Yanshan Au deposit, Penglai City, Yantai, Shandong, Chinai

Regional Level Types
Yanshan Au deposit	Deposit
Penglai City	County
Yantai	Prefecture
Shandong	Province
China	Country

The outcropping strata in the Yanshan mining area are dominated by Quaternary alluvial deposits, while Precambrian metamorphic basement rocks occur locally. The relics of the Neoarchean Jiaodong metamorphic rock group occur as lenticular inclusions within the Jiuqu and Bijiaoshan unit plutons, while the lithology is mainly composed of plagioclase hornblendite and biotite gneiss. Three groups of fault systems, namely NE-, NNE-, and NS-trending faults, developed in the mining area, with the NE–NNE trending faults controlling the distribution of ore bodies. The most prominent of these faults is the Huluxian fault, with alteration zones and ore bodies predominantly occurring in the secondary faults of its footwall. The intrusive rocks are roughly delineated by the Huluxian fault, with Guojialing granite located in the east and Linglong granite in the west. These two types of granite serve as direct ore-hosting wall rocks and occur in the form of batholiths. These magmatic activities are closely associated with gold mineralization, as evidenced by the presence of ore-bearing altered fractures within granitic rocks. The contact zone between these two granite types controls the distribution of the industrial ore bodies within the gold mine. Seven mineral veins of industrial significance have been identified within the mining area, with a total of gold metal content of 4.8 tons and an average grade of 5.29 × 10−6 g/t. The ore bodies within these veins are predominantly thin and vein-like, with an average thickness of approximately 1 m. They exhibit shapes such as veins, lenses, and pods, often displaying gentle undulations along the dip and local areas of expansion and contraction. The sections in which faults transition from steep to gentle are frequently associated with thicker ore bodies and enriched gold deposits. The exploration depth of the largest, the No. 8 ore vein, has surpassed −900 m, and it remains open along both the dip and strike directions.
Hydrothermal alteration surrounding the orebodies and fractures is well developed, including silicification, sericitization, choritization, K-feldspar alteration, and carbonation . The alteration assemblages exhibit clear temporal relationships: (1) K-feldspar alteration represents a precursor stage predating mineralization; (2) pyritization, sericitization, and silicification constitute the coeval alteration suite most closely associated with gold deposition, defining the main ore-forming stage; (3) chloritization occurs multiphasically throughout mineralization; and (4) carbonatization represents a late stage of ore-forming hydrothermal activity. The alteration has a narrow range, with widths generally ranging from several meters to over ten meters. The mineralization process of the Yanshan gold deposit is divided into three stages: early quartz-pyrite, quartz-sericite-native gold-polymetallic sulfide, and late quartz-carbonate.

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References