Mineralization processes of gold and antimony in northern part of the Youjiang Basin,SW China:Constraints from LA-ICP-MS trace elements of fluorite from the Qinglong Sb(Au)and Nibao Au deposit
Many gold and antimony deposits in the Yunnan-Guizhou-Guangxi region in SW China are characterized with co-occurrence and symbiotic differentiation of Ao and Sb.However,the metallogenic relationship between Au and Sb and the difference between ore-forming processes of Au and Sb need to be further investigated.Fluorite,a common gangue mineral widely occurred in hydrothermal deposits,has been extensively studied to reveal the formation process of ore deposit.The Qinglong antimony deposit and the Nibao gold deposit in the Youjiang basin,with their matching mineralization ages and wallrock alteration characteristics,are selected as ideal objects for investigating the symbiotic differentiation of gold and antimony mineralization.Therefore,in this paper,we have carried out the in situ LA-ICP-MS trace element study of fluorites from the Qinglong antimony deposit and the Nibao gold deposit,in order to reveal the difference between their respective gold and antimony mineralization processes.Mineralogical and cathodoluminescence(CL)studies of fluorites reveal that three different stages of Sb-mineralization related fluorites in the Qinglong antimony deposit have been identified.Specifically,the first-stage fluorites have right-declined REE patterns with LREE-enriched and HREE-depleted characteristics.The second-stage fluorites are characterized by the MREE enrichment.The third-stage precipitated fluorites generally inherited the characteristics of REE distribution patterns of the second-stage fluorites though the third-stage fluorites have relatively low ∑REE contents.In general,the ∑REE values of fluorites are gredually decreased from the first-stage fluorites,second-stage fluorite to the third-stage fluorites.All fluorites have negative Ce anomalies.There are fluorites of two precipitation stages associated with the gold mineralization in the Nibao gold deposit.The first-stage fluorites have right-declined REE patterns,whilst the second-stage fluorites are characterized with MREE-enriched REE patterns.Their REE patterns are generally similar to those of fluorites in the Qinglong antimony deposit.Diagrams of Y/Ho,La/Ho,Tb/Ca,and Tb/La ratios for fluorites at different stages reveal that there are different genetic characteristics between fluorites of the early-ore-stage and those of the late-ore-stage.Especially,the early-ore-stage fluorite is of the dominant hydrothermal fluid filling genesis,while the late-ore-stage fluorite was formed in close association with the water-rock reaction which resulted in the input of a significant portion of host rock components into the late-stage ore-forming fluid,and the gradual increase of pH values and the decrease of total REE contents of the ore-forming fluids from the early-to late-stage.The comprehensive analysis suggested that the antimony mineralization in the Youjiang Basin is associated with the acidic ore-forming fluid which caused the dissolution of carbonate wallrock through the intensive water-rock reaction and thereby resulted in the formation of a significant of fluorite.Moreover,the increase of pH values and the decreaseof temperatures of the evolved ore-forming fluids could be contributed to the extensive precipitation of stibnite in the antimony deposit.Alternatively,the ore-forming fluids of gold deposits are characterized with weakly acidic to neutral nature.They caused the limited decarbonation of carbonate wallrocks and then resulted in the formation of a little fluorite and a large amount of dolomite,which is conducive to the formation of a large amount of Au-bearing pyrite.Based on the statistic analysis of REE data of stibnite and associated ore-related gangue minerals in antimony deposits in the Youjiang Basin,it is believed that the MREE enrichment characteristics for REE patterns of gangue minerals could be resulted from the LREE super-enrichment of a large amount of hydrothermal stibnite of antimony deposits.
LA-ICP-MStrace elementsfluoritegold and antimony depositsYoujiang Basin
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