摘要
西藏更乃矽卡岩矿床位于班公湖-怒江成矿带南侧,具有良好的铁与铟等多金属成矿潜力,尤其在该矿床发现了自然铟与羟铟石,为国内首次.更乃矿床为晚白垩世似斑状二长花岗岩侵位于下白垩统郎山组灰岩时发生双交代作用的产物,晚白垩世似斑状二长花岗岩为更乃矽卡岩型铁多金属矿床的矿化提供了岩浆热液来源.似斑状二长花岗岩K2O/Na2O为1.38～1.73,显示富钾特征.铝过饱和指数（A/CNK）变化于1.02～1.05之间,为过铝质系列,具S型花岗岩特征.里特曼指数（σ）为2.15～2.31,属钙碱性岩石系列.富集大离子亲石元素Rb、Th,贫Sr、Ba、P、Ti等元素.∑REE=108.03×10-6～258.74×10-6,稀土元素总量较高,（La/Yb）N为15.71～26.00,轻重稀土元素明显分异,Eu呈中等负异常（δEu=0.17～0.24）.似斑状二长花岗岩中锆石多呈柱状,Th/U的范围为0.50～2.17,（La/Yb）N为0.00～0.29,轻重稀土元素明显分异,δCe=4.32～1293.43,δEu=0.06～0.13,具有比较高的Ce正异常和中等的Eu负异常,显示岩浆锆石的特征.更乃岩体形成于班公湖-怒江洋向南俯冲结束之后的同碰撞阶段.研究表明,铟与锡之间以及铟与锌之间不存在相关关系,铟与铁之间具有很好的正相关关系,铟在铁矿石中含量为5.61×10-6～125.00× 10-6,平均值为49.01×10-6,铟呈独立矿物形式存在.铁、铟、铋金属的矿化是在同一期热液活动中形成,为岩浆来源.锆石的LA-ICP-MS定年结果表明,岩体的形成年龄为78.7±1.7 Ma,为燕山晚期岩浆活动的产物.
Gengnai skarn deposit is located in southern middle Bangong Co-Nujiang River metallogenic belt,Tibet.It has good geological conditions for Fe and In mineralization.What＇s more,it is the first time to find natural indium and jalindite in this deposit in China.The deposit formed in the dimetasomatism when the porphyritic monzonitic granite invaded the Langshan limestone,and the porphyritic monzonitic granite provided magmatic hydrothermal sources for the mineralization.The K2O/Na2O values of porphyritic monzonitic granite are in the range of 1.38～1.73,showing the characteristics of potassium-rich.The A/CNK values of porphyritic monzonitic granite are in the range of 1.02～ 1.05.Gengnai rock mass belongs to peraluminous granite,with S-type granite characteristics.Rittmann index （σ） values are in the range of 2.15～2.31,and the porphyritic monzonitic granite is a calc-alkaline rock series.In Gengnai porphyritic monzonitic granite,large ion lithophile elements such as Rb,Th are enriched,and elements such as Sr,Ba,P,Ti are poor.It has higher total REE （ΣREE=108.03 × 10-6～258.74 × 10-6）,and light and heavy REE has obviously fractionation with （La/Yb）N is 15.707 to 26.002.δEu=0.171～0.238,with medium negative Eu anomalies.Zircons in the porphyritic monzonitic granite are magmatic zircons.They are mostly columnar The Th/U values of zircons are in the range of 0.498～1.866,while the（La/Yb）N values are 0.00 ～ 0.29,light and heavy REE has obviously fractionation.The zircons have high positive Ce anomaly （δCe=4.32～1293.43） and medium negative Eu anomaly （δEu=0.06～0.13）.The Gengnai rock mass occurred in the collision orogenic phase after the Bangong Co-Nujiang River ocean subducted to the South.Studies have shown that there is no correlation between indium and tin,also between indium and zinc,but it has positive correlation between indium and iron.Indium content values of the iron ore are in the range of 5.61 × 10-6 ～ 125.00 × 10-6,and the average is 49.01 × 10-6,indium exist in the form of independent mineral.The mineralization of iron,indium,bismuth are formed in the same period of hydrothermal activity,and they are all magmatic source.The zircon LA-ICP-MS dating results of the porphyritic monzonitic granite is 78.7 ± 1.7 Ma,suggesting the porphyritic monzonitic granite was a product of late Yanshanian magmatism.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2013年第11期1679-1693,共15页
Acta Geologica Sinica
基金
国家"973"项目(编号2011CB403103)
国际地学计划项目(编号IGCP/SIDA-600)
国家科技支撑课题(编号2006BAB01A05)
中国地质调查局青藏专项(编号1212010818097)共同资助成果
