Chemical Composition and REE Pattern of Hydrothermally Deposited Albitite in Northern Guangdong Province
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摘要: 大沟谷含金钠长石岩带上为层状下为脉状产于震旦系乐昌峡群片岩中,主要由钠长石岩及碳酸盐岩组成。钠长石岩多为块状及条带状构造。钠长石岩和片岩化学成分不同,钠长石岩相对富集Al2 O3 、TiO2 、MnO、Na2O、P2O5,而贫Fe2O3 、FeO、MgO、CaO、K2 O。在主要氧化物组成的直角坐标图上,钠长石岩和片岩位于不同的区域及具不同的变化趋势。钠长石岩稀土元素含量较低,在 12.5 6× 10 -6～ 5 5.6 6× 10 -6之间,具较低的La/Yb(1.82～ 6.42 )、La/Sm(0.96～ 2.99)、Gd/Yb(0.99～ 2.71)比值,较大的δEu异常范围 (0.41～ 0.8),弱的δCe异常。钠长石岩地质产状特征及稀土元素特征表明其主要是热水沉积形成的。Abstract: Dagougu gola-bearing albitite belt,composed of albitite and carbonate rock,occurred as stratiform in the upper part and filled veins in the lower part in the Lechangxia Group Schist,Sinian Period．The albitite usually with banded and massive structure is composed primary of albite(80％±),quartz(1％～15％±),carbonate rock(1％--5％±),rutile(1％±),apatite(1％±)and pyrite with minor tourmnaline and magnetite；the carbonate rock。occurred in the same occurrence as those of albitite,consists predominantly of dolomite(ankerite)(> 75％),calcite(>15％),albite(5％±)with the same minor minerals as those of albitite． Main element compositions of the albitite differ from that of the Lechangxia Group Schist,the former is rich in A12O3。TiO2,Mno,Na2O。P2O5 and poor in Fe2O3,Feo,Mgo,Cao,K2O．The albitite and adjacent I．Lechangxia Group Schist lie in different domains in the major oxides variation diagram including TiO2-A12O3, AL2O3一SiO2,Mgo-Sio,TiO2-SiO2,Feo-Fe2O3,Mgo-Cao and reveal different variation tendency． The albitite has lower REE content,raring from l2．56×10-6to 55．66*10-6with lower La/Yb：1．82～6．42,La/Sm：0．96～2．99,Gd/Yb：O．99-2．71 ratios,negative Eu anomalies and weakly Ce anomalies．Chondrite-normalized patterns of REE in albitite differ from those of the Lechangxia Group Schist． Ccmbined field and geochemical data indicate that the Dagougu gold-bearing stratiform albitite do not represent the normal clastic sedimeents altered by sodium rich fluid．but owe its origin to hydrothermal sedimentation at or below the sediment-wlater interface in alkaline environment．
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Key words:
- albitite /
- REE /
- hydrothermal sedimentation Northern /
- Guangdong
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