The volcanic-intrusive rock sequences and metal mineralizations in rifted basin in the eastern Yunnan Province,China
Alkali magmatism exerts a distinctive influence on mineralization processes in metal ore-concentrated areas.However,deep exploration and mineral prediction in the study area face challenges due to the complex interplay of volcanic-intrusive rock sequences,metal mineralization,and superimposing magmatic-tectonic systems.This study focuses on two key regions in eastern Yunnan,China:the Dongchuan Fe-Cu-Au ore concentrated area(Proterozoic marginal rifted basin)and the Gejiu Sn-Cu-W-Cs-Rb polymetal ore concentrated area(Triassic back-arc rifted basin).By applying innovative tectonic lithofacies mapping techniques,we investigated the volcanic-intrusive rock sequences related to alkali magmatic activity,rifted basin evolution,rock associations,and superimposed magmatic-intrusive systems.This approach aims to elucidate the superimposed mineralization of IOCG,Cu-Co-rutile,and Sn-Cu-W-Cs-Rb polymetallic deposits in the region.Our investigation has yielded several noteworthy findings.Firstly,Neoarchean alkali rocks in the Dongchuan Fe-Cu-Au ore-concentrated area are composed of calcite albitite(2520±14 Ma)and Fe-rich alkalipicrite(2529±77 Ma).The Neoarchean-Paleoproterozoic Xiaoliukou Formation Complex(＞2.50 Ga),particularly its upper part exhibiting homotopy in different lithofacies(2.50 to 1.80 Ga),serves as the new host strata for Cu-Co-rutile-REE mineralizations.These strata have been reworked by Mesoproterozoic volcanic-intrusive rocks in the Dongchuan Fe-Cu-Au ore-concentrated area.Secondly,during the Mesoproterozoic stage of volcanic rifting basins,alkaline rocks,including Fe-Na-rich alkali basic rocks,Fe-K-rich trachyte,and Fe-rich alkali diabase-gabbros,formed as part of the first member of the Yinmin Formation.Xikuangshan-type Fe-Cu deposits,or IOCG deposits,are hosted in the second to third members of the Mesoproterozoic Yinmin Formation.Additionally,Fe-K-rich trachyte in the footwall of the Fe-Cu orebody hosts monazite-type REE mineralization.The IOCG system and rutile superimposing mineralization are formed in alkaline Ti-Fe-rich gabbros(1097 to 1047 Ma),alkaline Ti-Fe-rich diorites,and alkaline monzoporphyry,all of which formed during the Greenville Orogeny in eastern Yunnan.Thirdly,Triassic alkalipicrite and tephrite,with primary enrichment of Sn-Cu-Zn-Li-Rb-Cs,were produced in the Triassic arc-back rifted basin in the Gejiu area of eastern Yunnan Province,China.These rocks were subsequently superimposed by leucogranite intrusion,which played a pivotal role in the formation of Sn-Cu-W-Cs-Rb-bearing phlogopite-type skarn.Finally,alkali rocks with initial metal enrichment in the early stage of the rifted basin evolution were superimposed by later-stage alkaline intrusive rocks with metal mineralization.This process represents the primary mechanism for metal mineralization in the rifted basin in eastern Yunnan.Breccia-pipes formed by magmatic hydrothermal fluids in the alkaline magmatic-intrusive tectonic system control the hypernormal enrichment of Cu-Co-rutile-REE mineralization.Conversely,leucogranite intruded into alkalipicrite and tephrite with Sn-Cu-W-Cs-Rb primary enrichment is responsible for the hypernormal enrichment of Sn-Cu-W-Cs-Rb-bearing phlogopite-type skarn.
marginal riftedbasinback-arc rifted basinvolcanic-intrusive rock sequencestectonics of volcanic eruption-magmatic intrusionalkaline rockskey mineralseastern Yunnan
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