As large gaps in their formation age (>170 Ma) between pegmatites and Halong granites, it indicates that pegmatites from the Kaluan mining area have no genetic relationship with the Halong granite. (3) Zircons from the pegmatites of Kaluan mining area have lower positive εHf(t) values (+0.64~+2.50), with larger TDM2 model ages of 1,090~1,213 Ma, similar to zincon Hf isotopes of the Keketuohai NO. 3 pegmatite and the Kelumute No. 112 pegmatite, indicating that the pegmatites were created by crust thickening and decompression melting in a post-collision tectonic setting. (4) The geochemistry of Halong granites shows the characteristics of high silicon(SiO2 = 71.97%~74.94%) and aluminum(Al3O2 = 12.13%~15.22%), moderate alkali contents(K2O+Na2O = 6.69%~9.14%), relatively abundant in K(K2O /Na2O = 1.06~1. |
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