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Multi-stage scheelite geochemistry constrains the genesis of tungsten mineralization at the Ligongling breccia pipe in the Yangchuling porphyry system, South China
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DOI：10.1016/j.gexplo.2026.108091.png)
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Abstract
En 中文
The Ligongling ore-bearing breccia pipe, located in the Yangchuling district of South China, exhibits complex breccia textures with large clast-size variations and intense matrix mixing, indicating a magmatic-hydrothermal origin. Despite these observations, the genetic relationships and precipitation mechanisms of scheelite in this system remain poorly constrained. Scheelite is the predominant ore mineral, occurring in three primary ore types: greisen-type, breccia-type, and vein-type. Greisen-type scheelite (Sch A) occurs in porphyritic granodiorite and forms by primary magmatic fluids. The breccia-type ore contains two scheelite subtypes: Sch B1 and Sch B2. Sch B1 shows REE patterns similar to those of granitoids and exhibits pronounced positive Eu anomalies, suggesting intense water-rock interaction during brecciation. Decompression is interpreted as the main mechanism triggering scheelite precipitation. In contrast, Sch B2 shares REE signatures with Sch A. Vein-type mineralization includes four assemblages: quartz-K-feldspar-scheelite veins (Sch C1), quartz-sericite-scheelite-molybdenite veins (Sch C2), hydrothermal metasomatic veins (Sch C3), and monomineralic scheelite veins (Sch C4). The consistent mineral paragenesis, well-defined formation sequence, similar oscillatory zoning patterns, and comparable geochemical signatures collectively indicate that multiple pulses of hydrothermal fluids precipitated Sch A, Sch B2, and Sch C1. The trace-element composition of scheelite reflects substitution mechanisms that differ among ore types. Most scheelite types exhibit grayish-white alteration rims (Sch C3) observed under scanning electron microscope cathodoluminescence (SEM-CL). These rims record progressive depletion of Nb, Ta, Mo, Y, and TREE, accompanied by localized Sr enrichment. Monomineralic scheelite veins (Sch C4) are characterized by undetectable Na, notable Sr enrichment, minimal concentrations of Nb, Ta, Mo, TREE, and Y, as well as pronounced positive Eu anomalies and patterns depleted in MREE, suggesting the influence of meteoric water. All scheelite samples display 87Sr/86Sri ratios ranging from 0.71162 to 0.71628, consistent with contributions from both parental magma and Neoproterozoic metasedimentary rocks. Ligongling scheelite mineralization resulted from multistage processes, including episodic magmatic fluid pulses, water-rock interaction, decompression-induced precipitation, late-stage dissolution-reprecipitation, and meteoric-water mixing.
Keywords:
Ligongling
Breccia pipe
Scheelite geochemistry
In situ Sr isotopes
Precipitation mechanisms
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