Magmatic fertility of porphyry Ag-Pb-Zn deposits revealed by zircon and apatite chemistry: An example of the Lengshuikeng Ag-Pb-Zn deposit in South China

IF 3.4 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Journal of Geochemical Exploration Pub Date : 2025-03-20 DOI:10.1016/j.gexplo.2025.107757

Xinlu Hu , Yongpeng Ouyang , Runling Zeng , Jinwei Li , Libo Li , Yi Shang

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Abstract

Porphyry Ag-Pb-Zn deposits are globally rare, with limited understanding of their magma origins, compositions, and physical-chemical conditions. To address this, we conducted a comprehensive investigation of the chemical and SrNd isotopic composition of apatites, along with the UPb dating, trace element analysis, and LuHf isotopic analysis of zircons from the igneous rocks at the giant Lengshuikeng Ag-Pb-Zn deposit in South China. The igneous rocks at Lengshuikeng are primarily composed of granite porphyry, K-feldspar granite porphyry, and volcanic rocks of the Daguding and Ehuling Formations. LA-ICP-MS zircon UPb dating yielded ages 159.7 ± 2.0 Ma for the rhyolitic tuff of the Ehuling Formation, 159.0 ± 2.3 Ma for the granite porphyry, and 152.5 ± 1.9 Ma for the K-feldspar granite porphyry. Combined with previously published age data, we propose that the Ehuling Formation experienced at least two eruption stages: the first at ca. 160 Ma (S1), and the second at 147–138 Ma (S2). The K-feldspar granite porphyry intruded in two stages, dated at 152.5 Ma (S1) and 138–136.6 Ma (S2). The evolutionary sequence of igneous rocks is inferred as: Daguding Formation → Ehuling Formation (S1) → granite porphyry → K-feldspar granite porphyry (S1) → Ehuling Formation (S2) → K-feldspar granite porphyry (S2).

Zircons from these rocks show ε_Hf(t) values of −13 to −8.5. The (⁸⁷Sr/⁸⁶Sr)_i ratios and ε_Nd(t) values of apatite vary from 0.7075 to 0.7171 and from −12.7 to −4.5, respectively. Similar Sr-Nd-Hf isotopic compositions indicate a common source for these igneous rocks, all derived from partial melting of Paleo- to Mesoproterozoic continental crust. Comparable zircon Ce⁴⁺/Ce³⁺ and Ce/Ce^⁎ ratios and apatite Mn-Ce-Eu-Ga contents indicate similar oxidation states and water contents in the parental magmas. Compared to regional porphyry Cu deposits, the parental magma of the Lengshuikeng Ag-Pb-Zn deposit has lower oxygen fugacity and S concentration. Apatites from the ore-forming granite porphyry have significantly higher concentrations of Cu, Zn and Cl than those from other igneous rocks. Our study suggests that the metal and Cl⁻ contents within parental magma, rather than the oxidation state and water content, are key factors controlling porphyry Ag-Pb-Zn mineralization. Apatite Cu, Zn and Cl contents can serve as valuable indicators of magma fertility in porphyry Ag-Pb-Zn deposits.

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由锆石和磷灰石化学揭示的斑岩型银铅锌矿床岩浆富性——以华南冷水坑银铅锌矿床为例

斑岩型银铅锌矿床是全球罕见的，对其岩浆起源、组成和物理化学条件的了解有限。为了解决这一问题，我们对中国南方冷水坑银铅锌矿大型火成岩中磷灰石的化学组成和SrNd同位素组成进行了综合研究，并对锆石进行了UPb定年、微量元素分析和LuHf同位素分析。冷水坑火成岩主要由花岗斑岩、钾长石花岗斑岩和大定组、二虎岭组火山岩组成。LA-ICP-MS锆石UPb定年结果显示，二虎岭组流纹凝灰岩年龄为159.7±2.0 Ma，花岗岩斑岩年龄为159.0±2.3 Ma，钾长石花岗岩斑岩年龄为152.5±1.9 Ma。结合前人发表的年龄资料，我们认为鄂户岭组至少经历了两次喷发阶段：第一次喷发约为160 Ma (S1)，第二次喷发为147 ~ 138 Ma （S2）。钾长石花岗斑岩侵入时间为152.5 Ma （S1）和138 ~ 136.6 Ma （S2）两期。火成岩演化顺序为：大定组→乙虎岭组（S1）→花岗岩斑岩→钾长石花岗岩斑岩（S1）→乙虎岭组（S2）→钾长石花岗岩斑岩（S2）。锆石的εHf(t)值为- 13 ~ - 8.5。磷灰石的（87Sr/86Sr）i比值为0.7075 ~ 0.7171,εNd(t)值为- 12.7 ~ - 4.5。相似的Sr-Nd-Hf同位素组成表明这些火成岩有共同的来源，均来自古-中元古代大陆地壳的部分熔融。锆石Ce4+/Ce3+和Ce/Ce的比值以及磷灰石Mn-Ce-Eu-Ga的含量表明母岩浆的氧化态和含水量相似。与区域斑岩型铜矿床相比，冷水坑银铅锌矿母岩浆具有较低的氧逸度和S浓度。成矿花岗斑岩磷灰石中Cu、Zn和Cl的含量明显高于其他火成岩磷灰石。研究表明，控制斑岩银铅锌成矿的关键因素不是氧化态和含水量，而是母岩浆中的金属和Cl−含量。磷灰石Cu、Zn、Cl含量可作为斑岩型银铅锌矿床岩浆富力的重要指标。

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来源期刊

Journal of Geochemical Exploration 地学-地球化学与地球物理

CiteScore

7.40

自引率

7.70%

发文量

148

审稿时长

8.1 months

期刊介绍： Journal of Geochemical Exploration is mostly dedicated to publication of original studies in exploration and environmental geochemistry and related topics. Contributions considered of prevalent interest for the journal include researches based on the application of innovative methods to: define the genesis and the evolution of mineral deposits including transfer of elements in large-scale mineralized areas. analyze complex systems at the boundaries between bio-geochemistry, metal transport and mineral accumulation. evaluate effects of historical mining activities on the surface environment. trace pollutant sources and define their fate and transport models in the near-surface and surface environments involving solid, fluid and aerial matrices. assess and quantify natural and technogenic radioactivity in the environment. determine geochemical anomalies and set baseline reference values using compositional data analysis, multivariate statistics and geo-spatial analysis. assess the impacts of anthropogenic contamination on ecosystems and human health at local and regional scale to prioritize and classify risks through deterministic and stochastic approaches. Papers dedicated to the presentation of newly developed methods in analytical geochemistry to be applied in the field or in laboratory are also within the topics of interest for the journal.