西藏玉龙斑岩铜矿床成矿斑岩起源及成矿意义

Origin and metallogenic significance of the porphyry intrusions in the Yulong porphyry Cu deposit, Xizang

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DOI 10.20086/j.cnki.yskw.2024.0612
刊名
Acta Petrologica et Mineralogica
年,卷(期) 2024, 43(6)
作者
作者单位

1. 中国地质科学院 地质研究所, 北京 100037;
2. 北京大学 地球与空间科学学院, 北京 100871;
3. 中国消防救援 学院, 北京 102202;
4. 北京科技大学 土木与资源工程学院, 北京 100083;
5. 西藏玉龙铜业股份有限公司, 西藏 昌都 854000

摘要
位于青藏高原东缘的玉龙超大型斑岩铜-钼矿床,是碰撞型斑岩铜矿的典型代表。根据现有研究发现,玉龙矿床的成矿斑岩和含矿斑岩的成矿潜力不同。为深入探讨该矿床的岩浆起源,并揭示控制其成矿潜力的内在因素,本文对玉龙矿区含矿的二长花岗斑岩和成矿的花岗斑岩进行了锆石U-Pb年代学、全岩主微量和Sr-Nd同位素对比研究。结果表明,花岗斑岩具有与二长花岗斑岩相近的结晶年龄(42~41 Ma),同时也具有相似的Sr-Nd同位素组成,其(87Sr/86Sr)i分别为0.706 0~0.707 6和0.706 2~0.706 7、εNd(t)分别为-2.9~-2.1和-4.6~-1.9,表明两者具有相同的岩浆起源。两期斑岩具有高K2O含量(平均值大于4%),较低的MgO、Mg#、Cr含量,显著的Nb、Ta负异常,较低的Nb/U和Ce/Pb值,重稀土元素相对轻稀土元素亏损,高Sr/Y值的地球化学特征,表明母岩浆起源于新生下地壳的部分熔融。锆石微量元素数据显示,两期斑岩均具有较高的Eu/Eu*(>0.44)、10 000×(Eu/Eu*)/Y(>3.6)、(Ce/Nd)/Y(>0.01)及较低的Dy/Yb值(<0.31,平均0.22),暗示两者均具有很高且相近的岩浆水含量; 二长花岗斑岩ΔFMQ为0.29~2.29(平均为1.44),花岗斑岩ΔFMQ为1.07~2.74(平均为1.80),两者均具有较高的岩浆氧逸度,但花岗斑岩氧逸度具有更大的变化范围,且较二长花岗岩的更高,暗示氧逸度的差异导致了两者的成矿性差异。
Abstract
The Yulong giant porphyry Cu deposit is located in the eastern margin of the Tibet Plateau. It is a typical representative of collisional porphyry copper deposits. Recent studies indicate disparities in the mineralization potential between the ore-forming and ore-bearing porphyries of the Yulong deposit. Here we present whole-rock main/trace elements, whole-rock Sr-Nd, zircon U-Pb, and zircon trace elements data for ore-bearing monzogranite porphyry and ore-forming granite porphyry of the Yulong deposit to delve into the magmagenesis of this deposit and the intrinsic factors influencing its mineralization potential. Zircon U-Pb dating shows that the Yulong porphyry were emplaced at ca. 42~41 Ma. Monzogranite porphyry and granite porphyry have similar Sr-Nd ratio, including high (87Sr/86Sr)i (0.706 0~0.707 6 and 0.706 2~0.706 7) with low εNd(t) (-2.9~-2.0 and -4.6~-1.9). High K2O (the average>4%), low MgO, Mg# and Cr, significant negative Nb and Tb anomalies, low Nb/U and Ce/Pb ratios were derived from partial melting of a thickened lower crust. Combine with adakitic signatures of monzogranite, including high SiO2, Al2O3 and Sr contents, low Y and Yb contents with high Sr/Y and La/Yb ratios, we propose that the Yulong metallogenic mother magma originated from the partial melting of the Cenozoic lower crust. Zircon trace-element analysis shows that the two porphyries of Yulong have high Eu/Eu*(>0.44), 10 000×(Eu/Eu*)/Y(>3.6), (Ce/Nd)/Y(>0.01) and lower Dy/Yb (<0.31, average 0.22), suggesting that both porphyries have high and similar magma water content. Moreover, trace elements in zircons shows that monzogranite porphyry ΔFMQ= 0.29~2.29 (average 1.44), and granite porphyry ΔFMQ=1.07~2.74(average 1.80). They both have high magmatic oxygen fugacity, but the granite porphyry has a larger range of variation. In addition, the oxygen fugacity is higher than that of monzogranite, suggesting that different oxygen fugacity may affect the differences in mineralization.
关键词
岩石地球化学;Sr-Nd同位素;锆石U-Pb定年;锆石微量元素;斑岩铜矿;西藏玉龙
KeyWord
geochemistry; Sr-Nd isotopes; zircon U-Pb dating; zircon trace elements; porphyry copper deposit; Yulong, Xizang
基金项目
页码 1578-1600
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孙茂妤,代作文,刘申态,李秋耘,周怿惟,杨志明*,侯增谦. 西藏玉龙斑岩铜矿床成矿斑岩起源及成矿意义 [J]. 岩石矿物学杂志. 2024; 43; (6). 1578 - 1600.

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