Gold Mineralization Of Alkali-rich Magmatism In Cenozoic, Western Yunnan Province, China

The porphyritic rocks are enriched in alkali content （K2O+Na2O>8 wt. %） from the western of Yunnan. The porphyritic rocks related to gold deposits typically formed within 70 to 20Ma, and concentrated in 35Ma and 25Ma. Jinping: 41.6～36.1Ma, Yaoan: 38.5～30 Ma, Yongping-Weishan: 55.7～19.17 Ma, Yongshen: 59.24～23.35 Ma, Beiya-Machangqing: 64.8～24.3 Ma, Jianchuan: 66.2～22 Ma, Zhongdian: 89.35～28.2 Ma.The alkali-rich porphyries: ⁸⁷Sr/⁸⁶Sr : 0.705448～0.711624; ¹⁴³Nd/¹⁴⁴Nd: 0.512296～0.512573;εNd（t）: -6.75～-1.75; ²⁰⁶Pb/²⁰⁴Pb: 18.045～18.791, ²⁰⁷Pb/²⁰⁴Pb: 15.47～15.719, ²⁰⁸Pb/²⁰⁴Pb: 38.327～39.138. the alkali-rich porphyries magmas from different areas have the same source. Magmas are formed by mixing of deep crust and mantle materials, which have developed in an active continental extension tectonic setting.The gold ores show closely temporal and spatial association with alkali-rich porphyries in that the ores occur directly as impregnated veinlet in the porphyritic rocks, the contact zone between rock and host, the explosive pipes and the surrounding of hydrothermal breccias.REE of rock minieral were 44.01～710.98 and 9.79～650.58,δEu were 0.7～1.26 and 0.44～1.64, LREE/HREE were 2.45～16.82 and 1.96～21.86,respectively. The porphyritic rocks’trace element patterns characterized by a high value of total REE, enrichment in light REE and a slight negative Eu anomalies. Comparison of REE patterns between the rocks and the gold deposits show that deposits have similar form, but have less REE contents and are more heavy REE distribution curve complicated than the rocks.Based on the feature similarity of the race element spider diagram,the alkali-rich porthyry in different areas have the same magmatic origin.The shape of diagram for transition element is“W”,which was consistent with mantle-derived alkaline complex.And compared with magmatites,the deposits have the similar feature.And the deposits are much more rich in transitional elements than magmatites,which shows suffered the reworking processes by the later ore fluid.The range ofδ³⁴S from alkali-rich porphyry is -4～6.6‰,which derived from mantle.The range ofδ³⁴S from deposit is the almost same with the magmatites,but a little more complicated because of influenced by later ore fluid.Geochemical characteristics show that the mineralization is closely related with the diagenesis, The source of ore-forming fluid is consistent with the source of alkali-rich magma , Which have the relationship with the deep crust-mantle mixed substances.