南岭西段沙坪钨矿区花岗岩独居石U-Pb定年及地质意义

Monazite U-Pb Geochronology of Granites in the Shaping Tungsten Deposit,Western Nanling Metallogenic Belt and Its Geological Significance

沙坪白钨矿床位于南岭成矿带西段苗儿山岩体西北部,产于晚侵入次细粒二云母二长花岗岩岩株中,整个岩株全岩钨矿化。为精确厘定沙坪白钨矿床的成岩成矿时代,本文利用LA-ICP-MS对花岗岩中的独居石进行U-Pb定年,获得岩株成岩年龄为405.0±2.1 Ma,表明沙坪白钨矿床形成于加里东晚期。结合前人研究资料,本文认为苗儿山岩体西北部加里东期的钨多金属成矿作用发生在430~405 Ma间,区域上经历了较高程度分异作用的加里东期花岗岩浆促成了钨的富集,为沙坪钨矿区晚侵入次的细粒二云母二长花岗岩钨的成矿作用提供了物源。苗儿山岩体北部有望在寻找加里东期钨多金属矿床方面取得进一步突破。

The Shaping Tungsten deposit,situated in the northwestern part of the Miao’ershan granite batholith,Western Nanling Metallogenic Belt,occurs in the late granite intrusion stock of fine two-mica monzogranite.The ore-bearing granite stock is almost wholly W-mineralized.In this study,LA-ICP-MS monazite U-Pb isotopic dating was performed on the fine two-mica monzogranite samples to determine the ages of diagenesis and mineralization.The monazite U-Pb analysis yielded the206Pb/238U ages of 405.0±2.1Ma,suggesting that the Shaping W deposit was formed in Late Caledonian.Our new dating results,combined with previously published ages,indicate that the W-polymetallic mineralization ages in the northwestern part of the Miao’ershan granite batholith should be between around 430 Ma to 405 Ma.The Caledonian granite in this area has experienced significant magmatic differentiation and contributed to the W enrichment,which could be the metal source for the later fine two-mica monzogranite of the Shaping deposit.The northern of the Miao’ershan batholith has great prospecting potential for Caledonian W-polymetallic deposit.