The Fluid Evolution in the Skarn Stages of the Baoshan Skarn Cu-Polymetallic Deposit, South China

IF 2.2 4区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
Minerals Pub Date : 2024-09-05 DOI:10.3390/min14090907
Ping Zheng, Ke Chen, Jun-Ke Zhang, Zhong-Fa Liu, Yong-Shun Li, Ming-Peng He
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Abstract

Baoshan is a world-class skarn Cu-polymetallic deposit located at the junction of the Nanling and Qin-Hang metallogenic belts in China. While there has been extensive research on the mineralogy and geochemistry of skarn deposits, studies on the fluid characteristics and evolutionary history from the early to late skarn stages in such deposits are still limited. In this study, we analyzed garnet and pyroxene from the early skarn stage and scheelite from the late skarn stage of the Baoshan deposit. We distinguished two generations of garnet (Grt1 and Grt2), one generation of pyroxene, and three generations of scheelite (Sch I, Sch II, and Sch III) on the basis of mineral assemblages and microscopic characteristics. Grt1 appears coarse-grained, and Grt2 cuts through Grt1 as veinlets. In Grt1, the andradite end-member increases from the core to the rim, while the grossular portion decreases (Ad35–36Gr59–61Sp3–4 to Ad59–61Gr36–37Sp2–3), and in Grt2, the andradite end-member significantly increases (Ad41–73Gr25–55Sp2–3). Grt1 and Grt2 have similar trace element compositions, with enrichment in Zr and depletion in Nb and Hf, depletion in LREE, enrichment in HREE, and weak negative Eu anomalies. Pyroxene coexists with Grt1 and is similarly cut by Grt2, with its composition mainly being diopside (Di82–99Hd0.6–15Jo0–3.2). Sch I and Sch II appear as anhedral to subhedral grains, while Sch III is predominantly found in veinlets. In Sch I and Sch II, most REEs enter the scheelite lattice via the Na-REE coupled substitution mechanism, with a smaller portion substituting Ca vacancies. In Sch III, the substitution mechanism involving Ca site vacancies may dominate. During the early skarn stage, the oxygen fugacity of the fluid gradually decreased from Grt1 and pyroxene to Grt2. In the late skarn stage, fluid oxygen fugacity remains stable from Sch I and Sch II to Sch III in shallow parts but significantly decreases in deeper parts. The garnet and pyroxene from the Baoshan deposit align with typical skarn Cu deposit compositions, while scheelite in the late skarn stage shows Sch I, Sch II, and shallow Sch III as skarn-type and deep Sch III as vein-type scheelite. Early skarn stage fluids were weakly acidic. Sch I, Sch II, and Sch III originated from fluids related to the Baoshan granite porphyry, with Sch III also showing evidence of water–rock interaction. This study reconstructed the fluid evolution history from the early to late skarn stages at the Baoshan deposit, providing insights into the ore-forming processes of other skarn deposits.
华南宝山矽卡岩铜多金属矿床矽卡岩阶段的流体演化
宝山是一个世界级的矽卡岩铜多金属矿床,位于中国南岭成矿带和秦杭成矿带的交界处。虽然人们对矽卡岩矿床的矿物学和地球化学进行了大量研究,但对此类矿床从早期矽卡岩阶段到晚期矽卡岩阶段的流体特征和演化历史的研究仍然有限。在这项研究中,我们分析了宝山矿床早期矽卡岩阶段的石榴石和辉石,以及晚期矽卡岩阶段的白钨矿。根据矿物组合和显微特征,我们区分了两代石榴石(Grt1 和 Grt2)、一代辉石和三代白钨矿(Sch I、Sch II 和 Sch III)。Grt1 看起来颗粒较粗,而 Grt2 则以细脉形式穿过 Grt1。在 Grt1 中,从岩心到岩缘,安长石端粒增加,而毛玻璃部分减少(Ad35-36Gr59-61Sp3-4 至 Ad59-61Gr36-37Sp2-3),而在 Grt2 中,安长石端粒显著增加(Ad41-73Gr25-55Sp2-3)。Grt1和Grt2的微量元素组成相似,Zr富集,Nb和Hf贫化,LREE贫化,HREE富集,Eu呈弱负异常。辉石与 Grt1 共存,并同样被 Grt2 切割,其成分主要为透辉石(Di82-99Hd0.6-15Jo0-3.2)。SchⅠ和SchⅡ呈正方体至次正方体晶粒,而SchⅢ则主要呈细脉状。在 Sch I 和 Sch II 中,大部分 REEs 通过 Na-REE 耦合取代机制进入白钨矿晶格,小部分取代 Ca 空位。在 Sch III 中,涉及 Ca 位点空位的置换机制可能占主导地位。在早期矽卡岩阶段,流体的氧富集度从 Grt1 和辉石逐渐下降到 Grt2。在矽卡岩晚期,流体氧富集度在浅部从 Sch I 和 Sch II 到 Sch III 保持稳定,但在深部明显下降。宝山矿床的石榴石和辉石符合典型的矽卡岩铜矿床成分,而矽卡岩晚期的白钨矿则表现为矽卡岩型的SchⅠ、SchⅡ和浅SchⅢ,以及脉石型的深SchⅢ。早期矽卡岩阶段的流体呈弱酸性。SchⅠ、SchⅡ和SchⅢ源于与宝山花岗斑岩有关的流体,其中SchⅢ还显示出水岩相互作用的迹象。这项研究重建了宝山矽卡岩矿床从早期到晚期的流体演化史,为其他矽卡岩矿床的成矿过程提供了启示。
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来源期刊
Minerals
Minerals MINERALOGY-MINING & MINERAL PROCESSING
CiteScore
4.10
自引率
20.00%
发文量
1351
审稿时长
19.04 days
期刊介绍: Minerals (ISSN 2075-163X) is an international open access journal that covers the broad field of mineralogy, economic mineral resources, mineral exploration, innovative mining techniques and advances in mineral processing. It publishes reviews, regular research papers and short notes. Our aim is to encourage scientists to publish their experimental and theoretical results in as much detail as possible. There is no restriction on the length of the papers. The full experimental details must be provided so that the results can be reproduced.
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