西藏多龙矿集区地堡Cu（Au）矿床含矿斑岩锆石U-Pb测年、Hf同位素组成及其地质意义

摘要

Objectives:The Dibao Cu(Au)deposit,located in the southern Qiangtang Terrane,northern Bangong Co—Nujiang suture zone,is a newly discovered porphyry—epithermal Cu(Au)deposit,with a good exploring prospect in Duolong ore concentration area. Methods:This articale did the fist study to the ore bearing porphyry via LA-ICP-MS zircon U-Pb dating,Hf isotope and trace element composition analysis. Results:According to the 23 points zircon dating data,it obtained zircon 206 Pb /238 U weighted average age of 122.0 ±2.5Ma (MSWD =0.34),consistented with the mineralization magmatism time limit in Duolong ore concentration area, is one of the most important part of Duolong ore concentration area. Trace element characteristics of zircons indicated that they are the same period of magmatic zircons. Their crystallization temperature is from 663℃to 850℃,an average of 765 ℃,via Ti thermometer of zircon,which suggested that their magma source region maybe have experienced partial molten under a water-saturated condition.Conclusion:Hf isotope analysis data show that ore-bearing porphyry zircon Hf isotope 176 Hf /177 Hf ratios are relatively high,0. 282726 ~0.283054,εHf (t)of 1.1 to 12.6,are positive,their material source have some mantle source composition,may be a newborn lower crust from crust—mantle mixed source.%西藏多龙矿集区地堡铜（金）矿位于班公湖—怒江缝合带北侧，羌塘地块南缘，是多龙矿集区中具有较好找矿前景的斑岩—浅成低温热液矿床。本文首次对地堡含矿斑岩进行LA-ICP-MS 锆石 U-Pb测年、微量元素和Hf同位素分析。含矿斑岩23个锆石点测试，获得锆石206Pb／238U加权平均值年龄为122.0±2.5Ma（MSWD＝0.34），与多龙矿集区成矿岩浆活动时限一致，是多龙矿集区的重要组成部分。锆石微量元素特征揭示地堡含矿斑岩中锆石为岩浆锆石，锆石Ti温度计计算出其结晶温度为663～850℃，平均为765℃，其岩浆源区可能经历了水饱和条件下的部分熔融作用。Hf同位素分析结果表明，地堡含矿斑岩锆石n（176 Hf）／n（177 Hf）值相对较高，为0.282726～0.283054，εHf（t）为1.1～12.6，均为正值，其物质来源有幔源组分的加入，可能为壳幔混源的新生下地壳。