华北陆块北缘哈毕力格铀矿床S、Pb同位素组成及对成矿作用的指示

doi:10.19657/j.geoscience.1000-8527.2020.03.15

摘要/Abstract

摘要：

哈毕力格铀矿床位于华北陆块北缘中段,主要受乌兰哈达—猴儿山背斜和区内断裂控制。铀矿化主要产于新太古界乌拉山群第二岩段石英岩中,一直被认为是变质成因铀矿床。在分析该矿床成矿地质背景和矿化特征的基础上,系统研究了矿石与围岩中黄铁矿的硫、铅同位素特征。数据表明,硫同位素组成变化于-4.7‰~12.9‰之间,暗示成矿流体主要来自岩浆热液,同时遭受了地层物质的混染。铅同位素组成(²⁰⁸Pb/²⁰⁴Pb=36.147~42.968,²⁰⁷Pb/²⁰⁴Pb=15.919~34.268, ²⁰⁶Pb/²⁰⁴Pb=19.488~168.032)远高于单阶段演化模式组成,不同样品的²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb线性关系良好,为典型的二阶段铅同位素演化体系,表明变质地层为成矿作用提供了铀源。通过放射性²⁰⁷Pb/²⁰⁶Pb计算,结合区域岩浆演化,认为古元古代(~1 805 Ma)区域变质作用促使乌拉山群铀发生初步富集,晚古生代(374 Ma)花岗闪长质岩浆分异出大量流体活化萃取变质地层中的铀,在有利构造空间富集成矿。

关键词: 硫同位素, 铅同位素, 铀成矿作用, 哈毕力格铀矿床, 华北陆块北缘

Abstract:

Habilig uranium deposit is located in the middle part of northern margin of North China Block, which is mainly controlled by the Ulanhada-Houershan anticline and regional faults. Uranium mineralization occurs mainly in quartzite of the second member of the Wulashan Group in the Neoarchaean, and has long been consi-dered to be a metamorphic uranium deposit. Based on the study of the geological setting and mineralization cha-racteristics of the deposit, the sulfur and lead isotope compositions of pyrite in ores and surrounding rocks are systematically analyzed. The analysis results show that the sulfur isotope value varies from -4.7‰ to 12.9‰, suggesting that source of ore-forming fluids are mainly from magmatic hydrothermal fluids and are contaminated by stratigraphic materials as well. Lead isotope composition (²⁰⁸Pb/²⁰⁴Pb=36.147-42.968, ²⁰⁷Pb/²⁰⁴Pb=15.919- 34.268, ²⁰⁶Pb/²⁰⁴Pb=19.488-168.032) is much higher than that of single-stage evolution model. ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb in different samples have a good linear relationship and represent a typical two-stage lead isotope evolution system, indicating that metamorphic strata provide uranium source for ore-forming fluid. Based on ²⁰⁷Pb/²⁰⁶Pb equation and history of regional magmatic evolution, it is considered that uranium was preliminarily enriched in the Wulashan Group because of the regional metamorphism in Paleoproterozoic (~1 805 Ma). In Late Paleozoic (374 Ma), a large amount of magmatic fluids generated from granodiorite magma, which have activated and extracted uranium from metamorphic strata and contributed to mineralization in favorable structure.

Key words: sulfur isotope, lead isotope, uranium mineralization, Habilig uranium deposit, northern margin of North China Block

中图分类号:

黄志新, 李子颖, 蔡煜琦, 朱斌, 任全. 华北陆块北缘哈毕力格铀矿床S、Pb同位素组成及对成矿作用的指示[J]. 现代地质, 2020, 34(03): 588-597.

HUANG Zhixin, LI Ziying, CAI Yuqi, ZHU Bin, REN Quan. Sulfur and Lead Isotopic Compositions of Habilig Uranium Deposit in Northern Margin of North China Block: Implication for Uranium Mineralization[J]. Geoscience, 2020, 34(03): 588-597.

