云南腾冲麻栗坝铜铅锌及锡锌铅矿化区岩浆岩及次生晕元素组合特征与复合成矿分析

Composite Cu-Pb-Zn and Sn-Zn-Pb mineralization in the Maliba area,Yunnan Province:Evidence from the magmatic features and secondary halo of ore forming elements

麻栗坝矿化区位于云南腾冲梁河-古永锡、铜多金属矿集区北部。矿化区中北部出露与闪长玢岩紧密共生的铜多金属矿化及绿泥石化,北部发育与黑云母及二云母花岗岩紧密共生的黄铁夕卡岩蚀变。为了分析矿化区内两类矿化蚀变及岩浆活动与成矿的关系,本文分析了黑云母及二云母花岗岩主量元素组成、闪长玢岩和黑云母花岗岩矿物组成、两矿化蚀变区域次生晕元素组合差异及工程验证其所揭示矿体成矿元素组合。闪长玢岩脉具角闪石-磁铁矿组合,显示氧化岩浆特征;黑云母及二云母花岗岩具高硅(72.93%~76.09%)、富碱(Na2O+K2O 7.11%~9.52%,K2O/Na2O>1)及过铝质(ANK 1.24~1.45)特征;黑云母及二云母花岗岩副矿物含钛铁矿及其锆石Ce4+/Ce3+比值低(5.78~192,平均77),显示还原岩浆特征。中北部铜多金属矿化区次生晕显示Cu、Pb、Zn综合异常,而北部黄铁夕卡岩蚀变区显示Sn、Zn、Ag综合异常。次生晕异常区工程验证发现铜多金属矿化区深部发育与闪长玢岩脉密切共生的铜铅锌矿体,黄铁夕卡岩化深部发育锡锌铅矿体。上述地质地球化学特征表明麻栗坝矿化区内既发生了与氧化岩浆岩热液有关的铜多金属成矿,也发生了与还原岩浆热液有关的锡多金属成矿。梁河-古永矿集区既发育锡多金属矿床,也发育铜多金属矿床,可能与矿集区内经历氧化和还原岩浆作用有关。

The Maliba mineralization anomaly area is located in the northern part of the Lianghe–Guyong Sn–Cu polymetallic ore-rich field in Tengchong county,Yunnan Province.Dioritic porphyrite associated with Cu(Pb–Zn)mineralization as well as skarn with biotite granite and muscovite granite were found in the central-northern and northern parts of the area,respectively.To elucidate the relationship between the Cu mineralization associated with the porphyrite and the skarn-type mineralization,and to further investigate the processes that trigger the formation of Cu-and Sn-polymetallic deposits in the Lianghe–Guyong ore-rich field,the major elemental compositions and zircon Ce4+/Ce3+values of biotite granite and two mica-granites,as well as the mineral compositions of the dioritic porphyrite and element association of secondary halo anomalies of the two types of mineralization,were systematically analyzed.The dioritic porphyry dike had a mineral assemblage of amphibole plus magnetite,which signifies a highly oxidized condition.The biotite granite and two mica-granites were characterized by a high silicon content(SiO2 of 72.93%–76.09%),high alkaline(Na2O+K2O of 7.11%–9.52%;K2O/Na2O>1),and peraluminous rocks(ANK of 1.24–1.45),which suggest an S-type affinity.The granites contained accessory ilmenite and exhibited a low zircon Ce4+/Ce3+ratio(5.78–192,average of 77),thus indicating a reduced magmatic origin.The Cu mineralization domain had a secondary halo of a Cu,Pb,and Zn integrated anomaly without significant Sn enrichment.On the other hand,the skarnization domain had a secondary halo of a Sn,Zn,and Ag integrated anomaly along with a significant depletion of Cu.The two secondary-halo integrated anomalies were proved to agree with Cu–Pb–Zn and Sn–Zn–Pb ore bodies,respectively.The distinctive magmatic features of the dioritic porphyry and granites,in addition to the corresponding different mineralization element associations in the Maliba area,demonstrate that the formation of Cu-polymetallic deposits and Sn-polymetallic deposits are associated with highly-oxidized magmatism and reduced magmatism,respectively.Hence,we suggest that the formation of Cu–Sn polymetallic deposits in the Lianghe–Gushui ore-rich region is genetically related to highly-oxidized and reduced magmatic activities.