Chemical changes during endoskarn and porphyry‐style alteration and Cu—Fe exoskarn mineralization in the Tonglushan system, eastern China

IF 1.1 4区 地球科学 Q3 GEOLOGY
Resource Geology Pub Date : 2023-01-01 DOI:10.1111/rge.12319
Fei Zhang, Ben J. Williamson, Clemens V. Ullmann, Hannah S. R. Hughes
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引用次数: 0

Abstract

Element mobility and chemical mass transfer are evaluated in the formation of Cu—Fe exoskarn deposits and endoskarn and minor porphyry‐style alteration in the Tonglushan quartz monzodiorite (QMD) system, eastern China. Endoskarn formation involved the migration of Ca into the QMD from the exoskarnification of carbonates (now marble) xenoliths and wall rocks, addition of Fe and Mn by magmatic‐hydrothermal fluids emanating from the interior of the QMD, and removal of alkali elements due to the replacement of feldspars and mica by prograde skarn minerals. Zirconium, Hf, U, and rare earth elements (REE) were added by hydrothermal fluids which were able to carry these often poorly mobile high field strength elements (HFSE) due to elevated F activity. Additions of Al were likely from Na‐rich fluids that also caused sodic alteration. Several factors favored mineralization within the exoskarns rather than endoskarns and QMD. The endoskarns were relatively oxidizing, as evidenced by a significant addition of Fe3+, which caused Cu to remain in magmatic‐hydrothermal fluids until they entered and precipitated sulphides in the more reducing environment of the exoskarns. Fluid migration from the QMD through the endoskarns and into the exoskarns was favored due to decarbonation of wall rock carbonates and related upwards migration of CO2 to produce a self‐sustaining chimney effect, which drew further fluids towards the carbonates to form, alter and mineralize the exoskarns. The higher porosity and permeability of the endoskarns compared with the QMD further promoted the lateral flow of Cu‐bearing fluids towards the exoskarns and limited porphyry‐style alteration and mineralization within the QMD. This proposed mechanism is only likely to be relevant for porphyry‐type systems developed predominantly within carbonate host rocks. Its significance for exploration models is that relatively poorly mineralized porphyry stocks in this setting may be associated with more substantive exoskarn deposits on their margins.
铜绿山体系内矽卡岩和斑岩型蚀变及Cu-Fe外矽卡岩成矿过程中的化学变化
研究了铜绿山石英二黄斑长岩(QMD)体系中Cu-Fe外矽卡岩、内矽卡岩和小斑岩型蚀变形成过程中的元素迁移和化学传质。内矽卡岩的形成过程包括:碳酸盐岩(现为大理岩)包体和围岩的外矽卡岩化作用使Ca迁移到QMD, QMD内部岩浆热液对Fe和Mn的补充作用,以及由前矽卡岩矿物取代长石和云母导致的碱元素的去除。热液流体添加了锆、铪、铀和稀土元素(REE),热液流体由于F活性升高而能够携带这些通常流动性差的高场强元素(HFSE)。添加的Al可能来自富钠液体,这也导致了钠的改变。有几个因素有利于外矽卡岩内的矿化,而不是内矽卡岩和QMD。内矽卡岩是相对氧化的,Fe3+的大量加入证明了这一点,这使得Cu留在岩浆热液中,直到它们进入并在更还原的外矽卡岩环境中沉淀硫化物。由于围岩碳酸盐的脱碳作用和二氧化碳的向上运移,形成了一个自我维持的烟囱效应,使得流体进一步流向碳酸盐,形成、改变和矿化了外矽卡岩,流体从QMD通过内矽卡岩进入外矽卡岩。与QMD相比,内矽卡岩的孔隙度和渗透率更高,进一步促进了含铜流体向外矽卡岩的侧向流动,限制了QMD内斑岩型蚀变和成矿作用。这种提出的机制只可能与主要发育于碳酸盐岩寄主岩中的斑岩型系统有关。它对勘探模式的意义在于,在这一背景下,相对较差的矿化斑岩储量可能与其边缘更实质性的外矽卡岩矿床有关。
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来源期刊
Resource Geology
Resource Geology 地学-地质学
CiteScore
2.30
自引率
14.30%
发文量
18
审稿时长
12 months
期刊介绍: Resource Geology is an international journal focusing on economic geology, geochemistry and environmental geology. Its purpose is to contribute to the promotion of earth sciences related to metallic and non-metallic mineral deposits mainly in Asia, Oceania and the Circum-Pacific region, although other parts of the world are also considered. Launched in 1998 by the Society for Resource Geology, the journal is published quarterly in English, making it more accessible to the international geological community. The journal publishes high quality papers of interest to those engaged in research and exploration of mineral deposits.
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