Origin Of The Rhodonite From Luziyuan Pb-Zn Mineral Deposit In West Yunnan And Its Geological Significance

Luziyuan super-large Pb-Zn-Fe polymetallic deposit is a typical representative of the serial similar deposits developed in Baoshan-Zhenkang block.Orebodies occurr as statiform-like along the strata,and the ore-bearing wall-rocks are mainly skarns.The geological,geophysical,geochemical explotation and remote sensing interpretation evidences all showed that the concealed rock body existed in the deep.While the inferred hidden body and the accurate mineralization age hasn't been uncovered and obtained in the known deposit,thus the ore genesis still remains controversial greatly.It is found in this research that there is an obvious positive correlation between rhodonite and iron,lead-zinc,and copper ores deeply in the deposit.In addition,the amount and grain size of rhodonite gradually increase down the deep.All these phenomena observed in the deposit are not only of great significance for us to understand the origin of it,but also typical signs of looking for the same type deposits.Major,trace,rare earth elements?REEs?and H-O isotope compositions of the rhodonite are studied in this paper,in combination with trace elements and REEs of actinolite,sphalerite as well as other minerals,the metallogenic material sources,ore-forming environments and ore genesis are then discussed.?1?Rhodonite genesis:the chemical constituents of rhodonite mainly comprises SiO2 of 47.01%?48.66%,MnO of 34.42%?40.19%,CaO of 7.52%?8.51%,FeO of 2.85%?8.76%,MgO of 0.22%?0.28%,and lower TiO₂ and Al₂O₃.In the MnSiO₃-FeSiO₃-CaSiO₃ diagram,all the data points fall into the rhodonite area,indicating that it is indeed rhodonite;The trace,rare earth elements and H-O isotopes all show that the formation of the rhodonite is associated with the deep magmatic hydrothermal fluid.Combined with geological characteristics of Luziyuan Pb-Zn-Fe polymetallic ore deposit,it is thought that the marble is replaced by the deep magmatic hydrothermal solutions carrying large amounts of Mn²⁺ upwelling along the fractured structure,and then rhodonite is formed.?2?Sources of ore-forming materials:The trace elements compositions of rhodonite,actinolite and sphalerite and their Y/Ho ratios are all characterized by close relation to the deep magmatic hydrothermal fluid.The rare-earth distribution pattern of sphalerite is consistent with that of Yanshanian epoch magmatic rocks such as Zhibenshan,Kejie and Caojian rock body in the block.H and O isotope points are plotted within the magmatite region.In combination with the stable?C,O,S?and radiogenic?Sr?isotopic analyses of the deposit by previous researchers,it is proposed that the ore-forming materials are mainly derived from the deep concealed magmatic rock body.?3?Metallogenic environment:Eu anomaly displays a gradual decreasing trend?i.e.a transition from positive into negative abnormity?from rhodonite,actinolite to sphalerite;and Th and U differentiation extent gradually reduces along this mineral order,too.Uniting the above results with studies on the homogeneous temperature of the fluid inclusions trapped in the rhodonite and quartz,it is suggested that metallogenic environment have experience a conversion from high-temperature oxidation condition of Skarn period to low-temperature reduction state of quartz-sulfide period,which is more conducive to the precipitation and enrichment of mineralization elements like Pb and Zn.?4?Ore genesis:It is synthetically considered that Luziyuan Pb-Zn-Fe polymetallic deposit is a distal Skarn-type lead-zinc deposit in association with Yanshanian concealed intermediate-acid magmatite.