图/表 8

图1 华北陆块北缘中段哈毕力格地区地质图 a.哈毕力格地区区域地质图;b.大地构造位置图;c.铀矿床地质图。

Fig.1 Geological maps of Habilig area in the middle part of northern margin of North China Block

图2 哈毕力格铀矿床代表性样品的岩石学与矿物学特征 a.灰黑色铀矿化石英岩;b.无色透明非矿化石英岩;c.铀矿化石英岩镜下照片;d.石英岩和钾长变粒岩接触界线;e.沿裂隙面发育的黄铁矿;f.细脉状黄铁矿;g.发育在黄铁矿裂隙内的晶质铀矿;h.发育在石英颗粒内部的晶质铀矿。

Fig.2 Representative petrological and mineralogical characteristics of Habilig uranium deposit

表1 哈毕力格铀矿床黄铁矿硫同位素组成和岩石铀钍含量

Table 1 Sulfur isotope composition of pyrites and U/Th content of rocks from Habilig uranium deposit

样号	岩性	矿物	δ³⁴S_V-CDT/ ‰	w(U)/ 10^-6	w(Th)/ 10^-6
HB13-50	石英岩	黄铁矿	6.6	9.5	2.29
HB13-55	石英岩	黄铁矿	9.0	1 456.0	5.46
HB13-58	变粒岩	黄铁矿	-4.7	437.0	426.00
HB13-65	角闪二云片岩	黄铁矿	12.9	8.8	10.70
HB13-71	石英岩	黄铁矿	3.4	159.0	4.18

表2 哈毕力格铀矿床黄铁矿Pb同位素组成

Table 2 Lead isotope composition of pyrite from Habilig uranium deposit

样号	岩性	矿物	²⁰⁸Pb/²⁰⁴Pb	标准误差	²⁰⁷Pb/²⁰⁴Pb	标准误差	²⁰⁶Pb/²⁰⁴Pb	标准误差
HB13-50	石英岩	黄铁矿	37.975	0.006	34.268	0.005	168.032	0.023
HB13-55	石英岩	黄铁矿	36.402	0.005	15.982	0.002	19.488	0.002
HB13-58	变粒岩	黄铁矿	42.968	0.005	15.919	0.002	20.946	0.002
HB13-65	角闪二云片岩	黄铁矿	41.312	0.006	16.330	0.002	22.230	0.003
HB13-71	石英岩	黄铁矿	36.147	0.007	18.453	0.003	35.922	0.006

图3 哈毕力格铀矿化区黄铁矿δ34S同位素组成(a)与地质储库中的δ34S组成[32](b)比较

Fig.3 Diagram of δ34S composition in pyrite (a) and comparison of Habilig uranium deposit and geological reservoirs (b)

图4 哈毕力格铀矿床黄铁矿的206Pb/204Pb与207Pb/204Pb同位素比值图解

Fig.4 Diagram of 206Pb/204Pb vs 207Pb/204Pb in pyrite from Habilig uranium deposit

表3 哈毕力格铀矿床黄铁矿异常铅等时线参数及原岩年龄计算结果

Table 3 Isochron parameters of radioactive lead in pyrite and protolith age of Habilig uranium deposit

样品类型	样品数量	相关系数	截距	斜率	成矿年龄t₂ / Ma	物源年龄t₁ / Ma
黄铁矿	5	0.999	13.627	0.123 1	374	1 805

图5 华北陆块北缘中段哈毕力格铀矿床成矿模式 a.新太古代(2 500 Ma)乌拉山群原始沉积地层形成;b.古元古代(2 500~1 805 Ma)乌拉山群发生区域变质作用形成富铀变质岩地层和少量铀矿化;c.古生代泥盆纪(374 Ma)岩浆流体作用下萃取地层铀在有利地段卸载形成铀矿化。

Fig.5 Metallogenic model of Habilig uranium deposit in the middle part of the northern margin of North China Block

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