摘要
滇西北衙斑岩金矿床是金沙江-哀牢山新生代富碱斑岩成矿带中规模最大的金多金属矿床,其已探明的金储量超过350t,伴生的铜、铅锌、铁、银、硫也达到大-中型规模,前人针对该矿床做了很多研究,但对于富碱斑岩与成岩成矿作用的关系一直存在较大的争议。本文以磷灰石为研究对象,比较北衙矿区内各岩体成矿差异,探讨磷灰石所记录的成岩成矿信息。研究表明,北衙矿区二长花岗斑岩成矿岩体与不成矿岩体的磷灰石均富F(>2%)、贫Cl(<0.02%),两者呈现近似的负相关;但成矿岩体中磷灰石具有相对较高的δEu值和较低的δCe值,表明成矿岩体氧化程度更高,从而减少含Fe硫化物的形成,使金属元素得以保存,在源区释放更多的Cu、Au元素,有利于成矿。同时,北衙矿区岩体磷灰石的(Sm/Yb)N比值的减小可能是由含Cl热液的出溶所导致的;与成矿岩体磷灰石相比,不成矿岩体磷灰石的低Ce/Pb和高Th/U值,反映了岩浆形成过程中不成矿岩体的流体活动性较弱,岩浆的分异不明显。对比研究显示,同为陆内碰撞环境形成的北衙矿床与成矿带北段玉龙矿床,其成矿岩体中磷灰石的F/Cl值明显高于俯冲环境中形成的普朗、春都和铜厂沟矿床的成矿岩体。
The Beiya porphyry gold-polymetallic deposit located in western Yunnan is the largest gold polymetallic deposit of Cenozoic Jinshajiang-Ailaoshan alkali-rich porphyry metallogenic belt.It’s proven gold reserves have exceeded 350t,and associated copper,lead and zinc,iron,silver,sulfur have reached medium-large scale.Abundant previous studies have focused on the genesis of Beiya deposit,but some controversies still remain regarding the relationship between alkali-rich porphyry diagenesis and goldpolymetallic mineralization.In this study,the major and trace element of apatite from the Beiya ore-bearing and ore-barren alkali-rich porphyries were analyzed,and their compositional differences would throw light on the diagenetic and mineralized information recorded in apatite.The results show that all apatites from the ore-bearing and barren monzogranite porphyries are rich in F（most of them2%）and lack of Cl（most of them0.02%）,and F versus Cl display a relatively negative correlation.The apatites from ore-bearing porphyries have a relatively higherδEu and obviously lowerδCe,indicating that the oxygen fugacity of ore-bearing porphyries is higher than barren porphyries.The high oxygen fugacity is favorable of mineralization because it can refrains the formation of Fe-bearing sulfides,store the metal elements and release more Cu,Au elements in the source.Meanwhile,the exsolution of Cl-bearing hydrothermal fluids caused the decrease of（Sm/Yb）Nin apatites from the Beiya porphyries.Compared to apatites from the Beiya orebearing porphyries,apatites from the Beiya barren porphyries have lower Ce/Pb and higher Th/U,and this reflects that the fluid activity of barren porphyries is weaker,leading to inconspicuous magmatic differentiation.It is also suggested that F/Cl in apatite from the ore-bearing porphyries could constrain the tectonic setting of porphyry deposits.For example,the F/Cl of apatites from the Beiya and Yulong ore-bearing porphyries are much higher than that from the Pulang,Chundu and Tongchanggou ore
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第7期2213-2224,共12页
Acta Petrologica Sinica
基金
国家重点基础研究发展规划(2015CB452605
2015CB452606)
国家自然科学基金项目(41602089)
中国地质调查局地质调查项目(12120114013501)
中国博士后基金(2015M581143)
高等学校学科创新引智计划(B07011)联合资助
关键词
磷灰石
成岩成矿作用
卤素
微量元素
滇西北衙金矿床
Apatite
Petrogenesis and mineralization
Halogens
Trace element
Beiya gold deposit in western Yunnan
