Study on geological characteristics and critical metal deportment of the Huangzhuyuan silver polymetallic deposit in Luzong basin, Anhui Province

Abstract

黄竹园银多金属矿床位于长江中下游成矿带庐枞矿集区东南缘，是成矿带断凹区火山岩盆地内首次发现的浅成低温热液型银多金属矿床，亟待开展矿床地质特征、金属元素特别是关键金属的赋存状态和矿床成因研究。黄竹园矿床矿体主要赋存于下白垩统砖桥组、双庙组火山岩及断裂破碎带中，呈层状、似层状产出；矿石类型主要有脉状、浸染状、细网脉状。本次工作基于矿床地质特征研究，通过对矿床中采集样品进行手标本及室内镜下观察、短波红外分析测试（SWIR）、扫描电子显微镜（SEM-EDS）、电子探针分析（EPMA）和自动矿物综合分析（TIMA）等方法，阐明了矿床中的主要蚀变矿化特征和成矿期次，重点开展银和关键金属赋存状态及矿床成因类型研究。研究结果表明，黄竹园矿床总体表现出靠近矿体部位发育绢云母-伊利石化，向外围矿化较弱部位变为蒙脱石-高岭石化；根据不同的矿物共生组合及其相互关系，将矿床的成矿过程从早到晚分为无矿化石英脉阶段、石英-银矿物-硫化物脉阶段和石英-碳酸盐脉阶段，其中石英-银矿物-硫化物脉阶段为该矿床最重要的银、铜成矿阶段。主要的银矿物为自然银、硫铜银矿和硫汞铜银矿。矿床中的主要关键金属矿物为辉砷钴矿和铁硫砷钴矿，呈不规则粒状镶嵌在辉铜矿和黄铁矿边缘。通过黄竹园矿床与国内外其他浅成低温热液矿床地质特征对比，本次工作认为黄竹园矿床是高硫型浅成低温热液矿化叠加于斑岩型矿化之上的复合成矿的典型实例。通过与矿区北部钱铺酸性蚀变岩帽（<1km）之间对比研究，提出黄竹园-钱铺酸性蚀变岩帽地区可能存在一大型斑岩-浅成低温热液成矿系统，为庐枞盆地下一步深部找矿提供了方向。;Huangzhuyuan silver polymetallic deposit is located in the southeastern margin of Luzong volcanic basin in the Middle-Lower Yangtze River Valley Metallogenic Belt (MLYB). It is the first discovered epithermal silver polymetallic deposit in the volcanic basin in the fault depression area of the MLYB. It is urgent to carry out a systematic study on the geological characteristics, the deportment of metals, especially critical metals, and the genesis of the deposit. Ore bodies are mainly hosted in the alteration zones and fractures of volcanic rocks of Zhuanqiao Formation and Shuangmiao Formation of Lower Cretaceous, as stratiform and lenses. Mineralization occurs as veins, disseminations and thin stockworks. Alteration and mineralization characteristics, mineral assemblages, especially the occurrence of Ag and critical metals and genesis of the deposit were discussed by hand specimens and microscopic observation, short wave infrared analyses (SWIR), scanning electron microscopy (SEM-EDS), electron probe analysis (EPMA) and TESCAN Integrated Mineral Analyzer (TIMA). The results show that Huangzhuyuan is characterized by muscovite-illite alteration of the ore body and montmorillonite-kaolinite alteration in the periphery of the deposit. The mineralization process of the deposit can be divided into three stage such as sulfide-barren quartz vein stage, quartz-silver-sulfides vein stage and quartz-calcite vein stage, of which quartz-silver-sulfides vein stage is the most important silver and copper mineralization stage. The main silver minerals are native silver, stromeyerite and danielsite. The main critical element minerals in the deposit are cobaltite and glaueodot, and are embedded in the margin of chalcopyrite and pyrite in irregular granular form. By comparing the geological characteristics of Huangzhuyuan deposit with other epithermal deposits globally, the Huangzhuyuan deposit is a porphyry-deposit overprinted by high sulfidation epithermal mineralization. By establishing relations with the surrounding Qianpu lithocap (less than 1km distance), it is indicated that there may be a large porphyry system in this area, and this indication provides a direction for further exploration in the deeper part of Luzong basin.