投稿时间：2021-11-14
修订日期：2022-03-19
网络发布日期：2022-07-07
中文摘要:含明矾石蚀变岩帽是斑岩-浅成低温热液成矿系统顶部的标志性蚀变，但关于其找矿指向性矿物——明矾石的特征系统地研究不够，特别是如何通过明矾石矿物学特征有效判断蚀变岩帽下伏的成矿潜力，是目前的难题。中国东南沿海地区已探明了以紫金山金-铜矿床、大矾山蚀变岩帽为代表的多个大型斑岩-浅成低温矿床和含明矾石蚀变岩帽，是探讨该问题的理想对象。文章以大矾山蚀变岩帽（面积约8 km2）为研究对象，利用短波红外光谱、电子探针、X射线衍射等技术分析手段，开展明矾石的矿物组合、类型和波谱等方面研究。结果表明，大矾山蚀变岩帽主要蚀变矿物为石英、明矾石、叶腊石、地开石、高岭石、白云母及少量蒙脱石，具有蚀变分带特征，中间主要为石英-明矾石-地开石和地开石-叶腊石蚀变带，南部主要为白云母化-蒙脱石蚀变带，北部为高岭石-白云母蚀变带。研究区的明矾石全为钾质明矾石，按晶形可分为粒状、叶片状和纤维状3种类型，明矾石颗粒普遍发育环带，暗示其形成过程中流体具脉冲式特征。明矾石的短波红外特征吸收峰在1477.69~1479.98 nm之间，具有从东南向西北逐渐变大的趋势，反映出热源可能位于西北部。结合区域地质背景，笔者认为大矾山蚀变岩帽是典型的酸性蚀变岩帽，该区的西北部靠近热源中心，其深部沿断裂带具有寻找浅成低温热液铜（金）矿床的潜力。
中文关键词:地球化学 短波红外 明矾石 斑岩-浅成低温热液系统 大矾山蚀变岩帽
Abstract:Alunite-bearing lithocap is a typical alteration at the top of the porphyry-epithermal mineralization system. However, the systematic study on the characteristics of alunite, an indicator mineral for prospecting, is insufficient, especially how to effectively judge the metallogenic potential under the lithocap through the mineralogical characteristics of alunite remains obscure. A number of large porphyry-epithermal deposits and alunite bearing lithocaps have been discovered in southeast China, such as the Zijinshan Au-Cu deposit and the Dafanshan lithocap, which is an ideal target for examining this issue. In this paper, we take Dafanshan lithocap (outcropping area of about 8 km2) as the research object. Based on mineral assemblages, types and spectrum of alunite by using short-wavelength infrared spectroscopy (SWIR), electron microprobe analysis (EMPA) and X-ray diffraction (XRD), the main alteration minerals in the Dafanshan lithocap include quartz, alunite, pyrophyllite, dickite, kaolinite, muscovite and minor montmorillonite. There is an alteration zoning at the Dafanshan lithocap:the middle zone is composed of quartz-alunite-dickite and dickite-pyrophyllite, the southern zone is dominated with muscovite-montmorillonite, and the northern zone is a kaolinite-muscovite alteration zone. All alunite grains in this area are potassic type, according to the crystal shape, the alunite can be divided into granular, flake-shaped and fibrous. The alunite grains generally have ring structure, indicating the fluid has pulse characteristics in the formation process. The typical alunite absorption peak at 1480 nm in the SWIR is between 1477.69 nm and 1479.98 nm, which shifts to higher wavelengths from the southeast to the northwest in the Dafanshan district, suggesting that the source of the hydrothermal fluids may be in the northwestern part. Combined with the regional geological background, We proposed that Dafanshan is a typical acid alteration lithocap, where the northwestern part is close to the hydrothermal center, and its deep part along the fault zone has the potential to find epithermal copper(gold) deposit.
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基金项目:本文得到国家自然科学基金项目（编号：41925011）和地调项目（编号：DD20201173）的联合资助
引用文本：
孙衍东,谢桂青,陈静.2022.福建南部大矾山蚀变岩帽的明矾石特征及其找矿指示[J].矿床地质,41(3):489~505SUN YanDong,XIE GuiQing,CHEN Jing.2022.Characteristics of alunite and its implication for mineral exploration in Dafanshan lithocap, southern Fujian Province, China[J].Mineral Deposits41(3):489~505
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