云南武定地区核桃箐铁铜矿热液活动特征及其与迤纳厂铁铜矿的异同

Hydrothermal activity of the Hetaoqing iron-copper deposit in Wuding, Yunnan and its similarities and differences with the Yinachang iron-copper deposit

关键词:  核桃箐铁铜矿床  热液蚀变  成岩环境  滇中

Key words:  Hetaoqing iron-copper deposit  hydrothermal alteration  diagenetic environment  central Yunnan

摘要:

核桃箐铁铜矿位于滇中武定断陷盆地内,与迤纳厂铁铜矿同属于滇中地区的IOCG型矿产。野外地质调查发现其成矿地质背景和矿床特征虽与迤纳厂铁铜矿有一定相似性,但富集的成矿元素类型和蚀变特征等方面却与迤纳厂不同。核桃箐矿区主要的赋矿地层为落雪组(Pt₂l),成矿元素只大量富集Fe元素,局部富集Cu元素,没有富集Au元素。矿石类型以致密块状磁铁矿石为主,围岩蚀变类型较少但具有一定的分带性,与矿化关系最为密切的蚀变是硅化。岩相学和地球化学研究发现,从围岩到蚀变岩,核桃箐矿区内主要的迁入元素是SiO₂、Al₂O₃、MnO和Na₂O,主要的迁出元素是CaO、MgO、H₂O和CO₂,表明核桃箐矿区内的硅化与去碳酸盐化是同时进行的,而钠化则与其同步或者稍晚于硅化。岩矿地球化学研究表明,核桃箐含矿围岩的n (SiO₂)/n (Al₂O₃)> 3.6,n (Al)/n (Al+Fe+Mn)> 0.5, n (Al₂O₃)/n (Al₂O₃+Fe₂O₃)=0.12~0.36,反映其形成于拉张环境、成岩时海水深度较浅的成岩特征。

Abstract:

Just like the Yinachang iron-copper deposit, the Hetaoqing iron-copper deposit in the Wuding fault basin, Yunnan is interpreted to be the iron oxide copper-gold deposit in central Yunnan. Although the similarities appear in the two above-mentioned iron-copper deposits, there are additional differences in ore-forming element type and alteration type. The Hetaoqing iron-copper deposit occurs in the Luoxue Formation (Pt₂l), and abounds only in the element Fe and minor amount of the element Cu, without the enrichment of the element Au. The ore types are represented by the dense massive magnetite ores, and silicatization is considered to be the main alteration type associated with the mineralization. The imported elements SiO₂, Al₂O₃, MnO and Na₂O and the exported elements CaO, MgO, H₂O and CO₂ have disclosed that the silicatization may coexist with the decarbonatization in the Hetaoqing iron-copper deposit, while the sodiumization is nearly synchronous with the silicatization and decarbonatization, or slightly later than the silicatization. In the ore-bearing wall rocks, all the values of n(SiO₂)/n(Al₂O₃) > 3.6, n(Al)/n(Al + Fe + Mn) > 0.5, and n(Al₂O₃)/n(Al₂O₃ + Fe₂O₃)=0.12-0.36 have reflected that the Hetaoqing iron-copper deposit was formed in the extensional environments with the shallower sea water depths during the diagenetic processes.