兰坪盆地白秧坪Cu-Pb-Zn-Ag多金属矿集区元素共生分异机制及物质来源

Study on paragenesis-separation mechanism and source of ore-forming element in the Baiyangping Cu-Pb-Zn-Ag polylmetallic ore deposit,Lanping basin,southwestern China

兰坪白秧坪Cu-Ag多金属矿集区夹持于金沙江和澜沧江断裂之间,属兰坪-思茅中新生代坳陷带之兰坪盆地北部,可分东矿带和西矿带二部分。本文通过对白秧坪金属矿集区东西2个矿带的矿石矿物电子探针分析、成矿元素含量和组合分析及S同位素的讨论得出:(1)东西2个矿带矿石矿物组合类型及微量元素组合特征具明显不同,前者矿石矿物组分较为简单,西带较为复杂,不仅有Pb、Zn和Cu的独立矿物,还存在Co和Bi的矿物;(2)东矿带Ag、As、Cd、Pb、Sb和Zn的富集从南到北依次减弱,Bi的富集依次增强,Cu的富集趋势越往北越富集,亏损元素为Co、Cr、Ni和V;西矿带Ag、Pb、Zn的富集属吴底厂和李子坪矿段最富集,而Cu则在小丫口和白秧坪矿段最富集。亏损元素为Ba、Co、Cr、Ni和V,但各个矿段这些元素的亏损程度有所不同,有的矿段部分元素有稍富集趋势;(3)Co、Ni和Cr等微量元素西带高于东带,而Sr、Pb、Zn和Ba元素则东带高于西带,与各自的矿物组合类型一致,且元素的共生分异机制与构造分带存在一定的耦合关系;(4)兰坪盆地火山岩为白秧坪多金属矿集区提供了主要物源,Mo、Co和Ni等元素显示其成矿可能与隐伏基性-超基性岩浆有关的深部来源有关;S同位素特征表明东西矿带金属硫化物硫源均以幔源为主。

Baiyangping Cu-Ag polymetallic ore district is located in the northern part of the Lanping-Simao foreland fold belt between the Jinshajiang-Ailaoshan and Lancangjiang faults,and the deposit can be divided into eastern and western ore zones.Based on electron microprobe analysis of ore minerals,ore-forming element content and S isotope composition,we included that（1） The type of ore minerals combination and trace elements characteristics are significantly different in two ore zone,the feature in eastern part is simple,whereas in western part is complex（occurring Pb,Zn and Cu independent mineral,in addition,having Co and Bi minerals）;（2） In eastern ore zone,the enrichment of Ag,As,Cd,Pb,Sb and Zn is weakened,enrichment of Bi and Cu is enhanced from south to north,moreover,the depletion of Co,Cr,Ni and V are appear in this area.In western ore zone,the enrichment of Ag,Pb and Zn are strong in Wudichang and Liziping.Cu is enriched in Xiaoyakou and Baiyangping.Otherwise,Ba,Co,Cr,Ni and V are depleted in different ore zones;（3） Co,Ni and Cr contents are higher in western ore zone,on the contrary,Sr,Pb,Zn and Ba contents are higher in eastern ore zone.These characteristics are consistent with their mineral assemblages＇ rules.There existed a certain relationship between the paragenesis-separation mechanism and tectonic zonation;（4） The volcanic rocks in Lanping basin have provided the main ore-forming source.The characteristics of Mo,Co and Ni indicated that the mineralization may have a close connection with mafic-ultramafic magma.S isotope features implied that the source of sulfur is mainly mantle source.