云南老王寨金矿煌斑岩地球化学研究

GEOCHEMISTRY OF LAMPROPHYRES IN LAOWANGZHAI GOLD ORE DISTRICT,YUNNAN

老王寨金矿煌斑岩稀土元素含量较高，平均约为１６０×１０￣（－６），稀土配分模式表现为轻稀土富集、重稀土亏损，且具有铕的负异常。地幔标准化的过渡元素分配型式呈“Ｗ”型，同中国东部碱性玄武岩相似。此外，煌斑岩中Ｃｒ，Ｎｉ含量高，以上都表明煌斑岩为地幔成因，是地幔部分熔融的产物。原生岩浆在演化分异的早期有铬尖晶石、橄榄石、黑云母及斜长石的结晶。煌斑岩中Ｂａ，Ｔｈ，Ｋ，Ｓｒ及稀土元素较高，而Ｎｂ，Ｐ呈明显亏损，表明岩浆上升过程中受到一定程度的壳层物质混染。

Rare earth elements of lamprophyres in Laowangzhai gold deposit,Yunnan,have a com-paratively higher content,averaged to about 160 ×10￣(-6) Their chondrite- normalized distribution pattern shows they are rich in LREE and lack of HREE and of negative anomaly of europium.Mantle-normalized transitional element distribution pattern of lamprophyres in the area demon-strates“W”shape.The high contents of Ni,Cr,and the high M value of 59 of lamprophyres mean that its primary magma were derived from the upper mantle. With the crystal differentiation,the abundance of Ni and Cr in lamprophyres has a reductive tendency, Which infers that fractionation of chromium-bearing mineral,such as spinel,olivine,biotite,plagioclase took place in the evolu-tion process.Chondrite-normalized distribution pattern of lithophile elements of lamprophyres indi-cates they are abundant in barium,thorium,potassium,strontium,REE and deficit in niobium and phosphorous,This implies that lamprophyre magma as ascending to the upper part of the crust had been contaminated.A reference value of partial melting of the mantle for the formation of lampro-phyre magma reaches 3.18 percent.