摘要
南秧田钨矿床位于滇东南老君山W-Sn矿集区,地处扬子地块和印支地块的结合部位,地质背景复杂并遭受了多期岩浆活动和区域变质事件,其成矿时代和成因一直存在争议。本文对矽卡岩型和长石-石英脉型白钨矿开展了年代学、原位微量元素、Sr同位素研究,分析了两类白钨矿年龄、成因以及物质来源的差异。结果表明,长石-石英脉内与白钨矿共生辉钼矿的Re-Os同位素等时线年龄为151.0±1.3Ma,明显晚于矽卡岩矿体年龄,属于后期成矿事件。矽卡岩型白钨矿的轻稀土富集、重稀土强烈亏损,Eu呈明显负异常(δEu=0.46),∑REE平均含量为65.60μg/g,Mo平均含量为240.16μg/g,Sr平均含量为883.43μg/g;长石-石英脉型白钨矿稀土呈Eu正异常(δEu=2.8)的平坦型,∑REE平均含量为194.40μg/g,Mo平均含量为16.01μg/g,Sr平均含量为129.26μg/g。以上两者微量、稀土元素含量的差别显示它们具有性质明显不同的流体来源,Eu异常指示矽卡岩型白钨矿形成于氧逸度较高的环境,长石-石英脉型白钨矿形成于还原性环境。矽卡岩白钨矿87 Sr/86 Sr值相对较低,并且比较均一,介于0.71319~0.71491之间,表明成矿流体主要来自岩浆热液;长石-石英脉型白钨矿87 Sr/86 Sr值较高且变化范围大,介于0.71537~0.72803之间,平均0.72079,呈现出变质流体特征。两种不同类型白钨矿Sr同位素都具有二元混合的特征,显示长石-石英脉型白钨矿对矽卡岩型白钨矿有叠加改造作用,成矿流体与围岩的强烈交代作用是白钨矿形成的关键。
BACKGROUND:The Nanyangtian scheelite deposit is an important skarn scheelite deposit in Yunnan Province,which is located in Laojunshan W-Sn deposit area,Southeast Yunnan.Due to its complex geological background and multi-stage metallogenic characteristics,its mineralization age and genesis remain controversial.OBJECTIVES:To explore the metallogenic age,genesis and material origins of two types of scheelite deposits in order to explore formation patterns.METHODS:Molybdenum Re-Os isotope dating was used to constrain the age,whereas in situ trace element and in situ Sr isotopes of scheelite were used to determine the composition of trace elements and Sr isotopes in scheelite.RESULTS:The Re-Os isochron age of molybdenite associated with scheelite in the feldspar-quartz mineral vein of Nanyantian was 151.0±1.3Ma,younger than the age of skarn mineralization,indicating a later mineralization event.The skarn-type scheelite was enriched in light rare earth elements with negative Eu anomaly(δEu=0.46).The average content of∑REE,Mo and Sr in skarn scheelite were 65.60,240.16 and 883.43μg/g,respectively.Feldspar-quartz vein-type scheelite showed a flat rare earth pattern with positive Eu anomaly(δEu=2.8)and average content of∑REE,Mo and Sr were 194.40,16.01 and 129.26μg/g,respectively.respectively.The skarn scheelite had a relatively low and uniform 87 Sr/86 Sr value of 0.71319 to 0.71491,indicating that the ore-forming fluids were mainly magmatic-hydrothermal in origin,whereas feldspar-quartz vein type scheelite had a wide 87 Sr/86 Sr range of 0.71537 to 0.72803,with an average of 0.72079,characteristic of metamorphic fluids.CONCLUSIONS:The differences in trace and rare earth element contents between two types of mineralization indicate that they have different fluid sources.The negative Eu anomaly of the skarn-type scheelite indicates a high oxygen fugacity environment,whereas the feldspar-quartz vein-type scheelite is formed in a reductive environment in terms of positive Eu anomaly.Sr isotopes of two different types of scheelite display a feature of binary mixing,indicating that feldspar-quartz vein-type scheelite has a superimposed transformation effect on skarn-type scheelite,and the strong metasomatism of ore-forming fluids and surrounding rocks is the key to the formation of scheelite.
作者
王忠强
李超
张定才
江小均
周利敏
严清高
WANG Zhong-qiang;LI Chao;ZHANG Ding-cai;JIANG Xiao-jun;ZHOU Li-min;YAN Qing-gao(Faculty of Land Resource Engineering,Kunming University of Science and Technology,Kunming 650093,China;National Research Center for Geoanalysis,Beijing 100037,China;Key Laboratory of Re-Os Isotope Geochemistry,Chinese Academy of Geological Sciences,Beijing 100037,China;Wenshan Malipo Zijin Tungsten Group Co.,LTD.Wenshan 663600,China)
出处
《岩矿测试》
CAS
CSCD
北大核心
2020年第2期285-299,共15页
Rock and Mineral Analysis
基金
国家自然科学基金项目(41673060,41873065)
关键词
白钨矿
原位Sr同位素
成矿时代
成矿流体来源
南秧田
scheelite
in situ Sr isotope
mineralization epoch
source of ore-forming fluid
Nanyangtian
